Spectral and photophysical properties of mono and dinuclear Pt(II) and Pd(II) complexes: An unusual emission behaviour

Article abstract of DOI:10.1016/j.poly.2004.09.029

Mononuclear complexes of the formula [M(N-N)(DHB)] and dinuclear complexes of the formula [M₂(BPY)₂(THB)] were synthesized and characterized. These complexes were found to show an optically active LLCT band and the platinum complexes of the series were found to show dual emitting states. Eight mononuclear complexes of the formula [M(N-N)(DHB)] and two binuclear complexes of the formula [M₂(BPY)₂(THB)] {where M = Pd(II) or Pt(II), N-N = 2,2′-bipyridine (BPY), 2,2′-biquinoline (BIQ), 4,7-diphenyl-1,10-phenanthroline (DPP), 1,10-phenanthroline (PHEN); DHB = dianion of 3,4-dihydroxybenzaldehyde and THB = tetraanion of 3,3′,4,4′-tetrahydroxy benzaldazine} were prepared and their electrochemical, spectral and photophysical properties were examined. These complexes were characterized by chemical analysis, IR and proton NMR spectroscopy. A detailed study on the absorption spectroscopy of these complexes was made. These complexes were found to show a low-energy solvatochromic ligand-to-ligand charge-transfer (LLCT) band. The electronic energies of these bands have been analyzed and compared with electrochemical data. Emission behaviour of the complexes of the series, [Pt(N-N)(DHB)], [Pt(N-N)(DHBA)] {where DHBA is the dianion of 3,4-dihydroxybenzoic acid} and [Pt₂(BPY) ₂(THB)] was also investigated. These platinum complexes were found to emit from a low-energy state at low temperature and a high-energy state at room temperature. Photophysics of these complexes is also discussed.

Full text of DOI:10.1016/j.poly.2004.09.029

Polyhedron 23 (2004) 3173–3183
www.elsevier.com/locate/poly
Spectral and photophysical properties of mono and dinuclear
Pt(II) and Pd(II) complexes: An unusual emission behaviour
a,
b
V. Anbalagan *, T.S. Srivastava
a
Department of Chemistry, Wichita State University, 1845, N. Fairmount, Wichita, KS 67260, USA
b
Department of Chemistry, Indian Institute of Technology, Powai, Bombay 400 076, India
Received 22 June 2004; accepted 30 September 2004
Available online 13 November 2004
Abstract
Eight mononuclear complexes of the formula [M(N-N)(DHB)] and two binuclear complexes of the formula [M2(BPY)2(THB)]
{where M = Pd(II) or Pt(II), N-N = 2,20-bipyridine (BPY), 2,20-biquinoline (BIQ), 4,7-diphenyl-1,10-phenanthroline (DPP), 1,
10-phenanthroline (PHEN); DHB = dianion of 3,4-dihydroxybenzaldehyde and THB = tetraanion of 3,30,4,40-tetrahydroxy benz-
aldazine} were prepared and their electrochemical, spectral and photophysical properties were examined. These complexes were
characterized by chemical analysis, IR and proton NMR spectroscopy. A detailed study on the absorption spectroscopy of these
complexes was made. These complexes were found to show a low-energy solvatochromic ligand-to-ligand charge-transfer (LLCT)
band. The electronic energies of these bands have been analyzed and compared with electrochemical data. Emission behaviour of the
complexes of the series, [Pt(N-N)(DHB)], [Pt(N-N)(DHBA)] {where DHBA is the dianion of 3,4-dihydroxybenzoic acid} and
[Pt2(BPY)2(THB)] was also investigated. These platinum complexes were found to emit from a low-energy state at low temperature
and a high-energy state at room temperature. Photophysics of these complexes is also discussed.
ꢀ 2004 Elsevier Ltd. All rights reserved.
Keywords: LLCT; Luminescence; Phosphorescence; Pt(II) and Pd(II)
1. Introduction
linear optics, photonic molecular devices and photolu-
minescent probes of biological systems [2–7]. By far
most work has been carried out on polypyridine com-
plexes of d6 metal ions [8] such as Ru(II), Os(II) and
Re(I), but not on the d8 metal complexes such as Pt(II)
or Pd(II). Some of the early studies were on Pt(II) com-
plexes such as [PtX4]2ꢀ {X = halide}, [Pt(diimine)X2]
and [Pt(diimine)]2+, for which emission was observed
only in frozen solvent glasses or in the solid state [9].
However, a few reports on photophysical properties of
d8 Pt(II) complexes of diimine in solution are available
[10–15]. Three classes of Pt(II) diimine complexes show-
ing fluid solution luminescence are distinguished by the
nature of their emissive triplet excited state, namely: (1)
diimine localized p–p*, (2) metal-to-ligand(diimine)
charge transfer (MLCT) and (3) mixed metal
ligand-to-ligand charge transfer or metal-mediated
Luminescent transition metal complexes have fasci-
nated photochemists for many decades [1], mainly be-
cause of the special features associated with these
complexes such as visible light absorption, photolumi-
nescence, long life times and relative inertness toward
unimolecular photochemistry [1f]. Growth in this area
has been driven by rapid advances in the techniques of
studying excited-state transient species and in the theory
of photoinduced electron transfer, solar energy conver-
sion, supramolecular assemblies, photocatalysis, non-
*
Corresponding author. Tel.: +1 316 978 7397; fax: +1 316 978
3431.
E-mail
addresses:
victor.anbalagan@wichita.edu,
victoria-
n1217@yahoo.com (V. Anbalagan).
0277-5387/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2004.09.029

3174
V. Anbalagan, T.S. Srivastava / Polyhedron 23 (2004) 3173–3183
ligand-to-ligand charge transfer (MMLLCT) or ligand-
to-ligand charge transfer (LLCT). In all these cases the
LUMO is predominantly centered on the diimine ligand.
Square-planar complexes containing both easily oxi-
disable and reducible ligands were found to show a
LLCT transition [16]. These transitions were highly
solvatochromic, of which some of them exhibit the
remarkable property of being luminescent in solution
[17]. Metal complexes possessing such a transition have
become the focus for numerous photochemical studies
due to large molar absorptivity of the transition [16].
The LLCT excited states had previously been noted
in some Zn(II) and Pt(II) complexes containing both
diimine and aromatic thiolate (dithiolate) ligands
[16c,16f]. Dance and Miller [16a] described the obser-
vation of a LLCT band for the first time in a Ni(II)
complex containing a-diimine and dithiolate. In gen-
eral, both electron-donating substituents on the thio-
late and electron-withdrawing substituents on the
diimine ligands would lower the LLCT transition en-
ergy. On the contrary, electron-withdrawing groups
on the thiolate and electron-donating substituents on
the diimine increase the transition energy. Thus, selec-
tive fine tuning of this excited state could be achieved
by altering the ligands (diimine or dithiolate) or chang-
ing the substituents on the ligand(s) or the metal ion(s)
[16,17].
The various diimines used are 4,7-diphenyl-1,10-
phenanthroline, 2,20-bipyridine, 2,20-biquinoline and
1,10-phenanthroline. The metal ions used are Pt(II)
and Pd(II). 3,4-Dihydroxybenzaldehyde and 3,4-dihyd-
roxybenzoic acid are used as the dianionic ligand.
3,30,4,40-Tetrahydroxybenzaldazine is used as the tetra-
anionic ligand to synthesise the dinuclear complexes.
2. Experimental
2.1. Starting materials
Potassium tetrachloroplatinate(II), palladium chlo-
ride, 1,10-phenanthroline monohydrate, 4,7-diphenyl-
1,10-phenanthroline (Loba-Chemie Indoauatranal Co.,
India), 2,20-biquinoline, potassium hydroxide (Merck,
India), 3,4-dihydroxybenzoic acid, 3,4-dihydroxybenz-
aldehyde (Fluka AG, Switzerland), hydrazine hydro-
chloride, ammonia, acetic acid (s.d.fine-CHEM Ltd.,
India) and 2,20-bipyridine (Glaxo Industries, India)
were bought, of reagent grade and used as such. The
reagent grade solvents were purified before use by
standard procedures [19]. Solvents of spectroscopic
grade were used for cyclic voltammetry and spectro-
scopic measurements.
The LLCT transitions have also been reported for a
variety of d8 metal complexes with catecholate and a-dii-
mine ligands [18], where the charge transfer takes place
from the catecholate ligand to the diimine ligand. Here
too, the electron-withdrawing substituents on the dii-
mine and the electron-donating substituents on the
catechol lower the LLCT transition energy and elec-
tron-donating substituents on the diimine and the elec-
tron-withdrawing substituents on the catechol increase
the LLCT transition energy. However, the solution-state
emission from these complexes has not been reported.
Many of them were found to be potential candidates
for generation of singlet molecular oxygen (1O2) since
2.2. Physical measurements
The chemical analyses of carbon, hydrogen and nitro-
gen for the complexes were performed using a Carlo
Erba Strumentazion Elemental Analyzer, Model 1106,
at R.S.I.C., Central Drug Research Institute, Lucknow.
The IR spectra of the complexes in KBr pellets were re-
corded with a Nicolet 170-Sx FT-IR spectrophotometer
in the region 4000–600 cmꢀ1. Electronic absorption
spectra of the complexes in various solvents were ob-
tained using a Shimadzu UV-265 UV–VIS spectropho-
tometer. The proton nuclear magnetic resonance (1H
NMR) spectra of the complexes were acquired using a
Varian VXR-300s NMR spectrometer in deuterated di-
methyl sulfoxide [(CD3)2SO]. Tetramethylsilane was
used as the internal reference. All the spectra were re-
corded in the range of 0–11 ppm. The cyclic voltammo-
grams of the complexes in acetonitrile (ꢁ10ꢀ3 M)
containing 0.1 M tetra(n-butyl)ammonium hexafluoro-
phosphate as supporting electrolyte were obtained on
a Model CV-IB Bioanalytical Cyclic Voltammetry appa-
ratus equipped with an Omnigraphic 2000 Recorder. A
single compartment cell was employed with an Ag/AgCl
reference-electrode (ꢀ0.041 V versus standard calomel
electrode, SCE), a platinum wire counter electrode and
a platinum working electrode (6 mm outer diameter).
The scan rate used was 200 mV/s. The solutions were
degassed for 15 min before recording the cyclic
voltammogram. Room-temperature excitation and
1
they produce O2 upon irradiation at the LLCT band
[18b,18c]. Here we report, for the first time, the solu-
tion-state luminescence of such complexes. We also re-
port the spectral and electrochemical behaviour of
these complexes. An attempt to make a correlation be-
tween redox potentials and the energy of the absorption
maxima is made. In addition, we synthesized two dinu-
clear complexes for comparison of the electronic proper-
ties since dinuclear complexes have been known to
luminesce at higher wavelength compared to related
monomers. It has been shown that dinuclear complexes
possess a low-lying excited state due to a large decrease
in the energy of the lowest p* orbital of the bridging lig-
ands upon complexation [3]. We also report the solvat-
ochromic LLCT transition and solution state
luminescence of these complexes.

V. Anbalagan, T.S. Srivastava / Polyhedron 23 (2004) 3173–3183
3175
luminescence spectra of the metal complexes were re-
corded in a Spex spectrofluorimeter equipped with a
Hamamadzu R928 photomultiplier tube (PMT). The
PMT was cooled externally by circulating cold water.
The emission spectra were corrected for excitation lamp
intensity variation and solvent emission. The fluores-
cence quantum yields were measured by an optically di-
lute method [24] using tryptophan in water as a standard
[25]. The quantum yield values were corrected for sol-
vent refractive index. Fluorescence lifetime measure-
ments were carried out by the single photon counting
technique using a nanosecond fluorescence spectrometer
from Applied Photophysics (model SP-170) with a
bright and stable nanosecond flash-lamp operating at
frequencies up to 200 kHz. The lamp was filled with
nitrogen gas. The PMT type XP 2020Q was used for
photodetection. Output of the multichannel analyzer
was analyzed for single, double or multi exponential de-
cay functions. The solutions were excited at 296, 316 or
337 nm. Phosphorescence measurements were made
using a SPEX 1934C phosphorimeter with a RCA
C13034 photomultiplier attachment having the facility
to provide corrected emission spectra. Metal complexes
dissolved in EPA mixture (10ꢀ6 M) were frozen in liquid
nitrogen (77 K) in a 10 mm quartz cuvette and the spec-
tra were recorded using different wavelengths of
excitation.
2.3.2. [Pd(PHEN)(DHB)] (2)
[Pd(PHEN)Cl2] (0.2 mmol) was dissolved in 50 cm3
of DMF. To this, 0.2 mmol of H2DHB dissolved in
1.6 cm3 of 0.25 N KOH in methanol was added slowly.
The solution was stirred for 30 min. Then the solution
was evaporated to 5 cm3 and cooled overnight. The pre-
cipitate formed was filtered and recrystallized from
DMF and dried in a vacuum desiccator over anhydrous
CaCl2. The yield obtained was 45%. 1H NMR
[(CD3)2SO]: d 8.85 (d, 2H, 2, 9), 8.91 (d, 2H, 4, 7),
8.23 (s, 2H, 5, 6), 8.08 (m, 2H, 3, 8), 6.64 (d, 1H, B),
6.68 (s, 1H, C), 6.39 (d, 1H, A), 9.5 (s, 1H, D). Anal.
Calc. for C19H12N2O3Pd: C, 53.98; H, 2.86; N, 6.63.
Found: C, 53.54; H, 2.85; N, 6.59%.
2.3.3. [Pd(BIQ)(DHB)] (3)
This complex was prepared according to the protocol
given for 1, replacing [Pd(BIQ)Cl2] with [Pd(BPY)Cl2].
1
The yield obtained was 60%. H NMR [(CD3)2SO]: d
9.35 (d, 1H, 3), 9.25 (d, 1H, 30), 9.01 (d, 2H, 4, 40),
8.85 (d, 2H, 5, 50), 8.23 (d, 2H, 6, 60), 7.89 (t, 2H, 7,
70), 8.07 (m, 2H, 8, 80), 6.92 (dd, 1H, B), 6.82 (d, 1H,
C), 6.51 (d, 1H, A), 9.55 (s, 1H, D). Anal. Calc. for
C25H16N2O3Pd: C, 60.19; H, 3.23; N, 5.62. Found: C,
59.80; H, 3.25; N, 5.66%.
2.3.4. [Pd(DPP)(DHB)] (4)
The complex was prepared by the procedure de-
2.3. Synthetic procedures
scribed for
2
using [Pd(DPP)Cl2] in place of
[Pd(PHEN)Cl2]. The yield obtained was 52%.
1H NMR [(CD3)2SO]: d 8.89 (m, 2H, 2, 9), 7.74 (s,
2H, 4, 7), 7.88 (s, 2H, 5, 6), 7.66 (m, 2H, 3, 8), 6.66 (d,
1H, B), 6.49 (s, 1H, C), 6.17 (d, 1H, A), 9.40 (s, 1H,
D). Anal. Calc. for C31H20N2O3Pd: C, 64.76; H, 3.51;
N, 4.87. Found: C, 64.96; H, 3.49; N, 4.86%.
[M(N-N)Cl2] {where M = Pd(II) or Pt(II) and N-N is
2,20-bipyridine (BPY), 2,20-biquinoline (BIQ), 4,7-diphe-
nyl-1,10-phenanthroline (DPP) and 1,10-phenanthroline
(PHEN)} were prepared by the reported procedures [20]
and characterized by the methods from the literature
[21,22].
2.3.5. [Pt(BPY)(DHB)] (5)
2.3.1. [Pd(BPY)(DHB)] (1)
[Pt(BPY)Cl2] (0.2 mmol) was dissolved in 25 cm3 of
DMF and filtered. To this 0.2 mmol of H2DHB dis-
solved in 1.6 cm3 of 0.25 N KOH in methanol was
added. The solution was stirred for 24 h at 60 ꢁC, then
the solvent was evaporated at 40 ꢁC. The crude product
obtained was recrystallized from chloroform and dried
in a vacuum desiccator over anhydrous calcium chlo-
ride. The yield obtained was 62%. 1H NMR [(CD3)2SO]:
8.55 (d, 2H, 3, 30), 8.38 (dt, 2H, 4, 40), 7.78 (t, 2H, 5, 50),
9.08 (d, 2H, 6, 60), 6.96 (d, 1H, B), 6.94 (s, 1H, C), 6.64
(d, 1H, A), 9.6 (s, 1H, D). Anal. Calc. for
C17H12N2O3Pt: C, 41.89; H, 2.48; N, 5.75. Found: C,
41.60; H, 2.45; N, 5.79%.
0.2 mmol of [Pd(BPY)Cl2] was dissolved in 25 cm3 of
hot acetonitrile (60 ꢁC). The solution was filtered while
hot to remove any undissolved material. To this
0.2 mmol of H2DHB dissolved in 1.6 cm3 of 0.25 N
KOH in methanol was added slowly and stirred for 30
min at the same temperature. Then the solution was
cooled to room temperature and kept in a refrigerator
overnight to obtain crystals of the complex. The com-
pound was filtered and washed with small amounts of
cold acetonitrile, water and methanol successively and
dried in a vacuum desiccator over anhydrous calcium
chloride. The compound was recrystallized from DMF
and 70% yield was obtained. 1H NMR [(CD3)2SO]:
8.58 (d, 2H, 3, 30), 8.36 (dt, 2H, 4, 40), 7.81 (t, 2H, 5,
50), 8.64 (d, 2H, 6, 60), 6.92 (dd, 1H, B), 6.77 (d, 1H,
C), 6.46 (d, 1H, A), 9.5 (s, 1H, D). Anal. Calc. for
C17H12N2O3Pd: C, 51.21; H, 3.03; N, 7.02. Found: C,
50.87; H, 3.05; N, 6.98%.
2.3.6. [Pt(PHEN)(DHB)] (6)
This complex was prepared by the method described
for 5 using [Pt(PHEN)Cl2] instead of [Pt(BPY)Cl2]. The
yield obtained was 42%. 1H NMR [(CD3)2SO]: d 9.59 (d,
2H, 2, 9), 8.99 (d, 2H, 4, 7), 8.23 (s, 2H, 5, 6), 8.12 (q,

3176
V. Anbalagan, T.S. Srivastava / Polyhedron 23 (2004) 3173–3183
2H, 3, 8), 6.94 (d, 1H, B), 6.90 (s, 1H, C), 6.60 (d, 1H,
A), 9.62 (s, 1H, D). Anal. Calc. for C19H12N2O3Pt: C,
44.62; H, 2.37; N, 5.48. Found: C, 45.21; H, 2.35; N,
5.48%.
2.3.11. [Pt2(BPY)2(THB)] (10)
[Pt(BPY)Cl2] (0.2 mmol) was dissolved in 25 cm3
DMF and filtered. To this 0.1 mmol of H4THB dis-
solved in 1.6 cm3 of 0.25 N KOH in methanol was
added. The solution was stirred for 24 h at 60 ꢁC, then
the solvent was evaporated at 40 ꢁC. The crude product
obtained was recrystallized from chloroform and dried
in a vacuum desiccator over anhydrous calcium chlo-
ride. The yield obtained was 62%. 1H NMR [(CD3)2SO]:
d 8.58 (d, 2H, 3, 30), 8.40 (d, 4H, 4, 40), 7.83 (m, 4H, 5,
50), 9.48 (d, 4H, 6, 60), 6.94 (dd, 2H, B), 6.65 (d, 2H, C),
6.65 (d, 2H, A), 9.6 (s, 2H, D). Anal. Calc. for
C34H24N6O4Pt2: C, 42.07; H, 2.49; N, 8.66. Found: C,
41.89; H, 2.53; N, 8.72%.
2.3.7. [Pt(BIQ)(DHB)] (7)
Preparation of this complex was made possible by
following the procedure given for 5 using [Pt(BIQ)Cl2]
instead of [Pt(BPY)Cl2]. The yield obtained was 62%.
1H NMR [(CD3)2SO]: d 9.49 (d, 2H, 3), 9.40 (d, 1H,
30), 8.94 (d, 2H, 4, 40), 8.19 (d, 2H, 5, 50), 8.03 (d, 2H,
6, 60), 7.85 (dt, 2H, 7, 70), 8.64 (m, 2H, 8, 80), 6.96 (d,
1H, B), 6.94 (s, 1H, C), 6.64 (d, 1H, A), 9.63 (s, 1H,
D). Anal. Calc. for C25H16N2O3Pt: C, 51.11; H, 2.75;
N, 4.77. Found: C, 51.27; H, 2.75; N, 4.80%.
The complexes [Pt(BPY)(DHBA)] (11), [Pt(PHEN)-
(DHBA)] Æ H2O (12) [Pt(BIQ)(DHBA)] (13) and
[Pt(DPP)(DHBA)] Æ H2O (14) were prepared and char-
acterized as reported in the literature [23].
2.3.8. Pt(DPP)(DHB) (8)
The complex was prepared according to the proce-
dure described for 5 using [Pt(DPP)Cl2] in place of
1
[Pt(BPY)Cl2]. The yield obtained was 48%. H NMR
[(CD3)2SO]: d 9.09 (t, 2H, 2, 9), 7.79 (s, 12H, 4, 7, 3,
8), 7.79 (s, 2H, 5, 6), 6.83 (m, 2H, B, C), 6.47 (d, 1H,
A), 9.56 (s, 1H, D). Anal. Calc. for C31H20N2O3Pt: C,
56.11; H, 3.04; N, 4.22. Found: C, 55.96; H, 3.01; N,
4.18%.
3. Results and discussion
3.1. Syntheses and characterization
Eight complexes of the formula, [M(N-N)(DHB)]
{where M = Pd(II) or Pt(II), N-N = 2,20-bipyridine
(BPY), 2,20-biquinoline (BIQ), 4,7-diphenyl-1,10-phen-
anthroline (DPP), 1,10-phenanthroline (PHEN)
and DHB = dianion of 3,4-dihydroxybenzaldehyde
(H2DHB)} were prepared and characterized. In general
these complexes were prepared by reacting stoichiomet-
ric quantities of the starting material, [M(N-N)Cl2] with
H2DHB in the presence of an appropriate amount of
KOH under a nitrogen atmosphere. An illustrative
example of the synthesis of [M(BPY)(DHB)] is shown
in Scheme 1.
2.3.9. Synthesis of 3,30,4,40-tetrahydroxybenzaldazine
(H4THB)
A solution of H2DHB (276 mg, 2 mmol in 10 cm3 of
methanol) was added dropwise to a solution containing
a mixture of 0.05 cm3 of hydrazinehydrochloride, 9 cm3
of distilled water and 1.5 cm3 of concentrated ammonia
solution. The contents were stirred for 3h at room tem-
perature, then the solution was neutralized with 1N ace-
tic acid to remove excess ammonia and cooled to get
yellow crystals of the compound. The product was
recrystallized from 50% methanol and the yield was
62%. The purity of the compound was checked using
The
various
complexes
prepared
are
[Pd(BPY)(DHB)] (1), [Pd(PHEN)(DHB)] (2), [Pd(BIQ)-
(DHB)] (3), [Pd(DPP)(DHB)] (4), [Pt(BPY)(DHB)] (5),
[Pt(PHEN)(DHB)] (6), [Pt(BIQ)(DHB)] (7) and
[Pt(DPP)(DHB)] (8).
The tetradentate ligand H4THB was synthesized by
coupling two molecules of H2DHB with hydrazinehy-
drochloride in the presence of liquid ammonia as de-
picted in Scheme 2.
1
TLC. H NMR [(CD3)2SO]: d 9.54 (s, 2H, E, E0), 9.25
(s, 2H, F, F0), 8.46 (s, 2H, D), 7.29 (d, 2H, C), 7.08
(dd, 2H, B), 6.81 (d, 2H, A). Anal. Calc. for
C14H12N2O4: C, 61.76; H, 4.44; N, 10.29. Found: C,
62.02; H, 2.49; N, 10.21%.
2.3.10. [Pd2(BPY)2(THB)] (9)
This complex was prepared according to the method
reported for 1 by adding 0.1 mmol of H4THB instead
of 0.2 mmol of H2DHB. The compound was recrystal-
lized twice from acetonitrile and dried in a vacuum des-
iccator over anhydrous calcium chloride. The yield was
Two complexes of the formula [M2(BPY)2(THB)]
{where M is Pd(II) or Pt(II) and BPY is 2,20-bipyridine
and THB is the tetraanion of tetrahydroxy benzalda-
zine} were prepared using the starting material
H4THB. The complexes prepared were [Pd2(BPY)2-
(THB)] (9) and [Pt2(BPY)2(THB)] (10). Four more plat-
inum complexes, namely [Pt(BPY)(DHBA)] (11),
[Pt(PHEN)(DHBA)] Æ H2O (12), [Pt(BIQ)(DHBA)] (13)
and [Pt(DPP)(DHBA)] Æ H2O (14) were prepared
for luminescence studies, according to the reported
procedure [23].
1
25%. H NMR [(CD3)2SO]: d 8.52 (d, 2H, 3, 30), 8.31
(dt, 4H, 4, 40), 7.78 (m, 4H, 5, 50), 8.59 (d, 4H, 6,
60), 6.87 (dd, 2H, B), 6.72 (d, 2H, C), 6.41 (d, 2H,
A), 9.52 (s, 2H, D). Anal. Calc. for C34H24N6O4Pd2:
C, 51.47; H, 3.05; N, 10.59. Found: C, 51.27; H,
3.05; N, 10.57%.

V. Anbalagan, T.S. Srivastava / Polyhedron 23 (2004) 3173–3183
3177
N
N
M
Cl
Cl
CHO
N
O
O
2KOH
+
M
HO
OH
N
[M(BPY)(DHB)]
CHO
M = Pd2+ or Pt2+
H2DHB
Scheme 1. Synthesis of [M(N-N)(DHB)] complexes.
HO
HO
2
OH
i. N2H4.HCl
HO
CH=N-N=CH
H4THB
OH
ii. NH4OH
iii. CH3COOH
OH
CHO
H2DHB
Scheme 2. Synthesis of H4THB.
Changes in the IR spectra in the ligand segment of
the [M(N-N)(DHB)] complexes are compared with that
of the parent chloro compounds of the formula [M(N-
N)Cl2], as well as with the free ligands. The ring fre-
quency of the a-diimine moiety is shifted to higher
frequency on complexation as compared to the free lig-
and. The presence of two additional sharp bands around
1250 and 1460 cmꢀ1 confirms the bonding of DHB to
the metal ion through ionized hydroxyl groups [26,27].
The band at 1460 cmꢀ1 is due to the skeletal stretching
vibration of the aromatic ring of DHB and the band at
1250 cmꢀ1 corresponds to the C–O stretching vibration
of DHB. In the case of binuclear complexes, the IR
spectra show a peak around 1560 cmꢀ1 due to the –
CH@N– group. There are strong peaks at 1275 cmꢀ1
(which is due to the –C–O– stretching) and around
1475 cmꢀ1 (which is due to the aromatic ring stretching
of THB). Observation of these two peaks indicates the
binding of THB to the metal ion through the –Oꢀ
group.
of the complexes generally experience upfield shifts
when compared to the parent chloro compound. This
could be due to stronger binding of DHB to the metal
ion than the chloride ions, or more back bonding from
the metal d-orbital to p* orbitals of the a-diimine lig-
ands as compared to chloride ions [20c,28]. The upfield
shift is remarkable (0.48 and 0.93 ppm for 1 and 5,
0
respectively) for the H6,6 protons of [M(BPY)(DHB)]
complexes. The H2,9 protons of [M(PHEN)(DHB)] com-
plexes experience maximum upfield shift (0.51 and 0.1
ppm for 2 and 6, respectively). A similar trend is also ob-
served in [M(DPP)(DHB)] complexes. The H2,9 protons
of 4 and 8 show upfield shifts of 0.52 and 0.66 ppm,
respectively. The phenyl protons in the fourth and sev-
enth positions experienced little upfield shifts when com-
pared to their parent chloro compounds. In the
1H NMR spectra of [M(BIQ)(DHB)] complexes, all
the protons of BIQ experience up- or downfield shifts
0
0
0
except the H6,6 protons. The protons H4,4 and H8,8
of 3 experience downfield shifts of 0.25 and 0.33 ppm,
The 1H NMR spectra of the complexes are compared
with the parent dichloro compounds in order to deter-
mine the bonding mode and stoichiometry of the com-
plexes. The signals are assigned on the basis of
chemical shifts and spin-spin interaction. The structure
and numbering scheme of the ligand protons of the com-
plexes are given in Figs. 1 and 2. The a-diimine protons
respectively, whereas the H5,5 and H7,7 protons experi-
ence upfield shifts of 0.09 and 0.26 ppm correspondingly
as compared to the parent chloro compound. The pro-
0
0
0
tons H3 and H3 of complexes 3 and 6 appear as two sep-
arate doublets rather than a single doublet as in the
parent chloro compound. This could be due to the fact
that the compound lacks planarity in solution which

3178
V. Anbalagan, T.S. Srivastava / Polyhedron 23 (2004) 3173–3183
4
6
makes the protons have different electronic environ-
0
ments. Thus, the protons H3 and H3 could resonate at
3
5
3'
7
9
4
4'
5'
5
8
3
different frequencies. Similar behaviour was observed
earlier in the case of [M(BIQ)(DHBA)] [23]. The free lig-
and, 3,4-dihydroxybenzaldehyde shows two peaks at
10.11 and 9.55 ppm due to the phenolic –OH protons,
but they are absent in the metal complexes. All other
protons (HA, HB, HC and HD) experience upfield shifts
in the complexes as compared to the free ligand, indicat-
ing the bonding of DHB to the metal ions. Similarly,
H4THB shows two peaks for the four phenolic –OH
protons at 9.54 and 9.29 ppm. These two peaks are ab-
sent in the metal complexes. The protons HD, HC and
HB experienc considerable upfield shifts in the complex
as compared to the free ligand. The structure and num-
bering scheme of the protons in the ligand and com-
plexes are given in Figs. 1 and 2. The 3J (195Pt–1H)
couplings in these complexes have not been observed
due to a decrease of chemical shielding anisotropy with
an increase in the magnetic field strength [28].
N
N
6
M
N
N
6'
2
O
M
O
O
O
A
C
C
A
B
D
R
B
D
R
M = Pd(II), R = -CHO
M = Pt(II), R = -CHO
(1)
(5)
M = Pd(II), R = -CHO
M = Pt(II), R = -CHO
(2)
(6)
M = Pt(II), R = -COOH (11)
M = Pt(II), R = -COOH (12)
4
3
3'
5
4'
5
6
5'
6'
N
6
N
4
M
7
O
8
O
7
3
8
8'
7'
N
N
2
9
A
C
M
O
O
These data suggest that both ligands are bonded to
the metal ion in the mixed-ligand complexes. The inte-
grated areas obtained for the protons of a-diimine and
DHB indicate the stoichiometry of these complexes cor-
responds to [M(N-N)(DHB)]. Similarly, the proton ratio
B
D
R
A
C
M = Pd(II), R = -CHO
M = Pt(II), R = -CHO
(3)
(7)
B
D
R
of BPY and THB indicate
a stoichiometry of
M = Pt(II), R = -COOH (13)
M = Pd(II), R = -CHO
M = Pt(II), R = -CHO
(4)
(8)
1
[M2(BPY)2(THB)]. The sharp H NMR spectral signals
observed in these complexes suggest them to be diamag-
netic. The proton NMR spectral, the IR and the elemen-
tal analysis data confirm the synthesis and the structures
assigned to them as shown in Figs. 1 and 2.
M = Pt(II), R = -COOH (14)
Fig. 1. Structure and numbering scheme of the protons of [M(N-
N)(DHB)] and [Pt(N-N)(DHBA)] complexes.
3.2. Electronic absorption spectra
E
HO
C
B' A'
F
The electronic absorption spectral data of these com-
plexes are given in Table 1. A representative spectrum is
shown in Fig. 3. The chloro complexes of the formula,
[M(N-N)Cl2] show four bands (bands are numbered in
increasing order of energy), whereas the complexes of
the formula [M(N-N)(DHB)] show five band maxima.
The bands in the UV region have been assigned on the
basis of band assignments of chloro complexes
[20c,29,30]. Thus, the bands 2 and 4 have been assigned
to charge-transfer transitions from a metal d-orbital to
p-antibonding orbitals of the a-diimine (MLCT). Bands
3 and 5 are assigned as the intra-ligand p–p* transition
of the a-diimine (IL). In addition, these complexes exhi-
bit a band in the visible region, which is strongly
dependent on the polarity of the solvent (band 1). The
absorption maximum of this band is found to shift with
a change of solvent. The energy of this band increases
with an increase in the polarity of the solvent (hydroxy-
lic as well as non-hydroxylic). The observed shift in
band maxima to higher energy in solvents of increasing
polarity is indicative of a polar ground state and non-
polar excited state as reported by Cummings and Eisen-
D
D'
HO
CH=N-N=CH
OH
F'
A
B
C'
OH
E'
H4THB
5
4
6
3
N
M
O
6'
O
C
B' A'
N
4'
5'
3'
D
D'
CH=N-N=CH
O
M
N
3'
5'
6'
4'
N
A
B
C'
O
3
[M2(BPY)2(THB)]
6
4
5
M = Pd(II) (9)
M = Pt(II) (10)
Fig. 2. Structure and numbering scheme of the protons of H4THB and
[M2(BPY)2(THB)] complexes.

V. Anbalagan, T.S. Srivastava / Polyhedron 23 (2004) 3173–3183
3179
Table 1
Electronic absorption spectral data of [M(N-N)(DHB)], [Pt(N-N)(DHBA)] and [M2(BPY)2(THB)] complexes in DMF at 298 K
Complex
Band maxima (kmax/nm)
Band 1
Band 2
Band 3
Band 4
Band 5
1
2
478 (3.73)a
476 (3.07)
598 (2.42)
492 (4.17)
496 (8.22)
475 (1.65)
622 (2.86)
518 (8.97)
465 (7.041)
510 (5.66)
510 (7.15)
512 (3.14)
640 (1.74)
531 (1.45)
364 (17.49)
363b (14.48)
372 (38.57)
350 (19.76)
361 (17.39)
360 (25.24)
374 (18.30)
360 (sh)
316 (21.50)
304 (26.20)
300 (17.80)
300 (19.62)
293 (51.18)
310 (sh)
266 (46.12)
270 (40.66)
267 (72.60)
267 (37.30)
272 (35.95)
264 (9.31)
267 (51.75)
269 (47.12)
266 (83.51)
280 (65.59)
259 (29.03)
265 (47.12)
266 (59.59)
274 (sh)
3
360 (38.57)
325 (sh)c
4
5
322 (16.87)
300 (sh)
6
271 (8.93)
314 (28.96)
296 (45.82)
304 (51.17)
313 (32.97)
289 (35.63)
280 (34.39)
327 (28.00)
309 (sh)
7
339 (28.62)
344 (21.75)
316 (44.53)
326 (34.85)
305 (sh)
8
9
362 (33.52)
388 (17.99)
330 (22.42)
325 (27.49)
377 (36.50)
410 (sh)
10
11
12
13
14
a
360 (sh)
333 (sh)
Molar absorptivity in e · 10ꢀ3 L molꢀ1 cmꢀ1 is given in parentheses.
Broad band.
Shoulder.
b
c
were observed when N-N was replaced from BPY to
PHEN or DPP. An increase in energy of this band
was observed when compared to [M(N-N)(DHBA)]
[23] and [M(N-N)(CAT)] [32]. Based on these observa-
tions this band has been assigned as a LLCT transition
from the HOMO of DHB to the LUMO of a-diimine
via the metal [23,32]. The observed trends in the energy
of this band can also be explained based on the above
assignment. Thus, the decrease in energy of
[M(BIQ)(DHB)] complexes when compared to
[M(BPY)(DHB)] complexes can be explained to be due
to the additional fused rings on the bipyridine, which
pulls down the LUMO to lower energy. The two phenyl
groups are perpendicular to the plane of 1,10-phen-
anthroline in the DPP complexes and are therefore not
expected to contribute much to conjugation in the com-
plex [33]. Hence, there is a small change in the energy of
transition between PHEN and DPP complexes. Because
of the electron-withdrawing group (–CHO) on the
phenyl ring of DHB, the HOMO of the complexes,
[M(N-N)(DHB)] further drops to lower energy. Thus,
the energy of transition for [M(N-N)(DHB)] complexes
increases when compared to the unsubstituted catechol
complexes, [M(N-N)(CAT)] or those substituted with a
carboxylic group, [M(N-N)(DHBA)] complexes [23].
This band assignment is supported by the solvent stud-
ies. With the increase in polarity of the solvent, the
HOMO is stabilized more and leads to an increase in
the energy of transition [29,30]. The LLCT band of pal-
ladium complexes is at higher energy as compared to the
platinum counterparts. This is due to increase in the lig-
and field of Pt(II) by 30–50% when compared to Pd(II).
The electronic spectra of the dinuclear complexes are
similar to the mononuclear complexes. There is a little
change in the position of the LLCT band but the molar
Fig. 3. Electronic absorption spectrum of 6 in DMF.
berg [12b]. This is in contrast to the small degree of solv-
atochromism observed for the MLCT band of transition
metal diimine complexes such as [Ru(bpy)3]2+ and re-
lated systems [8]. The effect of various solvents on the
k
max of this band is given in Table 2. An excellent corre-
lation of absorption band energy with solvent polarity
was found using Reichardtꢀs scale [31]. The plots of Rei-
chardtꢀs parameter (ET) of the solvents against absorp-
tion maxima gave two separate lines, one for
hydroxylic solvents and the other for non-hydroxylic
solvents [18,29,30]. A typical plot for 2 is given in
Fig. 4. This band was not observed in a solution con-
taining a 1:1 mixture of [M(N-N)Cl2] and H2DHB.
The energy of this band decreases when the a-diimine
is changed from BPY to BIQ. However, small changes

3180
V. Anbalagan, T.S. Srivastava / Polyhedron 23 (2004) 3173–3183
Table 2
Effect of hydroxylic and non-hydroxylic solvents on the LLCT band of [M(N-N)(DHB)] complexes
Solvent
Band maxima (kmax/nm)
1
2
3
4
5
6
7
8
Ethylene glycol
Methanol
Ethanol
416 (24.06)a
421 (23.74)
444 (22.53)
451 (22.16)
459 (21.80)
468 (21.36)
478 (20.90)
485 (20.61)
502 (19.94)
510 (19.61)
426 (23.49)
431 (23.18)
439 (22.78)
454 (22.01)
450 (22.23)
464 (21.54)
476 (20.99)
482 (20.76)
495 (20.20)
498 (20.07)
544 (18.38)
555 (18.03)
568 (17.60)
603 (16.58)
578 (17.31)
588 (17.01)
598 (16.71)
600 (16.68)
622 (16.09)
638 (15.68)
427 (23.43)
440 (22.71)
448 (22.34)
459 (21.81)
481 (20.79)
484 (20.66)
492 (20.33)
497 (20.14)
504 (19.83)
506 (19.78)
430 (23.26)
437 (22.87)
454 (22.03)
473 (21.16)
491 (20.35)
478 (20.91)
496 (20.15)
500 (20.01)
502 (19.94)
510 (19.61)
431 (23.19)
433 (23.08)
443 (22.57)
454 (22.01)
450 (22.23)
464 (21.54)
476 (21.03)
482 (20.76)
495 (20.20)
498 (20.07)
541 (18.48)
559 (17.90)
581 (17.20)
608 (16.45)
587 (17.03)
602 (16.61)
622 (16.09)
638 (15.68)
663 (15.09)
681 (14.68)
429 (23.33)
483 (20.71)
492 (20.34)
505 (19.81)
485 (20.62)
510 (19.62)
518 (19.31)
526 (19.00)
513 (19.51)
522 (19.16)
n-Propanol
Acetonitrile
N,N-Dimethyl sulfoxide
N,N-Dimethyl formamide
Acetone
Dichloromethane
Chloroform
a
Band maxima in kK molꢀ1 is given in parentheses.
Table 3
Electrochemical data of [M(N-N)(DHB)] complexes in CH3CN at
298 K
Complex
Reduction
I
Oxidation
I
II
II
1
2
3
4
5
6
7
8
a
ꢀ0.825a
ꢀ0.838
ꢀ0.850
ꢀ0.950
ꢀ0.985
ꢀ0.900
ꢀ0.915
ꢀ0.875
ꢀ1.213
ꢀ1.250
ꢀ1.250
ꢀ1.275
ꢀ1.270
ꢀ1.450
ꢀ1.250
ꢀ1.350
0.750
0.725
0.700
0.750
0.725
0.700
0.780
0.650
0.950
0.950
Potentials in volts vs. Ag/AgCl.
absence of the peak in the reversible scan or by the large
difference in potentials between two counter peaks. The
general electron transfer series for the complexes can be
represented by the following equations:
þeꢀ
ꢀeꢀ
0
½MðN-NÞðDHBÞꢂþ ꢀ½MðN-NÞðDHBÞꢂ
ð1Þ
ð2Þ
ð3Þ
þeꢀ
½MðN-NÞðDHBÞꢂ ꢀ½MðN-NÞðDHBÞꢂꢀ1
0
ꢀeꢀ
Fig. 4. Plot of ET vs. mmax for the LLCT band of 2.
þeꢀ
½MðN-NÞðDHBÞꢂꢀ1 ꢀ½MðN-NÞðDHBÞꢂꢀ2
ꢀeꢀ
extinction coefficient of this band is higher for the dimer
as compared to the monomer, and the position of the
MLCT band is considerably red-shifted in the dimer.
Since the binuclear complexes were found be soluble in
very few solvents, a complete solvent-studies could not
be made.
The formation of a charge transfer to the a-diimine
excited state formally involves the oxidation of the
HOMO and reduction of the a-diimine-based LUMO
[12b]. Thus, the potentials of the first reduction and oxi-
dation of the complexes can be related to the nature of
the orbitals in these redox processes. These orbitals are
the LUMO, consisting exclusively of a-diimine [34,35],
and the HOMO of DHB, and they are involved in the
charge-transfer transition (band 1) as described above.
The first reduction potential of [M(BIQ)(DHB)] com-
plexes lies at lower values as compared to
[M(BPY)(DHB)] complexes. This can be explained in
terms of the electron-withdrawing effect with increased
delocalizing effect of additional fused rings in the former
3.3. Electrochemical studies
The cyclic voltammetric data of complexes 1–8 are gi-
ven in Table 3. In general these complexes show diffuse,
irreversible and successive two one-electron reductions
and one quasi-reversible one-electron oxidation. Irre-
versibility of the reduction peaks was confirmed by the

V. Anbalagan, T.S. Srivastava / Polyhedron 23 (2004) 3173–3183
3181
Table 4
Photophysical data of [Pt(N-N)(DHB)], [Pt(N-N)(DHBA)] and
[Pt2(BPY)2(THB)] complexes in CH3CN
compared to the latter. Similarly, the oxidation poten-
tials of [M(BIQ)(DHB)] are higher than that of the
[M(BPY)(DHB)] counter parts. The [M(DPP)(DHB)]
complexes have a much smaller negative value for the
first reduction potential than [M(PHEN)(DHB)] com-
plexes. This could be due to the electron-withdrawing
nature of the substituted phenyl groups in DPP [33].
However, only a small change was noticed in the posi-
tion of the absorption bands (band 1) of
[M(PHEN)(DHB)] and [M(DPP)(DHB)]. The observed
difference in redox potentials of an electron transfer
process is normally controlled by both kinetic and ther-
modynamic parameters [36,37], whereas the absorption
band position is purely thermodynamically controlled.
Similar observations were found for another series of
complexes [23]. Cyclic voltammograms on the dinuclear
complexes could not be recorded due to insufficient sol-
ubility of these complexes in acetonitrile.
a
Complex Luminescence Luminescence
maxima
sa (ns) UL (·102)
excitation maxima
(kmax/nm)
(kmax/nm)
5
6
7
8
364
368
419
294
291
333
2.40
8.68
0.188
0.278
0.295
0.409
2.80
7.30
4.28
4.29
416
398
355
319
284
3.49
10.70
10
470
422
370
336
295
9.20
0.204
3.4. Luminescence studies
11
12
13
14
364
363
422
291
290
332
1.40
8.77
0.881
0.232
0.292
2.788
The luminescence studies of the complexes were car-
ried out in acetonitrile at room temperature. These com-
plexes do not show emission on excitation at the LLCT
band at room temperature. However, these complexes
were found to be luminescent at room temperature on
excitation at the MLCT/ILCT band. Only the platinum
derivatives were found to show emission at room tem-
perature. This may be due to the lack of structural rigid-
ity of the Pd(II) complexes as compared to the Pt(II)
complexes. The parent dichloro complexes of Pt(II)
did not show emission at room temperature. The lumi-
nescence band maxima of these complexes are given in
Table 4. Representative luminescence and excitation
spectra are given in Fig. 5(a) and (b). The energies of
the MLCT (band 2) and IL (band 3) lie very close to
each other in the electronic spectra of these complexes.
On excitation at these bands, these complexes show
luminescence at room temperature. The energy of the
emission maxima of these complexes lies in the following
order: 4 ꢁ 8 > 6 ꢁ 10 > 5 ꢁ 7 ꢁ 9. This order can be ex-
plained in terms of p-conjugation. The difference in en-
ergy between 5, 7 and 9 is very small. This may be due to
the only one additional double bond present in 5 and 9
as compared to 7. The difference in energy between 6, 10
and 5, 9 can be attributed to the presence of two addi-
tional phenyl groups in DPP. Similar behaviour has ear-
lier been observed by Watts and Crosby [38] for
ruthenium complexes. In the case of 4 and 8 the larger
red shift in emission maximum is due to the additional
fused rings in the BIQ system. The large Stokes shift ob-
served in the excitation spectra of these complexes indi-
cates that the ground state geometry of these complexes
differs largely with the excited state. The quantum yields
of luminescence (/L) of these complexes are included in
Table 4. The /L values were determined with reference
1.53
8.74
3.80
5.60
414
394
350
319
299
4.80
12.20
a
Experimental error is less than 5%.
to tryptophan in water [25]. The DPP derivative is found
to show a larger quantum yield than any other complex.
Similar behaviour was earlier reported for DPP com-
plexes of ruthenium [39].
Two of the complexes were tested for phosphores-
cence at low temperature. Both complexes 1 and 5 were
found to show phosphorescence at 77 K. They were ex-
cited at various wavelengths to obtain the same spec-
trum. The phosphorescence spectrum of 5 is shown in
Fig. 6. The phosphorescence spectrum of 5 shows a
band around 600 nm which is due to the emission from
the lowest excited state, namely the LLCT state as re-
ported earlier for a similar complex [40].
The fluorescence lifetime measurements were done in
acetonitrile. The fluorescence lifetime shows a bi-expo-
nential decay. The multiple lifetimes found for these
complexes suggest the possibility of more than one emit-
ting state for these complexes. Multiple state lumines-
cence has been reported for a number of metal
complexes [41]. Hence, it is concluded that there is a
mixing of MLCT and IL excited states as proposed by
Balzani and co-workers [42] for a different set of Pt(II)
complexes.

3182
V. Anbalagan, T.S. Srivastava / Polyhedron 23 (2004) 3173–3183
cle can be found, in the online version at doi:10.1016/
j.poly.2004.09.029.
References
[1] (a) J.P. Paris, W.W. Brandt, J. Am. Chem. Soc. 81 (1959) 5001;
(b) J.N. Demas, G.A. Crosby, J. Mol. Spectrosc. 26 (1968) 72;
(c) M. Wrighton, D.L. Morse, J. Am. Chem. Soc. 96 (1974) 998;
(d) T.J. Meyer, Prog. Inorg. Chem. 87 (1983) 952;
(e) A.J. Lees, Chem. Rev. 87 (1987) 711;
(f) A. Juris, V. Balzani, F. Barigelletti, S. Campagna, P. Belser,
A. von Zelewsky, Coord. Chem. Rev. 84 (1988) 85;
(g) J.A. Zuleta, M.S. Burberry, R. Eisenberg, Coord. Chem. Rev.
97 (1990) 47;
(h) A.L. Balch, V.J. Catalano, M.M. Olmstead, Inorg. Chem. 29
(1990) 585;
(i) C.B. Blanton, Z. Murtaza, R.J. Shaver, D.P. Rillema, Inorg.
Chem. 31 (1992) 3230;
(j) W.B. Connick, V.M. Miskowski, V.H. Holding, H.B. Gray,
Inorg. Chem. 39 (2000) 2582.
[2] T.J. Meyer, Acc. Chem. Res. 22 (1989) 163.
[3] V. Balzani, F. Scandola, Supramolecular Photochemistry, Ellis
Horwood, Chichester, 1991.
[4] E. Pelizzetti, N. Serpone (Eds.), Homogeneous and Heteroge-
neous Photocatalysis, Reidel, Dordrecht, Holland, 1985.
[5] L-T. Cheng, W. Tam, D.F. Eaton, Organometallics 9 (1990) 2865.
[6] P.N. Prasad, B.A. Reinhardt, Chem. Mater. 2 (1990) 660.
[7] A.E. Friedman, J.-C. Chambron, J.-P. Sauvage, N.J. Turro, J.K.
Barton, J. Am. Chem. Soc. 112 (1990) 4960.
[8] (a) J.P. Sauvage, J.P. Collin, J.C. Chambron, S. Guillerez, C.
Coudret, V. Balzani, F. Barigelletti, L. De Cola, L. Flamigni,
Chem. Rev. 94 (1994) 993;
Fig. 5. (a) Luminescence spectrum of 7 in acetonitrile at 298 K.
(b) Excitation spectrum of 7 in acetonitrile at 298 K.
(b) V. Balzani, A. Juris, M. Venturi, S. Campagna, S. Serroni,
Chem. Rev. 96 (1996) 759;
(c) V. Anbalagan, K. Rosa, D.P. Rillema, Coord. Chem. Rev.
(communicated).
[9] (a) V.M. Miskowski, V.H. Holding, Inorg. Chem. 28 (1989) 1529;
(b) D.L. Web, L.A. Rosiello, Inorg. Chem. 10 (1971) 2213;
(c) V.M. Miskowski, V.H. Holding, C.M. Che, Y. Wang, Inorg.
Chem. 32 (1993) 2518;
(d) F.D. Camassea, F. Castelli, L.A. Rosiello, J. Lumin. 8 (1973)
71;
(e) M. Martin, M.-B. Krough-Jesperson, M. Hsu, J. Tewksbury,
M. Laurent, K. Viswanath, H. Patterson, Inorg. Chem. 22
(1983) 647.
[10] J. DePriest, G.Y. Zheng, N. Goswami, D.M. Eichorn, C. Woods,
D.P. Rillema, Inorg. Chem. 39 (2000) 1955, and references therein.
[11] M. Maestri, D. Sandrani, v. Balzani, A. von Zelewsky, C.
Deuschel-Corniolev, P. Jolliet, Helv. Chim. Acta 71 (1988) 1053.
[12] (a) J.A. Zuleta, C.A. Chesta, R. Eisenberg, J. Am. Chem. Soc.
111 (1989) 8916;
Fig. 6. Phosphorescence spectrum of 5 in EPA glass at 77 K.
4. Conclusion
(b) S.D. Cummings, R. Eisenberg, J. Am. Chem. Soc. 118 (1996)
1949;
This study shows that various mixed-ligand com-
plexes of Pt(II) and Pd(II) can exhibit a LLCT band.
The platinum complexes of this series were found to
emit from a low-energy state at low temperature and a
high-energy state at room temperature.
(c) W. Paw, S.D. Cummings, M.A. Mansour, W.B. Connick,
D.K. Geiger, R. Eisenberg, Coord. Chem. Rev. 171 (1998) 125;
(d) W.B. Connick, D. Geiger, R. Eisenberg, Inorg. Chem. 38
(1999) 3264;
(e) M. Hissler, J.E. McGarrah, W.B. Connick, D.K. Geiger, S.D.
Cummings, R. Eisenberg, Coord. Chem. Rev. 208 (2000) 115.
[13] C.W. Chan, L.K. Cheng, C.M. Che, Coord. Chem. Rev. 132
(1994) 87.
Appendix A. Supplementary data
[14] Y. Zhang, K.D. Ley, K.S. Schanze, Inorg. Chem. 35 (1996) 7102.
[15] W.B. Connick, H.B. Gray, J. Am. Chem. Soc. 119 (1997) 11620.
[16] (a) I.G. Dance, R.T. Miller, J. Am. Chem. Soc. 95 (1973)
6970;
A representative lifetime trace is available from the
publishers. Supplementary data associated with this arti-

V. Anbalagan, T.S. Srivastava / Polyhedron 23 (2004) 3173–3183
3183
(b) L. Kumar, K.H. Puthraya, T.S. Srivastava, Inorg. Chim. Acta
86 (1984) 173;
[25] O. Kalisky, J. Feitelson, M. Ottolenghi, Biochemistry 20 (1981)
2051.
(c) R. Benedix, D. Pitsch, K. Schone, H. Hennig, Z. Anorg. Allg.
Chem. 42 (1986) 102;
[26] D.G. Brown, J.T. Reiprecht, G.C. Vogel, Inorg. Nucl. Chem.
Lett. 12 (1976) 399.
(d) G.E. Matsubayashi, M. Hirao, T. Tanaka, Inorg. Chim. Acta
144 (1988) 217;
[27] P.A. Wiklund, D.G. Brown, Inorg. Chem. 15 (1976) 396.
[28] P.S. Pregosin, Annu. Rep. NMR Spectrosc. 17 (1986) 285.
[29] A.B.P. Lever, Inorganic Electronic Spectroscopy, 2nd ed., Else-
vier, Amsterdam, 1984, pp. 203–376.
(e) T.A. Perkins, D.B. Pourreau, T.L. Netzel, K. Schanze, J.
Phys. Chem. 93 (1989) 4511;
(f) R. Benedix, H. Hennig, H. Kunkely, A. Vogler, Chem. Phys.
Lett. 175 (1990) 483.
[30] J. Burgess, Spectrochim. Acta 23 (1970) 506.
[31] C. Reichardt, Angew. Chem., Int. Ed. Engl. 4 (1965) 29.
[32] S.S. Kamath, V. Uma, T.S. Srivastava, Inorg. Chim. Acta 166
(1989) 91.
[17] H. Hennig, D. Rehorek, R.D. Archer, Coord. Chem. Rev. 65
(1985) 1.
[18] (a) V. Anbalagan, T.S. Srivastava, J. Photochem. Photobiol. A 66
(1992) 345;
[33] S. Musumeli, E. Rizzareth, F. Fragala, S. Summaratano, R.P.
Bonomo, Inorg. Chem. Acta 7 (1973) 660.
(b) V. Anbalagan, T.S. Srivastava, J. Photochem. Photobiol. A 89
(1995) 113;
[34] A. Vogler, H. Kunkely, J. Hlavatch, A. Merz, Inorg. Chem. 23
(1984) 506.
(c) V. Anbalagan, T.S. Srivastava, J. Photochem. Photobiol. A 77
(1994) 141.
[35] P.S. Braterman, J. Song, F.M. Wimmer, S. Wimmer, W. Kaim,
A. Klein, R.D. Peacock, Inorg. Chem. 31 (1992) 5084.
[36] J.A. Davies, V. Uma, J.G. Mierzwink, J. Electroanal. Chem. 196
(1985) 239.
[19] B.S. Furniss, A.J. Hannaford, V. Roger, P.W.G. Smith, A.R.
Tachell, Vogelꢀs Textbook of Practical Organic Chemistry, 4th ed.,
Longman, London, 1978, pp. 264–279.
[37] M.K. DeArmound, K.W. Hamok, D.W. Wertz, Coord. Chem.
Rev. 64 (1985) 65.
[20] (a) F.A. Palacsay, J.V. Rund, Inorg. Chem. 8 (1969) 524;
(b) V. Kumar, M.M. Rao, N. Ahmed, Indian J. Chem. 17 (1979)
217;
[38] R.J. Watts, G.A. Crosby, J. Am. Chem. Soc. 93 (1971) 3184.
[39] G.D. Hager, R.J. Watts, G.A. Crosby, J. Am. Chem. Soc. 97
(1975) 7037.
(c) S.S. Kamath, V. Uma, T.S. Srivastava, Inorg. Chim. Acta 161
(1989) 49;
[40] S.S. Kamath, S. Shukla, T.S. Srivastava, Bull. Chem. Soc. Jpn. 64
(1991) 1351.
(d) B.J. Malormiek, E.N. Joyes Jr., R.I. Kaplan, Inorg. Synth. 13
(1971) 217.
[41] (a) M.M. Glezen, A.J. Lees, J. Am. Chem. Soc. 110 (1988)
6243;
[21] P.M. Gidney, R.D. Gillard, B.T. Heaton, J. Chem. Soc., Dalton
Trans. (1973) 132.
(b) M.K. DeArmound, C.M. Carlin, Coord. Chem. Rev. 36
(1981) 325.
[22] L.A. Rosiello, Gazz. Chim. Ital. 97 (1967) 1177.
[23] V. Anbalagan, T.S. Srivastava, Polyhedron 13 (1994) 291.
[24] J.N. Demas, G.A. Crosby, J. Am. Chem. Soc. 93 (1971) 2841.
[42] M. Maestri, D. Sandrani, V. Balzani, A. Von Zewlesky, C.
Deuschel-Corniolev, P. Joliet, Helv. Chim. Acta 71 (1988) 1053.