Interplay of metallophilic interactions, π-π Stacking, and ligand substituent effects in the structures and luminescence properties of neutral PtII and PdII aryl isocyanide complexes

Article

pubs.acs.org/IC

Interplay of Metallophilic Interactions, π−π Stacking, and Ligand

Substituent Eﬀects in the Structures and Luminescence Properties of

Neutral Pt^IIand Pd^IIAryl Isocyanide Complexes

Ilya M. Sluch,^†Anthea J. Miranda,^†Oussama Elbjeirami,^‡,§Mohammad A. Omary,^‡

and LeGrande M. Slaughter*^,†

^†Department of Chemistry, Oklahoma State University, Stillwater, Oklahoma 74078, United States

^‡Department of Chemistry, University of North Texas, Denton, Texas 76203, United States

S

* Supporting Information

ABSTRACT: Packing interactions in the crystal structures of

a series of cis-M(CNAr)₂Cl₂complexes (M = Pt, Pd; Ar =

substituted phenyl) were examined and correlated with the

luminescence properties of the Pt complexes. The structures of

the PhNC and p-tolyl isocyanide complexes exhibit extended

chains of metallophilic interactions with M···M distances of

3.24−3.25 and 3.34 Å, respectively, with nearly isostructural Pt

and Pd compounds. Both structure types contain void

channels running parallel to the M···M chains. The channels

are 3−4 Å wide and vacant for the phenyl structures, while

those in the p-tolyl structures are up to 7.6 Å wide and contain

water. These channeled structures are stabilized by a

combination of metallophilic bonding and aryl π−π stacking interactions. The Pt structure with 4-F substituents also features

extended Pt···Pt chains, but with longer 3.79 Å distances alternating with shorter 3.37 Å contacts. Structures with 4-CF₃and 4-

OMe substituents exhibit mostly isolated dimers of M···M contacts. In complexes with 2,6-dimethylphenyl isocyanide, steric

hindrance precludes any short M···M contacts. The primary eﬀect of aryl substitution is to provide alternative packing motifs,

such as CF₃···π and CH₃···π interactions, that either augment or disrupt the combination of metallophilic contacts and π−π

stacking needed to stabilize extended M···M chains. Diﬀerences in the Pt and Pd structures containing 4-F and 4-OMe

substituents are consistent with a higher driving force for metallophilic interactions for Pt versus Pd. The M−C and M−Cl bond

distances indicate a slightly higher trans inﬂuence for aryl isocyanides bound to Pt versus Pd. The three extended Pt···Pt chain

structures display luminescence assignable to (dσ*→pσ) excited states, demonstrating the existence of substantial orbital

communication along the metal−metal chains. Face-indexing shows that the preferred crystal growth axis is along the metal−

metal chains for the luminescent structures. Variable temperature structural studies showed that both M···M and π−π

interactions contract upon cooling. Overall, this study suggests that synergy with π−π and other interactions is necessary to

stabilize extended M···M chain structures. Thus, eﬀorts to design functional materials based on metallophilic bonding must

consider the full array of available packing motifs.

short M···M contacts,⁵as do a range of square planar Pt^IIand

INTRODUCTION

Attractive “metallophilic” interactions between d⁸, d¹⁰, and s²

metal ions are increasingly being recognized as important

determinants of solid-state structure as well as potential sources

■

linear Ag^Iand Au^Icomplexes.^1b,6Pt^IIdiimine complexes

crystallize as diﬀerent polymorphs that have distinct colors as a

result of changes in crystal packing or solvation eﬀects that

modulate the Pt···Pt distances.⁷Metallophilic attractions are

much weaker than covalent bonds but can be as strong as

hydrogen bonds.²This relative weakness means that these

interactions can be easily disrupted by steric eﬀects as well as by

other crystal packing forces such as π−π,⁸CH−π,⁹metal−π,¹⁰

hydrogen bonding,¹¹and halogen bonding¹²interactions.

However, metallophilic bonding often coexists with these

other packing motifs,¹³suggesting that a suitable combination

of useful material properties.¹These attractions, which are

attributed to correlation eﬀects enhanced by relativistic eﬀects,²

can manifest themselves in the crystalline state as dimers,

oligomers, extended chains, or sheets of metal complexes with

M···M contacts less than the sum of van der Waals radii.³The

electronic communication facilitated by these interactions can

lead to a number of interesting properties. Partial oxidation of

[Pt(CN)₄]²⁻salts results in contraction of the Pt···Pt distances

from 3.3 Å to 2.7−3.0 Å with concomitant onset of one-

dimensional electrical conductivity.⁴These same salts also

display strong luminescence that depends on the presence of

Received: May 25, 2012

A

dx.doi.org/10.1021/ic301104a | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

of packing forces can synergistically stabilize the M···M

interactions. This interplay of packing interactions is likely

responsible for the known tendency of some metal complexes

to form polymorphs that diﬀer in the degree of metal−metal

contact and exhibit distinct properties.^7,14Particularly intriguing

are examples in which the extent of metal−metal interaction

changes upon incorporation of solvents into the crystalline

lattice.^7,15Such complexes can display so-called vapochromi-

c^{15e,h−j,n,16}and/or vapoluminescent^{13m,15d,f,g,o−r,17}behavior, in

which diﬀusion of volatile organic compounds into voids or

channels in the crystal structure induces changes in color or

luminescence properties, respectively. Because these phenom-

ena are potentially useful in the design of sensors,^15o,18

understanding the factors that favor channeled or porous

structures containing metallophilic interactions is an important

goal.

We recently reported new polymorphs of M(CNPh)₂Cl₂(M

= Pt, Pd) that represent the ﬁrst examples of extended M···M

chain compounds containing solvent-free channels.¹⁹The

channels appear to be stabilized by a synergistic combination

of metallophilic and aryl π−π interactions. The chain form of

Pt(CNPh)₂Cl₂is luminescent under UV excitation, whereas the

previously known dimeric form²⁰is nonluminescent, clearly

indicating that luminescence in the compound requires

extended Pt···Pt contacts. However, the channels are too

narrow (3.0−4.0 Å) to admit solvents that might perturb the

Pt···Pt bonding and thus the luminescence properties. Toward

an eventual goal of designing luminescent materials with

tunable pore sizes for sensing of volatile molecules, we have

studied the structures and luminescence properties of a series of

Pt and Pd dichloride complexes of substituted arylisocyanide

ligands (Chart 1). Isocyanide ligands are both strong σ-donors

and -donating groups on the arylisocyanide ligands while also

exploring the steric eﬀects of this substitution. A simple orbital

depiction predicts that metallophilic attractions should be

enhanced by conﬁguration interaction of the ﬁlled bands arising

2

from metal d_zorbitals with empty p and s bands, resulting in a

net stabilization of the d_zelectrons.⁷We hypothesize that

2

adding electron-donor substituents should strengthen metal-

2

lophilic bonding by raising the antibonding d_z(dσ*) states in

energy, thereby increasing the degree of conﬁguration

interaction. However, these substituents also change the steric

proﬁle of the arylisocyanide, which may either disrupt or

enhance the π−π stacking interactions that can synergistically

stabilize extended M···M interactions in these complexes.¹⁹

Another goal of this study is to compare the structures of

identically ligated palladium and platinum complexes in order

to gain insights into the relative importance of metallophilic

attractions versus other packing forces. Owing to the lanthanide

contraction, Pt has a very similar covalent radius to Pd^25,26and

often forms nearly isostructural complexes,²⁷but Pd experi-

ences smaller relativistic eﬀects that are believed to impart

weaker metallophilic bonding.^2a,28Therefore, any signiﬁcant

diﬀerences in the crystal structures of isoleptic Pd and Pt

complexes may indicate that metallophilic interactions play a

key structure-directing role. We also report spectroscopic

studies conﬁrming that luminescence depends on the presence

of extended Pt···Pt chains and temperature-dependent

crystallographic studies that identify which intermolecular

interactions dominate at lower temperatures as thermal motion

is attenuated. All of these studies suggest that stabilization of

luminescent structures containing Pt···Pt chains requires a

synergistic combination of metallophilic bonding with π−π, and

sometimes CH···π, interactions. Importantly, these synergistic

packing arrangements can stabilize luminescent structures

containing extended channels. In the case of Pt/Pd(CNC₆H₄-

p-CH₃)₂Cl₂, we have identiﬁed channels with the largest

continuous widths yet reported for structures containing

metallophilic interactions.

Chart 1. Isocyanide Complexes Studied in This Work

EXPERIMENTAL SECTION

■

General Considerations. All manipulations were performed

under air at ambient temperature. CH₂Cl₂(Pharmco) was washed

with concentrated H₂SO₄, water, aqueous NaHCO₃, and again water,

and then distilled from P₂O₅prior to use. Hexanes (Pharmco), n-

hexane (Acros, 95%), cyclohexane (Acros, p.a.), and Et₂O (Acros)

were dried over and distilled from Na/benzophenone ketyl prior to

use. Chlorobenzene (Aldrich, 99+% spectrophotometric grade) and

1,2-dichlorobenzene (Acros, 99%) were used as received. NMR

solvents were purchased from Cambridge Isotope Laboratories.

CD₃CN and CDCl₃were used as received. CD₂Cl₂was dried by

stirring over activated 4 Å molecular sieves, and then stored over and

vacuum distilled from P₂O₅prior to use. 2,6-Dimethylphenyl

isocyanide (≥98%) was purchased from Fluka and used as received.

All other arylisocyanides were synthesized from the corresponding

anilines via phase-transfer Hofmann reactions.²⁹Caution! Aryl

isocyanides are vile-smelling liquids that must be handled in well-ventilated

fume hoods. (COD)PdCl₂and (COD)PtCl₂were prepared by

literature procedures.³⁰

and appreciable π-acceptors; both properties are thought to

reinforce M···M interactions.²¹Extended metallophilic bonding

has been reported in isocyanide-containing double salts of the

type [Pt(CNR)₄][PtX₄] (X = anionic donor)^15e,22as well as in

15f,23

neutral complexes of the types Pt(CNR)₂(CN)₂

and

(benzoquinolinate)Pt(CNR)Cl.^13jHowever, the structures and

luminescence properties of neutral Pt^IIbis(isocyanide) dihalide

complexes have not been systematically studied, despite the fact

that analogous linear halide−isocyanide complexes of Au^Iare

known to be strongly luminescent and to engage in extensive

metallophilic bonding.^21a,c,d,24

NMR spectra were recorded on Varian GEMINI 2000 (300 MHz)

and Unity INOVA (400 and 600 MHz) spectrometers. IR spectra

were acquired on a Perkin-Elmer System 2000 FT-IR or a Thermo

Nexus 670 FT-IR with 0.5 cm⁻¹resolution and weak apodization.

Elemental analyses were performed by Desert Analytics (Tucson,

Arizona) or Midwest Microlab (Indianapolis, Indiana).

This study aims to examine the electronic eﬀects on

metallophilic bonding of placing diﬀerent electron-withdrawing

Synthesis of Isocyanide Complexes. A modiﬁcation of a

published route to similar complexes³¹was used. Isocyanide (2.2

B

dx.doi.org/10.1021/ic301104a | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

Table 1. Crystallographic Data for Complexes 1−8

1

2

3

4

formula

M_r

C₁₆H₈Cl₂F₆N₂Pt

608.23

C₁₆H₈Cl₂F₆N₂Pd

519.54

C₁₄H₈Cl₂F₂N₂Pt

508.21

C₁₄H₈Cl₂F₂N₂Pt

508.21

C₁₄H₈Cl₂F₂N₂Pd

419.52

T (K)

115(2)

100(2)

115(2)

300(2)

115(2)

cryst syst

space group

a (Å)

monoclinic

P2₁/c

monoclinic

P2₁/c

monoclinic

P2₁/n

monoclinic

P2₁/n

triclinic

Pi

̅

14.2940(9)

17.9417(11)

14.7000(9)

90

14.7788(10)

17.9280(11)

14.0492(10)

90

6.7933(2)

18.2047(5)

24.2898(6)

90

6.9450(2)

18.2518(7)

24.5576(9)

90

9.5569(4)

13.2609(5)

24.577(1)

97.089(3)

94.043(2)

104.483(2)

2976.0(2)

8

b (Å)

c (Å)

α (deg)

β (deg)

γ (deg)

V (Å³)

Z

93.597(4)

90

91.740(4)

90

90.084(2)

90

90.897(2)

90

3762.5(4)

8

3720.7(4)

8

3003.92(14)

8

3112.5(2)

8

D_calcd(g cm⁻³

)

2.147

1.855

2.247

2.169

1.873

μ (mm⁻¹

)

7.802

1.345

9.711

1.619

reﬂns measured

43 604

41 955

63 428

36 446

36 222

reﬂns unique [R_int]

reﬂns obsd [I > 2σ(I)]

R1, wR2 [I > 2σ(I)]

R1, wR2 (all data)

9320 [0.0323]

8130

10 152 [0.0390]

8231

7427 [0.0563]

7156

7729 [0.0339]

5744

16 700 [0.0509]

14 880

0.0218, 0.0496

0.0288, 0.0527

0.0301, 0.0629

0.0430, 0.0679

0.0278, 0.0722

0.0291, 0.0727

0.0296, 0.0527

0.0505, 0.0585

7

0.0484, 0.1261

0.0566, 0.1298

8

a

5a

6a

formula

M_r

C₁₄H₁₀Cl₂N₂Pt

472.23

C₁₄H₁₀Cl₂N₂Pd

383.54

C₁₆H₁₄Cl₂N₂Pt

C₁₆H₁₄Cl₂N₂Pd

b

500.28

411.59

T (K)

cryst syst

space group

a (Å)

300(2)

298(2)

tetragonal

P4/mnc

24.5366(1)

6.5728(1)

90

298(2)

tetragonal

P4/mnc

24.5268(2)

6.5445(1)

90

monoclinic

P2₁/c

monoclinic

P2₁/c

15.9578(6)

15.3189(5)

6.5520(3)

90

15.9320(3)

15.3613(4)

6.5166(1)

90

b (Å)

c (Å)

α (deg)

β (deg)

γ (deg)

V (Å³)

Z

92.184(2)

90

92.144(1)

90

1600.51(11)

4

1593.73(6)

4

3957.12(6)

8

3936.94(8)

8

b

D_calcd.(g cm⁻³

μ (mm⁻¹

)

1.960

1.598

1.679

1.389

)

9.088

1.486

7.356

1.209

reﬂns measured

34 875

38 374

31 545

21 135

reﬂns unique [R_int]

reﬂns obsd [I > 2σ(I)]

R1, wR2 [I > 2σ(I)]

R1, wR2 (all data)

6574 [0.0439]

5540

7208 [0.0408]

5460

2043 [0.0315]

1706

2661 [0.0309]

2109

0.0391, 0.1138

0.0482, 0.1189

0.0262, 0.0589

0.0415, 0.0637

0.0188, 0.0453

0.0397, 0.0979

0.0515, 0.1024

0.0260, 0.0470

a

b

Structural data for 5a,b and 6a at 100 K and 6b at 115 K were previously communicated (ref 19). Calculated from data treated with SQUEEZE.

equiv) was added to a stirred solution of (COD)MCl₂(0.20−0.65

mmol) in 10 mL of dry CH₂Cl₂, and the mixture was stirred for 10

min at 25 °C. Dropwise addition of dry hexanes and dry Et₂O resulted

in precipitation of a yellow crystalline solid, which was ﬁltered, washed

with dry hexanes and dry Et₂O, and dried in vacuo overnight.

Characterization data for Pd(CNC₆H₄-p-CF₃)₂Cl₂(2),³²Pt-

(CNPh)₂Cl₂(5),¹⁹and Pd(CNPh)₂Cl₂(6)¹⁹were previously

reported. Data for newly characterized compounds are given below.

Pt(CNC₆H₄-p-CF₃)₂Cl₂(1). Yield 0.206 g, 93%. ¹H NMR (300 MHz,

CDCl₃): δ 7.76 (8H, AB, J = 9.0 Hz, C = 6.0 Hz). ¹³C NMR (151

MHz, CD₃CN): δ 133.0 (q, ²J_CF=33 Hz, Ar para), 130.0 (m, ArNC),

meta), 113.9 (m, Ar ipso). IR (Nujol mull) ν_max/cm⁻¹: 2255 (m), 2218

(m), 2202 (w). Anal. Calcd for C₁₄H₈N₂F₂Cl₂Pt: C, 33.09, H, 1.59, N,

5.51. Found: C, 33.06, H, 1.65, N, 5.51.

1

Pd(CNC₆H₄-p-F)₂Cl₂(4). Yield 0.216 g, 79%. H NMR (400 MHz,

CD₃CN): 7.71 (4H, m, ortho H), 7.30 (4H, m, meta H). ¹³C NMR

1

(151 MHz, CD₂Cl₂): δ 164.3 (d, J_CF= 255 Hz, Ar para), 130.0 (d,

³J_CF= 9.5 Hz, Ar ortho), 125.1 (br s, ArNC), 122.0 (br s, Ar ipso),

2

117.9 (d, J_CF= 24 Hz, Ar meta). IR (Nujol mull) ν_max/cm⁻¹: 2244

(m), 2241 (m), 2227 (m). Anal. Calcd for C₁₄H₈N₂F₂Cl₂Pd: C, 40.08,

H, 1.92, N, 6.68. Found: C, 40.26, H, 2.14, N, 6.60.

Pt(CNC₆H₄-p-CH₃)₂Cl₂(7). Yield 0.151 g, 82%. ¹H NMR (400 MHz,

CD₃CN): δ 7.43 (8H, AB, J = 8.9 Hz, C = 32 Hz), 2.40 (6H, s, CH₃).

¹³C NMR (151 MHz, CD₃CN): δ 143.3 (s, Ar para), 131.3 (s, Ar

ortho), 127.8 (s, Ar meta), 124.1 (br s, ArNC), 112.8 (br s, Ar ipso),

21.5 (CH₃). IR (Nujol mull) ν_max/cm⁻¹2255 (m), 2216 (m). Anal.

Calcd for C₁₆H₁₄N₂Cl₂Pt: C, 38.41, H, 2.82, N, 5.60. Found: C, 38.88,

H, 3.08, N, 5.41.

3

1

129.1 (s, Ar ortho), 128.0 (q, J_CF=3.8 Hz, Ar meta), 124.4 (q, J_CF

=

272 Hz, CF₃), 116.0 (br s, Ar ipso). IR (Nujol mull): ν_max/cm⁻¹2242

(m), 2207 (m). Anal. Calcd for C₁₆H₈N₂F₆Cl₂Pt: C, 31.59, H, 1.33, N,

4.61. Found: C, 31.63, H, 1.47, N, 4.61%.

1

Pt(CNC₆H₄-p-F)₂Cl₂(3). Yield 0.148 g, 72%. H NMR (400 MHz,

CD₃CN): 7.70 (4H, m, ortho H), 7.28 (4H, m, meta H). ¹³C NMR

1

Pd(CNC₆H₄-p-CH₃)₂Cl₂(8). Yield 0.062 g, 75%. ¹H NMR (300

MHz, CD₃CN): δ 7.44 (8H, AB, J = 8.9 Hz, C = 26 Hz), 2.41 (6H, s,

(151 MHz, CD₂Cl₂): δ 163.9 (d, J_CF= 254 Hz, Ar para), 129.9 (d,

2

³J_CF= 9.5 Hz, Ar ortho), 122.5 (s, ArNC), 117.6 (d, J_CF= 24 Hz, Ar

C

dx.doi.org/10.1021/ic301104a | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

Table 2. Crystallographic Data for Complexes 9−12

9a

9b

9c

10a

formula

M_r

C₁₆H₁₄Cl₂N₂O₂Pt 0.5(CH₂Cl₂)

C₁₆H₁₄Cl₂N₂O₂Pt·0.25(C₆H₅Cl)

C₁₆H₁₄Cl₂N₂O₂Pt·0.5(C₆H₄Cl₂)

C₁₆H₁₄Cl₂N₂O₂Pd

443.59

574.74

115(2)

triclinic

560.42

115(2)

triclinic

605.78

115(2)

triclinic

T (K)

115(2)

cryst syst

space group

a (Å)

triclinic

P1

̅

P1

̅

8.9518(1)

15.3609(2)

15.4429(3)

113.331(1)

97.016(1)

100.525(1)

1872.06(5)

4

8.9948(1)

15.2550(2)

15.3945(2)

112.743(1)

97.176(1)

100.283(1)

1872.55(4)

4

13.2283(2)

13.9112(2)

14.4607(2)

107.146(1)

101.539(1)

118.042(1)

2055.44(7)

4

12.2899(3)

12.3550(3)

14.1451(3)

96.317(1)

104.314(1)

118.329(1)

1765.62(8)

4

b (Å)

c (Å)

α (deg)

β (deg)

γ (deg)

V (Å³)

Z

D_calcd(g cm⁻³

μ (mm⁻¹

)

2.039

1.988

1.958

1.669

)

7.935

7.827

7.233

1.362

reﬂns measured

52 148

41 322

48 699

25 068

reﬂns unique [R_int]

reﬂns obsd [I > 2σ(I)]

R1, wR2 [I > 2σ(I)]

R1, wR2 (all data)

10 028 [0.0330]

8534

9268 [0.0341]

7934

10 180 [0.0286]

9445

8490 [0.0256]

7194

0.0186, 0.0374

0.0271, 0.0398

0.0202, 0.0410

0.0279, 0.0433

0.0159, 0.0354

0.0183, 0.0361

11

0.0225, 0.0503

0.0301, 0.0534

12

10b

formula

M_r

C₁₆H₁₄Cl₂N₂O₂Pd·C₆H₄Cl₂

C₁₈H₁₈Cl₂N₂Pt

528.33

C₁₈H₁₈Cl₂N₂Pd

590.58

115(2)

triclinic

439.64

115(2)

triclinic

T (K)

cryst syst

space group

a (Å)

115(2)

triclinic

P1

̅

P1

̅

P1

̅

13.576(2)

13.705(2)

14.780(2)

76.369(9)

64.259(8)

71.257(9)

2330.7(6)

4

8.0404(2)

10.4016(3)

10.8137(3)

85.111(1)

80.174(1)

87.225(1)

887.35(4)

2

8.0383(1)

10.4097(1)

10.7831(1)

85.4011(4)

80.3707(5)

87.6240(5)

886.353(16)

2

b (Å)

c (Å)

α (deg)

β (deg)

γ (deg)

V (Å³)

Z

D_calcd(g cm⁻³

μ (mm⁻¹

)

1.683

1.977

1.647

)

1.277

8.207

1.348

reﬂns measured

63 527

19 552

14 163

reﬂns unique [R_int]

11 529 [0.0632]

10 129

4379 [0.0274]

4245

4363 [0.0182]

4226

reﬂns obsd [I > 2σ(I)]

R1, wR2 [I > 2σ(I)]

R1, wR2 (all data)

0.0279, 0.0708

0.0331, 0.0738

0.0139, 0.0336

0.0147, 0.0339

0.0158, 0.0399

0.0166, 0.0404

1

CH₃). ¹³C NMR (101 MHz, CD₂Cl₂): δ 143.5 (s, Ar para), 131.0 (s,

Ar ortho), 127.3 (s, Ar meta), 21.9 (CH₃); ArNC and Ar ipso not

detected. IR (Nujol mull) ν_max/cm⁻¹2253 (m), 2225 (m). Anal. Calcd

for C₁₆H₁₄N₂Cl₂Pd: C, 46.67; H, 3.42; N, 6.86. Found: C, 46.70; H,

3.65, N, 6.68.

Pt(CNC₆H₃-2,6-Me₂)₂Cl₂(11). Yield 0.146 g, 86%. H NMR (400

MHz, CDCl₃): δ 7.32 (2H, t, J = 7.6 Hz, para H), 7.18 (4H, d, J = 7.6

Hz, meta H), 2.50 (12H, s, CH₃). ¹³C NMR (151 MHz, CDCl₃): δ

136.2 (s, Ar ortho), 130.8 (s, Ar para), 128.5 (s, meta), 18.8 (CH₃);

ArNC and Ar ipso not detected. IR (KBr pellet) ν_max/cm⁻¹: 2229 (m),

2201 (m). Anal. Calcd for C₁₈H₁₈N₂Cl₂Pt: C, 40.92, H, 3.43, N, 5.30.

Found: C, 40.43, H, 3.40, N, 5.37.

Pt(CNC₆H₄-p-OMe)₂Cl₂(9). Yield 0.162 g, 78%. ¹H NMR (400

MHz, CD₃CN): δ 7.57 (4H, d, J = 9 Hz, ortho H), 7.03 (4H, d, J = 9

Hz, meta H), 3.84 (6H, s, OCH₃). ¹³C NMR (151 MHz, CD₃CN): δ

162.4 (s, Ar para), 129.7 (s, Ar ortho), 119.1 (s, ArNC), 115.9 (s, Ar

meta), 112.1 (br s, Ar ipso), 56.6 (OCH₃). IR (Nujol mull) ν_max/cm⁻¹:

2244 (m), 2213 (m). Anal. Calcd for C₁₆H₁₄N₂O₂Cl₂Pt·0.2CH₂Cl₂

1

Pd(CNC₆H₃-2,6-Me₂)₂Cl₂(12). Yield 0.116 g, 59%. H NMR (400

MHz, CD₂Cl₂): δ 7.35 (2H, t, J = 7.6 Hz, para H), 7.15 (4H, d, J = 7.8

Hz, meta H), 2.49 (12H, s, CH₃). ¹³C NMR (101 MHz, CD₂Cl₂): δ

136.9 (s, Ar ortho), 131.4 (s, Ar para), 128.7 (s, meta), 18.9 (CH₃);

ArNC and Ar ipso not detected. IR (KBr pellet) ν_max/cm⁻¹: 2229 (m),

2212 (m). Anal. Calcd for C₁₈H₁₈N₂Cl₂Pd: C, 49.17, H, 4.13, N, 6.37.

Found: C, 48.72, H, 4.14, N, 6.52.

1

(solvent content by H NMR): C, 35.42, H, 2.64, N, 5.10. Found: C,

35.60, H, 2.55, N, 5.09.

Pd(CNC₆H₄-p-OMe)₂Cl₂(10). Yield 0.088 g, 61%. H NMR (400

1

MHz, CD₃CN): δ 7.59 (4H, d, J = 9 Hz, ortho H), 7.04 (4H, d, J = 9

Hz, meta H), 3.85 (6H, s, OCH₃). ¹³C NMR (101 MHz, CD₃CN): δ

162.7 (s, Ar para), 129.8 (s, Ar ortho), 116.1 (s, Ar meta), 56.6

(OCH₃); ArNC and Ar ipso not detected. IR (Nujol mull) ν_max/cm⁻¹:

2238 (m), 2220 (m). Anal. Calcd for C₁₆H₁₄N₂O₂Cl₂Pd: C, 43.32, H,

3.18, N, 6.31. Found: C, 43.01, H, 3.30, N, 6.07.

X-ray Crystal Structure Determinations: General. X-ray

diﬀraction data were collected on a Bruker SMART APEX II

diﬀractometer with a CCD detector using a combination of ϕ and

ω scans. The crystal-to-detector distance was 6.0 cm. A Bruker

Kryoﬂex liquid nitrogen cooling device was used for low-temperature

data collections. Unit cell determination and data collection utilized

D

dx.doi.org/10.1021/ic301104a | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

a

Table 3. Metal−Metal Interactions in the Crystal Structures of M(CNAr)₂Cl₂Complexes

b

structure

M

aryl substituent

M···M (Å)

M···M···M (deg)

L₂MCl₂stagger angle

1

2

3

Pt

Pd

Pt

4-CF₃

4-F

Pt1−Pt2 3.5359(2)

Pd1−Pd2 3.5019(3)

Pt1−Pt2 3.3747(3)

Pt1−Pt2 [1 + x, y, z] 3.7858(4)

Pd1−Pd2 3.3659(9)

139°

138°

144°

140°

180°

145°

180°

139°

180°

143°

Pt−Pt−Pt 143.078(9)

Pd1−Pd2−Pd2 155.76(3)

Pd3−Pd4−Pd4 148.54(3)

Pt−Pt−Pt 160.74(2)

4

Pd

4-F

Pd2−Pd2 [−x, 1 − y, 2 − z] 3.890(1)

Pd3−Pd4 3.4289(9)

Pd4−Pd4 [1 − x, 1 − y, 1 − z] 3.893(1)

Pt1−Pt1 [x, 1.5 − y, 0.5 + z] 3.2455(3)

Pt1−Pt1 [x, 1.5 − y, −0.5 + z] 3.2455(3)

Pd1−Pd1 [x, 1.5 − y, 0.5 + z] 3.2370(3)

Pd1−Pd1 [x, 1.5 − y, −0.5 + z] 3.2370(3)

Pt1−Pt1 [1 − x, 1 − y, 1 − z] 3.4001(2)

Pd1−Pd1 [1 − x, 1 − y, 1 − z] 3.3986(4)

Pt1−Pt1 [−0.5 + y, 0.5 + x, 0.5 − z] 3.3393(1)

Pt1−Pt1 [−0.5 + y, 0.5 + x, −0.5 − z] 3.3393(1)

Pd1−Pd1 [−0.5 + y, 0.5 + x, 0.5 − z] 3.3406(1)

Pt1−Pt1 [−0.5 + y, 0.5 + x, −0.5 − z] 3.3406(1)

Pt1−Pt2 3.4960(1)

Pt1−Pt2 3.4726(2)

Pt1−Pt2 3.2461(1)

Pd1−Pd1 [1 − x, 1 − y, 1 − z] 3.4643(3)

Pd1−Pd2 3.5387(6)

Pd1−Pd1 [1 − x, 1 − y, 1 − z] 3.4947(6)

Pd2−Pd2 [1 − x, 2 − y, 1 − z] 3.5117(6)

Pt1−Pt1 [−x, 1 − y, 1 − z] 3.95

Pt1−Pt1 [1 − x, 1 − y, 1 − z] 4.13

Pd1−Pd1 [−x, 1 − y, 1 − z] 3.95

5a

6a

Pt

Pd

Pd−Pd−Pd 157.40(1)

5b

6b

Pt

Pd

Pt

c

7

4-Me

Pt−Pt−Pt 159.5(1)

c

8

Pd

143°

Pd−Pd−Pd 156.77(2)

9a [9·0.5(CH₂Cl₂)]

9b [9·0.25(PhCl)]

9c [9·0.5(C₆H₄Cl₂)]

10a

Pt

Pd

4-MeO

140°

144°

180°

148°

180°

10b [10·C₆H₄Cl₂]

Pd1−Pd1−Pd2 157.516(9)

Pd1−Pd2−Pd2 150.243(9)

11

12

Pt

2,6-Me₂

Pt−Pt−Pt 168.8

Pd−Pd−Pd 170.0

Pd

Pd1−Pd1 [1 − x, 1 − y, 1 − z] 4.12

a

b

From low temperature diﬀraction data (100−115 K) unless otherwise indicated. Calculated as the average Cl−M−M−Cl dihedral angle for

complexes linked by M···M interactions. From data collected at 298 K.

c

the Bruker APEX2 software package.³³Data integration employed

SAINT.³⁴Multiscan absorption corrections were implemented using

SADABS.³⁵X-ray diﬀraction experiments employed graphite-mono-

chromated Mo Kα radiation (λ = 0.710 73 Å). Structures were solved

by direct methods and reﬁned by full-matrix least-squares on F²using

the SHELXTL software suite.³⁶Non-hydrogen atoms were assigned

anisotropic temperature factors, and hydrogen atoms were included in

calculated positions with ﬁxed isotropic U. Face indexing of crystals to

identify crystal growth axes was performed using the APEX2

software.³³Packing interactions were identiﬁed, analyzed, and plotted

using MERCURY³⁷and SHELXTL/XP.³⁶Speciﬁc details of structural

determinations are provided below and in Tables 1 and 2.

X-ray Crystal Structures of Pt/Pd(CNC₆H₄-p-CF₃)₂Cl₂(1, 2). The

CF₃group of C47 in each structure was treated as rotationally

disordered between two orientations using a two-part model for F10,

F11, and F12. The reﬁned occupation ratios of the two orientations

were 0.59:0.41 for 1 and 0.81:0.19 for 2. Least-squares restraints were

employed to attain reasonable thermal parameters on these F atoms.

X-ray Crystal Structure of Pt(CNC₆H₄-p-F)₂Cl₂(3). With the aid of

ROTAX³⁸the crystal used to obtain 115 K data was modeled as a two-

component pseudomerohedral twin (twin law: 1 0 0, 0 −1 0, 0 0 −1).

The reﬁned proportion of the twin components was

0.689(1):0.311(1). The crystal used for room temperature structure

determination did not exhibit twinning.

0.457(1):0.543(1), with a reﬁned twin law of −1 0 0, 0 −1 0, 0.56 0.56

1.

X-ray Crystal Structures of Pt/Pd(CNC₆H₄-p-CH₃)₂Cl₂(7, 8).

Crystals of 7 and 8 gave diﬀraction patterns indicative of severe

twinning at 115 K, and standard twin deconvolution procedures failed

to produce solvable data sets. Room temperature data did not show

these problems, suggesting that a phase change destroyed the integrity

of the crystals at low temperatures. Final data were collected at 298 K.

To correct for electron density arising from disordered solvent,

diﬀraction data were treated with the SQUEEZE procedure in

PLATON.⁴²SQUEEZE analyses were consistent with 20 H₂O

molecules per unit cell in the sample of 7 examined and 13 molecules

of H₂O per unit cell in the sample of 8 examined.

X-ray Crystal Structures of M(CNC₆H₄-p-OCH₃)₂Cl₂·x(solvent)

(9a−c, 10b). Discrete solvent molecules were located in the diﬀerence

Fourier maps of 9a−c and 10b and reﬁned as part of the structural

models. In the case of 9b, the chlorobenzene molecule was modeled as

disordered between two orientations related by an inversion center in

a 50:50 occupancy ratio. Appropriate least-squares restraints were

applied to aid reﬁnement of the PhCl molecule.

Temperature Dependence of Unit Cell Parameters. For samples

of 3, 5a, and 7, limited data sets were collected at ﬁve 50 K increments

from 300 to 100 K. Samples were allowed to equilibrate for three

hours at each temperature before data were collected. At each

temperature, a set of 200−350 diﬀraction images was obtained, and

cell parameters were reﬁned using SAINT.³⁴

Photophysical Measurements. Steady-state luminescence spectra

were acquired with a PTI QuantaMaster model QM-4 scanning

spectroﬂuorometer equipped with a 75-W Xe lamp, emission and

excitation monochromators, excitation correction unit, and a PMT

detector. The emission and excitation spectra were corrected for the

X-ray Crystal Structure of Pd(CNC₆H₄-p-F)₂Cl₂(4). With the aid of

CELL_NOW³⁹and TWINABS,⁴⁰a crystal of 4 was modeled as a two-

component nonmerohedral twin.⁴¹For 36 222 reﬂections in the scaled

data set, 6.5% were singles assigned to twin component 1, 6.5% were

singles assigned to component 2, and 87% were composite reﬂections.

Final reﬁnement was performed on both twin components using data

in HKLF5 format. The reﬁned proportion of twin components was

E

dx.doi.org/10.1021/ic301104a | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

wavelength-dependent detector response and Xe lamp intensity,

respectively. Temperature dependent studies were acquired with an

Oxford optical cryostat using liquid helium or liquid nitrogen as

coolant. Lifetime data were acquired using a nitrogen laser interfaced

with a tunable dye laser and a frequency doubler, as part of

ﬂuorescence and phosphorescence subsystem add-ons to the PTI

instrument. The 337.1 nm line of the N₂laser was used to pump a

freshly prepared 1 × 10⁻²M solution of the organic continuum laser

dye Coumarin-540A in ethanol, the output of which was tuned and

frequency doubled to attain the suitable excitation wavelength (based

on the steady-state luminescence excitation spectra) used to generate

the time-resolved data. Absorption spectra were acquired with a Cary

100 double-beam UV−vis spectrophotometer for dilute solutions of

complexes in freshly distilled CH₂Cl₂.

with ring centroid−centroid distances, as the interplanar

spacings (and angles, for nonparallel contacts) vary signiﬁ-

cantly.⁸

Structures of 1 and 2, Pt/Pd(CNC₆H₄-p-CF₃)₂Cl₂. Slow

diﬀusion of cyclohexane into chlorobenzene solutions of 1 and

2 led to formation of X-ray quality crystals. The structure of

Pt(CNC₆H₄-p-CF₃)₂Cl₂(1) has an asymmetric unit consisting

of two crystallographically nonequivalent complexes linked by a

Pt1···Pt2 contact of 3.5359(2) Å (Table 3). This distance is in

the expected range for a van der Waals contact,⁴⁵suggesting a

weak contribution, if any, from metallophilic bonding. A second

packing motif is aryl π−π stacking. The C21 ring⁴⁶of the Pt1

complex forms a slightly oﬀset π−π interaction with the C41

ring of a Pt2 complex in a neighboring asymmetric unit, with

the two CF₃groups oriented approximately 60° apart. The C41

ring, in turn, is involved in a slightly oﬀset π−π interaction with

an inversion-related C41 ring, but with the CF₃groups oriented

180° apart. The combination of these π−π interactions results

in a four-ring π-stack (center, Figure 1). A third type of packing

interaction comprises CF₃−π interactions between inversion-

related pairs of C31 rings on the Pt2 complex. The C31 rings

do not directly overlap, instead adopting a parallel orientation

with the p-CF₃groups projecting over the adjacent rings (red

dashes, Figure 1). One F atom of each of these CF₃groups

(F8) exhibits a close contact with the adjacent C31 ring, lying

3.13 Å from the plane of the ring and 3.20 Å from the ring

centroid.

RESULTS AND DISCUSSION

■

Crystallographic Studies. This study focused on a series

of 4-substituted phenyl isocyanides (R = CF₃, F, Me, OMe) in

order to vary the isocyanide electronic properties with minimal

steric perturbation (complexes 1−4 and 7−10, Chart 1).

Complexes of 2,6-dimethylphenyl isocyanide (11, 12) were also

prepared in order to examine how increased steric bulk near the

metal would aﬀect the solid-state structure.^43,44Initial crystal

growth attempts utilized slow diﬀusion of n-hexane into

concentrated CH₂Cl₂solutions of the complexes. If no X-ray

quality crystals were obtained, further attempts were made

using slower diﬀusing solvent pairs such as cyclohexane/

chlorobenzene.

Metal−metal contacts are compiled in Table 3. A summary

of all observed packing interactions is given in Table 4, and a

Metallophilic contacts are limited to isolated interactions

between two complexes, with no extended Pt···Pt chains. On

the face of the square plane opposite the Pt1···Pt2 contact, Pt2

is “capped” by an apparent metal−π interaction¹⁰with the C11

ring of a neighboring Pt1 complex. No such interaction is seen

for Pt1.

Table 4. Average Number of Metal−Metal, π−π, and Other

Packing Interactions per Complex

structure # M···M ≤ 3.4 Å # M···M 3.5−4.1 Å # π−π

other

The palladium congener Pd(CNC₆H₄-p-CF₃)₂Cl₂(2)

crystallizes in the same space group as 1 and has very similar

unit cell parameters (Table 1). All of the packing interactions

observed for 1 are also present for 2 (Figure S1, Supporting

Information). The Pd1···Pd2 distance is slightly shorter at

3.5019(3) Å, reﬂecting the slightly smaller van der Waals radius

of Pd versus Pt.⁴⁵All of the interplanar and intercentroid

distances for arene π−π and related interactions are within 0.1

Å of those seen for 1.

Structures of 3 and 4, Pt/Pd(CNC₆H₄-p-F)₂Cl₂. Long

rods of Pt(CNC₆H₄-p-F)₂Cl₂(3) were obtained by slow

diﬀusion of the n-hexane/CH₂Cl₂solvent pair. Similarly to 1,

the structure of 3 has two crystallographically nonequivalent

complexes per asymmetric unit. A Pt1···Pt2 contact of

3.3747(3) Å is present between the two complexes (Table

3). This distance is less than the sum of van der Waals radii and

thus consistent with metallophilic bonding. These dimers are

linked by substantially longer interdimer Pt2···Pt1 contacts of

3.7858(4) Å, resulting in extended zigzag chains of alternating

long and short Pt···Pt interactions along the crystallographic a

axis (Figure 2a). These chains are interdigitated with adjacent

chains related by a 2₁screw axis along b through peripheral

π−π interactions. These π−π interactions repeat along the a

direction, forming extended C11−C41−C11−C41 and C21−

C31−C21−C31 stacks with interplanar separations of 3.31−

3.41 Å. The combination of Pt···Pt π−π interactions results in

two-dimensional sheets of interlinked complexes parallel to the

ab plane (Figure 3a). The nearly coplanar arrangement of aryl

rings in each complex appears to facilitate the synergistic

combination of these two interactions. Along the c direction,

1

0

1

1.5

1 CF₃−π

1 Pt−π

1 CF₃−π

1 Pd−π

2

0

1

1.5

3

1

2

1

2

1

2

0

1

4

0.5

0

4

5a

5b

6a

6b

7

2

2 CH−π

2 CH₃−π

3 CH₃−π

1.5 CH−π

1 CH₃−π

2 CH₃−π

1 CH−π

1 CH₃−π

4 CH₃−π

0

1

0

2

0

1

0

2

8

0

2

9a

9b

9c

1

1.5

2

1

0

10a

10b

0

0.5

2

2.5

11

12

0

2

0

complete tabulation is provided in Table S1 (Supporting

Information). All π−π interactions with interplanar spacings

less than 3.8 Å are considered to be signiﬁcant.^8,15jFor

purposes of discussion, π−π interactions involving overlap of at

least ¹/₃of the adjacent rings are designated as “oﬀset”, whereas

those involving a single edge of each ring are described as

“peripheral”. Note that these categories do not correlate clearly

F

dx.doi.org/10.1021/ic301104a | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

Figure 1. Partial packing diagram of 1, showing Pt···Pt interactions, aryl π−π stacking interactions (center), and CF₃−π interactions (red dashes).

Figure 3. Crystal packing in 4-ﬂuorophenyl isocyanide complexes. (a)

View down the Pt···Pt chains of 3, showing interlinking via π−π

interactions to form two-dimensional sheets. (b) Side view of a sheet

formed by π−π stacking interactions between dimers-of dimers in 4.

Similar sheets formed by Pd3/Pd4 complexes are shown in Figure S4

(Supporting Information).

Figure 2. Comparison of M···M interactions in 4-ﬂuorophenyl

isocyanide complexes. (a) Portion of an extended Pt···Pt chain in

the crystal structure of 3. View is approximately down the c axis. (b)

direction (Figure 2b). Unlike 3, the metal−metal contacts do

One of the dimers-of-dimers present in 4. A crystallographically

independent second dimer-of-dimers (Pd3/Pd4) is shown in Figure

S3 (Supporting Information).

not form extended chains. The dimers-of-dimers are slipped

along c relative to the nearest neighboring stack, and the closest

Pd1···Pd1 contact is 5.93 Å. The isocyanide aryl groups are

nearly parallel to the metal coordination plane as in 3,

adjacent sheets pack only through van der Waals contacts

between aryl rings and/or Cl ligands (Figure S2, Supporting

Information).

facilitating a network of peripheral π−π stacking interactions.

However, every third complex in a stack is rotated by

approximately 30°, unlike the eclipsed arrangement of every

other complex in 3, so the resulting π−π stacking pattern is

more complex. Each dimer-of-dimers is linked via π−π

interactions to the two neighboring stacks in the positive and

negative a direction and to two other inversion-related stacks

(Figure 3b). The result is two-dimensional sheets of interlinked

dimers-of-dimers parallel to the ab plane. The Pd3−Pd4 pair of

complexes forms an analogous sheet structure with Pd3

replacing Pd1 and Pd4 replacing Pd2 (Figure S4, Supporting

Information). The Pd1−Pd2 sheets alternate with Pd3−Pd4

sheets along the c axis, with only van der Waals contacts linking

them. A further diﬀerence from 3 is that the Pd3 and Pd4

complexes are canted in the opposite direction from the Pd1

For the palladium analogue Pd(CNC₆H₄-p-F)₂Cl₂(4),

identical crystal growth conditions led to a structure that is

notably diﬀerent from 3. The asymmetric unit of 4 contains two

pairs of associated Pd complexes, for a total of four

crystallographically independent molecules. The two pairs of

complexes form two separate but similar supramolecular

assemblies. Pd1 and Pd2 are separated by a short distance of

3.3659(9) Å. This pair is linked into a “dimer-of-dimers”

through a longer contact of 3.890(1) Å between Pd2 and its

inversion-related symmetry equivalent, resulting in a short−

long−short M···M contact motif similar to that seen in 3, but

with the contacts running approximately along the [110] lattice

G

dx.doi.org/10.1021/ic301104a | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

and Pd2 complexes, forming a herringbone-like arrangement of

the alternating sheets (Figure S5, Supporting Information). The

distinct packing arrangement of 4 results in a slightly higher

packing index (68.8%) relative to the Pt analogue 3 (68.1%),⁴⁷

apparently at the expense of extended metal−metal inter-

actions.

Structures of 5a and 6a, Chain Form of Pt/Pd-

(CNC₆H₅)₂Cl₂. As previously communicated, crystal growth of

M(CNC₆H₅)₂Cl₂from n-hexane/CH₂Cl₂provided long yellow

rods of the chain forms 5a/6a, whereas slower crystal growth

from chlorobenzene/cyclohexane aﬀorded the dimer poly-

morphs 5b/6b.¹⁹Compounds 5a and 6a feature extended

zigzag chains of metal atoms with short M···M contacts (Figure

4), two “bands” of π−π interactions (Figure 5a), and void

Figure 4. Portion of a Pt···Pt chain in the crystal structure of 5a. View

is approximately down the a axis. A comparable view of the Pd

analogue 6a is shown in Figure S6 (Supporting Information).

Figure 5. (a) View along the c axis of 5a, showing aryl π−π

interactions between C11 rings (blue dashes) and C21 rings (yellow

dashes). (b) Space-ﬁlling view along the c axis, showing empty

channels at (¹/₄, ³/₄, z) and (³/₄, ¹/₄, z) and CH−π interactions

(orange). A comparable view of the Pd analogue 6a is shown in Figure

S7 (Supporting Information).

channels parallel to the metal chains (Figure 5b). The channels

are walled by phenyl rings, which are canted relative to the

metal coordination plane at dihedral angles of 65−73°. Also

apparent is a CH···π contact between the para hydrogen of

each C21 ring and the ipso carbon of an adjacent C11 ring.

These interactions form part of the walls of the channels

(Figure 5b).

Structures of 5b and 6b, Dimer Form of Pt/

Pd(CNC₆H₅)₂Cl₂. The dimer polymorphs 5b and 6b contain

only isolated M···M contacts of 3.40 Å, signiﬁcantly longer than

those in the chain polymorphs. Only one π−π interaction

occurs per complex: an oﬀset interaction between C21 rings of

inversion-related complexes (Figure 6). A pair of CH···π

contacts between the para hydrogens of the C21 rings and C11

on the opposite complex reinforces these π−π interactions. All

other crystal packing occurs through nonspeciﬁc molecular

contacts. The more eﬃcient overall packing in 5b/6b

(respective packing indices 67.6% and 67.3%) versus 5a/6a

(packing indices 63.1% and 63.5%),⁴⁸albeit at the expense of

extended M···M contacts, is facilitated by a diﬀerent orientation

of the Ph rings. They are canted in the same direction at

dihedral angles of 64−67°, in contrast to the disrotatory

arrangement seen in 5a/6a.

Figure 6. View of two dimers of 5b linked by π−π (center) and CH−π

(orange dash) interactions. A comparable view of the Pd analogue 6b

is shown in Figure S8 (Supporting Information).

parameters and molecular packing arrangements. All non-

hydrogen atoms except the ortho and meta carbons are located

on a crystallographic mirror plane. The p-tolyl rings are rotated

to dihedral angles of exactly 90° relative to the coordination

plane. Adjacent complexes related by a c glide are staggered at

approximate angles of 143°, similar to the arrangement seen in

5a/6a. This allows them to form zigzag chains of metallophilic

interactions along the c axis, with uniform M···M contacts of

3.34 Å (Figure 7). Each complex also forms slightly oﬀset π−π

Structures of 7 and 8, Pt/Pd(CNC₆H₄-p-CH₃)₂Cl₂. Long

yellow rods of 7 and 8 formed upon slow diﬀusion of

cyclohexane into chlorobenzene solutions of the complexes.

Crystals of both complexes showed near-identical unit cell

H

dx.doi.org/10.1021/ic301104a | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

interactions with the C11 and C21 rings of two complexes

related by a 4-fold rotation axis (Figure 8).

of solvent as judged by the presence of diﬀerence Fourier peaks.

Attempts to model this electron density as discrete molecules of

solvents used in synthesis or crystallization were unsuccessful.

Assignment of peaks as partially occupied oxygen atoms led to

reasonable reﬁnement, but physically meaningful arrangements

of water molecules were not identiﬁed. Therefore, the

SQUEEZE procedure⁴²was utilized to correct the structural

data for the disordered electron density (see the Experimental

Section). Although the amount of water in the channels

appeared to vary for diﬀerent samples, the two types of

channels contained roughly equal amounts of disordered

electron density in each case.

Structures of 9a−c, Pt(CNC₆H₄-p-OCH₃)₂Cl₂·x(solvent).

Large crystals were obtained both by diﬀusion of an Et₂O/n-

hexane mixture into a CH₂Cl₂solution of 9 and by diﬀusion of

cyclohexane into a chlorobenzene solution of 9. The two types

of crystal have nearly identical unit cell parameters and packing

arrangements and diﬀer only in the identity of the occluded

solvent: 0.5 molecule of CH₂Cl₂per Pt in the ﬁrst case (9a)

and 0.25 molecule of chlorobenzene in the second case (9b).

The asymmetric units of 9a and 9b consist of two

independent complexes joined by Pt···Pt contacts of 3.50 Å

(9a, Figure 9) or 3.47 Å (9b, Figure S11, Supporting

Information). Two types of π−π interaction are present:

peripheral interactions between the C11 and C21 rings of

inversion-related Pt1 complexes, and oﬀset stacking between

the C31 rings of inversion-related Pt2 complexes. The steric

demands of the OCH₃substituents appear to hinder extensive

π−π stacking and reduce the eﬃciency of the observed π−π

interactions. In particular, the interaction between the C11 and

C21 rings deviates signiﬁcantly from a parallel arrangement

(dihedral angle 15−16°). In addition, three CH₃···π inter-

actions are apparent, with one CH₃hydrogen atom located

2.8−3.3 Å from the centroid of a neighboring aryl ring in each

case (Figure 9a, Table S1).

Figure 7. Portion of a Pt···Pt chain in the crystal structure of 7. View is

approximately perpendicular to the c axis. A comparable view of the Pd

analogue 8 is shown in Figure S9 (Supporting Information).

The occluded solvents in 9a,b occupy channels that run

along the a axes (Figure 9b). The channels appear to be

stabilized by a combination of Pt···Pt dimer formation, π−π

stacking, and CH₃···π interactions, with no speciﬁc packing

motif dominating. Unlike the channeled structures of 5a/6a

and 7/8, there are no extended M···M interactions in 9a,b. The

Pt square planes are tilted relative to the channel axis instead of

being perpendicular as in 5a/6a and 7/8. The maximum

continuous widths of the channels are only 3.2 Å, but they

contain deeper indentations that allow them to accommodate

solvent molecules. The channel walls are not lined by aryl ring

π-systems as in 5a/6a, but rather by chloride ligands and aryl

ring peripheries. The channels occupy 11% of the unit cell

volume in 9a and 9b, similarly to the vacant channels of 5a/6a.

Crystals of 9 were also grown by slow diﬀusion of

cyclohexane into a 1,2-dichlorobenzene solution of the complex

in an attempt to prepare a solvent-free crystalline form. Instead,

a new solvate structure (9c) containing 0.5 equiv of o-C₆H₄Cl₂

per Pt was obtained. As in 9a,b, the asymmetric unit contains

two complexes joined by a Pt···Pt contact. The two complexes

in 9c pack more closely than those in 9a,b, giving a shorter

Pt···Pt distance of 3.25 Å, despite being staggered at a similar

angle (143°, versus 140° for 9a,b). This does not appear to

result from any single factor, but rather from the cumulative

eﬀects of a diﬀerent array of packing interactions.

Figure 8. View along the c axis of 7. Square channels are apparent at

(¹/₂, ¹/₂, z) and (1, 1, z), and rhombic channels are visible at (1, ¹/₂, z)

and (¹/₂, 1, z). A comparable view of the Pd analogue 8 is shown in

Figure S10 (Supporting Information).

The combination of M···M and π−π packing interactions

results in two sets of inﬁnite channels running parallel to the

M···M chains (Figure 8). Channels of the ﬁrst set are square-

shaped and centered on 4-fold rotation axes, with the channel

walls formed by C21 aryl rings. The methyl group of each C21

ring forms a a CH₃···π interaction^49,50with the ipso carbon on

the adjacent wall of the channel, creating a whorl-like

arrangement. The second set consists of rhombic channels

walled by C11 aryl rings. The square channels have minimum

channel widths of 4.6 Å between opposite walls and maximum

diagonal widths of 5.9 Å, accounting for the van der Waals radii

of atoms lining the channels. The rhombic channels have

minimum widths of 3.9 Å and maximum widths of 7.6 Å. Both

types of channel are signiﬁcantly larger than the 3−4 Å wide

channels of 5a/6a and occupy a larger portion of the unit cell

volume: 20%, versus 11% for 5a/6a. Unlike the empty channels

of 5a/6a, the channels of 7 and 8 contain a signiﬁcant amount

The solvent molecules do not occupy channels in 9c, but

rather occur as π−π stacked dimers that are “boxed in” by the

C21, C31, and C41 aryl rings (Figure 10). The o-C₆H₄Cl₂

I

dx.doi.org/10.1021/ic301104a | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

These stacks continue inﬁnitely along the [111] lattice

direction (Figure S12, Supporting Information). The aryl

rings of the Pt2 complex are rotated at dihedral angles of 76°

and 88° relative to the coordination plane in order to

accommodate these π−π interactions. The Pt1 complex

forms peripheral π−π interactions with an inversion-related

Pt1 complex through both the C11 and C21 rings. There is less

involvement of CH₃···π interactions compared to 9a,b, with

only one example involving the C31 ring. However, two aryl

CH···π contacts are present, one between neighboring

complexes (C41 and C11 rings) and one between the o-

C₆H₄Cl₂solvent and the C21 ring of a complex (Figure 10 and

Figure S13, Supporting Information).

Structures of Pd(CNC₆H₄-p-OCH₃)₂Cl₂·(10a) and 1,2-

Dichlorobenzene Solvate (10b). In contrast to 9, slow

diﬀusion of n-hexane into CH₂Cl₂solutions of 10 produced a

solvent-free form of the compound (10a). The two crystallo-

graphically independent complexes of 10a are oriented with

their coordination planes in a nonparallel arrangement

(dihedral angle 69°), precluding any close Pd1···Pd2 contacts.

Each Pd1 complex forms a head-to-tail dimer with an inversion-

related complex at a Pd1···Pd1 distance of 3.46 Å (Figure 11).

Figure 9. (a) Partial packing diagram of 9a, showing Pt···Pt contacts

(magenta dashes), π−π interactions (yellow dashes), and CH₃−π

interactions (orange dashes). View is along a CH₂Cl₂-ﬁlled channel

(center) running along the a axis. (b) View perpendicular to the

solvent-ﬁlled channels of 9a, with CH₂Cl₂molecules shown in a space-

ﬁlling representation. Comparable views of the chlorobenzene solvate

9b are shown in Figure S11 (Supporting Information).

Figure 11. View of a Pd1 dimer in 10a, showing Pd···Pd contact (pink

dash) and aryl π−π interactions with Pd2 complexes (yellow dashes).

Additional packing interactions of 10a are shown in Figure S14

(Supporting Information).

The Pd2 complexes do not form any short Pd···Pd interactions.

The orientations of the aryl rings also diﬀer relative to 9a−c.

Both rings are nearly parallel to the coordination plane for the

Pd2 complex, but one of the rings (C21) is rotated by 67° in

the Pd1 complex. This allows the C21 ring to form oﬀset π−π

stacking interactions with the C31 and C41 rings of two

neighboring Pd2 complexes. In combination with peripheral

π−π contacts between inversion-related C31 rings, these

interactions form 6-ring π stacks that run along the [011]

direction. The C11 ring of the Pd1 complex does not exhibit

any π−π interactions, but it is involved in two CH₃···π

interactions, one with an inversion-related C11 ring and one

with the C21 ring of a neighboring Pd1 complex (Figure S14,

Supporting Information).

Crystal growth of 10 using the 1,2-dichlorobenzene/n-

hexane solvent pair, under conditions identical to those used to

obtain 9c, led to a C₆H₄Cl₂solvate (10b) that is diﬀerent from

9c. Like 9c, 10b has two crystallographically independent

complexes linked by a Pd···Pd interaction, but there are also

two independent C₆H₄Cl₂molecules, giving a 1:1 Pd/solvent

ratio, in contrast to the 2:1 Pt/solvent ratio in 9c. The

Pd1···Pd2 dimers form inﬁnite chains of Pd···Pd interactions

(Figure 12), although these are signiﬁcantly longer than the

Figure 10. Packing of Pt complexes around a π−π stacked pair of 1,2-

dichlorobenzene solvent molecules in 9c. A CH- interaction (orange)

and a portion of the extended C41-solvent−solvent-C41 π−π stacking

interactions (center) are shown. Additional packing views of 9c are

shown in Figures S12 and S13 (Supporting Information).

solvent engenders more extensive π−π stacking than is seen in

9a,b. The o-C₆H₄Cl₂dimers form π−π interactions with the

C41 rings of Pt2 complexes, which in turn engage in peripheral

π−π stacking with the C41 rings of neighboring complexes.

J

dx.doi.org/10.1021/ic301104a | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

layers (Figure 13), whereas CH₃···π interactions between

inversion-related C31 rings exist in the Pd2 layers (Figure S15,

Supporting Information). Oblique CH−π interactions link the

C21 rings in the Pd1 layers to C31 rings in the adjacent Pd2

layers (Figure S16).

Structures of 11 and 12, Pt/Pd(CNC₆H₃-2,6-Me₂)₂Cl₂.

Crystals of 11 and 12 were obtained by diﬀusion of n-hexane

into CH₂Cl₂solutions of the compounds. The structures of 11

and 12 are nearly identical. The complexes form inﬁnite stacks

along the a axis, with adjacent complexes adopting a near head-

to-tail orientation that is slightly laterally oﬀset to accommodate

steric interactions between the bulky aryl groups (Figure 14).

Figure 12. Portion of a Pd···Pd chain in the crystal structure of 10b.

View is approximately perpendicular to the b axis.

isolated Pt···Pt contacts of 3.25 Å in 9c. Each Pd1 and Pd2

forms a head-to-tail interaction with an inversion-related

complex, with respective Pd1···Pd1 and Pd2···Pd2 distances

of 3.49 and 3.51 Å. The Pd1···Pd2 contacts are longer at 3.54 Å,

despite the stagger angle (148°) being similar to those in

structures such as 5a/6a and 9c with shorter M···M distances.

The Pd1 and Pd2 complexes appear to be pushed slightly apart

to accommodate other packing interactions.

As in 9c, the C₆H₄Cl₂solvent molecules in 10b facilitate π−π

interactions, but to an even greater extent. Each of the two

C₆H₄Cl₂molecules forms a π−π stacked dimer with an

inversion-related molecule, with each dimer surrounded by

isocyanide aryl rings. Both dimers are incorporated into inﬁnite

stacks of π−π interactions running roughly perpendicular to the

Pd···Pd chains, with solvent dimers alternating with π−π-

stacked pairs of inversion-related aryl rings (Figure 13). These

π stacks occur in layers involving only the C11 rings of the Pd1

complexes or only the C41 rings of the Pd2 complexes for the

two independent sets of solvent molecules. Oﬀset π−π contacts

involving inversion-related C21 rings also occur in the Pd1

Figure 14. Extended head-to-tail stacking in the crystal structure of 11.

Pt···Pt distances alternate between 3.95 Å (bottom two complexes)

and 4.13 Å. A comparable view of the Pd analogue 12 is shown in

Figure S17 (Supporting Information).

The alternating M···M distances of 3.95 and 4.12−4.13 Å are

too long to signify signiﬁcant metallophilic interactions. The

steric demands of the aryl rings apparently preclude any π−π

interactions. However, neighboring stacks along the b and c

axes are linked via reciprocal CH₃···π interactions between

inversion-related C11 and C21 rings, respectively (Figures S18

and S19, Supporting Information).

Discussion of Crystal Packing Interactions. Table 4

divides observed M···M contacts into short interactions likely

to have some contribution from metallophilic bonding, and

longer ones where the proximity of the metal atoms may be a

fortuitous result of other interactions. The dividing line of 3.4 Å

is twice the van der Waals radius of Pt.⁴⁵The M···M distances

range from 3.24 to 3.25 Å for 5a/6a and 9c to 3.95−4.13 Å for

11/12. All interactions less than 3.4 Å exhibit a staggered

geometry, with adjacent complexes rotated by angles of 138−

144° (last column, Table 3). This arrangement appears to

minimize steric interactions between the ligands, thereby

facilitating close contacts between the metal atoms. By contrast,

many of the longer interactions (i.e., those in 4, 10a, 10b, and

11/12), as well as the borderline 3.40 Å contacts of 5b/6b,

feature a head-to-tail arrangement of complexes with a rotation

angle of 180°. This geometry is more plausibly ascribed to

interactions of molecular dipoles than to orbital-based M···M

interactions. However, several longer interactions (i.e., those in

1/2, 3, 9a, 9b, and Pd1···Pd2 in 10b) show staggered

geometries. This suggests that formation of both optimal

M···M contacts and dipole−dipole interactions may be

Figure 13. Packing diagram of the Pd1 layer of 10b, showing extended

stacks of C11−C11-dichlorobenzene−dichlorobenzene π−π interac-

tions and an isolated C21−C21 π−π interaction (center). View is

approximately down the b axis, and the extended π−π stacking runs

along the c axis. Packing in the Pd2 layer and between layers is shown

in Figures S15 and S16 (Supporting Information).

K

dx.doi.org/10.1021/ic301104a | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

prevented by ligand steric properties or the need to

accommodate other packing interactions.

which have chains of short M···M contacts, as well as for 1/2

and 11/12, in which only longer interactions are present. Given

that metallophilic interactions are expected to be stronger for

Pt,²⁸this suggests that these interactions do not play a

dominant role in determining the solid-state structures, but

instead are only one component in an array of packing forces.

However, we observed¹⁹that the nonchain polymorph of

M(CNPh)₂Cl₂forms more readily for Pd (6b) than for Pt

(5b), suggesting that stronger metal−metal bonding in Pt could

result in diﬀerent structures being obtained for the two metals

in some cases. The diﬀerences observed in the structures of

M(CNC₆H₄-p-F)₂Cl₂(3 versus 4) and M(CNC₆H₄-p-

OCH₃)₂Cl₂(9a−c versus 10a,b), although complicated, are

consistent with a stronger driving force for Pt···Pt versus

Pd···Pd interactions. Pd complex 4 has one less “long” Pd···Pd

contact per dimer in its dimer-of-dimers structure compared

with the linked dimer structure of Pt congener 3, and the

remaining interdimer M···M contact is 0.1 Å longer than those

in 3. However, 4 does not appear to achieve any greater degree

of aryl π−π interactions compared with 3. Instead, the overall

packing eﬃciency is slightly higher (68.8% for 4 versus 68.1%

for 3), allowing 4 to minimize free volume⁵²and achieve more

nonspeciﬁc intermolecular contacts. The diﬀerences in M-

(CNC₆H₄-p-OCH₃)₂Cl₂structures are more complex. Com-

pounds 9a−c feature Pt···Pt contacts with staggered geometries

similar to those in the chain structures 5a/6a and 7/8, though

only 9c has a Pt···Pt distance less than 3.4 Å, whereas 10a,b

contain primarily head-to-tail interactions. The degree of M···M

contact in the unsolvated Pd complex 10a is diminished relative

to the solvated Pt structures 9a−c, with only half the complexes

in 10b involved in a M···M contact. The comparison of the o-

dichlorobenzene solvates is ambiguous, with fewer but shorter

M···M contacts in 9c versus 10b. Notably, the number of π−π

interactions is increased for 10a,b relative to 9a−c, suggesting a

shift in the balance of packing forces toward π−π contacts,

possibly at the expense of shorter M···M interactions, on

moving from Pt to Pd.

Discussion of Channel Formation. The examples of 5a/

6a and 7/8 imply that a synergistic combination of aryl π−π

and metallophilic interactions is required to stabilize structures

that feature both extended M···M contacts and empty or

solvent-ﬁlled channels. Combinations of other interactions can

also lead to channels, as shown by 9a,b, but these do not

contain extended metallophilic interactions. In both 5a/6a and

7/8, the channels are walled by isocyanide aryl rings. The

square channels of 7/8 share a common feature with the

channels of 5a/6a in that each aryl para substituent forms an

interaction with an adjacent wall of the channel (Figures 5 and

8). The CH₃substituents in 7/8 expand the channels

signiﬁcantly relative to 5a/6a. However, the larger p-CF₃and

p-OMe groups clearly cannot accommodate such an arrange-

ment. In the case of p-F, the lack of a channeled structure may

be due to a weaker driving force for M···M bonding (vide

supra), or, alternatively, may result from an unfavorable

electrostatic match between ﬂuorine and an adjacent aryl

ring. Finally, the existence of the nonchanneled polymorphs of

M(CNPh)₂Cl₂(5b/6b) shows that the driving force for a more

eﬃciently packed structure⁵²can outweigh the favorable

combination of aryl π−π and metallophilic interactions.

There is no clear correlation between the degree of metal−

metal interaction and the electronic properties of the

arylisocyanide substituents. The most extensive metal−metal

contacts are seen for 5a/6a and 7/8, both of which contain

zigzag chains with two short contacts per metal atom. Although

electron-releasing substituents could hypothetically enhance

metallophilic bonding by increasing the degree of conﬁguration

interaction,⁷the metal−metal contacts are actually longer in 7/

8 (R = p-CH₃, Hammett σ = −0.14)⁵¹than in 5a/6a (R = H, σ

= 0). Furthermore, structures containing the electron-releasing

p-OMe substituent (9a−c and 10a,b ; σ = −0.29) showed only

isolated M···M contacts, all of them longer than 3.4 Å except

for the 3.25 Å Pt···Pt distance of 9c. The complexes with the

strongest electron-withdrawing substituents, 1/2 (R = p-CF₃, σ

= 0.53), show a similar degree of metal−metal contact to the p-

OMe structures, with only isolated M···M distances of ∼3.5 Å.

The sterically hindered complexes 11/12 (R = 2,6-Me₂) exhibit

only longer head-to-tail contacts (≥4.0 Å) that preclude any

metallophilic interactions.

The overall pattern suggests that substituents with smaller

steric demands generally lead to increased metallophilic

contacts. However, Pt complex 3 (R = p-F, σ = 0.15) provides

some evidence that electron-withdrawing groups may reduce

the tendency for M···M interactions to form. Complexes with

phenyl isocyanide (5a) and bulkier but more electron-rich p-

tolyl isocyanide (7) are both able to accommodate extended

chains of short Pt···Pt contacts. The steric bulk of a p-F

substituent falls between those of H and Me, so it is likely that

an extended chain structure would be feasible for 3 as well.

Instead, 3 adopts a structure intermediate between an extended

chain and isolated dimers, with short, staggered Pt···Pt contacts

alternating with longer ones. Notably, the number of aryl π−π

interactions is increased in 3 relative to 5a and 7 (Table 4).

It is evident that π−π and related packing interactions can

either disrupt M···M interactions or synergistically stabilize

them. Both structures with extended chains of short M···M

contacts, 5a/6a and 7/8, exhibit two π−π interactions and two

CH···π contacts per complex. Thus, it seems likely that these π

interactions play an important role in stabilizing the aryl-walled

channels in these two structure types. Aryl π−π interactions

reach a maximum of four per complex in 3 and 4, in which the

p-F substituents provide little steric hindrance to packing and

also possibly reduce the driving force for metallophilic

interactions through electronic eﬀects (vide supra). The bulkier

p-CF₃and p-OMe groups in 1/2, 9a−c, and 10a,b result in

more complicated packing schemes that include CF₃···π or

CH₃···π interactions, though 1.5−2.5 π−π interactions per

complex are still present in each case. The complexes with

ortho-substituted aryl rings, 11/12, are sterically prevented from

forming any π−π interactions and show only CH₃···π contacts.

The ﬁne balance between diﬀerent packing interactions is

apparent in the crystallization behavior of 9. In 9a and 9b,

CH₃···π interactions predominate, and their combination with

π−π interactions and isolated Pt···Pt contacts stabilizes

channels that can accommodate either CH₂Cl₂(9a) or

chlorobenzene (9b). Addition of 1,2-C₆H₄Cl₂(9c) causes a

shift to more extensive π−π stacking while reducing the

number of CH₃···π interactions and allowing a closer approach

of the Pt atoms.

A survey of related compounds shows that the channels of 7

and 8 are among the largest known for structures supported by

metallophilic bonding. The vapochromic compound Tl[Au-

(C₆Cl₅)₂] was reported to have channels up to 10.47 Å wide

Notably, the structures of isoleptic Pt and Pd complexes are

almost identical in most cases. This is true for 5a/6a and 7/8,

L

dx.doi.org/10.1021/ic301104a | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

Figure 15. Luminescence spectra of macrocrystalline (a−c) and powder (d−f) samples of 5a, 7, and 3. Excitation spectra were recorded at the

emission maxima. Excitation wavelengths used for emission spectra are given in Table 5.

based on the distance between Au atoms.^15hHowever, analysis

of the structure with PLATON^42bshows that there is no

discernible void space in the unsolvated form, and solvated

forms contain solvents that are bound to Tl rather occupying

true channels.¹⁵ⁱA gold(I) carbene complex was found to

crystallize with acetone, benzene, or chlorobenzene occupying

channels with maximum widths of ∼5 Å.^15m(2,2′-

Bipyrimidine)PtCl₂crystallizes with 2.3 Å × 7.0 Å channels

that are narrower and slightly shorter than the rhombic

channels of 7/8,⁷yet able to accommodate N-methylpyrroli-

done solvent molecules.⁵³The structure of closely related

Pt(CNC₆H₄-p-C₂H₅)₂(CN)₂has octagonal channels with

maximum widths of 4.5−4.7 Å that contain toluene or

hexane,^15fwhereas Pt(CNⁱPr)₂(CN)₂forms channels that

accommodate benzene despite their narrow widths (1.6 × 6.6

Å²).^15qA recently reported structure of (benzoquinolinate)Pt-

(CN^tBu)Cl has channels with widths of 2.6 × 3.9 Å²that

contain CHCl₃.^13jAt ﬁrst glance, it is surprising that the

channels of 7 and 8 do not accommodate hexane or CH₂Cl₂,

given that the solvent-ﬁlled channels in the above-cited

structures all have smaller widths. However, closer inspection

reveals that the published examples all contain deeper

indentations that are wider than the maximum continuous

channel widths, similarly to structures 9a,b. By contrast, the

channels of 7 and 8 have smooth, nonindented channel walls

composed primarily of aryl ring π-surfaces, as do the narrower

channels of 5a and 6a. Although such uniform walls could be

desirable for facile diﬀusion of molecules into the channels, the

channels of 7 and 8 do not appear to be wide enough to

accommodate solvents other than H₂O despite their large

continuous channel widths. The accommodation of H₂O in

apparently hydrophobic, arene-walled channels in 7/8 is

notably similar to the spontaneous uptake of H₂O by single-

walled carbon nanotubes.⁵⁴

Luminescence Studies. Luminescence in extended Pt···Pt

chain structures is often attributed to excited states centered on

2

the valence bands formed by overlap of d_zorbitals along the

Pt···Pt chains.^6a,18aBecause such behavior would provide

evidence for metallophilic interactions involving substantial

orbital overlap, we tested large crystals (>0.7 mm) of all of the

Pt(CNAr)₂Cl₂complexes for luminescence.

M

dx.doi.org/10.1021/ic301104a | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

Visible luminescence was detected for crystals of 3, 5a, and 7,

with each exhibiting broad, unstructured emission peaks at low

energies (λ_max∼600−730 nm; Figure 15a−c and Table 5).

(³MMLCT) states involving dσ*(Pt)→ π*(ligand) transi-

tions^{13j,14d,15j,n,56}or to metal-centered (³MC) states involving

dσ*→ pσ transitions.^5,15f,23As the arylisocyanide ligands

become more electron-rich, both the Pt dz²(dσ*) and

isocyanide π* orbitals should rise in energy. The observed

Table 5. Luminescence Data for 5a, 7, and 3

3

trend in emission maxima would be consistent with MMLCT

complex

excitation wavelength

415 nm

T, K

λ_max, nm (τ, μs)

if these two orbitals are destabilized by diﬀerent amounts,

provided these diﬀerences are well reﬂected in the emissive

excited state geometries. However, absorption spectra of dilute

solutions of 3, 5, and 7 exhibit low-wavelength maxima that are

5a crystal

295

225

150

77

650 (1.7)

661

699

57

709 (4.1)

617 (1.1)

635

2

likely attributable to d_z→ π* transitions, yet vary little as a

5a powder

415 nm

295

220

150

77

function of ligand substituent (Figures S21−S23 and Table S4,

Supporting Information). This indicates a fairly constant gap

between dσ* and π* orbitals in this series, suggesting that

³MMLCT-based emission maxima should also vary little,

although excited-state distortions could complicate this

picture.^21c,58We favor a metal-centered (³MC) assignment

for the luminescent states in 3, 5a, and 7, as the Pt pσ orbitals

should be little aﬀected by ligand donor strength, whereas dσ*

orbitals should be destabilized by stronger donors. This

assignment is consistent with literature precedent for other

luminescent Pt···Pt chain compounds containing isocyanide

ligands.^15f,23

660

670 (3.7)

674 (1.5)

709

7 crystals

7 powder

415 nm

420 nm

295

180

77

729 (5.1)

695 (0.9)

717

295

220

150

77

728

732 (5.5)

590

3 crystal

390 nm

295

180

77

603

The temperature-dependent luminescence spectra of 3 show

features not observed for 5a and 7. Luminescence of 3 is weak

at 295 K, and the emission maximum changes only slightly

from 295 to 180 K before shifting to the red by >60 nm at 77 K

(Figure 15c and Table 5). These observations, as well as the

broadness of the 77 K emission peak and a shoulder at lower

wavelength, suggest two diﬀerent phosphorescent excited states

that dominate at diﬀerent temperatures. A blue shift in the

excitation peak between 180 and 77 K is consistent with a

diﬀerent luminescence process at 77 K. In addition, excitation

of 3 at a longer wavelength corresponding to the room

temperature excitation maximum (450 nm) resulted in a 47 nm

blue-shift for the 77 K emission but did not aﬀect the emission

maxima at higher temperatures (Table 5). A plausible

666 (5.0)

591 (2.1)

601

a

450 nm

295

180

77

619 (6.3)

582 (1.5)

3 powder

360 nm

77

a

Emission plots for 3 at 450 nm excitation are shown in Figure S20

(Supporting Information).

Crystals of 3, which consists of weakly linked Pt···Pt dimers,

showed noticeably weaker luminescence compared with 5a and

7, which have uniformly short Pt···Pt distances (Table 3). None

of the crystals containing isolated Pt···Pt dimers was

luminescent, strongly suggesting that the luminescence of 3,

5a, and 7 arises from electronic states involving communication

along the extended Pt···Pt chains. Luminescence spectra

measured at several temperatures from 295 to 77 K showed

the expected increases in intensity due to attenuation of

nonradiative decay processes, as well as red shifts in the

emission maxima upon cooling. Such red shifts are character-

istic of luminescent Pt···Pt chain compounds and are attributed

to contraction of the Pt···Pt distances at low temper-

ature,^{6a,15j,18a,55}which strengthens metallophilic bonding and

2

explanation is that eﬀective overlap of Pt 5d_zand 6p orbitals,

which is required for luminescence based on spatially

3

delocalized MC states, only occurs at very low temperatures

at which the weak interdimer Pt···Pt contacts of 3 are

signiﬁcantly contracted (vide infra). As the temperature

increases, 3 behaves more as an isolated Pt···Pt dimer structure,

allowing other phosphorescent states to be populated. Although

³MMLCT-based emission from isolated Pt···Pt dimers is

known for complexes of certain ligands,⁵⁹this is unlikely to

account for the higher-temperature phosphorescence of 3,

given that no luminescence was observed for any of the other

isocyanide-ligated Pt···Pt dimer structures (i.e., 1, 5b, 9a−c).

The higher-temperature emission of 3 is more plausibly

attributed to an excimer-like state arising from ligand π→π*

transitions in π-stacked complexes. There is precedent for

excimer-based emission occurring at similar energies in Pt

complexes that also show ³MMLCT-based luminescence.^56b,c,60

This assignment is consistent with the greater prominence of

π−π interactions in the structure of 3 compared 5a and 7

(Table 4).

thereby raises the dσ* states of the d_zband in energy.⁷

2

Emission lifetimes suggest phosphorescent excited states at all

temperatures (Table 5).

It is well established that the emission maxima of related

Pt···Pt chain structures, most notably salts of [Pt(CN)₄]⁻, shift

to lower energy as the Pt···Pt distances decrease.⁵Interestingly,

the emission spectra of crystalline 3, 5a, and 7 do not show this

trend. The emission maximum of 7 (729 nm at 77 K) is lower

in energy than that of 5a (709 nm), although the Pt···Pt

distances are longer in 7. However, compound 3 has the

highest emission energy (666 nm), consistent with its longer

Pt···Pt distances. Rather than correlating with Pt···Pt distances,

the emission energies appear to reﬂect the isocyanide aryl

substituent. More electron-rich arylisocyanides (e.g., p-Me-

C₆H₄NC in 7) shift the emission maxima to lower energies.

Luminescence in Pt···Pt chain compounds has commonly been

attributed either to metal-metal-to-ligand charge transfer

Luminescence spectra of powder samples of 3, 5, and 7,

which were identical to those used to grow the larger crystals,

were also obtained. Powder X-ray diﬀraction conﬁrmed that all

three samples were composed of the same crystalline phase as

the larger single crystals (Figures S24−S26, Supporting

Information). The emission spectra of powdered 5 and 7

N

dx.doi.org/10.1021/ic301104a | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

closely resemble those of the macrocrystalline samples, with

similar red shifts seen upon cooling (Figure 15d,e). By contrast,

the powder sample of 3 showed no detectable luminescence at

room temperature and only weak luminescence at 77 K, with

the emission maximum of 582 nm matching the room-

temperature spectrum of macrocrystalline 3 rather than the 77

the largest decreases in the relevant distances. To further

evaluate the relative importance of extended M···M inter-

actions, we have examined the temperature dependence of

structures 3, 5a/6a, and 7. For 3 and 5a/6a, full structures were

determined at 300 and 100−115 K, allowing direct

comparisons of structural changes (Table 6). To provide

3

K spectrum. We hypothesize that the delocalized MC states

responsible for the 77 K emission in macrocrystalline 3 are

destabilized in smaller microcrystals, in which the Pt···Pt chains

have a reduced spatial extent, allowing population of π→π*

states instead. A similar eﬀect of crystallite size may be

responsible for the blue shifts of 26−39 nm observed in the

emission peak of powdered 5 relative to the macrocrystalline

sample (Table 5), although this eﬀect is not seen for 7.

Table 6. Temperature Dependence of Selected Structural

Parameters

aryl π−π

interplanar

separation

aryl π−π

centroid−

centroid

structure

T

M···M (Å)

other

5a

300 K 3.3183(8)

100 K 3.2455(3)

300 K 3.3152(3)

100 K 3.2370(3)

3.43 Å (C11−

3.86 Å

4.07 Å

3.82 Å

3.91 Å

3.87 Å

4.04 Å

3.83 Å

3.89 Å

3.90 Å

4.15 Å

CH−π

C11)

2.91 Å

Face Indexing of Crystals. In our preliminary report,¹⁹

face-indexing of crystals of 5a and 6a revealed that the preferred

crystal growth axis was along the extended M···M chains. To

probe whether this is a general phenomenon, we face-indexed

samples of the other luminescent Pt···Pt chain compounds, 3

and 7. Both compounds form long, rod-shaped crystals, and

face-indexing conﬁrmed that the long axis corresponds to the

direction of the M···M chains in each case (Figure 16): the

3.76 Å (C21−

C21)

3.32 Å (C11−

C11)

CH−π

2.90 Å

3.56 Å (C21−

C21)

6a

3.42 Å (C11−

C11)

CH−π

2.92 Å

3.75 Å (C21−

C21)

3.32 Å (C11−

C11)

CH−π

2.91 Å

3.56 Å (C21−

C21)

3

300 K Pt1−Pt2

3.46 Å (C11−

C41 #1)

3.47 Å (C11−

C41 #2)

3.4913(3)

Pt1−Pt2 [1 +

x, y, z]

3.8809(3)

3.43 Å (C21−

C31 #1)

3.36 Å (C21−

C31 #2)

3.36 Å (C11−

C41 #1)

3.41 Å (C11−

C41 #2)

3.86 Å

4.26 Å

3.72 Å

3.97 Å

115 K Pt1−Pt2

3.3747(3)

Pt1−Pt2 [1 +

x, y, z]

3.7858(4)

3.34 Å (C21−

C31 #1)

3.31 Å (C21−

C31 #2)

3.71 Å

4.10 Å

Figure 16. Face-indexed crystals of (a) 3 and (b) 7. Yellow lines

indicate face normals.

[100] lattice direction (i.e., the a axis) in the case of 3, and the

[001] lattice direction (i.e., the c axis) in the case of 7. Complex

8, the near-isostructural Pd analogue of 7, also shows preferred

growth along the c axis, corresponding to the Pd···Pd chain

direction (Figure S27). Notably, the Pd 4-ﬂuorophenyl

isocyanide complex 4 forms rods similar in appearance to

those of 3, but the preferred growth axis does not correlate with

any speciﬁc packing interaction. Instead, the crystals grow

further insights into the temperature dependence of packing

interactions, changes in the unit cell parameters of 3, 5a, and 7

over the 100−300 K range were also examined (Figure 17).

For 5a, the Pt···Pt distances decrease by 2.2% on cooling

from 300 to 100 K. The aryl π−π interactions show an even

greater decrease, with interplanar separations shrinking by 3.2%

for the C11 rings and 5.3% for the C21 rings. The c and b unit

cell axes of 5a both contract by ∼2% upon cooling to 100 K

(Figure 17), which can be ascribed to the shortening of the

Pt···Pt distances and C21 aryl π−π interactions, respectively.

Interestingly, the a axis shows a signiﬁcant lengthening (∼2%)

upon cooling. This appears to be an indirect result of the

decreased aryl−aryl interplanar separations. In order to

accommodate closer π−π interactions with neighboring

complexes, the PhNC ligands bow outward slightly. This

results in a larger spread between the para carbon atoms of the

Ph groups at 100 K (C14−Pt−C24 angle 89.3° at 300 K and

91.2° at 100 K), which leads to the observed increase in a.

Structural changes in the Pd congener 6a are nearly identical to

those seen in 5a, with aryl π−π separations again showing

larger decreases than M···M distances upon cooling (Table 6).

preferentially along the [1 2 0] lattice direction (Figure S28),

̅

which is roughly perpendicular to the direction of π−π stacking

and does not parallel the Pd···Pd “linked dimer” contacts.

These results support the view that a combination of extended

metallophilic interactions and π−π stacking contributes

signiﬁcantly to driving force for crystal formation in 3, 5a/6a,

and 7/8. Complex 4 provides evidence that π−π interactions

alone do not provide enough thermodynamic impetus to

determine the preferred crystal growth axis.

Temperature Dependence of Packing Interactions.

Pt···Pt distances can shorten signiﬁcantly upon cooling a crystal

when extended metallophilic interactions play a prominent role

in crystal packing.^15j,55As thermal motions decrease, packing

interactions that are the most favorable are expected to show

O

dx.doi.org/10.1021/ic301104a | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

the structure distorts away from tetragonal symmetry by

random contractions in either a or b in diﬀerent regions of the

crystal in order to preserve as many of these interactions as

possible. This results in loss of single crystallinity at low

temperatures.

The linked-dimer Pt···Pt chains of 3 show decreases in both

the intradimer Pt···Pt distances (by 3.4%) and the longer

interdimer Pt···Pt distances (by 2.3%). These are the largest

percent contractions of Pt···Pt distances in the series. The aryl

π−π interactions show reductions in interplanar separations of

1.5−2.7% and decreases in centroid−centroid distances of 3.7−

4.2%. The a unit cell axis, which corresponds to the direction of

both the Pt···Pt chains and the π−π stacking interactions,

shows the largest change upon cooling from 300 to 115 K,

shrinking by ∼2% (Figure 17). This contraction in the Pt···Pt

packing axis is comparable to those seen in 5a and 7, despite

the presence of weaker interdimer Pt···Pt contacts in 3. We

postulate that this is due to the presence of synergistic π−π

stacking interactions running along the same axis. Although

adjacent chains of complexes are linked by aryl π−π

interactions along b (Figure 3a), this cell axis does not change

measurably upon cooling. Instead, the π−π stacked complexes

shift diagonally as the centroid−centroid distances decrease,

and this is accommodated by a slight contraction (∼1%) along

c and a decrease of 0.8° in β.

Comparison of Bond Lengths for Pt and Pd

Complexes. The crystallographic data provide an opportunity

to examine diﬀerences in structural parameters for a series of

isoleptic Pd and Pt isocyanide complexes. Average values of

M−C, M−Cl, and CN bond lengths for each structure are

shown in Table 7. The Pd−C bond lengths [av 1.937(1) Å] are

slightly but consistently longer than the Pt−C bond lengths [av

1.911(1) Å], with an average diﬀerence of +0.027(2) Å. The

M−Cl bond lengths diﬀer by a much smaller amount in the

opposite direction [av Pd−Cl 2.308(1); av Pt−Cl 2.315(1) Å;

av diﬀerence −0.006(2) Å]. The diﬀerences in M−C bond

lengths could plausibly be attributed to the slightly larger

covalent radius of Pd [1.39(6) Å] versus Pt [1.36(5) Å],²⁵but

this does not explain the shorter M−Cl bond lengths for Pd. A

consistent explanation is that the isocyanide ligands form

stronger bonding interactions with Pt than with Pd, thereby

lengthening the opposing Pt−Cl bonds via the trans inﬂuence.

The average ν(CN) frequencies from the IR spectra are

lower by 3−12 cm⁻¹for the Pd complexes versus the isoleptic

Pt complexes in all cases except 9/10 (Table S3, Supporting

Information), suggesting that increased π-backbonding is at

least partly responsible for the observed diﬀerences in M−C

Figure 17. Temperature dependence of unit cell parameters.

The structure of the p-tolyl Pt complex 7 could not be

determined at low temperature due to a phase change below

250 K that resulted in loss of single crystallinity. However, cell

parameters were estimated over the 100−300 K range by

repeatedly indexing a set of reﬂections that appeared to

correspond to a single crystalline domain. These data indicated

that the c axis contracted by ∼2.5%, whereas the lengths of the

a and b axes stayed almost constant. The c axis corresponds to

the direction of the extended Pt···Pt chains. The a axis shrank

slightly relative to b below 250 K. We speculate that the

structure of 7 is unable to accommodate contractions in both

Pt···Pt distances and aryl π−π stacking upon cooling, and that

a b

,

Table 7. Selected Bond Distances for Pt and Pd Complexes

Pt structure

M−C (av), Å

M−Cl (av), Å

CN (av), Å

Pd structure

M−C (av), Å

M−Cl (av), Å

CN (av), Å

1

1.911(3)

1.906(5)

1.911(8)

1.910(2)

1.918(4)

1.913(2)

1.912(3)

1.913(1)

1.909(4)

2.312(1)

2.316(4)

2.321(4)

2.320(3)

2.319(4)

2.311(2)

2.311(3)

2.315(3)

2.319(1)

1.147(2)

1.153(6)

1.15(1)

2

1.939(2)

1.938(3)

1.939(2)

1.937(2)

1.936(3)

1.934(6)

1.939(4)

2.305(2)

2.308(3)

2.308(8)

2.310(5)

2.305(4)

2.309(3)

2.310(2)

1.147(2)

1.141(3)

1.140(3)

1.144(1)

1.139(7)

1.144(1)

1.148(2)

3

4

5a

5b

6a

6b

1.149(2)

1.129(4)

1.147(2)

1.146(3)

1.144(2)

1.151(3)

c

7

8

9a [9·0.5(CH₂Cl₂)]

9b [9·0.25(PhCl)]

9c [9·0.5(C₆H₄Cl₂)]

11

10a

10b [10·C₆H₄Cl₂]

12

1.932(1)

2.308(2)

1.145(1)

a

b

A detailed listing of bond lengths and angles is given in Table S2 (Supporting Information). Determined from low temperature data sets (100−

c

115 K) unless otherwise noted. Determined from data at 298 K.

P

dx.doi.org/10.1021/ic301104a | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

Notes

bond lengths and trans inﬂuence. The observed shortening of

CN bond lengths by an average of −0.004(2) Å for Pd

complexes relative to the Pt analogues further supports this

explanation. Structurally, the diﬀerences in metal−ligand bond

lengths are minor, and they do not appear to signiﬁcantly

impact the crystal packing of Pt versus Pd complexes.

The authors declare no competing ﬁnancial interest.

^§Deceased, January 2012. Most recent address: King Fahd

University of Petroleum & Minerals, KFUPM Box 418,

Dhahran 31261, Kingdom of Saudi Arabia.

ACKNOWLEDGMENTS

■

CONCLUSION

We thank the National Science Foundation (CAREER Award

CHE-0645438 to L.M.S. and CHE-0911690 to M.A.O.) for

funding. I.M.S. was partly supported by an REU grant from the

National Science Foundation (CHE-0649162). Sri Subrama-

nium and Yohan Mathota Arachchige (OSU) are thanked for

assistance in obtaining spectroscopic data.

■

Metal−metal contacts of 3.5 Å or shorter are present in all

studied Pt/Pd(CNAr)₂Cl₂complexes except for those with

ortho CH₃groups (11/12), in which they are sterically

precluded. Only in the cases of 5a/6a (Ar = Ph), 7/8 (Ar =

C₆H₄-p-CH₃), and 3 (Ar = C₆H₄-p-F) are extended chains of

metallophilic interactions present. In each of these cases, π−π

stacking interactions between isocyanide aryl rings also feature

prominently in the crystal packing network. The primary eﬀects

of aryl ring substitution are to change the steric properties of

the isocyanide ligands and to create possibilities for alternative

packing motifs (e.g., CH₃···π and CF₃···π) that can either

augment or disrupt M···M interactions, rather than to promote

or to disfavor metallophilic bonding through electronic eﬀects.

However, the relative weakness of Pt···Pt bonding in p-F

substituted 3 compared with sterically similar 5a suggests that

electronic eﬀects may play at least a minor role in promoting

metallophilic interactions. Evidence that metallophilic bonding

plays an important, though probably not dominant, role in

determining crystal packing arrangements is seen in the

stronger M···M interactions for Pt complexes versus their

nonisostructural Pd analogues in 3/4 and 9a−c/10a,b as well

as the orientation of the preferred crystal growth axes of 3, 5a/

6a, and 7/8 along the extended M···M chains. The Pt···Pt

chain-centered luminescence of 3, 5a, and 7, as well as the

temperature dependence of their packing interactions and cell

axes, also support a substantial role for metallophilic bonding in

these structures, although the latter studies also conﬁrmed the

importance of π−π interactions.

This study implies that eﬀorts to design luminescent

materials based on extended metallophilic bonding cannot

rely on Pt···Pt interactions to dominate molecular packing

arrangements. Instead, the full array of possible intermolecular

interactions must be taken into account. In particular, a

synergistic combination of π−π stacking and M···M contacts,

with additional CH···π or CH₃···π interactions that do not

disrupt these interactions, appears to be a promising formula

for luminescent extended chain structures. With judicious

choice of ligands, the creation of channeled, M···M chain

structures with cavity sizes exceeding the 7.6 Å width obtained

in the structures of 7/8 should be possible, creating

opportunities for luminescent materials that are responsive to

volatile molecules diﬀusing into these structural voids.

REFERENCES

■

(1) (a) Schmidbaur, H. Gold Bull. 2000, 33, 3−10. (b) Balch, A. L.

Gold Bull. 2004, 37, 45−50. (c) Dias, H. V. R.; Diyabalanage, H. V. K.;

Eldabaja, M. G.; Elbjeirami, O.; Rawashdeh-Omary, M. A.; Omary, M.

A. J. Am. Chem. Soc. 2005, 127, 7489−7501. (d) Hayoun, R.; Zhong,

D. K.; Rheingold, A. L.; Doerrer, L. H. Inorg. Chem. 2006, 45, 6120−

6122. (e) Elbjeirami, O.; Omary, M. A. J. Am. Chem. Soc. 2007, 129,

́

11384−11393. (f) Schneider, J.; Lee, Y.-A.; Perez, J.; Brennessel, W.

W.; Flaschenreim, C.; Eisenberg, R. Inorg. Chem. 2008, 47, 957−968.

(g) Doerrer, L. H. Comments Inorg. Chem. 2008, 29, 93−127.

(h) Phillips, V.; Willard, K. J.; Golen, J. A.; Moore, C. J.; Rheingold, A.

L.; Doerrer, L. H. Inorg. Chem. 2010, 49, 9265−9274.

(2) (a) Pyykko, P. Chem. Rev. 1997, 97, 597−636. (b) Pyykko, P.

̈

Angew. Chem., Int. Ed. 2004, 43, 4412−4456. (c) Pyykko, P. Inorg.

̈

Chim. Acta 2005, 358, 4113−4130.

(3) (a) Schmidbaur, H.; Schier, A. Chem. Soc. Rev. 2008, 37, 1931−

1951. (b) Katz, M. J.; Sakai, K.; Leznoff, D. B. Chem. Soc. Rev. 2008,

37, 1884−1895.

(4) Williams, J. M. Adv. Inorg. Chem. 1983, 26, 235−268.

(5) Gliemann, G.; Yersin, H. Struct. Bonding (Berlin) 1985, 62, 87−

153.

(6) (a) Houlding, V. H.; Miskowski, V. M. Coord. Chem. Rev. 1991,

111, 145−152. (b) Omary, M. A.; Patterson, H. H. Inorg. Chem. 1998,

37, 1060−1066. (c) Catalano, V. J.; Malwitz, M. A. Inorg. Chem. 2003,

42, 5483−5485.

(7) Connick, W. B.; Marsh, R. E.; Schaefer, W. P.; Gray, H. B. Inorg.

Chem. 1997, 36, 913−922.

(8) (a) Hunter, C. A.; Sanders, J. K. M. J. Am. Chem. Soc. 1990, 112,

5525−5534. (b) Janiak, C. Dalton Trans. 2000, 3885−3896.

(9) Nishio, M.; Hirota, M.; Umezawa, Y. The CH/π Interaction:

Evidence, Nature, and Consequences; Wiley-VCH: New York, 1998.

(10) Lindemann, S. V.; Rathore, R.; Kochi, J. K. Inorg. Chem. 2000,

39, 5707−5716.

(11) Steiner, T. Angew. Chem., Int. Ed. 2002, 41, 48−76.

(12) Metrangolo, P.; Neukirch, H.; Pilati, T.; Resnati, G. Acc. Chem.

Res. 2005, 38, 386−395.

(13) (a) Vicente, J.; Chicote, M.-T.; Abrisqueta, M.-D.; Guerrero, R.;

Jones, P. G. Angew. Chem., Int. Ed. Engl. 1997, 36, 1203−1205.

(b) Puddephatt, R. J. Chem. Commun. 1998, 1055−1062. (c) Hao, L.;

Mansour, M. A.; Lachicotte, R. J.; Gysling, H. J.; Eisenberg, R. Inorg.

Chem. 2000, 39, 5520−5529. (d) Hunks, W. J.; Jennings, M. C.;

Puddephatt, R. J. Inorg. Chem. 2002, 41, 4590−4598. (e) Stork, J. R.;

Olmstead, M. M.; Balch, A. L. Inorg. Chem. 2004, 43, 7508−7515.

ASSOCIATED CONTENT

■

S

* Supporting Information

(f) Sundararaman, A.; Zakharov, L. N.; Rheingold, A. L.; Jakle, F.

̈

Additional tables, packing diagrams, luminescence plots, and

crystal images; UV−vis absorption spectra; powder X-ray

diﬀraction data; and thermal ellipsoid plots. This material is

available free of charge via the Internet at http://pubs.acs.org.

Chem. Commun. 2005, 1708−1710. (g) Zhang, J.-P.; Wang, Y.-B.;

Huang, X.-C.; Lin, Y.-Y.; Chen, X.-M. Chem.Eur. J. 2005, 11, 552−

561. (h) Stork, J. R.; Olmstead, M. M.; Fettinger, J. C.; Balch, A. L.

Inorg. Chem. 2006, 45, 849−857. (i) Saitoh, M.; Balch, A. L.; Yuasa, J.;

́

Kawai, T. Inorg. Chem. 2010, 49, 7129−7134. (j) Díez, A.; Fornies

́

, J.;

Larraz, C.; Lalinde, E.; Lopez, J. A.; Martín, A.; Moreno, M. T.; Sicilia,

́

AUTHOR INFORMATION

■

V. Inorg. Chem. 2010, 49, 3239−3251. (k) Kilpin, K. J.; Gower, M. L.;

Telfer, S. G.; Jameson, G. B.; Crowley, J. D. Inorg. Chem. 2011, 50,

1123−1134. (l) Yang, C.; Elbjeirami, O.; Palehepitiya Gamage, C. S.;

Corresponding Author

*E-mail: lms@chem.okstate.edu.

Q

dx.doi.org/10.1021/ic301104a | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

Dias, H. V. R.; Omary, M. A. Chem. Commun. 2011, 47, 7434−7436.

(22) Connelly, N. G.; Crossley, J. G.; Orpen, A. G.; Salter, H. J.

Chem. Soc., Chem. Commun. 1992, 1564−1568.

(23) Sun, Y.; Ye, K.; Zhang, H.; Zhang, J.; Zhao, L.; Li, B.; Yang, G.;

Yang, B.; Wang, Y.; Lai, S.-W.; Che, C.-M. Angew. Chem., Int. Ed. 2006,

45, 5610−5613.

(24) (a) Ecken, H.; Olmstead, M. M.; Noll, B. C.; Attar, S.; Schlyer,

B.; Balch, A. L. J. Chem. Soc., Dalton Trans. 1998, 3715−3720.

(b) White-Morris, R. L.; Olmstead, M. M.; Balch, A. L.; Elbjeirami, O.;

Omary, M. A. Inorg. Chem. 2003, 42, 6741−6748. (c) Elbjeirami, O.;

Omary, M. A.; Stender, M.; Balch, A. L. Dalton Trans. 2004, 3173−

3175.

́

(m) Lasanta, T.; Olmos, M. E.; Laguna, A.; Lopez-de-Luzuriaga, J. M.;

Naumov, P. J. Am. Chem. Soc. 2011, 133, 16358−16361.

(14) (a) Osborn, R. S.; Rogers, D. J. Chem. Soc., Dalton Trans. 1974,

1002−1004. (b) Herber, R. H.; Croft, M.; Coyer, M. J.; Bilash, B.;

Sahiner, A. Inorg. Chem. 1994, 33, 2422−2426. (c) Toronto, D. V.;

Weissbart, B.; Tinti, D. S.; Balch, A. L. Inorg. Chem. 1996, 35, 2484−

2489. (d) Yam, V. W.-W.; Wong, K. M.-C.; Zhu, N. J. Am. Chem. Soc.

2002, 124, 6506−6507. (e) White-Morris, R. L.; Olmstead, M. M.;

Balch, A. L. J. Am. Chem. Soc. 2003, 125, 1033−1040. (f) Stork, J. R.;

Olmstead, M. M.; Balch, A. L. J. Am. Chem. Soc. 2005, 127, 6512−

6513. (g) Gussenhoven, E. M.; Olmstead, M. M.; Fettinger, J. C.;

Balch, A. L. Inorg. Chem. 2008, 47, 4570−4578. (h) Nishiuchi, Y.;

Takayama, A.; Suzuki, T.; Shinozaki, K. Eur. J. Inorg. Chem. 2011,

1815−1823.

(25) Crystallographic data indicate that Pt has a slightly smaller

covalent radius than Pd. See: Cordero, B.; Gom

A. E.; Reves, M.; Echeverría, J.; Cremades, E.; Barragan

Dalton Trans. 2008, 2832−2838.

́

ez, V.; Platero-Prats,

́

, F.; Alvarez, S.

(26) For discussions of a similar trend in Au versus Ag, see:

(a) Tripathi, U. M.; Bauer, A.; Schmidbaur, H. J. Chem. Soc., Dalton

Trans. 1997, 2865−2868. (b) Omary, M. A.; Rawashdeh-Omary, M.

A.; Gonser, M. W. A.; Elbjeirami, O.; Grimes, T.; Cundari, T. R.;

Diyabalanage, H. V. K.; Palehepitiya Gamage, C. S.; Dias, H. V. R.

Inorg. Chem. 2005, 44, 8200−8210.

(15) (a) Biedermann, J.; Gliemann, G.; Klement, U.; Range, K.-J.;

Zabel, M. Inorg. Chim. Acta 1990, 169, 63−70. (b) Biedermann, J.;

Gliemann, G.; Klement, U.; Range, K.-J.; Zabel, M. Inorg. Chim. Acta

1990, 171, 35−40. (c) Biedermann, J.; Gliemann, G.; Klement, U.;

Range, K.-J.; Zabel, M. Inorg. Chem. 1990, 29, 1884−1888.

(d) Mansour, M. A.; Connick, W. B.; Lachicotte, R. J.; Gysling, H.

J.; Eisenberg, R. J. Am. Chem. Soc. 1998, 120, 1329−1330. (e) Buss, C.

E.; Anderson, C. E.; Pomije, M. K.; Lutz, C. M.; Britton, D.; Mann, K.

R. J. Am. Chem. Soc. 1998, 120, 7783−7790. (f) Buss, C. E.; Mann, K.

R. J. Am. Chem. Soc. 2002, 124, 1031−1039. (g) Kato, M.; Omura, A.;

Toshikawa, A.; Kishi, S.; Sugimoto, Y. Angew. Chem., Int. Ed. 2002, 41,

(27) For selected examples, see: (a) Iball, J.; MacDougall, M.;

Scrimgeour, S. Acta Crystallogr., Sect. B 1975, B31, 1672−1674.

(b) Textor, M.; Oswald, H. R. Z. Anorg. Allg. Chem. 1974, 407, 244−

256. (c) Canty, A. J.; Skelton, B. W.; Traill, P. R.; White, A. H. Aust. J.

Chem. 1992, 45, 417−422. (d) Marino, N.; Fazen, C. H.; Blakemore, J.

D.; Incarvito, C. D.; Hazari, N.; Doyle, R. P. Inorg. Chem. 2011, 50,

2507−2520.

3183−3185. (h) Fernan

M.; Olmos, M. E.; Perez, J.; Laguna, A.; Mohamed, A. A.; Fackler, J. P.,

Jr. J. Am. Chem. Soc. 2003, 125, 2022−2023. (i) Fernandez, E. J.;

Lopez-de-Luzuriaga, J. M.; Monge, M.; Montiel, M.; Olmos, M. E.;

Perez, J.; Laguna, A.; Mendizabal, F.; Mohamed, A. A.; Fackler, J. P., Jr.

́ ́

dez, E. J.; Lopez-de-Luzuriaga, J. M.; Monge,

́

(28) (a) Pyykko, P. Chem. Rev. 1988, 88, 563−594. (b) Maliarik, M.;

̈

́

Nagle, J. K.; Ilyukhin, A.; Murashova, E.; Mink, J.; Skripkin, M.; Glaser,

́

J.; Kovacs, M.; Horvath, A. Inorg. Chem. 2007, 46, 4642−4653.

́

(29) (a) Gokel, G. W.; Widera, R. P.; Weber, W. P. Org. Synth. 1976,

55, 96−99. (b) Curran, D. P.; Liu, H.; Josien, H.; Ko, S. B. Tetrahedron

1996, 52, 11385−11404.

Inorg. Chem. 2004, 43, 3573−3581. (j) Wadas, T. J.; Wang, Q.-M.;

Kim, Y.-J.; Flaschenreim, C.; Blanton, T. N.; Eisenberg, R. J. Am.

Chem. Soc. 2004, 126, 16841−16849. (k) Wong, K. M.-C.; Zhu, N.;

(30) Drew, D.; Doyle, J. R. Inorg. Synth. 1990, 28, 346−349.

(31) (a) Michelin, R. A.; Facchin, G.; Uguagliati, P. Inorg. Chem.

1984, 23, 961−969. (b) Michelin, R. A.; Zanotto, L.; Braga, D.;

Sabatino, P.; Angelici, R. J. Inorg. Chem. 1988, 27, 85−92.

(32) Wanniarachchi, Y. A.; Slaughter, L. M. Chem. Commun. 2007,

3294−3296.

(33) APEX2, Version 2.0; Bruker AXS: Madison, WI, 2006.

(34) SAINT, Version 7.23A; Bruker AXS: Madison, WI, 2001.

(35) Sheldrick, G. M. SADABS, Version 2.10; Bruker AXS Inc.:

Madison, WI, 2000.

(36) Sheldrick, G. M. SHELXTL, Version 6.14; Bruker AXS Inc.:

Madison, WI, 2000.

(37) MERCURY, Version 2.4.5; Cambridge Crystallographic Data

Center: Cambridge, U.K., 2011.

(38) Parsons, S.; Gould, R. O. ROTAX; University of Edinburgh:

Edinburgh, U.K., 2003.

(39) Sheldrick, G. M. CELL_NOW; Bruker AXS: Madison, WI,

2004.

(40) Sheldrick, G. M. TWINABS, Version 2008/2; Bruker AXS:

Madison, WI, 2008.

(41) Parsons, S. Acta Crystallogr., Sect. D 2003, D59, 1995−2003.

(42) (a) van der Sluis, P.; Spek, A. L. Acta Crystallogr., Sect. A 1990,

46, 194−201. (b) Spek, A. L. PLATON, A Multipurpose Crystallo-

graphic Tool; Utrecht University: Utrecht, The Netherlands, 2007.

(43) Crystal structures of 5 (refs 19 and 20), 6 (ref 19), 11 (ref 44a),

and 12 (ref 44b) have been previously reported.

Yam, V. W.-W. Chem. Commun. 2006, 3441−3443. (l) Gil, B.; Fornies

́

,

J.; Gomez, J.; Lalinde, E.; Martín, A.; Moreno, M. T. Inorg. Chem.

́

2006, 45, 7788−7798. (m) Rios, D.; Pham, D. M.; Fettinger, J. C.;

Olmstead, M. M.; Balch, A. L. Inorg. Chem. 2008, 47, 3442−3451.

(n) Du, P.; Schneider, J.; Brennessel, W. W.; Eisenberg, R. Inorg.

Chem. 2008, 47, 69−77. (o) Ni, J.; Wu, Y.-H.; Zhang, X.; Li, B.; Zhang,

L.-Y.; Chen, Z.-N. Inorg. Chem. 2009, 48, 10202−10210. (p) Ni, J.;

Zhang, L.-Y.; Wen, H.-M.; Chen, Z.-N. Chem. Commun. 2009, 3801−

3803. (q) Drew, S. M.; Smith, L. I.; McGee, K. A.; Mann, K. R. Chem.

Mater. 2009, 21, 3117−3124. (r) Ni, J.; Zhang, X.; Wu, Y.-H.; Zhang,

L.-Y.; Chen, Z.-N. Chem.Eur. J. 2011, 17, 1171−1183.

(16) (a) Exstrom, C. L.; Sowa, J. R., Jr.; Daws, C. A.; Janzen, D.;

Mann, K. R. Chem. Mater. 1995, 7, 15−17. (b) Daws, C. A.; Exstrom,

C. L.; Sowa, J. R., Jr.; Mann, K. R. Chem. Mater. 1997, 9, 363−368.

(c) Grove, L. J.; Rennekamp, J. M.; Jude, H.; Connick, W. B. J. Am.

Chem. Soc. 2004, 126, 1594−1595. (d) Grove, L. J.; Oliver, A. G.;

Krause, J. A.; Connick, W. B. Inorg. Chem. 2008, 47, 1408−1410.

(17) Rawashdeh-Omary, M. A.; Rashdan, M. D.; Dharanipathi, S.;

Elbjeirami, O.; Ramesh, P.; Dias, H. V. R. Chem. Commun. 2011, 47,

1160−1162.

(18) (a) Kato, M. Bull. Chem. Soc. Jpn. 2007, 80, 287−294.

́

(b) Luquin, A.; Elosua, C.; Vergara, E.; Estella, J.; Cerrada, E.; Bariain,

C.; Matías, I. R.; Garrido, J.; Laguna, M. Gold Bull. 2007, 40, 225−233.

(19) Sluch, I. M.; Miranda, A. J.; Slaughter, L. M. Cryst. Growth Des.

2009, 9, 1267−1270.

(20) Jovanovic,

Dalton Trans. 1972, 1178−1181.

(21) (a) Schneider, W.; Angermaier, K.; Sladek, A.; Schmidbaur, H.

Z. Naturforsch., B: J. Chem. Sci. 1996, 51, 790−800. (b) Aullon, G.;

́ ́

B.; Manojlovic-Muir, L.; Muir, K. W. J. Chem. Soc.,

́ ́

(44) (a) Vicente, J.; Arcas, A.; Fernandez-Hernandez, J. M.

Organometallics 2007, 26, 6155−6169. (b) Drouin, M.; Perreault, D.;

Harvey, P. D.; Michel, A. Acta Crystallogr., Sect. C 1991, C47, 752−

754.

́

Alvarez, S. Chem.Eur. J. 1997, 3, 655−664. (c) Elbjeirami, O.;

Yockel, S.; Campana, C. F.; Wilson, A. K.; Omary, M. A.

Organometallics 2007, 26, 2550−2560. (d) Elbjeirami, O.; Gonser,

M. W. A.; Stewart, B. N.; Bruce, A. E.; Bruce, M. R. M.; Cundari, T. R.;

Omary, M. A. Dalton Trans. 2009, 1522−1533.

(45) Bondi, A. J. Phys. Chem. 1964, 68, 441−451.

(46) Aryl rings are referenced using the number of the ipso carbon.

(47) Packing indices were calculated as percent occupied volume

using PLATON (ref 42b), with the van der Waals radii of both Pt and

Pd set to 1.72 Å.

R

dx.doi.org/10.1021/ic301104a | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

(48) Packing indices were calculated for low temperature structures

(100−115 K) with identical van der Waals radii assumed for Pt and Pd

(see ref 47).

(49) It has been proposed that methyl groups attached to phenyl

rings or electronegative groups are capable of forming CH−π

interactions; see ref 9, Chapter 1.

(50) de Almeida, E. T.; Mauro, A. E.; Santana, A. M.; Ananias, S. R.;

Netto, A. V. G.; Ferreira, J. G.; Santos, R. H. A. Inorg. Chem. Commun.

2007, 10, 1394−1398.

(51) (a) Exner, O. In Correlation Analysis in Chemistry; Chapman, N.

B., Shorter, J., Eds.; Plenum Press: New York, 1978, pp 439−540.

(b) Shorter, J. Pure Appl. Chem. 1997, 69, 2497−2510.

(52) Brock, C. P.; Dunitz, J. D. Chem. Mater. 1994, 6, 1118−1127.

(53) Channel widths were estimated from space-ﬁlling plots of

published structural data, using van der Waals radii for all atoms.

Distances were calibrated from unit cell edges.

(54) (a) Pascal, T. A.; Goddard, W. A.; Jung, Y. Proc. Natl. Acad. Sci.

U.S.A. 2011, 108, 11794−11798. (b) Kyakuno, H.; Matsuda, K.;

Yahiro, H.; Inami, Y.; Fukuoka, T.; Miyata, Y.; Yanagi, K.; Maniwa, Y.;

Kataura, H.; Saito, T.; Yumura, M.; Iijima, S. J. Chem. Phys. 2011, 134,

244501/1−244501/14.

(55) (a) Connick, W. B.; Henling, L. M.; Marsh, R. E.; Gray, H. B.

Inorg. Chem. 1996, 35, 6261−6265. (b) Kato, M.; Kosuge, C.; Morii,

K.; Ahn, J. S.; Kitagawa, H.; Mitani, T.; Matsushita, M.; Kato, T.; Yano,

S.; Kimura, M. Inorg. Chem. 1999, 38, 1638−1641. (c) Field, J. S.;

Gertenbach, J.-A.; Haines, R. J.; Ledwaba, L. P.; Mashapa, N. T.;

McMillin, D. R.; Munro, O. Q.; Summerton, G. C. Dalton Trans. 2003,

1176−1180.

(56) (a) Miskowski, V. M.; Houlding, V. H. Inorg. Chem. 1991, 30,

4446−4452. (b) Bailey, J. A.; Hill, M. G.; Marsh, R. E.; Miskowski, V.

M.; Shaefer, W. P.; Gray, H. B. Inorg. Chem. 1995, 34, 4591−4599.

(c) Lai, S.-W.; Lam, H.-W.; Lu, W.; Cheung, K.-K.; Che, C.-M.

Organometallics 2002, 21, 226−234.

(57) (a) Isci, H.; Mason, W. R. Inorg. Chem. 1975, 14, 913−918.

(b) Miller, J. S.; Marsh, D. G. Inorg. Chem. 1976, 15, 2293−2295.

(58) Vorontsov, I. I.; Kovalevsky, A. Y.; Chen, Y.-S.; Graber, T.;

Gembicky, M.; Novozhilova, I. V.; Omary, M. A.; Coppens, P. Phys.

Rev. Lett. 2005, 94, 193003.

(59) (a) Roundhill, D. M.; Gray, H. B.; Che, C.-M. Acc. Chem. Res.

1989, 22, 55−61. (b) Ma, B.; Djurovich, P. I.; Yousufuddin, M.; Bau,

R.; Thompson, M. E. J. Am. Chem. Soc. 2005, 127, 28−29.

́ ́

(60) Díez, A.; Fornies, J.; Fuertes, S.; Lalinde, E.; Larraz, C.; Lopez, J.

A.; Martín, A.; Moreno, M. T.; Sicilia, V. Organometallics 2009, 28,

1705−1718.

S

dx.doi.org/10.1021/ic301104a | Inorg. Chem. XXXX, XXX, XXX−XXX

Article Doi

Interplay of metallophilic interactions, π-π Stacking, and ligand substituent effects in the structures and luminescence properties of neutral PtII and PdII aryl isocyanide complexes

DOI: 10.1021/ic301104a

Source and publish data:

Authors:

Article abstract of DOI:10.1021/ic301104a

Full text of DOI:10.1021/ic301104a

Products guided by the article

R&D Labs maybe for 1401718-21-5

Relevant to this article

Hot Product