Synthesis, characterization, and theoretical calculations of mononuclear copper(II) benzoate complex with 2-propylimidazole, [Cu(PIM)2(PhCOO)2]

Article abstract of DOI:10.1016/j.molstruc.2009.12.038

A mononuclear copper(II) complex, [Cu(PIM)₂(PhCOO)₂] (1) [where PIM = 2-propylimidazole] has been synthesized and characterized by elemental analysis, IR, UV-Vis, TGA, and single crystal X-ray diffraction. The structural analysis indicated that Cu(II) atom in the complex is six-coordinated in a distorted octahedral geometry by two N atoms from two 2-propylimidazole and four O atoms from two benzoate ligands. In addition, based on crystal structural data, quantum chemistry calculation in DFT/B3LYP level has been used to reoptimize and explore the electronic structure of the compound 1; time-dependent DFT (TD-DFT) calculations have also been performed in order to elucidate its spectroscopic properties. All parameters from the calculations are in well accordance with our experimental result.

Full text of DOI:10.1016/j.molstruc.2009.12.038

Journal of Molecular Structure 967 (2010) 54–60
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, characterization, and theoretical calculations of mononuclear
copper(II) benzoate complex with 2-propylimidazole, [Cu(PIM)2(PhCOO)2]
b
a
Xian Peng a, Guang-hua Cui a, , De-jie Li , Tong-fei Liu
*
a College of Chemical Engineering and Biological Technology, Hebei Polytechnic University, 46 West Xinhua Road, Tangshan 063009, Hebei, PR China
b School of Chemistry and Chemical Engineering, University of Jinan, 106 Jiwei Road, Jinan 250022, Shandong, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 9 October 2009
Received in revised form 13 December 2009
Accepted 19 December 2009
Available online 28 December 2009
A mononuclear copper(II) complex, [Cu(PIM)2(PhCOO)2] (1) [where PIM = 2-propylimidazole] has been
synthesized and characterized by elemental analysis, IR, UV–Vis, TGA, and single crystal X-ray diffraction.
The structural analysis indicated that Cu(II) atom in the complex is six-coordinated in a distorted octa-
hedral geometry by two N atoms from two 2-propylimidazole and four O atoms from two benzoate
ligands. In addition, based on crystal structural data, quantum chemistry calculation in DFT/B3LYP level
has been used to reoptimize and explore the electronic structure of the compound 1; time-dependent
DFT (TD-DFT) calculations have also been performed in order to elucidate its spectroscopic properties.
All parameters from the calculations are in well accordance with our experimental result.
Ó 2009 Elsevier B.V. All rights reserved.
Keywords:
Copper complex
Crystal structure
Benzoic acid
Density functional calculations
2-Propylimidazole
1. Introduction
estimated by using the density functional theory (DFT) method,
and time-dependent DFT (TD-DFT) calculations have also been
The design, synthesis, and crystal engineering of coordination
complexes continue to be a quite active research field because of
their enchanting structures and potential applications as func-
tional materials [1–7]. Especially, the coordination chemistry of
imidazole and its derivatives has captured the considerable atten-
tion of chemists for several decades [8,9]. The investigations in bio-
logical importance, supramolecular chemistry, electronic spectra,
gas adsorption separation, and the artificial nuclease activity under
appropriate conditions have been well represented [10–16]. On the
other hand, copper is an essential trace element required by all liv-
ing organisms, and plays a key role as an integral component of
many enzymes [17,18]. Thus, the biological functional Cu(II) com-
plexes with imidazole-based ligands have been widely studied and
reported. With the further research of the series, various substi-
tuted imidazoles have been also used as the co-ligand so that the
structural and electronic effects on the biologically important
Cu–N (imidazole) bond could be well-elucidated [19,20].
used for analysis of the electronic spectrum and spectroscopic
properties. At present, DFT is commonly being used to assess the
electronic structure of transition metal complexes [21–25]. It
meets with the requirements of being accurate, easy to use, and
being fast enough to allow the study of relatively large molecules
of transition metal complexes.
2. Experimental
2.1. Materials and general methods
All the reagents and solvents were purchased from commercial
sources and used without further purification. Elemental analyses
were performed on Perkin–Elmer 240C automatic analyzer. The
Infrared (IR) spectrum was recorded from KBr pellets in the range
of 4000–400 cmÀ1 on a Nicolet FT-IR 170SX spectrometer. The UV–
Vis spectra were recorded on Shimadzu UV-3600 spectrophotome-
ter equipped with a PTC-348WI temperature controller in the range
of 190–1100 nm. Thermal stability (TG-DTA) studies were carried
out on a NETZSCH TG 209 thermal analyzer from room temperature
However, the complexes of 2-propylimidazole (PIM), a 2-substi-
tuted derivative of the imidazole, have rarely been reported. In
order to obtain more insight into the metal complexes of 2-propy-
limidazole ligand, we herein report the successful preparation and
structural characterization of the [Cu(PIM)2(PhCOO)2] (1) complex.
Furthermore, the electronic structure of the compound has been
to 700 °C under N2 atmosphere with a heating rate of 10 °C minÀ1
.
2.2. Synthesis of complex
[Cu(PIM)2(PhCOO)2] (1). Basic copper(II) carbonate (221 mg,
1 mmol) was treated with an aqueous solution (10 mL) of benzoic
* Corresponding author. Tel.: +86 0315 2592170; fax: +86 0315 2592169.
E-mail address: tscghua@126.com (G.-h. Cui).
0022-2860/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2009.12.038

X. Peng et al. / Journal of Molecular Structure 967 (2010) 54–60
55
Table 1
acid (488 mg, 4 mmol) in a steam bath until the solid disappeared.
Crystal data and structure refinement for [Cu(PIM)2(PhCOO)2].
The solution was then filtered and diluted to approximately 40 mL
with water. An ethanol solution (10 mL) of 2-propylimidazole
(441 mg, 4 mmol) is then added to above solution. The resultant
clear-blue solution is warmed on a steam bath for 1 h. The volume
is kept constant by periodic addition of water. Then the solution is
filtered and allowed to stand at room temperature. Blue single
crystals of 1 were harvested after 5 days. They are filtered, washed
with water and ethanol and then air-dried. Yield: 58% (based on
basic copper(II) carbonate). Anal. Found (%): C 59.50, H 5.81, N
10.72. Calc.(%) for C26H30N4O4Cu (Fw = 526.09): C 59.31, H 5.70,
N 10.65. FT-IR (cmÀ1): 3100 (m), 2976 (s), 1600 (s), 1535 (vs),
1473 (m), 1391 (vs), 1152 (w), 1051 (w), 1023 (w), 847 (m), 729
(s). UV–vis peaks (kmax, nm): 731.3, 265.7.
Empirical formula
Formula weight (g molÀ1
Crystal colour/habit
Temperature (K)
C26H30N4O4Cu
526.09
Blue block
293(2)
)
Wavelength (Å)
Crystal system, space group
0.71073
Triclinic, P1
ꢀ
Unit cell dimensions
a (Å)
b (Å)
c (Å)
7.8338(16)
8.3275(17)
11.503(2)
a
(°)
b (°)
(°)
84.88(3)
70.14(3)
63.00(3)
627.0(2)
c
Volume (Å3)
Z
1
Dcalc (Mg mÀ3
)
1.393
0.910
275
2.3. X-ray crystallographic
Absorption coefficient (mmÀ1
F(000)
)
Crystal size (mm)
h range for data collection (°)
Index ranges
0.24 Â 0.23 Â 0.16
1.89–28.08
À10 6 h 6 10, À10 6 k 6 10,
À13 6 l 6 15
9179/2949 [0.0206]
Suitable single crystal of the title complex was mounted on
glass fibers for X-ray measurement. Reflection data were collected
at 20 °C on a Bruker Smart 1000 CCD diffractometer with graphite-
Reflections collected/Independent
[Rint
monochromated Mo–Ka radiation (k = 0.71073 Å) and a x–2h scan
]
mode. Unit cell constants and orientation matrix were improved by
least-squares refinement of reflections thresholded from the entire
dataset. Integration was performed with SAINT [26], using this im-
proved unit cell as a starting point. Precise unit cell constants were
calculated in SAINT from the final merged dataset. All the mea-
sured independent reflections were used in the structure analyses,
and semi-empirical absorption corrections were applied using the
SADABS program [27]. Crystal structure was solved by the direct
method and subsequently completed by the difference Fourier
recycling. All the non-hydrogen atoms were refined anisotropically
using full-matrix, least-squares technique. All the hydrogen atoms
were positioned geometrically and refined using a riding model for
the title complex. All the calculations were performed using the
program SHELXTL program [28]. Atomic scattering factors were
those incorporated in the computer programs. The crystallographic
data and experimental details of the data collection and the struc-
ture refinement were given in Table 1.
Completeness to h = 28.08°
Data/restraints/parameters
Goodness-of-fit on F2
96.6%
2949/0/160
0.999
R1 = 0.0271, wR2 = 0.0750
R1 = 0.0287, wR2 = 0.0761
0.222 and À0.306
Final R indices [I > 2
r
(I)]a
R indices (all data)
Largest difference in peak and hole
(e ÅÀ3
)
a
2
R1
=
R
||Fo| À |Fc||/
R
|Fo| and wR2={
R
[w(Fo À Fc2)2]/[w(Fo2)2]}1/2, [Fo > 4
r
(Fo)].
a 1:4:4 M ratio in water/alcohol mixed solvent. The result of ele-
mental analyses for the complex is in good agreement with the
theoretical requirements of their compositions (X-ray analysis).
This compound is stable in air. In the IR spectrum, the characteris-
tic bands of the C=C and C=N stretching modes of 2-propylimidaz-
ole was observed at ꢀ1600 and ꢀ1473 cmÀ1. Bands at 2976 and
729 cmÀ1 can be assigned to the N–H stretching and bending fre-
quencies of the PIM ligand, respectively. Asymmetric and symmet-
ric C=O stretching modes of the coordinated benzoate moieties
were evidenced by very strong, slightly broadened bands at
ꢀ1535 and ꢀ1381 cmÀ1. In comparison with benzoic acid, it can
be found that the stretching characteristic bands of all carboxylate
groups in the title complex are of redshift being due to the coordi-
nation of O atom to copper(II) atom, which is consistent with the
results of the X-ray analysis.
2.4. Computational details
The gas phase geometry of the [Cu(PIM)2(PhCOO)2] was opti-
mized without any symmetry restriction in the doublet state with
the DFT method using the hybrid B3LYP functional of GAUSSIAN-
*
03. The calculation was performed by using the standard 6-31G
basis set for C, H, N, and O atoms, and effective core potentials basis
set LanL2DZ for Cu atom in the title complex [29]. The optimized
geometry of the complex was verified by performing a frequency
calculation. All the vibrations in the calculated vibrational spec-
trum of the complex were real, thus the optimized geometry corre-
sponds to true energy minimum. The optimized geometry along
the coordinates was further verified by frozen distance optimiza-
tions, which also served to obtain information about the charge/
spin distributions and molecular orbital information. Net atomic
charges had been obtained using the Natural bond orbital (NBO)
analysis of Weinhold and Carpenter [30]. All calculations were
carried on a Pentium IV computer with the GAUSSIAN-03 suite of
software packages [31].
3. Results and discussion
3.1. Synthesis and spectral characterization of 1
The title complex 1 was synthesized by the reaction of basic
copper(II) carbonate with benzoic acid and 2-propylimidazole in
Fig. 1. A view of the molecular structure of the [Cu(PIM)2(PhCOO)2].

56
X. Peng et al. / Journal of Molecular Structure 967 (2010) 54–60
Table 2
Table 3
The selected experimental and optimized bond lengths (Å) and angles (°) for
Intermolecular H-bonding contacts detected in the [Cu(PIM)2(PhCOO)2] complex.
[Cu(PIM)2(PhCOO)2].
D–H. . .A
d(D–H) (Å)
0.860
d(H. . .A) (Å)
d(D. . .A) (Å)
\DHA (°)
Parameters
Experimental values
Optimized values
N(2)–H(2 N). . .O(2)i
2.072
2.861
152.22
Cu(1)–O(1)
Cu(1)–O(1A)
Cu(1)–N(1)
Cu(1)–N(1A)
Cu(1)–O(2)
Cu(1)–O(2A)
1.9753(12)
1.9753(12)
1.9882(14)
1.9882(14)
2.6404(13)
2.6404(13)
180.0
90.73(6)
89.27(6)
90.73(6)
89.27(6)
180.0
124.89(4)
55.11(4)
88.87(5)
91.13(5)
55.11(4)
124.89(4)
91.13(5)
88.87(5)
180.0
1.9746
1.9746
2.0066
2.0066
2.5396
2.5396
179.99
90.17
89.83
90.17
89.83
180.0
122.32
57.68
93.36
86.64
57.68
122.32
86.64
93.36
i
The O(2) atom from adjacent benzoate ligand of another same unit connected by
intermolecular H-bonding, i = 1 + x, y, z.
O(1A)–Cu(1)–O(1)
O(1A)–Cu(1)–N(1A)
O(1)–Cu(1)–N(1A)
O(1)–Cu(1)–N(1)
O(1A)–Cu(1)–N(1)
N(1A)–Cu(1)–N(1)
O(1A)–Cu(1)–O(2)
O(1)–Cu(1)–O(2)
N(1A)–Cu(1)–O(2)
N(1)–Cu(1)–O(2)
O(1A)–Cu(1)–O(2A)
O(1)–Cu(1)–O(2A)
N(1A)–Cu(1)–O(2A)
N(1)–Cu(1)–O(2A)
O(2)–Cu(1)–O(2A)
179.99
Symmetry code: A À x, Ày + 1, Àz + 1.
3.2. Description of the crystal structure of complex 1
[Cu(PIM)2(PhCOO)2] (1). The mononuclear complex 1 crystal-
ꢀ
lizes in the triclinic space group P1 and has an inversion centric
Fig. 3. Electrostatic potential map of the [Cu(PIM)2(PhCOO)2]. Yellow denotes the
positive regions. Blue indicates the negative regions. (For interpretation of the
references to colour in this figure legend, the reader is referred to the web version of
this article.)
symmetry with the Cu(II) atom being in the center of inversion.
The asymmetric unit of the complex consists of half of a central
Cu(II) ion, one benzoate, and one PIM ligand. Fig. 1 gives a perspec-
tive view of the molecular structure with atoms labeling. The se-
lected bond lengths and angles are listed in Table 2. In the
structure of 1, the Cu(II) atom occupies the center of a Jahn–Teller
distorted octahedral geometry and is six-coordinated by two N
atoms of two PIM [1.9882(14) Å for Cu(1)–N(1)] and four carboxyl-
ate O atoms from two benzoate groups [1.9753(12) Å for Cu(1)–
O(1), 2.6404(13) Å for Cu(1)–O(2) ]. The two-N-donors from two
PIM and two-O-donors from two benzoates form the basal plane;
the remaining two benzoate-O-donors constitute the axial direc-
tions. The axial Cu–O [Cu(1)–O(2)] distances are longer than those
on the equatorial positions being comparable to the values re-
ported in the literature [16b], indicating that the O(2)-donor is
more loosely bound with the metal center.
Fig. 2. 1D double-bridged chain structure of the title complex constructed by intermolecular H-bonds: (a) viewed along the b-axis and (b) viewed along the c-axis.

X. Peng et al. / Journal of Molecular Structure 967 (2010) 54–60
57
Table 4
additional weak interactions. Comprehensive analysis C–HÁ Á Á
p
interaction carried out with the program PLATON [32] shows that
the HÁ Á Áring centroid (HÁ Á ÁCg) distance is 2.84 Å, CÁ Á ÁCg distance is
3.6195(19) Å, HÁ Á Áring plane perpendicular distance is 2.785 Å, and
the C–HÁ Á ÁCg angle is 138°, being below the optimal value (180°)
Natural atomic charges and natural electron configuration of part atoms in the
[Cu(PIM)2(PhCOO)2] complex.
Atoms
Net Charge
Electron Configuration
Cu(1)
O(1)
O(1A)
O(2)
O(2A)
N(1)
N(1A)
1.32497
[core]4s(0.33)3d(9.30)4p(0.01)4d(0.02)5p(0.01)
[core]2s(1.72)2p(5.04)3p(0.01)3d(0.01)
[core]2s(1.72)2p(5.04)3p(0.01)3d(0.01)
[core]2s(1.72)2p(5.00)3p(0.01)3d(0.01)
[core]2s(1.72)2p(5.00)3p(0.01)3d(0.01)
[core]2s(1.36)2p(4.19)3p(0.02)
À0.77747
À0.77738
À0.74343
À0.74332
À0.57808
À0.57813
for the strongest C–HÁ Á Á
p interaction, which may be due to the ste-
ric constraint in the molecular packing. The
c angle is found to be
11.47°.
The bond valence theory is an effective and important method
for understand the intensity of coordinate bonds. In order to ex-
plore the coordination bonds of the complex, the bond valences
were calculated by the formula of Sij = exp[(Rij À rij)/B], where Rij
is the bond-valence parameter (in the formal sense Rij is the single
bond length between i and j atoms), rij is bond length between i
and j atoms and B was taken as 0.37 [33].
[core]2s(1.36)2p(4.19)3p(0.02)
12000
The RCu–O and RCu–N were taken as 1.679 [34] and 1.713 [35],
respectively. The computed bond valences of the copper(II) center
are SCu(1)–O(1) = 0.449, SCu(1)–O(2) = 0.075 and SCu(1)–N(1) = 0.475, thus
the computed valence of the Cu atom is 1.998 valence units. The
deviation of valence sum range larger than 0.5–0.1 valence units
can indicate omission or misinterpretation of coordination sphere.
It can be considered that in the complex the copper atom is six-
coordinated even weak interactions are included. In addition, it is
noteworthy that Cu(1)–O(2) bond-valence is smaller than Cu(1)–
O(1) and Cu(1)–N(1), indicating that Cu(1)–O(2) bond is a reason-
ably weak coordination.
300
200
100
0
10000
8000
6000
4000
2000
600
700
800
0
200
3.3. Geometry optimization and population analysis
400
600
800
1000
Wavelength ( , nm)
The geometry of [Cu(PIM)2(PhCOO)2] was optimized in doublet
state using the DFT method with the B3LYP functional. The opti-
mized geometric parameters are collected in Table 2. In general,
the predicted bond lengths are somewhat longer than the values
from the X-ray crystal structure data, and the general trends ob-
served in the experimental data are well reproduced in the calcu-
lations. The differences both the calculated and experimental value
are 0.1 Å smaller for all the selected bond lengths and 5° for all the
selected bond angles. Some discrepancies between the theoretical
and experimental structural parameters could be attributed to the
intermolecular hydrogen bonding in the crystal, because the theo-
retical study has been done on an isolated molecule.
Fig. 4. The experimental (black) and calculated (red) electronic absorption spectra
of [Cu(PIM)2(PhCOO)2]. (For interpretation of the references to colour in this figure
legend, the reader is referred to the web version of this article.)
Analysis of the crystal packing of 1 shows that a 1D chain is
formed by the linkage of hydrogen bonds between O atoms of ben-
zoate ligand and the H atoms of the imidazole ring [N(1)–
H(2B)Á Á ÁO(2)i (i = 1 + x, y, z)] (Fig. 2). The related hydrogen-bonding
bond distance and angle are as follows: H(2B)Á Á ÁO(2) = 2.861(2) Å
and N–HÁ Á ÁO = 152°, being in the normal range of such interactions
(Table 3). Another noteworthy structural feature of 1 is that one
ortho-H atoms (H4B) from the side chain of imidazole point to-
wards the centre of an imidazole ring (Cg: N1–C1–N2–C2–C3, sym-
metry related by the transformation of 1 – x, 1 – y, 1 – z) to form
The calculated net charge on the Cu atom in [Cu(PIM)2(Ph-
COO)2] is equal to 1.32497 deviating significantly from the formal
charge +2, being a result of charge donation from the donor atoms
of ligands. Namely, the net charge of coordinated N and O atoms
Table 5
The assignments of the calculated transitions to experimental absorption bands and electronic transition properties of the title complex.
The most important orbital excitations
Transition character
Calculated (nm)
E (eV)
Oscillator strength
Experimental (nm)
HOMO-6(b)?LUMO(b)
HOMO-8(b)?LUMO(b)
HOMO-11(b)?LUMO(b)
HOMO-3(b)?LUMO(b)
HOMO-1(b)?LUMO(b)
HOMO-2(b)?LUMO+1(b)
HOMO-14(b)?LUMO(b)
HOMO-2(b)?LUMO+1(b)
HOMO-3(b)?LUMO(b)
HOMO-1(b)?LUMO(b)
832.9
740.3
614.5
541.2
493.1
1.49
1.67
1.85
2.23
2.43
0.0002
0.0013
0.0007
0.0003
0.0005
–
p
p
p
p
p
p
p
p
p
p
p
(benzoate)/dyz
/
p
(PIM)?dx2
Ày2
Ày2
731.3
(benzoate)/dxy
/
p(PIM)?dx2
–
–
–
(benzoate)/dz2?dx2Ày2
(benzoate)/ (PIM)?dx2
(benzoate)/dyz
(benzoate)/ (PIM)?dx2
(PIM)/dyz?dx2 Ày2
p
Ày2
/p(PIM)?dx2
Ày2
p
Ày2
444.2
339.0
2.87
3.41
0.0035
0.0116
–
–
(benzoate)/
p
(PIM)?dx2
Ày2
Ày2
(PIM)?dx2
(benzoate)/
p
(PIM)?dx2
(benzoate)/dyz
/p
Ày2
*
HOMO-4(
HOMO-9(b)?LUMO(b)
HOMO-5( )?LUMO(
HOMO-3(b)?LUMO(b)
HOMO-2(b)?LUMO+1(b)
HOMO( )?LUMO+4(
HOMO-5(b)?LUMO+2(b)
a
)?LUMO+1(
a
)
(benzoate)?
)/
(benzoate)?
p
(benzoate)
314.6
281.9
3.94
4.39
0.0007
0.0036
–
–
(P,
r p(benzoate)?dx2
Ày2
a
a
)
p
p
p
p
p
p
*(benzoate)
271.3
259.4
4.56
4.78
0.0264
0.0002
265.7
(benzoate)/
p
p
(PIM)?dx2
Ày2
Ày2
(benzoate)/
(PIM)?dx2
a
a)
(PIM)?
p
*(PIM)
(PIM)/dxy?p
*(PIM)

58
X. Peng et al. / Journal of Molecular Structure 967 (2010) 54–60
range from À0.77747 to À0.57808, showing that part electrons
transfer from N and O atoms to Cu atom and the coordinate bonds
come into being. The obtained positive charges of every benzoate
ligand and every PIM ligand from Cu(II) ion are 0.21055 and
0.12684, respectively, indicating that the interaction of copper
ion and benzoate ligand is stronger than that of PIM ligand. More-
over, the electrostatic potential also demonstrates that such strong
coordination behavior of the benzoate ligands with Cu atom and
the benzoate ligands are yet quite well activity after coordinated
(Fig. 3).
conclude that the Cu atom coordination with N and O atoms is on
3d (3dx2 and 3 dz2 are revealed by NBO orbital analysis) and 4s
Ày2
orbits. The electron number of N 2s orbit is 1.36 and 2p that of or-
bit is 4.19, showing that the N atoms form coordination bonds with
Cu atom by using 2s and 2p (mainly from 2px orbit indicated by
NBO orbit analysis) orbits. In the same way, all O atoms supply
electrons of 2s (1.72) and 2p (range from 5.00 to 5.04) to Cu and
form the coordination bonds. Thus, according to Valence-bond the-
ory the [Cu(PIM)2(PhCOO)2] complex shows covalent-type Cu-li-
gand interactions.
As shown in Table 4, the electron number of Cu 3d orbit is 9.30
and that of 4s orbit is 0.33 (the electron numbers of 4d, 4p and 5p
are so small that can be omitted). From the above analysis we can
The energy of the title complex in ground state is À1.99 Â 106
kcal/mol. The HOMO(b) and LUMO(b) energies of molecular orbitals
are À5.74 eV and À1.25 eV, respectively, indicating that this config-
Fig. 5. Contour plots and energy of the selected b-spin HOMO and b-spin LUMO orbitals active in the electronic transitions for the title complex.

X. Peng et al. / Journal of Molecular Structure 967 (2010) 54–60
59
uration is stable. Dipole moment of the complex is 0.0001 Debye,
indicating the nonpolarization.
served in the temperature range of 270.5–584.5 °C, which is attrib-
uted to the release of one benzoate group and one benzene ring
residue (33.04% theoretical weight loss) leading to the decomposi-
tion of the complex to CuO with a residual mass of 17.20% (in good
agreement with the calculated value of 16.68%).
3.4. Electronic spectrum and spectroscopic properties
The nature of the transitions observed in the UV–vis spectrum
of the title complex has been studied by the time-dependent
density functional (TD-DFT) method. The calculated electronic
spectrum of [Cu(PIM)2(PhCOO)2] in comparison with the experi-
mental one is presented in Fig. 4. The most important calculated
electronic transitions and their assignments to the observed
absorption bands of the complex were presented in Table 5. The
UV–vis spectra of the complex display clearly the two absorption
bands at 731.3 and 265.7 nm. The selected b-spin electron orbitals
and energies of the title complex are given in Fig. 5.
4. Conclusion
A mononuclear copper(II) complex with both benzoate and 2-
propylimidazole ligands has been synthesized and structurally
characterized and its geometric parameters, electronic structure,
spectroscopic property, and thermal property were investigated
by combining X-ray crystallography, spectroscopy, DFT/TD-DFT
theoretical calculations and TG-DTA test. The optimized geometry
from calculations is in well agreement with that from X-ray single-
crystal structural determination. In addition, the electronic struc-
ture is well evaluated on the calculation, as well as the spectro-
scopic characterizations from experiments and calculations also
march well. In summary, this work has combined the theoretical
calculation and experimental characterizations into the investiga-
tion of coordination complex, a strategy being useful for similar
systems in coordination chemistry.
TD-DFT calculations showed that the calculated absorption
maxima (740.3 and 271.3 nm) are based on the b-spin LUMO fron-
tier orbital as the main arrival orbital of transitions and the ligand
p
bonding orbitals as the main starting ones of transitions. Because
of the Cu 3dx2 orbital character of the b-spin LUMO (mentioned
Ày2
above), these absorption bands should be mainly ascribed to sim-
ilar ?dx2 ligand-to-metal charge transfer (LMCT). As shown
p
Ày2
in Table 5, the TD-DFT calculated results are in well agreement
with experimental ones.
5. Supplementary Materials
In general, the absorption bands in experimental UV–vis spectra
originate from the transitions from ground state to excited states
with higher energy [36–38]. According to our TD-DFT calculations,
the absorption band at 740.3 nm with an oscillator strength 0.0013
can be correlated to the 731.3 nm band in experimental electronic
spectrum. This absorption maximum is mainly associated with the
transition from HOMO-8(b) to LUMO(b) with configuration inter-
action coefficient up to 0.93, and can be reasonably ascribed to
CCDC-750290 contains the supplementary crystallographic
data for 1. This data can be obtained from the Cambridge Crystal-
lographic Data Center, 12 Union Road, Cambridge CB2 1EZ, UK;
Fax: +44 1223 336033; E-mail: deposit@ccdc.cam.ac.uk.
Acknowledgements
p(benzoate)/p(PIM)?dx2
ligand-to-metal charge transfer
Ày2
(LMCT) and dxy?dx2Ày2 ligand field (LF) transitions. Similarly, the
calculated absorption maximum at 271.3 nm with an oscillator
strength 0.0264 can be correlated to the band at 265.7 nm absorp-
tion band in experimental spectrum. This absorption maximum is
mainly associated with transition from HOMO-3(b) to LUMO(b)
with configuration interaction coefficient up to 0.88 and transition
from HOMO-2(b) to LUMO+1(b) with configuration interaction
The authors are grateful to Scientific Research Fund of Hebei
Provincial Education Department (Project, 2006114) for financial
support.
References
[1] B. Moulton, M.J. Zaworotko, Chem. Rev. 101 (2001) 1629.
[2] K. Kim, Chem. Soc. Rev. 31 (2002) 96.
[3] M.J. Rosseinsky, Microporous Mesoporous Mater. 73 (2004) 15.
[4] S. Noro, S. Kitagawa, T. Akutagawa, T. Nakamura, Prog. Polym. Sci. 34 (2009)
240.
coefficient up to 0.31, thus it can be mainly ascribed to
p(benzo-
ate)/ (PIM)?dx2 ligand-to-metal charge transfer (LMCT).
p
Ày2
In addition, some predicted absorption bands could not been
observable in experimental UV–vis spectrum, being mainly due
to their relatively low oscillator strengths and higher transition
energies required. These calculated absorption bands mainly arise
[5] O.M. Yaghi, M. O’Keeffe, N.W. Ockwig, H.K. Chae, M. Eddaoudi, J. Kim, Nature
423 (2003) 705.
[6] J.-R. Li, D.J. Timmons, H.-C. Zhou, J. Am. Chem. Soc. 131 (2009) 6368.
[7] K. Seki, W. Mori, J. Phys. Chem. B 106 (2002) 1380.
[8] J.P. Zhang, X.M. Chen, Chem. Commun. (2006) 1689.
[9] B. Wang, A.P. Côté, H. Furukawa, M. O’Keeffe, O.M. Yaghi, Nature 453 (2008)
207.
[10] J.-R. Li, R.J. Kuppler, H.-C. Zhou, Chem. Soc. Rev. 38 (2009) 1477.
[11] M. Waisberg, P. Joseph, B. Hale, D. Beyersmann, Toxicology 192 (2003) 95.
[12] J. Yang, J.F. Ma, Y.Y. Liu, J.C. Ma, S.R. Batten, Cryst. Growth Des. 8 (2008) 4383.
[13] J.F. Ma, J. Yang, G.L. Zheng, L. Li, J.F. Liu, Inorg. Chem. 42 (2003) 7531.
[14] H. Ohtsu, Y. Shimazaki, A. Odani, O. Yamauchi, W. Mori, S. Itoh, S. Fukuzumi, J.
Am. Chem. Soc. 122 (2000) 5733.
from
p(benzoate)/p(PIM)?dx2
ligand-to-metal charge transfer
Ày2
(LMCT) and dyz?dx2Ày2 ligand field (LF) transitions of b-spin elec-
*
p(benzoate)?p (benzoate) intraligand (IL) tran-
tron orbitals and
sition of -spin electron orbitals.
a
In summary, our TD-DFT calculations predict the all absorption
bands in experimental UV–vis spectrum for the title complex.
Meanwhile, it can be conclude that the low-lying absorption bands
[15] R. Konecny, J. Li, C.L. Fisher, V. Dillet, D. Bashford, L. Noodleman, Inorg. Chem.
38 (1999) 940.
[16] (a) H. Ohtsu, S. Itoh, S. Nagatomo, T. Kitagawa, S. Ogo, Y. Watanabe, S.
Fukuzumi, Chem. Commun. (2000) 1051;
are
p
?dx2
and/or (P,
r)?dx2
ligand-to-metal charge transfer
Ày2
Ày2
(LMCT) without almost d?d ligand field (LF) transition in nature.
(b) D.E. Billing, B.J. Hathaway, P. Nicholls, J. Chem. Soc. A (1970) 1987.
3.5. Thermal properties
´
[17] B. Barszcz, A. Jabłonska-Wawrzycka, K. Stadnicka, J. Jezierska, Polyhedron 27
(2008) 3500.
The thermal stability of the complex 1 in N2 atmosphere was
examined by the TG-DTA techniques in the temperature range of
20–1000 °C. The thermal decomposition process of the complex
can be divided into two steps from the TG curve. The first weight
loss of 51.77% between 191.6 and 270.5 °C corresponds to the re-
lease of two PIM ligands and one CO2 molecule (50.28% theoretical
weight loss). The DTA curve of the complex indicates that it is an
endothermic process. The second weight loss of 31.03% was ob-
[18] D.R. Brown, H. Kozłowski, J. Chem. Soc., Dalton Trans. (2004) 1907.
[19] H.G. Ang, W.L. Kwik, G.R. Hanson, J.A. Crowther, M. McPartlin, N. Choi, J. Chem.
Soc., Dalton Trans. (1991) 3139.
[20] I. Degtyarenko, X. Biarnés, R.M. Nieminen, C. Rovira, Coord. Chem. Rev. 252
(2008) 1497.
[21] B. Machura, J. Mrozin´ ski, R. Kruszynski, J. Kusz, Polyhedron 27 (2008) 3013.
[22] T. Shi, S.Y. He, X.F. Wang, Y.B. Wang, Z.X. Tang, Z.Y. Wen, J. Mol. Struct.
(Theochem) 732 (2005) 201.
[23] P. Pogány, A. Kovács, K.M. Szécsényi, V.M. Leovac, Spectrochim. Acta. Part A 71
(2008) 1466.

60
X. Peng et al. / Journal of Molecular Structure 967 (2010) 54–60
[24] L. Peters, M.F. Tepedino, T. Haas, E. Hübner, U. Zenneck, N. Burzlaff, Inorg.
Chim. Acta 362 (2009) 2678.
[25] Z.M. Su, Y.H. Kan, Z.H. Huang, Y. Liao, Y.Q. Qiu, R.S. Wang, Synth. Met. 137
(2003) 1095.
[26] BRUKER, SMART, SAINT and SHELXTL, BRUKER AXS, Madison, Wisconsin, USA,
1998.
[27] G.M. Sheldrick, SADABS, University of Göttingen, Germany, 1996.
[28] G.M. Sheldrick, SHELXS97 and SHELXL97, University of Göttingen, Germany,
1997.
Pomelli, J.W. Ochterski, P.Y. Ayala, K. Morokuma, G.A. Voth, P. Salvador, J.J.
Dannenberg, V.G. Zakrzewski, S. Dapprich, A.D. Daniels, M.C. Strain, O.
Farkas, D.K. Malick, A.D. Rabuck, K. Raghavachari, J.B. Foresman, J.V. Ortiz,
Q. Cui, A.G. Baboul, S. Clifford, J. Cioslowski, B.B. Stefanov, G. Liu, A.
Liashenko, P. Piskorz, I. Komaromi, R.L. Martin, D.J. Fox, T. Keith, M.A. Al-
Laham, C.Y. Peng, A. Nanayakkara, M. Challacombe, P.M.W. Gill, B. Johnson,
W. Chen, M.W. Wong, C. Gonzalez, J.A. Pople, Gaussian 03, Revision C.02,
Gaussian, Inc., Wallingford CT, 2004.
[32] A. L. Spek, PLATON, A Multipurpose Crystallographic Tool, Utrecht University,
Utrecht, The Netherlands, 2000.
[29] Y.P. Tong, S.L. Zheng, J. Mol. Struct. 841 (2007) 34.
[30] F. Weinhold, J.E. Carpenter, The Structure of Small Molecules and Ions, Plenum,
New York, 1988. pp. 227.
[33] L. Sieron, M. Bukowska-Strzyzewska, Acta Crystallogr. C 55 (1999) 1230.
[34] M. O’Keeffe, N.E. Brese, Acta Crystallogr. B 47 (1997) 192.
[31] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R.
Cheeseman, J.A. Montgomery Jr., T. Vreven, K.N. Kudin, J.C. Burant, J.M.
Millam, S.S. Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G.
Scalmani, N. Rega, G.A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K.
Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao,
H. Nakai, M. Klene, X. Li, J.E. Knox, H.P. Hratchian, J.B. Cross, C. Adamo, J.
Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C.
[35] M. O’Keeffe, N.E. Brese, J. Am. Chem. Soc. 113 (1991) 3226.
[36] B. Machura, A. Switlicka, M. Wolff, J. Kusz, R. Kruszynski, Polyhedron 28 (2009)
´
1348.
´
[37] B. Machura, A. Switlicka, R. Kruszynski, J. Mrozin´ ski, J. Kłak, J. Kusz, Polyhedron
27 (2008) 2959.
[38] H.H. Li, Z.R. Chen, Y.G. Ren, J.Q. Li, C.C. Huang, B. Zhao, Chin. J. Struct. Chem. 24
(2005) 1375.