Self-assembly of luminescent alkynyl-based platinum-cadmium complexes containing auxiliary diimine or terpyridine ligands.

Article abstract of DOI:10.1021/ic9002109

Reaction of different "Cd(N-N)₂²⁺" (N-N = bpy, dmbpy, phen) or "Cd(trpy)²⁺" fragments with cis- or trans-(5) dianionic bis(alkynyl)platinate substrates [Pt(C₆F ₅)₂(C=CR)₂]^2-

Full text of DOI:10.1021/ic9002109

5250 Inorg. Chem. 2009, 48, 5250–5262
DOI: 10.1021/ic9002109
Self-Assembly of Luminescent Alkynyl-Based Platinum-Cadmium Complexes
Containing Auxiliary Diimine or Terpyridine Ligands.
,†
†
†
‡
,†
ꢀ
ꢀ
ꢀ
ꢀ
Jesus R. Berenguer,* Belen Gil, Julio Fernandez, Juan Fornies, and Elena Lalinde*
†
´
´
´
Departamento de Quımica-Grupo de Sıntesis Quımica de La Rioja, UA-CSIC, Universidad de La Rioja, 26006,
‡
~
´
ꢀ
ꢀ
Logrono, Spain, and Departamento de Quımica Inorganica, Instituto de Ciencia de Materiales de Aragon,
´
Universidad de Zaragoza-Consejo Superior de Investigaciones Cientıficas, 50009 Zaragoza, Spain
Received February 2, 2009
Reaction of different “Cd(N-N)22+” (N-N = bpy, dmbpy, phen) or “Cd(trpy)2+” fragments with cis- or trans- (5) dianionic
bis(alkynyl)platinate substrates [Pt(C6F5)2(CtCR)2]2- (R = Ph a, Tol b) leads to the generation of novel bimetallic
neutral Platinum-Cadmium derivatives, which show photoluminescence (PL) strongly influenced by the structure and
the media. In complexes [cis-Pt(C6F5)2(CtCR)2Cd(N-N)2] (N-N = bpy (1), dmbpy (2), phen (3)), the dianionic cis-bis
(alkynyl)platinate fragment interacts with the “Cd(N-N)2+2” unit mainly through both the CR atoms (d(Cd-CR) = 2.417
(5)-2.554(5) A) and the Pt center (d(Pt-Cd) ∼ 3.10 A); while in complexes [cis-Pt(C6F5)2(CtCR)2Cd(trpy)] (4),
probably because of the presence of only three Cd-N bonds, the Pt-Cd interaction is enhanced (d(Pt-Cd) ∼ 3.00
A), the Cd(II) atom being additionally solvated with acetone or H2O. By contrast, in complexes [trans-Pt-
(C6F5)2(CtCR)2Cd(bpy)2] (6) the Cd center is found to be in a distorted trigonal-bipyramid coordination, interacting
with one of the Pt-CR bonds of the platina-bis(alkynyl) unit with very short Cd-CR (2.376(10) A) and Pt-Cd (2.8931
(6) A) bond distances. Bimetallic complexes 1-4, having cis-configured platinum fragments, exhibit, in solid state,
blue and/or green phosphorescence with contribution of close emissive states of different natures: metal (Pt, Cd)
perturbed ππ* intraligand (alkynyl, polyimine) manifolds mixed, to a greater (trpy complexes 4) or lesser extent, with
(Pt-Cd) charge transfer (MM0CT). In glassy state (2-MeTHF, 77 K), complexes 1b-4b exhibit structured emissions
mainly ascribed to (diimine 1b-3b, trpy 4b) 3ππ phosphorescence, likely mixed with some ligand (alkyne) to ligand
(imine) charge transfer (3LL0CT). Complexes 6 are not emissive in solid state at room temperature. At 77 K they display
a high energy 3IL/3MLCT (L = CtCR) blue-shifted emission relative to 5 and, in the case of 6b, an additional low
energy feature, tentatively ascribed to ππ stacking interactions, in accordance with the presence of very short π
contacts (3.25 A) found in the extended lattice of 6b.
π
3 3 3
Introduction
and material science.1-11 Within this field, alkynyl metal
complexes represent an active area of interest with manifold
emissive origins depending on the structural features, as well
as on the nature of the metal, alkynyl substituents, and coli-
gands.12-21 In particular, it is now widely recognized that the
propensity for metalophillic interactions in d10 (CuI, AgI,
AuI, HgII) and d8 (PtII) alkynyl compounds determines their
There is a growing interest in luminescent metal complexes
because of their potential application in molecular electronic
*To whom correspondence should be addressed. E-mail: elena.lalinde@
unirioja.es (E.L.), jesus.berenguer@unirioja.es (J.R.B.).
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2009 American Chemical Society
pubs.acs.org/IC
Published on Web 05/04/2009

Article
Inorganic Chemistry, Vol. 48, No. 12, 2009 5251
solid state structures and plays a key role in their luminescent
properties.12-22 Furthermore, the potentially bridging char-
acter of the alkynyl ligands, either through the electron
density of the CtC units or by using internal or terminal
polypyridyl-functionalized alkynyl entities, makes them ideal
groups for design multicomponent or heterometallic com-
plexes that usually exhibit more efficient long-lived and often
dual photoluminescence with wider ranges of colors.15,23-30
Within this field, although considerable work has been
carried out on alkynyl compounds in relation with d10 (group
11 and HgII) metals,7,12,15,21,22,25-39 relatively few studies
have explored the chemistry of homo40-43 and heteropoly-
nuclear d10-cadmium(II) alkynyl systems44-47 and little is
known about their photophysical behavior.44-47 In view of
this fact and given the recent interest in complexes contain-
ing unusual PtIIfCdII donor-acceptor bonds,45,46,48-51 we
have been involved in examining the reactivity of anio-
nic alkynyl platinates toward CdII salts, with the aim of
synthesizing photoluminescent heteropolynuclear complexes
stabilized by either η2 Cd alkynyl and/or Pt-Cd bond-
3 3 3
3 3 3
ing interactions.44-47 We have found that the degree of
interaction of CdII with the alkynyl entities and the basic
platinum center seems to be modulated by the number and
nature of the ligands around the divalent CdII.
Thus, the first documented CdII alkynyl complexation was
reported in the tetranuclear sandwich-type anionic cluster
[{Pt(CtCPh)4}2(CdCl)2]2- (A, Chart 1), stabilized by eight
μ-κCR-alkynyl and four short Pt Cd bonding interactions.
3 3 3
This cluster (A) containing cationic “CdCl+” units was
generated, together with the 1:2 adduct [{Pt(CtCPh)4}
(CdCl2)2]2- (B, Chart 1) having neutral CdCl2 entities
and μ-η2-alkynyl Cd interactions, by reaction of [Pt-
3 3 3
(CtCPh)4]2- with CdCl2 (1:2 molar ratio).44 Furthermore,
the mixed platinates [cis-Pt(C6F5)2(CtCR)2]2- are able to
stabilize, through η2 alkyne interactions, not only the neutral
CdCl2 unit (C, Chart 1), but also a naked CdII (D, Chart 1),
the latter by reaction with Cd(NO3)2 regardless of the molar
ratio used.47 Curiously, if the reaction takes place in the
presence of cyclen (1,4,7,10-tetraazacyclodecane) the plati-
num center effectively competes with the alkynyl ligands,
affording an unusual bimetallic derivative (E, Chart 1) con-
taining a very short Pt-Cd bond (2.764(1) A) and retaining
only a weak interaction with one of the alkynyl fragments.46
These results prompted us to investigate the coordination of
the alkynyl platinates cis- and trans-[Pt(C6F5)2(CtCR)2]2-
(R = Ph, Tol) toward CdII in the presence of stronger
chelating polyimine ligands such as 2,20-bipyridine (bpy),
5,50-dimethyl-2,20-bipyridine (dmbpy), 1,10-phenanthroline
(phen), and 2,20,60,200-terpyridine (trpy). We note that these
ligands have been widely used for the synthesis of coordina-
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(C6F5)2(CtCR)2] (R = Ph,58 Tol47) and (NBu4)2[trans-Pt-
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5252 Inorganic Chemistry, Vol. 48, No. 12, 2009
Berenguer et al.
Chart 1
procedures. Other reagents such as 2,20-bipyridine (bpy), 5,50-
dimethyl-2,20-bipyridine (dmbpy), 1,10-phenantroline (phen)
and 2,20,60,200-terpyridine (trpy) were obtained from commercial
sources.
using SHELXS-97 (2a, 4b)63 or Patterson and Fourier methods
using DIRDIF92 (1a, 3a, 4a, 6b).64 The absorption corrections
were performed using SORTAV65 (1a, 2a, 3a, 4a, 6b) or
XABS266 (4b).The structures were refined by full-matrix least-
squares on F2 with SHELXL-97,63 and all non-hydrogen atoms
were assigned anisotropic displacement parameters. The hydro-
gen atoms were constrained to idealized geometries fixing
isotropic displacement parameters 1.2 times the Uiso value of
their attached carbon for the aromatic and 1.5 times for the
methyl groups. For complex 6b, which crystallizes in the non-
centrosymmetric space group Cc, the crystal chosen for this
structural analysis was found to be an inversion twin with
occupancy 0.249(6) for the second component. Several re-
straints have been used to model one acetone molecule in 2a
and 4b. Finally, all the structures present some residual peaks
greater than 1 e A-3 in the vicinity of the metal atoms (or the
crystallization solvent for 2a and 4b), but with no chemical
meaning.
X-ray Crystallography. Details of the structural analyses
for all complexes are summarized in Table 1. Colorless crystals
of 1a and 3a were obtained by slow diffusion of a solution
of Cd(ClO4)2 6H2O (∼4 mg) in acetone into a solution of
3
(PMePh3)2[cis-Pt(C6F5)2(CtCPh)2] (12 mg) and the N-N ligand
(4 mg, bpy 1a; phen 3a) also in acetone at room temperature. For
complexes 2a and 6b yellow crystals were obtained by cooling
(-30 °C) saturated solutions of the corresponding crude solids
in acetone. Colorless or yellow crystals of 4a or 4b, respectively,
were obtained by slow diffusion of n-hexane (4a) or isopropy-
lether (4b) into the respective solutions of the complexes in
acetone. One (3a) or two (4a) molecules of acetone, one molecule
of acetone, and 0.75 of water (2a) or three molecules of acetone
and one of water (4b) were found in the corresponding asym-
metric units. For complex 1a, one molecule of acetone was
found in the corresponding asymmetric unit. Nevertheless, the
use of the program SQUEEZE60,61 showed the presence of one
void of 300 A3 containing 47 electrons. This fits well with the
presence of 0.75 molecules of acetone in each asymmetric unit,
which have been, thus, included in the empirical formula
Results and Discussion
Synthesis and Characterization. As shown in Scheme 1
(i), treatment of (PMePh3)2[cis-Pt(C6F5)2(CtCR)2] (R =
Ph a, Tol b) with Cd(ClO4)2 6H2O and 2 equiv of diimine
3
ligand (bpy, dmbpy, phen) in acetone affords the bime-
tallic neutral Platinum-Cadmium complexes [cis-Pt-
(C6F5)2(CtCR)2Cd(N-N)2] (N-N = bpy (1), dmbpy
(2), phen (3)) as pale yellow or white (2b) solids in mod-
erate yields (43-62%). It is noteworthy that the same
products are obtained using only 1 equiv of diimine
ligands but in lower yields. Similarly, the reaction of
(1a 1.75(CH3)2CO). For complex 6b, two molecules of acetone
3
were found in the corresponding asymmetric unit, one of them
being disordered. In spite of many attempts, we could not
resolved the disorder adequately, and it was modeled using
the program SQUEEZE,60,61 which found the unit cell to
contain two voids of 592 A3 containing 56 electrons. This fits
well with the presence of one molecule of acetone in each
asymmetric unit, which has been, thus, included in the empirical
(PMePh3)2[cis-Pt(C6F5)2(CtCR)2] with Cd(ClO4)2 6H2O
3
formula (6b 2(CH3)2CO). X-ray intensity data were collected
3
in the presence of the tridentate 2,20,60,200-terpyri-
dine (trpy) ligand gives rise to the corresponding
with a NONIUS-κCCD area-detector diffractometer, using
graphite-monochromated Mo KR radiation. Images were pro-
cessed using the DENZO and SCALEPACK suite of pro-
grams62 and the structures were solved by Direct Methods
(63) Sheldrick, G. M. SHELX-97, a program for the refinement of crystal
::
::
structures; University of Gottingen: Gottingen, Germany, 1997.
(64) Beursken, P. T.; Beursken, G.; Bosman, W. P.; de Gelser, R.; Garcı
´
a-
(60) Van der Sluis, P.; Spek, A. L. Acta Crystallogr. 1990, A46, 194.
(61) Spek, A. L.; SQUEEZE, incorporated into PLATON: A Multi-
purpose Crystallographic Tool; Utrecht University: Utrecht, The Nether-
lands, 2005.
Granda, S.; Gould, R. O.; Smith, J. M. M.; Smykalla, C. The DIRDIF92
program system, Technical Report of the Crystallography Laboratory;
University of Nijmegen: The Netherlands, 1992.
(65) Blessing, R. H. Acta Crystallogr. 1995, A51, 33.
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(66) Parkin, S.; Moezzi, B.; Hope, H. J. Appl. Crystallogr. 1995, 28, 53.

Article
Inorganic Chemistry, Vol. 48, No. 12, 2009 5253
Table 1. Crystallographic Data for 1a 1.75(CH3)2CO, 2a (CH3)2CO 0.75H2O, 3a (CH3)2CO, 4a 2(CH3)2CO, 4b 3(CH3)2CO H2O, and 6b 2(CH3)2CO
3
3
3
3
3
3
3
3
1a 1.75
(CH3)2CO
2a (CH3)2
CO 0.75H2O
3a
(CH3)2CO
4a 2
(CH3)2CO
4b 3
(CH3)2CO H2O
6b 2
(CH3)2CO
3
3
3
3
3
3
3
3
empirical formula
C53.25 H36.5
Cd F10 N4 O1.75 Pt
1258.64
293(2)
triclinic; P1
C55 H40 Cd F10
N4 O1.75 Pt
1282.40
173(1) 293(2)
monoclinic, P21/n triclinic, P1
C55 H32 Cd
F10 N4 O Pt
1262.34
C49 H33 Cd
F10 N3 O2 Pt
1193.27
293(2)
triclinic, P1
C99 H68 Cd2 F20 C56 H42 Cd
N6 O4 Pt2 F10 N4 O2 Pt
2400.57
Fw
T (K)
crystal system,
space group
a (A)
b (A)
c (A)
R (deg)
β (deg)
1300.43
173(1)
triclinic, P1
223(1)
monoclinic, Cc
11.4895(2)
12.1929(3)
19.8162(5)
91.2460(10)
91.6520(10)
116.060(2)
2490.96(10)
2
15.3110(2)
19.9720(3)
17.0120(3)
90
97.2920(10)
90
5160.05(14)
4
1.651
11.1692(2)
12.4612(2)
19.4842(5)
92.6990(10)
102.5990(10)
116.275(2)
2340.91(8)
2
12.5370(2)
14.1520(2)
15.6139(3)
116.1620(10)
92.1180(10)
113.7240(10)
2197.53(6)
2
15.1965(2)
15.5331(2)
19.7826(3)
83.9210(10)
87.1790(10)
76.5470(10)
4514.53(11)
2
16.9220(3)
25.2140(6)
13.8280(3)
90
107.598(2)
90
5623.9(2)
4
1.536
γ (deg)
volume (A3)
Z
Dcalcd (Mg/m3)
1.678
1.791
3.525
1.803
3.750
1.766
3.651
absorption coefficient 3.309
(mm-1
F(000)
3.201
2.938
)
1180
4.12 to 25.68
2512
1.97 to 27.91
1228
2.06 to 27.97
1160
3.56 to 27.48
2336
1.38 to 25.68
2552
3.49 to 26.37
θ range for data
collection (deg)
no of data/restraints/ 9380/0/615
params
12280/14/668
11000/0/651
10058/0/599
16860/2/1196
10995/2/636
goodness-of-fit on F2a 1.039
1.020
1.015
R1 = 0.0434,
wR2 = 0.1052
R1 = 0.0550,
wR2 = 0.1132
1.004
0.984
1.066
final R indices
[I > 2σ(I)]a
R1 = 0.0416,
wR2 = 0.0849
R1 = 0.0611,
wR2 = 0.0897
1.028 and -0.997
R1 = 0.0403,
wR2 = 0.0954
R1 = 0.0627,
wR2 = 0.1048
R1 = 0.0378,
wR2 = 0.0744
R1 = 0.0577,
wR2 = 0.0786
R1 = 0.0585,
wR2 = 0.1595
R1 = 0.0799,
wR2 = 0.1823
R1 = 0.0420,
wR2 = 0.1128
R1 = 0.0467,
wR2 = 0.1156
R indices (all data)a
largest diff peak
and hole (e.A -3
1.649 and -1.315 1.380 and -2.390 1.296 and -1.415 1.891 and -3.081 1.214 and -1.039
)
P
P
P
P
P
a
R1 = ||Fo| - |Fc||/ |Fo|; wR2 = [ w(Fo2 - Fc2)2/ wFo
]
2 1/2; goodness of fit = { [w(Fo2 - Fc2)2]/(Nobs - Nparam)}1/2; w = [σ2(Fo) + (g1P)2 +
g2P]-1; P = [max(Fo2;0 + 2Fc2]/3.
Scheme 1
bimetallic neutral complexes [cis-Pt(C6F5)2(CtCR)2Cd
(trpy)] (R = Ph 4a, Tol 4b, Scheme 1, ii) as pale yellow
(4a) or white (4b) solids. For both derivatives colorless
crystals suitable for X-ray studies were obtained by slow
diffusion of n-hexane (4a) or isopropylether (4b) into
saturated solutions of the crude solids in acetone. As
can be observed in Figures 2 (4a) and 3 (4b), in both cases
the “in situ” generated dicationic “Cd(trpy)+2” unit
captures a solvent molecule (acetone 4a; acetone or
H2O 4b) to give a 6-coordinate environment upon co-
ordination to the corresponding bis(alkynyl)platinate
fragment. However, we noted that in both cases the
crystals lost the solvent acetone molecules easily when
in contact with air.
We have recently found that the [trans-Pt
(C6F5)2(CN)2]2- dianionic isomer exhibits a greater ten-
dency to form Pt-Tl bonds than the corresponding
cis- one.67 Thus, we considered it of interest to explore
the behavior of the related [trans-Pt(C6F5)2(CtCR)2]2-
(R = Ph 5a,59 Tol 5b) toward the “in situ” generated
“Cd(bpy)2+2” unit. The precursor (NBu4)2[trans-Pt
ꢀ
(67) Fornies, J.; Garcıa, A.; Lalinde, E.; Moreno, M. T. Inorg. Chem.
´
2008, 47, 3651.

5254 Inorganic Chemistry, Vol. 48, No. 12, 2009
Berenguer et al.
(C6F5)2(CtCTol)2] 5b has been prepared with this aim,
following a similar synthetic procedure to that previously
reported for the phenylethynyl derivative59 (see Experi-
mental Section for details and characterization). As
shown in Scheme 1 (iii), the use of the corresponding
trans- isomers as precursors in the analogous reactions
with Cd(bpy)2+2 in acetone affords the bimetallic neutral
derivatives [trans-Pt(C6F5)2(CtCR)2Cd(bpy)2] (R = Ph
6a, Tol 6b) as a white (6a) or a bright yellow solid (6b) in
moderate yields (62% 6a, 45% 6b).
All 1-4, 6 complexes are air and moisture stable solids
and were characterized by elemental analysis, conductiv-
ities, mass spectrometry, and IR and NMR spectroscopy.
In particular, we noted that once isolated the phenylethy-
nyl derivatives (1a-4a, 6a) are insoluble in common
organic solvents, except in acetone in which they are
1
soluble enough to record the corresponding H and 19F
NMR spectra, but not for conductivity measurements
(see Experimental Section). In addition, single crystal
X-ray diffraction studies have been carried out for
1a-4a, 4b, and 6b confirming their formulations. Per-
spective views of the corresponding molecular structures
are shown in Figures 1 (1a), S1 (2a), S2 (3a), 2 (4a), 3 (4b)
and 4 (6b), and selected bond lengths and angles are listed
in Tables 2 (1-4a), 3 (4b), and 4 ( 6b).
Figure 1. Molecular structure of complex [cis-Pt(C6F5)2(CtCPh)2Cd-
(bpy)2] 1a with the ellipsoidsdrawnat50% probabilityleveland hydrogen
atoms omitted for clarity.
The molecular structures of 1a-3a can be visualized by
assuming a distorted octahedral coordination around the
CdII center, formed by two identical chelating bpy (1a),
dmbpy (2a), or phen (3a) ligands and the dianionic cis-bis
(phenylethynyl)platinate, which interacts with the cad-
mium center mainly through both CR atoms and the Pt
center. In the trpy derivatives (4), the cadmium center also
adopts a distorted octahedral geometry, being bonded
not only to the three nitrogen trpy atoms and the [Pt]-
2-
(CtCR)2 unit (R = Ph a, Tol b) but also to an oxy-
gen-donor solvent molecule, acetone in 4a (Figure 2,
d(Cd-O) = 2.461(3) A), and acetone (Figure 3a,
d(Cd-O) = 2.651(8) A) or H2O (Figure 3b, d(Cd-O) =
2.399(5) A) in the case of 4b. A search in the Cambridge
database68 did not come up with any complex containing
acetone as a ligand toward CdII cation. However, the obs-
erved Cd-O(acetone) distance in 4a (2.461(3) A) is simi-
lar to the Cd-O(OH2) separation (2.399(5) A) found in
the second molecule of 4b, and both of them are compar-
able to those reported for reference complexes contain-
ing other ketonic type molecules,69-73 H2O49,74-77 or
Figure 2. Molecular structure of the adduct [cis-Pt(C6F5)2(CtCPh)2-
Cd(trpy){(CH3)2CO}] (4a (CH3)2CO), with the ellipsoids drawn at 50%
probability level and hydrogen atoms omitted for clarity.
3
tetrahydrofurane77 ligands. The longer Cd(1)-O(1)(acet-
one) distance (2.651(8) A) found in 4b indicates a weaker
interaction. It is worthy to note that, in spite of the
dicationic nature of the cadmium units and the known
ability of [cis-Pt(C6F5)2(CtCR)2]2- to act as an alkyny-
lating agent,78-80 no alkynylation process occurs in any
case, although a σ-migration of one alkynyl group toward
the CdII center unit should give a less polar doubly
alkynyl σ/π type complex. However, this structural fea-
ture keeps the electron density on the platinum center
(68) Search performed with The Cambridge Structural Database 5.30
(November 2008); The Cambridge Crystallographic Data Centre, 2008.
(69) Chen, X.-D.; Mak, T. C. W. Inorg. Chem. Commun. 2005, 8, 393.
(70) Goher, M. A. S.; Mautner, F. A.; Abu-Youssef, M. A. M.; Hafez, A.
K.; Badr, A. M.-A. J. Chem. Soc., Dalton Trans. 2002, 3309.
(71) Danil de Namor, A. F.; Chahine, S.; Kowalska, D.; Castellano, E. E.;
Piro, O. E. J. Am. Chem. Soc. 2002, 124, 12824.
ꢀ
(72) Casas, J. S.; Castellano, E. E.; Garcıa-Tasende, M. S.; Sanchez, A.;
´
Sordo, J.; Zukerman-Schpector, J. Z. Anorg. Allg. Chem. 1997, 623, 825.
(73) Balegroune, F.; Braunstein, P.; Douce, L.; Dusausoy, Y.; Grandjean,
D.; Knorr, M.; Strampfer, M. J. Cluster Sci. 1992, 3, 275.
(74) Bazzicalupi, C.; Bencini, A.; Bianchi, A.; Borsari, L.; Danesi, A.;
Giorgi, C.; Mariani, P.; Pina, F.; Santarelli, S.; Valtancoli, B. Dalton Trans.
2006, 5743.
and, presumably, allows it to form stronger Pt Cd
3 3 3
ꢀ
ꢀ
(75) Granifo, J.; Garland, M. T.; Baggio, R. Inorg. Chem. Commun. 2004,
7, 77.
(76) Hu, T.-L.; Zou, R.-Q.; Li, J.-R.; Bu, X.-H. Dalton Trans. 2008, 1302.
(77) Breitinger, B. K. In Coomprehensive Coord. Chem.; Mccleverty, J.,
Meyer, T. J., Eds.; Pergamon Press: Elmsford, NY, 2004; Vol. 6, pp 1254-
1292.
(78) Ara, I.; Berenguer, J. R.; Eguizabal, E.; Fornies, J.; Lalinde, E.;
Martınez, F. Organometallics 1999, 18, 4344.
(79) Ara, I.; Berenguer, J. R.; Eguizabal, E.; Fornies, J.; Lalinde, E.;
Martın, A.; Martınez, F. Organometallics 1998, 17, 4578.
(80) Fornies, J.; Gomez-Saso, M. A.; Lalinde, E.; Martı
M. T. Organometallics 1992, 11, 2873.
´
ꢀ
ꢀ
´
´
ꢀ
ꢀ
´
nez, F.; Moreno,

Article
Inorganic Chemistry, Vol. 48, No. 12, 2009 5255
Figure 4. (a)
Molecular
structure
of
complex
[trans-Pt-
(C6F5)2(CtCTol)2Cd(bpy)2] 6b with the ellipsoids drawn at 50% prob-
ability level and hydrogen atoms omitted for clarity. (b) Detail of the
intra- and intermolecular ππ stacking observed along the c axis for 6b.
Molecules are simplified for clarity.
could be considered essentially non-bonding. We note
that these distances are above the sum of the van
der Waals radii (2.52 A)81 of carbon (1.43 A) and the
ionic radii of CdII (cn 6, 1.09 A), and clearly longer to
that seen in previous asymmetrical η2-alkynyl Cd der-
ivatives, such as C (Chart 1, Cd-CR, Cβ 2.405(3),
2.556(4) A).47
In all 1a-4a and 4b molecules the Cd center is dis-
placed from the corresponding Pt(II) coordination planes
(1.1507(4) A 1a; 1.4342(1) A 2a; 1.2261(4) A 3a; 1.3740(3) A
4a; 1.2473(5)-1.3254(5) A 4b A), generating non-
planar V-shaped PtC4Cd cores. The Cd-N distances
fall in the range 2.317(6) to 2.413(4) A, which are
not unusual76,77 for a six-coordinated environment
at Cd.81-85
Figure 3. (a) Molecular structure of (a) the adduct [cis-Pt-
(C6F5)2(CtCTol)2Cd(trpy){(CH3)2CO}] (4b (CH3)2CO) and (b) the ad-
3
duct [cis-Pt(C6F5)2(CtCTol)2Cd(trpy)(OH2)] (4b (OH2)). Ellipsoids are
drawn at 50% probability level and hydrogen atoms omitted for clarity.
3
bonding interactions. In fact, the Pt-Cd separations
ranging from 2.9998(3) A in 4a to 3.1162(3) A in 2a
are comparable to those seen in the dianionic clusters
[{Pt(μ-CtCPh)4}2(CdCl)2]2- A (Chart 1, 2.96 A)44 or
[Pt9(CO)18(μ3-CdCl2)2]2- (2.931(4)-3.023(4) A),51 and
clearly shorter than those observed in the η2 alkynyl
complexes B-D (Chart 1) (3.18-3.31 A).44,47 However,
these distances are significantly longer than other unsup-
ported Pt(II)-Cd(II) bonds such as those found in E
(Chart 1, 2.764(1) A)46 or [Pt(Phpy)2Cd(cyclen)]+2 (2.639
(1) A).48 As mentioned above, the CdII is mainly inter-
acting with the CR carbon atoms of the CtCR groups
(μ-κCR bonding) with Cd-CR bond distances ranging
from 2.354(7) to 2.554(5) A, which are comparable
to those seen in the [{cis-Pt(C6F5)2(μ-CtCPh)2}Cd]2-
dianion D (2.376(12)-2.418(10) A).47 The distances
between the CdII center and the external Cβ carbon atoms
are significantly longer (2.741(8)-2.950(7) A), so they
(81) Winter, M. The Periodic Table on the W.W.W.; The University of
Shefield and Web Elements Ltd.: U.K., 2008; www.webelements.com.
(82) Yam, V. W.-W.; Pui, Y.-L.; Cheung, K.-K. New J. Chem. 1999, 23,
1163.
(83) Anjali, K. S.; Pui, Y.-L.; Yam, V. W.-W.; Vittal, J. J. Inorg. Chim.
Acta 2001, 319, 57.
(84) Gou, L.; Wu, Q.-R.; Hu, H.-M.; Qin, T.; Xue, G.-L.; Yang, M.-L.;
Tang, Z. X. Polyhedron 2008, 27, 1517.
´
(85) Holloway, C. E.; Melnık, M. J. Organomet. Chem. 1996, 522, 167,
and references therein.

5256 Inorganic Chemistry, Vol. 48, No. 12, 2009
Berenguer et al.
˚
Table 2. Selected Bond Lengths [A] and Angles [deg] for Complexes [cis-Pt(C6F5)2(CtCPh)2Cd(bpy)2] 1.75(CH3)2CO 1a 1.75(CH3)2CO, [cis-Pt(C6F5)2(CtCPh)2Cd-
3
3
(dmbpy)2] (CH3)2CO 0.75H2O 2a (CH3)2CO 0.75H2O, [cis-Pt(C6F5)2(CtCPh)2Cd(phen)2] (CH3)2CO 3a (CH3)2CO, and [cis-Pt(C6F5)2(CtCPh)2Cd(trpy)] 2(CH3)2CO
3
3
3
3
3
3
3
4a 2(CH3)2CO
3
1a 1.75(CH3)2CO
2a (CH3)2CO 0.75H2O
3a (CH3)2CO
4a 2(CH3)2CO
3
3
3
3
3
Pt-Cd
Pt-CR
Pt(1)-Cd(1)
Pt(1)-C(13)
Pt(1)-C(21)
Pt(1)-C(1)
3.1086(4)
2.039(5)
2.030(5)
2.056(5)
2.072(5)
1.209(7)
1.195(7)
2.527(5)
2.432(5)
2.917(7)
2.918(6)
2.320(4)
2.368(4)
2.378(5)
2.365(4)
3.1162(3)
2.018(5)
2.025(5)
2.059(4)
2.069(4)
1.195(6)
1.224(7)
2.498(4)
2.478(4)
2.896(5)
2.841(5)
2.339(4)
2.413(4)
2.372(4)
2.342(4)
3.0990(4)
2.014(5)
2.032(5)
2.075(5)
2.069(5)
1.212(7)
1.200(7)
2.417(5)
2.554(5)
2.911(6)
2.913(7)
2.375(4)
2.380(4)
2.336(4)
2.382(4)
2.9998(3)
2.013(4)
2.008(4)
2.061(4)
2.052(4)
1.208(5)
1.220(6)
2.446(4)
2.410(4)
2.851(5)
2.782(6)
2.334(3)
2.335(3)
2.382(3)
Pt-Cipso(C6F5)
CR-Cβ
Pt(1)-C(7)
C(13)-C(14)
C(21)-C(22)
Cd(1)-C(13)
Cd(1)-C(21)
Cd(1)-C(14)
Cd(1)-C(22)
Cd(1)-N(1)
Cd(1)-N(2)
Cd(1)-N(3)
Cd(1)-N(4)
Cd(1)-O(1)
C(13)-Pt(1)-C(21)
Pt(1)-C(13)-C(14)
Pt(1)-C(21)-C(22)
C(13)-C(14)-C(15)
C(21)-C(22)-C(23)
C(13)-Cd(1)-C(21)
C(13)-Cd(1)-N(1)
C(13)-Cd(1)-N(2)
C(13)-Cd(1)-N(3)
C(13)-Cd(1)-N(4)
C(21)-Cd(1)-N(1)
C(21)-Cd(1)-N(2)
C(21)-Cd(1)-N(3)
C(21)-Cd(1)-N(4)
C(13)-Cd(1)-O(1)
C(21)-Cd(1)-O(1)
Cd-CR
Cd- Cβ
Cd-N
Cd-O
CR-Pt-CR
Pt-CR-Cβ
2.461(3)
95.5(2)
98.2(2)
174.5(5)
170.5(5)
178.1(6)
172.8(6)
76.6(2)
93.8(2)
176.8(4)
178.8(4)
175.1(5)
174.8(4)
72.8(2)
110.0(2)
173.3(1)
97.9(1)
93.5(1)
93.5(1)
100.5(1)
170.3(1)
106.6(1)
97.5(2)
170.3(5)
174.3(5)
172.0(6)
176.5(6)
75.3(2)
177.5(4)
178.0(4)
178.9(4)
172.4(4)
75.6(1)
95.1(1)
104.7(1)
94.5(1)
CR-Cβ-Cγ
CR-Cd-CR
CR-Cd-N
96.3(2)
93.9(2)
166.3(2)
100.5(2)
93.0(2)
100.6(2)
102.8(2)
166.5(2)
97.9(2)
164.0(2)
102.7(2)
105.3(2)
90.4(2)
101.8(2)
91.7(2)
162.4(2)
121.5(1)
168.1(1)
99.1(1)
CR-Cd-O
153.9(1)
87.4(1)
˚
Table 3. Selected Bond Lengths [A] and Angles [deg] for 4b 3(CH3)2CO H2O
3
3
4b (CH3)2CO
4b H2O
3
3
Pt-Cd
Pt-CR
Pt(1)-Cd(1)
Pt(1)-C(1)
Pt(1)-C(10)
Pt(1)-C(19)
Pt(1)-C(25)
C(1)-C(2)
C(10)-C(11)
Cd(1)-C(1)
Cd(1)-C(10)
Cd(1)-C(2)
Cd(1)-C(11)
Cd(1)-N(1)
Cd(1)-N(2)
Cd(1)-N(3)
Cd(1)-O(1)
3.0095(6)
Pt(2)-Cd(2)
Pt(2)-C(46)
Pt(2)-C(55)
Pt(2)-C(64)
Pt(2)-C(70)
C(46)-C(47)
C(55)-C(56)
Cd(2)-C(46)
Cd(2)-C(55)
Cd(2)-C(47)
Cd(2)-C(56)
Cd(2)-N(4)
Cd(2)-N(5)
Cd(2)-N(6)
Cd(2)-O(2)
3.0320(5)
2.001(8)
2.030(8)
2.050(7)
2.062(8)
1.216(10)
1.192(10)
2.491(6)
2.405(8)
2.950(7)
2.792(9)
2.329(6)
2.338(6)
2.353(6)
2.399(5)
2.017(8)
2.004(8)
2.065(8)
2.048(7)
1.213(10)
1.225(10)
2.464(7)
2.354(7)
2.948(7)
2.741(8)
2.345(6)
2.317(6)
2.329(6)
2.651(8)
Pt-Cipso(C6F5)
CR-Cβ
Cd-CR
Cd- Cβ
Cd-N
Cd-O
CR-Pt-CR
Pt-CR-Cβ
C(1)-Pt(1)-C(10)
Pt(1)-C(1)-C(2)
Pt(1)-C(10)-C(11)
C(1)-C(2)-C(3)
C(10)-C(11)-C(12)
C(1)-Cd(1)-C(10)
C(1)-Cd(1)-N(1)
C(1)-Cd(1)-N(2)
C(1)-Cd(1)-N(3)
C(10)-Cd(1)-N(1)
C(10)-Cd(1)-N(2)
C(10)-Cd(1)-N(3)
C(1)-Cd(1)-O(1)
C(10)-Cd(1)-O(1)
94.9(3)
172.2(6)
178.3(7)
173.9(8)
170.2(8)
75.8(3)
99.7(2)
112.7(2)
97.4(2)
105.5(2)
170.5(2)
113.5(2)
168.4(2)
96.7(2)
C(46)-Pt(2)-C(55)
Pt(2)-C(46)-C(47)
Pt(2)-C(55)-C(56)
C(46)-C(47)-C(48)
C(55)-C(56)-C(57)
C(46)-Cd(2)-C(55)
C(46)-Cd(2)-N(4)
C(46)-Cd(2)-N(5)
C(46)-Cd(2)-N(6)
C(55)-Cd(2)-N(4)
C(55)-Cd(2)-N(5)
C(55)-Cd(2)-N(6)
C(46)-Cd(2)-O(2)
C(55)-Cd(2)-O(2)
94.7(3)
175.8(6)
178.2(7)
176.0(8)
170.0(8)
74.5(3)
97.6(2)
109.8(2)
94.9(2)
103.0(2)
172.1(2)
117.9(2)
164.9(2)
94.1(2)
CR-Cβ-Cγ
CR-Cd-CR
CR-Cd-N
CR-Cd-O
Furthermore, the molecular structure of 6b (Figure 4a)
differs from the isomer 1a in the geometry of both metallic
centers. Thus, the CdII is bonded to four nitrogen atoms
(2.325(7)-2.409(7) A) (see Table 4) of two bpy ligands
and completes a five-coordination environment, being
bonded to one of the mutually trans Pt-CR bonds.

Article
Inorganic Chemistry, Vol. 48, No. 12, 2009 5257
characteristic νCtC (2040-2075 cm-1) and νx-sensC6F5
(780-800 cm-1) bands, confirming the retention of the
cis- geometry of the platinate entities. In the diimine
derivatives (1-3), the expected shift to lower wavelengths
of the νCtC bands (2075-2060 cm-1) relative to the
precursors (PMePh3)2[ cis-Pt(C6F5)2(CtCR)2] (R = Ph
2096, 2083 cm-1; R = Tol 2091, 2078 cm-1) is lesser than
˚
Table 4. Selected Bond Lengths [A] and Angles [deg] for complex [trans-
Pt(C6F5)2(CtCTol)2Cd(bpy)2] 2(CH3)2CO 6b 2(CH3)2CO
3
3
Pt(1)-Cd(1)
Pt(1)-C(10)
Pt(1)-C(25)
C(10)-C(11)
Cd(1)-C(2)
Cd-N(2)
2.8931(6) Pt(1)-C(1)
1.973(11) Pt(1)-C(19)
2.031(10)
2.078(8)
1.238(16)
2.376(10)
2.360(6)
2.325(7)
2.057(8)
C(1)-C(2)
1.226(15) Cd(1)-C(1)
2.916(10) Cd-N(1)
2.409(7)
2.342(7)
Cd-N(3)
that observed in the trpy complexes (4a 2060, 2044 cm-1
;
Cd-N(4)
4b 2054, 2040 cm-1), suggesting that the interaction of the
Cd centers of the Cd(N-N)2+2 units with the alkynyl
ligands is presumably weaker. With regard to the trans
complexes 6, it is worth noting that their IR spectra
confirm not only the presence of terminal and bridging
alkynyl ligands but also the formation of the donor-
acceptor Pt(II)fCd(II) bond. Thus, they show one med-
ium νCtC band (2068 cm-1) slightly shifted to lower
wavenumbers when compared with the precursors [trans-
C(2)-C(1)-Pt(1)
C(1)-C(2)-C(3)
N(1)-Cd(1)-N(2)
N(3)-Cd(1)-N(4)
N(2)-Cd(1)-N(3)
C(1)-Cd(1)-N(3) 106.8(3)
C(1)-Cd(1)-N(1) 95.4(2)
171.4(7)
C(11)-C(10)-Pt(1) 176.4(8)
C(10)-C(11)-C(12) 174.4(12)
179.1(10)
69.6(2)
70.2(3)
94.9(3)
N(2)-Cd(1)-N(4)
N(1)-Cd(1)-N(3)
N(4)-Cd(1)-Pt(1)
C(1)-Cd(1)-N(4)
C(1)-Cd(1)-N(2)
87.5(3)
98.8(3)
90.7(2)
110.2(3)
155.3(3)
The bonding interaction with the platinate unit can be
compared to that seen in [cis-{Pt(C6F5)2(CtCPh)2}Cd-
(cyclen)]46 (E, Chart 1), but in 6b the Pt-Cd vector
exhibits a bigger displacement from the normal of the
Pt coordination plane toward the alkynyl fragment (50.8
(2)°). Thus, the Pt-Cd bond distance of 2.8931(6) A
(Table 4) is slightly shorter to that found in 1a (3.1086
(4), Table 2), but somewhat longer to that seen in the
Pt-Cd cyclen derivative E (2.764(1) A)46 (Chart 1). As a
consequence, the Cd-Pt-C(1) angle (54.4(3)°) is more
acute than that found in E (60.53°), and the Cd-CR
carbon length is significantly shorter (2.376(10) A in 6b
vs 2.493(4) A in E). However, despite the fact the C(1)t
C(2);Tol fragment is acting as μ-κCR-alkynyl bridging
and the C(10)tC(11)-Tol one as terminal, their struc-
tural parameters (angles at CR and Cβ and CtC bond) are
identical within experimental error (Table 4). The coor-
dination of the Cd(bpy)2 unit seems to slightly affect the
Pt-CR bonds (Pt-C(1) = 2.031(10) A vs Pt-C(10) =
1.973(11) A). It is now well established that in many
heteropolynuclear Pt-M (M = Ag, Tl, Pb) pentafl-
uorophenylplatinate complexes the presence of short
Pt(C6F5) 2(CtCR)2]2- (R = Ph 5a 2077 cm-1 59
; R = Tol
5b 2079 cm-1), which is attributed to the μ-η1CtCR
bridging group. Interestingly, in both complexes the
strong νCtC band due to the terminal alkynyl ligand
appears notably shifted to higher frequencies (2104 6a;
2108 cm-1 6b). This fact is consistent with the formation
of the PtfCd bond, which decreases the electron density
at the Pt(II) center and, as a consequence, its donor
capability toward the π* orbitals of the CtCR groups.
We have previously observed similar behavior in some
alkynyl-based Pt-Tl complexes that have Pt-Tl
27,29
bonds.
6b derivatives (see Experimental Section) are consistent
Conductivity measurements of 1b- 4b and
with the integrity of the bimetallic complexes in solution.
1
However, fluxional behavior is evident by H and 19F
NMR spectroscopy (CD3COCD3). Thus, the 1H and 19
F
NMR of the cis derivatives 1-4 are very simple, revealing
the presence of only one set of alkynyl, chelating (diimine
1- 3, trpy 4), and C6F5 groups. The proton spectra
indicate that both halves of the chelating ligands are
equivalent and the 19F NMR spectra display typical
AA0MM0X systems (2 o-F, p-F, 2 m-F), also indicating
effective equivalence of the o-F atoms, as well as the m-F
atoms. Similar spectra were found for representative
complexes 1b and 4b at low temperature (see Experimen-
tal Section). The observed spectra could be explained by
assuming a very fast inversion of the central bent
(V-shape) dimetallacycle [Pt](CtCR)2[Cd], without
excluding a possible simultaneous free rotation of the
C6F5 rings around the Pt-C ipso bonds. This behavior has
been previously observed in many bi- and trinuclear
complexes stabilized by either strongly bent chelating
o-F M contacts plays a key role contributing to the
3 3 3
final stability of the complex.86 In 6b the dihedral angles
formed by the pentafluorophenyl rings with the platinum
coordination plane are 62.7 (3)° and 55.7(3)°; but the
shortest Cd o-F separation (Cd(1) F(1) 3.499(7) A)
3 3 3
3 3 3
is longer than the sum of the van der Waals radii (3.05
A),81 showing that such contacts are not present here.
Further inspection of the crystal structures reveals the
presence of several types of weak non-covalent interac-
tions (π π,C-H π, C-H O, and C-H F con-
3 3 3
3 3 3
3 3 3
3 3 3
tacts), leading to the generation of supramolecular 3-D
networks (see Additional Supramolecular Details in Sup-
porting Information). For complex 6b, the existence of
type (V shape) or slightly bent (σ,π type) double alkynyl
78,87,88
bridging systems [M](μ-CtCR)2[M0].
Because of
intra- and intermolecular π π contacts between one
3 3 3
their low solubility, only the 13C{1H}NMR spectrum of
4b could be obtained, which displays the expected signals
for the trpy ligand and one set of CtCTol groups. In
accordance with previous observations,47 the CR and Cβ
carbon atoms are significantly up and downfield shifted,
respectively, in relation to the precursor (δCR/Cβ 90.4/
113.3 in 4b vs 117.3/103.7 in [cis-Pt(C6F5)2(CtCTol) 2]2-),
C6F5 ring and a bpy ligand of each molecule gives rise
to an infinite monodimensional organization along the
c axis (see Figure 4b and also Supporting Information,
Figure S8). These π π contacts are relatively strong
3 3 3
(∼3.25 A), having influence on the luminescence (see
Optical Properties).
The most relevant features observed in the IR spectra
of the cis derivatives 1-4 are the presence of two
ꢀ
(87) Berenguer, J. R.; Fornies, J.; Lalinde, E.; Martı
´
n, A.; Serrano, B. J.
ꢀ
(86) Fornies, J.; Martın, A. In Metal Clusters in Chemistry; Braunstein,
´
Chem. Soc., Dalton Trans. 2001, 2926, and references therein.
ꢀ
ꢀ
P., Oro, L. A., Raithby, P. R., Eds.; Wiley-VCH: Weinheim, 1999; Vol. 1,
(88) Berenguer, J. R.; Fornies, J.; Gomez, J.; Lalinde, E.; Moreno, M. T.
p 417.
Organometallics 2001, 20, 4847, and references therein.

5258 Inorganic Chemistry, Vol. 48, No. 12, 2009
Berenguer et al.
Table 5. Absorption Data for 1b-6b and 5a in CH2Cl2 (5 ꢀ 10-5 M)
compound
absorption /nm (103ε/M-1 cm-1
)
1b
2b
3b
4b
5a
5b
6b
227sh (42.5), 245 (45.3), 286 (48.6), 294 (45), 307sh (35.8)a
230sh (43.2), 262 (61.3), 303 (57.3), 315sh (45.2)a
237 (58.8), 258sh (57.8), 274 (61.3), 292sh (47.0), 311 (20.1)a
233 (50.5), 268 (22.6), 307 (21.9), 321 (20.6), 334 (17.7)
232 (28.2), 295 (30.8), 334 (30.3), 342sh (28.9)
230 (25.3), 293 (32.0), 331 (31.3), 338sh (30.0)
228sh (30.8), 246 (34.7), 295 (36.8), 307sh (28.1), 336 (12.3)a
a Tail over 360 nm.
a feature which also confirms that the interaction of the
alkynyl ligand with the CdII center is present in solution.
For the trans derivatives 6, their scarce solubility pre-
cluded also their characterization by 13C{1H} NMR
1
spectroscopy. Again, the H and 19F NMR spectra in
CD3COCD3 at room temperature are very simple, reveal-
ing only one set of bpy, alkynyl, and C6F5 rings (see
Experimental Section). By decreasing the temperature to
173 K, similar AB (Tol) and AA0MM0X (2o-F; 2m-F; p-F)
spin systems were observed for aromatic protons and
fluorine of C6F5 groups for the tolylethynylderivative 6b.
Moreover, the addition at this low temperature of a small
Figure 5. Absorption spectra of 1b (dark line), 2b (light line), and 3b
(dashed line) in CH2Cl2 (5 ꢀ 10-5 M).
absorptions follow the order 292 nm 3b (phen) > 307 1b
(bpy) >303, 315sh 2b (dmbpy), although complex 3b also
exhibits a low energy shoulder at 311 nm. The fact that the
lowest energy absorption appears in the bimetallic complex
having the “Cd(dmbpy)2” unit, with the higher π*(N-N)
orbital, suggests that the diimine ligands are not likely to
be the target orbital. In the three complexes, this low
energy absorption is blue-shifted in relation to the mixed
1IL/1MLCT (CtCTol) band in the bis(alkynyl)platinate
amount of the precursor (NBu4)2[trans-Pt(C6F5)2
1
(CtCTol) ] 5b gives rise to H and 19F NMR spectra
2
containing separate signals of 6b and 5b, thus suggesting
that fast dissociation of the “Cd(bpy) 2+” unit is not
2
responsible for the apparent D2h symmetry. The observed
spectra are presumably caused by a fast exchange of the
“Cd(bpy)22+” unit between both alkynyl groups with
simultaneous migration above and below the platinum
coordination plane (see Supporting Information, Figure
S9). Nevertheless, simple free rotation of C6F groups
5
with the simultaneous fast alkynyl exchange of the cad-
mium unit is also likely.
With the aim of explore the strength of the Pt-Cd
interaction in solution, we have tried to record the
195Pt{1H} NMR spectra for the bimetallic derivatives 4b
and 6b, which are the more soluble complexes, and, for
comparison, that of the trans configured precursor 5b.
Unfortunately any signal has been detected for 4b and 6b
(range -2500 to -5000 ppm) while, as is shown in
Supporting Information, Figure S10, complex (NBu4)2-
[trans-Pt(C6F5)2(CtCTol)2] 5b exhibits the platinum
resonance at δ -4062 as the expected quintuplet of
quintuplets because of coupling to the four ortho (3J =
417 Hz) and meta (4J = 88 Hz) fluorine atoms.
precursor (PMePh3)2[cis-Pt(C6F5)2(CtCTol) ] (311, 334sh
2
nm). It seems likely that the interaction of the Platinum and
both CR alkynyl atoms with the Cd(N-N) 2+2 unit causes a
stabilization of the Pt/CtC based highest occupied molecu-
lar orbital (HOMO). Under this assumption and the fact that
ππ* intraligand transition of the diimine ligands also occurs
at similar energies, the lower energy features are assigned as
admixtures of MLCT (d(Pt)fπ*CtCTol) and intraligand
IL (CtCTol, diimine) transitions. The trpy derivative 4b
exhibits a more complex profile in this region, with three
peaks (at ca. 307, 321, 334 nm), in agreement with a remark-
able contribution of the low-lying trpy localized IL state, also
likely with some admixture of alkynyl (ππ* CtCTol) and
MLCT(Ptfalkynyl) charge transfer.
On the basis of our previous work26,27,46,47,89 and other re-
lated recent studies90,91 on alkynyl platinum complexes, the
lowest energy absorption (334, 342sh 5a; 331, 338sh 5b) in the
mononuclear complexes (NBu4)2[trans-Pt(C6F5)2(CtCR)2]
5 (R = Ph a, Tol b) is attributed to an admixture of
ππ*(CtCR) 1IL/dπ(Pt)fπ*(CtCR) MLCT, with a predo-
minant intraligand character. In both complexes, this band is
red-shifted compared to the corresponding cis isomers Q2[cis-
Pt(C6F5)2(CtCR)2] (R = Ph 310, 325 nm; R = Tol 311, 331
nm)47 in agreement with previous observations in related cis-
and trans- configured bis(alkynyl)bis(phosphine)platinum
complexes, confirming that the extent of π delocalization
through the Pt is more efficient when the alkynyl groups are
Optical Properties
The electronic spectra of the tolylethynyl binuclear deri-
vatives 1b-6b were recorded in CH2Cl2 (Table 5) and 2-
MeTHF (Supporting Information, Table S1), without any
significant modification with the solvent change, except for a
better vibronic resolution on CH2Cl2 spectra. The related
phenylethynyl complexes 1a-4a, 6a are rather insoluble, so
their UV-vis spectra could not be performed. The CH2Cl2
5 ꢀ 10-5 M UV-vis spectra of 1b-6b show high energy
absorptions (220-295 nm) and low energy bands at about
303-336 nm. The former are assigned as intraligand transi-
tions (ππ*) of anionic (C6F5, CtCTol) and neutral diimine
(1b-3b, 6b) or trpy ligands (4b). As can be observed in
Figure 5 for complexes 1b-3b, the more intense low energy
ꢀ
ꢀ
(89) Benito, J.; Berenguer, J. R.; Fornies, J.; Gil, B.; Gomez, J.; Lalinde,
E. Dalton Trans. 2003, 4331.
ꢀ
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(90) Gagnon, K.; Aly, S. M.; Brisach-Wittmeyer, A.; Bellows, D.; Berube,
J.-F.; Caron, L.; Abd-El-Aziz, A. S.; Fortin, D.; Harvey, P. D. Organome-
tallics 2008, 27, 2201.
(91) Cooper, T. M.; Krein, D. M.; Burke, A. R.; McLean, D. G.; Rogers,
J. E.; Slagle, J. E.; Fleitz, P. A. J. Phys. Chem. B 2006, 110, 4369.

Article
Inorganic Chemistry, Vol. 48, No. 12, 2009 5259
(1131-1606 cm-1), and the extremely long lifetimes (i.e.,
120 μs for 3b) are suggestive of emission coming from 3ππ*
intraligand centered states. Although, the influence of the
diimine groups in the maxima is minimal (see Table 6), this
lower energy band is ascribed to metal-perturbed (Pt, Cd)
ππ* alkynyl (CtCTol) phosphorescence, likely mixed with
some ππ*(diimine) character. The high energy emission,
that is observed at about 450 nm (77 K) for 1b and 2b,
resembles that seen in the precursor (PMePh3)2[cis-Pt
(C6F5)2(CtCTol)2] at low temperature (451max, λex 360
nm),47 being thus assigned to a 3IL πfπ* (CtCTol) mani-
fold. It is worth noting that for complex 1b the emission
profile at 77 K exhibits two peaks at 453 and 483 nm, but
whereas the decay monitoring at 450 nm fits to one compo-
nent (81 μs), the band at 483 nm fits to two components with
different lifetimes (152 μs 14%; 68 μs 86%), in agreement
with the presence of two emissive states or weakly coupled
relaxation channels. In contrast to this behavior, complex 4b
containing the “Cd(trpy)” unit shows, at room temperature,
a broad featureless peak at 527 nm with a monoexponential
decay lifetime of 12 μs, which is slightly blue-shifted at 77 K
(517 nm). This blue shift is most likely to be caused by
increased environment rigidity, which is consistent with the
reduced thermal vibrational relaxation.93,94 In this complex,
band shape lacks the typical structure associated with those
ligand-centered transitions, pointing to a more metal (Pt, Cd)
character associated with the transition. Moreover, at 77 K
the emission phosphorescence fits well to a biexponential
decay, having a major component (88%) of 50 μs and a minor
one (12%) in the milliseconds range (1.1 ms), suggesting that
it also has ligand contribution. Thus, this emission could
be tentatively attributed to the coupling of metal-metal
(Pt-Cd) charge transfer (MM0CT) and intraligand (trpy,
CtCTol) transitions.
In the related phenylethynyl derivatives 1a-4a, the influ-
ence of the chelating diimine ligand is more apparent. As can
be observed in Supporting Information, Figure S11, the
terpyrydyne bimetallic complex 4a exhibits a structured
emission at 298 K (493, 520 nm) which becomes well resolved
at 77 K (460sh, 485max, 523, 560sh nm). Both, the weak
shoulders at 460 nm and the dual exponential decay mon-
itored at the λmax (485 nm)with two long lifetime components
of 30.2 (55%) and 0.6 (45%) milliseconds, suggest the
contribution of close emissive states. The vibronic spacing
of the more intense emission at 77 K (1499, 1263 cm-1) is in
agreement with the implication of the trpy ligand in the
emission. Structured profiles (443-523 nm) with dual ex-
ponential decays in the millisecond range (0.3-30.2 ms) are
also seen for 1a-3a at low temperature (77 K) (see Support-
ing Information, Figure S11). Hence, we conclude that these
emissions are most likely originated from metal (Pt, Cd)
perturbed spin-forbidden ligand centered states, involving
the coligands in the cationic cadmium unit (trpy 4a, N-N 1a-
3a) and the CtCPh groups. No clear correlation can be made
when comparing the emission of both series (a vs b) or when
comparing the nitrogen donor coligands in each series.
For 1b-4b, the emission spectra have been recorded in
solution (2-MeTHF, 77 K, 298 K, Supporting Information,
Table S2). In frozen 2-MeTHF glasses, all complexes exhibit
Figure 6. Absorption spectra of 5b (dark line) and 6b (light line) in
CH2Cl2 (5 ꢀ 10-5 M).
mutually trans.92 We have also observed that the intensity of
1
this low energy MLCT/1IL(CtCR) band is remarkably
higher in the trans derivatives than in the related cis ones
(i.e., 338 nm, ε = 30.0 ꢀ 103 M-1cm-1 in 5b vs 331 nm, 7.2 ꢀ
103 M-1cm-1 in (PMePh3)2[cis-Pt(C6F5)2(CtCTol)2]47)
illustrating again the good electronic communication of the
ethynyl fragments in the former, and the stronger CT
character (more allowed) of the transition in the trans
geometry. As can be seen in Figure 6 the most remarkable
difference of the UV spectra of complex 6b, built from 5b and
“Cd(bpy)2+2”, in comparison to its precursor 5b is the
weaker intensity of the 1MLCT/1IL transition (336 nm,
ε = 12.3 ꢀ 103 M-1 cm-1 6b vs 338 nm, ε = 30.0 ꢀ 103
M-1 cm-1 5b), thus suggesting that the formation of the
Pt-Cd bond probably hinders communication between the
tolylethynyl fragments. The small hipsochromic shift (2 nm)
is in accordance with the expected decrease of the electron
density on the platinum center upon formation of the Pt-Cd
bond, which increases the energy of the 1MLCT component.
However, the band is broader than in 5b and exhibits
a long tail extending to the visible, in agreement with its
yellow color.
All complexes (except 6) display luminescence in solid state
and for the tolyl ethynyl derivatives emission is also observed
in 2-MeTHF both at 298 (weak) and at 77 K. The photo-
physical data are summarized in Tables 6 (solid) and S2
(solution, glass), and illustrative examples are shown in
Figures 7 and 8 (1b-4b), S11 (1a-4a), 9 (5b), and 10 (6b).
As can be observed in Figure 7, in solid state at room
temperature the tolylethynyl complexes 1b-3b exhibit a
similar low energy green emission (λmax 495 1b, 2b; ∼505
nm 3b), clearly structured in 1b and 2b, together with a very
weak emission on the high energy side (∼ 450 1b, 2b; 440-473
nm 3b). The lifetime of the low energy band fits to a
monoexponential decay in the range of microseconds (32 μs
1b; 43 μs 2b; 14 μs 3b), indicative of triplet parentage. At 77 K,
the contribution of the high energy component increases in1b
and 2b, while complex 3b mainly shows the low energy
emission as a better structured band (492, 521 nm). The
apparent vibronic structure observed in the lower energy
band, either at room (827-934 cm-1) or low temperature
(93) Bai, D.-R.; Wang, S. Organometallics 2006, 25, 1517.
(94) Ferraudi, G. J. Elements of Inorganic Photochemistry; John Wiley
and sons: New York, 1988.
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Dalton Trans. 2008, 4926.
(92) Dı

5260 Inorganic Chemistry, Vol. 48, No. 12, 2009
Berenguer et al.
Table 6. Photophysical Data for Complexes 1-6 in Solid State
compound
(T/K)
λemmax /nm
τ
1a
1b
2a
2b
3a
3b
4a
4b
5a
5b
6a
6b
298
77
441sh, 475sh, 508sh, 534max, 570sh (λex 370)
443sh, 472max, 504 (λex 320-360)
450sh, 495max, 517 (λex 325-360)
453, 483, 521sh (λex 320-420)
450max,467sh, 515sh (λex 370)
461max, 501sh (λex 350-380)
450sh, 495max, 519 (λex 335-365)
450sh, 486max, 518sh, 565sh (λex 330-415)
485sh, 495sh, 529 (λex 370)
485sh, 523 (λex 366)
9 μs (λem 534)
3.5 (68%), 0.3 (32%) ms (λem 472)
32 μs (λem 517)
81 μs (λem 453); 152 (14%), 68 (86%) μs (λem 483)
8 μs (λem 452)
1.4 (84%), 19.2 (16%) ms (λem 461)
43 μs (λem 495)
257 (63%), 83 (37%) μs (λem 450); 373 (92%), 65 (8%) μs (λem 485)
9 μs (λem 529)
26.1 (47%), 0.83 (53%) ms (λem 523)
14 μs (λem 505)
1.1 (4%), 0.12 (96%) ms (λem 492)
14 μs (λem 493)
30.2 (55%), 0.6 (45%) ms (λem 485)
12 μs (λem 527)
298
77
298a
77
298
77
298a
77a
298
77
440sh, 473sh, 505max, 527sh (λex 370-400)
440sh, 492max, 521 (λex 330-425)
493max, 520 (λex 368-445)
460sh, 485, 523, 560sh (λex 360)
527 (λex 360-420)
298
77
298
77
298
77
298
77
298
77
298
77
517 (λex 330-400)
1.1 (12%), 0.05 (88%) ms (λem 515)
16 μs (λem 460)
16 μs (λem 457)
17 μs (λem 465)
18 μs (λem 460)
460max, 480, 503sh (λex 370)
457max, 478, 492, 504 (λex 360)
465max, 480sh, 510sh (λex 380)
460max, 480, 492, 505 (λex 367)
no emissive
448max, 495 (λex 370)
no emissive
455max, 520max, (λex 370)
13 μs (λem 448)
14 μs (λem 455); 11 μs (λem 520)
a Weak emission
clear structured bands with vibronic spacing (∼1450-1590;
990-1271; 1083-1222 cm-1), which are characteristic of the
C-N and C-C stretching motion of the chelating N-hetero-
cycle frameworks. As can be observed in Figure 8, the
emission maxima (433 1b, 445 2b, 451 3b, and 438 nm 4b)
correlate well with those seen in the N-containing free ligands
mixed 3IL/3MLCT (πfπ*(CtCR)/dπ(Pt)/π*(CtCR))
manifold. In the tolylethynyl derivative 5b the emission
maxima is slightly red-shifted in relation to 5a (460 5b vs
457 nm 5a at 77 K), and in both complexes a slight red-shift in
energy is observed when comparing with the corresponding
Q2[cis-Pt(C6F5)2(CtCR)2] (R = Ph 444 nm, R = Tol
451 nm, 77 K).47 This feature is consistent with previous
theoretical calculations95 carried out on bis(acetylide) neutral
complexes, which indicate that the mixing of dπ (and p)
orbitals of the Pt center with the π and π* MOs of the alkynyl
groups leads to π-type conjugation through the metal center,
this delocalization being favored in the trans isomers.96 The
emission has also been examined in solution (Supporting
Information, Table S2). At 298 K, a very weak high energy
structured emission is detected (λma1x 400 5a, 402 nm 5b) in
2-MeTHF tentatively ascribed as IL fluorescence. Upon
freezing at 77 K, well resolved site-selectivity dual structured
emissions are observed, both in CH2Cl2 and 2-MeTHF
glasses. As is seen in Figure 9 for 5b, in CH2Cl2 5 ꢀ 10-4
M glass excitation at 350 nm gives rise to a low energy
emission with λmax at 452 nm, whereas excitation at shorter
wavelengths (λmax 320 nm) produces a similar structured
profile but shifted to higher energies (λmax 437 nm). As it is
also observed, the corresponding excitation spectra differ
mainly on the low energy red-side, suggesting the presence
of sample heterogeneity in the glass or two close emissive
states. The observation of dual site-selectivity emissions
in alkynyl platinum complexes is not unprecedented.47,97-99
(∼370, λex = 330 bpy; 394, λex = 340 dmbpy; 400, 420, λex
=
370 phen; 441, λex = 384 nm trpy). This similarity allows us to
assign the emission to intraligand (diimine 1b-3b, trpy 4b)
3ππ* phosphorescence though, the presence of multicompo-
nents in the lifetime decays (see Supporting Information,
Table S2) suggests that other states could also contribute
somehow to the emission. Because of the electron donating
properties of the platina-bis(alkyne) unit and the acceptor
character of the polyimine groups, some mixing with a ligand
(alkyne) to ligand(imine) charge transfer (3LL0CT) mediated
through the metallic (Cd or Pt, Cd) core can not be excluded.
Weaker, but also structured (1402-1103 cm-1), emission
profiles are observed in fluid (298 K) solution. The emission
onsets are blue-shifted in compared to those observed in
glassy solutions and occur at very similar energies (∼402,
∼425, ∼450 nm) in all 1b-4b complexes, probably because of
their broader appearances. Only the trpy derivative 4b
exhibits an additional (less intense) low energy peak centered
at 492 nm, probably coming from an emissive state related to
the Pt Cd bonding interaction. Although too weak for
3 3 3
lifetime measurements, the high energy band in all derivatives
is tentatively assigned to 3IL(polyimine), since it is related to a
similar low energy excitation feature located at 360 nm well
above the 1IL absorption maxima (see Supporting Informa-
tion, Table S2).
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(95) Beljonne, D.; Wittmann, H. F.; Kohler, A.; Graham, S.; Younus, M.;
Lewis, J.; Raithby, P. R.; Khan, M. S.; Friend, R. H.; Bredas, J. L. J. Chem.
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As many bis(alkynyl)platinum complexes, trans config-
ured anionic precursors 5a and 5b also exhibit luminescence
in solid state, at both room and low temperature (77 K). The
emissions show the expected structured bands (see Table 6)
with progressive spacing modes indicative of thecombination
of CtC and aryl rings, which, on the basis of previous
assignments, is attributed to phosphorescence coming from
::
B. 2007, 111, 929.
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Article
Inorganic Chemistry, Vol. 48, No. 12, 2009 5261
Figure 9. Normalized site-selectivity dual emission and excitation spec-
tra of 5b in CH2Cl2 glass (5 ꢀ 10-4 M) at 77 K.
Figure 7. Normalized emission spectra for crystalline samples of 1b, 2b,
3b, and 4b at different temperatures.
Figure 10. Normalized emission and excitation spectra of solid 6b
at 77K.
3
3
ascribed to the presence of two distinct ππ* and MLCT
3
(or mixed ππ/3MLCT) excited states that are not coupled.
Because of the difference in the excitation spectra (Figure 9),
a similar explanation could be operative in complexes 5, but
the simultaneous existence of different conformers seems
more likely.
Complexes 6a and 6b are essentially nonemissive in solid
state at 298 K. Upon cooling (77 K), 6a shows a structured
emission (478, 495 nm), while 6b displays two luminescence
bands (455 and 520 nm, see Figure 10) regardless of the λex
used (350-400 nm). For this latter (6b), lifetime measure-
ments (see Table 6) and excitation spectra in both maxima
suggest that each emission derives from a different excited
state. In frozen solution (Supporting Information, Table S2),
complex 6b only exhibits a slightly structured high energy
emission (445, 482 nm CH2Cl2; 449, 492 nm 2-MeTHF),
suggesting that the low unstructured energy emission cen-
tered at 520 nm seen in solid state at 77 K is likely to be due to
Figure 8. Normalized emission spectra of 1b, 2b, 3b, 4b in 2-MeTHF
glasses (5 ꢀ 10-4 M) at 77K.
π
π stacking interactions. In support of this assignment,
In particular, splitting in the phosphorescence at low tem-
perature has been attributed to the existence of different
conformers (planar or twisted) that can not equilibrate in the
frozen matrix.97-99 We recently observed a similar photo-
selection in the trimetallic complex (NBu4)2[{cis-Pt(C6F5)2-
(μ-CtCPh)2}2Cd] (D, Chart 1),47 and it was tentatively
3 3 3
such intra- and intermolecular π π interactions were ob-
3 3 3
served in the extended lattice of 6b in solid state (see
Figure 4b). The resemblance of the high energy emissions
with those seen in the precursors5 is suggestive of an emission
coming from the platinate unit “[trans-Pt(C6F5)2(CtCR)2]”

5262 Inorganic Chemistry, Vol. 48, No. 12, 2009
Berenguer et al.
(3IL/3MLCT manifold) perturbed by the short donor-
acceptor PtfCd bond. The small hipsochromic shift seen
for 6a (448 nm) and 6b (455 nm) in solid state at 77 K in
relation to the precursors 5a (457 nm) and 5b (460 nm),
respectively, could probably be attributed to the stabilization
of the energy of the Pt(d)/πCtCR based HOMO because of
the formation of the PtfCd donor-acceptor bond.
(Pt-Cd) charge transfer (MM0CT) and intraligand (trpy,
CtCTol) transitions. In the glassy state (2-MeTHF) com-
plexes 1b-4b exhibit structured emissions mainly ascribed to
3
(diimine 1b-3b; trpy 4b) ππ* phosphorescence, probably
mixed with some ligand (alkyne) to ligand (polyimine) charge
3
transfer LL0CT. In the related phenylethynyl derivatives
1a-4a, the influence of the polyimine is more apparent,
exhibiting structured profiles with dual exponential decays
in the millisecond range, which are likely to originate from
metal (Pt, Cd) perturbed spin forbidden ligand-centered
states (poliimine and CtCPh groups). In complexes [trans-
Pt(C6F5)2(CtCR)2Cd(bpy)2] 6, the formation of the very
short Pt-Cd bonds (2.8931(6) A, 6b) quenches the blue
emission (3IL(CtCR)/3MLCT manifold) of the precursors
(NBu4)2[trans-Pt(C6F5)2(CtCR)2] 5 in solid state at room
temperature. At 77 K, these bimetallic derivatives display a
high energy structured band assigned to the mixed 3IL/MLCT
(L = CtCR) manifold perturbed by the donor-acceptor
PtfCd bond and, in the case of 6b, an additional low energy
feature (which is absent in 2-MeTHF solution fluid and glass),
tentatively ascribed to ππ stacking interactions.
Conclusions
In summary, the utilization of anionic cis- or trans-[Pt
(C6F5)2(CtCR)2]2- (R = Ph, Tol) as building blocks for
the in situ generated “Cd(N-N)22+” and “Cd(trpy)2+” units
successfully gives heterobimetallic Pt-Cd complexes 1-4
and 6. It is interesting to note that while the cis- precursors
connect the “Cd(N-N)22+” units through both Pt-CR
bonds, completing distorted pseudo-octahedral environ-
ments around the Cd center in complexes [cis-Pt-
(C6F5)2(CtCR)2Cd(N-N)2] 1-3, the trans- isomers emp-
loy only one of the Pt-CR bonds, giving rise to a
distorted trigonal-bypyramidal coordination in [trans-Pt-
(C6F5)2(CtCR)2Cd(bpy)2] (6). As a consequence, both the
Pt-Cd and Cd-CR bond distances are remarkably shorter in
6b in relation to 1a-3a. The cadmium center of the dicationic
“Cd(trpy)2+” unit in [cis-Pt(C6F5)2(CtCR)2Cd(trpy)] 4a
and 4b has a similar distorted octahedral environment to
those of 1-3, being also bonded to both Pt-CR of the
Acknowledgment. We thank the Spanish MICINN for
financial support (Projects CTQ2008-06669-C02-01, 02).
J.F. wishes to thank the CAR for a grant.
Supporting Information Available: Complete details concern-
ing the synthesis and spectroscopic characterization of the
complexes 1-6. Data for the electronic spectra of 1b-6b and
5a recorded in 2-MeTHF (Table S1). Data for the emission
spectra and lifetimes measurements of complexes 1- 6 in
solution at 298 and 77 K (Table S2). ORTEP view of the
complexes 2a and 3a (Figures S1 and S2). Additional Supramo-
lecular details and figures of the three-dimensional organization
of complexes 1a, 2a, 3a, 4a, 4b, and 6b (Figures S3-S8).
Proposed dynamic process for complex 6b in solution (Figure
S9). 195Pt{1H} NMR spectrum of complex 5b in CD3COCD3 at
298 K (Figure S10). Emission spectra of crystalline samples of
1a, 2a, 3a, and 4a at 298 and 77 K (Figure S11). Crystallographic
data in CIF format. This material is available free of charge via
the Internet at http://pubs.acs.org.
2-
[Pt](CtCR)2 unit and contacting weakly with a solvent
molecule (acetone 4a; acetone/H2O 4b). In solid state, bime-
tallic complexes 1-4, having cis-configured platinum frag-
ments, show blue and/or green phosphorescence with
contribution of states of different nature. For the tolylder-
ivatives 1b-3b, the high energy structured emissions (blue
3
region) were assigned to a IL πfπ*(CtCTol) manifold,
while the lower energy features (green region) to metal (Pt-
Cd) perturbed alkynyl CtCTol phosphorescence, likely
mixed with some diimine character. Complex 4b, having
shorter Pt-Cd bond, exhibits a green emission (527 nm,
298 K, monoexponential decay; 517 nm, 77 K, biexponential
decay) tentatively attributed to the coupling of metal-metal