The C-N coupling reaction of pendant naphthyl group of palladium(II) complexes of 1-alkyl-2-(naphthyl-β-azo)imidazoles. Structural characterization, spectral and redox properties, and correlation with DFT computed data

Article abstract of DOI:10.1016/j.ica.2009.12.050

The reaction of Pd(β-NaiR)Cl₂ (2) [β-NaiR (1) = 1-alkyl-2-(naphthyl-β-azo)imidazoles] with ArNH₂ in MeCN has yielded a C-N coupled product chloro[1-alkyl-2-{(7-imidoaryl)naphthyl-β-azo}imidazole-N,N′,N′′]palladium(II), Pd(β-NaiR-N-Ar)Cl (3-5) and coupling takes place at ortho-C-H position of pendant naphthyl group. The structural confirmation has been achieved by single crystal X-ray structure determination of the representative complexes, Pd(β-NaiEt)Cl₂ (2b) and Pd(β-NaiEt-N-C₆H₄-Cl-p)Cl (5b). The electronic spectra of the products, 3-5, exhibit characteristic transition within 600-900 nm those are absent in Pd(β-NaiR)Cl₂ (2). Cyclic voltammogram shows one oxidative response and two ligand reductions. The products are emissive. The excited state decays via radiative and non-radiative biexponential routes. The electronic structure, spectra and redox properties are explained by DFT computation.

Full text of DOI:10.1016/j.ica.2009.12.050

Inorganica Chimica Acta 363 (2010) 831–840
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The C–N coupling reaction of pendant naphthyl group of palladium(II) complexes
of 1-alkyl-2-(naphthyl-b-azo)imidazoles. Structural characterization, spectral
and redox properties, and correlation with DFT computed data
P. Pratihar a, T.K. Mondal a, P. Raghavaiah b, C. Sinha a,
*
a Department of Chemistry, Jadavpur University, Kolkata 700 032, India
b School of Chemistry, National Single Crystal X-ray Diffractometer Facility, University of Hyderabad, Hyderabad 500 046, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The reaction of Pd(b-NaiR)Cl2 (2) [b-NaiR (1) = 1-alkyl-2-(naphthyl-b-azo)imidazoles)] with ArNH2 in
MeCN has yielded a C–N coupled product chloro[1-alkyl-2-{(7-imidoaryl)naphthyl-b-azo}imidazole-
N,N0,N00]palladium(II), Pd(b-NaiR–N–Ar)Cl (3–5) and coupling takes place at ortho-C–H position of pen-
dant naphthyl group. The structural confirmation has been achieved by single crystal X-ray structure
determination of the representative complexes, Pd(b-NaiEt)Cl2 (2b) and Pd(b-NaiEt–N–C6H4–Cl-p)Cl
(5b). The electronic spectra of the products, 3–5, exhibit characteristic transition within 600–900 nm
those are absent in Pd(b-NaiR)Cl2 (2). Cyclic voltammogram shows one oxidative response and two ligand
reductions. The products are emissive. The excited state decays via radiative and non-radiative biexpo-
nential routes. The electronic structure, spectra and redox properties are explained by DFT computation.
Ó 2009 Elsevier B.V. All rights reserved.
Received 16 November 2009
Accepted 23 December 2009
Available online 7 January 2010
Keywords:
Pd-naphthylazoimidazoles
C–N coupling reaction
Electrochemistry
Luminescence
DFT computation
1. Introduction
pyridylazoimidazoles [56], azopyridines [57], azopyrimidines
[58], and azoantipyrine [59]. Pyridine- and pyrimidine-azo metal-
Transition metal-catalyzed organic synthesis leading to the
formation of C–C, C–N, C–O, and C–S bonds [1–5] has numerous
industrial applications. Palladium-catalyzed coupling reactions
have been extensively studied over the past three decades
[6–11]. Extensive study in carbon–nitrogen bond formation has
developed new synthetic methodologies. N-Arylation is achieved
by copper [12–14], nickel [15,16], and palladium [17–19] cataly-
sis. Among these three, palladium-based methods are most prom-
ising. Palladium-catalyzed C–N bond forming reactions have
developed a versatile and efficient synthetic route [20,21,19,22].
The coordination of organic molecules to metal ions has affected
the chemical nature of the molecules [23] and serves as effective
template, and the suitable orientations and electronic require-
ment of ligands are responsible for chemical reactions [24–46].
For example, arylazoheterocycles do not show any nucleophilic
reaction at free ligand state while metallated-arylazoheterocycles
show easy reactions viz., hydroxylation [40,41], thiolation [42–44],
lated complexes exhibit aryl-amination reaction at the pendant
aryl ring [30–39,45,46,60]. In this work we account on the reac-
tion of Pd(b-NaiR)Cl2 (b-NaiR = 1-alkyl-2-(naphthyl-b-azo)imida-
zoles) with ArNH2. The structural characterization has been
done by single crystal X-ray diffraction study. The electrochemical
and luminescence properties of the complexes are examined.
2. Results and discussion
2.1. Synthesis
Dichloro-(1-alkyl-2-(naphthyl-b-azo)imidazole)palladium(II) com-
plexes, Pd(b-NaiR)Cl2 (2), are used in this work. The reaction be-
tween Pd(b-NaiR)Cl2 and ArNH2 (1:1 molar ratio) in presence of
Et3N in MeCN solution under stirring and refluxing for 12 h has
yielded reddish-brown product (Scheme 1). This has been identi-
fied as amine coupled product abbreviated as Pd(b-NaiR–N–Ar)Cl
(3–5) [where, R = CH3 (a), CH2CH3 (b), CH2Ph (c); Ar = X–C6H4
where X = H (3), Me (4), Cl (5)].
The C–N coupling takes place via C–H activation of ortho C(6)–H
bond to the azo function in the pendant naphthyl ring (B-ring) of b-
NaiR and forms palladium(II) complex of tridentate N,N0,N00-chelat-
ing ligand (N, N0, N00 refer to N(imidazole), N(azo), and N(arylamine)
respectively). Microanalytical data support the composition of the
aryl-amination [45,46] reaction. Azoheterocycles are
p-acidic
molecules and this property may be regulated by ring size, num-
ber of heteroatoms, substituents in the heterocyclic ring and side
arm to azo function [47–52]. We have synthesised azoheterocy-
cles such as azoimidazoles [53,54], naphthylazoimidazoles [55],
* Corresponding author. Tel.: +91 94 3330 9907; fax: +91 33 2414 6584.
E-mail address: c_r_sinha@yahoo.com (C. Sinha).
complexes (see Section 3). There are two
a-C–H groups, C(6)–H
0020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2009.12.050

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P. Pratihar et al. / Inorganica Chimica Acta 363 (2010) 831–840
4
5
5
A
N
4
N
N
Cl
NH2
R
Pd
Cl
N
N
R
MeCN, reflux
Et3N
N
15
C
Pd
6
+
16
17
N
N
Cl
N
8
B
X
13
X
9
8
19
18
9
13
12
10
12
11
10
11
Pd( β-NaiR)Cl2 (2)
Pd(β-NaiR-N-Ar)Cl (3-5)
R = CH3 (a), CH2CH3 (b), CH2Ph (c); Ar = X-C6H4, where X = H (3), Me (4), Cl (5)
Scheme 1. C–N coupling reaction and atom numbering pattern.
and C(8)–H. The possibility of C(8)–H activation may be ruled out
due to steric crowding of proximate C(9)–H.
N(1)–Pd–N(3), 78.20(13)° is comparable with Pd(azoheterocy-
cle)Cl2 system [40,41,55,61–63]. The pendant naphthyl is twisted
by 42.9(6)° from the plane. A 1-D supramolecule is developed by
Cl(2)–H(2)–C(2) interaction [dH–Cl, 2.76(1) Å; dC–Cl, 3.61(1) Å and
C–H–Cl, 152.5(1)°].
The 1H NMR spectra of b-NaiR (1), Pd(b-NaiR)Cl2 (2) and Pd(b-
NaiR–N–Ar)Cl (3–5) have been compared to determine the
bonding and stereochemistry. The NMR signals were assigned to
individual proton on the basis of chemical shifts, spin–spin interac-
tion and their effect on substitution. The imidazole-H (4 and 5-H)
(A-ring) and N-aryl-H (C-ring) appear in the up-field side (Table 1).
Effect of substituent X (X–C6H4–N–) on the signal movement of C-
ring, 15-H–19-H appear in accordance with the electromeric effect
of the group. It is observed that the electron donating substituent
(Me) moves the signal upfield d while electron withdrawing group,
–Cl, moves them towards the downfield with reference to Pd(b-
NaiR–N–C6H5)Cl (3). N-Aryl ring (ring C) is a better electron donor
and may assist efficient intramolecular charge transfer transition.
This may be reason for large up-field shifting of ligand protons
(8-H–13-H) in the fused compound.
2.2.2. Pd(b-NaiEt–N–C6H4–Cl-p)ClꢀC6H6 (5b)
A molecular view of Pd(b-NaiEt–N–C6H4–Cl-p)ClꢀC6H6 (5b) is
shown in Fig. 2a and the selected bond parameters are listed in Ta-
ble 2. The structure shows the C–N coupling of p-Cl–C6H4–NH2 at
C(6)–H bond of pendant naphthyl ring coordinated b-NaiEt in
Pd(b-NaiEt)Cl2 (2b) (Fig. 1). Thus, the ligand is a tridentate N(imid-
azole) (N), N(azo) (N0), N(amine) (N00) donating agent. The chelate
bite angles N(1)–Pd(1)–N(2) and N(2)–Pd(1)–N(4) are 81.16(10)°
and 79.49(10)°, respectively. The Pd atom lies within the square
plane defined by N3Cl donor centers (deviation, <0.01). The pen-
dant p-chlorophenyl ring is inclined at an angle of 67.8(4)° with
the principal plane. There are three types of Pd(1)–N bonds:
Pd(1)–N(imidazole) [Pd(1)–N(4)], 2.015(3) Å]; Pd(1)–N(azo)
[Pd(1)–N(2)], 1.946(3) Å] and longest Pd(1)–N(arylamine) [Pd(1)–
N(1)], 2.027(2) Å]. The N@N bond length (1.326(3) Å) is 0.05 Å
elongated than the Pd(b-NaiEt)Cl2 (Fig. 2a, Table 2). It may be
2.2. Molecular structures
2.2.1. Pd(b-NaiEt)Cl2 (2b)
The spectral characterization of Pd(b-NaiR)Cl2 has been re-
ported elsewhere [55]. The single crystal X-ray structure of
Pd(b-NaiEt)Cl2 (2b) is shown in Fig. 1 and bond parameters are
given in Table 2. b-NaiEt acts as a bidentate N, N0 chelator (N,
N(imidazole); N0, N(azo)). The Pd–N(azo) (2.073(3) Å) is longer
than Pd–N(imidazole) (1.979(3) Å) distance and follows general
observation to the reported structures [40,41,55,61–64]. The Pd–
Cl distances are also very close to each other (Pd(1)–Cl(1),
2.2692(11); Pd(1)–Cl(2), 2.2798(10) Å). The N@N distance is
1.272(4) Å which is slightly longer than free ligand value
due to better electronic movement from filled d
p(Pd) to the low-
lying *(N@N) of ligand which is enhanced via C–N fusion with
p
electronically labile aromatic-amine. The immediate consequence
of back bonding has been reflected in the shortened Pd–N(azo)
distance, Pd(1)–N(2)], 1.946(3) Å compare to the Pd–N(imidazole)
[Pd(1)–N(4)], 2.015(3) Å] and Pd–N(arylamine) [Pd(1)–N(1)],
2.027(2) Å] distances. The shorter N(azo)–C(naphthyl-B) distance,
[N(2)–C(8)] 1.345(4) Å relative to N(azo)–C(imidazole-A), [N(3)–
C(17)] 1.383(4) Å may be due to backbone conjugation in the
coordinated tridentate ligand. Both the N(azo)–C(imidazole-A),
[N(3)–C(17)] 1.383(4) Å and N(imino)–C(naphthyl-B) distances,
(1.250(2) Å) [56,65]. It may be due to dp(Pd) ? p*(N@N) charge
delocalization through chelated function. The chelate angle
Table 1
1H NMR spectral data of Pd(b-NaiR–N–Ar)Cl (3–5) in CDCl3.
Compound d/ppm (J/Hz)
4-Ha
5-Ha
8-Ha
9-Ha
10–13-Hc
15, 19-Ha
16,18-H
17-Hb
N–CH3
N–CH2
(N–CH2)CH3 17-CH3
d
d
(3a)
(3b)
(3c)f
(4a)
(4b)
(4c)f
(5a)
(5b)
(5c)f
7.13 (7.0) 6.51 (7.0) 7.36 (7.0) 7.55 (7.0) 7.90–8.15 7.65a (8.0) 7.54b (8.0) 7.54 (8.0) 3.74
7.13 (7.0) 6.68 (7.0) 7.33 (7.0) 7.51 (7.0) 7.88–8.10 7.60c
7.16 (7.0) 6.78 (7.0) 7.33 (7.0) 7.52 (7.0) 7.91–8.18 7.57c
7.55b (8.0) 7.55 (8.0)
7.42b (8.0) 7.42 (8.0)
4.55e (10.0) 1.48b (8.0)
5.15d
7.10 (7.0) 6.47 (7.0) 7.35 (7.0) 7.58 (7.0) 7.84–8.12 7.48a (8.0) 6.96a (8.0)
3.72
3.78
2.32
2.34
2.27
7.05 (7.0) 6.48 (7.0) 7.31 (7.0) 7.50 (7.0) 7.90–8.15 7.40a (8.0) 6.82a (8.0)
3.97e (10.0) 1.44b (7.0)
5.70d
7.05 (7.0) 6.43 (7.0) 7.35 (7.0) 7.52 (7.0) 7.92–8.15 7.46
6.80a (8.0)
7.12 (7.0) 6.60 (7.0) 7.31 (7.0) 7.50 (7.0) 7.91–8.17 7.48a (8.0) 7.50a (8.0)
7.12 (7.0) 6.57 (7.0) 7.36 (7.0) 7.55 (7.0) 7.94–8.20 7.64a (8.0) 7.55a (8.0)
4.46e (10.0) 1.54b (8.0)
5.08d
7.05 (7.0) 6.60 (7.0) 7.32 (7.0) 7.55 (7.0) 7.90–8.13 7.58c
7.47a (8.0)

P. Pratihar et al. / Inorganica Chimica Acta 363 (2010) 831–840
833
Fig. 1. Thermal ellipsoidal plot (30% probability) of Pd(b-NaiEt)Cl2 (2b).
Table 2
feature is the ring C–C distance in B-ring: C(7)–C(8) has been elon-
gated by 0.05 Å from that of ring-A and ring-C parameters. This
concludes that the ring-B is more efficiently involved in conjuga-
tion than that of other rings (A and C). This is also supported by
shortening of Pd(1)–N(2) distance (1.946(3) Å) with reference to
Pd(1)–N(1), 2.027(2) and Pd(1)–N(4), 2.015(3) Å.
0
Selected bond length (AÅ) and angles (°) of 2b and 5b.
X-ray
Theoretical
2b
Pd(1)–N(1)
Pd(1)–N(3)
Pd(1)–Cl(1)
Pd(1)–Cl(2)
N(1)–N(2)
N(2)–C(1)
N(2)–C(4)
Cl(1)–Pd(1)–Cl(2)
N(1)–Pd(1)–N(3)
N(3)–Pd(1)–Cl(1)
N(1)–Pd(1)–Cl(1)
N(3)–Pd(1)–Cl(2)
N(1)–Pd(1)–Cl(2)
2.073(3)
1.979(3)
2.2692(11)
2.2798(10)
1.272(4)
1.368(5)
1.354(5)
90.72(4)
78.20(13)
91.41(10)
169.61(9)
177.86(10)
99.66(9)
2.112
2.013
2.321
2.332
1.289
1.362
1.387
90.36
76.89
91.42
168.3
175.8
100.2
The packing view shows the presence of benzene of crystallization.
A
p
–
p
network is developed by Cg(3)–Cg(6), (3.268 Å, symmetry: ꢁx,
ꢁy, 1 ꢁ z), Cg(5)–Cg(5)* (3.389 Å, symmetry: ꢁx, y, 1/2 ꢁ z), Cg(6)–
Cg(5) (3.172 Å, symmetry: ꢁx, y, 1/2 ꢁ z) (where Cg(3) =
N(4) ? C(17) ? N(5) ? C(19) ? C(18); Cg(5) = C(7) ? C(8) ? C(9) ?
C(10) ? C(11) ? C(16);
C(15) ? C(16)) with C–H–
2.649 Å; C–p, 3.551 Å, C–H–p
Cg(6) = C(11) ? C(12) ? C(13) ? C(14) ?
interactions (C(2)–H(2) ? Cg(3): H–
, 150°, symmetry: ꢁx, y, 1/2 ꢁ z) and
, 3.491 Å, C–H– , 133°,
p
p,
C(20)–H(20B) ? Cg(6): Hꢀꢀꢀ
p
, 2.709 Å; Cꢀꢀꢀ
p
p
symmetry: ꢁx, ꢁy, 1 ꢁ z) to hold C6H6 in supramolecular cavity
5b
N(1)–Pd(1)
N(2)–Pd(1)
N(4)–Pd(1)
N(2)–N(3)
Cl(1)–Pd(1)
C(1)–N(1)
C(7)–N(1)
C(7)–C(8)
C(8)–N(2)
C(17)–N(3)
C(17)–N(4)
C(17)–N(5)
C(18)–N(4)
C(19)–N(5)
C(7)–C(16)
2.027(2)
1.946(3)
2.015(3)
1.326(3)
2.2973(10)
1.428(4)
1.330(4)
1.435(4)
1.345(4)
1.383(4)
1.327(4)
1.349(4)
1.374(4)
1.377(4)
1.464(4)
1.425(4)
1.341(5)
1.437(4)
1.350(5)
121.36(19)
81.16(10)
79.49(10)
160.63(11)
173.70(7)
98.51(8)
100.66(8)
2.065
1.980
2.053
1.312
2.347
1.416
1.342
1.451
1.353
1.367
1.338
1.358
1.369
1.388
1.472
1.427
1.357
1.441
1.372
121.7
80.48
78.75
159.2
176.3
97.87
102.9
(Fig. 2b).
2.3. Spectral studies
2.3.1. IR spectra
The cis-PdCl2 configuration of Pd(b-NaiR)Cl2 is supported [66]
by two
m
(Pd–Cl) stretches at 330 and 310 cmꢁ1 while a single
transmission at 310–320 cmꢁ1 is observed in the amine fusion
products (3–5). The sharp single band at 1320–1345 cmꢁ1 in
Pd(b-NaiR–N–Ar)Cl (3–5) is referred to m(N@N) which has been
shifted to lower frequency by 15–20 cmꢁ1 from that of Pd(b-
NaiR)Cl2. This supports the coordination of azo-N to PdII. The
significant reduction in azo frequency may be due to charge delo-
calization from N–Ar fragment (ring C) to the azo function intra-
molecularly [45,46].
C(8)–C(9)
C(9)–C(10)
C(10)–C(11)
C(18)–C(19)
C(1)–N(1)–Pd(1)
N(2)–Pd(1)–N(1)
N(2)–Pd(1)–N(4)
N(4)–Pd(1)–N(1)
N(2)–Pd(1)–Cl(1)
N(4)–Pd(1)–Cl(1)
N(1)–Pd(1)–Cl(1)
2.3.2. Electronic spectra and singlet excited state
The absorption bands of Pd(b-NaiR)Cl2 are recorded in acetoni-
trile solution. The spectral pattern of Pd(b-NaiR–N–Ar)Cl (3–5)
(Fig. 3) exhibits multiple transitions in the visible to NIR region
(500–850 nm). The spectral data are collected in Table 3. The
electron donating substituent (X = Me) shifts the absorption max-
ima to longer wavelength region while an electron withdrawing
group (X = Cl) shifts the band to shorter region relative to –C6H5
(C-ring). The electron donating substituents destabilize the MOs
and thus energy of HOMO is increased. The substituent X (at
[N(1)–C(7)] 1.330(4) Å are noticeably shorter than that of N(imi-
no)–C(phenyl-C) distance, [N(1)–C(1)] 1.428(4) Å. [Aromatic rings
are abbreviated as: imidazole, A; naphthyl, B; phenyl, C]. Important

834
P. Pratihar et al. / Inorganica Chimica Acta 363 (2010) 831–840
Fig. 2a. Thermal ellipsoidal plot (30% probability) of Pd(b-NaiEt–N–C6H4–Cl-p)ClꢀC6H6 (5b).
Fig. 2b.
p–p Network (C–H–p network is not shown for clarity) holds C6H6 in the cavity (5b).
C-ring) influences more prominently to the LUMOs (vide infra, DFT
computation).
observed florescence decay fits nicely with bi-exponential decay
profile for the ligands and the complexes (Fig. 4) which is sup-
The photoluminescence properties of the complexes (3–5) are
studied at room temperature (298 K) in MeCN solution. The ligands
(b-NaiR) are photo-inactive. Pd(b-NaiR)Cl2 and amine coupled
products Pd(b-NaiR–N–Ar)Cl exhibit emission upon excitation at
300–450 nm (Fig. 3, Table 3). The chelation of ligand to the metal
ion gives structural rigidity and inhibits vibrational loss [67]. This
may be one of the reasons of showing emission property of metal
complexes.
ported by goodness-of-fit (
yses. We have used mean fluorescence life time (
v
2) (Table 3) data in the regression anal-
sf = a1s1 + a2s2
where a1 and a2 are relative amplitudes of decay process). Radia-
tive and non-radiative rate constants (kr and knr) are calculated
and data show usual higher knr value than kr.
2.4. Electrochemistry
Life time data of the complexes are taken in acetonitrile solu-
tion when excited at 370 nm (Table 3). The fluorescence decay
curve was deconvoluted with respect to the lamp profile. The
The electrochemical properties of Pd(b-NaiR–N–Ar)Cl (3–5)
have been investigated by cyclic voltammetry. The results are gi-
ven in Table 4 and a representative voltammogram is shown in

P. Pratihar et al. / Inorganica Chimica Acta 363 (2010) 831–840
835
25000
20000
15000
10000
5000
0
a
b
d
c
300
400
500
600
700
800
900
Wavelength / nm
Fig. 3. Absorption spectra of (a) Pd(b-NaiBz)Cl2 (2c), (b) Pd(b-NaiBz–N–C6H4–Me-p)Cl (4c) and fluorescence spectra of (c) Pd(b-NaiBz)Cl2 (2c), (d) Pd(b-NaiBz–N–C6H4–Me-p)Cl
(4c) in acetonitrile solution at room temperature.
3-
Fig. 5. Pd(b-NaiR)Cl2 exhibit two quasireversible (DEp > 100 mV)
]
N
N
[
N
C
reduction couples at negative to SCE and have been assigned to
the reduction of azo group [30–39,57]. Pd(b-NaiR–N–Ar)Cl (3–5)
show three successive redox couples. One redox couple appears
at positive side to SCE in the potential range 0.9–1.1 V and is oxi-
dative in nature. This redox response is quasireversible in nature
ð5Þ
4-
+ e
]
N
N
[
N
C
which is supported from
D
Ep P 80 mV (
D
Ep = [Epa ꢁ Epc], peak-
2.5. DFT calculation and explanation of electronic spectra and redox
properties
to-peak separation). One electron nature of the redox couple is
supported from ipa/ipc (ꢂ1.0) and differential pulse voltammetry
(DPV). Palladium(II) is hardly oxidisable, so this oxidative response
is referred to the ligand oxidation of azonaphthylarylamine (che-
lating ring 2), Eq. (1). Two redox responses those appear at nega-
tive to SCE are reductive in nature. The reduction is regarded as
the electron accommodation in the LUMO characterized by
azoamine function. There are four successive redox accessible lev-
els in –N@N–C@N– group (Eqs. (2)–(5)). In this series of complexes
we observe two negative couples and they may correspond to
reductions Eqs. (2) and (3).
The full geometry optimization of the representative complexes
2b and 5b have been performed using density functional theory.
Geometric parameters in the singlet ground-state configuration
are summarized in Table 2. Bond lengths and angles are in good
agreement with the X-ray values. Pd–N lengths are slightly overes-
timated (about 0.02–0.04 Å). The same trend is observed for Pd–Cl
bonds, where the difference is ꢃ0.05 Å. The N@N bond is longer
(0.018 Å) in 2b, whereas it is shorter (0.014 Å) in 5b relative to
the X-ray values. The formal charge of Pd atom is 0.659; azo-Ns
are N(1), ꢁ0.198; N(2), ꢁ0.241 in 2b and of Pd, 0.724, azo-Ns are
N(1), ꢁ0.188; N(2), ꢁ0.328 in 5b. The charge on the chloride li-
gands is also smaller than ꢁ1, and are ꢁ0.493, and ꢁ0.581 in 2b
and 5b, respectively. This informs overlapping of ligand orbitals
with metal orbitals.
+
N
N
N
N
R
Cl
R
II
Cl
II
Pd
Pd
-e
N
N
N
+e
N
ð1Þ
N
N
The HOMO of 2b has 30% Pd(dp) and 51% Cl(pp) contribution
with reduced ligand(L) character (19%) whereas in 5b, 06% Pd,
68% chelated ligand (L) and 26% p-Cl-phenyl character (Fig. 6).
The LUMO carries 81–92% ligand characteristics with major con-
tribution from azo (N@N) function and energy gap with HOMOs
X
X
]
N
N
N
N
(20.9 ꢄ 103 cmꢁ1
)
for
2b
and
2.14 eV
[
[
[
N
C
are
2.59 eV
(17.3 ꢄ 103 cmꢁ1) for 5b, respectively (Fig. 7). The HOMOꢁ1 to
ð2Þ
ð3Þ
ð4Þ
+ e
HOMOꢁ4 are composed of Cl(p
p) orbital 50–80%, L 20–35%, and
) for 2b. For 5b, the HOMOꢁ1 and HOMOꢁ4 are
-
N
N
N
]
[
N
C
10–15% Pd(d
dominated by chelated ligand (86–87%), HOMOꢁ2 and HOMOꢁ3
are characterized by Cl(p ) function with minor contribution
from (15–25%) Pd(d
p
-
N
]
]
N
C
C
p
p
). The HOMOꢁ5 in both the complexes has
2-
+ e
Pd(d
Pd(d
p
p
) character (75–76%). Similarly, the LUMO+1 has ꢃ50%
]
N
N
[
N
C
C
) character with reduced contribution from chelating ligand
2-
and Cl(pp).
N
N
Pd(b-NaiEt)Cl2 (2b) shows reasonably intense transition at 566
(oscillator strength f, 0.270 nm, Table 5) corresponding to
3-
+ e
HOMO ? LUMO, Cl(pp)/Pd(dp) ? N@N(p*) which appears at
]
N
[
N
shorter wavelength, 501 nm. The most intense transition at

836
P. Pratihar et al. / Inorganica Chimica Acta 363 (2010) 831–840
Table 3
UV–Vis, emission spectral data and decay rates of Pd(b-NaiR)Cl2 and Pd(b-NaiR–N–Ar)Cl in MeCN.
Compound
(sꢁ1
kmax/nm(10ꢁ3 [dm3 molꢁ1 cm-1])
e
kex/nm
kem/nm
/
sf
(ns)
v2
kr ꢄ 10ꢁ9
knr ꢄ 10ꢁ9
f
)
(sꢁ1
)
(sꢁ1
)
(2a)
(2b)
(2c)
(3a)
273(10.63), 394(13.48), 496(6.24)
245(14.81), 390(10.28), 501(5.69)
272(16.78), 382(21.34), 395(19.50), 507(6.62)
285(20.43), 354(10.54), 409(4.29), 487(1.72), 640(1.13), 700(2.29), 805(1.93), 354
881(1.39)
273
245
272
424
350
382
415
0.003 2.17
0.010 2.01
0.044 2.12
0.036 6.38
0.97 0.001
1.00 0.005
0.98 0.021
1.13 0.006
0.459
0.493
0.451
0.151
(3b)
278(13.92), 356(9.94), 410(3.65),482(1.75), 640(1.47), 700(3.38), 806(2.61),
356
414
0.027 7.93
1.11 0.003
0.123
879(1.92)
(3c)
(5a)
274(18.84), 364(11.65), 523(2.43), 663(1.20), 728(1.75), 804(1.59), 879(1.15)
278(15.21), 355(7.72), 415(2.68), 480(1.29), 643(0.67), 702(1.38), 805(1.72),
880(1.32)
364
355
426
412
0.037 2.75
0.036 7.88
1.02 0.013
1.21 0.005
0.351
0.122
(5b)
(5c)
(4a)
(4b)
(4c)
270(17.11), 286(15.43), 358(11.48), 415(4.30), 487(2.26), 643(1.37), 703(2.84), 358
805(3.07), 880(2.33)
269(16.19), 295(12.81), 363(10.90), 402(7.17), 503(1.93), 649(0.94), 708(1.76), 363
805(2.03), 881(1.54)
416
424
417
414
412
0.021 7.42
0.039 2.91
0.034 6.24
0.033 7.49
0.049 2.63
1.10 0.003
1.00 0.013
1.15 0.005
1.12 0.004
1.05 0.019
0.132
0.331
0.155
0.129
0.361
276(13.54), 352(7.46), 413(2.77), 479(1.36), 640(0.89), 699(1.81), 807(1.13),
879(0.84)
352
283(17.52), 357(12.51), 406(5.41), 488(2.23), 638(1.40), 700(3.19), 805(3.00), 357
879(2.19)
278(16.88), 353(8.99), 416(3.09), 476(1.26), 642(0.66), 702(1.85), 806(1.41),
879(0.91)
353
kex – excitation wavelength; kem – emission wavelength; Uf – fluorescence quantum yield,
s
f – mean fluorescence life time, v2 – goodness of fit, kr – radiative rate constant, knr
– non-radiative rate constant.
1000
100
10
1000
100
10
1
1
0
50
100
150
200
0
50
100
150
200
Time (ns)
Time (ns)
(a) Pd(β-NaiCH2Ph)Cl2
(b) Pd(β-NaiEt-N-C6H5 )Cl
Fig. 4. Bi-exponential decay profile ( ) and fitting curve (––) in MeCN. Excitation is carried out at 370 nm.
Table 4
Cyclic voltammetric dataa of Pd(b-NaiR–N–Ar)Cl (3–5).
390 nm. The introduction of the p-substituted anilines in 2 has
dramatically changed the composition of MOs; the HOMO,
which is principally palladium-localised in 2b, shows mainly
chelating ligand characteristics in 5b. TD-DFT of Pd(b-NaiEt–N–
C6H4-p-Cl)ClꢀC6H6 (5b) determines intense absorption at 725 nm
(f, 0.192, Table 5), that signifies ligand centred transition and
experimental spectrum shows transitions at 703, 805, and
880 nm. Transitions at 528 nm (f, 0.007) and 465 nm (f, 0.040)
are LMCT and ILCT, respectively, these bands experimentally ob-
served at 487 nm. Similarly transitions at 430 nm (f, 0.027) and
413 nm (f, 0.047) are the mixture of XLCT and MLCT. Transitions
in UV region in both the complexes are all ligand centred
transitions.
Compound
Oxidation E/V (
D
Ep/mV)
Reduction E/V (DEp/mV)
(3a)
(3b)
(3c)
(4a)
(4b)
(4c)
(5a)
(5b)
(5c)
0.90 (180)
1.00 (200)
1.07 (170)
0.92 (180)
0.98 (170)
1.02 (180)
1.02 (180)
1.07 (160)
1.10 (180)
ꢁ0.44 (170), ꢁ0.93 (190)
ꢁ0.50 (100), ꢁ1.17 (120)
ꢁ0.51 (115), ꢁ1.00 (130)
ꢁ0.49 (140), ꢁ1.28 (180)
ꢁ0.55 (150), ꢁ1.18 (190)
ꢁ0.45 (140), ꢁ1.22 (180)
ꢁ0.41 (120), ꢁ1.00 (170)
ꢁ0.36 (150), ꢁ1.07 (180)
ꢁ0.35 (140), ꢁ0.96 (180)
a
Solvent MeCN, supporting electrolyte [Bu4N](ClO4), Pt-disk milli working
electrode, Pt-wire auxiliary electrode, reference electrode SCE, at 298 K, E = 0.5
(Epa + Epc) where Epa is anodic peak potential and Epc is cathodic peak potential,
Ep = |Epa ꢁ Epc|; scan rate – 100 mV/s.
D
The complex 5b shows emission on excitation at 358 nm. The TD-
DFT calculation gives two intense transitions in this region: at 272 nm
(f, 0.215) and 341 nm (f, 0.232) corresponding to HOMOꢁ6 ? LUMO,
435 nm (f, 0.494) corresponding to HOMOꢁ1/HOMOꢁ2 ? LUMO,
Cl(p )/L( ) ? N@N( *) is also higher than experimental band,
L(p
)/L0(
p) ? L(p*) and HOMO ? LUMO+2, L(
p p) ? L(p*), respec-
)/L0(
p
p
p
tively. These are intra-ligand, p ? p* transitions.

P. Pratihar et al. / Inorganica Chimica Acta 363 (2010) 831–840
837
3.2. Physical measurements
Microanalytical data (C, H, N) were collected on Perkin–Elmer
2400 CHNS/O elemental analyzer. Spectroscopic data were ob-
tained using the following instruments: UV–Vis spectra, Lambda
25, Perkin–Elmer L 120-000 A; IR spectra (KBr disk, 4000–
200 cmꢁ1), FTIR RX 1, Perkin–Elmer; 1H NMR spectra, Bruker (AC)
300 MHz FTNMR spectrometer. Emission was examined by LS 55
Perkin–Elmer spectrofluorimeter at room temperature (298 K) in
MeCN under degassed condition. Electrochemical measurements
were performed using computer-controlled PAR model 270
VERSASTAT electrochemical instruments with Pt-disk electrodes.
All measurements were carried out under a nitrogen environment
at 298 K with reference to saturated calomel electrode (SCE) in ace-
tonitrile using [nBu4N][ClO4] as supporting electrolyte. The re-
ported potentials are uncorrected for junction potential.
Luminescence property was measured using LS-55 Perkin–El-
mer fluorescence spectrophotometer at room temperature
(298 K) in CH3CN solution by 1 cm path length quartz cell. The
fluorescence quantum yield of the complexes was determined
using carbazole laser dye as a reference with a known /R (fluo-
rescence quantum yield of reference) of 0.42 in MeCN [60]. The
complex and the reference dye were excited at 270–285 for
Pd(b-NaiR)Cl2 and 340–355 nm for Pd(b-NaiR–N–C6H4–X)Cl,
maintaining nearly equal absorbance (ꢃ0.1), and the emission
spectra were recorded from 300 to 500 nm for 2 and 360–
650 nm for 3–5. The area of the emission spectrum was inte-
grated using the software available in the instrument and the
quantum yields were calculated according to the following
equation:
Fig. 5. Cyclic voltammogram of Pd(b-NaiMe–N–C6H5)Cl (3a) in MeCN.
3. Experimental
3.1. Materials
1-Alkyl-2-(naphthyl-b-azo)imidazoles (b-NaiR, 1; R = CH3 (a),
CH2–CH3 (b), CH2Ph (c)) were prepared by reported procedure
[55]. PdCl2 was purchased from Arrora Matthey, Kolkata, India.
Pd(b-NaiR)Cl2 (2) were prepared by reported procedure [55,60].
Aniline, p-toluidine, p-chloroaniline were received from Sisco Re-
search Lab (SRL). The purification of acetonitrile and preparation
of n-tetra butylammonium perchlorate [nBu4N][ClO4] for electro-
chemical work were done as before [68]. Dinitrogen was purified
by bubbling through an alkaline pyrogallol solution. Solvents used
for solvatochromic study were purified by reported procedure [68].
Other chemicals and solvents were of reagent grade and were used
without further purification. Commercially available SRL silica gel
(60–120 mesh) was used for column chromatography.
/S=/R ¼ ½AS=ARꢅ ꢄ ½ðAbsÞR=ðAbsÞSꢅ ꢄ ½gS2
=
gR2
ꢅ
Here /S and /R are the fluorescence quantum yield of the sam-
ple and the reference, respectively; AS and AR are the area under the
fluorescence spectra of the sample and the reference, respectively,
(Abs)S and (Abs)R are the respective optical densities of the sample
and the reference solution at the wavelength of excitation, and gS
HOMO
HOMO-1
LUMO
LUMO+1
E, -6.16 eV; Pd, 30%; E, -6.26 eV; Pd, 11%; E, -3.57 eV; Pd, 06%; E, -2.41 eV; Pd, 49%;
L, 19%; Cl, 51%
L, 34%; Cl, 55%
L, 92%
L, 18%; Cl, 33%
(a)
HOMO
HOMO-1
LUMO
LUMO+1
E, -5.16 eV; Pd, 06%; E, -6.17 eV; Pd, 10%; E, -3.02 eV; Pd, 07%; E, -1.92 eV; Pd, 48%;
L, 68%; L/, 26%
L, 24%; L/, 63%
L, 81%; L/, 11%
L, 25%; L/, 14%; Cl,
13%
(b)
Fig. 6. Contour plots of the selective frontier molecular orbitals of (a) Pd(b-NaiEt)Cl2 (2b) and (b) Pd(b-NaiEt–N–C6H4–Cl-p)Cl (5b).

838
P. Pratihar et al. / Inorganica Chimica Acta 363 (2010) 831–840
Fig. 7. Energy level correlation of MOs of Pd(b-NaiEt)Cl2 (2b) and Pd(b-NaiEt–N–C6H4–Cl-p)Cl (5b) in gas phase.
Table 5
Selected list of excitation for 2b and 5b at TD-DFT/B3LYP/6-31G(d) level calculation.
Excitation energy(eV)
Wavelength k, nm
Osc. strength (f)
Major contribution
Character
2b
*
) ? N@N(p ), (XLCT, MLCT)
2.191
2.847
565.8
435.3
0.270
0.494
(67%)HOMO ? LUMO
Cl(p
Cl(p
Cl(p
p
p
p
)/Pd(d
p
*
p
(38%)HOMOꢁ2 ? LUMO
(24%)HOMOꢁ1 ? LUMO
(64%)HOMOꢁ5 ? LUMO
(53%)HOMOꢁ15 ? LUMO
(25%)HOMOꢁ16 ? LUMO
(19%)HOMOꢁ9 ? LUMO+1
(17%)HOMOꢁ15 ? LUMO
)/L(
)/L(
p
p
) ? N@N(
), (XLCT, ILCT)
) ? N@N(
p
*), (XLCT, ILCT)
3.247
4.963
5.006
381.7
249.7
247.6
0.095
0.152
0.222
Pd(dp) ? N@N(p
*), MLCT
L(
L(
p
p
) ? L(
) ? L(
p
p
p
*), ILCT
*), ILCT
) ? Pd(dp), (LMCT, XMCT)
), ILCT
Cl(p
p)/L(
*
L(p
) ? L(
p
5b
1.711
2.346
2.666
2.885
2.999
3.328
3.631
4.352
724.8
528.4
465.0
429.8
413.3
372.5
341.4
284.9
0.192
0.007
0.040
0.027
0.047
0.215
0.232
0.176
(72%)HOMO ? LUMO
L(
L(
L0(
Cl(p
Cl(p
p
p
p
)/L0(
)/L0(
)/L(
p
p
p
) ? L(
) ? Pd(d
) ? L(
*), ILCT
) ? L(
p
*), ILCT
(90%)HOMO ? LUMO+1
(64%)HOMOꢁ1 ? LUMO
(82%)HOMOꢁ2 ? LUMO
(56%)HOMOꢁ3 ? LUMO
(54%)HOMOꢁ6 ? LUMO
(59%)HOMO ? LUMO+2
(52%)HOMO ? LUMO+3
p), LMCT
p
p)/Pd(d
p
p
*), (XLCT, MLCT)
), XLCT
*
)/Pd(dp) ? L(p ), (ILCT, MLCT)
*
p
p
) ? L(
L(p
L(p
L(p
)/L0(
)/L0(
)/L0(
p
p
p
*
) ? L(
) ? L(
p
p
), ILCT
*), ILCT
and
g
R are the values of refractive index for the respective solvent
3.3. Preparation of chloro[1-methyl-2-{(7-imidophenyl)naphthyl-b-
azo}imidazole-N,N0,N00]palladium(II), Pd(b-NaiMe–N–C6H5)Cl, (3a)
used for the sample and the reference. Fluorescence lifetimes were
measured using a time-resolved spectrofluorometer from IBH, UK.
The instrument uses
a
picosecond diode laser (NanoLed-07,
To an acetonitrile solution (20 ml) of Pd(b-NaiMe)Cl2 (0.08 mg,
0.20 mmol) was added slowly aniline (0.04 mg, 0.43 mmol) in the
same solvent (10 ml). And 0.2 ml triethylamine was added to this
solution. The reaction mixture was stirred and refluxed for 12 h.
The colour of the solution changed gradually from orange-red to
reddish-brown. The solution was evaporated in air, and the residue
was washed thoroughly first with water (2 ꢄ 5 ml) and then with
50% aqueous-ethanol (3 ꢄ 5 ml). The residue was dissolved in
dichloromethane (10 ml) and the solution was chromatographed
over silica gel column (60–120 mesh). A reddish-brown band
was eluted by MeCN. The eluted solution on evaporation in vacuo
gave pure compound. Reddish-brown compound was isolated in
52% yield. This product is the coupled product, Pd(b-NaiMe–N–
C6H5)Cl, (3a). A red band was also eluted by acetonitrile and had
remained uncharacterized till date. Anal. Calc. for C20H16N5ClPd
(3a): C, 51.34; H, 3.42; N, 14.97. Found: C, 51.29; H, 3.32; N,
408 nm) as the excitation source and works on the principle of
time-correlated single photon counting [67,69,70]. The instrument
responses function is ꢃ230 ps at FWHM. To eliminate depolariza-
tion effects on the fluorescence decays, measurements were done
with magic angle geometry (54.7°) for the excitation and emission
polarizers. The observed decays palladium(II) complexes fitted
well with a bi-exponential function as in Eq. (7), where s’s are
the fluorescence lifetime and
a is the pre-exponential factor. For
the fits, the reduced v2 values were within 0.9–1.3 and the distri-
bution of the weighted residuals were random among the data
channels. sf is mean fluorescence life time (meaning of the symbols
are usual) [67].
IðtÞ ¼ ½a1 expðꢁt=s1Þ ꢁ a2 expðꢁt=s2Þꢅ
sf ¼ a1s1 þ a2s2
ð6Þ
ð7Þ

P. Pratihar et al. / Inorganica Chimica Acta 363 (2010) 831–840
839
14.88%. M.p. 280–282 °C. IR data (cmꢁ1
1320,
(C@N) 1564 cmꢁ1. Anal. Calc. for C21H18N5ClPd (3b): C,
52.34; H, 3.74; N, 14.54. Found: C, 52.31; H, 3.72; N, 14.52%. M.p.
240–243 °C, yield 50%, IR data (cmꢁ1
(Pd–Cl) 325, (N@N)
1335,
(C@N) 1552 cmꢁ1. Anal. Calc. for C26H20N5ClPd (3c): C,
57.41; H, 3.68; N, 12.88. Found: C, 57.43; H, 3.64; N, 12.81%. Com-
pound (3c), M.p. 285–290 °C, yield 55%, IR data (cmꢁ1
(Pd–Cl)
311, (N@N) 1325,
(C@N) 1555 cmꢁ1. Anal. Calc. for C21H18N5ClPd
(4a): C, 52.34; H, 3.74; N, 14.54. Found: C, 52.30; H, 3.71; N,
14.51%. M.p. 281–284 °C, yield 48%, IR data (cmꢁ1
(Pd–Cl) 315,
(N@N) 1332,
(C@N) 1545 cmꢁ1. Anal. Calc. for C22H20N5ClPd
(4b): C, 53.28; H, 4.04; N, 14.13. Found: C, 53.25; H, 4.01; N,
14.11%. M.p. 244–248 °C, yield 51%, IR data (cmꢁ1
(Pd–Cl) 310,
(N@N) 1343,
(C@N) 1560 cmꢁ1. Anal. Calc. for C27H22N5ClPd
(4c): C, 58.12; H, 3.95; N, 12.56. Found: C, 58.09; H, 3.91; N,
12.49%. M.p. 252–255 °C, yield 50%, IR data (cmꢁ1
(Pd–Cl) 325,
(N@N) 1344,
(C@N) 1562 cmꢁ1. Anal. Calc. for C20H15N5Cl2Pd
(5a): C, 47.81; H, 2.99; N, 13.94. Found: C, 47.82; H, 2.91; N,
13.81%. M.p. 260–262 °C, yield 46%, IR data (cmꢁ1
(Pd–Cl) 333,
(N@N) 1351,
(C@N) 1572 cmꢁ1. Anal. Calc. for C21H17N5Cl2Pd
(5b): C, 48.84; H, 3.29; N, 13.57. Found: C, 48.81; H, 3.22; N,
13.49%. M.p. 251–255 °C, yield 49%, IR data (cmꢁ1
(Pd–Cl) 311,
(N@N) 1342,
(C@N) 1550 cmꢁ1. Anal. Calc. for C26H19N5Cl2Pd
(5c): C, 53.98; H, 3.29; N, 12.11. Found: C, 53.85; H, 3.21; N,
12.01%. M.p. 278–280 °C, yield 47%, IR data (cmꢁ1
(Pd–Cl) 313,
(N@N) 1337,
(C@N) 1551 cmꢁ1
) m(Pd–Cl) 310, m(N@N)
Table 6
Crystallographic data of Pd(b-NaiEt)Cl2 (2b) and Pd(b-NaiEt–N–C6H4–Cl-p)ClꢀC6H6
m
(5b).
Pd(b-NaiEt)Cl2
(2b)
Pd(b-NaiEt–N–C6H4–Cl-p)ClꢀC6H6
(5b)
)
m
m
m
Chemical formula C15H14Cl2N4Pd
C21H17Cl2N5Pd, 0.5(C6H6)
555.75
Brown
Formula weight
Crystal colour
Crystal size
(mm3)
427.60
Brown
)
m
m
m
0.42 ꢄ 0.32 ꢄ 0.18 0.42 ꢄ 0.24 ꢄ 0.22
)
m
Crystal system
Triclinic
Orthorhombic
Pbcn
ꢀ
Space group
P1
m
m
0
7.2498(5)
10.0632(7)
12.4475(9)
15.8106(8)
a (AÅ)
0
b (AÅ)
0
20.4401(11)
14.0167(8)
)
m
m
m
c (AÅ)
a
(°)
68.4470(10)
83.6770(10)
73.7870(10)
811.01(10)
90.00
90.00
90.00
4529.8(4)
b (°)
)
m
c
(°)
m
m
0
V (AÅ3)
Z
2
8
)
m
T (K)
293(2)
0.71073
298(2)
0.71073
m
m
0
k (AÅ)
2h Range (°)
hkl Range
3.52 6 2h 6 52.04
ꢁ8 6 h 6 8
ꢁ12 6 k 6 12
ꢁ15 6 l 6 15
1.751
3.26 6 2h 6 52.02
ꢁ19 6 h 6 16
ꢁ19 6 k 6 25
ꢁ17 6 l 6 17
1.630
)
m
m
m
qcalc (g cmꢁ3
)
)
m
l
(Mo K
(mmꢁ1
Reflection
collected
a
)
)
1.474
1.078
m
m
.
8510
24310
Unique reflections 3174
3369
Ra
0.0386
0.0869
1.035
0.0349
0.0847
1.036
3.4. X-ray structure determination
wRb
Goodness -of-fit
The X-ray quality single crystals of Pd(b-NaiEt)Cl2 (2b) and
Pd(b-NaiEt–N–C6H4–Cl-p)ClꢀC6H6 (5b) were grown by slow diffu-
sion of benzene into dichloromethane solution of the complex at
298 K. A summary of the crystallographic data and structure
refinement parameters are given in Table 6. Data were collected
with the Bruker SMART CCD using graphite-monochromatized
a
R1
wR2 = [
=
R
|Fo ꢁ Fc|/
RFo.
b
2
4
R
w(Fo ꢁ Fc2)/
Rw Fo ] r
1/2, w = 1/[ 2(F2) + (0.0433P)2 + 0.0000P] for (2b);
w = 1/[r
2(F2) + (0.0485P)2 + 1.4923P] for (5b).
Mo Ka radiation (k = 0.71073 Å). Unit cell parameters were deter-
4. Conclusion
mined from least-squares refinement of setting angles with 2h in
the range 3.52 6 2h 6 52.04 for 2b and 3.26–52.02° for 5b. Data
were corrected for Lp effects and for linear decay. Semi-empirical
absorption corrections based on multi-scans were applied. The
structure was solved by direct method using SHELXL-97 [71] and
successive difference Fourier syntheses. All non-hydrogen atoms
were refined anisotropically. The hydrogen atoms were fixed geo-
metrically and refined using riding model. All calculations were
carried out using SHELXL-97 [72], ORTEP-32 [73], PLATON-99 [74]
programs.
Palladium assisted C–N coupling reaction of arylamine (ArNH2)
with coordinated b-NaiR (1-alkyl-2-(naphthyl-b-azo)imidazoles))
in Pd(b-NaiR)Cl2 is examined in this work. The coupled products
have been characterized by spectroscopic and electrochemical
studies. The complexes are potentially fluorescent in solution and
the excited state decay follows bi-exponential decay process. The
absorption and emission processes are dependent on polarity of
the solvent. The electronic and redox properties are explained by
theoretical calculation of optimized geometry of the ligand and
complexes.
3.5. Computational methods
Acknowledgments
Full geometry optimizations were carried out using the density
functional theory method at the (R)B3LYP [75]. All elements except
palladium were assigned the 6-31G(d) basis set. The SDD basis set
with effective core potential was employed for the palladium atom
[76,77]. The vibrational frequency calculations were performed to
ensure that the optimized geometries represent the local minima
and there are only positive eigen values. All calculations were per-
formed with GAUSSIAN03 program package [78]. Vertical electronic
excitations based on B3LYP optimized geometries were computed
using the time-dependent density functional theory (TD-DFT) for-
malism [79–81] in acetonitrile using conductor-like polarizable
continuum model (CPCM) [82–84]. GaussSum [85] was used to cal-
culate the fractional contributions of various groups to each molec-
ular orbital.
Financial support from the University Grants Commission, New
Delhi and CAS-UGC (New Delhi) sanctioned to the Department of
Chemistry, Jadavpur University are gratefully acknowledged.
Appendix A. Supplementary material
DFT calculated orbital energies, orbital compositions (Table S4)
and selected list of excited energies (Table S5) are given as Supple-
mentary data.
CCDC 723282 and 723283 contains the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data

840
P. Pratihar et al. / Inorganica Chimica Acta 363 (2010) 831–840
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