Rhomboidal heterometallic alkynyl based Pt2Cd2 clusters: Structural, photophysical, and theoretical studies

Article abstract of DOI:10.1021/ic100072a

Reactions between [Pt(C≡CR)₄]^2- (R = Tol a, C₆H₄OMe-4 b, C₆H₄OMe-3 c) and Cd²⁺ depend on the media and the alkynyl substituent, leading to the formation of yellow tetranuclear solvate complexes [Pt(C≡CR) ₄Cd(acetone)]₂ 1a,b(acetone)₂ and [Pt(C≡CC₆H₄OMe-3)₄Cd(dmso)]₂ 1c(dmso)₂ or white polymeric solvate-free species [Pt(C≡CR)₄Cd]_x ′a-c. Treatment of 1a,b(acetone)₂ or ′a-c with N-donor ligands affords a series of tetranuclear clusters [Pt(C≡CR)₄CdL]₂ (L = py; 2a-c. R = Tol; L = NC₅H₄CH₃-4 3, NC ₅H₄CF₃-4 4, pzH 5). X-ray crystallographic studies reveal that, in the tolyl complexes (2a, 4, and 5), the Cd-L ²⁺ unit is closely bonded to one Pt-C_α(acetylide) bond (Pt-Cd = 2.7, Cd-C_α ～ 2.48 A), and the resulting Pt(C≡CTol)₄CdL unit dimerizes by two additional η²-Cd-acetylide and a weaker Pt...Cd bonding interaction leading to a planar unsymmetrical rhomboidal metal core. By contrast, the m-methoxyphenyl derivatives (2c, 1c(dmso)₂) form symmetrical Pt ₂Cd₂ cores, with each Cd bonded (coordination number, C.N. = 5) to the incoming ligand (pyridine 2c, dmso 1c(dmso)₂) and four Pt-C_α bonds (Pt-Cd ～ 2.85; Cd-C_α 2.470(10)-2.551(5) A) of different Pt^II fragments. Evidence of ligand dissociation was found for the solvate (1a,b(acetone)₂, 1c(dmso)₂) and NC₅H₄CF₃-4 (4) derivatives by NMR and UV-vis absorption spectra. All tetranuclear aggregates exhibit bright blue to green luminescence in the solid state. Time-dependent density functional theory (TD-DFT) calculations were performed to shed light on the nature of the electronic transitions. In the solvate 1a,b(acetone) ₂ and 1c(dmso)₂, emissions have been assigned to a platinum-alkynyl to cadmium charge transfer (³MLL′CT), mixed with some intraligand ³IL(C≡CR) character. In the imine derivatives 2-5, they are suggested to come from an excited state of large Pt(d)/πC≡CR→π*(imine) MLL′CT character, mixed with some Pt(d)/π(C≡CR)→Pt₂Cd₂/π *C≡CR (ML′L′CT) contribution.

Full text of DOI:10.1021/ic100072a

4232 Inorg. Chem. 2010, 49, 4232–4244
DOI: 10.1021/ic100072a
Rhomboidal Heterometallic Alkynyl Based Pt2Cd2 Clusters: Structural,
Photophysical, and Theoretical Studies
ꢀ
ꢀ
ꢀ
ꢀ
Jesus R. Berenguer, Julio Fernandez, Belen Gil, Elena Lalinde,* and Sergio Sanchez
´
´
´
Departamento de Quımica-Grupo de Sıntesis Quımica de La Rioja, UA-CSIC, Universidad de La Rioja,
~
26006, Logrono, Spain
Received January 13, 2010
Reactions between [Pt(CtCR)4]2- (R=Tol a, C6H4OMe-4 b, C6H4OMe-3 c) and Cd2þ depend on the media and the
alkynyl substituent, leading to the formation of yellow tetranuclear solvate complexes [Pt(CtCR)4Cd(acetone)]2 1a,
b(acetone)2 and [Pt(CtCC6H4OMe-3)4Cd(dmso)]2 1c(dmso)2 or white polymeric solvate-free species [Pt(Ct
CR)4Cd]x 10a-c. Treatment of 1a,b(acetone)2 or 10a-c with N-donor ligands affords a series of tetranuclear clusters
[Pt(CtCR)4CdL]2 (L=py; 2a-c. R=Tol; L=NC5H4CH3-4 3, NC5H4CF3-4 4, pzH 5). X-ray crystallographic studies
reveal that, in the tolyl complexes (2a, 4, and 5), the Cd-L2þ unit is closely bonded to one Pt-CR(acetylide) bond
2
˚
(Pt-Cd = 2.7, Cd-CR ∼ 2.48 A), and the resulting “Pt(CtCTol)4CdL” unit dimerizes by two additional η -Cd-
acetylide and a weaker Pt Cd bonding interaction leading to a planar unsymmetrical rhomboidal metal core. By
contrast, the m-methoxyphenyl derivatives (2c, 1c(dmso)2) form symmetrical Pt2Cd2 cores, with each Cd bonded
(coordination number, C.N.=5) to the incoming ligand (pyridine 2c, dmso 1c(dmso)2) and four Pt-CR bonds (Pt-Cd
3 3 3
II
˚
2.85; Cd-CR 2.470(10)-2.551(5) A) of different Pt fragments. Evidence of ligand dissociation was found for the
solvate (1a,b(acetone)2, 1c(dmso)2) and NC5H4CF3-4 (4) derivatives by NMR and UV-vis absorption spectra. All
tetranuclear aggregates exhibit bright blue to green luminescence in the solid state. Time-dependent density func-
tional theory (TD-DFT) calculations were performed to shed light on the nature of the electronic transitions. In the
solvate 1a,b(acetone)2 and 1c(dmso)2, emissions have been assigned to a platinum-alkynyl to cadmium charge
3
transfer (3MLM0CT), mixed with some intraligand IL(CtCR) character. In the imine derivatives 2-5, they are
suggested to come from an excited state of large Pt(d)/πCtCRfπ*(imine) MLL0CT character, mixed with some
Pt(d)/π(CtCR)fPt2Cd2/π*CtCR (ML0M0CT) contribution.
Introduction
the metal, the coligands, or the electronic nature of the alky-
nyl fragments.
Transition metal complexes with alkynyl ligands have been
widely used in the design of photoluminescent materials with
interesting spectroscopic properties1-10 suitable in the field
of fundamental and applied material science.11 In these
systems excited-state properties are controlled by changing
Recently, homo and heteropolynuclear aggregates contain-
ing closed or pseudo closed shell (d10, d8, d10s2) metal ions
have also gained increasing interest, in part because of their
intriguing luminescent properties, which have been attri-
buted to the presence of metallophilic bonds.12 In this respect,
considerable experimental work has clearly demonstrated the
influence of the metallophilic interactions in the structure and
luminescence of alkynyl metal complexes of CuI, AgI, AuI,
HgII (d10)1,3-6 and PtII(d8).6,13,14 Despite the fact that the
chemistry of heteropolynuclear complexes with alkynyl brid-
ging ligands has been an active research area, studies relative
to their optical properties are scarce in the literature.4,8,15-17
Within this field we and others have demonstrated that
homoleptic18-28 and heteroleptic29-36 anionic σ-alkynyl pla-
tinates are excellent building blocks for the synthesis of
heteropolynuclear Pt-M (M=d10, s2) complexes that show
interesting structures and intriguing photophysical proper-
ties. These investigations have allowed us to observe that,
depending on the Lewis-acidic metal and the basic platinate
*To whom correspondence should be addressed. E-mail: elena.lalinde@
unirioja.es.
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r
pubs.acs.org/IC
Published on Web 04/09/2010
2010 American Chemical Society

Article
Inorganic Chemistry, Vol. 49, No. 9, 2010 4233
substrate, the final heterometallic aggregates are basically
coinage d10 metal ions such as CuI or AgI exhibit a remarkable
preference for the electron-rich alkynyl entities,18,20,24,33,36-38
we still know very little about the factors controlling the final
structures and properties of related PtII-CdII heterometallic
systems.19,21,29,30,39 For instance, we have found that Cd-
(NO3)2 reacts with [cis-Pt(Rf)2(CtCR)2]2- (Rf = C6F5) to
form {Pt2Cd}2- species featuring only tweezer-like η2-
(alkyne)-Cd bonds.29 However, while the dicationic “Cd-
(N-N)22þ” and “Cd(trpy)2þ” (trpy=2,20,60,200-terpyridine)
units form bimetallic complexes in which the CdII contacts
stabilized: (a) by η2-alkynyl-M bonds and Pt M second-
3 3 3
ary interactions or (b) by significant Pt-M bonds and/
or secondary η(alkyne) M bonds. In this respect, while
3 3 3
(11) For some reviews see: (a) Belluco, U.; Bertani, R.; Michelin, R. A.;
Mozzon, M. J. Organomet. Chem. 2000, 600, 37. (b) Long, N. J.; Williams, C.
K. Angew. Chem., Int. Ed. 2003, 42, 2586. (c) Bruce, M. I.; Low, P. J. Adv.
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ꢀ
(e) Akita, M.; Koike, T. Dalton Trans. 2008, 3523. (f) Nguyen, P.; Gomez-Elipe,
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Onishi, M.; Ishizaka, S.; Kitamura, N.; Nakao, Y.; Sakaki, S. Chem.;Eur. J.
2009, 15, 4238. (c) Yue, C.; Yan, C.; Feng, R.; Wu, M.; Chen, L.; Jiang, F.; Hong,
3 3 3
A)30 center, the “Cd(cyclen)2þ” unit affords a related com-
plex [cis-Pt(Rf)2(CtCPh)2Cd(cyclen)] featuring a very short
PtfCd bond (2.764(1) A) and retaining only a weak inter-
action with one of the alkynyl fragments.39
ꢀ
ꢀ
Within this area some time ago21 we found that [Pt-
M. Inorg. Chem. 2009, 48, 2873. (d) Fernandez, E. J.; Laguna, A.; Lopez-de-
ꢀ
Luzuriaga, J. M. Dalton Trans. 2007, 1969. (e) Fornies, J.; García, A.; Lalinde,
(CtCPh)4]2- reacts with Cd(ClO4)2 6H2O to give an inso-
ꢀ
E.; Moreno, M. T. Inorg. Chem. 2008, 47, 3651. (f) Falvello, L. R.; Fornies, J.;
3
luble material of the expected stoichiometry [PtCd(Ct
CPh)4]n A as a white solid. However, attempts to obtain
crystals of A only caused partial hydrolysis, yielding a very
unusual decanuclear cluster [Pt4Cd6(CtCPh)4(μ-CtCPh)12-
(μ3-OH)4] (yellow crystals) stabilized not only by bridging
ꢀ
ꢀ
Garde, R.; García, A.; Lalinde, E.; Moreno, M. T.; Steiner, A.; Tomas, M.; Uson, I.
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Inorg. Chem. 2006, 45, 2543. (g) Falvello, L. R.; Fornies, J.; Lalinde, E.; Menjon,
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B.; García-Monforte, M. A.; Moreno, M. T.; Tomas, M. Chem. Commun. 2007,
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Inorg. Chem. 2008, 47, 6353. (l) Katz, M. J.; Ramnial, T.; Yu, H.-Z.; Leznoff, D.
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Chem. Soc. 2007, 129, 11384. (n) Xia, B.-H.; Zhang, H.-X.; Che, C.-M.; Leung,
K.-H.; Phillips, D. L.; Zhu, N.; Zhou, Z.-Y. J. Am. Chem. Soc. 2003, 125, 10362.
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Eur. J. 2005, 11, 4535.
hydroxy groups but also by Pt Cd and η2-Cd-acetylide
3 3 3
interactions.21 As an extension of this work, we considered it
to be of interest to study the neutralization reactions of other
homoleptic derivatives [Pt(CtCAr)4]2- containing better
electron donating alkynyl groups (Ar = Tol, C6H4OMe-4,
C6H4OMe-3), with Cd(ClO4)2 6H2O and to investigate the
3
reactivity of the resulting neutral Pt-Cd systems toward
some nitrogen donor ligands with a twofold objective: (1) to
prepare some new heterometallic homoleptic {Pt(CtCR)4-
Cd}n aggregates that enable a better characterization of this
kind of systems, and (2) to obtain access to novel neutral
alkynyl based {Pt(CtCR)4CdLx}n compounds to know
whether simple N-donor ligands would have any influence
and be able to tune the luminescence properties.
(15) Koshevoy, I. O.; Lin, Y.-C.; Karttunen, A. J.; Haukka, M.; Chou,
P.-T.; Tunik, S. P.; Pakkanen, T. A. Chem. Commun. 2009, 2860.
(16) Wei, Q.-H.; Yin, G.-Q.; Zhang, L.-Y.; Shi, L.-X.; Mao, Z.-W.; Chen,
Z.-N. Inorg. Chem. 2004, 43, 3484.
(17) Koshevoy, I. O.; Karttunen, A. J.; Tunik, S. P.; Haukka, M.;
Selivanov, S. I.; Melnikov, A. S.; Serdobintsev, P. Y.; Pakkanen, T. A.
Organometallics 2009, 28, 1369 and ref. therein.
ꢀ
ꢀ
(18) Charmant, J. P. H.; Fornies, J.; Gomez, J.; Lalinde, E.; Merino, R. I.;
Moreno, M. T.; Orpen, A. G. Organometallics 1999, 18, 3353.
In this contribution we report the preparation and optical
properties of a series of some solvate [Pt(CtCR)4Cd(S)]2
(1(S)2, S = acetone, dmso) and unsolvated complexes
[Pt(CtCR)4Cd]x 10, and a series of tetranuclear clusters
[Pt(CtCR)4CdL]2 (2-5, L = N donor). In addition, time-
dependent density functional theory (TD-DFT) calculations
were carried out on 1c(dmso)2, 2a, 2c, 4, and 5, with the aim of
characterizing the highest few occupied and lowest few
unoccupied molecular orbitals, thus gaining insight into the
nature of their photophysical properties.
ꢀ
ꢀ
(19) Charmant, J. P. H.; Falvello, L. R.; Fornies, J.; Gomez, J.; Lalinde,
E.; Moreno, M. T.; Orpen, A. G.; Rueda, A. Chem. Commun. 1999, 2045.
ꢀ
ꢀ
(20) Ara, I.; Fornies, J.; Gomez, J.; Lalinde, E.; Moreno, M. T. Organo-
metallics 2000, 19, 3137.
ꢀ
ꢀ
(21) Fornies, J.; Gomez, J.; Lalinde, E.; Moreno, M. T. Inorg. Chem.
2001, 40, 5415.
ꢀ
ꢀ
(22) Berenguer, J. R.; Fornies, J.; Gomez, J.; Lalinde, E.; Moreno, M. T.
Organometallics 2001, 20, 4847.
ꢀ
(23) Berenguer, J. R.; Fornies, J.; Gil, B.; Lalinde, E. Chem.;Eur. J.
2006, 12, 785.
ꢀ
ꢀ
(24) Gil, B.; Fornies, J.; Gomez, J.; Lalinde, E.; Martın, A.; Moreno, M.
´
T. Inorg. Chem. 2006, 45, 7788.
(25) Yam, V. W.-W.; Hui, C.-K.; Yu, S.-Y.; Zhu, N. Inorg. Chem. 2004,
43, 812.
(26) Yin, G.-Q.; Wei, Q.-H.; Zhang, L.-Y.; Chen, Z.-N. Organometallics
2006, 25, 580.
(27) Wei, Q.-H.; Yin, G.-Q.; Ma, Z.; Shi, L.-X.; Chen, Z.-N. Chem.
Commun. 2003, 2188.
Experimental Section
Materials and Methods. All reactions were carried out under
argon atmosphere using solvents from a solvent purification
system (MBRAUW MB SPS-800). Elemental analyses were
carried out with a Perkin-Elmer 2400 CHNS/O microanalyzer.
IR spectra were recorded on a Nicolet Nexus FT-IR Spectro-
meter from Nujol mulls between polyethylene sheets. 1H NMR
spectra were recorded on a Bruker ARX 300 spectrometer;
chemical shifts are reported in parts per million (ppm) relative
(28) Yam, V. W.-W.; Yu, K.-L.; Cheung, K.-K. J. Chem. Soc., Dalton
Trans. 1999, 2913.
ꢀ
ꢀ
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(29) Fernandez, J.; Fornies, J.; Gil, B.; Gomez, J.; Lalinde, E.; Moreno,
M. T. Organometallics 2006, 25, 2274.
ꢀ
ꢀ
(30) Berenguer, J. R.; Gil, B.; Fernandez, J.; Fornies, J.; Lalinde, E. Inorg.
Chem. 2009, 48, 5250.
ꢀ
ꢀ
(31) Ara, I.; Berenguer, J. R.; Fornies, J.; Gomez, J.; Lalinde, E.; Merino,
R. I. Inorg. Chem. 1997, 36, 6461.
ꢀ
ꢀ
(32) Charmant, J. P. H.; Fornies, J.; Gomez, J.; Lalinde, E.; Merino, R. I.;
(36) Dıez, A.; Garcıa, A.; Lalinde, E.; Moreno, M. T. Eur. J. Inorg. Chem.
´ ´
Moreno, M. T.; Orpen, A. G. Organometallics 2003, 22, 652.
2009, 3060.
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
(33) Ara, I.; Berenguer, J. R.; Eguizabal, E.; Fornies, J.; Gomez, J.;
(37) Fornies, J.; Gomez, J.; Lalinde, E.; Moreno, M. T. Inorg. Chim. Acta
Lalinde, E. J. Organomet. Chem. 2003, 670, 221.
2003, 347, 145.
ꢀ
ꢀ
ꢀ
(34) Berenguer, J. R.; Dı
´
ez, A.; Fernandez, J.; Fornies, J.; Garcı
´
a, A.; Gil,
(38) Fornies, J.; Fuertes, S.; Martın, A.; Sicilia, V.; Lalinde, E.; Moreno,
´
B.; Lalinde, E.; Moreno, M. T. Inorg. Chem. 2008, 47, 7703.
M. T. Chem.;Eur. J. 2006, 12, 8253.
ꢀ ꢀ~
´
(39) Fornies, J.; Ibanez, S.; Martın, A.; Gil, B.; Lalinde, E.; Moreno,
ꢀ
(35) Fornies, J.; Fuertes, S.; Martı
´
n, A.; Sicilia, V.; Gil, B.; Lalinde, E.
Dalton Trans. 2009, 2224.
M. T. Organometallics 2004, 23, 3963.

4234 Inorganic Chemistry, Vol. 49, No. 9, 2010
Berenguer et al.
to external tetramethylsilane, SiMe4, and coupling constants in
hertz(Hz). Complex4is the only soluble enough to register its 195Pt
NMR spectrum, being recorded on a Bruker ARX 400 spectro-
meter; chemical shift is reported in ppm relative to Na2PtCl6 in
D2O. UV-vis spectra were recorded on a Hewlet Packard 8453
spectrometer. Diffuse reflectance UV-vis (DRUV) data of
pressed powder were recorded on a Shimazdu UV-3600 spectro-
photometer with a Harrick praying mantis accessory, and recal-
culated following the Kubelka-Munk function. Excitation and
emission spectra were obtained on a Jobin-Yvon Horiba Fluoro-
log 3-11 Tau-3 spectrofluorimeter. The lifetime measurements
were performed operating in the phosphorimeter mode (with a
F1-1029 lifetime emission PMT assembly, using a 450 W Xe
lamp). Quantum yields in the solid state were measured upon
excitation at 400 nm (2a, 2c, 3, and 4), 420 nm (2b), or 430 nm (5)
using a F-3018 Integrating Sphere mounted on a Fluorolog 3-11
Tau-3 spectrofluorimeter. Data were fittered using the Jobin-
Yvon software package. (NBu4)2[Pt(CtCR)4] (R=Tol, C6H4-
OMe-4, C6H4OMe-3)40 were prepared as reported, and other
reagents were obtained from commercial sources.
[Pt(CtCC6H4OMe-4)4Cd]x 10b as a white solid with high
yield (∼ 90%).
Data for 1b(acetone)2: Anal. Calcd for C78H68O10Cd2Pt2
(1780.37): C, 52.62; H, 3.85. Found: C, 51.92; H, 3.15. IR
(cm-1): ν(CtC) 2095 (sh), 2057 (m), 2018 (sh), 1987 (sh);
1
ν(CdO) 1691 (s). H NMR (δ, 300.13 MHz, CDCl3): 7.43 (d,
J=7.8 Hz, 16H, C6H4, C6H4OMe-4); 6.67 (d, J=7.8 Hz, 16H,
C6H4, C6H4OMe-4); 3.57 (s, 24H, OCH3, C6H4OMe-4); 2.17 (s,
12H, CH3COCH3).
Data for 1b: Anal. Calcd for C72H56O8Cd2Pt2 (1664.21): C,
51.96; H, 3.39; Found: C, 51.85; H, 3.10. IR (cm-1): ν(CtC)
1
2053 (s), 2027 (sh). H NMR (δ, 300.13 MHz, CD2Cl2): 7.41
(dbr, J ∼ 8.5 Hz, 16H, C6H4, C6H4OMe-4); 6.68 (d, J=8.5 Hz,
16H, C6H4, C6H4OMe-4); 3.57 (s, 24H, OCH3, C6H4OMe-4).
Data for 10b: Anal. Calcd for C36H28O4CdPt (832.11): C,
51.96; H, 3.39; Found: C, 51.85; H, 3.22. IR (cm-1): 2055 (s),
2029 (sh). 1H NMR (δ, 300.13 MHz, d6-dmso, yellow solution):
7.20 (d, J=8.4 Hz, 16H, C6H4, C6H4OMe-4); 6.82 (d, J=8.4 Hz,
16H, C6H4, C6H4OMe-4); 3.72 (s, 24H, OCH3, C6H4OMe-4).
Preparation of [Pt(CtCC6H4OMe-3)4Cd]x (10c). Cd(ClO4)2
3
Preparation of [Pt(CtCTol)4Cd(acetone)]2 (1a(acetone)2).
Cd(ClO4)2 6H2O (0.110 g, 0.262 mmol) was added to a colorless
6H2O (0.104 g, 0.248 mmol) was added to a solution of
(NBu4)2[Pt(CtCC6H4OMe-3)4] (0.300 g, 0.248 mmol) in acet-
one (∼15 mL), and the mixture was stirred for 15 min. In this
case, complex 10c precipitated as a final cream-white solid which
was filtered, washed with acetone and air-dried (0.145 g, 70%).
Anal. Calcd for C36H28O4CdPt (832.11): C, 51.96; H, 3.39.
Found 51.57; H, 3.42. IR (cm-1): ν (CtC) 2040 cm-1 (m). 1H
NMR (δ, 300.13 MHz, d6-dmso, yellow solution): 7.12 (t, J=7.7
Hz, 4H5, C6H4OMe-3); 6.86 (d, J=7.3 Hz, 4H4 or 6, C6H4O-
3
solution of (NBu4)2[Pt(CtCTol)4] (0.300 g, 0.262 mmol) in
acetone (10 mL), and the mixture stirred for 15 min. The yellow
solid obtained 1a(acetone)2 was filtered and washed with acet-
one (0.123 g, 56%). Anal. Calcd for C78H68O2Cd2Pt2 (1652.38):
C, 56.70; H, 4.15. Found: C, 56.96; H, 4.36. IR (cm-1): ν(CtC)
1
2120 (w), 2078 (sh), 2057 (m), 2025 (sh); ν(CdO) 1662 (s). H
NMR (δ, 300.13 MHz, CDCl3): 7.37 (d, J=7.6 Hz, 16H, C6H4,
Tol); 6.94 (d, J=7.6 Hz, 16H, C6H4, Tol); 2.17 (s, overlapping of
24H, CH3, Tol and 12H, CH3, CH3COCH3). 1H NMR (δ,
300.13 MHz, CD3COCD3): 7.10 (d, J = 7.1 Hz, 16H, C6H4,
Tol); 6.85 (d, J=7.1 Hz, 16H, C6H4, Tol); 2.24 (s, 24H, CH3,
Tol). The low solubility of this complex precludes its character-
ization by 13C{1H} NMR.
Me-3); 6.81 (s, 4H2, C6H4OMe-3); 6.73 (d, J=7.5 Hz, 4H4 or 6
,
C6H4OMe-3); 3.72 (s, 12H, OCH3, C6H4OMe-3). Not soluble
enough for 13C{1H} NMR.
Preparation of [Pt(CtCTol)4Cd(py)]2 (2a). A solution of
complex 1a(acetone)2 (0.150 g, 0.091 mmol) in CH2Cl2 was
treated with excess of pyridine (500 μL, 6.20 mmol). Slow
evaporation of the resulting bright yellow solution at 0° gene-
rates yellow-greenish crystals of 2a (0.115 g, 75%). Anal. Calcd
for C82H66N2Cd2Pt2 (1694.42): C, 58.13; H, 3.93; N, 1.65.
Found: C, 58.02; H, 3.92; N, 1.60. IR (cm-1): ν(CtC) 2108
(w), 2094 (sh), 2084 (s). ΛM(CH2Cl2): ∼ 0 Ω-1 cm2 mol-1. 1H
Preparation of [Pt(CtCTol)4Cd]2 (1a). Prolonged vacuum
treatment (∼48 h) at ∼60° of the yellow solid 1a(acetone)2 (0.123
g, 0.074 mmol) causes the elimination of acetone molecules
giving complex 1a as an orange-brown solid (0.114 g, 100%).
Anal. Calcd for C72H56Cd2Pt2 (1536.22): C, 56.29; H, 3.67.
Found: C, 56.50; H, 3.91. IR (cm-1): ν(CtC) 2054 (s). 1H NMR
(δ, 300.13 MHz, CDCl3): 7.36 (d, J=7.5 Hz, 16H, C6H4, Tol);
6.94 (d, J=7.5 Hz, 16H, C6H4, Tol); 2.17 (s, 24H, CH3, Tol). 1H
NMR (δ, 300.13 MHz, CD3COCD3): Shows the same pattern
than 1a(acetone)2.
3
3
NMR (δ, 300.13 MHz, CDCl3): 8.92 (sbr, 4H2,6, py); 7.66 (t, J=
7.4 Hz, 2H4, py); 7.17 (m, 4H3,5, py); 6.84 (d, J=7.5 Hz, 16H,
C6H4, Tol); 6.59 (d, J=7.5 Hz, 16H, C6H4, Tol); 2.14 (s, 24H,
CH3, Tol). The low solubility of this complex precludes its
characterization by 13C{1H} NMR.
Preparation of [Pt(CtCTol)4Cd]x (10a). 1a(acetone)2 (0.100 g,
0.061 mmol) was treated with CH2Cl2 (∼ 15 mL) yielding a
yellow solution. By stirring at room temperature ∼15 min a
white solid [Pt(CtCTol)4Cd]x 10a separates (0.030 g, 32%). This
solid is only soluble in dmso. Anal. Calcd for C36H28CdPt
(768.11): C, 56.29; H, 3.67. Found: 56.53; H, 3.99. IR(cm-1):
ν(CtC) 2055 (s), 2023 (sh). 1H NMR (δ, 300.13 MHz, d6-dmso,
yellow solution): 7.15 (d, J=7.8 Hz, 8H, C6H4, Tol); 7.05 (d, J=
7.8 Hz, 8H, C6H4, Tol); 2.05 (s, 12H, CH3, Tol).
Preparation of [Pt(CtCC6H4OMe-4)4Cd(py)]2 (2b). This
complex was prepared in a similar way to complex 2a starting
from [Pt(CtCC6H4OMe-4)4Cd]2 1b (0.150 g, 0.090 mmol) and
pyridine (500 μL, 6.20 mmol). The resulting yellow mixture was
stirred for 30 min at room temperature, and the yellow solid thus
obtained 2b was filtered, washed with CH2Cl2, and dried in
vacuum (0.140 g, 85%). A similar result is obtained start-
ing from 1b(acetone)2. Anal. Calcd for C82H66N2O8Cd2Pt2
(1822.41): C, 54.04; H, 3.65; N, 1.54. Found: C, 53.92; H,
3.42; N, 1.78. IR (cm-1): ν(CtC) 2112 (sh), 2085 (m). 1H
Reaction of (NBu4)2[Pt(CtCC6H4OMe-4)4] with Cd-
(ClO4) 6H2O. The reaction of (NBu4)2[Pt(CtCC6H4OMe-
NMR (δ, 300.13 MHz, d6-dmso): 8.58 (d, J=4.19 Hz, 4H2,6
,
,
3
py); 7.78 (t, J=7.7 Hz, 2H4, py); 7.38 (dd, J=5.6; 7.7 Hz; 4H3,5
4)4] 2H2O (0.300 g, 0.242 mmol) in acetone (∼10 mL) and
3
Cd(ClO4)2 6H2O (0.101 g, 0.242 mmol) was analogous to the
py); 7.20 (d, J=8.6 Hz, 16H, C6H4, C6H4OMe-4); 6.82 (d, J=8.6
Hz, 16H, C6H4, C6H4OMe-4); 3.72 (s, 24H, OCH3, C6H4OMe-
4). 13C{1H} NMR: not soluble enough.
3
previously described one causing the precipitation of a yellow
solid which was filtered, washed with acetone, and air-dried,
yielding [Pt(CtCC6H4OMe-4)4Cd(acetone)]2 1b(acetone)2 as a
deep yellow solid (0.115 g, 56%). Prolonged (∼3 h) vacuum
treatment at ∼40 °C causes the loss of the acetone mole-
cules yielding 1b as a brown-orange solid. The yellow 1b-
(acetone)2 or brown-orange 1b solids dissolve in CH2Cl2 yielding
an initial yellow solution from which gradually precipitates
Preparation of [Pt(CtCC6H4OMe-3)4Cd(py)]2 (2c). A white
suspension of [{Pt(CtCC6H4OMe-3)4}Cd]x (10c) (0.150 g, 0.180
mmol) was treated with excess of pyridine (500 μL, 6.20 mmol).
Slow evaporation of the resulting bright yellow solution at 0 °C
generates yellow-greenish crystals of 2c (0.090 g, 55%). Anal.
Calcd for C82H66N2O8Cd2Pt2 (1822.41): C, 54.04; H, 3.65;
N, 1.54. Found C, 53.82; H, 3.57; N, 1.75. IR (cm-1): ν(CtC)
2086 (m). 1H NMR (δ, 300.13 MHz, CD2Cl2): 8.83 (s, 4H2,6, py);
7.70 (t, J=7.7 Hz, 2H4, py); 7.24 (st, J ∼ 6.7 Hz; 4H3,5, py); 6.72
ꢀ
ꢀ
(40) Benito, J.; Berenguer, J. R.; Fornies, J.; Gil, B.; Gomez, J.; Lalinde,
E. Dalton Trans. 2003, 4331.

Article
Inorganic Chemistry, Vol. 49, No. 9, 2010 4235
(t, J=7.5 Hz, 8H5, C6H4, C6H4OMe-3); 6.56-6.50 (m, 24H,
C6H4, C6H4OMe-3); 3.44 (s, 24H, OCH3, C6H4OMe-3). 13C-
{1H} NMR: not soluble enough.
δHA - δHB separation of the AB system (C6H4, Tol) becomes
gradually smaller, collapsing into a singlet at 223 K. Data at 223 K:
12.00 (s, 2NH, pzH); 7.50 (s, 2H5, pzH); 7.17 (s, 2H3, pzH); 6.71 (s,
32H, C6H4, Tol);6.30(s, 2H4,pzH);2.16(s, 24H, CH3, Tol);2.01(s,
Preparation of [Pt(CtCTol)4Cd(NC5H4CH3-4)]2 (3). This
complex was prepared in a similar way to complex 2a starting
from 1a(acetone)2 (0.200 g, 0.121 mmol) and excess of NC5H4-
CH3-4 (500 μL, 5.10 mmol). In this case, 3 precipitated as a pale
yellow microcrystalline solid (0.193 g, 93%). Anal. Calcd for
C84H70N2Cd2Pt2 (1722.47): C, 58.57; H, 4.10; N, 1.63. Found:
C, 58.53; H, 4.05; N, 1.51. IR (cm-1): ν(CtC) 2102 (sh), 2094
(sh), 2085 (s). ΛM(CH2Cl2): ∼ 0 Ω-1 cm2 mol-1. 1H NMR (δ,
12H, CH3COCH3). ΔGq for H3,H5 interconversion ≈58.43 kJ
293
mol-1. The low solubility of this complex precludes its characteri-
zation by 13C{1H}.
Computational Details for DFT Calculations. All calculation
on complexes 1c(dmso)2, 2a, 2c, 4, and 5 were carried out using the
molecular geometry obtained through X-ray diffraction analysis.
Keeping all distances, angles, and dihedral angles frozen, single
point density functional theory (DFT) calculations with the
Gaussian0341 program were performed, using Becke’s three-para-
meter functional combined with Lee-Yang-Parr’s correlation
functional42-44 (B3LYP). The basis set used was the LanL2DZ45
effective core potential for the metal centers and 6-31G(d,p) for
the ligand atoms. The time-dependent density-functional theory
(TD-DFT) calculation was carried out using the polarized conti-
nuum model approach implemented in the Gaussian 03 software.
Percentage compositions of molecular orbitals were calculated
using the AOMix program.46,47
3
3
300.13 MHz, CDCl3): 8.73 (sbr, 4H2,6, NC5H4CH3-4); 6.94 (bs,
J=7.4 Hz, 4H3,5, NC5H4CH3-4); 6.87 (d, J=7.8 Hz, 16H, C6H4,
Tol); 6.61 (d, J=7.8 Hz, 16H, C6H4, Tol); 2.28 (s, 6H, CH3,
NC5H4CH3-4); 2.16 (s, 24H, CH3, Tol). The low solubility of
this complex precludes its characterization by 13C{1H} NMR.
Preparation of [Pt(CtCTol)4Cd(NC5H4CF3-4)]2 (4). Excess
of NC5H4CF3-4 (1000 μL, 7.98 mmol) was added to a solution
of [Pt(CtCTol)4Cd(acetone)]2 1a(acetone)2 (0.205 g, 0.124
mmol) in 10 mL of CH2Cl2. The resulting yellow solution was
kept at -30° for 3 days, affording greenish yellow crystals of 4
(0.100 g, 44%). Anal. Calcd for C84H64N2F6Cd2Pt2 (1830.39):
C, 55.12; H, 3.52; N, 1.53. Found: C, 54.79; H, 3.41; N, 1.30. IR
(cm-1): ν(CtC) 2115 (s), 2089 (s), 2069 (m). ΛM(CH2Cl2): ∼ 0
X-ray Crystallography. Details of the structural analyses for
all complexes are summarized in Table 1. Yellow crystals of
1c(dmso)2 were obtained by slow diffusion of Et2O into a
saturated solution of 10c in dmso/CH2Cl2 1:1. For 2a, 2c, and
5, yellow crystals were grown by slow evaporation at 0 °C of the
corresponding solutions of the complexes in CH2Cl2 (2a, 2c) or
CH2Cl2/acetone 1:1 (5). Finally, greenish yellow crystals of 4
were obtained by cooling a mixture of 4 and NC5H4CF3-4 at
-30 °C in CH2Cl2. One (1c(dmso)2, 2a) or 0.5 (2c, 4) molecules of
CH2Cl2 and one molecule of acetone (5) were found in the
corresponding asymmetric units. Furthermore, for 5, the exi-
stence of weak hydrogen interactions between the N-H of the
pyrazole ligand and the oxygen atom of the acetone was con-
firmed. X-ray intensity data were collected with a NONIUS-
κCCD area-detector diffractometer, using graphite-monochro-
matic Mo-KR radiation. Images were processed using the
DENZO and SCALEPACK suite of programs,48 and the struc-
tures were solved by Direct Methods using SHELXS-97.49 The
absorption correction was performed using MULTI-SCAN50
(2a, 2c, 4 and 1c(dmso)2) or XABS251 (5), with the WINGX
program suite.52 The structures were refined by full-matrix least-
squares on F2 with SHELXL-97,49 and all non-hydrogen atoms
were assigned anisotropic displacement parameters. For com-
plex 5, the correct assignment of the position for the N(N-H)
atom of the pzH ligand was confirmed by examination of the
ΔMSDA values for bonds involving these atoms,53,54 after refin-
ing the structure in three different ways (with the identities of the
C and N in one position, reversed, and with 50/50 hybrid scatter-
ing factor at each of the affected atomic sites). The hydrogen
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. Several restraints have been used to model the CH2Cl2
molecule in 1c(dmso)2 and the positional disorder presented by
Ω-1 cm2 mol-1 1H NMR (δ, 300.13 MHz, CDCl3, equili-
.
3
3
brium mixture of 1a and 4 in about molar ratio 3:2): 8.89 (d,
J = 4.4 Hz, 4H2,6, NC5H4CF3-4); ∼ 7.35 (d, 13H, H3,5 of
NC5H4CF3-4 overlapped with d, C6H4, Tol, 1a); 6.93 (d, J=
7.4 Hz, 9H, C6H4, Tol, 1a); 6.88 (d, J ≈ 7.9 Hz, 7H, C6H4, Tol,
4); 6.65 (d, J ≈ 7.9 Hz, 7H, C6H4, Tol, 4); 2.17 (s, 24H, CH3, Tol,
1
1a and 4). H NMR of 4 þ NC5H4CF3-4 (6 equiv) (δ, 300.13
MHz, CDCl3): 8.87 (d, J=4.9 Hz, H2,6, NC5H4CF3-4); ∼ 7.42
(d, H3,5, NC5H4CF3-4); 7.00 (d, J=7.8 Hz, C6H4, Tol); 6.54 (d,
J=7.8 Hz, C6H4, Tol); 2.17 (s, 6H, CH3, Tol). 195Pt NMR of 4 þ
NC5H4CF3-4 (6 equiv) (δ, 85.68 MHz, CD2Cl2): -3761 (s,
1
1J(195Pt-111Cd)=1855 Hz, J(195Pt-113Cd)=1941 Hz). The
low solubility of this complex precludes its characterization by
13C{1H} NMR.
Preparation of [Pt(CtCTol)4Cd(pzH)]2 (5). A CH2Cl2 (10 mL)
solution of 1a(acetone)2 (0.200 g, 0.121 mmol) was treated with pzH
(0.018 g, 0.264 mmol). Then, acetone (∼ 10 mL) was added to the
resulting yellow solution, and the mixture was slowly evaporated at
0 °C generating yellow crystals with stoichiometry 5 2acetone
3
3
(0.180 g, 83%). Anal. Calcd for C78H64N4Cd2Pt2 2C3H6O
(1788.53): C, 56.41; H, 4.28; N, 3.13. Found: C, 56.31; H, 3.86;
N, 3.50. IR (cm-1):ν(N-H) 3600 (m), 3462 (m); ν(CtC) 2112 (sh),
2104 (sh), 2096 (m), 2081 (m), 2061 (sh); ν(CdO)acetone 1607 (m).
1
ΛM(CH2Cl2): ∼ 0 Ω-1 cm2 mol-1. H NMR (δ, 300.13 MHz,
3
3
CD2Cl2): 11.97 (sbr, 2NH, pzH); ∼ 7.3 (br, 4H3,5, pzH); 6.84
(16H), 6.74 (16H) (AB system, J=7.8 Hz, C6H4, Tol); 6.27 (pt, J=
2.4 Hz, 2H4, pzH), 2.20 (s, 24H, CH3, Tol); 2.10 (s, 12H,
CH3COCH3). Upon cooling, the resonance due to H3 and H5
broadens (Tcoalescence ∼ 293 K) and finally splits (∼ 282 K), and the
(41) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
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Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Farkas, O.; Tomasi,
J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson,
G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.;
Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.;
Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratman, R. E.; Yazyev, O.;
Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.;
Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V.
G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.;
Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.;
Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith,
T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill,
P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A.
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4236 Inorganic Chemistry, Vol. 49, No. 9, 2010
Berenguer et al.
Table 1. Crystallographic Data for 1c(dmso)2 2CH2Cl2, 2a 2CH2Cl2, 2c CH2Cl2, 4 CH2Cl2, and 5 2 Acetone
3
3
3
3
3
1c(dmso)2 2CH2Cl2
3
2a 2CH2Cl2
3
2c CH2Cl2
3
empirical formula
Fw
T (K)
crystal system, space group
a(A)
b(A)
c(A)
R(deg)
β(deg)
C78H72Cd2Cl4O10Pt2S2
1990.26
173(1)
monoclinic, P21/n
13.3388(4)
14.4103(8)
20.8566(12)
90
108.259(3)
90
3807.1(3)
2
1.736
C42H35CdCl2NPt
932.10
173(1)
triclinic; P1
9.8650(2)
13.8180(3)
14.4500(3)
69.9970(10)
81.6860(10)
89.4250(10)
1829.82(7)
2
1.692
4.575
908
C83H68Cd2Cl2N2O8Pt2
1907.27
173(1)
monoclinic, P21/n
14.4841(4)
13.1672(4)
20.6477(3)
90
91.4520(10)
90
3936.56(17)
2
1.609
γ(deg)
volume (A3)
Z
Dcalcd (Mg/m3)
absorption coefficient (mm-1
F(000)
)
4.465
1944
4.197
1860
θ range for data collection (deg)
no of data/restraints/params
goodness-of-fit on F2 a
3.25 to 25.68
7202/5/442
1.011
R1 = 0.0586, wR2 = 0.1232
R1 = 0.1129, wR2 = 0.1442
1.681 and -1.360
2.09 to 27.89
8671/0/437
1.016
R1 = 0.0347, wR2 = 0.0690
R1 = 0.0491, wR2 = 0.0730
1.015 and -1.138
3.38 to 25.68
7445/0/464
1.025
R1 = 0.0302, wR2 = 0.0776
R1 = 0.0399, wR2 = 0.0827
1.704 and -0.980
final R indexes [I > 2σ(I)]a
R indexes (all data)a
largest diff peak and hole (e.A -3
)
4 CH2Cl2
3
5 2acetone
3
empirical formula
Fw
T (K)
crystal system, space group
a(A)
b(A)
c(A)
C85H66Cd2Cl2F6N2Pt2
1915.28
173(1)
monoclinic, C2/c
17.9732(5)
26.8534(8)
15.9466(4)
90
102.5110(10)
90
7513.7(4)
4
1.693
C42H38CdN2OPt
894.23
173(1)
triclinic; P1
9.6288(4)
13.8741(5)
14.3504(6)
71.144(2)
80.783(2)
87.744(2)
1790.62(12)
2
1.659
4.530
876
R(deg)
β(deg)
γ(deg)
volume (A3)
Z
Dcalcd (Mg/m3)
absorption coefficient (mm-1
F(000)
)
4.402
3720
θ range for data collection (deg)
no of data/restraints/params
goodness-of-fit on F2 a
3.53 to 27.10
8276/6/454
1.039
R1 = 0.0285, wR2 = 0.0654
R1 = 0.0378, wR2 = 0.0698
1.109 and -1.360
2.95 to 25.68
6666/0/431
1.025
R1 = 0.0455, wR2 = 0.1195
R1 = 0.0483, wR2 = 0.1225
2.623 and -2.553
final R indexes [I > 2σ(I)]a
R indexes (all data)a
largest diff peak and hole (e A-3
)
P
P
P
P
P
a R1 = ||Fo| - |Fc||/ |Fo|; wR2 = [ w(Fo2 - Fc2)2/ w(Fo2)2]1/2; goodness of fit = { [w(Fo2 - Fc2)2]/(Nobs - Nparam)}1/2; w = [σ2(Fo) þ (g1P)2 þ
g2P]-1; P = [max(Fo2;0 þ 2Fc2]/3.
the CF3 group of the NC5H4CF3-4 ligand in 4. Finally, all the
structures show some residual peaks greater than 1 e A-3 in the
vicinity of the platinum atoms or solvent molecules, but with no
chemical meaning.
free-acetone species [Pt(CtCR)4Cd]x (R = Tol 10a; R =
C6H4OMe-4 10b), which are similar to 10c, and gradually
precipitating (∼15 min) as white powders.
All attempts to obtain crystals of either the solvate 1a,
b(acetone)2 or the free solvent 10a-c species failed. The
most significant and distinctive spectroscopic feature is
observed in their IR spectra. Thus, the IR spectra of the
solvate complexes 1a,b(acetone)2 exhibit several ν(CtC)
bands (2120, 2078 (sh), 2057, 2025 (sh) 1a(acetone)2; 2095
(sh), 2057, 2018 (sh) cm-1 1b(acetone)2) consistent with the
presence of different alkynyl coordination modes (terminal
and bridging). This pattern is comparable to that observed
for the tetranuclear derivatives (2a,b,3-5), suggesting that
these solvates have, in the solid state, a tetranuclear sand-
wich structure [Pt(CtCR)4Cd(acetone)]2 1a,b(acetone)2,
similar to those found for 1c(dmso)2 and 2-5, in which
the acetone molecules are bonded to the Cd center (see
Scheme 1). By contrast, the free-solvent derivatives 10a-c
exhibit one ν(CtC) band (with a shoulder in 10a and 10b) in
the typical range of η2-alkynyl bridging ligands (2055, 2023
(sh) cm-1 10a; 2055, 2029 (sh) cm-1 10b; 2040 cm-1 10c).
Results and Discussion
Synthesis and Spectroscopic Characterization. As is
shown in Scheme 1, the reaction of [Pt(CtCR)4]2- with
cadmium perchlorate depends on the R substituent. Thus,
treatment of the tolyl- and p-methoxyphenyl-alkynyl plati-
num(II) derivatives with Cd2þ in acetone leads to the form-
ation of solvate complexes of stoichiometry [Pt(CtCR)4-
Cd(acetone)]2 1a,b(acetone)2 (R=Tol a, C6H4OMe-4 b) as
bright yellow solids. By contrast, a similar reaction starting
from (NBu4)2[Pt(CtCC6H4OMe-3)4] results in the precipi-
tation of a solvent-free species [Pt(CtCC6H4OMe-3)4Cd]x
10c as a white solid. The acetone solvate 1a,b(acetone)2
dissolve only in chlorinated solvents (CH2Cl2, CHCl3) al-
1
lowing their characterization by H NMR in CDCl3 solu-
tion (freshly prepared solution, see Experimental Section).
However, in solution these species are unstable, evolving to

Article
Inorganic Chemistry, Vol. 49, No. 9, 2010 4237
Scheme 1
This spectroscopic feature, together with their white color
and null solubility in common polar and/or weak donor
organic solvents (CH2Cl2, CHCl3, CH3COCH3, THF,
NCMe), suggest that they are presumably of polymeric
nature. It is likely that, in the final free-acetone spe-
cies 10a-c, the CdII ions shift toward an “in-plane”
bis-(η2-alkyne) tweezer-like coordination, in such a way
that each platinate fragment acts as bis-(chelating) bridging
ligand between consecutive cadmium centers. The stabili-
zation of a naked CdII ion by four η2 alkynyl ligands has
been recently found in the trinuclear anions [{(Rf)2Pt(μ-
CtCR)2}2Cd]2- (Rf=C6F5).29 Curiously complexes 10a-c
proved to be only slightly soluble in d6-dimethylsulfoxide,
allowing their characterization by 1H NMR spectroscopy
(see Experimental Section). However, in this strong donor
solvent the color of the white solids change to yellow, and
the small amount that is dissolved (with sonication) yielded
deep-yellow solutions, thus indicating that the (CH3)2SO
molecules interact with the cadmium centers stabilizing
tetranuclear species [Pt(CtCR)4Cd(dmso)]2 analogous to
complexes 2-5. Fortunately, after many attempts a few
yellow crystals suitable for X-ray could be obtained by slow
diffusion of Et2O into a saturated dmso/CH2Cl2 solution
of 10c, confirming the formation of the solvate [Pt(CtCC6-
H4OMe-3)4Cd(dmso)]2 1c(dmso)2.
Tetranuclear aggregates [Pt(CtCR)4CdL]2 (L = py;
R=Tol 2a, C6H4OMe-4 2b, C6H4OMe-3 2c. R=Tol; L=
NC5H4CH3-4 3, NC5H4CF3-4 4, N2C3H4 (pzH) 5) were
easily synthesized by treatment of either the acetone
solvate 1a,b(acetone)2 or the polymeric 10a-c species with
the corresponding N-donor ligand. It is worth noting that
the same products are obtained even if a large excess of
the corresponding ligand is used, indicating the strong
bonding preference of CdII for the platinum alkyne frag-
ments. The complexes were isolated as yellow crystals (2a,
2c, 4, 5) or microcrystalline yellow powder (2b, 3), and
their identities were confirmed by microanalysis and
spectroscopic means. The IR spectra of 2a,b, 3-5 show
several ν(CtC) stretching bands in the 2115-2069 cm-1
range, in agreement with the presence of terminal and
different unsymmetric bridging ligands, while one ν(CtC)
stretching band is found (2086 cm-1) in the spectrum of 2c,
which is consistent with the presence of only one type
of bridging alkynyl ligand, all these facts being confirmed
by X-ray crystallography.
Because of the low solubility of these complexes, only
the 1H and 195Pt (for 4) could be recorded. In particular,
2b is only soluble in d6-dmso, but in this strong donor
1
solvent the H NMR pattern reveals (see Experimental
Section) the presence of free pyridine and an identical AB
pattern for the aryl C6H4OMe-4 protons to that seen for
the precursor 10b in d6-dmso, suggesting that similar
[Pt(CtCC6H4OMe-4)4Cd(dmso)]2 species are present in
this solvent. Complexes 2a,c and 3 dissolve in CD2Cl2 (2c)
or CDCl3 (2a, 3) and both the low field shifts of the
pyridine ortho protons (ΔH2,6=0.46 2a; 0.27 ppm 2c, 3)
and the pattern of the aryl C6H4R protons, shifted to low
frequencies in relation to [Pt(CtCC6H4R)4]2-, support
that the tetranuclear aggregates retain their integrity in
solution. Complexes 4 and 5 are found to be involved in
dynamic processes. In the case of 4, and probably because
of the lower basicity of the NC5H4CF3-4 ligand, its
proton spectrum (CDCl3) shows the presence of an equili-
brium mixture of the precursor 1a and 4 (δ 6.88, 6.65; AB
system C6H4Me-4) in about a molar ratio of 3:2. To
investigate this behavior, the proton spectra of 1a were
recorded in the presence of increased amounts of NC5H4-
CF3-4. As shown in Supporting Information, Figure S1,
upon addition of 2 equiv of NC5H4CF3-4, the pattern ob-
served is identical to that obtained with crystals of com-
plex 4. Upon progressive addition of ligand, the resona-
nces of 1a gradually decrease, whereas those of complex 4
increase, and a large excess of pyridine (6 equiv) is
required to completely move the equilibrium toward

4238 Inorganic Chemistry, Vol. 49, No. 9, 2010
Berenguer et al.
complex 4. The presence of only one set of pyridine
protons (δ 8.87 H2,6; 7.42 H3,5), very close to those of
free NC5H4CF3-4 (δ 8.81 H2,6; 7.51 H3,5), supports its
involvement in a fast additional exchange with complex 4.
The pyrazole derivative 5 exhibits (CD2Cl2), in addition
to the aromatic tolyl protons, two characteristic reso-
nances at δ 11.97 (br) and at 6.27 ppm (pt, J=2.4 Hz) due
to the H1 and H4 protons of the pyrazole, but only a broad
signal (∼ 7.34 ppm) for H3 and H5, indicating that they
are also involved in a dynamic process. Upon cooling,
q
coalescence is observed at about 293 K (ΔG293 ∼ 58.43
KJ mol-1) and, finally, the resonance split into two
Figure 1. 195Pt{1H}NMR spectra of 4 þ NC5H4CF3-4 (6 equiv) in
3
CD2Cl2 at 298 K.
discrete signals (δ 7.50 and 7.17 ppm). Addition of a
slight excess of pzH to this solution at room temperature
(r.t.) only causes a significant sharpening of the H3,5
resonance and a slight upfield shift for H1 (δ 11.78 ppm),
thus suggesting that a fast dissociative ligand process could
be responsible for the observed average of H3 and H5 pro-
tons in this complex. The 195Pt NMR spectrum of a CDCl3
solution containing 4 and NC5H4CF3-4 (1:4 molar ratio)
could be also recorded (Figure 1), showing the presence of a
singlet at -3761 ppm with both 111Cd (1J(195Pt-111Cd)=
1855 Hz) and 113Cd (1J(195Pt-113Cd)=1941 Hz) satellites.
The observed relative ratio 1:3:1 matches that expected for
a tetranuclear Pt2Cd2 aggregate, ruling out the formation of
binuclear Pt-Cd units (expected ratio 1:4:1) in the presence
of excess of pyridine. We are not aware of previously re-
ported one bond 195Pt-111,113Cd coupling constants.55-57
In 4, both the remarkable downfield of the platinum
resonance in relation to the anionic precursor (NBu4)2-
[Pt(CtCTol)4] (δ -4187 ppm) and the high value of the
Pt-Cd coupling constants are indicative of a relatively
strong PtfCd dative bond.
Figure 2. Molecular structure of [Pt(CtCTol)4Cd(py)]2 2a. Only atoms
of the central core (Pt2Cd2(CtC)8) are drawn as ellipsoids at the 50%
probability level and hydrogen atoms omitted for clarity.
X-ray Diffraction Studies. Perspective views of the
molecular structures of tolylacetylide derivatives 2a, 4
and 5 are represented in Figures 2, Supporting Informa-
tion, Figure S2, and Figure 3, respectively, whereas those
of the m-methoxyphenylacetylide complexes 2c and the
solvate 1c(dmso)2 are shown in Figures 4 and 5. Selected
bond lengths and angles are listed in Table 2. As can be
seen, the molecules can be visualized as 2:2 adducts giving
rise to final rhomboidal Pt2Cd2 cores, which are very
unsymmetrical in the tolyl complexes (2a, 4, 5) and
symmetrical in the m-methoxy derivatives 2c and 1c-
(dmso)2. One of the most striking features is that, in spite
of the relatively hard nature of the acidic CdII ion and the
presence of excess of ligand, it only forms one Cd-N-
(imine) bond (2.239(3) A 2a; 2.245(4) 2c; 2.277(3) 4;
2.221(4) 5). Similarly, in the solvate 1c(dmso)2 the Cd is
bonded to the oxygen atom of one dimethylsulfoxide
molecule with a typical58 bond distance of 2.224(6) A.
Curiously, in the tolylacetylide aggregates 2a, 4, and 5, the
Cd center of the resulting formed dicationic unit CdL2þ
Figure 3. Molecular structure of [Pt(CtCTol)4Cd(pzH)]2 2acetone
3
5 2acetone. Only atoms ofthe central core(Pt2Cd2(CtC)8) andnitrogens
3
of the pyrazole ligand are drawn as ellipsoids at the 50% probability level,
while hydrogen except H2, which is involved in H O(acetone) contacts,
are omitted.
3 3 3
forms a very short PtfCd donor-acceptor bond with the
corresponding tetraalkynyl platinate. In fact, the Pt-
(10)-Cd(1) bond length (2.6999(3) A 2a; 2.7460(3) A 4;
2.6952(4) A 5) is shorter than the sum of the covalent radii
(1.36 (Pt) þ 1.44 (Cd)=2.8 A)59 and lies in lower range of
reported PtII-CdII bond distances, being shorter to that
found in [cis-Pt(C6F5)2(CtCPh)2Cd(cyclen)] (2.764(1)
A)39 and close to the shortest one reported to date by
Ito et al.55 in the cation [(Phpy)2PtCd(cyclen)]2þ (2.6389-
(8) A, Phpy =2-phenylpyridinate). Although this fact
points to the presence of a significant donation of the
electron density from the dz2(Pt) orbital to the CdII cation,
the Pt-Cd vector displaces from the normal to the plati-
nate fragment (27.96° 2a; 32.01° 4; 26.94° 5) toward
(55) Yamaguchi, T.; Yamazaki, F.; Ito, T. J. Am. Chem. Soc. 1999, 121,
7405.
(56) Chen, W.; Liu, F.; Nishioka, T.; Matsumoto, K. Eur. J. Inorg. Chem.
2003, 4234.
(57) Femoni, C.; Kaswalder, F.; Iapalucci, M. C.; Longoni, G.; Zachini,
S. Chem. Commun. 2006, 2135.
(58) (a) Marques, L. L.; de Oliveira, G. M.; Lang, E. S. Z. Anorg. Allg.
Chem. 2006, 632, 2310. (b) Reddy, H. K.; Zhang, Ch.; Shlemper, E. O.;
Schrauzer, G. N. Inorg. Chem. 1992, 31, 1673. (c) Halasz, I.; Horvat, M.; Biljan,
T.; Mestrovic, E. J. Chem. Cryst. 2008, 38, 793. (d) Defazio, S.; Cini, R.
Polyhedron 2003, 22, 1355.
one of the platinum-alkynyl units (Pt-C19-C20), also
0
allowing a close Cd-CR contact (Cd-C190 2.491(4) A 2a;
ꢀ
ꢀ
(59) Cordero, B.; Gomez, V.; Platero-Prats, A. E.; Reves, M.; Echeverria,
ꢀ
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Article
Inorganic Chemistry, Vol. 49, No. 9, 2010 4239
second platinate fragment is remarkably weaker (Pt(1)-
Cd(1) 3.1186(3) A 2a; 3.0872(3) A 4; 3.1290(4) 5), though
still below the van der Waals limit (3.33 A).61 The result-
ing unsymmetrical rhomboidal metallic Pt2Cd2 array is
planar in 2a and 5 and slightly distorted in 4 (torsion angle
10.58°), with relatively long Pt Pt (4.2525(2) A 2a;
3 3 3
4.0360(2) A 4; 4.3017(3) A 5) and Cd Cd (3.9934(4)
3 3 3
A 2a; 4.1948(4) A 4; 3.9503(6) A 5) separations. Curi-
ously, in 2a and 5 the corresponding pyridine and pyra-
zole planes are nearly contained in the metallic plane
(small dihedral angles of 18.56° 2a and 18.64° 5). In
complex 4, probably because of the low basicity of the
NC5H4CF3-4, the pyridine plane is twisted 38.35° and
the Cd-N vector is also slightly tilted (∼15°) in relation to
the plane of the N-donor ligand (see Figure 2a), suggest-
ing a misdirected interaction. As far as the bonding mode
of the alkynyl ligands is concerned, it is noteworthy that,
in agreement with the IR spectra, there are two ligands
(C(28)-C(29)-Tol) that remain as terminal groups (one
from each platinate unit), two acting as μ-κ2CR bridging
ligands, and the remaining four that exhibit a rather
unsymmetrical μ-κ2CR:η2 bridging mode. Despite this
dissimilarity no clear correlation can be found between
the bonding mode and their structural details (see
Table 2). The pyrazole derivative 5 crystallizes in the P1
space group with one molecule of acetone in the unsym-
metrical unit, whose oxygen atom (O1) is involved in
intermolecular hydrogen bonds with the N-H hydrogen
atom of the corresponding pyrazole groups (Figure 3).
The H(2) O(1) and N(2) O(1) distances (2.198 and
Figure 4. Zenith view of the molecular structure of [Pt(CtCC6H4OMe-3)4-
Cd(py)]2 2c (50% probability ellipsoids). Aryl and pyridil atoms are
simplified and hydrogen atoms are omitted for clarity.
3 3 3
3 3 3
2.861 A respectively) and the N(2)-H(2)-O(1) angle
(133.82°) are within the usual range for this type of
contacts.62-66
The structures of the m-metoxyalkynyl derivatives 2c
and 1c(dmso)2 (Figures 4 and 5, respectively) display a
symmetrical framework in which the two tetraalkynyl
platinates are eclipsed and both cationic cadmium units
symmetrically bisect the alkynyl entities, being bonded to
four Pt-CR bonds (two associated with each platinum
unit). As a consequence, in both derivatives the alkynyl
ligands display a μ-κ2CR bonding mode and the CdII ion is
in an approximately square pyramidal geometry, with the
midpoint of the four Pt-CR bonds occupying the basal
plane, and the pyridine (2c) or the dmso (1c(dmso)2) at
the apex. Probably because of the higher coordination
number (C.N. =5), the Cd-CR distances (range 2.471-
(5)-2.551(5) A 2c; 2.470(10)-2.508(10) A 1c(dmso)2)
are slightly longer to those found for the μ-κ2CR and
μ-κ2CR:η2 bridging ligands in the tolyl-acetylide deriva-
tives (2.409(4)-2.495(5) A). In the final rhomboidal planar
Pt2Cd2E2 (E=N, O) cores, the four PtfCd bonds are now
nearly symmetrical (Pt-Cd 2.8001(4), 2.8505(4) A 2c;
2.9052(8), 2.9114(8) A 1c(dmso)2). The value of the mean
Pt-Cd separation in the pyridine complex 2c (∼2.825 A) is
only somewhat shorter than the corresponding average
Figure 5. Molecular structure of [Pt(CtCC6H4OMe-3)4Cd(dmso)]2 1c-
(dmso)2. Only atoms of the central core (Pt2Cd2(CtC)8) and dmso are
drawn as ellipsoids at the 50% probability level, and hydrogen atoms are
omitted for clarity.
2.474(4) A 4; Cd-C19 2.495(5) A 5). The resulting neutral
{Pt(CtCR)4CdL} unit dimerizes by rather unsymmetri-
cal η2 interactions of the CdII with two mutually cis
alkynyl fragments of the other unit, thus completing a
distorted tetrahedral coordination around the CdII (See
Supporting Information, Figure S2c for 4). The observed
Cd alkynyl interactions take place mainly with the CR car-
bon atoms, with Cd-CR distances in the range 2.409(4) to
2.450(4) A. The Cd-Cβ separations (2.644(4)-2.736(4)
A) are remarkably longer (0.22-0.32 A) and only close to
the sum of the van der Waals radii (2.7 A) of Csp (1.78 A)60
and the ionic radii of CdII (C.N. 4, 0.92 A),61 suggesting
that the interaction with these atoms is very weak.
Notwithstanding, to accommodate these weak Cd Cβ
3 3 3
bonding interactions the platinate units displaced each
other (ca. 1.33 A 2a; 1.85 A 4; 1.97 A 5), retaining
an eclipsed disposition in 2a and 5 or with a slight twisting
(∼ 14°) in complex 4 (see Supporting Information, Figure
S2). As a consequence of this relative orientation, the
interaction of the Cd center with the platinum of the
(62) Jeffrey, G. A. An introduction to Hydrogen Bonding; Oxford University
Press: New York, 1997.
(63) Lyssenko, K. A.; Antipin, M. Y. Russ. Chem. Bull., Int. Ed. 2006,
55, 1.
(64) Knope, K. E.; Cahill, C. L. Inorg. Chem. 2009, 48, 6845.
(65) Xie, J.; Abrahams, B. F.; Wedd, A. G. Chem. Commun. 2008, 576.
(66) Reddy, L. S.; Chandrau, S. K.; George, S.; Babu, N. J.; Naugia, A.
Cryst. Growth Des. 2007, 7, 2675.
(60) Szafert, S.; Gladysz, J. A. Chem. Rev. 2003, 103, 4175.
(61) Winter, M. The Periodic Table on the W.W.W.; The University of
Shefield and Web Elements Ltd.: U. K., 2008;www.webelements.com.

4240 Inorganic Chemistry, Vol. 49, No. 9, 2010
Berenguer et al.
Table 2. Selected Bond Lengths [A] and Angles [deg] for 2a 2CH2Cl2, 4 CH2Cl2, 5 2acetone, 2c CH2Cl2, and 1c(dmso)2 2CH2Cl2
3
3
3
3
3
2a 2CH2Cl2
3
4 CH2Cl2
3
5 2acetone
3
1c(dmso)2 2CH2Cl2
3
2c CH2Cl2
3
Pt(1)-Cd(1)
Pt(10)-Cd(1)
Pt-CR
3.1186(3)
2.6999(3)
2.005(3)-2.028(5)
2.435(4), 2.450(4)
2.669(4), 2.718(4)
2.491(4)
3.0872(3)
2.7460(3)
2.001(4)-2.028(4)
2.409(4), 2.417(3)
2.644(4), 2.736(4)
2.474(4)
3.1290(4)
2.6952(4)
1.993(5)-2.026(5)
2.424(5), 2.429(5)
2.644(5), 2.701(6)
2.495(5)
2.9052(8)
2.9114(8)
2.007(10)-2.027(11)
2.470(10)-2.508(10)
2.8001(4)
2.8505(4)
2.009(4)-2.017(5)
2.471(5)-2.551(5)
Cd-CR
Cd-Cβ
0
Cd-CR
CR-Cβ
1.194(6)-1.228(5)
2.239(3)
1.199(5)-1.209(5)
2.277(3)
1.204(8)-1.215(8)
2.221(4)
1.187(13)-1.207(13)
1.202(7)-1.213(7)
2.245(4)
Cd(1)-N(1)
Cd(1)-O(5)
Cd(1)-Pt(1)-Cd(10)
Pt(1)-Cd(1)-Pt(10)
Pt-CR-Cβ
2.224(6)
102.27(2)
77.73(2)
173.6(9)-175.4(9)
173.4(12)-175.6(11)
86.362(8)
93.638(8)
173.7(3)-177.1(4)
172.7(4)-178.0(4)
91.772(9)
87.356(8)
172.0(3)-175.2(3)
171.2(4)-177.5(5)
85.068(11)
94.933(11)
174.8(5)-178.2(5)
172.3(6)-177.9(6)
97.261(10)
82.740(10)
172.5(5)-178.8(4)
171.0(5)-176.7(5)
CR-Cβ-Cγ
values between the shortest and the longest Pt-Cd dis-
tances found in the unsymmetrical tolyl-derivatives (avera-
ges 2.9092 A 2a; 2.9166 A 4; 2.9121 A 5), suggesting that
stabilization of these clusters involves a synergistic combi-
nation of Pt Cd, Cd alkynyl, and Cd-N bonding
3 3 3 3 3 3
interactions. It should be pointed out that in 2c and 1c-
(dmso)2, the presence of OMe substituents favors the
existence of weak intermolecular non-covalent interactions,
which lead to the generation of a complex supramolecular
network (see Supporting Information, Figure S3 as illus-
tration for 2c) and, probably, are also playing a significant
role in the stabilization of the final symmetrical Pt2Cd2
cores with a five coordination environment around the
CdII. Although it is less obvious why similar symmetrical
aggregates are not favored in the tolyl derivatives, it is clear
that the preferred formation of a very short PtfCd bond in
these latter (2a, 4, and 5) seems to be responsible for the
absence of an interaction of the CdII with one of the alkynyl
ligands, resulting in a final lower tetrahedral coordination.
Figure 6. Absorption spectra of 1c(dmso)2 in a mixture CH2Cl2:dmso
(9:1) (pink) and 2a (red), 2c (black), 3 (blue), and 5 (orange) in CH2Cl2
(5 ꢀ 10-5 M).
Photophysical Characterization
in-plane η2-Cd complexation, which probably lowers the
energy of the alkynyl based highest occupied molecular
orbital (HOMO).29 The shift to higher energies observed
for 1a,b(acetone)2 in the low energy band suggests that, in
CH2Cl2 solution, the acetone molecules are likely lost
and the CdII centers probably move toward an in-plane
η2-coordination with the alkynyl ligands. In accordance
with this suggestion, the progressive addition of acetone
to the CH2Cl2 solution causes the growth of a new low
energy band (372 nm, 1a(acetone)2; 377 nm, 1b(acetone)2;
see Supporting Information, Figure S6 for 1b(acetone)2)
similar to those observed for the tetranuclear aggregates
2-5 (vide infra), thus suggesting the coordination of the
acetone molecules to Cd, with the concomitant formation
of the solvate [Pt(CtCR)4Cd(acetone)]2 species in solu-
tion to some extent. Similarly, only in the presence of an
excess of dmso (mixture CH2Cl2:dmso 9:1) does the spec-
trum of 1c(dmso)2 show two low energy bands (348 and
371 nm), and a similar pattern to that observed for the
pyridine clusters (345, 377 nm 2a, 348, 375 nm 2c and 348,
376 nm 3), which seems to be characteristic of the tetra-
nuclear cluster entities [Pt2(CtCR)8Cd2L2] (Figure 6).
Along the same lines, the existence of a remarkable
dissociation of the NC5H4CF3-4 ligand for 4, was also
confirmed by UV-vis spectroscopy. By way of illustra-
tion, Figure 7 shows the spectra of the precursor 1a-
(acetone)2 and the microcrystalline solid 4, together with
the changes observed upon addition of NC5H4CF3-4.
Absorption Spectroscopy. The absorption data for all
the complexes are summarized in Supporting Informa-
tion, Table S1. In the solid state, the diffuse-reflectance of
the yellow tetranuclear aggregates are characterized by a
distinctive low energy feature in the range of 370 for 2c to
385 nm for 2b with a long tail to ∼475 nm, which is absent
in the white solvent-free 10a-c derivatives. By way of
illustration, the spectra of the free 10c and solvate 1c-
(dmso)2 and the pyridine adducts 2a-c are given in
Supporting Information, Figures S4 and S5, respectively.
As mentioned above, the solvates 1a,b(acetone)2
[Pt(CtCR)4Cd(acetone)]2, are only soluble in chlorinate
solvents, in which they are unstable evolving to solvent-
free insoluble derivatives 10a-c. The spectra of freshly
prepared CH2Cl2 solutions of both complexes (see Sup-
porting Information, Figure S6 for 1b(acetone)2) show
several high energy features (200-266 nm, see Supporting
Information, Table S1) due to intraligand transitions
and a low energy absorption (316 nm 1a(acetone)2; 319
nm 1b(acetone)2), which appear remarkably blue-shifted
in relation to the lowest 1ππ IL/dπ(Pt)fπ*(CtCR)
MLCT manifold in the corresponding precursors
[Pt(CtCR)4]2- (CH2Cl2; 335, 345sh R = Tol; 344 R =
C6H4OMe-4). Similar hypsochromic shifts have been
previously observed in tweezer-like heterometallic Pt-Cd
complexes and have been attributed to the existence of
a lesser electronic dπ(Pt)/CtC interaction caused by the

Article
Inorganic Chemistry, Vol. 49, No. 9, 2010 4241
1
The band at ∼316 nm, which resembles the IL/MLCT
band of the precursor, is progressively depleted, while the
band at 376 nm due to 4 grows and a shoulder at 348 nm,
typical of the tetranuclear aggregates, is also clearly seen
when more than 10 equiv of NC5H4CF3-4 are added. The
presence of a clear isosbestic point indicates that a simple
equilibrium between 1a and 4 is involved.
the coordination of pyridine ligands causes a slight red
shift in the absorption maxima, most likely because of an
increased character from platina-alkynyl to pyridine
charge transfer character MLL0CT, as suggested by
TD-DFT calculations.
Emission Spectroscopy. Probably because of the rigi-
dity of the tetranuclear rhomboidal systems, aggregates
1a,b(acetone)2, 1c(dmso)2, 2-5 are strongly emissive in
the solid state (298, 77 K), with high quantum yields in the
4.5-36.3% range for the nitrogen coordinated deriva-
tives 2-5 (Table 3). The latter also exhibit moderate
luminescence in CH2Cl2 solution at 298 K. The calculated
emission lifetimes fit to monoexponential decays in the
range of microseconds, revealing their triplet state paren-
tage. Figure 8 shows the emission spectra of the yellow
solvate complexes in the solid state at 298 and 77 K.
They exhibit a bright greenish luminescence (488 nm
1a(acetone)2, 515 nm 1b(acetone)2, 500 nm 1c(dmso)2),
which is blue-shifted and slightly structured at 77 K (λmax
484 nm 1a(acetone)2, 489 nm 1b(acetone)2, 492 nm 1c-
(dmso)2), pointing to the involvement of the alkynyl
ligands in the excited state. The emission occurs at lower
energies compared to that of the anionic precursors,40
The two distinctive low energy absorptions exhibit a
small dependence on the alkynyl substituents and the
coligands at cadmium. Thus, a slight blue shift is observed
from 2a (Tol, py) to 2c (C6H4OMe-3, py) and, in the tolyl
derivatives, the energy follows the order 5 (367 nm) >
1a(acetone)2 (372 nm) > 2a (377 nm) ∼ 3 (377 nm) ∼ 4
(376 nm). Following previous assignments,24,30,34,38 these
low energy absorptions are primarily attributed to an
admixture of singlet Pt/π(CtCR)fπ*(CtCR) (MLCT)
and platinum-ligand to cadmium charge transfer Pt-
(CtCR)fCd. Alternatively, we denoted the transition
as MLM0CT (M=Pt, M0 =Cd) with intraligand (1ππ
CtCR) character. In the observed trend the influence of
the nature of the coligands at Cd is not so clear. However,
1
Figure 7. Absorption spectra of freshly prepared solution of 1a-
(acetone)2 (black) and 4 (dashed) in CH2Cl2 (5 ꢀ 10-5 M). In light gray,
successive additions of 2, 6, 8, 18, and 38 equiv of NC5H4CF3-4 to the
solution of 4, showing the growth of the band at 376 nm and the
appearance of a shoulder at 348 nm, together with the decrease of the
band at 316 nm upon the addition of ligand.
Figure 8. Normalized emission spectra for solid samples of 1a(acetone)2
(black), 1b(acetone)2 (red), and 1c(dmso)2 (blue) at 298 (solid line) and 77
K (dashed).
Table 3. Emission Data for Complexes 1-5
solid state λemmax/nm [τ/μs] {φ/%}
complex
298 K
77 K
CH2Cl2 5 ꢀ 10-5 M (298 K) λmemax/nm [τ/μs]
10a
10b
a
a
a
514 [8.8]
525 [7.8]
468max, 507sh
484, 512sh [14.3]
501 [13.0]
489, 509sh
540 [11.4]
492max, 532sh
479 [9.3]
500 [9.2]
b
b
b
10c
1a(acetone)2
488 [13.5]
510 [12.7]
515
560 [10.7]
500
490 [8.0] {4.5}
520 [7.2] {15.2}
492 [14.5] {6.9}
488 [11.7] {10.5}
505 [14.1] {13.3}
545 [10.2] {36.3}d
1a
1b(acetone)2
1b
1c(dmso)2
2a
2b
2c
3
533
b
469, 512sh [9.6]
477, 512sh [17.6]
506 [15.1]
528 [11.0]
532
4
5
546c
567 [9.1]
530 [8.7]d
a Not emissive at 298 K. b Not soluble. c Measured with excess of NC5H4CF3-4 (1:10). d Measured over crystals containing acetone molecules
(5 2acetone).
3

4242 Inorganic Chemistry, Vol. 49, No. 9, 2010
Berenguer et al.
as rigidochromism, has been previously observed in
other heteropolynuclear Pt2M4 (M=Cu, Ag, Au) com-
plexes,38,67 being attributed to structural changes in the
excited state, which are more favorable in solution than in
the rigid lattice of the solid.68 Curiously, with exception of
the pyrazole derivative 5 (712 cm-1), the extent of the red-
shifts in solution is higher in the unsymmetrical tolyl-
alkynyl derivatives (1646 2a, 1695 3, and 1487 cm-1 4)
than in the symmetrical meta-methoxyalkynyl complex
2c (1385 cm-1). It is likely that the clusters in solution
adopt a symmetrical Pt2Cd2 central core with a final
square-planar pyramidal coordination around the Cd
centers, which could be closer to that seen for 2c in the
solid state (C.N. = 5) than for the unsymmetrical tolyl
derivatives (distorted tetrahedral C.N. = 4). It is note-
worthy that the excitation spectra in solution resemble the
corresponding absorption spectra, suggesting that the
emission comes from the tetranuclear {Pt2(CtCR)8Cd2-
L2} aggregates (see Supporting Information, Figure S9
for complex 3). As can be seen in Figure 9, the emission
energy was found to change upon variation of both the
alkynyl ligand and the N-donor ligand at cadmium. The
latter has a prominent effect on the emission energy,
following the same trend in the solid state (488 3 > 490
2a > 505 4 > 545 nm 5) as in solution (532 3 > 533 2a >
546 4 > 567 nm 5), which is in line with the electron-
accepting ability of the N-imine ligand (NC5H4CH3-4 <
NC5H5 <NC5H4CF3-4 < pzH). Furthermore, both at
298 and at 77 K the emission energy of 2b (520 nm 298 K;
500 nm 77 K) is red-shifted in relation to 2c (492 nm 298
K; 469 nm 77 K) and 2a (490 nm 298 K; 479 nm 77 K).
This fact reflects the role of the better electron delocaliza-
tion between the CtC and aryl in the p-methoxyphenyl-
ethyl fragment, which reduces the transition gap. Taking
into account these trends and the salient features of the
frontier orbitals (see below), which indicate the role of the
pyridine ligands in the lowest unoccupied molecular
orbitals LUMO and LUMOþ1 for complexes 2a, 2c,
and 4 and of the Pt2Cd2 metallic core in the pyrazole
derivative 5, we suggest that the emission comes from an
excited state of large Pt(d)/π(CtCR)fπ*(imine) MLL0-
CT character, mixed with Pt(d)π(CtCR)fPt2Cd2/π*-
(CtCR) (MLM0CT) contribution, this latter being parti-
cularly remarkable in complex 5. It should be noted that
the observed trend coincides only roughly with the calcu-
lated triplet excitations from DFT calculations, and for
complexes 4 and 5 this is even reversed (see Supporting
Information, Table S2). This suggests that in these sys-
tems the calculated forbidden absorption is likely only a
poor approximation to the emissive excited state. In addi-
tion, in the case of the pyrazole complex 5 the presence of
the acidic N-H proton and its involvement in the dyna-
mic process (vide supra) through a possible interaction
with the alkynyl fragments could be responsible for the
remarkable red shift (calculated 434 nm, experi-
mental 538 nm). Upon cooling the CH2Cl2 solutions to
77 K, the emission bands shift remarkably to higher
energies exhibiting somewhat structured profiles (see
Supporting Information, Figure S10) with λmax at
460 2a, ∼ 450 (3, 4) and 496 nm 5. Although less struc-
tured, the emissions of 2a, 3, and 4 resemble those found
Figure 9. Emission spectra at room temperature of complexes 2a (red),
2b (light blue), 2c (white), 3 (blue), 4 (green), and 5 (yellow) in the solid
state (solid lines) and 5 ꢀ 10-5 M CH2Cl2 solution (dotted lines).
and decreases (Tol > C6H4OMe-3 > C6H4OMe-4) with
the electron donating ability of the alkynyl groups,
indicating that they must be involved in the lowest excited
state. We assign the emission in these solvates as plati-
num-alkynyl to cadmium charge transfer with intraligand
3
character MLM0CT/3ILCtCR (Pt(d)/π(CtCR)fPt-
(Pz)Cd(s)/π*(CtCR)), as supported by the DFT studies
(vide infra). Interestingly, the acetone molecules are
removed from the solvate derivatives 1a,b(acetone)2 upon
prolonged vacuum at about 60-70 °C (48 h, 1a(acetone)2;
34 h, 1b(acetone)2), affording final ochre-orange solids
(1a,b), which are weakly emissive (photographic images
are shown in Supporting Information, Figure S7), dis-
playing broader red-shifted emission bands centered at
about 510 nm (1a) and 560 nm (1b), respectively (see
Supporting Information, Figure S8 for 1a). The process is
reversible for several cycles (at least 4), and the initial
yellow colors and green luminescence are recovered upon
exposure of the orange solids to a drop of acetone. We
think that the loss of acetone probably takes place with
retention of the sandwich type structure. The change in
color and the observed bathochromic shift in the emis-
sions could be ascribed to the existence of stronger out of
plane alkynyl-η2-cadmium bonding interactions in 1a,b in
relation to the solvates, which presumably lower the
energy of the π*(CtCAryl) fragments, reducing the
transition gap. The white free solvent-insoluble mate-
rials 10(a-c) are, however, only weakly emissive at low
temperature (see Table 3).
At room temperature microcrystalline solids 2-5 dis-
play (Figure 9, solid lines) structureless emission bands in
the range of 488 to 545 nm. Despite the presence of very
short Pt-Cd donor-acceptor bonds, in all cases the
emission maxima are blue-shifted at 77 K (469-530 nm
see Table 3), suggesting that these bonds are not the
primary contributors to the emissive manifolds. Interest-
ingly, the emission band of these complexes is signifi-
cantly red-shifted in CH2Cl2 solution (Figure 9, dotted
lines) from those in the solid state. This behavior, denoted
(67) Umakoshi, K.; Saito, K.; Arikawa, Y.; Onishi, M.; Ishizaka, S.;
Kitamura, N.; Nakao, Y.; Sakaki, S. Chem.;Eur. J. 2009, 15, 4238.
(68) Ford, P. C.; Cariati, E.; Bourassa, J. Chem. Rev. 1999, 99, 3625.

Article
Inorganic Chemistry, Vol. 49, No. 9, 2010 4243
Table 4. Molecular Orbital Composition in Terms of Ligands and Metals for Complexes 1c(dmso)2, 2a, 2c, 4, and 5
1c(dmso)2 2a 2c
Pt Cd CtCR dmso Pt Cd CtCR py Pt Cd CtCR py Pt Cd CtCR py Pt Cd CtCR pzH
4
5
MO
LUMOþ3
LUMOþ2
LUMOþ1
LUMO
3
5
4
2
11
10
94
82
85
67
79
78
81
80
1
3
1
0
0
0
1
1
0
1
29 13
4
54
2
96
3
97
97
0
0
0
0
0
0
25 10
16
60
9
84
5
91
91
0
0
0
0
0
0
27 13
4
58
2
95
2
3
0
3
1
25
9
69
90
17
1
0
0
0
0
14
15
14
14
1
1
0
2
1
2
0
0
15
10
16
14
1
1
1
2
1
2
0
0
15
14
12
19
1
1
1
1
2
2
98 18 11
98 29 13
0
0
0
1
53
58
83
86
82
79
22 11
2
9
2
HOMO
20
21
16
18
1
1
2
2
86
83
85
83
84
88
83
84
84
85
76
78
15
13
17
18
2
0
1
3
HOMO-1
HOMO-2
HOMO-3
0
0
in (NBu4)2[Pt(CtCTol)4] (λmax 447, 465, 475, 480 nm),40
suggesting that in frozen CH2Cl2 their emissions could be
3
tentatively ascribed to a IL(ππ*)/3MLCT manifold of
the platinate fragments. The change of emission origin
from the MLL0CT [Pt(d)/π(CtCR)fπ*(pyridine)] ex-
cited state to a mixed 3ILππ*(CtCR)/3MLCT manifold
by lowering of the medium temperature indicates that
these two excited states are likely close-lying in energy.
However, for 5 the emission is broader and red-shifted in
relation to [Pt(CtCTol)4]2-, clearly showing the influ-
ence of the “Cd(pzH)” units.
Molecular Orbital Calculations. DFT calculations are
currently used to establish electronic structures and spec-
tral transitions. In this work, single point (DFT) and TD-
DFT calculations were performed for 1c(dmso)2, 2a,c, 4,
and 5. Table 4 summarizes the orbital compositions for all
five complexes in terms of ligands and metals. As can be
seen, the calculations reveal some differences between the
pyridine-cadmium coordinated aggregates (2a,c, 4) and
complexes 1c(dmso)2 and 5. The three pyridine complexes
2a,c and 4 have similar frontier orbitals, those of 2a are
shown in Figure 10, and those of 2c and 4 in Supporting
Information, Figure S11. In these complexes, the last
highest occupied molecular orbitals possess a strong
alkynyl and platinum character. Thus, the HOMO and
HOMO-1 derive from the combination of the Pt(II) dπ
orbitals (∼ 15%) with two mutually trans π(CtCAryl)
(83-86%) alkynyl ligands on each platinate fragment,
and the HOMO-2 and HOMO-3 are similar, but are built
up from the other mutually trans alkynyl ligands. The
LUMO and LUMOþ1 are mainly composed of the π* of
the pyridine ligands (97% 2a; 91% 2c; 98% 4) with a
negligible contribution of metals (Cd ∼ 1%) and alkynyl
fragments. However, the LUMOþ2, which is ∼0.43 (2a),
0.34 (2c), and 0.79 eV (4) higher than the LUMO, has
alkynyl (54-60%) and remarkable Pt2Cd2 metallic (Pt(p)
25-29%/Cd(s) 10-13%) character. As can be seen in
Table 4 (see also Figure 10 and Supporting Information,
Figure S11), for complexes 1c(dmso)2 and 5, the composi-
tion of the HOMOs (HOMO-3 to HOMO) is essentially
similar to those for 2a,c and 4, being composed of
platinum and alkynyl ligands. However, in these deriva-
tives there is a major difference in the unoccupied orbitals,
because the LUMO and LUMOþ1 are now metal and
alkynyl ligand based. Thus, for both 1c(dmso)2 and 5 the
LUMO is a cluster-localized Pt2Cd2 metallic orbital (Pt
(22-29%), mainly pz; Cd (11-13%) mainly s), which
exhibits σ Cd-Cd bonding character with remark-
able alkynyl contribution (67, 58%). In the LUMOþ1
the contribution of cadmium in both complexes is
similar to that of LUMO, while that of Pt(II) is lower.
Figure 10. Frontierorbital plots for 2a and 1c(dmso)2 obtained byDFT.
The difference between 1c(dmso)2 and 5 is observed in
the following unoccupied orbitals. In 1c(dmso)2 the
LUMOþ2 and LUMOþ3 have preponderant alkynyl
contribution, while in the pyrazole derivative 5 the
LUMOþ2 is composed of 90% of pzH, and the
LUMOþ3 contains contributions from pzH (69%)
and CtCTol (25%).
The nature of the absorption features were explored by
TD-DFT calculations using the polarized continuum model
in which the solvent is simulated as a continuum of uniform
dielectric constant. Calculated transitions energies in CH2-
Cl2 solutions (first singlets) with strong oscillator strengths,
which have a higher contribution to the absorption spectra,
are summarized in Supporting Information, Table S2. For
complex 1c(dmso)2, the lowest-energy absorptions (HO-
MO-n to LUMO) involve transitions from platinum-alky-
nyl orbitals based (PtCtCR) to the LUMO, a (Pt2Cd2)/
π*CtCR orbital, which can be assigned as MLM0CT (M=
Pt, M0=Cd) platinum-alkynyl-to-cadmium charge transfer.
The calculated values (353, 346, 331 nm) can be related
to experimental values seen in CH2Cl2 (371, 348sh nm)
(Figure 6). A similar assignment can be made for complex 5.
In this complex, the three lowest computed absorptions are
calculated at 380, 356, and 351 nm, resulting mainly from

4244 Inorganic Chemistry, Vol. 49, No. 9, 2010
Berenguer et al.
HOMOfLUMO, HOMO-3fLUMO, and HOMO-1f
LUMOþ1, respectively. Experimentally, the lowest band
is located at 367 nm, exhibiting a long tail spreading down to
∼430 nm. In the pyridine derivatives the lowest energy
absorptions calculated (348-369 nm 2a; 345-370 nm 2c;
329-395 nm 4) correspond to the excitations from HOMO-
n to LUMO, LUMOþ1, and LUMOþ2 (see Supporting
Information, Table S2). Therefore, as the LUMO and
LUMOþ1 are π* orbitals localized in the pyridine ligands
and LUMOþ2 is Pt2Cd2/π*CtCR based in these aggre-
gates, the two low energy absorptions can be assigned as
admixture of PtCtCRfπ*(pyridine) (MLL0CT) and
MLM0CT. This involves charge transfer from the platina-
alkynyl fragments to the pyridine ligand, mainly in the
lowest feature for 2a,c (Figure 6), but also to the metallic
core and π*CtCR (Pt2Cd2/π*CtCR).
a μ-κCR bonding mode. Probably because of the rigidity of
these tetranuclear heterometallic systems (2-5) all clusters
display bright solid state (Φ from 4,5 to 36.3%) and solution
phosphorescence. As noted in the Introduction, it is now well
established that the presence of d8 d10 metallophilic inter-
3 3 3
actions has a remarkable impact on the emission of hetero-
polynuclear complexes. In these systems, probablybecause of
the presence of low-lying π* orbitals on alkynyl and pyridine
ligands, the contribution of the Pt Cd bonds is less signi-
3 3 3
ficant, and clearly these bonds are not the primarly contri-
butorsto theemissive manifolds. In the solid state and in fluid
solution the emission maxima depend on the alkynyl sub-
stituent and the coligands. Both the experimental data and
TD-DFT calculations suggest that excitation of these clusters
moves electron density from both platina-alkynyl fragments
toward low-lying orbitals, which have strong metallic/alky-
nyl (Pt2Cd2/π*CtCR) character in the case of the solvate
and pyrazole (5) derivatives or a remarkable contribution of
the π* pyridine groups in the pyridine derivatives 2-4. In the
pyrazole derivative 5, the possible interaction between the
NH protons with the alkynyl fragments could be responsible
for the lower HOMO-LUMO gap observed experimentally.
All these properties may be useful in potential practical
applications.
Conclusions
In summary, a series of sandwich-type tetranuclear yellow
solvate complexes [Pt(CtCR)4Cd(acetone)]2 1a,b(acetone)2
(Tol a, C6H4OMe-4 b) or [Pt(CtCC6H4OMe-3)4Cd(dmso)]2
1c(dmso)2 or white polymeric free solvate [Pt(CtCR)4Cd]x
10a-c are generated from reaction between the anionic
homoleptic substrates [Pt(CtCR)4]2- and Cd2þ. The forma-
tion of the white polymeric insoluble species, likely stabilized
by η2-alkynyl bonds, results from the weakness of the
Acknowledgment. We thank the Spanish MICINN for
financial support (Project CTQ2008-06669-C02-02).
J.F. thanks the CAR (Colabora 09/15) and S.S. thanks
the CSIC for a grant. We also thank CESGA for com-
puter support.
Cd acetone bonding interactions. In fact, 1a,b(acetone)2
3 3 3
are not stable in chlorinated solvents, evolving irreversibly to
the final insoluble 10a,b species. However, in the solid state,
the solvates 1a,b(acetone)2, which exhibit a bright green
luminescence (488 a, 515 nm b), reversibly lost the acetone
molecules affording ochre-orange solids with a very weak
red-shifted emission (∼510 1a, 560 1b). It has been found that
addition of N-donors ligands results in the formation of
stable 2-5 tetranuclear complexes, in which two dicationic
CdL2þ units are stabilized by the synergistic combination of
Pt Cd and Cd alkynyl bonding interactions. As re-
Supporting Information Available: Diffuse reflectance and
absorption data for complexes 1-5 in the solid state and solu-
tion, respectively (Table S1). Calculated transition energies in
CH2Cl2 solutions for 1c(dmso)2, 2a, 2c, 4, and 5 (Table S2). 1H
NMR of a CDCl3 solution of 1a upon progressive additions of
NC5H4CF3-4 (Figure S1). ORTEP views of complex 4 (Figure
S2). Supramolecular details and views of the tridimensional
organization of complex 2c (Figure S3). Solid diffuse reflectance
of complexes 10c, 1c(dmso)2, 2a, 2b, and 2c (Figures S4 and S5).
Absorption spectra of a freshly prepared solution of 1b-
(acetone)2 in CH2Cl2 and in different mixtures of CH2Cl2:
acetone (Figure S6). Photographic images under white and
UV light of 1a(acetone)2 and its reversible transformation
into 1a (Figure S7). Emission spectra of 1a(acetone)2 and 1a in
the solid state at 298 K (Figure S8). Absorption and excitation
spectra of a CH2Cl2 5 ꢀ 10-5 M solution of 3 (Figure S9).
Emission spectra of CH2Cl2 5 ꢀ 10-5 M solutions of 2a, 3, 4,
and 5 at 77 K (Figure S10). Frontier orbital plots for 2c, 4,
and 5 (Figure S11). Crystallographic data in CIF format. This
material is available free of charge via the Internet at http://
pubs.acs.org.
3 3 3
3 3 3
vealed by X-ray crystallographic studies, the meta-methoxy-
alkynyl derivatives (1c(dmso)2 and 2c), which exhibit a
different kind of secondary weak extended intermolecular
interactions, form a planar symmetrical rhomboidal Pt2Cd2
framework (Pt Cd ∼ 2.85 A) in which the CdII center
3 3 3
adopt a final pyramidal geometry (C.N.=5). By contrast, the
tolylacetylide derivatives (2, 4, and 5) display planar unsym-
metrical metallic frameworks with two short (∼2.7 A) and
two weaker (∼3.1 A) bonding interactions, in which the
CdII centers achieve a lower distorted four coordinated
tetrahedral environment. As a consequence, these latter
exhibit three different alkynyl ligation modes (μ-η2, μ-κCR
and σ-CtCR), while in 1c(dmso)2 and 2c all alkynyls adopt