Octahedral Ni(II) and Cu(II) complexes with a new hexadentate (NSN) 2 donor ligand: Synthesis, characterization, X-ray structure and DFT calculations

Article abstract of DOI:10.1016/j.poly.2014.03.052

Coupling of arylthioether diazonium salts with acetylacetone in NaOH medium produced the hexadentate ligand HL. This ligand can undergo keto-enol tautomerism in solution. It acts as a monoanionic hexadentate (N,S,N,N,S,N) chelator and forms 1:1 isostructural complexes, [Ni(L)](ClO₄) (1) and [Cu(L)](ClO₄) (2), with Ni(II) and Cu(II) respectively. The complexes have been characterized by spectral analysis. The pseudo octahedral geometries of the complexes are confirmed by single crystal X-ray diffraction studies. The X-ray and spectral characterizations confirmed the existence of the keto form of the ligand in the complexes. The electronic structures and spectral properties of the ligand and the complexes have been explained by DFT and TDDFT calculations.

Full text of DOI:10.1016/j.poly.2014.03.052

Polyhedron 76 (2014) 29–35
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Octahedral Ni(II) and Cu(II) complexes with a new hexadentate (NSN)2
donor ligand: Synthesis, characterization, X-ray structure and DFT
calculations
⇑
Mahendra Sekhar Jana, Ajoy Kumar Pramanik, Tapan Kumar Mondal
Inorganic Chemistry Section, Department of Chemistry, Jadavpur University, Kolkata 700032, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Coupling of arylthioether diazonium salts with acetylacetone in NaOH medium produced the hexaden-
tate ligand HL. This ligand can undergo keto-enol tautomerism in solution. It acts as a monoanionic hexa-
dentate (N,S,N,N,S,N) chelator and forms 1:1 isostructural complexes, [Ni(L)](ClO4) (1) and [Cu(L)](ClO4)
(2), with Ni(II) and Cu(II) respectively. The complexes have been characterized by spectral analysis. The
pseudo octahedral geometries of the complexes are confirmed by single crystal X-ray diffraction studies.
The X-ray and spectral characterizations confirmed the existence of the keto form of the ligand in the
complexes. The electronic structures and spectral properties of the ligand and the complexes have been
explained by DFT and TDDFT calculations.
Received 8 November 2013
Accepted 23 March 2014
Available online 5 April 2014
Keywords:
Octahedral Ni(II) and Cu(II) complexes
Hexadentate arylazothioether ligand
X-ray structure
Ó 2014 Elsevier Ltd. All rights reserved.
DFT and TDDFT calculations
1. Introduction
tions [19–24]. Moreover, the presence of nickel-sulfur and -
nitrogen bonds at the active sites of several hydrogenases [25]
The coordination chemistry of N, S donor ligands has received a
great deal of attention due to the stability, chemical and electro-
chemical activities, and biological relevance of the corresponding
complexes [1–7]. Thiols and thioethers are ubiquitous donor func-
tions in the active sites of many naturally occurring metalloen-
zymes. In the coordination sphere of redox active metal ions
such as iron, cobalt, copper, etc., sulfur-ligands affect a high redox
potential because the reduced metal center is a softer cation and
therefore more efficiently coordinated by the soft sulfur donors
[8,9].
Polydentate ligands with thioether moieties are often used for
the synthesis of model complexes to mimic the spectroscopic
and structural properties of the active sites of metalloproteins
[10–13]. Complexes containing N, S donor ligands have biological
relevance as several bioactive molecules contain similar donor
environments [14–18]. The potential role played by nickel(II) and
copper(II) ions, being present in the active sites of a large number
of metalloproteins, have encouraged the design of new ligand
frames having nitrogen–sulfur donor centres, characterization of
nickel and copper complexes as models for providing a better
understanding of biological systems and for assisting in the devel-
opment of new homogeneous catalysts for selective catalytic reac-
and carbon monoxide dehydrogenases [26] has stimulated interest
in nickel chemistry with mixed sulfur and nitrogen donor ligands
[27].
The substitution of an aryl diazonium group at the active meth-
ylinic carbon of acetylacetone and the study of azo-hydrazone tau-
tomerism have been reported elsewhere [28–30]. Herein, we have
synthesized the new hexadentate N(pyridyl), S(thioether) and
N(azo) donor ligand, HL by substituting both of the active methy-
lene protons and eliminating an acetyl group in strongly alkaline
medium. The structural characterization of the ligand has been car-
ried out by 1H NMR and mass spectroscopy, and elemental analy-
sis. The octahedral Ni(II) and Cu(II) complexes with this ligand
have been synthesized and characterized by different experimental
techniques abetted with theoretical computations.
2. Experimental
2.1. Materials and methods
2-((Pyridine-2-yl)methylthio)benzenamine was prepared fol-
lowing the reported procedure [31]. 2-Aminothiophenol and 2-
(chloromethyl)pyridine were purchased from Sigma Aldrich. All
other chemicals and solvents were of reagent grade and used as
received.
⇑
Corresponding author. Tel.: +91 033 24146666x2453; fax: +91 033 24146584.
E-mail address: tkmondal@chemistry.jdvu.ac.in (T.K. Mondal).
http://dx.doi.org/10.1016/j.poly.2014.03.052
0277-5387/Ó 2014 Elsevier Ltd. All rights reserved.

30
M.S. Jana et al. / Polyhedron 76 (2014) 29–35
Table 1
Crystal data and details of the structure determination for 1 and 2.
Crystal data
1
2
Formula
C
27H23N6NiOS2, ClO4
C27H23CuN6OS2, ClO4
674.62
monoclinic
P21/c
9.708(5)
27.984(5)
11.326(5)
90
108.210(5)
90
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
669.79
triclinic
P11
ꢀ
9.867(5)
10.955(5)
14.746(5)
110.041(5)
95.807(5)
106.865(5)
1396.9(11)
2
a
(°)
b (°)
c
(°)
V (Å3)
2923(2)
4
1.533
Z
qcalc (g cmÀ3
)
1.592
0.990
l
(mmÀ1
)
1.030
F(000)
688
1380
Data collection
T (K)
293(2)
293(2)
k (Å)
0.71073
0.71073
hmin–max (°)
hkl range
Total, Unique Data, Rint
1.51–25.08
2.03–27.16
À10 to 11, À13 to 13, À17 to 17
19751, 4859, 0.0284
3649
À12 to 12, À35 to 35, À14 to 14
47254, 6460, 0.1036
3121
Observed data [I > 2r (I)]
Refinement
N
ref, Npar
R, wR2 (I > 2
R, wR2 (all data)
Goodness-of-fit (GOF)
Residual density (e ÅÀ3
4859, 379
6460, 379
r
(I))
0.0426, 0.1015
0.0631, 0.1121
1.037
À0.287 and 0.544
0.0604, 0.1259
0.1521, 0.1259
1.002
À0.473 and 0.453
)
Microanalytical data (C, H, N) were collected from a Perkin-
Elmer 2400 CHNS/O elemental analyzer. Spectroscopic data were
obtained using the following instruments: UV–Vis spectra, Perkin
Elmer; model Lambda 25; IR spectra (KBr disk, 4000–400 cmÀ1),
Perkin Elmer; model spectrum RX-1; 1H NMR spectra, Bruker
(AC) 300 MHz FTNMR spectrometer. ESI mass spectra were
recorded on a Micromass Q-ToF mass spectrometer. Molar conduc-
tance was measured using a Systronics conductivity meter (Model
304) using ca. 10À3 M solutions in acetonitrile. Magnetic suscepti-
bilities were measured on a Gouy balance using Hg[Co(SCN)4] as
the calibrant. Diamagnetic corrections were made using Pascal’s
constants.
2.2. Synthesis of the ligand (HL)
2-((Pyridine-2-yl)methylthio)benzenamine (3.46 g, 16 mmol)
was dissolved in 20 mL of ca.6 M hydrochloric acid and diazotized
by adding 10 mL sodium nitrite (1.10 g, 16 mmol) solution at a
N2+Cl-
NH2
NH2
Na/ Dry MeOH
NaNO2/ HCl
S
S
0 - 5 0C
N
Cl
N
SH
N
O
O
(5M NaOH solution)
O
OH
N
N
N
N
N
N
N
NH
S
S
S
S
N
N
N
N
enol form
keto form
Scheme 1. Synthetic route of ligand HL.

M.S. Jana et al. / Polyhedron 76 (2014) 29–35
31
Table 2
J = 4.1 Hz, 1H), 7.87 (d, J = 7.9 Hz, 2H), 7.05–7.50 (m, 12H), 4.16
(s, 4H), 2.62 (s, 3H). UV–Vis (acetonitrile, kmax, nm (e
, MÀ1 cmÀ1)):
Some selected X-ray and calculated (DFT/B3LYP method) bond distances (Å) and
angles (°) for 1 and 2.
460 (18392), 304 (17220), 265 (29260).
M = Ni (1)
M = Cu (2)
X-ray
Calc.
X-ray
Calc.
2.3. Synthesis of the complexes
Bonds (Å)
M(1)–N(1)
M(1)–N(2)
M(1)–N(5)
M(1)–N(6)
M(1)–S(1)
M(1)–S(2)
N(2)–N(3)
N(4)–N(5)
C(13)–N(3)
C(13)–N(4)
C(13)–C(14)
C(14)–O(1)
2.122(3)
1.998(3)
1.994(3)
2.137(3)
2.3667(16)
2.3595(15)
1.293(3)
1.291(3)
1.349(5)
1.352(5)
1.500(5)
1.205(5)
2.193
2.040
2.033
2.188
2.412
2.403
1.289
1.287
1.346
1.354
1.510
1.216
2.427(4)
1.957(3)
1.945(3)
2.379(4)
2.3294(17)
2.3368(17)
1.295(5)
1.291(5)
1.355(5)
1.323(5)
1.499(6)
1.214(5)
2.402
2.011
2.002
2.385
2.382
2.374
1.298
1.307
1.364
1.359
1.510
1.228
To a 15 mL methanolic solution of HL (0.15 g, 0.29 mmol), a
Ni(ClO4)2Á6H2O solution (0.11 g, 0.30 mmol) was added dropwise
under stirring conditions. The stirring was further continued for
4 h. The resultant deep pink solution was kept for slow evaporation
of the solvent. After a week, a pink crystal suitable for a single crys-
tal X-ray diffraction study of 1 was found. Yield: 0.14 g, 73%.
Microanalytical data for C27H23ClN6NiO5S2 (1). Anal. Calc.: C,
48.42; H, 3.46; N, 12.55. Found: C, 48.52; H, 3.47; N, 12.58%. IR
(KBr disc, cmÀ1): 1666
(ClOÀ4 ). UV–Vis (acetonitrile, kmax
(8420), 528 (8162), 497 (5438), 427 (2628), 317 (7225), 263
m
(C@O), 1601
m
(C@N), 1356
m(N@N), 1093
m
,
nm
(e,
MÀ1 cmÀ1)): 563
Angles (°)
(14967). Molar conductance (acetonitrile, kM,
X
À1 molÀ1 cm2):
N(1)–M(1)–N(2)
N(1)–M(1)–N(5)
N(1)–M(1)–N(6)
N(1)–M(1)–S(1)
N(1)–M(1)–S(2)
N(2)–M(1)–N(5)
N(2)–M(1)–N(6)
N(2)–M(1)–S(1)
N(2)–M(1)–S(2)
N(5)–M(1)–N(6)
N(5)–M(1)–S(1)
N(5)–M(1)–S(2)
N(6)–M(1)–S(1)
N(6)–M(1)–S(2)
S(1)–M(1)–S(2)
87.58(10)
96.02(10)
175.12(9)
83.48(8)
94.27(8)
90.44(11)
94.77(10)
86.17(8)
176.58(8)
88.25(10)
176.59(8)
86.51(8)
92.40(8)
83.61(8)
96.89(4)
88.16
96.77
172.7
82.06
93.43
89.51
96.23
85.11
174.5
89.06
174.5
85.11
92.52
82.71
99.21
91.28(12)
96.13(12)
168.52(11)
79.57(9)
89.53
97.92
168.0
79.75
92.41
91.39
98.25
86.03
177.0
91.03
176.5
86.10
91.62
80.19
96.52
128. leff (B.M.): 3.03.
Complex 2 was prepared following the same procedure as
described above by the reaction of Cu(ClO4)2Á6H2O (0.10 g,
0.28 mmol) with HL (0.11 g, 0.30 mmol) and the resultant pink
solution was kept for slow evaporation to grow single crystals suit-
able for an X-ray diffraction study. Yield: 0.13 g, 68%.
91.57(9)
91.19(13)
96.40(12)
87.09(9)
176.71(9)
92.24(12)
175.32(10)
86.88(10)
92.28(9)
Microanalytical data for C27H23ClCuN6O5S2 (2). Anal. Calc.: C,
48.07; H, 3.44; N, 12.46. Found: C, 48.14; H, 3.46; N, 12.49%. IR data
(KBr disc, cmÀ1): 1658
and 1086
557 (9443), 521 (9013), 490 (5868), 412 (12329), 293 (23645),
m
(C@O), 1602
m
(C@N), 1353
m
(N@N), 1118
m
(ClO-4). UV–Vis (acetonitrile, kmax, nm (
e
, MÀ1 cmÀ1)):
81.03(9)
95.04(4)
263 (26473). Molar conductance (acetonitrile, KM
, X -
À1 molÀ1
cm2): 135. leff (B.M.): 1.97.
temperature of 0 °C. The diazotized solution was added under stir-
ring conditions to acetylacetone (0.80 g, 8 mmol) dissolved in
30 mL of 5 M sodium hydroxide solution. A deep red precipitate
was formed which was collected by filtration. The residue was dis-
solved by adding 1(N) HCl and then NaOH solution was added to it
for re-precipitation of the compound. It was filtered and washed
with distilled water dried over CaCl2. Yield: 3.08 g, 75%.
2.4. Crystal data collection and refinement
Single crystals suitable for X-ray diffraction of 1 and 2 were
grown by slow evaporation of the reaction mixture in methanol
over a week. Details of the crystal analysis, data collection and
structure refinement data are given in Table 1. Data were collected
using a Bruker AXS Kappa Apex-II diffractometer equipped with an
Apex-II CCD area detector using a graphite monochromator, Mo K
radiation (0.71073 Å). Reflection data were recorded using the
scan technique. For complex 1, out of 19 751 collected data, 4859
Microanalytical data for C27H24N6OS2 (HL). Anal. Calc.: C, 63.26;
H, 4.72; N, 16.39. Found: C, 63.26; H, 4.71; N, 16.37%. IR (KBr disc,
a
x
cmÀ1): 3365–3256 (NH), 2926
m
(CH), 1677
m(C@O), 1584 m(C@N),
1438
m
(N@N). 1H NMR (CDCl3, d, ppm): 14.97 (s, 1H), 8.42 (d,
Fig. 1. ORTEP plot of 1 with 35% ellipsoidal probability, with the atom numbering scheme.

32
M.S. Jana et al. / Polyhedron 76 (2014) 29–35
Fig. 2. ORTEP plot of 2 with 35% ellipsoidal probability, with the atom numbering scheme.
with I > 2
r
(I) within the h range 1.51 < h < 25.08° and for 2, out of
(I) within the h range
3260–3375 cmÀ1 along with a sharp peak at 1676 cmÀ1 in the IR
spectrum indicates the existence of the keto form of the ligand
(see Section 2) (Scheme 1). The (C@N) and (N@N) bands
43 413 collected data, 5650 with I > 2
r
2.03 < h < 26.00° were used for the structure solution. The data
were corrected for Lorentz polarization effects, and absorption cor-
rections were made using SADABS [32]. The structures were solved
and refined by full-matrix least-squares techniques on F2 using
the SHELXS-97 program [33]. All non-hydrogen atoms were refined
anisotropically. Hydrogen atoms were generated using SHELXL-97
[33], their positions calculated based on the riding model, with
thermal parameters equal to 1.2 times that of the associated C
atoms, and participated in the calculation of the final R-indices.
Molecular structures were drawn with the ORTEP-3 [34] program.
m
m
appeared at 1625 and 1438 cmÀ1 respectively. In the course of
the reaction HL loses its N–H proton in the presence of Et3N and
the negative charge so formed is stabilized by resonance with
the two adjacent azo groups. The keto form of the ligand has been
established in the octahedral Ni(II) and Cu(II) complexes,
[Ni(L)](ClO4) (1) and [Cu(L)](ClO4) (2). The IR spectra of the com-
plexes show a sharp peak at 1658–1666 cmÀ1, corresponding to
m
(C@O) of the ligand. The m(N@N) band in the complexes is red
shifted and observed at 1353–1356 cmÀ1. This is due to participa-
tion of the N@N bond in resonance with the negative charge
and d
conductance values in the range 128–132
p
(M) ? p⁄(N@N) back donation. The complexes show molar
2.5. Computational method
X
À1 molÀ1 cm2 in
acetonitrile solution, corresponding to a 1:1 electrolyte.
Full geometry optimizations were carried out using the density
functional theory (DFT) method at the UB3LYP level for 1 and 2
[35,36]. All elements, except Ni and Cu, were assigned to the 6-
31G(d) basis set [37,38]. The LanL2DZ basis set, with an effective
core potential for Ni and Cu, was used [39]. The vibrational fre-
quency calculations were performed to ensure that the optimized
geometries represent the local minima and that there are only
positive eigen values. All calculations were performed with the
GAUSSIAN03 program package [40] with the aid of the GaussView
visualization program. Vertical electronic excitations based on
B3LYP optimized geometries were computed using the time-
dependent density functional theory (TDDFT) formalism [41–43]
in methanol using a conductor-like polarizable continuum model
(CPCM) [44–46]. GaussSum [47] was used to calculate the frac-
tional contributions of various groups to each molecular orbital.
3.2. Molecular structures of 1 and 2
The molecular structures of the complexes were confirmed by
single crystal X-ray diffraction studies. The bond parameters show
the distorted octahedral geometry around Ni and Cu in the iso-
structural complexes 1 and 2, respectively. Selected bond distances
and bond angles are given in Table 2. The ORTEP views with the atom
numbering schemes are shown in Figs. 1 and 2 for 1 and 2, respec-
tively. The hexadentate (N,S,N,N,S,N) donor ligand coordinates
with central metal ion with two pyridyl-N, two thioether-S and
two azo-N atoms. The ligand in the complexes is mono anionic
and the negative charge is delocalized between two adjacent azo
groups, N(2)–N(3) and N(4)–N(5). Consequently, the azo bond dis-
tances (N(2)–N(3), 1.293(3) Å in 1 and 1.295(5) Å in 2, N(4)–N(5),
1.291(3) Å in 1 and 1.291(5) Å in 2) are elongated compared to
the N@N distances in related reported complexes [48,49] and the
C(13)–N(3), 1.349(5) Å in 1, 1.355(5) Å in 2, and C(13)–N(4),
1.352(5) Å in 1 and 1.355(5) Å in 2, bond distances are shorter than
the expected C–N single bond distance. The O(1)–C(14) bond
(1.205(5) Å in 1 and 1.214(5) Å in 2) in the complexes perfectly
match with C@O (keto) distances and well correlate with the
3. Results and discussion
3.1. Synthesis and formulation
The new hexadentate ligand HL was synthesized by diazotiza-
tion of 2-((pyridine-2-yl)methylthio)benzenamine followed by
coupling with acetylacetone in NaOH solution (Scheme 1). It was
characterized by elemental, mass and spectral analysis. The mass
spectrum shows a peak at m/z 513([MÀH]+) corresponding to HL.
1H NMR analysis in CDCl3 has found a singlet at 14.97 ppm,
corresponding to the N–H proton, and a broad stretching at
m
(CO) stretching value (1658–1666 cmÀ1) in the IR studies. The
C–C distance (C(13)–C(14), 1.500(5) Å in 1 and 1.499(6) Å in 2)
adjacent to the C@O function has single bond character. The M–
N(azo), 1.998(3)/1.994(3) Å in 1 and 1.957(3)/1.945(3) Å in 2,

M.S. Jana et al. / Polyhedron 76 (2014) 29–35
33
bonds are much shorter than the M–N(pyridyl), 2.122(3)/
occupied molecular orbitals are composed of mainly a ligand group
of orbitals, with a reduced contribution of d (Ni) orbitals. The b-
spin occupied orbitals are also concentrated on the ligand, with a
minor contribution (12%) of d -spin unoc-
2.137(3) Å in 1 and 2.427(4)/2.379(3) Å in 2, bond distances, which
p
well support the d
p
(M) ? p⁄(N@N) back donation process and
elongation of axial bonds in the complexes. The Cu–N(azo) bonds
p
(Ni) in HOMOÀ2. The
a
are ꢀ0.045 Å shorter than the Ni–N(azo) distances, indicating facile
cupied MOs and the b-spin LUMO has ligand character, but
d
p
(M) ? p⁄(N@N) back donation in complex 2 compared to com-
LUMO+1 and LUMO+2 of b-spin have 62% and 75% metal dx2
Ày2
plex 1. The M–S(thioether) distances (2.3667(16)/2.3595(15) Å in 1
and 2.3294(17)/2.3368(17) Å in 2) are well matched to reported
bond distances [48–51]. Most importantly the X-ray structure met-
rical parameters show that the Cu–N(azo) and Cu–S(thioether)
bond distances in 2 are shorter than the Ni–N(azo) and Ni–S(thio-
ether) distances in 1, whereas the Cu–N(pyridyl) in 2 bond dis-
tances are significantly longer than Ni–N(pyridyl) distances in 1.
and dz2 character, with a reduced contribution from the ligand
(Table S1, Fig. S2). Similarly, the SOMO and other
and unoccupied molecular orbitals for 2 are composed of a ligand
group of orbitals with a minor contribution (25%) of the d (Cu)
orbital in HOMOÀ3. The b-spin occupied orbials have ligand char-
acter, with a d
(Cu) contribution in HOMOÀ2 and HOMOÀ3. The
a-spin occupied
p
p
b-spin LUMO has dp (Cu) character and other low energy unoccu-
pied orbitals have p⁄(L) character (Table S2, Fig. S3).
3.3. Electronic structure DFT calculations
3.4. Spectral properties and TDDFT calculations
The coordinates obtained from single crystal X-ray diffraction
data for complexes 1 and 2 were optimized using the DFT/UB3LYP
(LANL2DZ/6-31G(d)) level of calculations in triplet (S = 1) and dou-
blet (S = ½) states respectively. The optimized bond parameters
well correlate with the X-ray data (Table 2).
For complex 1, the singly occupied molecular orbitals (SOMOs)
are concentrated on the ligand (95%). The other low energy a-spin
To simulate the experimental electronic spectra, TDDFT/B3LYP/
CPCM calculations for HL, 1 and 2 have been performed in metha-
nol. The calculated vertical electronic transitions calculated by the
TDDFT method are given in Tables 3–5 for HL, 1 and 3 respectively.
The ligand in methanol shows peaks at 460, 304, 265 and
203 nm. The low energy band corresponds to a mixture of n ? p⁄
Table 3
Vertical electronic excitations calculated by the TD DFT/B3LYP/CPCM method and experimental absorption bands of HL.
Eexcitation (eV)
kexcitation (nm)
Osc. strength f
Key transitions
Character
kexpt. (e )
, MÀ1 cmÀ1
2.4245
2.8139
511
441
0.02
0.17
(67%) HOMO ? LUMO+1
(59%) HOMO–1 ? LUMO
(21%) HOMO ? LUMO+1
(74%) HOMO–3 ? LUMO+1
(40%) HOMO–4 ? LUMO
(23%) HOMO–8 ? LUMO
(56%) HOMO ? LUMO+3
(24%) HOMO ? LUMO+2
(64%) HOMO–5 ? LUMO
(65%) HOMO–1 ? LUMO+2
n ? p⁄
n/
460 (18392)
p ?
p⁄
3.8413
3.8946
323
318
0.14
0.09
p
p
?
?
p⁄
p⁄
304 (17220)
4.2143
294
0.09
n ? p⁄
4.3214
4.3749
287
283
0.09
0.08
p
p
?
?
p⁄
p⁄
265 (29260)
Table 4
Vertical electronic excitations calculated by the TD DFT/UB3LYP/CPCM method and experimental absorption bands of 1.
Eexcitation (eV)
kexcitation (nm)
Osc. strength f
Key transition
Character
kexpt. (e )
, MÀ1 cmÀ1
2.1940
2.4597
2.6082
565
504
475
0.05
0.05
0.22
(72%) HOMO–1(b) ? LUMO(b)
ILCT
ILCT
ILCT
563 (8420)
528 (8162)
497 (5438)
(87%) HOMO–2(
a
) ? LUMO(
a
)
(35%) HOMO(b) ? LUMO(b)
(32%) HOMO–2(b) ? LUMO(b)
(37%) HOMO–2(b) ? LUMO(b)
(23%) HOMO(b) ? LUMO(b)
ILCT, MLCT
ILCT, MLCT
ILCT
2.6653
465
0.17
3.8552
4.1717
322
297
0.27
0.09
(81%) HOMO–1(
a
) ? LUMO+2(
a
)
ILCT
ILCT
317 (sh)
(47%) HOMO–3(b) ? LUMO+3(b)
(25%) HOMO–4(b) ? LUMO+3(b)
(72%) HOMO–5(b) ? LUMO+3(b)
4.5465
273
0.31
ILCT
263 (14967)
Table 5
Vertical electronic excitations calculated by the TD DFT/UB3LYP/CPCM method and experimental absorption bands of 2.
Eexcitation (eV)
kexcitation (nm)
Osc. strength f
Key transition
Character
kexpt.
(
e
, MÀ1 cmÀ1
)
2.1589
2.3932
2.4078
574
518
515
0.06
0.08
0.07
(94%) HOMO–1(b) ? LUMO(b)
(77%) HOMO–2(b) ? LUMO(b)
(41%) HOMO(b) ? LUMO+1(b)
(31%) HOMO–8(b) ? LUMO(b)
(65%) HOMO–3(b) ? LUMO(b)
(88%) HOMO–4(b) ? LUMO+1(b)
(42%) HOMO–6(b) ? LUMO+1(b)
(27%) HOMO–8(b) ? LUMO+1(b)
(67%) HOMO–4(b) ? LUMO+1(b)
(78%) HOMO–5(b) ? LUMO+1(b)
(36%) HOMO–7(b) ? LUMO+1(b)
(33%) HOMO–8(b) ? LUMO+1(b)
LMCT, ILCT
LMCT, ILCT
LMCT, ILCT
557 (9443)
521 (9013)
490 (5868)
2.5407
3.01292
3.4027
488
411
364
0.03
0.04
0.25
LMCT, ILCT
ILCT
ILCT
412 (12329)
3.9969
4.1929
4.6769
310
296
265
0.13
0.22
0.37
ILCT
ILCT
ILCT
293 (sh)
263 (26473)

34
M.S. Jana et al. / Polyhedron 76 (2014) 29–35
Appendix A. Supplementary data
CCDC 821874 and 810470 contains the supplementary crystal-
lographic data for 1 and 2. These data can be obtained free of
charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk. Supplementary data associated with this
article can be found, in the online version, at http://dx.doi.org/
10.1016/j.poly.2014.03.052.
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Acknowledgements
Financial support received from the Department of Science and
Technology, New Delhi, India is gratefully acknowledged. M.S. Jana
and A.K. Pramanik are thankful to CSIR, New Delhi, India for
fellowships.

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