Synthesis and luminescence of cyclometalated compounds with nitrile and isocyanide ligandst

Article abstract of DOI:10.1021/om800845c

Mononuclear cationic cyclometalated palladium complexes [Pd(CΛN)(NCMe)₂]C1O₄ [CΛN = benzo-quinolinate (bzq) 1, 2-phenylpyridinate (ppy) 2], analogous to the previously described platinum complexes [Pt(CΛN)(NCMe) ₂]C1O

Full text of DOI:10.1021/om800845c

Organometallics 2009, 28, 1705–1718
1705
Synthesis and Luminescence of Cyclometalated Compounds with
Nitrile and Isocyanide Ligands†
‡
§
§
,‡
§
´
Alvaro D´ıez, Juan Fornie´s, Sara Fuertes, Elena Lalinde,* Carmen Larraz,
Jose´ A. Lo´pez,§ Antonio Mart´ın,§ M. Teresa Moreno,‡ and Violeta Sicilia*,
Departamento de Qu´ımica, Grupo de S´ıntesis Qu´ımica de La Rioja, UA-CSIC, UniVersidad de La Rioja,
26006, Logron˜o, Spain, Departamento de Qu´ımica Inorga´nica, Instituto de Ciencia de Materiales de
Arago´n, Facultad de Ciencias, UniVersidad de Zaragoza-CSIC, Plaza. S. Francisco s/n 50009 Zaragoza,
Spain, and Departamento de Qu´ımica Inorga´nica, Instituto de Ciencia de Materiales de Arago´n, Escuela
UniVersitaria de Ingenier´ıa Te´cnica Industrial, UniVersidad de Zaragoza-CSIC, Campus UniVersitario del
Actur, Edificio Torres QueVedo, 50018, Zaragoza, Spain
ReceiVed September 1, 2008
Mononuclear cationic cyclometalated palladium complexes [Pd(C∧N)(NCMe)2]ClO4 [C∧N ) benzo-
quinolinate (bzq) 1, 2-phenylpyridinate (ppy) 2], analogous to the previously described platinum complexes
[Pt(C∧N)(NCMe)2]ClO4 [C∧N ) bzq 3, ppy 4], and the isocyanide platinum benzoquinolinate
[Pt(bzq)(CNR)2]X (R ) tert-butyl (t-Bu, 5), 2,6-dimethylphenyl (Xyl, 6), 2-naphthyl (2-Np, 7); X )
-
-
ClO4 a, PF6 b) have been prepared and characterized. The solid-state structures of the cation
[Pt(C∧N)(CN-Xyl)2]+ with different counteranions (6a and 6b) were found to be different in terms of
packing, although in both cases they were dominated by π-π intermolecular interactions. The influence
of the counteranion in the UV-vis spectra, both in solution and in the solid state of 5-7, is negligible.
Time-dependent density-functional theory calculations on cation [Pt(C∧N)(CN-Xyl)2]+ (6+) have been
1
1
performed, suggesting that the lowest absorption is IL in nature mixed with some MLCT character.
Acetonitrile platinum complexes (3, 4) are photoluminescent at low temperature (77 K) and at room
temperature, whereas analogous palladium complexes (1, 2) are emissive only at 77 K (solid-state and
glassy acetonitrile). Isocyanide derivatives 5-7 are intensely luminescent in all media. The emissions
are assigned to ligand-centered fluorescence, to mixed 3LC/3MLCT phosphorescence, or to excimeric (or
3
3
ground-state) ππ* or MMLCT [σ*(M)fπ*(C∧N)] transitions depending on the medium and the
excitation wavelength. The effect of the counteranion in governing the degree of aggregation and the
extent of the interactions seem to be relatively important, especially in a rigid medium, with the smaller
-
ClO4 inducing a more excimeric character. The tendency to form π-π excimers and/or Pt · · · Pt
-
-
oligomerization follows the order CN-2-Np > CN-t-Bu > CN-Xyl and ClO4 > PF6 .
applied as phosphorescent dopants in the fabrication of highly
efficient organic light-emitting devices (OLEDs).26-28 Com-
pared to analogous Pt(II) luminophores, luminescent cyclopal-
ladated complexes are rare, and with very few exceptions,29-31
most systems emit only at low temperatures and with low
Introduction
Platinum cyclometalated complexes have received consider-
able attention in recent years because of their interesting
photochemical and photophysical properties such as good
stability, high photoluminescence quantum yields, short triplet-
state lifetimes (several microseconds), and ease of spectral
tuning.1-25 Many of these complexes have been successfully
(7) He, Z.; Wong, W. Y.; Yu, X.; Kwok, H. S.; Lin, Z. Inorg. Chem.
2006, 45, 10922.
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Weinstein, J. A. Inorg. Chem. 2006, 45, 9410.
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(12) Jude, H.; Krause Bauer, J. A.; Connick, W. B. Inorg. Chem. 2005,
44, 1211.
† Dedicated to Professor Antonio Laguna on the occasion of his 60th
anniversary.
* Corresponding authors. E-mail: forniesj@unizar.es. Fax: (+34)976-
761159. E-mail: elena.lalinde@dq.unirioja.es. Fax: (+34)941-299621. E-
mail: sicilia@unizar.es. Fax: (+34)976-762189.
‡ Universidad de La Rioja, UA-CSIC.
§ Facultad de Ciencias, Universidad de Zaragoza-CSIC.
Escuela Universitaria de Ingenier´ıa Te´cnica Industrial, Universidad de
Zaragoza-CSIC.
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10.1021/om800845c CCC: $40.75
2009 American Chemical Society
Publication on Web 02/17/2009

1706 Organometallics, Vol. 28, No. 6, 2009
D´ıez et al.
efficiency.32-38 Emission of isolated Pt(II) cyclometalated
complexes is typically assigned to ligand-centered (LC) and/or
metal-to-ligand charge transfer (MLCT) states. In addition, the
square-planar structure of Pt(II) complexes gives rise to the
possibility of ground- and excited-state interactions including
aggregation and excimer or exciplex formation,4,6,13,15,16,39
depending on the concentration and proximity of the molecules,
leading to marked red shifts relative to the mononuclear emission
spectra. These transitions are assigned to metal-metal-to-ligand
charge transfer (MLCT) or excimeric ligand-to-ligand charge
transfer. In addition, some investigations have shown that the
color and emissive properties of crystalline Pt(II) bipyridyl,
terpyridyl, or cyclometalated salts are highly dependent upon
the chosen counterion for crystallization,40-45 and differences
in the extent of π-π and/or Pt · · · Pt interactions are usually
invoked to explain the phenomena.
Thus, photoluminescence-tuning Pt(II) complexes from near-
UV to deep red have been reported. There are two alternatives
for tuning emission in isolated complexes: modification of the
cyclometalating ring system or variation of the ancillary ligands.
Our research group has used both methodologies. We have
reported efficient color tuning by employing heteroleptic Pt(II)
complexes with one bidentate cyclometalating ligand (benzo-
quinolinate ligand) and monodentate ancillary ligands such as
phosphine,17 alkynylphosphine,17 alkynyl,46 or cyanide ligands47
incorporating substituents with different electronic behavior.
Furthermore, we have employed a terdentate ligand [C∧N∧C
(HC∧N∧C ) 2,6-diphenylpyridine)] introducing alkynyl, CN,
S-2py, or CH2COCH3 anionic groups into the fourth site.4
In this report, we describe the synthesis, structure, and
photophysical properties of C∧N coordinated palladium and
platinum complexes [C∧N ) benzoquinolinate (bzq), 2-phe-
nylpyridinate (ppy)] incorporating monodentate ligands with
different electron-withdrawing/donating properties. For com-
parative purposes, we have chosen groups isoelectronic to the
previously studied anionic alkynyl ligands: a weak-field ligand
as the acetonitrile (NCMe) molecule and strong-field ligands
as isocyanide groups (CNR; R ) t-Bu, Xyl, 2-Np). In recent
years, several platinum(II) and palladium(II) complexes based
on nitrile44,48,49 or isocyanide39,50-55 ligands have attracted a
great deal of interest as components in luminescent chro-
mophores. The behavior, as sensors, of the Magnus-type double-
salts [Pt(CNR)4][Pt(CN)4] (R ) alkyl, aryl)50,56-61 or mixed
compounds [cis-Pt(CN)2(CNR)2]50,54 originated by thermal
reorganization of the corresponding double salts is noteworthy.
The recent studies on [cis-Pt(CN)2(CN-t-Bu)2] showing the
formation of very luminescent 1D nanomaterials62 are of great
interest.
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Results and Discussion
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Luminescence of Cyclometalated Compounds
Organometallics, Vol. 28, No. 6, 2009 1707
Scheme 1
corresponding CNR ligands in methanol affords the perchlorate
salts [Pt(bzq)(CNR)2]ClO4 [R ) t-Bu (5a), Xyl (6a), 2-Np (7a)]
in very high yield (>90%). By contrast, compounds
[Pt(bzq)(CNR)2]PF6 [R ) t-Bu (5b), Xyl (6b), 2-Np (7b)] were
prepared in a one-pot reaction by treatment of [{Pt(C∧N)(µ-
Cl)}2] (A) with 4 equiv of CNR and 2 equiv of NaPF6 in
acetone. All of these compounds were isolated with a similar
appearance of yellow solids that were air stable for long periods
(months). All compounds have been fully characterized both
in the solid state and in solution (see Experimental Section).
They show the expected [Pt(bzq)(CNR)2]+ peak (100%), and
their conductivity measurements (nitromethane or acetonitrile)
confirm their behavior as 1:1 electrolytes.64 The proton NMR
1
spectra (assigned on the basis of H-1H COSY experiments)
do not vary significantly with the anion and exhibit the expected
Scheme 2. Numerical Scheme for NMR Purposes
3
signals for the bzq and CNR ligands. The JPt-H2 values for
compounds 5-7 [34.5-37.8 Hz] are smaller than that found in
compound [Pt(bzq)(NCMe)2]ClO4 (3) (46 Hz), in agreement
with the stronger trans influence of C (CNR) with respect to N
(NCMe).70 Well-resolved 13C{1H} NMR spectra are also
observed for complexes 5b and 6b (except for the Pt-CNR
resonance; see Experimental Section for details). The 195Pt NMR
nucleus for the tert-butyl isocyanide derivative 5b (δ -4246)
is slightly more shielded in relation to the CN-Xyl derivative
(δ -4168 6b), a feature that could be related to the presence of
the electron-withdrawing xylyl ring in 6b. The IR spectra show
two absorptions at about 2200 cm-1 due to ν(CtN), which
appear, as expected, shifted to higher frequencies with respect
to the corresponding free ligands (CN-t-Bu: 2125 cm-1, CN-
Xyl: 2131 cm-1, CN-2-Np: 2123 cm-1) similar to that reported
for complexes with terminal isocyanide ligands.39,50-52,54,61,71,72
Single crystals of compounds 6a and 6b were obtained and
studied by X-ray crystallography (Figures 1 and 2). Selected
bond parameters are given in Table 1. In both cations, the
platinum(II) center exhibits a distorted square-planar environ-
ment due to the small bite angle of the cyclometalated ligand
(bzq) [81.57(9)° in 6a and 81.37(8)° in 6b]. This angle and the
(B), ppy (D)] with AgClO4 in a 1:2 molar ratio in MeCN. After
removing the AgCl, both compounds were obtained from their
corresponding solutions as white, analytically pure solids (see
Scheme 1, path a, and Experimental Section). Compounds
[Pt(C∧N)(NCMe)2]ClO4 [C∧N ) bzq (3), ppy (4)] were prepared
in the same way as 1 and 2, as reported earlier.47 Conductivity
measurements on 1 and 2 in acetonitrile confirm their behavior
as 1:1 electrolytes.64 Their IR spectra show the expected
absorptions due to the perchlorate (Td) anion65 and the σ-donor
N-coordinated acetonitrile molecules in a cis disposition.66,67
They were characterized by NMR spectroscopy in acetonitrile
solutions (see Scheme 2 and Experimental Section). The correct
assignment of the eight aromatic protons was made on the basis
of 2D NMR 1H-1H COSY experiments. It is worth noting that
both complexes show only one signal at 1.99 ppm (6H) probably
due to the lability of acetonitrile ligands. This fact contrasts
with the two different signals at δ ≈ 1.99 (3 H) and 2.65 (3 H)
observed in the analogous platinum compounds (3 and 4). This
behavior has been previously observed in other related aceto-
nitrile palladium complexes,68 being attributed to the lower
kinetic inertness of palladium(II) complexes with respect to the
platinum ones in substitution processes.69 Compound 3 was used
as a starting material in the synthesis of the isocyanide
derivatives described below.
∧
∧
Pt-NC N and Pt-CC N bond lengths are similar to those observed
for other bzq platinum compounds.17-19,46 Two xylylisocyanide
ligands complete the coordination sphere of platinum(II). The
Pt-CCNXyl bond lengths are comparable to those observed in other
Pt(II) isocyanide complexes,39,50-52,54,62,72-74 the distances trans
∧
to NC N being slightly shorter, in agreement with the smaller trans
influence of the nitrogen atom relative to the metalated carbon atom.
The CN-Xyl ligands are almost linearly coordinated, and the deviation
∧
from ideal angles is highest in the CN-Xyl trans to CC N in 6a. In
both molecules, one of the CN-Xyl groups is not coplanar with the Pt
coordination plane, forming dihedral angles of 70.2° 6a (CN-Xyl trans
∧
∧
to CC N) and 53.0° 6b (CN-Xyl trans to NC N), respectively. In both
complexes, the cations are arranged as head-to-tail dimers through
moderate intermolecular π-π interactions2,6,13,32,39,75-79 between bzq
ligands, which are stronger in 6a (3.30 vs 3.45 Å 6b) (Figures
Synthesis and Characterization of [Pt(bzq)(CNR)2]X [R
) t-Bu, Xyl, 2-Np; X ) ClO4-, PF6-]. The cationic species
[Pt(bzq)(CNR)2]+ were isolated as the ClO4 and PF6 com-
pounds through two different paths (see Scheme 1, paths b and
c, and Experimental Section). Replacement of the acetonitrile
molecules in [Pt(bzq)(NCMe)2]ClO4 3 with 2 equiv of the
-
-
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1708 Organometallics, Vol. 28, No. 6, 2009
D´ıez et al.
Figure 1. (a) Molecular structure of complex [Pt(bzq)(CN-Xyl)2]ClO4 (6a). Ellipsoids are drawn at the 50% probability level. Hydrogen
atoms are omitted for clarity. (b) View of the stacking of the cations showing the π-π interactions.
Figure 2. (a) Molecular structure of complex [Pt(bzq)(CN-Xyl)2]PF6 (6b). Ellipsoids are drawn at the 50% probability level. (b) View of
the stacking of the cations showing the π-π interactions.
1b and 2b). In 6a, neighboring dimers are arranged in such a
way that the xylyl ring of the coplanar group overlaps with one
bzq ligand (3.38 Å). For 6b, the shortest interaction between
dimers is found between the xylyl rings of the isocyanide groups,
which are not coplanar (∼3.63 Å) with the platinum coordina-
tion plane. As is shown in Figure 2a, in this compound (6b),
weak contacts between the anion (PF6-) and the cation are
observed, with the shortest P-F · · · H(bzq) distance found being
ca. 2.28 Å (F · · · H-C 164.1°). Despite the differences reported
in the crystal packing due to the influence of the counteranion,
both crystals have a similar yellow color, in accordance with
the very long Pt · · · Pt distances (4.91(1) Å 6a, 5.47(1) Å 6b).
(78) Houlding, V. H.; Miskowski, V. M. Coord. Chem. ReV. 1991, 111,
145.
(79) Connick, W. B.; Marsh, R. E.; Schaefer, W. P.; Gray, H. B. Inorg.
Chem. 1997, 36, 913.

Luminescence of Cyclometalated Compounds
Organometallics, Vol. 28, No. 6, 2009 1709
Table 1. Selected Bond Lengths [Å] and Angles [deg] for 6a · CH2Cl2
and 6b · CH2Cl2
band with a maximum at 475 nm, assigned to a combination of
1MMLCT [dσ*(Pt) f π*(C∧N)] and π-π* transitions due to
Pt · · · Pt and π-π stacking interactions among monomers.2,6,14,78
We note that the solid-state UV-vis absorptions for complex
[Pt(ppy)(NCMe)2]CF3SO3 have been attributed to ligand-
centered π-π* transitions.82
Due to solubility reasons, the UV-vis spectra of the
isocyanide complexes 5 and 6 have been examined only in
CH2Cl2, DMF, and MeCN and for 7 in DMF and MeCN (see
Table 2). The electronic spectra of these compounds in solution
(∼10-4 M) show no dependence on the counteranion. In
addition, as can be observed in Figure S2a, which includes the
spectra of the perchlorate derivatives (5a-7a) in acetonitrile,
the influence of the corresponding isocyanide substituent in the
low-energy bands is minimal (Table 2), thus suggesting a very
low contribution of the co-ligands on the HOMO. These
absorptions (>350 nm) are conventionally assigned to a spin-
allowed metal-to-ligand charge tranfer 1MLCT [dπ(Pt)fπ*(bzq)]
transition, although, as commented above, a ligand-centered
1LC(bzq) contribution cannot be excluded and overlapping with
spin-forbidden transitions is also possible.
6a · CH2Cl2
6b · CH2Cl2
Pt-C(1)
1.916(3)
2.013(3)
2.034(2)
2.059(2)
1.149(3)
1.400(3)
1.150(3)
1.410(3)
88.20(10)
93.16(10)
97.23(9)
81.57(9)
175.6(2)
171.3(3)
176.6(2)
169.5(2)
1.956(2)
1.970(3)
2.051(2)
2.049(2)
1.149(3)
1.409(3)
1.159(3)
1.399(3)
92.98(9)
91.78(8)
93.87(8)
81.37(8)
174.5(2)
175.4(2)
175.3(2)
179.7(2)
Pt-C(10)
Pt-C(29)
Pt-N(3)
N(1)-C(1)
N(1)-C(2)
N(2)-C(10)
N(2)-C(11)
C(1)-Pt-C(10)
C(1)-Pt-C(29)
C(10)-Pt-N(3)
C(29)-Pt-N(3)
C(1)-N(1)-C(2)
C(10)-N(2)-C(11)
N(1)-C(1)-Pt
N(2)-C(10)-Pt
Absorption Spectra and Theoretical Calculations. Com-
pounds 1-4 show low solubility and stability in common organic
solvents (dichloromethane, acetone, methanol), except in acetoni-
trile, in which the electronic absorption spectra were carried out
(Figure 3, ∼10-4 M; see also Table 2). With reference to previous
assignments in analogous C,N-cyclometalated platinum and pal-
ladium(II) complexes reported earlier,2,4-12,14-25,36,80 the high-
energy intense bands (λ < 325 nm, ε > 104 M-1 cm-1) are assigned
to metal-perturbed, ligand-centered transitions (1LC π-π*)17-20,36
within the bzq or ppy ligands, while the less intense low-energy
absorptions (λ > 325 nm) are tentatively ascribed to a mixture of
spin-allowed metal-to-ligand charge transfer (1MLCT) and ligand-
centered 1LC(bzq) transitions. We note that recent studies on related
anionic compounds such as (NBu4)[Pt(bzq)(CN)2]47 and
(NBu4)[Pt(bzq)(CtCPh)2]46 suggest that the lower energy bands
To shed some light, TD-DFT calculations have been carried
out for cation 6+ using B3LYP hybrid functional theory, which
agree well with the experimental structure (see Figure S3 and
Table S1 for details), the most remarkable difference being that
both Xyl rings are nearly perpendicular to the platinum
coordination plane. The molecular orbitals involved in the main
excited states have been drawn in Figure S4, and the relative
compositions of the different energy levels in terms of compos-
ing fragments are reported in Table 3. As can be seen in Figure
4a and Table 3, the HOMO is primarily composed of the bzq
ligand (93%) with some contribution of the Pt center, while
the LUMO consists mainly of the bzq ligand (72%) with some
contribution of Pt(5dπ) (12%) and CN-Xyl ligand (16%)
orbitals. The calculated excited states in acetonitrile solution
(the first eight singlets and four triplets) are listed in Table S2,
and the selected allowed transitions are shown (bars) together
with experimental absorption maxima in Figure 4b. Calculations
indicate that there is a considerable orbital mixing for the
transitions, and only a maximum at 384 nm is predicted, which
agree roughly with the observed low-energy maximum (∼398
nm 6b). The major contribution to this band (∼90%) involves
the HOMOfLUMO transition, suggesting a remarkable ligand-
1
1
are described as a mixture of MLCT/1LC or MLCT/1LL′CT
1
transitions, respectively. In agreement with the partial MLCT
character associated with these transitions,17,30,33,81 a remarkable
blue shift is observed in the palladium complexes (1 and 2) in
comparison to those of the analogous platinum ones (3 and 4). As
shown in Figure 3, the lowest energy band in the benzoquinolinate
complexes 1 and 3 is bathochromically shifted in relation to that
of 2 and 4 due to the presence of a more extended conjugation in
the bzq ligand relative to the phenylpyridinate group.18,23
The solid-state diffuse reflectance UV-vis spectra show
differences with respect to those observed in acetonitrile solution
(see Figure S1), especially 3 (orange color), which exhibits a
1
centered (1LC bzq) character mixed with small MLCT char-
acter. This assignment is consistent with the modest negative
solvatochromism observed for complexes 5-7 on going from
the least to the most polar solvent investigated (CH2Cl2, DMF,
and MeCN) (see Table 2 and Figure S5a). In the solvents
investigated, the lowest energy absorption band at ca. 400 nm
for the six complexes follows Beer’s law in the concentration
range from 5 × 10-5 to 10-3 M, suggesting that no remarkable
aggregation occurs within this concentration range (see Figure
S2b for complex 7b in MeCN). However, a much weaker band
(ε ∼ 20 M-1 cm-1) is barely discernible at lower energy in
very concentrated solutions (10-2 M) in CH2Cl2, DMF, and
MeCN for the tert-butyl and xylylisocyanide derivatives (Figure
S5b for 6b). For the naphthylisocyanide complexes (only soluble
at this concentration in DMF), it might be obscured by the tail
(80) Kvam, P. I.; Puzyk, M. V.; Cotlyr, V. S.; Balashev, K. P.; Songstad,
J. Acta Chem. Scand. 1995, 49, 645.
(81) Pe´rez, S.; Lo´pez, C.; Caubet, A.; Bosque, R.; Solans, X.; Bard´ıa,
M. F.; Roig, A.; Molins, E. Organometallics 2004, 23, 224.
(82) Burney, J. R. Ph.D., University of Minnesota, 2006, ISBN 976-0-
542-89002-4.
Figure 3. Normalized UV-vis absorption spectra of 1-4 in
acetonitrile (10-4 M).

1710 Organometallics, Vol. 28, No. 6, 2009
D´ıez et al.
Table 2. Absorption Data for Compounds 1-7 at Room Temperature
compound
λ
abs/nm (103 ꢀ M-1 cm-1) (solution ∼10-4 M)
λabs/nm (solid)
[Pd(bzq)(NCMe)2]ClO4 (1)
215 (39), 234 (38.8), 275 (13.6),285 (16.7), 348 sh (15.9), 365 (2.8), 380 (3)
MeCN
308, 375
[Pd(ppy)(NCMe)2]ClO4 (2)
[Pt(bzq)(NCMe)2]ClO4 (3)
217 (27.1), 245 (19.5), 255 (20.3), 301 (5.7), 313 (5.3), 338 (3.3) MeCN
212 (33.8), 232 (37.1), 241 (35.4), 265 (15.5), 281 (17.1), 297 (13.2), 369
(2.5), 397 (1.7) MeCN
260-350
312, 402, 475
[Pt(ppy)(NCMe)2]ClO4 (4)
[Pt(bzq)(CN-t-Bu)2]ClO4 (5a)
241 (24.8), 266 (16.7), 312 (6.8), 323 (6.7), 357 (2.2), 375 sh (1.6) MeCN
235 (57.5), 250 (29.3), 256sh (26.3), 288sh (19.6), 300 (23.4), 345 (2.0), 385
(2.9), 402 (2.9) CH2Cl2
300-380
300, 385, 400, 465
267(15.5), 284sh (22.2), 298 (27.3), 340 (2.4), 380 (3.2), 396 (3.5) DMF
209 (29.48), 229 (40.3), 248 (24.6), 285sh (16.4), 295 (19.5), 338 (1.6), 378
(2.3), 395 (2.4) MeCN
220sh (8.4), 235 (29.8), 250 (26.5), 285sh (17.8), 298 (21.5), 343 (1.5), 382
(2.4), 402 (2.6) CH2Cl2
259 (21.2), 286sh (13.9), 298 (17.4), 380 (0.8), 398 (1.3) DMF
210 (25.4), 234 (30.8), 250 (25.8), 280 (16.8), 295 (20.7), 375 (2.6), 394
(2.9) MeCN
242 (43.5), 252sh (39.2), 290sh (25.9), 302 (27.6), 346 (2.2), 390 (2.9), 404
(2.8) CH2Cl2
270 (29.8), 288sh (32.6), 293 (33.6), 342 (4.2), 382 (3.8), 401 (4.0) DMF
233 (44.1), 281sh (29), 297 (27.8),
340 (2.3), 380 (2.7), 400 (2.8) MeCN
221sh (18.3), 235 (57.0), 252sh (38.5), 285 (26.4), 300 (24.7), 345 (2.4), 390
(2.7), 405 (2.6) CH2Cl2
[Pt(bzq)(CN-t-Bu)2]PF6 (5b)
[Pt(bzq)(CN-Xyl)2]ClO4 (6a)
[Pt(bzq)(CN-Xyl)2]PF6 (6b)
300, 390, 470
308, 380, 400, 465
310, 400, 465
260 (30.0), 285 (18.4), 292 (18.3), 305 (18.7), 340sh (3.3), 400 (2.1) DMF
212 (26.2), 235 (30.6), 252 (28.1), 280 (21.6),
295 (22.9), 379 (2.3), 398 (2.5) MeCN
[Pt(bzq)(CN-2-Np)2]ClO4 (7a)
[Pt(bzq)(CN-2-Np)2]PF6 (7b)
282 (39,7), 308 (38), 340 (10.3), 380 (4.3), 404 (3.8) DMF
234 (120), 244 (88.3), 292 (30,9), 310 (27.0), 340sh (6.4), 384 (2.3), 400
(2.5) MeCN
260 (49.0), 285 (29.6), 294 (27.9), 320sh (18.2), 345sh (4.9), 400 (0.4) DMF
235 (132), 244 (99.5), 292 (37.1), 310 (31.7), 342sh (7.5), 380 (3.8), 400
(3.7) MeCN
320-490
320-490
Table 3. Population Analysis (%) for 6+
complexes 7, having the 2-naphthylisocyanide ligand, display
an intense broad profile from 320 to 490 nm, with a long tail
extending to 530 nm, which is probably due to the presence of
stronger π-π stacking in the solid microcrystalline samples.
Emission Spectroscopy. The acetonitrile platinum(II) deriva-
tives [Pt(bzq)(NCMe)2]ClO4 3 and [Pt(ppy)(NCMe)2]ClO4 4 are
photoluminescent at low (77 K) and room temperature both in
the solid state and in MeCN solution. However, as has been
MO
CNXyl
Pt
bzq
L+2
L+1
39
71
16
1
11
8
12
6
50
21
72
93
97
0
2
0
1
LUMO
HOMO
H-1
H-2
H-3
H-4
H-5
H-6
H-7
H-8
1
2
100
91
100
97
2
0
7
0
2
18
84
54
80
14
33
2
13
of the main band. The wavelength of this band is very similar
in each case (range CH2Cl2: 464-467 nm; DMF: 462-465;
MeCN 461-464 nm) and displays a weaker degree of solva-
tochromism than the more intense band, but following the same
order. This band agrees with the first calculated spin-forbidden
triplet in 6+ (∼458 nm, Table S2) and could be attributed to
the direct population of a triplet state of mixed LL′CT/LC/
MLCT character, facilitated by the high spin-orbit coupling
associated with the platinum(II) ion. Notwithstanding, the heavy
atom effect in the isocyanide complexes 5-7 seems to be not
very effective not only because the intensity of the band is very
weak (only observed at 10-2 M) but also due to the fact that all
derivatives 5-7 exhibit dual emission (fluorescence and phos-
phorescence) in solution at 298 K (see below).
Concerning the solid state, similar colors of microcrystalline
samples of 5-7 were observed for different counteranions, and
we noted that the λmax for the same complex but with different
anions are almost identical. For 5 and 6, the solid diffuse
reflectance UV-vis spectra (Figure S6 for complexes a) exhibit
two intense low-energy absorptions at similar energy to those
seen in solution (382, 402 nm 5a in solid vs 385 and 402 in
CH2Cl2). This suggests that the observed (6, see Figures 1b and
2b) or possible (5) π-π interactions between monomers have
a very small effect in their absorption maxima. By contrast,
Figure 4. Frontier orbital plots for 6+ obtained by DFT.
Calculated absorption spectrum (bars) of 6+ in MeCN and
experimental UV-vis spectrum of 6b in MeCN (10-4 M) at
298 K.

Luminescence of Cyclometalated Compounds
Organometallics, Vol. 28, No. 6, 2009 1711
previously observed in related palladium compounds,32-38
[Pd(bzq)(NCMe)2]ClO4 1 and [Pd(ppy)(NCMe)2]ClO4 2 are
emissive only at 77 K. This behavior is not unusual in palladium
complexes because of the presence of low-lying metal-centered
(MC) excited states, which deactivates the potentially lumines-
cent MLCT and LC levels through thermally activated surface-
crossing processes.32 The results are summarized in Table 4.
The emission of 4 in fluid (298 K) MeCN solution is not
concentration-dependent, exhibiting in the concentration range
10-5-10-3 M a typical structured emission (478, 512, 543 nm)
with vibronic spacing (1389, 1115 cm-1) (Figure 5, 10-4 M),
S9). It is worth noting that both emissions for 1 and 2 occur at
lower energies than in the corresponding platinum solvates 3
and 4, suggesting stronger interactions between adjacent excited
monomers. The observed low-energy emissions in the solid state
3
for 1-4 are tentatively attributed to excimeric-like ππ* and/
or 3MMLCT [σ*(M)fπ*(C∧N)] transitions localized on excited
interacting adjacent monomers by π-π and/or M-M interac-
tions. Curiously, in all derivatives the observed emission
maximum in the solid state appears blue-shifted with respect
to that seen in the rigid glassy acetonitrile solution (Table 4), a
fact that is more remarkable in the platinum complexes [3 (30
nm), 4 (35 nm)]. This behavior seems to indicate that packing
of cations and anions in the solid lattice occurs in such a way
that it causes a greater separation between interacting adjacent
metallic cations than in glassy solutions (g10-4 M).
3
consistent with an emission coming from a mixed LC(ππ*)/
3MLCT emissive state.21 In contrast, concentrated solutions of
complex 3 (10-3 M and 10-4 M, Figure 5) result in a high-
energy structureless band centered at 437 nm with a very short
lifetime (9 ns), by excitation in the range 330-370 nm.
However, as shown in Figure S7, the intensity of this emission
band decreases with the concentration, being essentially not
detectable at 10-5 M. The unstructured shape, the short lifetime,
and the intensity dependence on the concentration suggest that
this emission could be tentatively ascribed to excimer fluores-
cence.83 In support of this assignment, its excitation spectrum
(367 nm max) differs from that obtained in glass state at 77 K,
monitoring at the λmax of the mixed 3LC/ 3MLCT emissive state
(486 nm).
On the basis of the combination of the strong-field cyclom-
etalating ligand and strong-field isocyanide ancillary ligands,
high-efficiency luminescence would be expected for the iso-
cyanide complexes 5-7. At room temperature, the behavior of
complexes 5a and 5b in CH2Cl2 solutions (5 × 10-5-10-3
M
range) is similar to that of related 6a and 6b; therefore only the
emission spectra of 5a and 5b are presented (Figures 7, 8, and
S10). By excitation at λmax > 360 nm (Figures 7 and S10), all
of them show a structured emission band (λmax ∼470 5, ∼475
nm 6, see Table 4) whose excitation spectra mimic the
absorption spectra in the low-energy region, being ascribed to
a mixed 3LC/3MLCT excited state, probably with a remarkable
3LC character (see below for emission spectra in other solvents).
However, excitation at higher energies (λ e 330 nm) results in
an additional high-energy structured emission band at 345 nm,
Interestingly, upon cooling the solutions to the glassy state
(77 K), the emission spectra of 1-4 are concentration-dependent
and very similar to each other (see Figure 6 for complex 4). In
diluted solutions (10-5 M, white-cream glasses) all of them
exhibit a high-energy structured band, which is ascribed to a
3
along with the LC/3MLCT band at 470 nm. An intermediate
3
typical mixed LC/3MLCT transition of the monomer species.
additional structureless emission band centered at ca. 430 nm
The emission maxima follow the order 460 (2) < 471 (1) <
476 (4) < 486 nm (3). This tendency is in accordance with the
presence of a higher energy HOMO in platinum derivatives and
a lower energy LUMO in the benzoquinolinate complexes,
is also observed using concentrated solutions (10-3 M) when
-
the counterion is PF6 (5b, 6b) or at concentrations up to 5 ×
-
10-5 M when the counterion is ClO4 (5a, 6a). Although too
3
weak for lifetime measurements, the high-energy structured
emission (345-385 nm) clearly originates from a ligand-
centered (bzq) predominantly spin-allowed 1(ππ*) excited state
(fluorescence). Additional support arises from the small Stokes
shift between the excitation and emission spectra (see Figure 7
for 5b) and the fact that this high-energy emission is comparable
to that of the free ligand (Hbzq: 349, 366, 385 nm). As can be
seen in Figure S10, the excitation spectrum monitoring at the
intermediate unstructured band (430 nm) differs from that
obtained monitoring the structured high- and low-energy emis-
sions, suggesting a different emissive manifold of difficult
assignment. As reported above, this behavior indicates that the
intersystem crossing (ISC) and/or internal conversion (IC)
between emissive states is probably of low effectiveness at room
temperature. Clearly the change of the weakly coordinated
NCMe molecules by the stronger σ-donating isonitrile CNR
ligands in the “Pt(bzq)” core probably reduces the degree of
platinum-benzoquinolinate (Pt-Cbzq) orbital (σ and π) interac-
tions, which seems to be crucial to the manifestation of the heavy
atom effect.85
which decreases the energy of the MLCT state. When the
concentration increases (10-4 and 10-3 M, orange glasses), this
band disappears and only an unstructured emission maximizing
at λmax 680 nm (Pt 3, 4), 720 nm (Pd 1), and 703 nm (Pd 2),
respectively, is observed. As shown in Figure 6, the excitation
spectrum corresponding to this new 680 nm emission appears
at ca. 480 nm, while the excitation spectrum of the diluted
solution (10-5 M) monitored at 486 nm (3) and 476 nm (4)
gives rise to a structured high-energy profile, suggesting a
different origin for these two emissions. This feature and the
change of color of the glasses from cream-white (10-5 M) to
orange (10-3 M) indicate that these low-energy emissions are
presumably due to emissive ground-state aggregates generated
by M-M (3MMLCT) and/or π-π interactions,4,6,32,39,84 al-
though the existence of excimeric-like emissions cannot be
excluded. In agreement with this suggestion, the observed
emissions in the solid state are quite similar. Thus, at room
temperature (Figure S8), both yellow platinum derivatives, 3
and 4, show unstructured and symmetrical low-energy, exci-
meric-like emissions centered at 630 and 595 nm, respectively,
which undergo a red shift on cooling (650 3, 645 nm 4).
Interestingly, although the white palladium compounds 1 and
2 are not emissive at room temperature in the solid state, cooling
at 77 K resulted in a very low-energy and unstructured excimeric
emission maximizing at 703 and 690 nm, respectively (Figure
For complex 6a, the dependence of the lifetime in deaereated
CH2Cl2 solution measured at 470 nm has been examined. The
lifetime decreases slightly in the 2.5 × 10-5 to 10-4 M range
from 3.08 to 2.67 µs. As can be observed in Figure S11,
the observed emission decay rate constants (Kobs ) 1/τobs
)
increase linearly with the concentration, fitting well to the
Stern-Volmer equation of the form Kobs ) Ko + KQ[Pt], where
(83) Yamaji, M.; Tsukada, H.; Nishimura, J.; Shizuka, H.; Tobita, S.
Chem. Phys. Lett. 2002, 357, 137.
(84) Siemeling, U.; Bausch, K.; Fink, H.; Bruhn, C.; Baldus, M.;
Angerstein, B.; Plessow, R.; Brockhinke, A. Dalton Trans. 2005, 2365.
(85) Hu, J.; Yip, J. H. K.; Ma, D. L.; Wong, K. Y.; Chung, W. H.
Organometallics 2009, 28, 51.

1712 Organometallics, Vol. 28, No. 6, 2009
D´ıez et al.
Table 4. Emission Data for Complexes 1-7
medium (Ta/K)
em/nm (λexc/nm)
compound
λ
τ/µsa
[Pd(bzq)(NCMe)2]ClO4
solid (77)
703 (425-470)
2.4
1.6
(1)
MeCNb (77)
MeCNc (77)
720 (360-400)
471, 481sh, 506, 545
(345-385)
[Pd(ppy)(NCMe)2]ClO4
(2)
solid (77)
690 (350-400)
MeCNb (77)
MeCNc (77)
703 (385)
460, 483, 494, 521
(330-350)
[Pt(bzq)(NCMe)2]ClO4
(3)
solid (298)
solid (77)
630 (425-510)
0.2
650 (460-520)
1.5
MeCN (298)
MeCNb (77)
MeCNc (77)
solid (298)
solid (77)
437 (330-370)
9 ns
680 (425-475)
486, 523, 564 (350-375)
595 (425-525)
[Pt(ppy)(NCMe)2]ClO4
(4)
2.3 (68.3%), 0.4 (31.7%)
3.3
645 (425-480)
MeCN (298)
478, 512, 543
(320-380)
MeCNb (77)
MeCNc (77)
solid (298)
solid (77)
680 (385-485)
476, 512, 543 (325-380)
476, 504, 590 (350-450)
500, 538max, 575, 620sh
(370-460)
[Pt(bzq)(CNt-Bu)2]ClO4
(5a)
57.3 (12.3%), 14.3 (87.7%)
1310 (61.3%), 280 (38.7%)
(500, 538)
538, 640 (475)
650 (510)
e
CH2Cl2 (298)
345, 367, 385,430, 470,
502, 534 (300)
2 ns (430)
430, 470, 502, 534 (360)
470, 502, 534 (400)
502, 535, 582 (330-420)
10 ns (540)
e
CH2Cl2 (77)
243 (76.2%), 17.2 (23.8%)
(502)
256 (33.6%), 37.1 (66.4%)
(535)
165 (10.3%), 13.0 (89.7%)
(582)
[Pt(bzq)(CNt-Bu)2]PF6
(5b)
solid (298)
solid (77)
504max, 535 (360-460)
508max, 545, 590 (360-440)
345, 367, 385, 410, 470,
502, 543 (280-330)
9.6 (504)
73.6 (508)
e
CH2Cl2 (298)
5 ns (470)
470, 502, 543 (360-400)
502, 535, 590 (360-400)
475, 485, 500, 540 (360-430)
e
CH2Cl2 (77)
469 (502)
[Pt(bzq)(CN-Xyl)2]ClO4
solid (298)
76.9 (17%), 27.6 (83%)
(500)
(6a)
solid (77)
498, 536, 580 (350-475)
345max, 367, 385, 433max,
476max, 509, 545
806 (498)
e
CH2Cl2 (298)
(290-310)
476max, 509, 545 (400)
506, 535, 615 (300-400)
e
CH2Cl2 (77)
244 (19.4%), 26.4 (80.6%)
(506);
106.5 (15.5%), 11.9
(84.5%) (615)
[Pt(bzq)(CN-Xyl)2]PF6
solid (298)
solid (77)
495, 518, 556 (360-475)
98.4 (495); 89.8 (518);
68.6 (560)
209.3 (495)
(6b)
495, 505, 528, 570
(360-460)
e
CH2Cl2 (298)
348, 366, 385, 406sh, 475,
507, 548 (280-320)
475, 507, 548 (360-400)
502, 532, 590 (360-420)
635 (500)
e
CH2Cl2 (77)
141.4 (502)
[Pt(bzq)(CN-2-Np)2]ClO4
(7a)
solid (298)
solid (77)
0.4 (75.5%), 0.08 (24.5%)
97.9 (9.3%), 26.9 (90.7%)
(590)
590 (350-450)
590sh, 675 (500)
29.4 (8.1%), 1.8 (91.9%)
(675)
11.9 (0.3%), 1.9 (99.7%)
2.1 (98.6%), 11.8 (1.4%)
4.0 (94.1%), 12.3 (5.9%)
0.4 (5.2%), 3.4 ns (94.8%) (545)
MeCNd (298)
MeCNd (77)
666 (367-420)
690 (500),
735 (540)
327, 345, 360 (277)
480 sh, 545, 650 (320-390)
MeCNe (298)
650 (450)
7.7 ns (650)
MeCNe (77)
solid (298)
solid (77)
741 (540)
3.2
[Pt(bzq)(CN-2-Np)2]PF6
(7b)
630 (420-500)
573 (370-420)
573, 685 (500)
620, 660sh (360-420)
710 (520)
4.2 (60%); 0.06 (40%)
149.8
MeCNd (298)
MeCNd (77)
0.9
13.6
775 (590)
MeCNe (298)
330, 345, 364, 380 (280)
394, 400, 416 (360)
480sh, 540, 650sh (400)
735 (540)
MeCNe (77)
9.4
b
c
d
e
a Air-equilibrated samples. Concentrated (10-3, 10-4 M). Diluted (10-5 M). 10-3 M. 5 × 10-5 M.

Luminescence of Cyclometalated Compounds
Organometallics, Vol. 28, No. 6, 2009 1713
Figure 5. Normalized emission spectra of 3 and 4 in MeCN at
Figure 8. Normalized excitation and emission spectra of 5a and
5b at 77 K in dichloromethane (5 × 10-5 M).
298 K (10-4 M).
provides an indication of the susceptibility of the complex to self-
quench through excimer formation (Figure S11). The lifetime of
emission at infinite dilution τo is 3.2 µs, and the value of KQ (0.65
× 109 M-1 s-1) (determined from the linear variation of Kobs as a
function of the concentration) indicate little self-quenching.16,86,88-90
An additional solvent-dependent emission study at room
temperature in diluted solution (5 × 10-5 M) has been carried
out in more polar solvents (DMF and MeCN), and the results
are collected in Table S3. It is remarkable that although dual
fluorescence (1ππ*) and phosphorescence (3LC/3MLCT) is still
observed in all complexes, the emissions are clearly dominated
by the high-energy structured fluorescence bands probably due
to the quenching effect of these donor solvents (as an illustration
see Figure S12 for complex 5b). In addition, the intermediate
band located at ∼430 nm, which is seen in CH2Cl2, also
disappears in these solvents. Concerning the solvent effect on
the maxima (>470 nm), its influence is negligible (Table S2),
which is in agreement with emission emanating mainly from a
3LC excited state. Notwithstanding, for 6a in acetonitrile, a low
unstructured feature located at 575 nm (3ππ* excimeric in
nature) is also observed.
Figure 6. Normalized excitation and emission spectra of 4 in MeCN
at 77 K (10-4 and 10-5 M).
1
When the CH2Cl2 solutions are frozen, (ππ*) fluorescence
and intermediate (430 nm) emissions disappear, indicating
effective falling to low-lying emissive manifolds. However,
while the PF6- derivatives (5b and 6b) exhibit only a structured
-
band centered at ca. 502 nm, the ClO4 complexes also show
the presence of an additional low-energy unstructured manifold
(582 5a, 615 nm 6a). As an illustration of this different behavior,
the emission spectra of 5a and 5b in diluted 5 × 10-5
M
solutions at 77 K are shown in Figure 8. Similar spectra were
obtained at higher concentrations with the low-energy manifold
for 5a and 6a being more prominent. For the structured emission
of 5b and 6b, the absence of rigidochromism, together with
the negligible influence of the isocyanide ligand and the
extremely long lifetimes, which fit well to monoexponential
(86) Connick, W. B.; Geiger, D.; Eisenberg, R. Inorg. Chem. 1999, 38,
3264.
(87) Horvath, A.; Stevenson, K. L. Coord. Chem. ReV. 1996, 153, 57.
(88) Guo, F.; Sun, W.; Liu, Y.; Schanze, K. Inorg. Chem. 2005, 44,
4055.
(89) Williams, J. A. G.; Beeby, A.; Davies, E. S.; Weinstein, J. A.;
Wilson, C. Inorg. Chem. 2003, 42, 8609.
(90) Develay, S.; Blackburn, O.; Thompson, A. L.; Williams, J. A. G.
Inorg. Chem. 2008, 47, 11129.
Figure 7. Normalized excitation and emission spectra of 5b at 298
K in dichloromethane (5 × 10-5 M).
Ko ) (1/τo) is the emission rate constant at infinite dilution and
KQis the apparent rate constant of self-quenching,86,87 which

1714 Organometallics, Vol. 28, No. 6, 2009
D´ıez et al.
decays (air-equilibrated glasses, 469 µs 5b, 141.4 µs 6b), is
3
indicative of emission with primarily LC parentage. For the
ClO4- derivatives, lifetime measurements in all maxima always
fit to two components (see Table 4). The long component
dominant in the high-energy peaks is attributed to the structured
3LC emission, while the short component, which is predominant
in the low-energy band, is tentatively attributed to excimeric
3ππ* emission. In keeping with this notion, the excitation spectra
of 5a monitored at 502 and 585 nm are similar (see Figure 8).
It is worth noting that the phosphorescence lifetimes at 77 K
(and also in the solid state at 77 K) are longer than at room
temperature, suggesting that they are mainly determined by
nonradiative decay rates, which usually decrease with lowering
temperature.
We have also performed a temperature-dependent study on
the luminescence properties of a diluted 5 × 10-5 M deaereated
CH2Cl2 solution of 5a. In Figure S13 are collected emission
spectra and lifetimes as registered against the temperature in
the 298-77 K range. As can be observed, by decreasing slowly
the temperature the final emission profile obtained at 77 K is
slightly different than that observed by freezing the solution
suddenly (Figure S13b vs Figure 8). The most remarkable effect
is that the high structured emission decreases in intensity relative
to the low-energy excimeric feature and the peak maxima of
Figure 9. Normalized emission spectra of 7b in acetonitrile at 298
K at different concentrations.
structured (330, 345, 360, 380 nm) (394, 400, 416 nm) ligand-
centered 1ππ* emissions, with contribution of both bzq and CN-
2-Np groups (Figure 9).91 When the concentration increases
(10-4, 10-3 M), a new additional low-energy feature, which
maximizes at ca. 620 nm by exciting at 400 nm, is observed.
Similar behavior is observed for 7a in MeCN, but in this case
the low-energy feature is observed, as for complex 6a in MeCN,
even in a diluted 5 × 10-5 M solution (see Figure S14). As can
be seen in Figure S14 for 7a, the excitation spectra monitored
at the low-energy feature are different from that monitored at
the high-energy band, suggesting that the broad low-energy band
originates from an emissive state resulting from ground-state
aggregation of the complexes. In diluted (5 × 10-5 M) DMF
solution, the triplet mixed 3LC/3MLCT emission for both
complexes 7a and 7b is very weak, with emission maxima
slightly blue-shifted (∼470 nm in DMF vs 480 nm in MeCN).
In addition, by excitating at high energy (280-310 nm), the
3
the LC are broader and slightly blue-shifted (490, 528 nm vs
502, 535 nm). It may be noted that the lifetimes measured in
the 470-490 band are significantly larger than those obtained
in air-equilibrated solution, as would be anticipated due to its
triplet parentage. From Figure S13, it can be seen that by cooling
from 298 to 173 K, no energetic variation is observed in the
dual emission (fluorescence and phosphorescence), but the
intensity of the phosphorescence increases remarkably while
the fluorescence decreases to a lesser extent. The phosphores-
cence emission lifetime increases concomitantly, fitting to a
monoexponential decay from 298 to ca. 198 K (1.5 µs at 298
K to 51.8 µs at 198 K). At 173 K, which is close to the freezing
temperature (177.9 K), the lifetime increases rapidly and fits
two components [837.5 µs (55.8%), 256.5 µs (44%)], suggesting
the presence of two close emissive states. Below this temper-
ature, the structured emission shows a small bathochromic shift
(λmax ∼490 nm) and the low-energy unstructured feature ascribed
1
only emission observed (see Table S3) is ππ* fluorescence
(330, 345, 364, 380 nm). The tendency to form excimers is
lower than in acetonitrile and becomes apparent only at elevated
concentrations (∼10-3 M).
3
to ππ* excimer emission is observed (∼586 nm). Both the
In glassy (77 K) acetonitrile, the emission profile for 7a and
7b is similar and also depends on the concentration and the
excitation wavelength. Curiously, at low concentration (5 × 10-5
M) only one symmetric structureless band at very low energy
(741 nm 7a, 735 nm 7b, related to a maximum excitation peak
at 540 nm) is observed (see Figure 10 for 7a). This emission is
attributable to 3MMLCT [dσ*(Pt)fπ*] transitions, probably due
to the close distance and interaction between the platinum
centers. However, when the concentration increases to 10-3 M,
the glasses exhibit site-selective emission, presumably due to
presence of a biexponential decay with two very long lifetime
components at λmax ∼490 nm (similar to those seen in the solid
state at 77 K: 1045.9 (55.1%), 129.9 (44.9%) µs glass 77 K;
1310 (61.3%), 280 (38.7%) µs solid 77 K) and the very intense
excimer emission below 173 K could be indicative of the
existence of a crystallization process. However, we noted that
the maxima of both emissions are slightly different. For instance,
by exciting at ∼450 nm the maximum of excimer emission
occurs at 620 nm, which is different from that observed in the
solid state at 77 K (∼650 nm, Figure S16). The appearance of
excimer (or ground-state aggregate) emission at 77 K for glasses
but not at room temperature is not unprecendented and indicates
that the association constant could be too small to be observed
at room temperature.
3
3
3
the simultaneous presence of ππ* and MMLCT (dσ*π*)
transitions. Thus, two structureless symmetric bands at 690 nm
(λexc 500 nm) and 735 nm (λexc 540 nm) for complex 7a and at
710 nm (λexc 520 nm) and 775 nm (λexc 590) for 7b are seen
with 10-3 M solutions at 77 K. In both complexes the excitation
spectra monitored at the low-energy band (735 nm 7a, 775 nm
7b) are distinct from those monitored at the less energetic
emission (690 nm 7a, 710 nm 7b), indicating their different
For 7a and 7b, which are not soluble in CH2Cl2, the emission
spectra were recorded in MeCN (Table 4) and DMF (Table S3),
-
and again, the tendency to form excimers is higher in the ClO4
derivative 7a. Thus, in a diluted MeCN solution (5 × 10-5 M),
7b exhibits, by excitation in the low-energy absorption (380-400
nm), an asymmetric emission (480sh, 540 nm) ascribed to a
3
origin [3(dσ*π*) and ππ*]. Apparently, in diluted solution
glasses, the tendency to selectively form aggregates through
mixed LC/3MLCT excited state, while excitation at higher
3
(91) Fluorescence of 2-naphthylisocyanide occurs at 331, 346, 363, and
381 nm.
energies (280-320 nm) and 360 nm results in additional

Luminescence of Cyclometalated Compounds
Organometallics, Vol. 28, No. 6, 2009 1715
acetonitrile glasses (10-3 M, 77 K, see Figure 10), being
similarly assigned to 3ππ* and 3(dσ*π*) excited states, respec-
tively. This behavior, together with the reflectance diffuse
spectra (Figure S6), suggests that probably both ππ and Pt · · · Pt
contacts are prevalent in the crystal packing of both complexes
7a and 7b. The influence of the counterion is observed in the
CN-t-Bu derivatives. To illustrate this, the emission spectra of
5a and 5b are given in Figure S16. 5b (PF6-) exhibits only
typical structured profiles (298, 77 K) due to 3LC excited states,
while for 5a, containing the smaller ClO4- counterion, additional
3
emission due to excimeric ππ* is also evident, this being
predominant at 298 K.
Conclusions
In summary the synthesis and photophysics of a new series
of cationic cyclopalladated complexes [Pd(C∧N)(NCMe)2]ClO4
(C∧N ) bzq 1, ppy 2), analogous to the previously described
platinum complexes (3, 4)47 and isocyanide platinum derivatives
Figure 10. Normalized excitation and emission spectra of 7a in
acetonitrile at 77 K.
-
[Pt(bzq)(CNR)2]X (R ) t-Bu 5, Xyl 6, 2-Np 7; X ) ClO4 a,
-
PF6 b), are reported. The X-ray crystal structures of 6a and
6b reveal the presence of similar π-π stacking dimers that pack
through additional, slightly different, π-π interactions (bzq/
xylyl 6a or xylyl/xylyl 6b). Complexes 3 and 4 are strongly
emissive in all media (298 and 77 K), whereas the palladium
complexes are emissive only in rigid media at 77 K. Curiously
in acetonitrile solution complex 3 shows a high-energy unstruc-
tured emission band (ascribed to excimeric fluorescence),
whereas 4 exhibits a typical structured emission coming from
a 3LC(ππ*) emissive state with a small amount of the 3MLCT
state. At 77 K (glassy solutions), the emission spectra of all
acetonitrile complexes 1-4 are concentration-dependent, ex-
3
hibiting typical LC/3MLCT structured emissions at low con-
3
centration (10-5 M) and low-energy excimeric-like ππ* and/
or 3MMLCT [dσ*(Pt) f π*(C∧N)] unstructured bands at higher
concentrations, similar to those observed in the solid state at
room temperature (3, 4) and at 77 K (1-4).
On the basis of TD-DFT calculations on 6+, the lowest energy
absorption seen in the isocyanide complexes 5-7 is suggested
1
1
to be IL in nature mixed with some MLCT character. Their
emissive properties in fluid solution indicate that intersystem
crossing between singlet and triplet states is very inefficient,
probably due to the stronger σ-donating properties of the CNR
ligands, which reduces the heavy effect atom. Thus, for 5 and
6 in CH2Cl2 solutions, three different bands are observed: 1ππ*
fluorescence (345-385 nm), 3LC/3MLCT phosphorescence (λmax
∼470 nm), and a broad structureless emission at ca. 430 nm,
whose presence is concentration dependent. The λmax of
phosphorescence emission is not particularly sensitive to solvent
polarity, but it is considerably quenched in MeCN and DMF.
In addition, in these solvents the band at 430 nm is not observed.
Emission lifetimes for deaereated CH2Cl2 solutions of 5a reveal
little self-quenching, but the presence of oxygen decreases the
intensity of the phosphorescence. At 77 K (glassy CH2Cl2
solutions), the fluorescence and the intermediate band (430 nm)
Figure 11. Normalized emission spectra of [Pt(bzq)(CN-2-
Np)2]ClO4 7a in the solid state.
Pt · · · Pt interactions is prevalent, while at higher concentrations
both π-π and Pt · · · Pt emissive dimers and/or oligomers are
generated, which is further evident from the emission lifetime
measurements listed in Table 4.
The luminescence observed in the solid state for complexes
5-7 is quite similar to that observed in glasses at 77 K, and
only in the tert-butylisocyanide derivatives is the influence of
the counteranion clearly visible. Thus, despite the presence of
weak ππ stacking interactions found in the solid state (Figures
1 and 2) for the xylylisocyanide derivatives (6a, 6b), these
complexes exhibit vibronically structured emissions (298, 77
K) attributed mainly to the 3LC excited state. Notwithstanding
this, the emissions at 298 K are broader and their lifetime
measurements fit two components, suggesting that a small
excimeric character of the emission cannot be excluded (Figure
S15). By contrast, the 2-naphthylisocyanide complexes show,
at room temperature, an intense broad emission (635 nm 7a,
-
disappear and for the ClO4 derivatives (5a and 6a) phospho-
rescent excimeric-like 3ππ* emissions are observed. The emis-
sions of the 2-naphthylisocyanide derivatives (7) also exhibit a
similar solvent concentration and excitation wavelength depen-
-
dence both at room and at low (77 K) temperature, the ClO4
3
630 nm 7b) attributed to excimeric ππ* excited states. Upon
derivative 7a being more prone to show excimeric emission.
For these complexes (7) the low concentrated rigid glasses (5
× 10-5 M) exhibit only one structureless band at very low
energy (741 nm 7a, 735 nm 7b) due to a 3MMLCT [dσ*(Pt)fπ*]
transition. However, by increasing the concentration (10-4, 10-3
cooling to 77 K, two distinct emissions are resolved depending
on the excitation wavelength (see Table 4). As can be observed
in Figure 11 for complex 7a, both emissions (590, 675 nm 7a;
573, 685 nm 7b) mimic those observed in concentrated

1716 Organometallics, Vol. 28, No. 6, 2009
D´ıez et al.
3JH3-H2 ) 5.4, H3, bzq), 7.44 (t, 3JH8-H9/7 ) 7.3, H8, bzq), 7.36 (d,
3JH7-H8 ) 7.3, H7, bzq), 1.99 (s, 6H, MeCN).
M) of the glassy solutions, an interesting dual site-selective
emission (690, 735 nm 7a; 710, 775 nm 7b) is clearly observed
3
Synthesis of [Pd(ppy)(NCMe)2]ClO4 (2). This complex was
prepared in the same way as 1. AgClO4 (0.700 g, 3.381 mmol), D
(0.100 g, 1.688 mmol). 2: white color. Yield: 0.142 g, 95%. Anal.
Calcd for C15H14ClN3O4Pd: C, 40.74; H, 3.19; N, 9.50. Found: C,
40.42; H, 3.30; N, 9.73. IR (cm-1): 2331 (m, NCMe), 2320 (m,
NCMe), 2302 (m, νst(C-N), NCMe), 2291 (m, νst(C-N), NCMe);
1089 (s, ν3 ClO4-), 624 (s, ν4 ClO4-). ΛM (5 × 10-4 M acetonitrile
solution): 129.2 Ω-1 cm2 mol-1. 1H NMR (400.13 MHz, CD3CN,
due to the simultaneous presence of both excimeric ππ* and
3MMLCT transitions. The behavior of these isocyanide com-
plexes (5-7) in the solid state is similar to the rigid glasses,
and it is only in the CN-t-Bu derivatives that the influence of
the counteranion is visible. In general, the following tendency
3
to exhibit excimeric-like emission (3ππ* and/or dσ*π*) is
-
observed: CN-2-Np > CN-t-Bu > CN-Xyl and ClO4- > PF6
.
3
3
298 K, δ): 8.43 (d, JH2-H3 ) 4.4, H2, ppy), 8.04 (td, JH4-H3
)
3JH4-H5 ) 8.1, 4JH4-H2 ) 1.2, H4, ppy), 7.85 (d, 3JH5-H4 ) 8.1, H5,
Experimental Section
ppy), 7.55 (dd, JH6-H7 ) 7.6, JH6-H8 ) 1.5, H6, ppy), 7.32 (ddd,
3
3
General Considerations. The starting materials [{Pt(bzq)(µ-
Cl)}2] (A),92 [{Pd(bzq)(µ-Cl)}2] (B),93 [{Pt(ppy)(µ-Cl)}2] (C),20
and [{Pd(ppy)(µ-Cl)}2] (D)94 were prepared according to reported
procedures with slight modifications. The synthesis of [Pt-
(C∧N)(NCMe)2]ClO4 (C∧N ) bzq 3, ppy 4)47 has been previously
reported. The reactions were carried out without precautions to
exclude atmospheric oxygen or moisture. tert-Butylisocyanide (CN-
t-Bu), 2,6-dimethylphenylisocyanide (CN-Xyl), and 2-naphthyl-
isocyanide (CN-2-Np) were purchased from commercial suppliers.
Instrumental Methods. Infrared spectra were recorded in the
4000-200 cm-1 range on Perkin-Elmer 883 and Nicolet Nexus
FT-IR spectrophotometers using Nujol mulls between polyethylene
sheets. Conductivities were measured in ca. 5 × 10-4 mol dm-3
solutions with a Philips 9509 or a Crison GLP31 conductimeter.
C, H, and N analyses were carried out with a Perkin-Elmer 2400
microanalyzer. Mass spectra were recorded on a HP-5989B mass
spectrometer (ES technique). UV-visible spectra were obtained
on a Hewlet Packard 8453 spectrometer. NMR spectra were
recorded on Bruker ARX 300 and Bruker AVANCE 400 spec-
trometers. Chemical shifts are cited relative to SiMe4 (1H, external),
CFCl3 (19F, external), and 85% H3PO4 (31P, external) and Na2PtCl6
in D2O (195Pt). J are given in Hz, and assignments are based on
1H-1H COSY and gHSQC experiments (for complexes 5b and 6b).
Diffuse reflectance UV-vis (DRUV) spectra were recorded on a
Unicam UV-4 spectrophotometer equipped with a Spectralon RSA-
UC-40 Labsphere integrating sphere. The solid samples were
homogeneously diluted with silica. The mixtures were placed in a
homemade cell equipped with quartz window. Steady-state pho-
toluminescence spectra were recorded on a Jobin-Yvon Horiba
Fluorolog FL-3-11 Tau 3 spectrofluorimeter using band pathways
of 3 nm for both excitation and emission. Phosphorescence lifetimes
were recorded with a Fluoromax phosphorimeter accessory contain-
ing a UV xenon flash tube with a flash rate between 0.05 and 25
Hz. Phase shift and modulation were recorded over the frequency
range of 0.1-100 MHz. The lifetime data were fitted using the
Jobin-Yvon software package and the Origin 6.0 and 7.5 program.
Synthesis of [Pd(bzq)(NCMe)2]ClO4 (1). AgClO4 (0.712 g,
3.434 mmol) was added to a stirred suspension of B (0.110 g, 1.718
mmol) in MeCN (100 mL). After stirring at room temperature for
2 h in the dark, the mixture was filtered through Celite and the
resulting solution evaporated to dryness. Addition of Et2O (30 mL)
to the residue gave pure 3 as a white solid. Yield: 0.151 g, 94%.
Anal. Calcd for C17H14ClN3O4Pd: C, 43.79; H, 3.02; N, 9.01. Found:
C, 43.29; H, 2.65; N, 8.70. MS (ES+): m/z 325 [Pd(bzq)(NCMe)]+
75%. IR (cm-1): 2356 (m, NCMe), 2330 (m, sh, NCMe), 2305 (m,
νst(C-N), NCMe); 1097 (vs, ν3 ClO4-), 623 (s, ν4 ClO4-). ΛM (5
× 10-4 M acetonitrile solution): 122.6 Ω-1 cm2 mol-1.1H NMR
(400.13 MHz, CD3CN, 298K, δ): 8.65 (s, H2, bzq), 8.52 (d, 3JH4-H3
) 7.9, H4, bzq), 7.83 (AB, H5, bzq), 7.75 (AB, 3JH6-H5 ) 8.6, H6,
3JH3-H4 ) 8.1, JH3-H2 ) 4.4, JH3-H5 ) 1.2, H3, ppy), 7.25-7.10
3
4
(m, 3H, H7, H8, H9, ppy), 1.99 (s, 6H, CH3CN).
Synthesis of [Pt(bzq)(CN-t-Bu)2]ClO4 (5a). To a yellow
suspension of [Pt(bzq)(NCMe)2](ClO4) (3) (0.200 g, 0.36 mmol)
in methanol (15 mL) was added CN-t-Bu (83 µL, 0.72 mmol). After
2 h of stirring at room temperature, the solvent was evaporated to
dryness, and the residue was treated with methanol (7 mL). The
yellow solid was filtered and washed with Et2O. Yield: 0.22 g, 95%.
Anal. Calcd for C23H30ClN3O4Pt: C, 43.23; H, 4.10; N, 6.58. Found:
C, 43.15; H, 3.80; N, 6.69. MS (ES+): m/z 539 [Pt(bzq)(CN-t-
Bu)2]+ 100%. IR (cm-1): 2235 (s, ν(CtN)), 2210 (s, ν(CtN));
1097 (s, ν3, ClO4-), 623 (s, ν4, ClO4-). ΛM (5 × 10-4
M
1
nitromethane solution): 66.6 Ω-1 cm2 mol-1. H NMR (400.13
3
4
MHz, CD2Cl2, 298 K, δ): 8.97 (dd, JH2-H3 ) 5.2, JH2-H4 ) 1.2,
3
4
3JPt-H2 ) 34.5, H2, bzq), 8.60 (dd, JH4-H3 ) 8.1, JH4-H2 ) 1.2,
H4, bzq), 7.82 (AB, 3JH5-H6 ) 8.7, H5, bzq), 7.73 (m, H3, H9, bzq),
7.68 (dd, 3JH7-H8 ) 7.4, 4JH7-H9 ) 0.9, H7, bzq), 7.65 (AB, 3JH6-H5
) 8.7, H6, bzq), 7.58 (t, JH8-H9/7 ) 7.4, H8, bzq), 1.68 (s, 18H,
3
CH3, CN-t-Bu).
Synthesis of [Pt(bzq)(CN-t-Bu)2]PF6 (5b). To a yellow suspen-
sion of [{Pt(bzq)(µ-Cl)}2] (A) (0.150 g, 0.183 mmol) in acetone
(10 mL) were added CN-t-Bu (83 µL, 0.734 mmol) and NaPF6
(0.062 g, 0.366 mmol). After 15 min of stirring at room temperature,
the solvent was evaporated to dryness and the residue treated with
CH2Cl2 (20 mL) and filtered through Celite. Evaporation of the
filtrate to ca. 3 mL yielded 5b as a yellow solid, which was filtered
and washed with n-hexane. Yield: 0.174 g, 70%. Anal. Calcd for
C23H26F6N3PPt: C, 40.36; H, 3.83; N, 6.14. Found: C, 40.38; H,
3.73; N, 6.54. MS (ES+): m/z 539 [Pt(bzq)(CN-t-Bu)2]+, 100%.
IR (cm-1): 2236 (s, ν(CtN)), 2210 (s, ν(CtN)). ΛM (5 × 10-4
M
acetonitrile solution): 160.9 Ω-1 cm2 mol-1. 1H NMR (400.13 MHz,
CD2Cl2, 298 K, δ): 8.81 (d, 3JH2-H3 ) 5.2, 3JPt-H2 ) 34.5, H2, bzq),
8.48 (d, 3JH3-H4 ) 8.1, H4, bzq), 7.79 (AB, 3JH5-H6 ) 8.7, H5, bzq),
7.70 (m, H3, H9, H7, bzq), 7.65 (AB, 3JH6-H5 ) 8.7, H6, bzq), 7.57
3
(t, JH8-H9/7 ) 7.6, H8, bzq), 1.69 (s, 9H, CN-t-Bu), 1.68 (s, 9H,
CN-t-Bu). 19F NMR (282.40 MHz, CD2Cl2, 298 K, δ): -73.62 (d,
JP-F ) 711, PF6). 31P{1H} NMR (121.50 MHz, CD2Cl2, 298 K,
δ): -142.5 (sept, JP-F ) 711, PF6). 13C{1H} NMR (CD2Cl2, 75.50
2
MHz, 298 K, δ): 157.55 (s, C10), 153.15 (s, JPt-C ) 31.6, C2),
149.47 (s, C13/14), 143.89 (s, C13/14), 142.22 (s, C4), 136.10 (s, 2JPt-C
3
3
) 104, C9), 135.86 (s, JPt-C ) 48.1, C11/12), 132.21 (s, JPt-C
)
64.5, C8), 131.74 (s, C5), 129.37 (s, JPt-C ) 34.3, C11/12), 126.84
(s, C7), 125.51 (s, C6), 125.08 (s, C3), 31.48 (s, CH3, CN-t-Bu),
31.33 (s, CH3, CN-t-Bu). 195Pt NMR (86.02 MHz, CD2Cl2, 298 K,
δ): -4246 (s br).
3
Synthesis of [Pt(bzq)(CN-Xyl)2]ClO4 (6a). Complex 6a was
prepared as a yellow solid according to a similar procedure to that
for compound 5a starting from [Pt(bzq)(NCMe)2](ClO4) (3) (0.191
g, 0.34 mmol) and CN-Xyl (0.092 g, 0.69 mmol). Yield: 0.232 g,
92%. Anal. Calcd for C31H26ClN3O4Pt: C, 50.65; H, 3.57; N, 5.72.
Found: C, 50.91; H, 3.32; N, 5.70. MS (ES+): m/z 635.2
[Pt(bzq)(CN-Xyl)2]+, 100%. IR (cm-1): 2204 (s, ν(CtN)), 2184
(s, ν(CtN)); 1087 (s, ν3, ClO4-), 623 (s, ν4, ClO4-). ΛM (5 × 10-4
M nitromethane solution): 69.8 Ω-1 cm2 mol-1. 1H NMR (400.13
3
3
bzq), 7.73 (d, JH9-H8 ) 7.3, H9, bzq), 7.60 (dd, JH3-H4 ) 7.9,
(92) Pregosin, P. S.; Wombacher, F.; Albinati, A.; Lianza, F. J.
Organomet. Chem. 1991, 418, 249.
(93) Hartwell, G. E.; Lawrence, R. V.; Smas, M. J. Chem. Commun.
1970, 912.
(94) Craig, C. A.; Watts, R. J. Inorg. Chem. 1989, 28, 309.

Luminescence of Cyclometalated Compounds
Organometallics, Vol. 28, No. 6, 2009 1717
Table 5. Crystal data and structure refinement parameters for
5.39. Found: C, 53.72; H, 2.80; N, 5.27. MS (ES+): m/z 679.2
[Pt(bzq)(CN-2-Np)2]+, 100%. IR (cm-1): 2217 (s, ν(CtN)), 2190
(s, ν(CtN)); 1093 (s, ν3, ClO4-), 623 (s, ν4, ClO4-). ΛM (5 × 10-4
M nitromethane solution): 65.5 Ω-1 cm2 mol-1. 1H NMR (400.13
MHz, CD3CN, 298 K, δ): 8.67 (d, 3JH2-H3 ) 5.1, 3JPt-H2 ) 35, H2,
complexes 6a · CH2Cl2 and 6b · CH2Cl2
6a · CH2Cl2
6b · CH2Cl2
empirical formula
fw
C32H28Cl3N3O4Pt
820.01
C32H28Cl2F6N3PPt
865.53
3
temperature (K)
wavelength (Å)
cryst syst
space group
cryst dimens (mm)
a (Å)
b (Å)
c (Å)
R (deg)
(deg)
100(2)
0.71073
monoclinic
P2(1)/n
100(2)
0.71073
monoclinic
P1 21/n 1
bzq), 8.29 (d, JH4-H3 ) 7.9, H4, bzq), 8.24 (s, H1, Np), 8.16 (s,
H1′, Np), 7.84 (m, 7H, Np/bzq), 7.61 (m, 9H, Np/bzq), 7.47 (d, J
3
3
) 8.5, 1H, bzq), 7.41 (dd, JH3-H4 ) 7.9, JH3-H2 ) 5.1, H3, bzq).
Synthesis of [Pt(bzq)(CN-2-Np)2]PF6 (7b). A yellow suspension
of [{Pt(bzq)(µ-Cl)}2] (A) (0.100 g, 0.122 mmol) in acetone (10
mL) was treated with CN-2-Np (0.075 g, 0.488 mmol) and NaPF6
(0.040 g, 0.245 mmol), giving an initial red suspension. The mixture
was stirred for 15 min, changing the color to a yellow suspension.
The solvent was removed and the final residue was treated with
water (20 mL) and filtered. Yield: 0.176 g, 87%. Anal. Calcd for
C35H22F6N3PPt: C, 50.98; H, 2.69; N, 5.10. Found: C, 51.40; H,
2.89; N, 5.04. MS (ES+): m/z 678.8 [Pt(bzq)(CN-2-Np)2]+, 100%.
0.41 × 0.27 × 0.21 0.32 × 0.14 × 0.12
16.0067(2)
10.8311(2)
18.2324(3)
90
8.28410(10)
17.3713(2)
21.6571(2)
90
90.8380(10)
90
3116.24(6)
1.845
4
106.363(2)
90
3032.92(8)
1.796
γ (deg)
V (Å3)
Dcalc (Mg/m3)
Z value
4
µ(Mo KR) (mm-1
F(000)
)
4.934
1608
4.790
1688
IR (cm-1): 2215 (s, ν(CtN)), 2189 (s, ν(CtN)). ΛM (5 × 10-4
M
acetonitrile solution): 137.7 Ω-1 cm2 mol-1. 1H NMR (300.13 MHz,
CD3CN, 298 K, δ): 8.52 (d, 3JH2-H3 ) 4.8, 3JPt-H2 ) 35, H2, bzq),
8.21 (d, 3JH4-H3 ) 7.9, H4, bzq), 8.16 (s, H1, Np), 8.08 (s, H1′, Np),
7.82 (m, 6H, Np/bzq), 7.60 (m, 10H, Np/bzq), 7.40 (d, J ) 8.5,
θ range (deg)
3.82 to 25.10
20 262
5383
3.77 to 25.10
20 635
5517
no. of reflns measd
no. of obsd reflns
goodness of fit on F2
a
1.068
1.020
3
3
1H, bzq), 7.30 (dd, JH3-H4 ) 7.6, JH3-H2 ) 5.4, H3, bzq). The
low solubility of this complex precludes its characterization by
13C{1H} and 195Pt NMR.
final R indices [I > 2σ(I)]a R1 ) 0.0167,
wR2 ) 0.0403
R1 ) 0.0147,
wR2 ) 0.0375
R1 ) 0.0170,
wR2 ) 0.0381
R indices (all data)
R1 ) 0.0198,
wR2 ) 0.0170
Computational Details. The computational method used was
densityfunctionaltheory(DFT)withtheB3LYPexchange-correlation
functional,95-97 using the Gaussian 0398 program package. The
basic set used was the LanL2DZ effective core potential for the
platinum atom and 6-31G(d,p) for the remaining atoms. Cation 6+
was optimized as an isolated molecule from the solid-state geometry
at the DFT level of theory. The time-dependent density-functional
theory (TD-DFT) calculation was carried out using the polarized
continuum model approach implemented in the Gaussian 03
software.
a R1
)
∑(|Fo|
-
|Fc|)/∑|Fo|; wR2
)
[∑w(Fo
-
Fc2)2/∑wFo ]1/2
;
2
2
Goodness of fit ) {∑[w(Fo - Fc2)2]/(Nobs - Nparam)}1/2; w ) [σ2(Fo ) +
2
2
(g1P)2 + g2P]-1; P ) [max(Fo ;0) + 2Fc2]/3.
2
3
4
MHz, CD2Cl2, 298 K, δ): 9.14 (dd, JH2-H3 ) 5.3, JH2-H4 ) 1.0,
3JPt-H2 ) 37.8, H2, bzq), 8.61 (d, 3JH4-H3 ) 8.1, H4, bzq), 7.91 (d,
3
3
3JH9-H8 ) 7.6, JPt-H9 ) 48.7, H9, bzq), 7.89 (AB, JH5-H6 ) 8.7,
H5, bzq), 7.79 (d,3JH7-H8 ) 7.6, H7, bzq), 7.75 (dd, 3JH3-H4 ) 8.1,
3JH3-H2 ) 5.3, H3, bzq), 7.72 (AB, 3JH6-H5 ) 8.7, H6, bzq), 7.60 (t,
3JH8-H9/7 ) 7.6, H8, bzq), 7.36-7.23 (AB2, 2H4, 2H3, 2H5, Xyl),
2.53 (s, 12H, CH3-Xyl).
X-ray Structure Analysis of 6a · CH2Cl2 and 6b · CH2Cl2.
Crystal data and other details of the structure analyses are presented
in Table 5. Yellow needles were obtained by slow diffusion of
n-hexane (6a) or 2-propanol (6b) into dichloromethane (at 5 °C)
solutions of each compound. Single crystals were mounted in quartz
fibers in a random orientation and held in place with fluorinated
oil. Data collections were performed at 100 K temperature on an
Oxford Diffraction Xcalibur CCD diffractometer using graphite-
monochromated Mo KR radiation (λ ) 0.71073 Å) with a nominal
crystal to detector distance of 5.0 cm. Unit cell dimensions were
determined from the positions of 16 979 reflections from the main
data set for 6a · CH2Cl2 and from the positions of 18 152 reflections
from the main data set for 6b · CH2Cl2. Sets of data were collected
for the two structures based on ω-scans runs. The diffraction frames
were integrated and corrected for absorption using the Crysalis RED
package.99 Lorentz and polarization corrections were applied. The
structures were solved by direct methods. All non-hydrogen atoms
were assigned anisotropic displacement parameters. The hydrogen
atoms were constrained to idealized geometries and assigned
isotropic displacement parameters equal to 1.2 times the Uiso values
of their respective parent carbon toms (1.5 times for methyl H
atoms). Full-matrix least-squares refinement of these models against
F2 using the SHELXL-97 program100 converged to final residual
Synthesis of [Pt(bzq)(CN-Xyl)2]PF6 (6b). Complex 6b was
prepared as a yellow solid according to a similar procedure to that
for compound 5b starting from [{Pt(bzq)(µ-Cl)}2] (A) (0.100 g,
0.122 mmol), CN-Xyl (0.064 g, 0.488 mmol), and NaPF6 (0.041
g, 0.244 mmol). Yield: 0.145 g, 76%. Anal. Calcd for
C31H26F6N3PPt: C, 47.70; H, 3.36; N, 5.38. Found: C, 47.64; H,
3.12; N, 5.74. MS (ES+): m/z 635.4 [Pt(bzq)(CN-Xyl)2]+, 100%.
IR (cm-1): 2208 (s, ν(CtN)), 2187 (s, ν(CtN)). ΛM (5 × 10-4
M
acetonitrile solution): 164.7 Ω-1 cm2 mol-1.1H NMR (400.13 MHz,
CD2Cl2, 298 K, δ): 9.24 (d, 3JH2-H3 ) 5.2, 3JPt-H2 ) 37.8, H2, bzq),
3
3
3
8.71 (d, JH4-H3 ) 8.1, H4, bzq), 8.02 (d, JH9-H8 ) 7.6, JPt-H9
)
48.3, H9, bzq), 7.98 (AB, 3JH5-H6 ) 9.0, H5, bzq), 7.91 (d, 3JH7-H8
) 8.0, H7, bzq), 7.83 (AB, 3JH5-H6 ) 9.0, H6, bzq + H3 overlapped),
7.72 (t, 3JH8-H9/7 ) 7.7, H8, bzq), 7.52-7.33 (AB2, 2H4, 2H3, 2H5,
Xyl), 2.64 (s, 12H, CH3-Xyl). 19F NMR (282.40 MHz, CD2Cl2,
298 K, δ): -72.59 (d, JP-F ) 711, PF6). 31P{1H} NMR (121.50
MHz, CD2Cl2, 298 K, δ): -142.5 (sept, JP-F ) 711, PF6). 13C{1H}
NMR (75.50 MHz, CD2Cl2, 298 K, δ): 157.80 (s, C10), 153.37 (s,
2JPt-C ) 31.2, C2), 149.83 (s, C13/14), 148.08 (s, C13/14), 142.88 (s,
C4), 137.81 (s, 2Co, Xyl), 137.55 (s, C11/12), 136.94 (s, C9), 136.23
(s, 2Co, Xyl), 133.08 (s, Cp, Xyl), 132.70 (s, Cp, Xyl), 132.49 (s,
C8), 132.06 (s, C5), 130.35 (s, Cm, Xyl), 130.30 (s, Cm, Xyl), 129.78
(s, C11/12), 127.46 (s, C7), 125.71 (s, C3), 125.55 (s, Cipso, Xyl),
125.20 (s, C6), 120.77 (s, Cipso, Xyl), 20.36 (s, 2CH3, Xyl), 20.31
(s, 2CH3, Xyl). 195Pt NMR (86.02 MHz, CD2Cl2, 298 K, δ): -4168
(s br).
(95) Becke, A. D. Phys. ReV. A: At., Mol., Opt. Phys. 1988, 38, 3098.
(96) Lee, C.; Yang, W.; Parr, R. G. Phys. ReV. B: Condens. Matter
Mater. Phys. 1988, 37, 785.
(97) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
Synthesis of [Pt(bzq)(CN-2-Np)2]ClO4 (7a). Complex 7a was
prepared as a yellow solid according to a similar procedure to that
for compound 5a starting from [Pt(bzq)(NCMe)2](ClO4), 3 (0.161
g, 0.29 mmol), and CN-2-Np (0.089 g, 0.58 mmol). Yield: 0.203
g, 90%. Anal. Calcd for C35H22ClN3O4Pt: C, 53.96; H, 2.85; N,
(98) Frisch, M. J.; et al. Gaussian 03, ReVision E.01; Gaussian, Inc.:
Wallingford, CT, 2004 (see Supporting Information for complete cita-
tion).
(99) CrysAlis; RED. A program for Xcalibur CCD System X-ray
diffraction data reduction; Oxford Diffraction Ltd.: Oxford, UK, 2005.

1718 Organometallics, Vol. 28, No. 6, 2009
D´ıez et al.
indices given in Table 5. Final difference electron density maps
showed no peaks above 1 e Å-3 for both structures.
structure of cation 6+ and representative frontier orbitals for it
(Tables S1 and S2 and Figures S3 and S4). Table S3: Emission
data for complexes 5-7 in other solvents (5 × 10-5 M solutions at
298 K). Absorption spectra (Figures S1, S2, S5, S6). Emission
spectra (Figures S7-S16). Crystallographic data in CIF format. This
materialisavailablefreeofchargeviatheInternetathttp://pubs.acs.org.
Acknowledgment. This work was supported by the
Spanish Ministerio de Educacio´n y Ciencia and FEDER
funds(ProjectsCTQ2008-06669-C02-01,02/BQUandCTQ2005-
06807/BQU and a grant for A.D.).
OM800845C
Supporting Information Available: Drawing, table of atomic
coordinates, and excitation calculations for the DFT-optimized
(100) Sheldrick, G. M. SHELXL-97, a program for crystal structure
determination; University of Go¨ttingen: Go¨ttingen, Germany, 1997.