Structural and luminescence studies on π...π and Pt...Pt interactions in mixed chloro-isocyanide cyclometalated platinum(II) complexes

Article abstract of DOI:10.1021/ic902094c

[Pt(DZq)Cl(CNR)] [bzq = benzoquinolinate; R = tert-butyl (^tBu 1), 2-6-dimethylphenyl (Xyl 2), 2-naphthyl (2-Np 3)] complexes have been synthesized and structurally and photophysically characterized. 1 was found to co-crystallize in two distinct pseudopolymorphs: a red form, which exhibits an infinite 1 D-chain ([1]_∞) and a yellow form, which contains discrete dimers ([1]₂), both stabilized by interplanar π...π (bzq) and short Pt...Pt bonding interactions. Complex 3, generated through the unexpected garnet-red double salt isomer [R(bzq)(CN-2-Np)₂][Pt(bzq)Cl₂] 4, crystallizes as yellow Pt...Pt dimers ([3]₂), while 2 only forms π...π (bzq) contacting dimers. Their electronic absorption and luminescence behaviors have been investigated. According to Time-Dependent Density Functional Theory (TD-DFT) calculations, the lowest-lying absorption (CH₂Cl ₂) has been attributed to combined ¹ILCT and ¹MLCT/¹ML'CT (L = bzq, L' = CNR) transitions, the latter increasing from 1 to 3. In solid state, while the yellow form [1]₂ exhibits a green ³MLCT unstructured emission only at 77 K, the 1-D form [1]_∞. displays a characteristic low-energy red emission (672 nm, 298 K; 744 nm, 77 K) attributed to a mixed ³MMCT [d(σ*)→p(σ)]/³MMLCT [dσ*(M ₂)→σ(π*)(bzq)] excited state. However, upon exposure to standard atmospheric conditions, [1]_∞ shows an irreversible change to an orangeochre solid, whose emissive properties are similar to those of the crude 1. Complexes 2 and 3 (77 K) exhibit a structured emission from discrete fragments (³LC/³MLCT), whereas the luminescence of the garnet-red salt 4 is dominated by a low energy emission (680 nm, 298 K; 730 nm, 77 K) arising from a ³MMLCT excited state. Solvent (CH₂Cl₂, toluene, 2-MeTHF and CH₃CN) and concentration-dependent emission studies at 298 K and at 77 K are also reported for 1-3. In CH₂Cl₂ solution, the low phosphorescent emission band is ascribed to bzq intraligand charge transfer ³ILCT mixed with metal-to-ligand (L = bzq, L' = CNR) charge transfer ³MLCT/³ML'CT character with the Pt to CNR contribution increasing from 1 to 3, according to computational studies.

Full text of DOI:10.1021/ic902094c

Inorg. Chem. 2010, 49, 3239–3251 3239
DOI: 10.1021/ic902094c
Structural and Luminescence Studies on π π and Pt Pt Interactions in Mixed
3 3 3 3 3 3
Chloro-Isocyanide Cyclometalated Platinum(II) Complexes†
‡
§
§
,‡
§
§
ꢀ
ꢀ
ꢀ
ꢀ
´
´
Alvaro Dıez, Juan Fornies, Carmen Larraz, Elena Lalinde,* Jose A. Lopez, Antonio Martın,
M. Teresa Moreno,*,‡ and Violeta Sicilia
‡
´
´
´
Departamento de Quımica - Grupo de Sıntesis Quımica de La Rioja, UA-CSIC, Universidad de La Rioja, 26006,
§
~
´
ꢀ
ꢀ
Logrono, Spain, Departamento de Quımica Inorganica, Instituto de Ciencia de Materiales de Aragon, Facultad
de Ciencias, Universidad de Zaragoza-CSIC, Plaza S. Francisco s/n 50009 Zaragoza, Spain, and
´
ꢀ
ꢀ
Departamento de Quımica Inorganica, Instituto de Ciencia de Materiales de Aragon, Escuela Universitaria de
´
ꢀ
Ingenierıa Tecnica Industrial, Universidad de Zaragoza-CSIC, Campus Universitario del Actur, Edificio Torres
Quevedo, 50018, Zaragoza, Spain
Received October 22, 2009
[Pt(bzq)Cl(CNR)] [bzq = benzoquinolinate; R = tert-butyl (tBu 1), 2-6-dimethylphenyl (Xyl 2), 2-naphthyl (2-Np 3)]
complexes have been synthesized and structurally and photophysically characterized. 1 was found to co-crystallize in
two distinct pseudopolymorphs: a red form, which exhibits an infinite 1D-chain ([1]¥) and a yellow form, which contains
discrete dimers ([1]2), both stabilized by interplanar π π (bzq) and short Pt Pt bonding interactions. Complex 3,
3 3 3
3 3 3
generated through the unexpected garnet-red double salt isomer [Pt(bzq)(CN-2-Np)2][Pt(bzq)Cl2] 4, crystallizes as
yellow Pt Pt dimers ([3]2), while 2 only forms π π (bzq) contacting dimers. Their electronic absorption and
3 3 3
3 3 3
luminescence behaviors have been investigated. According to Time-Dependent Density Functional Theory (TD-DFT)
calculations, the lowest-lying absorption (CH2Cl2) has been attributed to combined 1ILCT and 1MLCT/1ML0CT (L =
bzq, L0 = CNR) transitions, the latter increasing from 1 to 3. In solid state, while the yellow form [1]2 exhibits a green
3MLCT unstructured emission only at 77 K, the 1-D form [1]¥ displays a characteristic low-energy red emission
(672 nm, 298 K; 744 nm, 77 K) attributed to a mixed 3MMCT [d(σ*)fp(σ)]/3MMLCT [dσ*(M2)fσ(π*)(bzq)] excited
state. However, upon exposure to standard atmospheric conditions, [1]¥ shows an irreversible change to an orange-
ochre solid, whose emissive properties are similar to those of the crude 1. Complexes 2 and 3 (77 K) exhibit a
structured emission from discrete fragments (3LC/3MLCT), whereas the luminescence of the garnet-red salt 4 is
dominated by a low energy emission (680 nm, 298 K; 730 nm, 77 K) arising from a 3MMLCT excited state. Solvent
(CH2Cl2, toluene, 2-MeTHF and CH3CN) and concentration-dependent emission studies at 298 K and at 77 K are also
reported for 1-3. In CH2Cl2 solution, the low phosphorescent emission band is ascribed to bzq intraligand charge
transfer 3ILCT mixed with metal-to-ligand (L = bzq, L0 = CNR) charge transfer 3MLCT/3ML0CT character with the Pt to
CNR contribution increasing from 1 to 3, according to computational studies.
Introduction
ambient conditions, and this is a feature that has led to the
recent interest in them as triplet emitters in organic light
emitting devices (OLEDs)2,3,8-18 or as interesting biosignaling
Luminescent cyclometalated platinum(II) complexes is a
topic of current research and has recently been the subject
of excellent comprehensive reviews.1-7 Many of such com-
plexes prove to be luminescent even in solution under
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† Dedicated to Prof. N. G. Connelly on the occasion of his retirement.
*To whom correspondence should be addressed. E-mail: elena.lalinde@
unirioja.es (E.L.); teresa.moreno@unirioja.es (M.T.M.). Fax: (þ34)941-299621.
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2010 American Chemical Society
Published on Web 03/10/2010
pubs.acs.org/IC

3240 Inorganic Chemistry, Vol. 49, No. 7, 2010
Dıez et al.
species.19 In these complexes, emission typically originates
from ligand centered (3LC) and/or metal-to-ligand charge
transfer (3MLCT) states. In addition, some square-planar
Pt(II) complexes with sterically undemanding ligands have
tendency to form stacking structures or dimers controlled by
Pt Pt and/or π π interactions, that exhibit red-shifted
(M = Pt, Pd)37-46 and mixed [cis-Pt(CN)2(CNR)2]37,47-49
and [trans-Pt(CN-p-C6H4-C2H5)2(CN)2]47 compounds, that
exhibit vapochromic and vapoluminescent properties, have
been reported, and a recent work has revealed that
[Pt(CN-tBu)2(CN)2] forms luminescent 1D nanostructures
by Pt Pt interactions.50 Despite the fact that related
3 3 3
3 3 3
3 3 3
phosphorescence derived from metal-metal-to-ligand charge
transfer (3MMLCT) and/or excimeric excited states.7,14,20-31
In general, their absorptions and emissions are strongly
dependent on the extent of Pt Pt and/or π π interac-
platinum isocyanide chloridesystemsof formula[Pt(CNR)4]-
[PtCl4] and [cis-Pt(CNR)2Cl2] have been long known,51-54
very few structures have been determined by X-ray crystal-
lography.55 A recent reinvestigation of [cis-Pt(CNPh)2Cl2]
has shown the formation of two different polymorphs under
different crystallization conditions. One of them contains
vacant channels that are stabilized by a combination of
extended Pt Pt interactions and π π stacking.56
3 3 3
3 3 3
tions, and consequently are highly dependent upon the
crystallization solvent, concentration, temperature, or the
counterion nature.23,31-36
Pt(II)-isocyanide complexes have aroused great interest in
recent years as components in luminescent chromophores. In
this area, diverse stacked double-salts [Pt(CNR)4][M(CN)4]
3 3 3
3 3 3
Pt(II) complexes bearing cyclometalated and isocya-
nide ligands have revealed interesting photophysical
properties,24,27,28,57 including low-energy emissions in fluid
solution. Along these lines, we have recently described the
synthesis of the isocyanide benzoquinolate Pt(II) complexes
[Pt(bzq)(CNR)2]X (R = tBu, Xyl, 2-Np; X = ClO4-, PF-6 )
and the influence of the counteranion and concentration on
their luminescent properties.31 In this report we describe the
preparation, structures, and photophysical properties of
the neutral complexes [Pt(bzq)Cl(CNR)] (R = tBu 1, Xyl 2,
2-Np 3) (Scheme 1). The tert-butylisocyanide derivative 1
shows solid-state pseudopolymorphic behavior. X-ray
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structures are reported for a red form [1 CHCl3]¥ ([1]¥),
3
which exhibits an infinite 1-D chain network and for a
yellow form [1 0.5H2O]2 ([1]2), which consists of discrete
3
dimers, both based on Pt Pt and π π (bzq) bonding
3 3 3
3 3 3
interactions. 2 only forms yellow crystals in which two
monomers are weakly contacting through π π (bzq)
3 3 3
interactions. With the 2-naphthylisocyanide ligand, two
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ꢀ
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derivative, which crystallizes as
a
Pt Pt dimer,
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M. A.; Llobet, A. Dalton Trans. 2006, 1188.
[Pt(bzq)Cl(CN-2-Np)]2 ([3]2), and the garnet-red double
salt [Pt(bzq)(CN-2-Np)2]þ[Pt(bzq)Cl2]- 4. The role of
crystal packing and the influence of the CNR ligand on
their luminescent properties are reported.
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reaction in diplatinum halide-bridge complexes is a
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Article
Inorganic Chemistry, Vol. 49, No. 7, 2010 3241
Scheme 1
complexes.58,59 By starting from dinuclear cycloplatinate
complexes, final [Pt(C-X)ClL] complexes with the incom-
ing ligand L cis- or trans- to the metalated carbon are
obtained, depending on the electronic and steric require-
ments of the ligands. Likewise, as is shown in Scheme 1,
t
[Pt(bzq)Cl(CNR)] (R = Bu 1, Xyl 2) were obtained as
orange (1) or yellow (2) solids in high yield by reaction of
[{Pt(bzq)(μ-Cl)}2] with 2 equiv of the corresponding CNR
in CH2Cl2. Interestingly, while crystallization of [Pt(bzq)-
Cl(CN-Xyl)] 2 from different solvents always results in
fine yellow needles, which are spectroscopically identical
to the initial solid (νCN at 2181s, 2140sh), slow crystal-
lization (CHCl3/Hexane, -30 ꢀC) of the orange powder 1
(νCN 2202 cm-1) simultaneously results in yellow [1]2 and
red [1]¥ crystals (Figure 1), which exhibit slight differences
in the νCN (2185, 2146sh [1]2; 2210, 2169sh cm-1 [1]¥).
The yellow form ([1]2) contains 0.5 molecules of H2O, as
has been confirmed by X-ray diffraction studies (see
below), and it is stable for months. However, the red
crystals ([1]¥) contain one molecule of CHCl3 per mono-
mer, which is rapidly lost, evolving to an orange-ochre
powder similar to the initial crude 1 (IR and photophysical
properties).
Curiously, when reaction was carried out with CN-2-
Np in the same conditions (Scheme 1), a garnet-red solid
resulted by precipitation with acetone, which was identi-
fied as a mixture of [Pt(bzq)Cl(CN-2-Np)] 3 and the salt
product[Pt(bzq)(CN-2-Np)2]þ[Pt(bzq)Cl2]- 4 (molarratio
∼1:1). In accordance with the formation of 4, the MALDI-
TOF spectrum of the garnet-red solid (mixture of 3 and 4)
showed a cluster of peaks with maximum at m/z 1089
(Figure 2a), the value and isotropic pattern of which
Figure 1. (a) Photographic images of the [Pt(bzq)Cl(CN-tBu)] yellow
[1 0.5H2O]2 and red [1 CHCl3]¥ pseudopolymorphs grown simulta-
neously from CHCl3/n-hexane solution at -30 ꢀC; (b) The same crystals
on the left but under UV light (365 nm).
3
3
correspond to the {[Pt(bzq)(CN-2-Np)2][Pt(bzq)Cl]}þ
species. As shown in Scheme 1, the salt complex 4 was
alternatively prepared by mixing an equimolar mixture
of [Pt(bzq)(CN-2-Np)2]PF6 and NBu4[Pt(bzq)Cl2] in
acetone. For 4, two characteristic strong νCN IR absorp-
tions slightly shifted to higher frequencies (2223 and
2192 cm-1) in relation to the precursor [Pt(bzq)(CN-
2-Np)2]PF6 (2215, 2189 cm-1 31
are observed. This fact
)
is likely an effect of the lower electron-backdonation to
the isocyanides because of the presence in the salt 4
of a Pt Pt bonding interaction. In solution (CH2Cl2,
3 3 3
CHCl3) 4 is unstable, evolving to the neutral final isomer
3, with CN-2-Np trans to nitrogen (bzq) (νCN 2185vs,
2142sh cm-1), as confirmed by X-ray diffraction study (see
below). This isomerization takes place through the forma-
tion of 30 (with CN-2-Np trans to metalated carbon) as is
shown by 1H NMR spectroscopy. As is seen in Supporting
Information, Figure S1, the characteristic H2 signal, which
(58) Jain, V. K.; Jain, L. Coord. Chem. Rev. 2005, 249, 3075.
ꢀ
ꢀ
(59) Vicente, J.; Arcas, A.; Galvez-Lopez, M. D. Organometallics 2009,
28, 3501.

3242 Inorganic Chemistry, Vol. 49, No. 7, 2010
Dıez et al.
and MALDI-TOF spectrum support its formulation as
a double salt [Pt(bzq)(CN-2-Np)2][Pt(bzq)Cl2], most
likely stabilized by a polar PtQ-Ptx electrostatic attrac-
tion, which in its turn would account for this deep
garnet-red color. Notwithstanding, the presence of more
or less extended chains in the crude solid cannot be
excluded.
The molecular structures of 1-3 (Figures 3-6, Table 1)
confirm that in all cases the isomer generated has the
isocyanide ligand trans to nitrogen of the bzq group, which
is a feature consistent with the transphobia effect.60-62 As
commented above, yellow crystals of [1 0.5H2O]2 ([1]2) and
3
red crystals of [1 CHCl3]¥ ([1]¥) were grown simultaneously
3
by slow diffusion of n-hexane into a CHCl3 solution of the
orange crude solid 1at -30 ꢀC. The distinguishing feature of
both crystal forms lies in their different packing arrange-
ment. In [1 0.5H2O]2 ([1]2), the four molecules found in the
3
asymmetric unit are oriented to approximately form a
square (Figure 3b), but the molecules are packed by dimers
in a head-to-head fashion (Figure 3c, torsion angle ∼23ꢀ),
stabilized by both close interplanar bzq π π interactions
3 3 3
[3.3139(1)-3.5795(1) A],14,24-27,29,30,63,64 and a short Pt Pt
3 3 3
distance (3.2732(4) A [Pt(1)-Pt(4)0] and 3.2394(4) A
[Pt(2)-Pt(3)0]). The water molecules are associated to
the lattice through weak hydrogen bonding between
the oxygen atoms and protons of the two tert-butyl
groups (O H of each dimer, 2.66(2), 2.64(2), 2.47(2) A)
3 3 3
(Figure 3c). In contrast, in the crystal packing of [1 CHCl3]¥
3
([1]¥) (Figure 4), the [Pt(bzq)Cl(CN-tBu)] units stack in a
columnar way along the a-axis with a Cl-Pt-Pt-CR twist
angle of 30.35ꢀ, thereby minimizing steric interactions be-
tween tBu groups and allowing a close proximity of neigh-
boring Pt centers. The extended 1D-chain exhibits
equivalent Pt(II)-Pt(II) distances of 3.3547(2) A and a
nearly linear Pt Pt Pt angle [169.12(2)ꢀ], thus indicat-
3 3 3 3 3 3
ing some degree of Pt Pt interactions along the chain. It is
noteworthy that the formation of columnar-stacked chain
Pt(II) structures stabilized by Pt Pt metallophilic interac-
3 3 3
3 3 3
Figure 2. (a) MALDI-TOF spectrum of the garnet-red solid (mixture of
3 and 4). Peak corresponding to {[Pt(bzq)(CN-2-Np)2][Pt(bzq)Cl]}þ
[4 - Cl]þ (experimental, black; simulated, red). (b) Photographic images
of the transformation of the garnet-red crude solid (mixture of 3 and 4) to
3 at 150 ꢀC for 1 h. (c) DSC curve of 4 from 25 to 200 ꢀC.
tions is now a well recognized process, and many examples
have been reported.7,20,34,37,49,50,56,65-67 In [1]¥, the shor-
test observed interplanar separation between the bzq ligands
[3.349(1) A] is also sufficiently close to suggest the simulta-
neous presence of π π interactions.14,24-27,29,30,63,64 The
3 3 3
is very sensitive to the stereochemistry around Pt, of 30
(δ = 9.15, green) and 3 (δ = 9.76, blue) is clearly observed
together with those of 4 (δ = 9.38, 9.08, red), 5 min after
the first spectrum was run. The signals of 4 disappear after
15 min, but total isomerization to 3 is only complete after 5
days. Interestingly, 3 was also obtained by a thermal (1 h at
150ꢀ) irreversible solid-state evolution ofthe initial mixture
of 3 and 4 (1:1) (Figure 2b and Scheme 1). This evolution
agrees with the differential scanning calorimetry (DSC)
measurement of 4 (Figure 2c), which shows an exothermic
peak (ΔH = -49 ( 5 kJ/mol) at about 152 ꢀC, that can be
attributed to the solid-solid transition (red to yellow).
All 1-4 complexes were also fully characterized by 1H
and 13C{1H} NMR spectroscopy and usual analytical
means (details are given in the Supporting Information).
For 1-3, crystals suitable for X-ray diffraction were
obtained, allowing the determination of their crystal
structures. However, all attempts that we made to obtain
crystals of 4 suitable for X-ray (monocrystal and powder)
were unsuccessful. In this complex, the spectroscopic data
red form ([1]¥) appears to pack in such a way as to minimize
void space, and this fact is consistent with a higher calculated
density of 2.003 g cm-1 for [1]¥ versus 1.954 g cm-1 for [1]2.
The crystal packing is additionally stabilized by intermole-
cular hydrogen bonds [C-H(solvent) Cl] (dC-H
2.572 A) between the H atoms of the occluded CHCl3
molecules and the Cl ligand (see Figure 4b). Several
=
Cl
3 3 3
3 3 3
(60) Vicente, J.; Abad, J. A.; Martı
nometallics 2002, 21, 4454.
(61) Vicente, J.; Arcas, J. A.; Farkland, A. D.; Ramı
Chem.;Eur. J. 1999, 5, 3066.
(62) Vicente, J.; Arcas, A.; Galvez-Lopez, M. D. Organometallics 2006,
25, 4247.
´
nez-Viviente, E.; Jones, P. G. Orga-
´
rez de Arellano, M. C.
ꢀ
ꢀ
(63) Supramolecular Chemistry; Steed, J. W., Atwood, J. L., Eds.; Wiley-
Interscience: Chichester, 2000.
(64) Houlding, V. H.; Miskowski, V. M. Coord. Chem. Rev. 1991, 111,
145.
(65) Comprehensive Organometallic Chemistry III; 3rd ed.; Canty, A., Ed.;
Elsevier: Amsterdam, The Netherlands, 2006; Vol. 8.
(66) Miller, J. S. Extended linear chain compounds; Plenum Press:
New York, 1982; Vol. 1-3.
(67) Williams, J. M. Adv. Inorg. Chem. Radiochem. 1983, 26, 235.

Article
Inorganic Chemistry, Vol. 49, No. 7, 2010 3243
Figure 3. (a) ORTEP drawing of the molecular structure of the monomer in the yellow form ([1 0.5H2O]2). (b) Asymmetric part of the unit cell. Ellipsoids
3
are drawn at the 50% probability level, and hydrogen atoms are omitted for clarity. (c) Crystal packing by dimers. The oxygen atoms for included water
molecules are colored red in the diagram.
Figure 4. (a). Crystal packing of the red form [1 CHCl3]¥ along a axis. (b) View down the a axis showing the relative orientation of adjacent
3
[Pt(bzq)Cl(CN-tBu)] molecules and the interaction between the Cl and HCCl3 molecule.
examples of platinum(II) compounds that exist in two
different color forms have been reported.68
9.00ꢀ, Pt(2)] and this coplanarity favors the existence of an
additional stacking pattern (Figure 6b) in which dimers are
In the molecular structure of 2 (yellow crystals, Figure 5)
there are no metallophilic interactions, probably because
of the steric hindrance of the Xyl ring, which is found to
form a dihedral angle of 43.80ꢀ with the platinum coordi-
nation plane. The molecules are oriented in head-to-tail
pairs with a short [3.293(8) A] interplanar separation
between the bzq groups (Figure 5b). Curiously, similar
arrangements were also found in both yellow cations of
arranged in close proximity by π π interactions [bzq-Np
3 3 3
groups 3.271(2)-3.360(2) A]. The long Pt Pt distances
3 3 3
between dimers [5.056(1) A and 5.301(1) A] and torsion
angles of 130.57(1)ꢀ [Pt(10)-Pt(1)-Pt(2)] and 129.37(1)ꢀ
[Pt(2)-Pt(10)-Pt(20)] indicate a notable slide from one to
another.
Photophysical Properties. Absorption Spectra. Elec-
tronic absorption spectra of 1-3 are recorded in several
solvents with increasing polarity (Toluene, 2-MeTHF,
CH2Cl2 and MeCN) and the data are summarized in
Supporting Information, Table S1. As an illustration, the
spectra in CH2Cl2 are shown in Figure 7a-c. They reveal
several intense absorptions (222 to 340 nm), which were
mainly considered to be due to intraligand (1IL, bzq,
CNR) and metal perturbed intraligand transitions. The
middle absorption envelope in the region 285-340 nm,
most likely have contributions from 1MLCT and 1LL0CT
transitions, according to DFT calculations (see below).
The low energy bands show little dependence on the
isocyanide substituent with a slight red-shift on going
from 1 to 3 (CH2Cl2, 396, 410 1; 397, 412 2; 398, 414 nm 3)
[Pt(bzq)(CN-Xyl)2]þ with ClO4- and PF6- 31 Despite the
.
yellow color of the crystals of the naphthylisocyanide
3 CH2Cl2, in this complex the two molecules found in
3
the asymmetric unit (Figure 6a) form a dimer linked by
short Pt Pt [3.1451(8) A ] and π π (bzq) [3.340(2) A]
3 3 3
3 3 3
interactions (torsion angle Cl-Pt-Pt-CR 28.52ꢀ). The
naphthyl groups are essentially coplanar with the respec-
tive platinum planes [dihedral angles 12.23ꢀ, Pt(1) and
(68) Often stacked in the solid state causes intense color and luminescence
based on Pt Pt electronic interactions. A search of the July 2009 version of
3 3 3
the Cambridge Structural Database (CSD) indicated the existence of 301
polymorphic or pseudopolymorphic platinum complexes, 13 of which have
at least one polymorph with an intermolecular Pt Pt interaction <3.5 A.
3 3 3

3244 Inorganic Chemistry, Vol. 49, No. 7, 2010
Dıez et al.
Figure 5. (a) ORTEP drawing of the molecular structure of 2. Ellipsoids are drawn at the 50% probability level, and hydrogen atoms are omitted for
clarity. (b) Crystal packing of 2.
Figure 6. (a) ORTEP drawing of the asymmetric part of [3 CH2Cl2]2. Ellipsoids are drawn at the 50% probability level, and hydrogen atoms are omitted
3
for clarity. (b) Crystal packing of [3 CH2Cl2]2.
3
Table 1. Selected Bond Lengths [A] and Bond Angles [deg] for [1 0.5H2O]2, [1 CHCl3]¥, 2, and [3 CH2Cl2]2
3
3
3
[1 0.5H2O]2
3
[1 CHCl3]¥
2
[3 CH2Cl2]2
3
3
Distances [A]
3.3547(2)
2.049(8)
Pt Pt
3 3 3
3.2732(4); 3.2394(4)
2.075(6)
2.011(7)
1.896(8)
1.152(10)
3.1451(8)
2.064(9), 2.090(9)
1.972(11), 2.011(11)
1.913(14), 1.915(11)
1.127(15), 1.130(14)
Pt-Nbzq
2.075(4)
1.998(5)
1.895(5)
1.139(7)
Pt-Corth
Pt-Cisocyanide
Cisocyanide-Nisocyanide
2.012(10)
1.899(12)
1.147(17)
Angles [deg]
Nbzq-Pt-Corth
81.5(3)
82.5(4)
178.1(13)
92.0(5)
93.4(2)
81.88(19)
179.0(5)
93.1(2)
82.4(4), 82.3(4)
176.4(11), 178.4(12)
91.6(4), 93.4(5)
92.3(3), 92.9(3)
Pt-Cisocyanide-Nisocyanide
Cisocyanide-Pt-Corth
Cl-Pt-Nbzq
178.7(7)
93.2(3)
94.08(17)
94.19(12)
and a modest negative solvatochromism (∼12 1; 13 nm 2
and 3) from toluene to MeCN (see Supporting Informa-
tion, Table S1 and Figure S2a for 3). These bands are
follows the Beer’s law in the concentration range from 5 ꢀ
10-5 M to 10-3 M (see Supporting Information, Figure
S2b,c for 3), suggesting that no obvious aggregation
occurs within this range. However, a very weak absorp-
tion [ε(M-1 cm-1) ∼2.4 1 < 3.2 2 < 6.1 3] at a longer
wavelength (∼465 nm), is discernible in very concentrated
solutions (10-2 M, Supporting Information, Figure S2d
for 3). This band could be attributed to the direct popula-
tion of a triplet state, following previous assignments in
1
attributed to admixture of intraligand πfπ* (bzq) IL
and metal-to-ligand [dπ(Pt)fπ*(bzq)] 1MLCT and
1
[dπ(Pt)fπ*(CNR)] ML0CT states, respectively, with
the metal-to-isocyanide charge transfer increasing from
1 to 3, as supported from DFT calculations. For all three
complexes, the lowest absorption band (410-414 nm)

Article
Inorganic Chemistry, Vol. 49, No. 7, 2010 3245
Figure 7. Experimental UV-vis spectra in CH2Cl2 (5 ꢀ 10-5 M) at 298 K and calculated absorption spectra (bars) in CH2Cl2 of 1 (a), 2 (b), and 3 (c).
Frontier orbital plots for 1 (d), 2 (e), and 3 (f) obtained by DFT.
Pt(II) cromophores;24,27-29,31,69,70 however, in these com-
plexes the formation of aggregates in some extent cannot
be excluded.
Interestingly, although the yellow crystals of [1]2, 2, and
3 form dimers with short π π and/or Pt Pt distances,
3 3 3
3 3 3
these are not reflected in their solid diffuse reflectance
UV-vis spectra (Supporting Information, Table S1 and
Figure 8 for [1]2), which are similar to those seen in
solution, probably because they are not of a long-range.
By contrast, the 1-D extended red form [1]¥ displays the
expected distinctive very low feature at 560 nm (Figure 8)
1
ascribed to a MMLCT [d(σ*)f σ(π*)] transition likely
with a slight intraligand 1[σ*(π)fσ(π*)] contribution. As
seen in Figure 8, the low energy absorption profile of the
crude orange 1 (λmax 480 nm) lies between those of [1]2
(short-range interactions) and [1]¥ (long-range inter-
actions). In support of the formulation proposed, the
garnet double-salt 4 also shows a distinct 1MMLCT
Figure 8. Normalized absorption spectra calculated from their reflec-
tance spectra of 1, [1]2, and [1]¥ in solid state.
(69) Berenguer, J. R.; Lalinde, E.; Torroba, J. Inorg. Chem. 2007, 46,
9919.
(70) Develay, S.; Blackburn, O.; Thompson, A. L.; Williams, J. A. G.
Inorg. Chem. 2008, 47, 11129.
strong broad band at 520 nm (Supporting Information,
Figure S3).

3246 Inorganic Chemistry, Vol. 49, No. 7, 2010
Dıez et al.
Table 2. Photophysical Data for 1-4
compound
1 orange
media (T/K)
solid (298)
solid (77)
yellow crystals (77)
red crystals (298)
red crystals (77)
CH2Cl2 5 ꢀ 10-5 M (298)
CH2Cl2 5 ꢀ 10-5 M (77)
CH2Cl2 10-3 M (77)
solid (298)
λ
em [nm]
τ [μs]
a
595 (λex 400)
11.8
66.2 (535)
[1]2 yellow form
[1]¥ red form
535max, 600sh (λex 400)
672 (λex 500-600)b
744 (λex 590)b
350max, 366, 385, 473, 500, 542 (λex 310)
473max, 505, 542 (λex 400)
475, 510, 560max (λex 400)
560, 640 (λex 480)
0.2 (473)
21.5 (560)
560 (λex 400)
24.0 (560)
14.6 (640)
12.4 (508)
560, 640max (λex 470)
485sh, 508max, 545, 600sh (λex 400)
2
10.7 (89%), 38.9 (11%) (545)
87.3 (82%), 265 (18%) (505)
88.3 (80%), 301 (20%) (545)
0.2 (350); 0.2 (473)c
solid (77)
505max, 545max, 580, 630sh (λex 400)
CH2Cl2 5 ꢀ 10-5 M (298)
CH2Cl2 5 ꢀ 10-5 M (77)
350, 370, 385, 473max, 505, 540sh (λex 315)
473max, 505, 540sh (λex 415)
490, 570max (λex 320)
80.1 (60%), 460 (40%) (490)
19 (60%), 117 (40%) (570)
28.3(60%), 128 (40%) (620)
82 ns(473), 0.8 (585), 0.3 (695)
490, 540, 620max (λex 400)
CH2Cl2 10-3 M (298)
CH2Cl2 10-3 M (77)
473max, 505, 540sh, 585, 695(λex 436)
585, 695max(λex 464)
550sh, 600-620max (λex 360-450)
685max (λex 500)
non-emissive
533max, 570, 615sh (λex 400-460)
350max, 365, 385, 475, 490, 500, 525sh (λex 330)
475, 490max, 501, 525sh (λex 400)
490, 500, 570max, 680 (λex 415)
680max (λex 490)
350, 366max, 385 (λex 300-320)
440, 474max, 490, 500, 522sh, 575sh (λex 370)
474max, 490, 500, 522sh, 575sh (λex 430)
550max, 585sh (λex 480)
2.2 (685)
3
solid (298)
solid (77)
33.1 (88%), 152 (12%) (533)
CH2Cl2 5 ꢀ 10-5 M (298)
0.1 (475)c
1.8 (570)
CH2Cl2 5 ꢀ 10-5 M (77)
CH2Cl2 10-3 M (298)
CH2Cl2 10-3 M (77)
490, 500, 580max (λex 330)
706 (λex 480)
1.7 (580)
2.5 (706)
4d
solid (298)
solid (77)
680 (λex 500-600)
675, 730max (λex 500)
e
e
a Weak emission at 590 nm (λex 440 nm). b In atmosphere totally exempt of humidity (see text). c See study of the dependence of the τobs versus [Pt] in
text. d 4 evolves to 3 in solution in about 30 min. e Too weak to be measured.
Emission Spectroscopy. Solid State. The photophysi-
cal data are summarized in Table 2 and Supporting
Information, Table S2. Powdered orange samples of 1
are only weakly emissive at 298 K, showing an emission
peak at about 590 nm, which is visibly more intense at
77 K (λmax 595 nm, τ = 11.8 μs) (Figure 9). Crystalline
crystal structure and recent theoretical calculations on
Pt Pt bonding systems,72-74 the emission is assigned,
3 3 3
as in other stacked platinum chain systems,7,50,64,75-78 to
mixed 3MMCT [d(σ*)fp(σ)] and 3MMLCT [dσ*(M)2f
σ(π*)(C∧N)] transitions. We observed that the crystalline
red form ([1]¥) lost its shine very quickly, and this was
followed by a gradual change in its color and emissive
behavior (Figure 10). In fact, the emission spectrum of
[1]¥ at 77 K in air exhibits the expected band at 744 nm
together with a small high-energy shoulder at 640 nm
(orange line in Figure 10). In a few minutes (10 min) this
shoulder grows and a new high-energy feature located at
590 nm is also detected upon excitation at 500 nm. The
relative intensities of the three bands depend on the
yellow form [1 0.5H2O]2 ([1]2) is not emissive at 298 K,
3
but displays a bright green-yellow unsymmetrical broad
emission (λmax 535 nm, tailing to 725 nm) with a relatively
long lifetime of 66.2 μs at 77 K. The lack of a clear
vibronic structure suggests that the emission is unlikely
3
to be IL.64,71 The broad shape and the time-resolved
phosphorescence measurements (Supporting Informa-
tion, Figure S4) are consistent with an only emission
band, which is tentatively assigned as 3MLCT phosphor-
escence. In this form, the H2O molecules are well trapped,
and all attempts to dry it under vacuum or by heating
without decomposition were unsuccessful. The crystalline
red form ([1]¥) exhibits, in a dry atmosphere under argon
at 298 K, a structureless emission centered at 672 nm,
which narrows and considerably shifts to lower energies
(λmax 744 nm, λexc 590 nm) at 77 K (Figure 9). In conjunc-
tion with the observed Pt Pt and π π contacts in its
ꢀ
(72) Aullon, G.; Alvarez, S. Chem.;Eur. J. 1997, 3, 655.
(73) Xia, B. H.; Che, C. M.; Phillips, D. L.; Leung, K. H.; Cheung, K. K.
Inorg. Chem. 2002, 41, 3866–3875.
(74) Koo, C. K.; Wong, K. L.; Lan, K. C.; Wong, W. Y.; Lam, M. H. W.
Chem.;Eur. J. 2009, 15, 7689.
(75) Kato, M.; Kosuge, C.; Morii, K.; Ahn, J. S.; Kitagawa, H.; Mitani,
T.; Matsushita, M.; Kato, T.; Yano, S.; Kimura, M. Inorg. Chem. 1999, 38,
1638.
(76) Kato, M.; Kishi, S.; Wakamatsu, Y.; Sugi, Y.; Osamura, T.;
Koshiyama, M.; Hasegowa, M. Chem. Lett. 2005, 34, 1368.
(77) Connick, W. B.; Henling, L. M.; Marsh, R. E.; Gray, H. B. Inorg.
Chem. 1996, 35, 6261.
3 3 3
3 3 3
(71) Kui, S. C. F.; Sham, I. H. T.; Cheung, C. C. C.; Ma, C. W.; Yan, B.;
Zhu, N.; Che, C. M.; Fu, W. F. Chem.;Eur. J. 2007, 13, 417.
(78) Bailey, J. A.; Hill, M. G.; Marsh, R. E.; Miskowski, V. M.; Schaefer,
W. P.; Gray, H. B. Inorg. Chem. 1995, 34, 4591.

Article
Inorganic Chemistry, Vol. 49, No. 7, 2010 3247
Figure 9. Normalized emission spectra of the crude solid 1 (77 K, λexc
Figure 10. Normalized excitation (top) and emission (down) spectra of
red crystals of [1 CHCl3]¥ in the solid state at 77 K: fresh crystals under
Ar (Red, λexc 590 nm); under air for 2 min (Orange, λexc 500 nm); upon
exposure to standard conditions for 10 min (Green, λexc 450 nm; Blue, λexc
500 nm) or for 4 days, λexc 400 nm (Black).
400 nm), of the yellow crystalline form [1 0.5H2O]2 (77 K, λexc 400 nm)
3
3
and of the red crystals [1 CHCl3]¥ (measured under Ar: red 298 K, λexc
500 nm; black 77 K, λexc 590 nm).
3
excitation wavelength (green and blue lines in Figure 10),
and the corresponding excitation spectra are different, thus
suggesting a different origin of these bands (Figure 10,
top). Thecolor of the samplegraduallychanges from redto
orange, and finally on standing for 4 days, anorange-ochre
powder is obtained. This final solid is not emissive at room
temperature, whereas at 77 K it mainly shows the high-
energy emission band located at ∼590 nm, similar to that
seen in crude solid 1 at 77 K (595 nm) (black line in
Figure 10). We suggest that the behavior observed arises
most likely from the fact that the initial loss of crystal-
lization solvent (CHCl3) causes a disruption of the lattice
and presumably a modification of the stacking. A change
from the initial nearly linear Pt-Pt-Pt chain (∼170ꢀ) to a
more slip-stacked (Pt-Pt-Pt < 170ꢀ, or even more
staggered) could result in a lengthening of the Pt-Pt
separation, explaining the change from red to orange and
the emission at about 640 nm. In the final orange-ochre
long lifetimes, which fit to two components (see Table 2),
suggest that the emission can be assigned to combined
3LC and 3MLCT transitions. The salt 4 displays a char-
acteristic low energy 3MMLCT emission band at 680 nm
(λexc 500-600 nm) in the solid state at 298 K, which, as
expected, red shifts to 730 nm upon cooling to 77 K
(Supporting Information, Figure S6).
Solution and Glass State. Complexes 1-3 are emissive
in solution at 298 K (see Table 2, Supporting Informa-
tion, Table S2, Figure 11, and Supporting Information,
Figures S7-S9). In diluted (5 ꢀ 10-5 M) CH2Cl2 solu-
tions they all exhibit fluorescence from the bzq ligand
1(ππ*) (350-425 nm) together with a vibronic structured
emission at 473-540 nm, upon excitation in the 290-
330 nm range (Figure 11 solid lines and time-resolved
spectra for 2 in Supporting Information, Figure S7,82). As
expected, excitation at their lowest energy absorption
(400-415 nm) only results in the corresponding low
energy vibronic band (dashed lines), whose excitation
spectrum resembles the absorption spectrum. For 1 and
2, the peak maxima (∼473, 505, 540 nm), and lifetimes are
nearly coincident, indicating a rather similar emissive
state. Only minor differences are found when compared
with the cationic derivatives [Pt(bzq)(CNR)2]þ (CH2Cl2,
470 nm R = tBu; 476 nm R = Xyl).31 For 3, with the most
conjugated and electron-withdrawn ligand (CN-2-Np),
the emission profile is slightly red-shifted and more com-
plex (475, 490, 500, 525 nm) having an additional peak
maximum at 490 nm, pointing to a different composition
of the low-lying emitting state. The phosphorescent emis-
sion is ascribed in the three complexes (1-3) mainly as
powder, the π π stacking between units is likely preva-
3 3 3
lent and responsible for the unstructured emission at about
590 nm. The modification of the photophysical properties
(vaprochromism and/or vapoluminescence, excimer gene-
ration) caused by structural rearrangements upon exposure
of platinum linear chain materials to solvents or by simple
grinding has now many precedents.7,37,50,79-81 However,
the observed change is not reversible, because when the
final orange-ochre powder is exposed to CHCl3 vapors, we
observed neither its transformation to the red form nor any
modification in the emission spectra.
Complex 2 in crystalline state at 298 K exhibits a broad
structured green emission (λmax 508 nm), which is slightly
blue-shifted at 77 K (505 nm) (Supporting Information,
Figure S5). In contrast, 3 in solid state is only emissive at
77 K displaying the typical structured band (λmax 533 nm)
due to the monomer. For both complexes the relatively
3
intraligand charge transfer ILCT on the benzoquinoli-
nate ligand, mixed with some 3MLCT/3ML0CT (L = bzq,
L0 = CNR) character, with the contribution of the
(82) For 2, which exhibited the more intense emission, time-resolved
emission in the millisecond time scale was examined, showing a similar decay
for the fluorescence and the phosphorescence, indicating that delayed
fluorescence is present, a feature which has precedents in alkynyl platinum
complexes. See: Bellows, D.; Aly, S. M.; Gros, C. P.; Ojaimi, M. E.; Barbe,
J. M.; Guilard, R.; Harvey, P. D. Inorg. Chem. 2009, 48, 7613.
(79) Wadas, T. J.; Wang, Q. M.; Kim, Y. J.; Flaschenreim, C.; Blanton,
T. N.; Eisenberg, R. J. Am. Chem. Soc. 2004, 126, 16841.
(80) Balch, A. L. Angew. Chem., Int. Ed. 2009, 48, 2641.
(81) Abe, T.; Itakura, T.; Ikeda, N.; Shinozaki, K. Dalton Trans. 2009,
711.

3248 Inorganic Chemistry, Vol. 49, No. 7, 2010
Dıez et al.
Stern-Volmer plot84 are in line with those reported for
related Pt(II) complexes.70,85-88
Even in diluted glassy CH2Cl2 solutions (77 K), all
complexes exhibit broad low energy emissions (560 1,
620 2 and 570, 680 nm 3) in addition to the structured
monomer emission band (λmax 475 1, 490 nm 2, 3)
(Supporting Information, Figure S11). The excitation
spectra monitoring the low energy band at around
570 nm for 1 and 3 and ∼620 nm for 2 closely resemble
their UV absorptions (∼400 nm), which is consistent with
excimer emission. We suggest that the red-shift observed
for this emission in 2 could be related to the different
nature of the interaction (bzq-aryl or aryl-aryl) between
the excited monomer and the adjacent molecule. In fact,
with excitation at higher energies, in the region of intra-
ligand transitions (320 nm), the excimer band in 2 also
maximizes at 570 nm (see Supporting Information,
Figure S12). However, the lowest energy feature centered
at 680 nm in 3 is related to a lower energy excitation
profile (∼490 nm), being therefore ascribed to mixed
3ππ*/3MMLCT transitions from aggregates formed in
the rigid matrix at 77 K. Excimeric emission and emission
from aggregates (3ππ*/3MMLCT) are predominant at
higher concentration (10-3 M) and the observed maxima
(∼560, 640 nm 1; 600-620, 685 nm 2; and 580, 706 nm 3)
(Supporting Information, Figure S13) compare well with
previously reported values.83 The emission energy of the
lowest band follows the order: R = tBu 1 640 nm > Xyl 2
685 nm >2-Np 3 706 nm, probably because of the
formation of dimers or aggregates with decreasing Pt-Pt
distances in the same order. In fact, the shortest Pt-Pt
Figure 11. Normalized emission spectra of 1-3 in CH2Cl2 (5 ꢀ 10-5 M)
at 298 K.
isocyanide (L0) being minimal in 1 and maximum in 3, as
supported by DFT studies.
The occurrence of low-energy emission, usually ascribed
to excimers or aggregates, is frequently encountered in
some Pt(II) complexes;7,14,21-24,26-31,83 therefore, the in-
fluence of the concentration was examined. The emission
profile is independent of complex concentration (down
10-3 M for 1 and 10-4 M for 2 and 3). In more concen-
trated solutions (10-4 to 10-3 M), two small low energy
broad bands at ∼585 and 695 nm were observed for 2, in
addition to the structured band around 475 nm
(Supporting Information, Figure S8). Similar excitation
spectra were obtained for the intermediate (∼585 nm) and
the monomer structured band (475 nm), which are con-
sistent with excimer emission. By contrast, the excitation
profile of the lowest energy band (695 nm) is red-shifted,
therefore, being tentatively ascribed to intermolecular
aggregation. At 10-3 M, compound 3 shows (Supporting
(or π π) distance in the crystal structures has been
3 3 3
found in complex 3 [3.1451(8) A 3 vs 3.2394(4), 3.2732(4)
A [1]2 or 3.3547(2) A [1]¥].
A solvent-dependent emission study was carried out at
298 K and at 77 K in diluted deoxygenated solutions (5 ꢀ
10-5 M) (toluene, 2-MeTHF, and CH3CN), the results
of which are shown in Supporting Information, Table S2.
At 298 K, complex 1 only exhibits a fluorescence band
(345-408 nm), whereas 2 and 3 exhibit fluorescence and
relatively weak phosphorescence without any appreci-
able energetic variation to their maxima in relation to
CH2Cl2 (see Supporting Information, Table S2 and
Table 2). Only 2 shows one additional low energy
(∼580 nm) manifold in CH3CN. In glassy state, 1 shows
3LC phosphorescence (λmax 474 nm in all solvents) and
also a low excimeric manifold (∼570 nm) in CH3CN.
For complexes 2 and 3 (77 K) the tendency to form
excimers and/or aggregates is higher. For 2, monomer
emission, [471 nm (toluene), 466 nm (2-MeTHF), 476 nm
(CH3CN)] and broad red features [∼600 nm (toluene);
570, 620 nm (2-MeTHF); 605, 710 nm (CH3CN)] are
seen in all solvents. Similarly, 3 also exhibits multiple
structured emissions with several maxima (λmax 478-
550 nm) and low energy features [∼590 max, ∼610 nm
(toluene and 2-MeTHF); 590, 690 nm (CH3CN)], which
are found to be predominant in the most polar solvent
(CH3CN).
1
Information, Figure S9), in addition to the ππ* fluores-
cence (λmax 350 nm, λexc < 320 nm) and the structured
band associated with the monomer (474-490 nm), two
new bands centered at about 440 nm and at 550 nm,
respectively. The unstructured band at 440 nm, which is
related to an excitation maximum at 370 nm and a
shoulder at about 350 nm, is tentatively ascribed, as in
[Pt(bzq)(CNR)2]Q,31 to excimer fluorescence. However,
the excitation profile of the low-energy emission (550 nm)
differs from that of the monomer emission, suggesting that
this likely results from intermolecular π π aggregation.
3 3 3
Investigation of the dependence of the emission lifetime
(τobs) on the concentration for 2 and 3 indicates that the
lifetimes decrease slightly in the 10-5 to 2 ꢀ 10-4 range
from 0.16 to 0.14 μs for 2 and 0.14 to 0.12 μs for 3
(Supporting Information, Figure S10). The estimated
values of τ0 [160 ns (2) and 137 ns (3)] and the self-
quenching constants [6.2 ꢀ 109 M-1 s-1 (2) and 4.23 ꢀ
109 M-1 s-1 (3)] obtained from extrapolation of the
ꢀ
(83) Kim, D.; Bredas, J. L. J. Am. Chem. Soc. 2009, 131, 11371.
(84) The concentration dependence was expressed by the formula 1/τobs
=
(86) Connick, W. B.; Geiger, D.; Eisenberg, R. Inorg. Chem. 1999, 38,
3264.
(87) Guo, F.; Sun, W.; Liu, Y.; Schanze, K. Inorg. Chem. 2005, 44, 4055.
(88) Williams, J. A. G.; Beeby, A.; Davies, E. S.; Weinstein, J. A.; Wilson,
C. Inorg. Chem. 2003, 42, 8609.
1/τ0 þ KQ[Pt], where τ0 is the lifetime at infinite dilution and KQ corresponds to
the self-quenching constant.
(85) Farley, S. J.; Rochester, D. L.; Thompson, A. L.; Howard, J. A. K.;
Williams, J. A. G. Inorg. Chem. 2005, 44, 9690.

Article
TD-DFT Calculations. To further understand the low
Inorganic Chemistry, Vol. 49, No. 7, 2010 3249
Table 3. Composition (%) of Frontier MOs in the Ground State for 1-3 in
CH2Cl2 Solution
energy absorption and emission characters of these com-
plexes in CH2Cl2, a theoretical investigation was under-
taken using the Time-Dependent Density Functional
Theory (TD-DFT). Complexes 1-3 were first fully opti-
mized in the gas phase using the B3LYP method with the
LanL2DZ basis set for Pt and the 6-31G(d,p) basis set
for the ligand atoms. The optimized S0 structures are
depicted in Supporting Information, Figures S14-S16,
the optimized coordinates for S0 state in Supporting
Information, Tables S3, S5, and S7, and the main geo-
metrical parameters, which are comparable to experi-
mental values, are tabulated in Supporting Information,
Table S9. The absorption spectra in CH2Cl2 solution for
1-3 were explored using the polarizable continuum
model, in which the solvent is simulated as a continuum
of uniform dielectric ε. The corresponding molecular
orbitals (electronic density diagrams) involved in the
main excited states have been drawn in Supporting
Information, Figures S17-S19, and their relative com-
position in terms of composing fragments are reported in
Table 3. The main conclusion of the frontier orbitals
analysis is that the contribution of the CNR ligands
increases on going from 1 to 3 as the π-conjugation of
the R group increases. Thus, the highest occupied mole-
cular orbitals (HOMOs, Figure 7d-f) are of π*{dπ(Pt)-
π*(bzq)-p(Cl)} character deriving from a similar config-
uration of the Pt center (∼20%), bzq ligand (∼72%) and
Cl- (∼8%) in the three complexes. However, whereas the
H-1 is also mainly localized on the bzq (90%) in 1, the
participation of the isocyanide ligand increases in 2 (21%
CN-Xyl), being clearly predominant in 3 (93% CN-2-
Np). With respect to the lowest unoccupied molecular
orbitals (LUMOs), they are composed of the bzq ligand
(90% 1, 81% 2; 63% 3) with a small contribution of Pt
(dπ) (5% 1; 6% 2; 7% 3) and isocyanide ligand, which
increases from 1 (4%) to 3 (29%). The Lþ1 is similar to
LUMO in 1, but for 2 and 3, the contribution of the
isocyanide ligand is still higher (29% CN-Xyl 2; 57% CN-
2-Np 3). Supporting Information, Table S10 shows the
calculated excited states in CH2Cl2 solution (first singlets)
with the oscillator strengths and the transitions with the
greatest contributions. Figure 7a-c depicts the selected
allowed transitions as bars with the experimentally mea-
sured absorptions spectra in CH2Cl2. As seen in Support-
ing Information, Table S10, the dipole-allowed lowest-
lying absorptions are at 391, 395, and 400 nm for 1, 2,
and 3, respectively, which reproduce, with some blue
shifts, the trend observed in the experimental spectra
(∼410 1, 412 2, 414 nm 3). The major contribution to this
band is the HOMOfLUMO transition (95% 1; 93% 2, 3);
therefore, the lowest-lying absorption is attributed to
the combined transitions of 1ILCT and 1MLCT/1ML0CT
(L = bzq; L0 = CNR), with this latter increasing from 1
to 3. Calculations indicate that there is considerable
orbital mixing for the rest of the transitions located at
higher energies (λ < 300 nm). A plausible assignment for
the remaining calculated transitions, taking into account
the nature of the orbitals involved, is included in the
Supporting Information, Table S10.
1
2
3
MO
CN-tBu Pt bzq Cl CN-Xyl Pt bzq Cl CN-Np Pt bzq Cl
Lþ3
Lþ2
Lþ1
LUMO
HOMO
H-1
18
20
2
46 27
15 64
8
0
0
0
8
1
1
24
49
29
13
0
35 36
6
0
0
0
7
1
1
2
5
84
17
57
29
0
3
3
4
7
13
80
40
63
0
0
0
0
7
0
1
1
0
4
7
6
47
64
81
6
5
92
90
4
0
21 71
20 72
13 65
64 17
39 21
20 73
5
1
7
93
90
6
21
18
93
12
0
2
H-2
H-3
0
7
80
6
0
21 49 29 38
22 71 92
57 25
92
9
H-4
H-5
2
13
5
2
1
76
2
15
4
2
22 46 30
23 46 30
Tables S4, S6, and S8). For comparison with S0, the
structural results are presented in Supporting Informa-
tion, Table S9. According to TD-DFT calculations, the
lowest-energy emissions in CH2Cl2 solution are rather
similarfor the three complexes (533 1, 534 2, and 532 nm 3),
which are slightly red-shifted in relation to those experi-
mentally observed (λem 473 1, 473 2, and 475 nm 3). A first
approach is that the lowest energy phosphorescent emis-
sion arises from the singly occupied molecular orbital
(SOMO) to the SOMO-1. Inspection of the two SOMOs
of the T1 reveals that the SOMO-1 is similar in the three
complexes and resembles the HOMO of the ground state,
being mainly contributed from the bzq and d(Pt) compo-
nents (81% bzq, 16% Pt, 3% Cl). The initial orbital
(SOMOs) is mainly localized on the bzq ligand (89% 1,
86% 2, 83% 3) with small contribution of Pt (7%) and the
isocyanide ligand (3% 1, 7% 2, 9% 3). Although the
contribution of the CNR ligand decreases in relation to
the LUMOs in the ground state, its participation in the
remaining minor contributions to the lowest phosphores-
cent emission also increases from the tert-butyl (1) to the
naphthylisocyanide (3) derivative. This fact is also illu-
strated on the more rigorous diagrams of the single-elec-
tron transitions, based on the TD-DFT calculation, which
are collected in Supporting Information, Figures S20-S22.
On the basis of these results, the phosphorescent emission
3
in CH2Cl2 solution for 1-3 has mainly ILCT character
located on the cyclometalated ligand perturbed by metal to
ligand charge transfer MLCT/3ML0CT (L = bzq; L0 =
CNR) with the contribution of the isocyanide increasing
3
from 1 (CNtBu) to 3 (CN-2-Np).
Conclusion
A new family of isocyanide-cyclometalated platinum com-
plexes 1-3 has been prepared and structurally and photo-
physically characterized. This study shows that the tert-
butylisocyanide complex 1 co-crystallizes in two pseudopo-
lymorphs: a red form [1 CHCl3]¥, which possesses an infinite
1-D chain network and a yellow form generated by discrete
dimers [1 H2O]2. Curiously, although both forms are stabi-
lized by interplanar π π and short Pt Pt bonding inter-
actions, only the extended red form [1 CHCl3]¥ shows the
3
3
3 3 3
3 3 3
3
characteristic low energy absorption (560 nm) and emission
features (672 nm, 298 K; 744 nm 77 K), typical of mixed
MMCT [d(σ*)fp(σ)] and MMLCT [dσ*(M2)fσ(π*)(bzq)]
The nature of the low-lying phosphorescent emissions
for 1-3 in CH2Cl2 was also addressed by optimization
of the first triplet state (T1) (Supporting Information,
transitions. Crystalline state [1 CHCl3]¥ is unstable in the
air, likely because of the loss of CHCl3 solvent, evolving
irreversibly to an orange-ochre solid, whose photophysical
3

3250 Inorganic Chemistry, Vol. 49, No. 7, 2010
Dıez et al.
properties are similar to those of the crude solid 1. The
molecules in [Pt(bzq)Cl(CN-Xyl)] 2 and [Pt(bzq)Cl(CN-
2-Np)] 3 arrange in π π (bzq) (2) and Pt Pt (3)
contacting dimers, which are found to exhibit typical
mononuclear 3LC/3MLCT emissions. Interestingly, the
yellow derivative 3 was found to be generated through
the garnet-red salt isomer [Pt(bzq)Cl2][Pt(bzq)(CN-2-Np)2] 4,
which displays a low energy emission arising from a
3MMLCT excited state.
Reaction of [Pt(bzq)(μ-Cl)]2 and CN-2-Np. Synthesis of
[Pt(bzq)Cl(CN-2-Np)] (3) and [Pt(bzq)Cl2][Pt(bzq)(CN-2-Np)2]
(4). To a yellow suspension of [{Pt(bzq)(μ-Cl)}2] (0.100 g, 0.122
mmol) in CH2Cl2 (15 mL), CN-2-Np (0.037 g, 0.244 mmol) was
added, and a red solution was obtained. After 1 h of stirring, the
solvent was evaporated to 2 mL, and the addition of 5 mL of
acetone resulted in the precipitation of a garnet-red solid,
identified as a mixture of 3 and 4 (∼ratio 1:1). The mixture
was heated at 150 ꢀC for 1 h, and 3 was obtained as a yellow solid
(0.070 g, 51%).
3 3 3
3 3 3
The solution (CH2Cl2) absorption and emission properties
of 1-3 were reasonably elucidated and well supported by
TD-DFT calculations. The low energy absorption bands are
assigned to an admixture of intraligand πfπ* (bzq) (IL) and
metal-to-ligand [dπ(Pt)fπ*(bzq)] MLCT and [dπ(Pt)f
π*(CNR)] ML0CT transitions, with the metal-isocyanide
chargetransfer growing from 1 to 3. In fluid dilutedsolutions,
these complexes display both intraligand (bzq) fluorescence
and monomer phosphorescence. Their phosphorescence ori-
ginates from mixed intraligand charge transfer on the cyclo-
Synthesis of [Pt(bzq)Cl2][Pt(bzq)(CN-2-Np)2] (4). [Pt(bzq)-
(CN-2-Np)2]PF6 (0.049 g, 0.059 mmol) was added over a yellow
suspension of NBu4[Pt(bzq)Cl2] (0.040 g, 0.059 mmol) in acet-
one (15 mL), and a red suspension was immediately obtained.
After 1 min of stirring, the suspension was filtered, and 4 was
obtained as a garnet-red solid (0.056 g, 84%).
Computational Details. The computational method used was
DFT with the B3LYP exchange-correlation functional,89-91
using the Gaussian 0392 program package. The basis set used
was the LanL2DZ effective core potential for the platinum
atom, and 6-31G(d,p) for the remaining atoms. TD-DFT
calculations were carried out combined with the conductor-like
polarizable continuum model approach (CPCM) implemented
in the Gaussian 03 software to study the nature of the singlet-
singlet transitions in the absorption spectra of 1-3 (CH2Cl2 as
solvent). The unrestricted (U)B3LYP was used to optimize the
low-lying triplet states of all the complexes for the investigation
of the nature of the emission states. The vertical emission
transitions were calculated also with a TD-DFT/CPCM ap-
proach with the model optimized for the T1 state and CH2Cl2 as
solvent. All the geometry optimizations were carried out with no
symmetry constraint.
3
metalated ligand ILCT [πfπ* (bzq)] and metal-to-ligand
(L = bzq, L0 = CNR) charge transfer excited states
(3MLCT/3ML0CT) with the Ptfisocyanide CT contribution
increasing from 1 to 3. Low-energy emissions due to excimer
formation and/or ground-state aggregates occur in concen-
trated (>10-4 M) solutions for 2 and 3 and for all complexes
in glass state (77 K) not only in CH2Cl2 but also in other
solvents (Toluene, 2-MeTHF, CH3CN), probably facilitated
by the presence of aromatic groups and/or Pt(II) Pt(II)
3 3 3
interactions as well as by their relatively long lifetimes.
Excimeric emission occurs around 560-580 nm, even in
diluted glasses, whereas emission from aggregates appears
at longer wavelengths in the order 640 nm tBu 1 > 685 nm
Xyl 2 > 706 nm Np 3, and is predominant in concentrated
(10-3 M) solutions.
X-ray Structure Analysis of [1 0.5H2O]2, [1 CHCl3]¥, 2, and
[3 CH2Cl2]2. Table 4 reports details of the structural analyses
3
3
3
for all complexes. Yellow ([1 0.5H2O]2, 2, [3 CH2Cl2]2) or
3
3
red ([1 CHCl3]¥) crystals were obtained by slow diffusion of
3
n-hexane into a CH2Cl2 ([1 0.5H2O]2, 2, [3 CH2Cl2]2) or CHCl3
([1 CHCl3]¥) solution of each compound at low tempera-
ture (-30 ꢀC). For complex [1]2, two molecules of H2O, for
complex [1]¥ one of CHCl3 and for complex [3 CH2Cl2]2 one
molecule of CH2Cl2 were found in the asymmetric unit ([1]2, 0.5
molecules of H2O and [3 CH2Cl2]2, 0.5 molecules of CH2Cl2 per
each molecule of the compound). X-ray data were collected with
3
3
3
These results demonstrate the impact of the electronic
effects and steric requirements of the CNR ligand, not only
in the formation of complexes 1-4 but also in their crystal
3
packing through short or long-range Pt Pt and/or π
π
3
3 3 3
3 3 3
interactions, which have a remarkable role in their photo-
physical properties. The judicious selection of the CNR
ligands, in which the R substituent can be widely modified,
could readily lead to remarkable tuning of their structural
and photophysical properties.
a NONIUS-κCCD area-detector ([1 0.5H2O]2, [1 CHCl3]¥, 2)
or a Bruker Smart CCD ([3 CH2Cl2]2) diffractometer, using
3
3
3
graphite-monochromated Mo-KR radiation (λ = 0.71073 A).
Images were processed using the DENZO and SCALEPACK
software93 for [1 0.5H2O]2, [1 CHCl3]¥, and 2 (carrying out
3
3
the absorption correction at this point for complex 2) or the
SAINT package for [3 CH2Cl2]2. The absorption correction
Experimental Section
3
was performed using MULTISCAN94 ([1 0.5H2O]2), XABS295
Instrumentation methods used for characterization of
the newly prepared platinum(II) complexes, photophysical
and spectroscopic studies together with the characterization
data for compounds 1-4 are described in the Supporting
Information.
3
([1 CHCl3]¥), or SADABS96 ([3 CH2Cl2]2). The structures were
solved by Patterson and Fourier methods using the DIRDIF92
3
3
program97 ([1 0.5H2O]2) or Direct Methods ([1 CHCl3]¥, 2,
3
3
Synthesis of [Pt(bzq)Cl(CN-tBu)] (1). CNtBu (28 μL, 0.244
mmol) was added to a yellow suspension of [{Pt(bzq)(μ-Cl)}2]
(0.100 g, 0.122 mmol) in CH2Cl2 (15 mL) to give an orange
solution. After stirring at room temperature for 5 min, the
solvent was evaporated to 1 mL, and n-hexane (2 mL) was
added. By cooling at -30 ꢀC, 1 precipitated as an orange solid
(0.084 g, 70%). In some cases, the product obtained was not
pure, and it was recrystallized from CHCl3/n-hexane at -30 ꢀC.
Synthesis of [Pt(bzq)Cl(CN-Xyl)] (2). To a yellow suspension
of [{Pt(bzq)(μ-Cl)}2] (0.100 g, 0.122 mmol) in CH2Cl2 (15 mL),
CN-Xyl (0.032 g, 0.244 mmol) was added, to immediately give
an orange solution. After 1 h of stirring, the solvent was
removed in vacuo to 2 mL causing the precipitation of 2 as a
yellow solid (0.082 g, 62%).
(89) Becke, A. D. Phys. Rev. A: At., Mol., Opt. Phys. 1988, 38, 3098.
(90) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B: Condens. Matter Mater.
Phys. 1988, 37, 785.
(91) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
(92) Frisch, M. J.; et al, Gaussian, Inc.: Wallingford, CT, 2004 (see
Supporting Information for complete citation).
(93) Otwinowski, Z.; Minor, W. In Methods in Enzymology; Carter, C. V.,
Jr., Sweet, R. M., Eds.; Academic Press: New York, 1997; Vol. 276A, p 307.
(94) Blessing, R. H. Acta Crystallogr. 1995, A51, 33.
(95) Parkin, I. P.; Slawin, A. M. Z.; Williams, D. J.; Woolins, J. D. Inorg.
Chim. Acta 1990, 172, 159.
(96) Sheldrick, G. M. SHELXL-97, a program for crystal structure
€
€
determination; University of Gottingen, Gottingen, Germany, 1997.
(97) Beursken, P. T.; Beursken, G.; Bosman, W. P.; de Gelder, R.; Garcı
´
a-
Granda, S.; Gould, R. O.; Smith, J. M. M.; Smykalla, C. The DIRDIF92
program system; University of Nijmegen: The Netherlands, 1992.

Article
Inorganic Chemistry, Vol. 49, No. 7, 2010 3251
Table 4. Crystal Data and Structure Refinement Parameters for Complexes [1 0.5H2O]2, [1 CHCl3]¥, 2, and [3 CH2Cl2]2
3
3
3
[1 0.5H2O]2
3
[1 CHCl3]¥
2
[3 CH2Cl2]2
3
3
empirical formula
formula weight
temperature (K)
wavelength (A)
crystal system
space group
crystal dimensions (mm)
a (A)
C18H17ClN2O0.5Pt
499.88
173(1)
C19H18Cl4N2Pt
611.24
173(1)
C22H17ClN2Pt
539.92
173(1)
C49H32Cl4N4Pt2
1208.77
100(2)
0.71073
triclinic
P1
0.71073
orthorhombic
Im2a
0.71073
monoclinic
P21/c
0.71073
monoclinic
P21/c
0.325 ꢀ 0.25 ꢀ 0.25
13.7227(4)
13.7343(3)
18.1103(5)
94.668(2)
92.7050(10)
90.712(2)
3397.71(16)
1.954
0.20 ꢀ 0.175 ꢀ 0.05
6.6792(4)
13.2361(6)
22.9268(13)
90
0.175 ꢀ 0.175 ꢀ 0.025
15.5637(59
7.5684(3)
17.1981(6)
90
0.29 ꢀ 0.28 ꢀ 0.21
14.447(3)
19.399(4)
15.120(3)
90
b (A)
c (A)
R (deg)
β (deg)
90
90
115.541(2)
90
105.974(4)
90
γ (deg)
V (A3)
2026.88(19)
2.003
1827.84(11)
1.962
4073.5(16)
1.971
D
calc (Mg/m3)
Z value
8
8.418
1904
4
7.456
1168
4
7.830
1032
4
7.166
2312
μ(Mo KR) (mm-1
F(000)
)
θ range (deg)
no. of reflns measd
1.13 to 27.48
52887
12789
3.55 to 27.48
2516
2420
2.96 to 27.49
4188
3304
1.75 to 25.02
19465
4633
no. of obsd reflns
Goodness of fit on F2a
final R indices [I > 2σ(I)]a
R indices (all data)
1.096
1.080
1.043
1.019
R1 = 0.0503, wR2 = 0.1199 R1 = 0.0327, wR2 = 0.0779 R1 = 0.0326, wR2 = 0.0615 R1 = 0.0529, wR2 = 0.1398
R1 = 0.0647, wR2 = 0.1295 R1 = 0.0360, wR2 = 0.0807 R1 = 0.0525, wR2 = 0.0698 R1 = 0.0855, wR2 = 0.1613
0.558(14)
absolute structure parameter
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(Fo2) þ (g1P)2 þ
g2P]-1; P = [max(Fo2;0) þ 2Fc2]/3.
[3 CH2Cl2]2) and refined by full-matrix least-squares on F2 with
298 K in different solvents (Table S1). UV-vis absorption
spectra of 3 in different solvents and in different concentrations
(Figure S2a-d). Emission data for 1-3 in toluene, 2-MeTHF
and CH3CN (5 ꢀ 10-5 M solutions at 298 K) (Table S2).
Absorption spectra calculated from the reflectance spectra for
2-4 (Figure S3). Time-resolved emission profiles for [1]2 in solid
state at 77 K (Figure S4). Excitation and emission spectra in the
solid state at 298 K and at 77 K of 2 (Figure S5) and of 4 (Figure
3
SHELXL-97.98 The hydrogen atoms were constrained to idea-
lized geometries and assigned isotropic displacement para-
meters equal to 1.2 times the Uiso values of their respective
attached carbon for the aromatic and CH2 hydrogen atoms and
that of 1.5 for the methyl groups. Complex [1 CHCl3]¥ crystal-
3
lizes in the non-centrosymmetric, polar, and achiral space group
Im2a. The absolute structure parameter (0.558(14); 0.442 in-
verse configuration) shows that the crystal chosen for this
analysis is an inversion twin. Thermal parameters of C17 were
fixed as the average between its own parameters and those
of C16 ones. To establish the identities of the N and metalated
C atoms of the 7,8-benzoquinolinate ligand, the structures
S6). Time resolved emission profiles of 2 in CH2Cl2 5 ꢀ 10-5
M
at 298 K (Figure S7). Excitation and emission spectra in CH2Cl2
10-3 M at 298 K of 2 (Figure S8) and of 3 (Figure S9). Plots of
the measurement luminescence decay constants versus concen-
tration of 2 and 3 (Figure S10). Emission spectra in CH2Cl2 5 ꢀ
10-5 M at 77 K of 1-3 (Figure S11) and of 2 at different
of [1 CHCl3]¥ and 2 were refined in 3 different ways (with the
3
identities of the C and N of the ligand in one position, with the
element types reversed, and with 50/50 hybrid scattering factor
at each of the atomics sites). Examination of the ΔMSDA values
for bonds involving theses atoms99,100 revealed the assignment
with the N atom trans to the isocyanide ligands. Final difference
electron density maps showed some peaks above 1 e A-3
for [1 0.5H2O]2, [1 CHCl3]¥, and [3 CH2Cl2]2, most of them
in the close vicinity of the Pt atoms or the solvent, with no
chemical meaning.
wavelengths (Figure S12). Emission spectra in CH2Cl2 10-3
M
at 77 K of 1-3 (Figure S13). Drawings and Tables of DFT
optimized atomic coordinates for ground state (S0) of the
optimized structures of 1-3 (Figures S14-S16 and Tables S3,
S5 and S7). DFT optimized atomic coordinates for T1 state of
1-3 (Tables S4, S6, and S8). Table of geometrical parameters of
the optimized structures of 1-3 (Table S9). Representative
frontier orbitals for 1-3 (Figures S17-S19). Selected low-lying
singlet excited states (Sn) computed by TD-DFT/CPCM
(CH2Cl2) for 1-3 with the orbitals involved, vertical excitation
energies and assignments (Table S10). Diagrams of the single-
electron transitions according to TD-DFT calculations (CH2Cl2)
for the lowest-energy emissions for 1-3 (Figures S20-S22).
Instrumentation methods used for characterization of the newly
prepared platinum(II) complexes, photophysical and spectro-
scopic studies, and characterization data of 1-4. Crystallo-
graphic data in CIF format. This material is available free of
charge via the Internet at http://pubs.acs.org.
3
3
3
Acknowledgment. This work was supported by the Spanish
MICINN (Projects CTQ2008-06669-C02-01,02/BQU and
CTQ2008-03860/BQU and a grant for A. Dıez).
´
Supporting Information Available: Control by 1H NMR
spectroscopy of 4 to 3 (Figure S1). Absorption data for 1-4 at
(98) Sheldrick, G. M. SHELX-97 a program for the refinement of crystal
€
€
structures; University of Gottingen: Gottingen, Germany, 1997.
(99) Speck, A. L. Acta Crystallogr. 1990, A46, C.
(100) Hirshfeld, F. Acta Crystallogr., Sect. A 1976, 32, 239.