Electronic influences on metallophilic interactions in [Pt(tpy)X][Au(C 6F5)2] double salts

Article abstract of DOI:10.1021/ic1008208

Four double salt compounds of the type [Pt(tpy)X][Au(C₆F ₅)₂], where tpy =2,2′:6′,2′-terpyridine and X = Cl, 3, Br, 4, I, 5, and CCPh, 6, and their platinum starting materials, [Pt(tpy)Br]Br · 2H₂O, 1, and [Pt(t

Full text of DOI:10.1021/ic1008208

Inorg. Chem. 2010, 49, 9265–9274 9265
DOI: 10.1021/ic1008208
Electronic Influences on Metallophilic Interactions in [Pt(tpy)X][Au(C6F5)2]
Double Salts
Val Phillips,† Kathryn J. Willard,‡ James A. Golen,§,|| Curtis J. Moore,§ Arnold L. Rheingold,§ and
Linda H. Doerrer*,†
†Chemistry Department, Boston University, 590 Commonwealth Avenue, Boston, Massachusetts 02215,
‡Chemistry Department, Barnard College, 3009 Broadway, New York, New York 10027, §Department of
Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Drive, La Jolla, California
92093-0358, and ||Department of Chemistry & Biochemistry, University of Massachusetts Dartmouth,
North Dartmouth, Massachusetts 02747
Received April 26, 2010
Four double salt compounds of the type [Pt(tpy)X][Au(C6F5)2], where tpy =2,20:60,200-terpyridine and X = Cl, 3, Br, 4, I,
5, and CCPh, 6, and their platinum starting materials, [Pt(tpy)Br]Br 2H2O, 1, and [Pt(tpy)(CCPh)]PF6 DMF H2O, 2,
3
3
3
have been synthesized and characterized. Complex 2 is a solvated form of the known and structurally characterized
[Pt(tpy)(CCPh)]PF6 species. All compounds were characterized by single-crystal X-ray diffraction, elemental
analyses, and solution electronic spectra. Structural characterization shows that compounds 3 and 4 are similar in
the solid state and form cation-anion stacking patterns while compounds 5 and 6 form chains of cations supported by
metallophilic interactions with anion partners on either side of the chains. Solution studies (UV-vis and fluorescence)
strongly suggest that there are no Pt Au interactions in solution state. Electronic structure calculations with density
3 3 3
functional theory (DFT) elucidate the subtle changes in the electronic scaffolding of the ions in these compounds and
show that predictions of metallophilic interactions are not straightforward but can be understood in terms of orbital
symmetry and the relative energies of the frontier orbitals.
Introduction
Since its initial empirical observation with gold in the
dication [(Ph3PAu)6C]2þ 1,2 metallophilicity3 has been ob-
wealth of examples displaying metallophilicity in homome-
tallic systems such as AuI AuI interactions4,5 or PtII PtII
3 3 3
3 3 3
combinations6 and few examples of interactions between
,
mixed metal, heterometallic derivatives such as PtII AuI,7
3 3 3
served in many other metal complexes having two or more
AuI AgI,13 and AuI TlI pairings.14 Among these exam-
metals associated via either closed-shell (e.g., d10 d10),4,5
3 3 3
3 3 3
ples of mixed metal systems is our work with PtII AuI
3 3 3
pseudo-closed-shell (d8 d8),6 or mixed (d8 d10)7-12 elec-
3 3 3
double salt complexes of the form [M]þ[M0]- composed
of heavy metal containing cations and anions.7,15-17 These
double salts were developed in a bottom-up approach to
atomically thin one-dimensional (1D) arrays of metal atoms.
Such highly anisotropic structures have been of interest
for many years as potentially electronically conducting
materials.18 Essential for electron transport through a chain
3 3 3
3 3 3
tronic configurations. A survey of the literature reveals a
*To whom correspondence should be addressed. E-mail: doerrer@
bu.edu.
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2010 American Chemical Society
Published on Web 09/24/2010
pubs.acs.org/IC

9266 Inorganic Chemistry, Vol. 49, No. 20, 2010
Phillips et al.
of metal atoms is close contact between eachneighboring pair
of metal ions. To facilitate close metal-metal contacts, we
imposed the following guidelines on our double salts: (1) both
cation and anion must contain metals with either closed-shell
or pseudo-closed-shell electronic configurations that favor
metallophilic interactions, (2) both cation and anion must
have linear or square planar geometry to minimize steric
hindrance, and (3) both cation and anion must be singly
charged for solubility purposes.15,16,19 A more detailed dis-
cussion of these systems can be found in a recent review.7
Using these guidelines, our laboratory has been successful
in synthesizing and characterizing a large family of double
salt complexes of the forms [PtIIL3X][AuIX2], [PtIIL3X]-
[AuIIIX4], [AuIIIL2X2][AuIX2], and [AuIIIL2X2][AuIIIX4]
where L2 and L3 are neutral bidentate or tridentate planar
ligands, respectively, and X is either a halogen or a pseudo-
halogen.7 The [PtL3X][AuX2] family is by far the most
developed, with most examples involving the well studied
[Pt(tpy)Cl]þ moiety.19 Structural characterization of some of
these complexes has revealed metallophilic interactions be-
cation,26 whichisanefficient chromophore incharge-transfer
systems using a sacrificial donor and an acceptor.27-35
Additionally, the [Pt(tpy)(CCPh)]þ species has been shown
to form metal-metal interactions with itself, making it a
more attractive candidate for our metallophilic purposes.36-38
The results of both innovations are reported herein.
In this work, we have developed a new family of double
salts of the type [Pt(tpy)X][Au(C6F5)2] (X=Cl, 3, Br, 4, orI, 5)
by combining the [Au(C6F5)2]- species with the [Pt(tpy)X]þ
moiety. Introducing a light-harvesting group into our new
double salt family was achieved via substituting CCPh for a
halide in the [Pt(tpy)X]þ moiety to form [Pt(tpy)(CCPh)[Au-
(C6F5)2], 6.
Experimental Section
General Considerations. Dichloro(1, 5-cyclooctadiene)-
platinum(II), phenylacetylene, and 2,20:60,200-terpyridine
were purchased from Sigma Aldrich Chemical Co. and used
as received. Spectral grade acetonitrile (CH3CN) was pur-
chased from Fisher Scientific and distilled before use from
CaH2 under N2. All other spectral grade reagents were used
without further purification. [Pt(tpy)Cl]Cl,39 [Pt(tpy)I]I,15
[Au(SC4H8)Cl],40 and [Bu4N][Au(C6F5)2]40 were prepared
according to literature methods. The compound [Pt(tpy)-
Br]Br16 was prepared similarly to the iodide derivative.15
Characterization and Instrumentation. All mass spectra were
collected using an Agilent 1100 LC/MSD with electrospray
ionization (ESI) and atmospheric pressure chemical ionization
(APCI) sources. Elemental analyses were performed by Quanti-
tative Technologies Inc. (QTI, Whitehouse, NJ 08888). Absorp-
tion spectra were collected on a Shimadzu 3600 UV-vis-NIR
spectrophotometer. Emission spectra were measured using an
Jobin Yvon Horiba FluoroMax 3 fluorimeter.
tween pairs of PtII PtII cations15 and metallophilic inter-
3 3 3
actions between PtII AuI,19 and AuIII AuIII species19
3 3 3
3 3 3
that can form infinite chains of contacts. This bottom-up
preparation of metallophilic chains has demonstrated the
feasibility of our double salt approach and laid the founda-
tions for two new modifications of these systems. First, the
low solubility of some complexes led to difficulties in recrys-
tallization suchthat with addedheat, undesiredX-type ligand
scrambling between the PtII and AuI ions and partial reduc-
tion of some AuIII anions to AuI anions was observed.19
Therefore, we sought alternative ligand derivatives that
would improve solubility and eliminate ligand scrambling
and reduction behaviors. We have chosen to increase the
solubility and substitutional robustness of the [AuX2]-
component by using the [Au(C6F5)2]- anion developed
by Uson et al.20,21 and used extensively by the Laguna
group.22 Both the robustness of this molecule and its ability
to form metal-metal interactions with both AgI and TlI metal
centers has been demonstrated in numerous reports.14,23-25
Additionally, the π-conjugated X group was proposed to
facilitate π-interactions with the tpy ligand of the [Pt(tpy)X]þ
moiety, thus favoring π-π stacking and stabilization of
cation-anion interactions.
X-ray Diffraction Studies. A summary of crystal data collec-
tion and refinement parameters for all compounds are given in
Table 1. Selected interatomic distances and angles are given in
Table 2. All data were collected on APEX-CCD-detector
equipped Bruker diffractometers. Data for compound 5 were
corrected for absorption using numerical methods, and all other
structures were corrected for absorption using semiempirical,
multiscan methods. All structures were solved by direct
methods, and the remaining non-hydrogen atoms were located
(27) Chakraborty, S.; Wadas, T. J.; Hester, H.; Flaschenreim, C.;
Schmehl, R.; Eisenberg, R. Inorg. Chem. 2005, 44, 6284.
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R. Inorg. Chem. 2005, 44, 6865.
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12576.
Second, we wanted to incorporate light harvesting
capability into these double salts with an eye to potential
photoconductivity. This goal has been pursued by availing
ourselves of the proven light-harvesting [Pt(tpy)(CCPh)]þ
(30) Du, P.; Schneider, J.; Jarosz, P.; Eisenberg, R. J. Am. Chem. Soc.
2006, 128, 7726.
(31) Du, P.; Schneider, J.; Luo, G.; Brennessel, W. W.; Eisenberg, R.
Inorg. Chem. 2009, 48, 4952.
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5653.
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J. Am. Chem. Soc. 2004, 126, 4958.
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Eisenberg, R. J. Phys. Chem. B 2007, 111, 6887.
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20, 4476.
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44, 791.
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(40) Du, P.; Schneider, J.; Li, F.; Zhao, W.; Patel, U.; Castellano, F. N.;
Eisenberg, R. J. Am. Chem. Soc. 2008, 130, 5056.
(19) Hayoun, R.; Zhong, D. K.; Rheingold, A. L.; Doerrer, L. H. Inorg.
Chem. 2006, 45, 6120.
(20) Uson, R.; Laguna, A.; Vicente, J. J. Chem. Soc., Chem. Commun.
1976, 353.
(21) Uson, R.; Laguna, A.; Laguna, M.; Fernandez, E. Inorg. Chim. Acta
1980, 45, L177.
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252, 1630.
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J. M.; Monge, M.; Pyykkoe, P.; Sundholm, D. J. Am. Chem. Soc. 2000, 122,
7287.
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Organometallics 2001, 20, 4476.

Article
Inorganic Chemistry, Vol. 49, No. 20, 2010 9267
Table 1. Summary of X-ray Data Collection Parameters
1
2
3
4
5
6
formula
FW
PtC15N3H15Br2O2 Pt2C49N7H41F12O2P2 PtAuC27N3H11F10Cl PtAuC27N3H11F10Br Pt2Au2C54N6H22F20I2 PtAuC35N3H16F10
624.21
1440.01
triclinic
P1
994.89
monoclinic
P2(1)/c
22.6983(12)
6.7619(4)
16.6367(9)
90
1039.35
monoclinic
P2(1)/c
22.7955(19)
7.7848(6)
16.6706(14)
90
2172.69
monoclinic
P2(1)/n
14.4040(9)
24.4020(15)
15.0590(10)
90
1060.56
monoclinic
P2(1)/n
16.7535(10)
7.5118(5)
23.6491(14)
90
cryst syst
space group
monoclinic
P2(1)/n
6.9548(7)
17.4240(18)
13.9923(14)
90
˚
a, A
13.1966(17)
14.043(2)
14.635(2)
89.604(4)
69.444(4)
71.091(4)
2384.8(6)
2
˚
b, A
˚
c, A
R, deg
β, deg
γ, deg
97.2600(10)
90
100.1760(10)
90
100.128(2)
90
105.2240(11)
90
96.0760(10)
90
3
˚
V, A
Z
1682.0(3)
4
2.465
2513.3(2)
4
2.629
2538.1(4)
4
2.720
5107.3(6)
4
2.826
2959.5(3)
4
2.380
F(calcd), g cm-3
2.005
6.024
M(Mo KR), mm-1 13.105
11.597
100(2)
3.02
12.953
123(2)
2.22
12.519
150(2)
9.770
100(2)
T, K
R(F), %a
R(wF2), %b
100(2)
3.81
7.45
100(2)
5.99
14.46
7.99
13.80
3.62
7.58
4.17
5.20
P
P
P
P
2
a R = ||Fo| - |Fc||/ |Fo|. b R(wF2) = { w(Fo2 - Fc2)2/ w(Fo2)2}1/2; w = 1/[σ2(Fo2) þ (aP)2 þ bP], P = [2Fc þmax(Fo,0)]/3.
from subsequent difference maps. All structures were refined
with anisotropic thermal parameters for all non-hydrogen
atoms; hydrogen atoms were treated as idealized contributions.
For compound 2 hydrogen atoms on water molecules were
method.47 Triply recrystallized [Pt(tpy)Br]Br (102.8 mg,
0.176 mmol) was added to approximately 10 mL of DMF.
Excess phenylacetylene (38.2 μL, 0.348 mmol) and
triethylamine (200.4 μL, 1.438 mmol) were added to the
suspension. The reaction flask was flushed with N2, and a
catalytic amount of CuI (4.0 mg, 0.0198 mmol) was added
to the reaction. Upon addition of catalyst, the slurry
turned red. The suspension was stirred under N2 for
3 days. On the third day, an excess of KPF6 (44.3 mg,
0.241 mmol) was added to the suspension and stirred for
approximately 6 h. A green solid was precipitated from
the suspension with the addition of water. The green solid
was isolated via vacuum filtration and recrystallized from
CH3CN and Et2O in 93.6% yield (80.3 mg). The UV-vis
spectrum has been reported previously.47
[Pt(tpy)Cl][Au(C6F5)2] (3). Solid [Bu4N][Au(C6F5)2]
(103.7 mg, 0.100 mmol) was added to a stirred orange
solution of [Pt(tpy)Cl]Cl (54.5 mg, 0.100 mmol) in a 5:1
CH3CN/H2O mix. A yellow precipitate formed immedi-
ately upon the addition. The resulting slurry was stirred
for 12 h at room temperature. The yellow product was
isolated via filtration, washed with three 5 mL portions of
CH2Cl2, and recrystallized from hot CH3CN to give a
yellow microcrystalline solid (87.8 mg, 88% yield). Yellow
needles suitable for X-ray diffraction were grown via
evaporation of a dilute DMF solution. Anal. Calcd (%)
for PtAuC27H11N3F10Cl: C, 32.60; H, 1.11; N, 4.22; F,
19.09. Found: C, 32.48; H, 1.27; N, 4.27; F, 19.02. ESI-MS:
m/z (%) 462.9 (100) [Mþ]; 530.7 (100) [M-]. UV-vis
(DMF) [λmax, nm (ε, M-1 cm-1)]: 334 (13,100), 326 (9790),
351 (10,030), 379 (2380).
found from a Fourier difference map and although short H
H
3 3 3
contacts were generated these hydrogen atoms were kept in the
refinement. All software is contained in various libraries
(SHELXTL, SMART, and SAINT) maintained by Bruker
AXS, Madison, WI.41
Electronic Structure Calculations. Density functional theory
(DFT) calculations used a QS8-2400C computer from Parallel
Quantum Solutions (PQS) with the Amsterdam Density Func-
tional Package 2008.0142-44 on all-electron, geometry-optimized
systems with TZ2P basis sets and the Vosko, Wilk, and Nusair45
local density approximation, and scalar relativistic corrections.
Calculations were carried out on six species with symmetry
enforced as indicated: [Pt(tpy)Cl]þ C2v, [Pt(tpy)(CCPh)]þ C2v,
[AuCl2]- D¥h, [AuCl(CN)]- C¥v, [Au(CN)2]- D¥h, and [Au-
(C6F5)2]- D2h. A comparison of intramolecular distances and
angles from crystallographic studies with the computational data
is presented in Supporting Information, Table S1. All structures
were confirmed by frequency calculations which showed no
negative frequencies.
Synthesis and Characterization
[Pt(tpy)Br]Br 2H2O (1). The yellow product was iso-
3
lated after the halide exchange reaction of [Pt(tpy)Cl]Cl
with 5 equiv of KBr, as previously reported.16 The yellow
solid was recrystallized three times from a hot aqueous
solution in 73.3% yield. Slow evaporation of a concen-
trated dimethylformamide (DMF) solution yielded yellow
needles suitable for X-ray diffraction. The UV-vis spec-
trum has been reported previously.46
[Pt(tpy)(CCPh)]PF6 1/2DMF /2H2O(2).This compound
was synthesized via a modification of the literature
1
[Pt(tpy)Br][Au(C6F5)2] (4). The yellow powder [Pt(tpy)-
Br]Br (65.0 mg, 0.11 mmol) was dissolved in a 10:2:1
mixture of CH3CN/DMSO/H2O to form a yellow solu-
tion. Upon addition of an equimolar amount of [Bu4N]-
[Au(C6F5)2] (114.0 mg, 0.11 mmol) to the solution, a
yellow precipitate formed and was isolated via filtration.
The yellow solid was obtained in 69.9% yield (56.2 mg)
after washing with ether and recrystallization from hot
CH3CN to give yellow X-ray quality needles. Anal. Calcd
(%) for PtAuC27H11N3F10Br: C, 31.20; H, 1.07; N, 4.04;
F, 18.03. Found: C, 31.14; H, 0.97; N, 4.03; F, 18.33. ESI-
MS: m/z (%) 508 (100) [Mþ]; 531 (100) [M-]. UV-vis
3
3
(41) Sheldrick, G. M. Acta Crystallogr., Sect. A. 2008, A64, 112.
(42) Katz, M. J.; Sakai, K.; Leznoff, D. B. Chem. Soc. Rev. 2008, 37, 1884.
(43) Te Velde, G.; Bickelhaupt, F. M.; Baerends, E. J.; Fonseca Guerra,
C.; Van Gisbergen, S. J. A.; Snijders, J. G.; Ziegler, T. J. Comput. Chem.
2001, 22, 931.
(44) Guerra, C. F.; Snijders, J. G.; Te Velde, G.; Baerends, E. J. Theor.
Chem. Acc. 1998, 99, 391.
(45) Vosko, S. H.; Wilk, L.; Nusair, M. Can. J. Phys. 1980, 58, 1200.
(46) Yip, H.; Cheng, L.; Cheung, K.; Che, C. J. Chem. Soc., Dalton Trans.
1993, 29, 2933.
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Chem. 2002, 41, 5653.

9268 Inorganic Chemistry, Vol. 49, No. 20, 2010
Phillips et al.
Table 2. Selected Interatomic Distances and Angles for Complexes 1-6
Scheme 1. Summary and Numbering Scheme of Compounds Used in
This Study
˚
(A)
complex
distances
angles
(deg)
1
Pt(1) Pt(1)
3 3 3
3.4674(4) Pt(1)-Pt(1)-Pt(1)
Pt(1) 4.2948(5) N(2)-Pt(1)-Br(1)
126.94(1)
178.27(15)
162.2(2)
Pt(1)
3 3 3
Pt(1)-N(1)
Pt(1)-N(2)
Pt(1)-N(3)
Pt(1)-Br(1)
2.029(5)
1.931(5)
2.016(5)
2.4218(7)
N(1)-Pt(1)-N(3)
2
Pt(1)
Pt(2)
Pt(2) 3.3579(6) N(1)-Pt(1)-N(3)
Pt(2) 3.3632(6) N(2)-Pt(1)-C(16)
161.32(15)
178.5(3)
177.0(7)
161.6(2)
179.1(3)
178.5(7)
3 3 3
3 3 3
Pt(1)-N(1)
Pt(1)-N(2)
Pt(1)-N(3)
Pt(1)-C(16)
C(16)-C(17)
Pt(2)-N(4)
Pt(2)-N(5)
Pt(2)-N(6)
Pt(2)-C(39)
C(39)-C(40)
2.013(6)
1.980(6)
2.015(6)
1.982(8)
1.187(11)
2.033(6)
1.957(6)
2.020(6)
2.978(7)
1.216(10)
Pt(1)-C(16)-C(17)
N(4)-Pt(2)-N(6)
N(5)-Pt(2)-C(39)
Pt(2)-C(39)-C(40)
3
4
5
Pt(1)
Au(1)
Au(1) 4.7470(3) N(2)-Pt(1)-Cl(1)
179.04(8)
162.43(12)
174.86(14)
99.58
3 3 3
Pt(1) 4.091(2)
N(1)-Pt(1)-N(3)
C(16)-Au(1)-C(22)
Pt(1)-Au(1)-Pt(1)
3 3 3
recrystallized from hot CH3CN and isolated as orange
needles suitable for X-ray diffraction in 69.9% yield
(173.8 mg). Anal. Calcd (%) for PtAuC27H11N3F10I: C,
29.85; H, 1.02; N, 3.87; F, 17.49. Found: C, 29.98; H, 1.02;
N, 3.82; F, 17.82. ESI-MS: m/z (%) 555 (100) [Mþ]; 531
(100) [M-]. UV-vis (DMF) [λmax, nm (ε, M-1 cm-1)]:
331 (11,300), 349 (10,100), 427 (1850).
[Pt(tpy)(CCPh)][Au(C6F5)2] (6). Solid [Bu4N][Au(C6F5)2]
(113.1 mg, 0.109 mmol) was added to an orange solution of
[Pt(tpy)(CCPh)](PF6) (73.3 mg, 0.109 mmol) in 50 mL of
CH3CN. An orange precipitate formed after approximately
1 h. The resulting slurry was stirred for 12 h at room
temperature and 100 mL of water were added to the slurry,
resulting in precipitation of more orange solid. The orange
product was isolated via filtration, washed with three 5 mL
portions of CH2Cl2, and recrystallized via diffusion of ether
into a DMF solution to form red crystals in 83% yield (100.0
mg). Anal. Calcd (%) for PtAuC35H16N3F10: C, 39.64; H,
1.52; N, 3.96; F, 17.91. Found: C, 39.91; H, 1.49; N, 4.02; F,
17.96. ESI-MS: m/z (%) 529.1 (100) [Mþ]; 530.7 (100) [M-].
UV-vis (DMF) [λmax, nm (ε, M-1 cm-1)]: 316 (12,300), 333
(12,400), 347 (13,900), 440 (shoulder) (4870).
Pt(1)-N(1)
Pt(1)-N(2)
Pt(1)-N(3)
Pt(1)-C(l1)
2.017(3)
1.941(3)
2.021(3)
2.2977(9)
2.039(3)
2.045(3)
Au(1)-C(16)
Au(1)-C(22)
Pt(1)
Au(1)
Au(1) 4.0574(3) N(2)-Pt(1)-Br(1)
178.70(10)
162.66(14)
174.78(16)
100.94
3 3 3
Pt(1) 4.7221(4) N(3)-Pt(1)-N(1)
3 3 3
Pt(1)-N(1)
Pt(1)-N(2)
Pt(1)-N(3)
Pt(1)-Br(1)
Au(1)-C(1)
Au(1)-C(7)
Pt(1)
Pt(1)
Pt(2)
2.018(3)
1.940(4)
2.017(4)
2.4069(5)
2.039(4)
2.042(4)
C(1)-Au(1)-C(7)
Pt(1)-Au(1)-Pt(1)
Pt(2) 3.6817(8) N(2)-Pt(1)-I(1)
Pt(1) 3.6376(7) N(1)-Pt(1)-N(3)
Pt(2) 4.3046(9) N(5)-Pt(2)-I(2)
179.7(4)
161.2(5)
177.9(3)
162.0(5)
177.6(7)
178.4(6)
166.72(2)
158.55(2)
3 3 3
3 3 3
3 3 3
Pt(1)-N(1)
Pt(1)-N(2)
Pt(1)-N(3)
Pt(1)-I(1)
Pt(2)-N(4)
Pt(2)-N(5)
Pt(2)-N(6)
Pt(2)-I(2)
Au(1)-C(31)
Au(1)-C(37)
Au(2)-C(43)
Au(2)-C(49)
2.031(12) N(4)-Pt(2)-N(6)
1.932(12) C(31)-Au(1)-C(37)
2.021(11) C(43)-Au(2)-C(49)
2.5819(11) Pt(2)-Pt(1)-Pt(1)
2.036(14) Pt(2)-Pt(2)-Pt(1)
1.955(13)
1.991(14)
2.5706(13)
2.060(15)
2.074(15)
Results and Discussion
2.040(16)
2.055(15)
A summary of all the new compounds prepared and their
numbering scheme is given in Scheme 1. Syntheses of these
double salts used a general metathesis route similar to our
previous synthetic methods, in which the double salt was
precipitated and filtered away from the soluble byproduct.7
Syntheses of the chloride and phenylacetylide derivatives
were relatively straightforward while preparation of the
bromide and iodide derivatives was more complicated be-
cause of [Pt(tpy)Cl]Cl impurities. To obtain better separation
of products, the starting [Pt(tpy)X]X material for these
derivatives was dissolved in an empirically determined sol-
vent mixture as shown in Scheme 2.
6
Pt(1)
Pt(1) 3.3466(3) N(1)-Pt(1)-N(3)
161.2(2)
178.0(2)
177.9(4)
175.8(5)
3 3 3
Pt(1)-N(1)
Pt(1)-N(2)
Pt(1)-N(3)
Pt(1)-C(16)
C(16)-C(17)
Au(1)-C(24)
Au(1)-C(24A) 2.121(5)
Au(2)-C(30) 2.109(5)
Au(2)-C(30A) 2.109(5)
2.022(4)
1.965(5)
2.019(4)
1.991(5)
1.179(6)
2.101(6)
N(2)-Pt(1)-C(16)
Pt(1)-C(16)-C(17)
C(24)-Au(1)-C(27)
C(24)-Au(1)-C(24A) 179.56(3)
C(30)-Au(2)-C(33) 178.0(4)
C(30)-Au(2)-C(30A) 177.97(7)
(DMF) [λmax, nm (ε, M-1 cm-1)]: 335 (20,100), 353
(15,800), 382 (shoulder) (3260).
Structural Characterization. Crystal data collection
and refinement parameters for complexes 1-6 are pre-
sented in Table 1, and selected interatomic distances and
angles are given in Table 2. The structure of complex 1 is
[Pt(tpy)I][Au(C6F5)2] (5). Red [Pt(tpy)I]I (122.9 mg,
0.18 mmol) was dissolved in a 10:2:1 mixture of
CH3CN/DMF/H2O to form an orange solution. Upon
addition of equimolar [Bu4N][Au(C6F5)2] (187.0 mg, 0.18
mmol), a yellow precipitate formed and was isolated via
filtration. After washing with ether, the yellow solid was
similar to its parent complex, [Pt(tpy)Cl]Cl 2H2O.32 The
þ3
asymmetric unit contains one [Pt(tpy)Br] moiety and
one bromide atom with two water molecules. As shown in

Article
Inorganic Chemistry, Vol. 49, No. 20, 2010 9269
Scheme 2. Synthesis of [Pt(tpy)X][Au(C6F5)2] for X=Br- (4) and I- (5)
Supporting Information, Figure S1, the platinum is co-
ordinated to three nitrogen atoms from the terpyridine
ligand with the fourth site occupied by a bromide
atom. The platinum center sits in a distorted square
planar environment with an N(2)-Pt(1)-Br(1) angle of
Figure 1. ORTEP of [Pt(tpy)Cl][Au(C6F5)2] (3) with 50% displacement
ellipsoids. Hydrogen atoms removed for clarity.
178.27(15)ꢀ. Like [Pt(tpy)Cl]Cl H2O, complex 1 forms
3
occupies the fourth coordination site. The PtII center sits
in a distorted square planar environment with an N(2)-
Pt(1)-Cl(1) angle of 179.04(8)ꢀ. In the anion, the AuI
center sits in a near linear environment between two aryl
groups with a C(16)-Au(1)-C(22) angle of 174.86(14)ꢀ.
Despite the low steric bulk above and below the
molecular plane in both the cation and the anion, the
close pairwise head-to-tail cation interactions with a short
˚
Pt Pt distance of 3.4674(4) A, followed by a long
3 3 3
˚
contact with its neighbor at a distance of 4.2948(5) A.
The pairwise Pt Pt distance in this structure is slightly
3 3 3
longer than that observed in the previously reported
[Pt(tpy)Br][AuBr2] complex.48 These pairwise interac-
tions extend in one direction to form an array of cations
(Supporting Information, Figure S2). The spaces between
the cation arrays are filled in by water molecules and
bromide counterions. As shown in Supporting Informa-
tion, Figure S2, each bromide ion sits between pairs of
Pt Au distances are significantly larger than the sum of
3 3 3
49
˚
the van der Waals radii of the two metals (3.41 A).
A
closer look at the structure, as shown in Figure 2, reveals
that the shortest contacts between the two species occurs
between Pt(1) of the cation and C(21) of the anion, with
˚
water molecules, which span 5.397(8) A from O(1)-Br(2)
(Supporting Information, Figure S2) and fill in the space
˚
alternating distances of 3.405(3) and 3.399(3) A. The
terpyridine group of the cation sits directly on top of
the aryl group of the anion, resulting in long Pt Au
between the long Pt Pt contacts. The Br(2)-H(1A)
3 3 3
˚
distance of 3.5(1) A between the pairwise interactions is
3 3 3
˚
distances (4.0901(2) and 4.7470(3) A). It appears that
much shorter (Supporting Information, Figure S2). The [Pt-
(tpy)Br]þ cation has been shown previously16 to participate
in infinite chains of metallophilic interactions.
The structure of complex 2 is unremarkable and similar
to that reported in the literature (Supporting Informa-
tion, Figure S3).36 The cations stack in a head-to-tail
fashion, forming a zigzag extended chain with two dis-
electrostatic attraction between the Pt(δþ) and Cortho(δ-)
dominates the crystal packing forces, shifting the gold
atom of the anion to the side of the platinum atom,
resulting in a zigzag pattern with Pt Au distances
3 3 3
outside of the sum of the van der Waals radii for the
two atoms. The packing of the complexes also exhibits
π-stacking between C6F5 groups on adjacent anions
(Supporting Information, Figure S4). As shown in Sup-
porting Information, Figure S4, one-dimensional arrays
of cations and anions line up parallel to one another with
two sets of interacting aryl groups on either side.
˚
tinct Pt Pt distances of 3.3579(6) and 3.3632(6) A
3 3 3
(Supporting Information, Figure S3). The empty spaces
between the cation chains are filled in by both solvent
(DMF, H2O) and counteranion (PF6-) species. This
solvated structure demonstrates the crystal packing sen-
sitivity to solvent conditions, with different recrystalliza-
tion methods yielding different colored crystals that have
The structure of complex 4 is similar to that of complex
3 and is shown in Supporting Information, Figure S5. The
asymmetric unit contains one cation and one anion. The
PtII center sits in a distorted square planar environment
with an N(2)-Pt(1)-Br(1) angle of 178.79(10)ꢀ. In the
anion, the AuI atom exhibits near linear coordination
with a C(1)-Au(1)-C(7) angle of 174.78(16)ꢀ. As shown
in Supporting Information, Figure S6, the stacking pat-
tern of the complex 4 is nearly identical to complex 3, with
the terpyridine group of the cation sitting directly on top
of the aryl group of the anion. Again, the closest contact
between the two moieties is between Pt(1) and C(2)
distinct Pt Pt distances between [Pt(tpy)(CCPh)]þ ca-
3 3 3
tions. For example, the CH3CN solvate of [Pt(tpy)-
(CCPh)]PF6 is dark purple and has two unique Pt Pt
3 3 3
26
contacts of 3.3747(9) and 3.3626(9) A. In the [Pt(tpy)-
˚
Cl]Cl case, the water solvate is yellow with pairwise
Pt Pt contacts, whereas the dimethylsulfoxide (DMSO)
solvate is red with infinite chains of Pt Pt metallophilic
3 3 3
3 3 3
interactions.6
The asymmetric unit of complex 3 is shown in Figure 1
with one cation and one anion. In the cation, three
nitrogen atoms of the terpyridine ligand occupy three
coordination sites of the PtII center, and the chloride
˚
(3.387(4) and 3.435(5) A), with the gold atom shifted
relative to the platinum atom, resulting in long Pt Au
3 3 3
(48) Schneider, J.; Du, P.; Jarosz, P.; Lazarides, T.; Wang, X.; Brennessel,
(49) Jarosz, P.; Thall, J.; Schneider, J.; Kumaresan, D.; Schmehl, R.;
W. W.; Eisenberg, R. Inorg. Chem. 2009, 48, 4306.
Eisenberg, R. Energy Environ. Sci. 2008, 1, 573.

9270 Inorganic Chemistry, Vol. 49, No. 20, 2010
Phillips et al.
Figure 4. Infinite chain of [Pt(tpy)I]þ moieties in [Pt(tpy)I][Au(C6F5)2]
(5) formed between Pt(2) Pt(2), Pt(2) Pt(1), and Pt(1) Pt(1) con-
tacts with the distances of unique Pt Pt distances of 3.6817(8),
3 3 3
3 3 3
3 3 3
3 3 3
-
˚
3.6376(7), and 4.3046(9) A, respectively. Counter [Au(C6F5)2] anions
and hydrogen atoms removed for clarity.
Unlike complexes 3 and 4, the cations and anions in
complex 5 do not stack in an alternating fashion. Instead,
the cations form an infinite zigzag array defined by three
unique Pt Pt distances of 3.6817(8) (Pt(1)-Pt(2)),
Figure 2. Extendedstackingof[Pt(tpy)Cl][Au(C6F5)2] (3) showing close
contacts between Pt(1) of the cation and C(21) of the anion with two
3 3 3
˚
3.6376(7) (Pt(1)-Pt(1)), and 4.3046(9) (Pt(2)-Pt(2)) A
crystallographically independent Pt C distances of 3.399(3) (C(21)-
3 3 3
as shown in Figure 4. The first two internuclear distances
between Pt(1)-Pt(2) and Pt(1)-Pt(1) are near the sum of
the van der Waals radii for the two metal centers, and
therefore could be considered a metallophilic interaction.
The zigzag chain of [Pt(tpy)I]þ moieties is characterized
by two angles of 158.55(2)ꢀ (Pt(1)-Pt(1)-Pt(2)) and
166.72(2)ꢀ (Pt(2)-Pt(2)-Pt(1)). This tetracationic unit,
Pt(1)-Pt(2)-Pt(2)-Pt(1), is repeated in one direction,
forming an infinite series of cations. The anions in the
structure stack in a slipped head-to-tail fashion, sup-
ported within by mutual π-interactions of the per-
fluoroaryl groups, and sandwich the cation chain
(Supporting Information, Figure S8), with a position
disorder of 92/8% for Au1/Au1B and 90/10% for Au2/
Au2B.
˚
Pt(1)) and 3.405(3) (Pt(1)-C(21)) A. Hydrogen atoms removed for clarity.
The structure of complex 6 contains one [Pt(tpy)-
(CCPh)]þ moiety and a disordered [Au(C6F5)2]- moiety
(Figures 5 and Supporting Information, Figure S9) in
which the [Au(C6F5)2]- anions exhibit a disorder with
interwoven or overlapping structures where the Au and
para-F atoms can be thought of as alternating positions.
This problem was treated by generating the second half of
each [Au(C6F5)2]- anion and then setting the occupancies
to 50%. This resulted in long Au(1)-C(24), Au(1)-C(24A)
distances of 2.101(6) and 2.121(5) and for Au(2)-C(30),
Figure 3. ORTEP of [Pt(tpy)I][Au(C6F5)2] (5) with 50% displacement
ellipsoids. Hydrogen atoms removed for clarity.
˚
distances of 4.057(3) and 4.7221(4) A. Similar to the
packing of complex 3, the aryl groups from adjacent
anions interact with each other, further stabilizing the
infinite chain of atoms (Supporting Information, Figure S7).
Unlike the recently reported [Pt(tpy)Br][AuBr2] structure,16
˚
this [Pt(tpy)Br][AuX2] double salt does not display Pt Au
interactions, but only interactions between the platinum
centers and the ortho-carbon of the aryl ring.
Au(2)-C(30A) distances of 2.109(5), 2.109(5) A compared
3 3 3
to 2.04-2.05 Au-C values in compound 5.
The crystal packing of complex 6 is similar to that of
complex 5, with the cations forming a channel supported
by close pairwise Pt Pt contacts insulated by slipped-
The structure of complex 5, [Pt(tpy)I][Au(C6F5)2], is
shown in Figure 3 with important distances and angles
listed in Table 2. The asymmetric unit contains two
cations and two anions. Similar to the PtII environment
reported for [Pt(tpy)I][AuI2], the PtII center of the cation
is coordinated by the three imine groups of the terpyr-
idine ligand with the fourth coordination site occupied by
iodide in a distorted square planar environment with an
N(3)-Pt(1)-N(1) angle of 161.2(5)ꢀ.15 The AuI center of
the anion rests in an almost linear environment with an
C(43)-Au(2)-C(49) angle of 178.4(6)ꢀ.
3 3 3
head-to-tail anions on either side (Figure 6). The geome-
try about the metal centers in both the cation and the
anion are similar to those of the starting materials. As
shown in Figure 6, the cations form a zigzag pattern with
˚
Pt Pt distances of 3.3466(3) and 4.3703(4) A. These
3 3 3
two distances define the tricationic unit, Pt(1A)-Pt-
(1B)-Pt(1A), that is repeated in one direction. Just as in
complex 5, the anions do not participate in metal-metal
interactions in this structure.

Article
Inorganic Chemistry, Vol. 49, No. 20, 2010 9271
Figure 7. Absorption spectra of [Pt(tpy)Cl]Cl and [Pt(tpy)Cl][Au-
(C6F5)2], 3.
Figure 5. ORTEP of [Pt(tpy)(CCPh)][Au(C6F5)2] (6) with 50% dis-
placement ellipsoids. Hydrogen atoms removed for clarity.
nature of the X ligand coordinated to the PtII center.51 The
more electron donating the ligand, the lower the energy of
this transition because of an increase in the metal-based
highest occupied molecular orbital (HOMO) energy, which
results in a smaller energy gap between the dz(Pt) and
π*(tpy) orbitals responsible for the transition.51 As pre-
dicted, the absorption of complex 6 is red-shifted relative to
that of the halides because of the electron donating pheny-
lacetylide group. The absorption profiles of complexes 3
and 6 are shown in Supporting Information, Figure S10
and clearly show this red shift of approximately 40 nm
in the visible range from roughly 420 nm (3) to roughly
460 nm (6).
Emission Spectra. In luminescent compounds, the en-
ergy and intensity of emission are generally governed by
(1) the energy gap between the HOMO (donor) and
lowest unoccupied molecular orbital (LUMO, acceptor)
orbitals, (2) the degree of orbital overlap, (3) reorganiza-
tion of the excited state, and (4) the average displacement
of the transferred electron.33 For [Pt(tpy)X]þ systems, the
HOMO is generally the dz2 orbital of the PtII center.33
Previous studies of [Pt(tpy)X]þ salts have shown some of
these species to be emissive at room temperature in
acetonitrile and acetonitrile/water solutions.50,51 The
[Pt(tpy)Cl]þ systems are non-emissive at room tempera-
ture, but when cooled to 77 K, these chloride complexes
are weakly emissive with only one excited state observed.50
Luminescence has been attributed to excitation of a metal-
based dz2 orbital (HOMO) electron of the metal center into
a ligand based LUMO.50 For systems where X is CCPh,
room temperature emission is observed and tends to be
more intense with a longer lived excited-state.28 The in-
creased emission intensity and stability of the excited-state
is attributed to a decrease in the HOMO-LUMO gap
because of an increase of the energy of the metal-based
HOMO fromtheσ-donationofthephenylacetylideintothe
metal dz2 orbital. For the same complex, a red shift in the
emission is observed when measured in the solid-state.26
This excitation has been assigned to a triplet-state metal-to-
metal-to-ligand charge transfer (3MMLCT), which arises
Figure 6. Infinite chain of [Pt(tpy)(CCPh)]þ moieties in [Pt(tpy)-
(CCPh)][Au(C6F5)2] (6) with Pt Pt contacts shown with dashed
3 3 3
˚
lines with an intradimer Pt(1(A))-Pt(1(B)) distance of 3.3466(3) A and an
-
˚
interdimer Pt(1(B))-Pt(1(A)) distance of 4.3703(4) A. Counter [Au(C6F5)2]
anions and hydrogen atoms removed for clarity.
Absorption Spectra. The room temperature absorption
spectra of all complexes were collected in DMF. The
absorption spectra for the double salt complexes 3, 4, 5,
and 6 are shown in the Supporting Information, Figure
S10. The solution spectra of the double salt complexes do
not differ from the spectra of the [Pt(tpy)X]þ starting
complexes. The UV-vis spectra of complexes [Pt(tpy)Cl]-
[Au(C6F5)2], 3, and [Pt(tpy)Cl]Cl are presented in Figure 7
and demonstrate that the Pt starting material and double
salt spectra are effectively identical in solution. Therefore,
the observed transitions are localized on the cations with
neglible anion interaction, indicating that the cation and
anion of the double salt do not interact in solution at these
concentrations.
Absorptions at high energies (<350 nm) with molar
absorptivities on the order of 104 M-1 cm-1 are assigned
to intraligand charge transfer (ILCT) of the cation’s
terpyridine ligand.50 The less intense absorptions at lower
energies (>400 nm) with molar absorptivities on the order
from significant Pt Pt interactions in the solid.26
3 3 3
3
of 103 M-1 cm-1 are assigned to the MLCT (metal-to-
In this study, all [Pt(tpy)X][Au(C6F5)2] complexes where
X is a halide are non-emissive at room temperature in
DMF. We did not anticipate the cation or the anion to be
independently luminescent at room temperature. As de-
scribed above, the halides are not sufficiently electron-
donating to raise the energy of the HOMO of the molecule.
Therefore, the HOMO-LUMO gap is too large of an
energetic barrier. For the double salt systems, however, we
ligand charge transfer) transitions, which are attributed to
the d(Pt)f π*(tpy) transition.50 As seen in previous sys-
tems, the lower energy transitions are dependent on the
(50) McMillin, D. R.; Moore, J. J. Coord. Chem. Rev. 2002, 229, 113.
(51) Aldridge, T. K.; Stacy, E. M.; McMillin, D. R. Inorg. Chem. 1994, 33,
722.

9272 Inorganic Chemistry, Vol. 49, No. 20, 2010
Phillips et al.
Figure 8. Molecular orbital (MO) calculations for [Pt(tpy)Cl]þ (left) and [Pt(tpy)(CCPh)]þ (right). Occupied orbitals are shown with black lines and red/
blue electron density pictures. Unoccupied orbitals are shown with gray lines and orange/turquoise pictures. For each cation, only four orbitals (two
occupied and two unoccupied) are explicitly depicted, and the levels to which they correspond are shown with arrows.
hypothesized that the LUMO of the [Au(C6F5)2]- moiety
would be closer in energy to the HOMO of the [Pt(tpy)X]þ
cation than in the [Pt(tpy)X]þX- salts, thus providing a
smaller energy gap for electron excitation. However, the
lack of luminescence of the double salt complexes suggests
that sucha transition does not occur in solution under these
conditions. The room temperature, solution state emission
of complex 6 in DMF does not differ from that of complex
2, which indicates that luminescence is attributed to the
[Pt(tpy)(CCPh)]þ species with no participation of the anion
in the double salt.
Therefore, electronic factors must also play a role in
determining solid-state interactions within this family of
compounds. An investigation with DFT was undertaken in
an effort to elucidate any of these electronic influences.
Our initial picture of metallophilic interactions in terms
of molecular orbitals involved a nucleophilic, metal-
based HOMO of the anion donating into an electrophilic
metal-based LUMO of the cation. In such an analysis, the
relative energy, symmetry, and composition of the HOMO
and LUMO of the moieties in question are potentially
relevant in the formation of metallophilic interactions.
Therefore, it is useful to inspect the MO diagrams of the
building blocks of our compounds. We note that state-
Electronic Structure Calculations. As described above,
complexes 3 and 4 display relatively long Pt Au dis-
3 3 3
tances, while complexes 5 and 6 form varying degrees of
Pt Pt interactions with no Pt Au interactions ob-
of-the-art computational work on noncovalent M
M
3 3 3
interactions has demonstrated the important role of dis-
persion and correlation effects.52-54 These effects are not
currently accurately accounted for in commercial DFT
programs and are furthermore not accessible to chemical
intuition for those who, like us, wish to use that intuition in
molecular design. The calculations discussed herein are
intended to provide testable hypotheses for this intuition.
Figure 8 shows an energy level diagram comparison
between [Pt(tpy)Cl]þ and [Pt(tpy)(CCPh)]þ, with only the
four orbitals under discussion depicted explicitly. In each
cation, the HOMO is largely based on the X group,
namely, the π-donating Cl in the first case and the
π-accepting CCPh in the second. The LUMO is also
similar between both compounds and is dominated by
the terpyridine ligand. We anticipated that the stronger
σ-donor character of CCPh versus Cl would raise the
energy of the dz2 orbital relative to the other occupied
frontier orbitals in the compound and thereby promote
metallophilic interactions between the PtII center of the
cation and the AuI center of the anion. This is clearly not
the case as the HOMO in the CCPh cation is higher
3 3 3
3 3 3
served in the solid state. Surprisingly, the [Pt(tpy)X]-
[Au(C6F5)2] double salts in this study do not behave like
our previously reported [Pt(tpy)Cl][Au(CN)2] or [Pt(tpy)-
CN][AuCl(CN)] double salts19 in the solid state, which
form infinite chains of Pt Au species defined by close
3 3 3
metal-metal contacts. There is no obvious steric reason
why the Pt and Au atoms cannot be in closer contact.
Therefore, in an attempt to understand the differences
between these earlier complexes and these new complexes
that exhibit long Pt Au distances, and some short
3 3 3
Pt Pt distances, we must consider both the steric and
3 3 3
the electronic differences among these [Pt]þ[Au]- double
salts. Considering first the steric properties of the new
complexes, the primary effect is that the extension of the
X group above and below the xy plane changes, increasing
in the following order: 3 ∼ 6<4<5. The greater spatial
extension of the CCPh group into the xy plane is not
believed to have a steric impact on the stacking, although
an electronic impact from π-π stacking cannot be ex-
cluded. To a first approximation, one would expect that
the complexes with the smaller X groups would form closer
metal-metal distances; however, this is not borne out by
the structural data in the absence of crystallization solvent.
(In the related [Pt(tpy)X][AuX2] system, the Br derivative
(52) Grimme, S.; Djukic, J.-P. Inorg. Chem. 2010, 49, 2911.
(53) Schwabe, T.; Grimme, S.; Djukic, J.-P. J. Am. Chem. Soc. 2009, 131,
14156.
(54) Hyla-Kryspin, I.; Grimme, S.; Djukic, J.-P. Organometallics 2009,
28, 1001.
exhibits shorter Pt Au distances than the chloride.17)
3 3 3

Article
Inorganic Chemistry, Vol. 49, No. 20, 2010 9273
Figure 9. From left to right, molecular orbital (MO) calculations for [Au(CN)2]-, [Au(CN)Cl]-, [AuCl2]-, and [Au(C6F5)2]-. Occupied orbitals are
shown with black lines and red/blue electron density pictures. Unoccupied orbitals are shown with gray lines and orange/turquoise pictures. For each anion,
three orbitals are depicted (from bottom to top) nσ, π, and (nþ1)σ. The appropriate labels are placed next to the energy levels to which they correspond.
relative to the dz2 than in the Cl instance, although
Pt Pt interactions are observed in 6.
4, we see strong interactions between the electron rich aryl
group of the anion and the electron rich platinum centers
of the cation, resulting in cation-anion stacking, with
the closest contact being between the ortho carbon and the
platinum center. In complexes 5 and 6, however, the
closest contact occurs between two relatively electron
rich platinum centers of the cations, resulting in a cation-
cation stacking pattern. The computational analysis sug-
gests that the [Au(C6F5)2]- is not suited to form metallo-
philic interactions with a [PtL3X]þ cation because its
σ-type frontier orbitals are not localized strongly enough
on the Au atom. This anion has been shown to form
many metallophilic interactions with Ag24,56-59 and
Tl,14,57,60-63 whose σ-donor orbitals for metallophilicity
are not so strongly directional as in [Pt(tpy)X]þ.
3 3 3
A similar comparison is presented in Figure 9 in which
four different [AuX2]- anions are shown. In previous
work, we have established that [Au(CN)2]- and [AuCl-
(CN)]- form infinite chains of metallophilic interactions
in [Pt]þ[Au]- double salts.19 With the same [Pt(tpy)Cl]þ
cation, however, the [AuCl2]- anion forms only half as
many metallophilic interactions. In the current work,
[Au(C6F5)2]- has formed no such close Pt Au contacts
3 3 3
with any [Pt(tpy)X]þ cation to date. For each anion, three
orbitals from each energy level diagram are labeled and
depicted: the highest occupied π-type orbital, the highest
occupied σ-type (labeled nσ), and lowest unoccupied σ-
type orbital (labeled (nþ1)σ). As for all bonding interac-
tions, the correct symmetry is a sine qua non. Metallo-
philic interactions can involve a σ-type overlap between
metal centers,3,55 and in the linear geometry of [AuX2]-
anions, the orbital that can interact metallophilically
must do so approximately perpendicular to the X-Au-X
line. All four anions have such an orbital available, but
only in the [Au(CN)2]- case is this orbital (effectively) the
HOMO. In the other three cases, the highest lying π-type
orbital is higher in energy that the σ-type, which may
reduce its propensity for metallophilic interactions. Signi-
ficantly, the HOMO in [Au(C6F5)2]- has substantial
electron density on the ortho carbon atoms, which inter-
act strongly with Pt in 3 and 4. Also important in
metallophilicity is an unoccupied σ-type orbital. In the first
three anions, the lowest σ-type orbital (not necessarily the
LUMO) has substantial metal character. However, this is
not the case in [Au(C6F5)2]-, where again the (nþ1)σ
orbital is dominated by the perfluoroaryl ring.
It is also true that the four different [Pt(tpy)X]þ cations
studied here have different electron densities on the Pt
atoms, which can influence whether or not these cations
interact with each other when they do not do so with an
anion. The most electron rich center is in the cation of 6,
and its crystal structure shows the shortest metallophilic
contacts within this series. The cation of 5 has previously
been shown to form only very long Pt Pt contacts with
3 3 3
itself,16 which phenomenon is attributed to the significant
(56) Uson, R.; Laguna, A.; Laguna, M.; Jones, P. G.; Sheldrick, G. M.
J. Chem. Soc., Chem. Commun. 1981, 1097.
(57) Uson, R.; Laguna, A.; Laguna, M.; Manzano, B. R.; Jones, P. G.;
Sheldrick, G. M. J. Chem. Soc., Dalton Trans. 1984, 285.
(58) Fernandez, E. J.; Gimeno, M. C.; Laguna, A.; Lopez-de-Luzuriaga,
J. M.; Monge, M.; Pyykkoe, P.; Sundholm, D. J. Am. Chem. Soc. 2000, 122,
7287.
(59) Fernandez, E. J.; Lopez-de-Luzuriaga, J. M.; Monge, M.; Olmos,
M. E.; Puelles, R. C.; Laguna, A.; Mohamed, A. A.; Fackler, J. P., Jr. Inorg.
Chem. 2008, 47, 8069.
(60) Fernandez, E. J.; Jones, P. G.; Laguna, A.; Lopez-de-Luzuriaga,
J. M.; Monge, M.; Perez, J.; Olmos, M. E. Inorg. Chem. 2002, 41, 1056.
(61) Fernandez, E. J.; Jones, P. G.; Laguna, A.; Lopez-de-Luzuriaga,
J. M.; Monge, M.; Montiel, M.; Olmos, M. E.; Perez, J. Z. Naturforsch., B:
Chem. Sci. 2004, 59, 1379.
(62) Fernandez, E. J.; Laguna, A.; Lopez-de-Luzuriaga, J. M.; Montiel,
M.; Olmos, M. E.; Perez, J. Inorg. Chim. Acta 2005, 358, 4293.
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M.; Olmos, M. E.; Perez, J. Organometallics 2006, 25, 1689.
Thus, the DFT computational analysis reveals two
delicate electronic forces that are both in play: metallo-
philic interactions and interactions of the C6F5 aryl ring
with either [PtL3X]þ cations or itself. In complexes 3 and
(55) Roundhill, D. M.; Gray, H. B.; Che, C. M. Acc. Chem. Res. 1989,
22, 55.

9274 Inorganic Chemistry, Vol. 49, No. 20, 2010
Phillips et al.
steric bulk of iodide. The [Pt(tpy)Cl]þ and [Pt(tpy)Br]þ
cations have exhibited metallophilic interactions with
themselves,6,15,16 and therefore the stacking in 3 and 4 is
attributed to both the electrostatic attraction between
cation and anion as well as the localization of HOMO
electron density in [Au(C6F5)2]- on the aryl rings, as
shown in Figure 9.
cation-anion interaction in the solution state. We believe
that the lack of Pt Au interactions is due to the ligand-
3 3 3
based HOMO and LUMO on the [Au(C6F5)2]- moiety as
revealed via electronic structure calculations, which do not
have orbitals of σ symmetry at the right energy to favorably
overlap with the directional dz2 orbital of the [Pt]þ cations. As
a result, the interactions in the double salt are observed to be
either Pt C ortho or Pt Pt interactions in the solid state.
3 3 3
3 3 3
Conclusions
We are cognizant of the possibility for alternative stacking
formations in the presence of crystallization solvent. Future
exploration of our double salt systems will investigate alter-
native [AuX2]- anions that have greater electron density
located in σ symmetry frontier orbitals of Au so as to favor
In summary, we have synthesized and characterized four
new double salt complexes of the type [Pt(tpy)X][Au(C6F5)2]
(X = Cl, 3, Br, 4, I, 5, CCPh, 6, as well as crystallographically
characterized two [Pt(tpy)X]Y starting materials (X=Y=Br,
1, and X=CCPh, Y=PF6, 2). Structural characterization
shows that these double salt complexes form two types of
structural motifs in the solid state. Complexes 3 and 4 form
direct M M contacts.
3 3 3
Acknowledgment. We thank Boston University, the
Boston University Center for Nanoscience and Nanobio-
technology (summer support for V.P.), and NSF (NSF-
EMT 08-517) for financial support.
chains of alternating cation-anion moieties with long Pt
3 3 3
Au distances that lie well outside of the range of metallophilic
interactions. Complexes 5 and 6 form cation stacks in
channels characterized by pairwise Pt Pt contacts in 6
3 3 3
Supporting Information Available: CIFs are given for com-
pounds 1-6 as well as additional figures for aryl group interac-
tions in complexes 3 and 4 (Figures S7 and S6), ORTEPs of
complexes 1, 4, and 2 (Figures S1, S6, and S8), crystal packing
diagrams for 1, 4, 5, and 6 (Figures S2, S6, and S7, S9), as well as
UV-vis spectra of 3, 4, 5, and 6 in S10. This material is available
free of charge via the Internet at http://pubs.acs.org.
and longer, barely metallophilic contacts in 5 with slipped-
head-to-tail anions surrounding the cation chains. Significant
metallophilic cation-anion interactions are absent in both
packing patterns. Solution spectra (UV-vis and fluores-
cence) of these double salt complexes are nearly identical to
their parent [Pt(tpy)X]þ complexes, indicating the absence of