Crystal structures, thermal, spectroscopic properties and DFT/TD-DFT based investigation of [M(bba)2(phen)] (M = Cu and Zn, bba = 2-benzoylbenzoato, phen = 1,10-phenanthroline)

Article abstract of DOI:10.1016/j.poly.2011.02.050

The bis(2-benzoylbenzoato)(1,10-phenanthroline)metal(II) (M = Cu, Zn) complexes [Cu(bba)₂(phen)] 1 and [Zn(bba)₂(phen)] 2 have been prepared and characterized by elemental analyses, IR and electronic spectroscopy, and X-ray crystallography techniques. The electronic structure and spectroscopic features of the title complexes have been further investigated by means of DFT and TD-DFT approaches. The calculated spectra of 1 and 2 have been simulated in order to give a more qualitative description of the experimental spectra. The thermal behaviours of the title complexes have been studied by means of simultaneous TG, DTG and DTA methods in a static air atmosphere. Thermogravimetric (TG) analysis has shown that 1 and 2 are thermally stable (T_decomp. > 227 °C).

Full text of DOI:10.1016/j.poly.2011.02.050

Polyhedron 30 (2011) 1389–1395
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Crystal structures, thermal, spectroscopic properties and DFT/TD-DFT based
investigation of [M(bba)2(phen)] (M = Cu and Zn, bba = 2-benzoylbenzoato,
phen = 1,10-phenanthroline)
b
b
c
Sema Caglar a, , Serkan Demir , Zerrin Heren , Orhan Büyükgüngör
⇑
a Department of Chemistry, Faculty of Arts and Sciences, Erzincan University, 24100 Erzincan, Turkey
b Department of Chemistry, Faculty of Arts and Sciences, Ondokuz Mayis University, 55200 Atakum, Samsun, Turkey
c Department of Physics, Faculty of Arts and Sciences, Ondokuz Mayis University, 55200 Atakum, Samsun, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
The bis(2-benzoylbenzoato)(1,10-phenanthroline)metal(II) (M = Cu, Zn) complexes [Cu(bba)2(phen)] 1
and [Zn(bba)2(phen)] 2 have been prepared and characterized by elemental analyses, IR and electronic
spectroscopy, and X-ray crystallography techniques. The electronic structure and spectroscopic features
of the title complexes have been further investigated by means of DFT and TD-DFT approaches. The cal-
culated spectra of 1 and 2 have been simulated in order to give a more qualitative description of the
experimental spectra. The thermal behaviours of the title complexes have been studied by means of
simultaneous TG, DTG and DTA methods in a static air atmosphere. Thermogravimetric (TG) analysis
has shown that 1 and 2 are thermally stable (Tdecomp. > 227 °C).
Received 27 October 2010
Accepted 21 February 2011
Available online 6 March 2011
Keywords:
2-Benzoylbenzoic acid
Copper(II) complex
Zinc(II) complex
Crystal structure
DFT studies
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
its derivatives are used in the synthesis of supramolecular coordi-
nation compounds [9], in the preparation of electron-transport
Carboxylate containing ligands as functional groups are one of
the most widely studied ligand class at the present because they
provide a good facility for the synthesis of compounds with inter-
esting topologies. In particular, many investigated and multifarious
copper(II) compounds are of interest, with versatile coordination
modes available from carboxylato groups: monodentate, chelate,
different types of CO2 bridges and O monoatomic bridges [1]; also
stable complexes of low coordination numbers are available with
flexible and sterically bulk ligands. Carboxylate complexes have re-
cently been employed as components of hybrid porous solids, such
as metal organic framework materials, their design aimed due to
the fact that they have a lot of applications in many fields of indus-
try by utilizing their high surface area, porosity, attractive adsorp-
tion, catalytic and magnetic properties or host–guest chemistry [2–
6]. Zinc and copper carboxylates have been widely and successfully
used in the field of supramolecular chemistry [7]. The relatively
less studied zinc complexes also have another importance, mim-
icking the active sites of enzymes containing zinc, which is critical
in related biological systems, and most of the studies focused on
model complexes of the metal [8]. Bba is a versatile polyfunctional
ligand, due to the presence of the negatively charged carboxylate
and carbonyl oxygen atoms. 2-Benzoylbenzoic acid (Hbba) and
materials [9], and sweeteners [10]. Although the crystal structure
of 2-benzoylbenzoic acid (Hbba = C14H10O3, also named o-benzoyl-
benzoic acid) was investigated in 1990 [11], only a limited number
of papers relating to bba complexes have been published so far and
they can probably be further investigated, with regard to the afore-
mentioned applications of the free ligand and its derivatives [12–
20].
As the first scope of our ongoing research, two new copper(II)
and zinc(II) complexes of the sterically bulky benzoylbenzoato
ligand (bba), together with the co-ligand 1,10-phenanthroline
(phen), have been synthesized. Their structural and spectroscopic
properties have been experimentally studied and theoretically
investigated in the framework of density functional theory (DFT)
and its time-dependent extension (TD-DFT) to probe the title com-
plexes more qualitatively and quantitatively beyond the experi-
mental findings.
2. Experimental
2.1. Materials and measurements
The reagents used in the syntheses were acquired from com-
mercial suppliers and used without further purification. The sol-
vents were distilled and dried by standards procedures. IR
⇑
Corresponding author. Tel.: +90 446 224 30 97; fax: +90 446 224 30 16.
E-mail address: semacaglar2002@hotmail.com (S. Caglar).
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.02.050

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S. Caglar et al. / Polyhedron 30 (2011) 1389–1395
spectra were recorded on a Bruker Vertex 80V FT-IR spectropho-
tometer in the 4000–450 cmꢀ1 range and at a resolution of
4 cmꢀ1. Electronic spectra were measured on a Unicam UV2 spec-
trometer in the 200–900 nm range and in methanol (MeOH) med-
ia. The elemental analyses were performed on an Elementar Micro
Vario CHNS analyzer. Thermal analysis curves (TG, DTA and DTG)
were recorded simultaneously on a Perkin–Elmer Diamond ther-
mal analyzer in a static air atmosphere. A sample of 5–10 mg
was used. The mass spectrum of 1 was recorded on an Agilent
6890 GC in fragmentor 150 eV at negative polarity.
2.4. Computational procedures
All computations herein were executed using the GAUSSIAN 03W
Revision E.01 program package [20] within an unrestricted formal-
ism for 1 and a restricted one for 2. The hybrid DFT-B3LYP func-
tional was used throughout the calculations. The flexible
LANL2DZ basis set was applied for geometry optimizations, vibra-
tional and TD-DFT analyses concerning the computational expense,
since the number of basis functions was 506 on 1 and 502 on 2
even at the B3LYP/LANL2DZ level of theory. Natural bond orbital
(NBO) analyses were performed at the optimized structures using
the 6-31G(d) basis set for C and H atoms, the 6-311+G(d) basis
set for the donor O and N atoms and the 6-311G(d) basis set for
metal atoms. The initial X-ray structures of the complexes were
used for the gas-phase geometry optimization and all the subse-
quent calculations were performed based on the optimized geom-
etries. Vibrational harmonic frequency analysis of the optimized
geometries was utilized to ensure that there were true local min-
ima having no imaginary frequencies. Also the wave function sta-
bilities were tested, and both formalisms adopted for 1 and 2
were found to be stable. TD-DFT excited-state calculations were
performed on ground, spin-doublet and quartet states for 1 and
the spin-singlet state for 2.
2.2. Synthesis of the complexes
The 2-Hbba ligand (0.136 g, 0.6 mmol) and M(CH3COO)2ꢁnH2O
(0.3 mmol) (M = Cu (0.060 g); M = Zn (0.065 g)) were dissolved in
MeOH (40 cm3) with continuous stirring at 100 °C. The protonation
of the acetate ions by Hbba resulted in the formation of bba. The
phen ligand (0.054 g, 0.3 mmol) was dissolved in MeOH (5 cm3)
and added dropwise to the first solution. X-ray quality blue crystals
of 1 and colourless crystals of 2 were obtained by slow evaporation
at room temperature after 2 weeks.
Yield for 1, 60%; dp: 227 °C; Anal. Calc. for C40H26N2O6Cu (1): C,
69.15; H, 3.74; N, 4.03. Found: C, 69.1; H, 3.68; N, 4.0%. Yield for 2:
70% dp: 272 °C; Anal. Calc. for C40H26N2O6Zn (2): C, 69.03; H, 3.74;
N, 4.03. Found: C, 69.01; H, 3.66; N, 3.97%.
The percentage molecular orbital compositions of 1 and 2 were
calculated from full population analysis of the optimized struc-
tures of 1 and 2 using the Virtual Molecular Orbital Designator
(VMODES) Software version 4.1 [21].
The simulation of calculated spectra of 1 and 2 and significant
percentage components of each transition were made by using
the SWIZARD program [22].
2.3. X-ray crystallography
Intensity data for the title compounds were collected using a
STOE IPDS-II area detector diffractometer (Mo K
a radiation,
0
3. Result and discussion
k = 0.71073 ÅA) at 293 K. The structures were solved by direct meth-
ods and were refined by a full-matrix least-squares procedure on F2
[19]. All non-hydrogen atoms were refined anisotropically. All
hydrogen atoms were included using a riding model. The details
of data collection, refinement and crystallographic data are sum-
marized in Table 1.
3.1. Thermal analysis
The thermal analysis plot of 1 is shown in Fig. 5. The thermal
decomposition of 1 starts at 220 °C with an accompanying melting
process. The elimination of the phen ligand and decomposition of
bba ligands by releasing CO2 take place in two steps over the
220–514 °C range, with a mass loss of 88.37% (calcd. 88.54%). The
mass spectrum of 1 indicates that the peak with m/e: 181 is related
to the decomposition fraction of the bba ligand remaining after CO2
Table 1
Crystal data and structure refinement parameters for 1 and 2 complexes.
1
2
Empirical formula
Formula weight
T (K)
C
40H26N2O6Cu
C40H26N2O6Zn
696.02
293
694.18
293
Wavelength (Å)
Crystal system
Space group
0.71073
monoclinic
P1
0.71073
monoclinic
P21/c
ꢀ
Unit cell dimensions
a, b, c (Å)
17.2851(8), 8.7804(3),
22.8090(10)
90, 108.694(3), 90
3279.1(2)
9.4467, 26.4889,
13.8741
90, 109.749, 90
3267.6(6)
4
a
, b,
c
(°)
V (Å)3
Z
4
Absorption coefficient
(mmꢀ1
Dcalc (mg mꢀ3
0.719
0.804
)
)
1.406
1.415
Crystal size (mm)
h Range for data collection
(°)
1.89; 26.50
1.54; 26.22
Measured reflections
Independent reflections
Absorption correctiona
Refinement method
26 262
6786
integration
full-matrix least-
squares on F2
0.0645
28 650
6523
integration
full-matrix least-
squares on F2
0.0519
Final R indices [F2 > 2 (F2)]
r
Goodness-of-fit (GOF) on F2 1.025
1.052
Largest difference in peak
0.27; ꢀ0.23
0.67; ꢀ1.26
Fig. 1. ORTEP III diagram and atom numbering scheme of 1. Displacement
ellipsoids are drawn at the 20% probability level.
and hole (e/Å3)

S. Caglar et al. / Polyhedron 30 (2011) 1389–1395
1391
Table 2
Selected distances and angles of the optimized and X-ray geometries of 1 and 2.
Bond lengths (Å)
Bond angles (°)
Bond
Exp.
Calc.
Angle
Exp.
Calc.
1
Cu1–N1
Cu1–N2
Cu1–O1
Cu1–O2
Cu1–O4
Cu1–O5
2.01(2)
1.99(2)
1.96(2)
2.54(2)
1.92(2)
2.76(2)
2.059
2.056
1.951
2.91
1.98
2.672
O1–Cu1–N1
O1–Cu1–N2
O1–Cu1–O2
O1–Cu1–O4
O2–Cu1–O4
O2–Cu1–N2
O4–Cu1–N1
O4–Cu1–N2
N2–Cu1–N1
O2–Cu1–N1
94.83(8)
172.86(7)
56.85(7)
90.33(7)
96.33(7)
116.67(8)
171.83(7)
93.56(7)
82.01(8)
91.80(8)
94.17
173.69
51.75
93.34
107.81
122.85
171.27
91.65
81.16
80.40
2
Zn1–N1
Zn1–N2
Zn1–O1
Zn1–O4
2.10(2)
2.09(2)
1.99(2)
1.95(2)
2.147
2.147
1.974
1.974
O1–Zn1–N1
O1–Zn1–N2
O1–Zn1–O4
O4–Zn1–N1
O4–Zn1–N2
N2–Zn1–N1
109.94(7)
113.23(7)
120.19(7)
109.15(7)
116.87(8)
79.76(8)
113.03
108.57
125.40
108.50
112.98
78.81
Fig. 4. A crystal packing diagram of 2, showing the CAHꢁ ꢁ ꢁZn interaction.
Fig. 2. A crystal packing diagram of 1, showing the CAHꢁ ꢁ ꢁ
p interaction.
experimental mass loss of 88.37% agrees well with the calculated
mass loss of 88.54% relating to the [Cu(bba)2(phen)] ? CuO + gas-
eous products process and suggests that the grey-black end prod-
uct is copper oxide.
The complex 2 begins to decompose at 272 °C with a melting
process (DTA curve). The first step is related to the elimination of
one phen and one bba ligand in the 252–355 °C range. The exper-
imental mass loss of 57.76% agrees with the calculated mass loss of
58.18%. In the second step, in the 355–525 °C range, the degrada-
tion of the bba ligand occurs with a mass loss of 33.15% (calcd.
32.32%). The second step is extremely exothermic (DTA at
471 °C) and is related to the burning of the organic residue. The
total mass loss of the whole decomposition process is 90.89%
(calcd. 88.30%).
3.2. Mass spectrum of 1
The mass spectrum of any substance exhibits ionization prod-
ucts that indirectly indicate the bond breaking points of the mole-
cule, because the same amount of energy is need both to break
bonds and to induce the related ionization process. Therefore, it
is useful to obtain more accurate information about thermal
decomposition products [23,24]. The analysis of the mass spectrum
of 1 revealed the ionization process of 1. The peak of abundance
2.1% (m/e = 514 g/mol) in the spectrum of 1 is related to the [Cu(b-
ba)2]+ molecular ion (MW = 513 g/mol), as seen in Fig. 6. The peak
of abundance 8.3% (m/e = 469 g/mol) is related to the [Cu(bba)(-
phen)]+ molecular ion (MW = 468 g/mol). The peaks of abundance
Fig. 3. ORTEP III diagram and atom numbering scheme of 2. Displacement
ellipsoids are drawn at the 20% probability level.
evolution. The DTA curve exhibits a small endothermic peak at
230 °C, probably related to removal of the phen ligand. The last
mass loss step of the complex is vigorous and strongly exothermic
(DTA at 372, 493 °C) and is related to the burning of the organic
residue. The decomposition process ends at 515 °C. The total

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S. Caglar et al. / Polyhedron 30 (2011) 1389–1395
Fig. 5. Thermal analyses spectrum of 1.
Fig. 6. Mass spectrum of 1.
31.1%, 76.0% and 98.3% (m/e = 225, 181 and 180 g/mol, respec-
tively) are related to the remaining fragments of the bba and phen
ligands (MW = 225, 181, and 180 respectively) (see Fig. 6).
[27] and [Cu(phen)2][CuCl2] [28] (Nor = norfloxacin, NO3 = nitrate
and ox = oxalato). The CuAObba bond distances in 1 are 1.92(2),
1.96(2) and 2.54(2) Å and these values are similar to those reported
in [Cu(bba)2(BZD)] (BZD = benzimidazole) [18]. The structural dis-
tortion index tau (
a distorted square–pyramidal geometry for 1 (
and b correspond to the two angles showing a tendency to linear-
ity). The -values of square-based-pyramidal and trigonal-bipyra-
midal extremes are 0 and 1, respectively [29]. Additionally, the
chains are cross-linked by CAHꢁ ꢁ ꢁ and ꢁ ꢁ ꢁ stacking interactions
(C4AH4ꢁ ꢁ ꢁCg5 2.83 Å and Cg2ACg7 3.61(2) Å) (see Fig. 2).
s
) was calculated as 0.017 and clearly suggested
3.3. Crystal structure of 1
s
=
a
– b/60, where a
The molecular structure of 1 with the atom labelling scheme is
shown in Fig. 1. Selected bond lengths and angles are listed in
Table 2. The structure consists of individual molecules of 1, in
which the copper(II) ion is coordinated by one phen and two bba
ligands, exhibiting a distorted square–pyramidal configuration of
the CuN2O3 type. The bba ligands behave as both monodentate
and bidentate ligands.
s
3.4. Crystal structure of 2
The CuANphen bond distances are 2.01(2) and 1.99(2) Å, respec-
tively and these values are similar to those reported for [Cu(Nor)(-
phen)(H2O)]NO3ꢁ3H2O [25], [Cu(HNor)(phen)(NO3)]NO3ꢁ3H2O [25]
The molecular structure of [Zn(bba)2(phen)] consists of neutral
molecules, as shown in Fig 3. Selected bond lengths and angles are
collected in Table 2. In 2, the Zn atom exhibits a slightly distorted
tetrahedral coordination geometry with a neutral bidentate phen
and [(phen)2Cu(
l
-L)Cu(phen)2]Lꢁ12.5H2O [26], whereas they are
significantly shorter than those reported for [Cu(ox)(phen)2]ꢁ5H2O

S. Caglar et al. / Polyhedron 30 (2011) 1389–1395
1393
Table 4
Percentage molecular orbital contributions of 1 from selected atoms and groups.
MO
H
Hꢀ1
Hꢀ2
Hꢀ3
L
L+1
L+2
E (eV)
Cu
ꢀ6.128 ꢀ6.268 ꢀ6.375 ꢀ6.63 ꢀ2.570 ꢀ2.419 ꢀ1.806
1.9
0.7
8.1
57.7
6.6
10.2
30.1
19.0
12.5
5.4
0.1
17.2
10.3
5.7
0.4
0.2
0.1
0.0
0.0
0.0
0.0
0.0
0.0
5.3
3.1
0.0
0.1
0.8
0.2
0.4
0.0
0.0
0.1
0.0
OCOꢀ1
OCOꢀ2
O1
63.2
16.8
43.5
0.4
0.1
0.1
0.3
0.0
0.1
0.0
0.1
11.5
14.5
4.0
2.0
24.4
32.2
2.8
O2
O4
O5
N1
4.4
11.0
5.8
0.0
0.2
7.4
20.6
3.3
N2
0.5
1.2
4.1
Table 5
Percentage molecular orbital contributions of 2 from selected atoms and groups.
MO
H
Hꢀ1
Hꢀ2
Hꢀ3
L
L+1
L+2
E (eV)
Zn
ꢀ6.455 ꢀ6.462 ꢀ6.572 ꢀ6.581 ꢀ2.856 ꢀ2.737 ꢀ1.639
0.0
8.1
7.2
1.7
5.1
2.0
5.7
0.0
0.0
0.1
5.8
6.6
1.7
4.4
1.6
3.8
0.0
0.0
0.1
25.4
21.8
6.0
0.2
22.7
26.4
7.0
0.1
0.3
0.0
0.1
0.1
0.0
0.0
0.0
0.0
4.2
4.3
0.0
1.9
2.0
0.7
0.4
0.7
0.4
0.1
0.1
Fig. 7. Superimpositions of the whole (top) and the coordination vicinity (bottom)
of the optimized (blue) and X-ray (orange) geometries of 1 and 2. (For interpre-
tation of the references to colour in this figure legend, the reader is referred to the
web version of this article.)
OCOꢀ1
OCOꢀ2
O1
0.3
0.1
0.0
0.1
0.0
13.2
13.2
O2
O4
O5
N1
15.3
6.9
17.8
0.0
19.0
6.0
16.3
0.0
N2
0.0
0.0
H, HOMO; Hꢀ1, HOMOꢀ1, etc. L, LUMO; L+1, LUMO+1, etc.
ligand and two anionic bba ligands, thus forming a ZnN2O2
chromophore.
In 2, the ZnANphen bond distances are 2.09(2) and 2.10(2) Å, and
these are significantly shorter than those found in [Zn(sac)(-
phen)2(H2O)]sac [30], [Zn(4-mpzdtc)2(phen)]ꢁH2O [31], [Zn(tda)(-
phen)]2ꢁ5H2O
[32],
[Zn(1,10-phen)LCl]
[33],
[Zn(phen)2(H2O)2]sac2ꢁH2O [34], [Zn(phen)(SO4)(H2O)2]n [35] and
[Zn(dbzdtc)2(1,10-phen)] [36]; but are nearly equal to those found
in [Zn(PDA)(phen)(H2O)] [37]. The ZnAObba bond distances are
1.95(2) and 1.99(2) Å in 2, and these are shorter than those found
in [Zn(bba)2(2,20-bipy)] (sac = saccharin, 4-mpzdtc = 4-methylpi-
perazinecarbodithioato, PDA = 1,4-phenylenediacetate and 2,20-
bipy = 2,20-bipyridine) [8]. The molecules are linked into chains
running along the a axis by CAHꢁ ꢁ ꢁZn (3.38 Å) interactions be-
tween the phenyl ring of the phen ligand and the zinc(II) ion (see
Fig. 4). This value is comparatively shorter than the van der Waals
interactions (3.45 Å).
3.5. Geometry optimization and NBO analysis
Fig. 8. Frontier molecular orbitals of 1 and 2.
The geometries of 1 and 2 were respectively optimized in the
doublet and singlet ground states and none of the imaginary fre-
quencies were detected by frequency analyses of the optimized
structures of 1 and 2. The calculated geometrical parameters of 1
and 2 are comparatively given with the experimental ones in Ta-
ble 2. The optimized structure of 2 is more consistent with the
X-ray structure than that of 1, as is also seen from the superimpo-
sitions of the optimized and X-ray structures of 1 and 2 in Fig. 7.
The calculated rms error for 1 is 1.60 Å, while it is 0.540 Å for 2.
However, except for the largest difference of 0.38 Å between the
optimized and experimental Cu1AO2 distances, the displacements
between the optimized and X-ray coordination vicinities of both 1
and 2 are smaller compared to those between the completely opti-
mized and X-ray structures, as seen from Fig. 7. The calculated rms
errors for the vicinities of the copper and zinc ions in 1 and 2 are
0.238 and 0.235 Å, respectively. The frontier molecular orbitals
Table 3
Selected experimental and calculated IR spectral dataa,b for Hbba ligand, 1 and 2
complexes.
Assignment
Hbba
Exp.
1
2
Calc. Exp.
Calc. Int.
Exp.
Calc. Int.
m
m
m
m
m
m
(OH)
aro(CH)
(C@O)
3445m
3060w
1673vs
3065w 3222 29
1667vs 1598 260 1664vs 1607 156
1563m 1554 268 1590s 1551 305
3065w 3198 22
asym(COOꢀ)
sym(COOꢀ)
(C@C)
1381vs
1607m 1633 36
1373vs
1610m 1632 59
w, Weak; m, medium; s, strong and vs, very strong.
Frequencies in cmꢀ1
.
a
b
Calculated intensities in km/mol.

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S. Caglar et al. / Polyhedron 30 (2011) 1389–1395
Table 6
Calculated and experimental spectral data of 1.
kmax (exp.)
kmax (calc.)
f (calc.)
Major contribution (calc.)
Major character
eV (calc.)
677
688
540
451
343
325
300
0.0064
0.0065
0.0043
0.0231
0.0100
0.0530
Hꢀ19(b) ? H(b)
Hꢀ20(b) ? H(b)
Hꢀ3(b) ? H(b)
Hꢀ3(b) ? L+1(b)
p
p
p
p
p
p
(phen) ? d/p⁄(bba)
(phen) ? d/p⁄(bba)
(bba) ? d/p⁄(bba)
(bba) ? p⁄(phen)
(bba) ? p⁄(bba)
1.80
2.30
2.75
3.62
3.81
4.13
346
308
Hꢀ1(
a) ? L+3(a)
Hꢀ18(b) ? H(b)
(phen)p
(bba) ? d/p⁄(bba)
in 2. In 1, bba acts as both monodentate and bidentate, whereas
in 2 bba acts as a monodentate ligand. In 2, the (OCO) value is
coherent for a monodentate carboxylate ligand (>200 cmꢀ1) [38].
The bands around 1581 cmꢀ1 correspond to the
(C@C) vibration
of the bba and phen ligands; the bands occurring at around
1250–1320 cmꢀ1 are due to
(CAO) vibrations. The bands around
934 and 710 cmꢀ1 correspond to the
(CAH) vibration in-plane
D
m
m
m
and out-of-plane bending for the ligands. The under or overestima-
tion of the observed frequencies by the calculations is due to the
negligence of anharmonicity corrections arising from inter or intra-
molecular effects. The calculated values were given without scal-
ing. The corresponding calculated intensities were utilized on the
qualitative assignments of the observed frequencies. Merely a con-
tradiction to the observed spectra is that there is no symmetric
OCOꢀ stretching mode found for the optimized structures of both
1 and 2, owing simply to asymmetric monodentate coordination
modes to the central ions.
Fig. 9. Overlapped version of the calculated (violet) and observed (red) spectra of 1.
(For interpretation of the references to colour in this figure legend, the reader is
referred to the web version of this article.)
3.7. Electronic spectra and TD-DFT calculations
The electronic spectra of both complexes are recorded in meth-
anolic solutions. The first 90 and the first 80 vertical excitations of
the geometry-optimized structures were calculated by the TD-DFT
approach for 1 and 2, respectively. Some high energy intra-ligand
transitions in the 200–300 nm region were not calculated due to
the large size of the systems. The calculated spectra were simu-
lated using a half-band width of 1500 cmꢀ1 and each transition
was represented by a lorentzian function implemented in the SWIZ-
(FMOs) of 1 and 2 are presented in Fig. 8 and the calculated molec-
ular orbital contributions (MOCs) from groups and atoms are listed
in Tables 4 and 5. All the MOs are mainly localized on the whole
structures of 1 and 2. The calculated HOMO–LUMO gaps are
3.558 and 3.599 eV for 1 and 2, respectively. The very low MOCs
from the central ions to the FMOs for both 1 and 2 suggest that
the essential interaction between the central ions and donor atoms
is coulomb-type from a theoretical insight.
Also NBO analysis was performed at the optimized structures to
examine the covalent character of the interactions between the do-
nor atoms and central ions. Therefore, the larger triple zeta 6-
311+G(d) basis set, expanded with one standard diffuse function,
was applied for the donor O and N atoms in order to obtain a better
description of the relatively long donor–acceptor interactions. Con-
sequently, no natural bond orbital was detected between the donor
atoms and central ions of both 1 and 2 and the case suggesting cou-
lomb-type interactions from full population analysis is also vali-
dated by the NBO analysis.
ARD program.
A distinct absorption maximum at 680 nm
(e
= 75 dm3 molꢀ1 cmꢀ1) in the observed spectrum of 1 was as-
signed to orbitally-forbidden d–d transitions. The counterpart of
the corresponding transition at 689 nm (f = 0.0064) in the calcu-
lated spectrum of 1 is qualitatively assigned as a b-spin
p ? d/p
transition by the TD-DFT results, since there are no oscillator
strengths that are larger than zero detected in the 600–700 nm re-
gion in the calculated spectrum of 1. Excitation energies, oscillator
strengths and major percentage components of each transition in 1
are given in Table 6. Both the calculated and the observed spectra
of 2 expectedly show no transition above 400 nm. The overlapped
version of the calculated and the observed spectra of 1 is given in
Fig. 9.
3.6. Infrared spectra
Some important calculated and experimental stretching vibra-
tional frequencies of the Hbba ligand and complexes 1 and 2 are
listed in Table 3. The medium band at about 3445 cmꢀ1 is attrib-
4. Conclusions
The newly synthesized Cu(II) and Zn(II) complexes have been
characterized by elemental analyses, UV–Vis, FT-IR, thermal analy-
ses and X-ray diffraction techniques. The most efficient density
functional hybrid method B3LYP calculations have been performed
to investigate the structural and electronic properties of the title
complexes. The X-ray crystal structure analysis shows that com-
pounds 1 and 2 consist of neutral monomeric units. The copper(II)
ion exhibits a distorted square–pyramidal geometry, while the zin-
c(II) ion exhibits a distorted tetrahedral geometry. The chains are
uted to the
(OH) vibration disappears from the functional region. This indi-
cates the deprotonated form of the carboxylic acid. The relatively
weak bands at 3065 cmꢀ1 are due to the aromatic
(CH) vibrations.
m(OH) vibration of the Hbba ligands. In 1 and 2, the
m
m
The absorption bands of the carbonyl group of bba in the com-
plexes are observed at 1667 cmꢀ1 in 1 and 1664 cmꢀ1 in 2. The
characteristic bands of the carboxylate anions have typical
m
(OCO)asym {1563 cmꢀ1 in 1, 1590 cmꢀ1 in 2} and
m
(OCO)sym
{1381 cmꢀ1 in 1, 1373 cmꢀ1 in 2} values. The calculated
(OCO)
values { (OCO)asym
(OCO)sym} are 182 cmꢀ1 in 1 and 217 cmꢀ1
D
cross-linked by CAHꢁ ꢁ ꢁ
p
and
pꢁ ꢁ ꢁ
p stacking interactions in 1 and
m
– m
the molecules are linked into chains running along the a axis by

S. Caglar et al. / Polyhedron 30 (2011) 1389–1395
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all the data obtained by calculations have revealed a more detailed
structural and electronic picture of investigated complexes in addi-
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Appendix A. Supplementary data
CCDC 790593 and 790592 contain the supplementary crystallo-
graphic 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, Cam-
bridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
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