Revised crystal and molecular structure, FT-IR spectra and DFT studies of chlorotetrakis(imidazole)copper(II) chloride

Article abstract of DOI:10.1016/j.molstruc.2012.06.028

Copper(II) complex with imidazole, [Cu(ImH)₄Cl]Cl, was prepared and characterized by a single crystal X-ray analysis and infrared spectroscopy. This complex is one of the two polymorphic forms of the title compound. The crystal and molecular structures, and the patterns of intermolecular hydrogen bonding in two polymorphs have been compared and discussed. The two forms crystallize in the same monoclinic space group (P2₁/n) with different unit cell parameters. The detailed assignments of the FT-IR spectra of the title complex have been made on the basis of theoretical studies of the [Cu(ImH)₄Cl]⁺ cation using the unrestricted B3LYP method and the combined basis set: 6-311++G(3df,3pd) for non-metal atoms and LanL2DZ for Cu. The bands at 285, 259 and 229 cm^-1 in the IR spectrum are assigned to the CuN(imidazole) stretching vibrations.

Full text of DOI:10.1016/j.molstruc.2012.06.028

Journal of Molecular Structure 1028 (2012) 49–56
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Revised crystal and molecular structure, FT-IR spectra and DFT studies
of chlorotetrakis(imidazole)copper(II) chloride
Barbara Morzyk-Ociepa , Ewa Ró z_ ycka-Sokołowska , Danuta Michalska b
a,
⇑
a
a
Institute of Chemistry, Environmental Protection and Biotechnology, Jan Długosz University, Armii Krajowej 13/15 Ave., 42-200 Cz e˛ stochowa, Poland
Faculty of Chemistry, Wrocław University of Technology, Smoluchowskiego 23, 50-370 Wrocław, Poland
b
h i g h l i g h t s
"
"
"
"
4
Crystal structure of the copper(II)-imidazole complex [Cu(ImH) Cl]Cl is reported.
The obtained complex is one of two polymorphic forms of the title compound.
The vibrational assignment has been made on the basis of B3LYP calculations.
ꢀ1
The CuAN(imidazole) stretching vibrations occur at 285, 259 and 229 cm in IR spectrum.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 6 May 2012
Received in revised form 11 June 2012
Accepted 12 June 2012
Available online 20 June 2012
Copper(II) complex with imidazole, [Cu(ImH) Cl]Cl, was prepared and characterized by a single crystal
X-ray analysis and infrared spectroscopy. This complex is one of the two polymorphic forms of the title
compound. The crystal and molecular structures, and the patterns of intermolecular hydrogen bonding in
two polymorphs have been compared and discussed. The two forms crystallize in the same monoclinic
4
space group (P2
of the title complex have been made on the basis of theoretical studies of the [Cu(ImH)
the unrestricted B3LYP method and the combined basis set: 6-311++G(3df,3pd) for non-metal atoms and
1
/n) with different unit cell parameters. The detailed assignments of the FT-IR spectra
+
4
Cl] cation using
Keywords:
Imidazole complex
Copper(II)
ꢀ1
LanL2DZ for Cu. The bands at 285, 259 and 229 cm in the IR spectrum are assigned to the CuAN(imid-
azole) stretching vibrations.
Polymorphs
Molecular structure
FT-IR spectrum
Copper–imidazole vibrations
Ó 2012 Elsevier B.V. All rights reserved.
1
. Introduction
may exist in two polymorphic forms [10–12]. Otieno et al. [10] first
4
determined the crystal structure of [Cu(ImH) Cl]Cl (monoclinic,
Copper is an essential trace element found in all living organ-
space group P2 /n; a = 8.843(1); b = 13.209(3); c = 13.866(3) Å;
1
isms. It has been detected in about 20 metalloenzymes, where it
adopts the oxidized Cu(II) or reduced Cu(I) states, allowing the me-
tal to play a pivotal role in the redox chemistry in cellular life [1,2].
The imidazole group of the histidyl residue is the metal binding
site in most of metalloproteins [3]. Therefore, coordination com-
pounds of imidazole (ImH) with copper and other metal ions have
been widely investigated as models of the proteins active sites [4–
and b = 90.00(1)°). In our work we have denoted this structure as
polymorph 1. The complex was obtained from a solution contain-
ing Cu(ClO
[11] also synthesized the title compound using imidazole and
CuCl O in methanol, but the space group and the unit cell
4
)
2
2 6 4
ꢁ6H O, KPF , ImH and CCl [10]. Li and coworkers
2
ꢁ2H
2
parameters were the same as those given in Ref. [10]. On the other
hand, Jian et al. [12] obtained the title complex by a reaction of
8
]. The detailed characteristics of structure and bonding in the cop-
CuCl
2
with excess imidazole in ethanol, and described the crystal
/c with the unit cell
per–imidazole systems provide the background for understanding
the functions of some copper enzymes.
structure as monoclinic, space group P2
parameters: a = 13.909(3); b = 8.8933(18); c = 15.086(7) Å; and
1
A search of the Cambridge Structural Database (CSD Version
b = 118.32(2)° (different than those reported in Refs. [10,11]).
5
.33 of November 2011) [9] has revealed that the title compound
In this work we have synthesized [Cu(ImH)
formed a single crystal X-ray diffraction study. According to our
results the space group is P2 /n, the unit cell parameters are simi-
4
Cl]Cl and per-
1
lar to those reported by Jian et al. [12], however, the crystal struc-
ture is determined with a much lower R value (R = 0.039) than that
⇑
Corresponding author. Tel./fax: +48 (34) 366 5322.
E-mail address: bmorzyk-ociepa@o2.pl (B. Morzyk-Ociepa).
0
022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2012.06.028

5
0
B. Morzyk-Ociepa et al. / Journal of Molecular Structure 1028 (2012) 49–56
achieved previously (0.061). This form of the title complex has
been denoted as polymorph 2.
2. Experimental
It should be noticed that the hydrogen bonding system in poly-
morph 1 [10,11] has not been discussed, as yet. Therefore, we have
carried out the detailed analysis of the hydrogen bonds organizing
the crystalline networks and compared the graph-set assignments
for these interactions in both polymorphs. This can allow to iden-
tify the similarities and differences between the various polymor-
phic structures [13].
2.1. Synthesis of [Cu(ImH) Cl]Cl
4
3
A solution of CuCl ꢁ2H O (2.5 mmol) in water (0.5 cm ) was
2
2
added to a warm solution of imidazole ImH (0.7 g, 10 mmol) in
3
ethanol (40 cm ) with stirring. The mixture was heated to about
315 K for several hours. The solution was filtered and the filtrate
was left for crystallization. After
a week blue crystals of
The other goal of this work was to make, for the first time, the
detailed assignment of the infrared spectrum of the title complex.
The FT-IR spectra have been measured in the frequency regions
[Cu(ImH) Cl]Cl were formed.
4
ꢀ
1
ꢀ1
2.2. X-ray diffraction analysis
4
000–400 cm and 700–50 cm . To aid the vibrational assign-
ments of the experimental spectra, the theoretical studies of the
+
The X-ray diffraction data were collected at 290(2) K, using an
XCALIBUR™ 3 CCD diffractometer with graphite-monochromated
Mo Ka radiation (k = 0.71073 Å). The structure was solved by direct
methods using the SHELXS-97 program [16] and refined by full-
[
4
Cu(ImH) Cl] cation have been performed by using the unre-
stricted density functional theory (DFT) method, similarly as in
our earlier studies of the copper(II) complexes [14,15].
2
matrix least-squares on F with SHELXL-97 [16]. The C-bound
Table 1
4
Crystal data for polymorph 2 of [Cu(ImH) Cl]Cl.
Formula
C
12
H
16Cl
406.78
Monoclinic (No. 14)
P2 /n
2 8
CuN
Formula weight
Crystal system
Space group
1
3
Z; calcd density (Mg/m )
4; 1.642
828
13.9415(6)
8.8838(3)
14.9122(7)
90
116.985(5)
90
1645.84(14)
290(2)
F(000)
a (Å)
b (Å)
c (Å)
a
(°)
b (°)
(°)
c
3
V (Å )
Temp. (K)
No. of data/parameters
2896/221
1.136
Goodness of fit on F2
R1 (I > 2
wR2 (I > 2
r
(I))
(I))
0.0391
0.0906
r
R1 (all data)
0.0680
wR2 (all data)
0.1344
0.746 and ꢀ0.554
Largest diff peak and hole e (Åꢀ3)
Fig. 2. An overlay of the molecular structures of the [Cu(ImH)
4
Cl]+ complex cation
in two polymorphs: 1 (black) and 2 (red). (For interpretation of the references to
colour in this figure legend, the reader is referred to the web version of this article.)
Table 2
Comparison of the selected experimental bond lengths (Å) and bond angles (deg) for
4
polymorphs 1 and 2 of [Cu(ImH) Cl]Cl and the theoretical values calculated for
+
[
4
Cu(ImH) Cl] ion.
Copper coordination sphere
1 [10]
2 (this work)
X-ray
X-ray
Theor.a
CuAN3
CuAN7
CuAN5
CuAN1
1.999(3)
1.997(2)
2.013(2)
2.009(2)
2.6146(8)
174.88(9)
89.23(13)
90.04(11)
158.48(9)
89.60(11)
92.25(9)
92.86(9)
97.91(7)
103.61(7)
2.009(3)
2.001(3)
2.012(4)
2.016(4)
2.052
2.052
2.080
2.073
2.502
169.6
88.9
89.5
163.3
89.4
CuACl(1)
2.6184(13)
175.22(16)
89.52(15)
89.93(15)
156.91(16)
90.50(14)
92.45(11)
92.19(11)
98.68(12)
104.40(12)
N3ACuAN7
N3ACuAN5
N3ACuAN1
N5ACuAN1
N7ACuAN1
N3ACuACl(1)
N7ACuACl(1)
N1ACuACl(1)
N5ACuACl(1)
95.2
95.2
97.5
99.2
Fig. 1. The view of the polymorph 2 of [Cu(ImH)
pyramidal environment around the copper ion, the numbering of atoms and the
CAHꢁ ꢁ ꢁCl hydrogen bonds (black dashed line).
4
Cl]Cl displaying the square
a
Calculations performed by the B3LYP method with the combined basis set:6-
11++G(3df,3pd) for the non-metal atoms and LanL2DZ for Cu.
3

B. Morzyk-Ociepa et al. / Journal of Molecular Structure 1028 (2012) 49–56
51
the KBr pellet technique. The far-infrared spectrum (700–50 cm 1
ꢀ
)
hydrogen atoms were introduced at the calculated positions as rid-
ing atoms, with the CAH distances of 0.93 Å, while the N-bound H
atoms were located from difference maps. For all H atoms, Uiso (H)
values were constrained to be 1.2 Ueq (C, N). Complete crystallo-
graphic data have been deposited at the Cambridge Crystallo-
graphic Data Centre and allocated under deposition number
CCDC 878724.
was recorded on FT-IR Perkin-Elmer 2000 spectrometer (with a
resolution of 2 cm ) using Nujol mull technique and polyethylene
windows.
ꢀ
1
2.4. Theoretical methods
The theoretical studies were performed for the [Cu(ImH)
4
Cl]+
9
complex cation, which is an open-shell system (d electron config-
2.3. Spectroscopic measurements
2+
uration of Cu ). Thus, the calculations of an electronic structure of
the complex were based on an unrestricted mechanism. The gradi-
ent corrected three-parameter hybrid functional B3LYP [17,18]
was used with the combined basis sets: 6-311++G(3df, 3pd)
[19,20] for the non-metal atoms and the LanL2DZ [21] basis set
ꢀ
1
The infrared spectrum in the region 4000–400 cm was mea-
ꢀ1
sured at 2 cm resolution on a Nicolet-Nexus spectrometer using
Table 3
Geometrical parameters of intermolecular interactions in the crystal structure of
for copper.
polymorph 2 of [Cu(ImH)
4
Cl]Cl.
+
Full geometry optimization of the [Cu(ImH)
4
Cl] cation was per-
Hydrogen bonds
formed using the X-ray structural parameters of the complex as the
starting data set. Since a spin contamination of the unrestricted
wavefunction may occur, therefore, the expectation value of the to-
tal spin, S , had to be examined. The final S was equal to 0.7500 in
the unrestricted B3LYP calculations, which was in perfect agree-
ment with the theoretical value of 0.7500 corresponding to the
doublet ground state wavefunction with no spin contamination
a,b
Motif
DAHꢁ ꢁ ꢁA
DAH
Hꢁ ꢁ ꢁA
Dꢁ ꢁ ꢁA
DAHꢁ ꢁ ꢁA
i
m
n
o
p
q
r
N2-H1ꢁ ꢁ ꢁCl(2)
N4-H2ꢁ ꢁ ꢁCl(2)
N6-H3ꢁ ꢁ ꢁCl(1)
N8-H4ꢁ ꢁ ꢁCl(2)
C2-H6ꢁ ꢁ ꢁCl(2)
0.86(6)
0.88(6)
0.80(6)
0.85(1)
0.93
0.93
0.93
0.93
0.93
2.52(6)
2.40(5)
2.50(6)
2.41(1)
2.80
2.80
2.76
2.80
2.89
3.190(5)
3.261(4)
3.260(5)
3.264(4)
3.656(5)
3.729(5)
3.648(5)
3.503(5)
3.614(6)
3.660(6)
135(5)
165(5)
160(6)
177(5)
154
176
159
133
135
2
2
ˆ
ˆ
ii
iii
iv
v
C6-H10ꢁ ꢁ ꢁCl(1)
C7-H11ꢁ ꢁ ꢁCl(2)
[
22]. Vibrational frequencies, IR intensities and normal modes
s
t
+
vi
were calculated for the optimized structure of the [Cu(ImH)
4
Cl]
C10-H14ꢁ ꢁ ꢁCl(1)
viii
C3-H7ꢁ ꢁ ꢁCg2
cation. The computed frequencies were not scaled.
ix
C9-H13 ꢁ ꢁ ꢁCg4
0.93
2.91
138
All computations were carried out using the GAUSSIAN 09 pack-
age [23]. The Chemcraft program [24] was applied for the visual
animation of vibrations and comparison of the calculated atom dis-
placements associated with normal modes.
pꢁ ꢁ ꢁ
p
interactions, Cgꢁ ꢁ ꢁCg distance
x
Cg1ꢁ ꢁ ꢁCg1
Cg1ꢁ ꢁ ꢁCg3
Cg3ꢁ ꢁ ꢁCg1
Cg3ꢁ ꢁ ꢁCg3
3.964(3)
viii
ix
3.912(4)
3.912(4)
3.886(4)
xi
3
. Results and discussion
a
Symmetry codes: i = (x, ꢀ1 + y, z); ii = (3/2 ꢀ x, -1/2 + y, 1/2 ꢀ z); iii = (x, 1 + y, z);
i
v = (5/2ꢀx, ꢀ1/2 + y, 1/2 ꢀ z); v = (3/2 ꢀ x, 1/2 + y, 1/2 ꢀ z); vi = (2 ꢀ x, 1 ꢀ y, ꢀz);
3
.1. Crystal and molecular structure of [Cu(ImH) Cl]Cl
4
viii = (1/2 + x, 3/2 ꢀ y, 1/2 + z); ix = (2 ꢀ x, 2 ꢀ y, ꢀz); x = (2 ꢀ x, 1 ꢀ y, 1 ꢀ z);
xi = (ꢀ1/2 + x, 3/2 ꢀ y, ꢀ1/2 + z).
b
Cg1, Cg2, Cg3 and Cg4 are the centroids of the N1AC1AN2AC3AC2,
The crystallographic data of 2 are collected in Table 1. A com-
parison of the crystal structures of two polymorphs of
Cu(ImH) Cl]Cl have shown that they crystallize in the same
N3AC4AN4AC6AC5, N5AC7AN6AC9AC8 and N7AC10AN8AC12AC11 imidazole
rings, respectively.
[
4
Fig. 3. Part of the crystal structures of 2 showing the NAHꢁ ꢁ ꢁCl (motifs m–p) and CAHꢁ ꢁ ꢁCl (motifs q–s) hydrogen bonds forming the sheets parallel to (001) plane. H atoms
not involved in hydrogen bonding have been omitted for clarity. Symmetry codes are given in Table 3.

5
2
B. Morzyk-Ociepa et al. / Journal of Molecular Structure 1028 (2012) 49–56
2
Cg3(viii)
a
Cl1(vi)
C10
Cg3(xi)
Cg1
C3
Cg2(viii)
C9 Cg3
Cg4(ix)
Cg1(x)
Cg1(ix)
0
b
c
1
c
Cg1(x)
Cl1(vi)
C10
Cg3(xi)
Cg1 C3
C9
Cg2(viii)
Cg3
Cg4(ix)
Cg1(ix)
Cg3(viii)
0
b
a
Fig. 4. Part of the crystal structure of 2 and 1 polymorphs of [Cu(ImH)
4
Cl]Cl showing the CAHꢁ ꢁ ꢁCl (motif t, pink dashed lines) and CAHꢁ ꢁ ꢁp (dotted black lines) hydrogen
bonds and interactions (blue solid lines) linking the cations (ball and sticks model), which belong to the (001) sheet with the cations (sticks model) of the adjacent
pꢁ ꢁ ꢁp
sheets. H atoms not involved in hydrogen bonding have been omitted for clarity. (For interpretation of the references to colour in this figure legend, the reader is referred to
the web version of this article.)
monoclinic space group, with ab in polymorph 2 corresponding to
ca in 1. The c axis in 2 is greater by ca 1.7 Å than the corresponding
b axis in 1, and the b angle in 2 is greater by ca 27° than that in 1.
Moreover, the differences in unit cell volumes and densities of

B. Morzyk-Ociepa et al. / Journal of Molecular Structure 1028 (2012) 49–56
53
these two polymorphs are ca 1.6%, whereas the values of packing
hydrogen bonds, two CAHꢁ ꢁ ꢁ
p
and four
p
ꢁ ꢁ ꢁ
p
supramolecular
index are 70.1% and 71.5% for 2 and 1, respectively. It is worth
noticing that the same or equivalent space group symbols are
not uncommon among polymorphs. Numerous examples exist of
the same space group occurring for polymorphs or for phase tran-
sitions between two phases of the same symmetry (often described
as isostructural or isosymmetric phase transitions) [25].
interactions, which play a significant role in formation of a contin-
uous three-dimensional network. The geometrical parameters of
these intermolecular interactions are collected in Table 3.
Fig. 3 illustrates a part of the crystal structures of 2 showing the
NAHꢁ ꢁ ꢁCl (motifs m–p) and CAHꢁ ꢁ ꢁCl (motifs q–s) hydrogen bonds.
Some of these hydrogen bonds can be described by the graph-set
To facilitate the comparison of two polymorphic structures, we
have used the same atom numbering system for 2 as that em-
ployed for 1 in Ref. [10]. Fig. 1 shows the perspective view of the
notation D [26].
+
The N6 atom, which belongs to the [Cu(ImH)
4
Cl] cation at (x, y,
z) acts as a hydrogen bond donor to the coordinated Cl(1) anion at
(x, 1 + y, z) forming a simple C(6) chain (motif o in Fig. 3). Each cat-
ion belonging to this chain is further connected with chloride Cl(2)
4
polymorph 2 of [Cu(ImH) Cl]Cl with the numbering of atoms and
the CAHꢁ ꢁ ꢁCl hydrogen bonds (black dashed line).
i
ii
The crystal structure of the title complex consists of discrete
anions by the N2AH1ꢁ ꢁ ꢁCl(2) (motif m), N4AH2ꢁ ꢁ ꢁCl(2) (motif n)
+
ꢀ
iv
[
Cu(ImH)
4
Cl] cation and Cl anion in the asymmetric unit, which
and N8AH4ꢁ ꢁ ꢁCl(2) (motif p) hydrogen bonds (symmetry codes
are linked by two weak C2AH6ꢁ ꢁ ꢁCl(2) and C7AH11ꢁ ꢁ ꢁCl(2) hydro-
gen bonds. The copper(II) ion has a distorted square-pyramidal
geometry. The basal coordination plane is formed by four N atoms
of the imidazole ligands, while the apical position is occupied by
the chlorine atom.
are given in Table 3). The combined effect of these four NAHꢁ ꢁ ꢁCl
hydrogen bonds generates a continuous two-dimensional sheet
parallel to the (001) plane, i.e. plane perpendicular to the longest
crystallographic c axis. This sheet is additionally stabilized by
two already mentioned C2AH6ꢁ ꢁ ꢁCl(2) and C7AH11ꢁ ꢁ ꢁCl(2) inter-
v
The corresponding geometrical parameters of the copper
complex in two polymorphs are very similar. Actually, the
actions and also by the C6AH10ꢁ ꢁ ꢁCl(1) (motif r) interaction that
+
link the cations into the C(6) chain. The [Cu(ImH)
4
Cl] cations
molecular structures of the Cu(ImH)
4
Cl monomers can be nearly
belonging to the adjacent sheets are further linked by one CAHꢁ ꢁ ꢁCl
2
2
overlaid, as shown in Fig. 2. This clearly indicates that the two
polymorphs are indeed pure packing variants of essentially iden-
tical compounds, i.e. the packing differences do not arise from
molecular geometry differences. The selected bond lengths and
bond angles in the coordination sphere of 1 and 2 are listed in
hydrogen bond (motif t) forming the R ð10Þ ring.
We have performed a similar detailed investigation of the inter-
molecular interactions in the crystal structure of polymorph 1. The
results have shown that in polymorph 1 all the hydrogen bonds
and
p p interactions occurring in 2 are also observed in 1, and
ꢁ ꢁ ꢁ
Table 2 together with the corresponding theoretical parameters
they can be described by the same graph-set descriptors as those
used for 2 (the results are presented in Supplementary material,
Table 2S and Fig. 1S). Thus, a formation of three-dimensional net-
work is a common characteristic of the crystal packing in these two
polymorphs.
+
calculated for the [Cu(ImH)
4
Cl] cation. The theoretical CuAN
bond lengths are too long by about 0.05–0.07 Å, whereas the cal-
culated CuACl atom distance is too short by about 0.12 Å, in
comparison with experiment. Considering the bond angles, the
largest difference (about 6.4°) is noted for N5ACuAN1. These
discrepancies between theory and experiment can be caused
by the intermolecular hydrogen bonding in crystal (it should
be remembered that the calculations refer to a complex in the
gas phase). All experimental bond lengths and bond angles and
the corresponding theoretical values for polymorph 2 are col-
lected in Table 1S (in Supplementary material).
Fig. 4 compares the parts of the crystal structures of 2 and 1 dis-
playing the CAHꢁ ꢁ ꢁCl (motif t, pink dashed lines) and CAHꢁ ꢁ ꢁ
(dotted black lines) hydrogen bonds. In addition, it shows the
interactions (blue solid lines), which link the cations (ball
p
pꢁ ꢁ ꢁp
and sticks model) belonging to the (001) sheet with the cations
(sticks model) of adjacent sheets. The main difference between
these polymorphs is seen in Fig. 4. In 2 (the upper structure), the
neighboring sheets are generated by the translational part of the
n-glide plane symmetry element, i.e. reflection through a plane
perpendicular to a sheet followed by translation (½ a + ½c). On
In the crystal structure of 2, apart from the two above-men-
tioned CAHꢁ ꢁ ꢁCl hydrogen bonds (shown in Fig. 1), there are other
two CAHꢁ ꢁ ꢁCl hydrogen bonds, four intermolecular NAHꢁ ꢁ ꢁCl
1
00
100
80
60
40
20
0
80
60
40
20
0
4000 3500 3000 2500 2000 2000 1800 1600 1400 1200 1000 800
600
-1
Wavenumber [cm-1]
Wavenumber [cm ]
4
Fig. 5. FT-IR spectrum of [Cu(ImH) .
Cl]Cl (polymorph 2), in the range 4000–500 cm 1
ꢀ

5
4
B. Morzyk-Ociepa et al. / Journal of Molecular Structure 1028 (2012) 49–56
ꢀ
1
the other hand, in 1 (the lower structure) these sheets are gener-
ated by the 2 screw axis.
The strong bands at 1580 and 1429 cm (Fig. 5) have been as-
signed to the bending d(NH) vibrations coupled with the (C@C)
and (C@N) stretching vibrations of the imidazole ring. The corre-
sponding strong bands in gaseous ImH were observed at lower fre-
1
m
m
ꢀ1
quencies, 1481 and 1406 cm , respectively [27]. This is in line
with a well known effect that upon formation of an intermolecular
hydrogen bond in the solid state, the frequency of d(NH) bending
vibration increases (while that of the stretching NAH mode de-
creases), in comparison to the modes in a bare molecule.
and a medium band at
094 cm are assigned to the CAN stretching vibrations. In the
4
3.2. The infrared spectrum of [Cu(ImH) Cl]Cl and DFT calculations
The FT-IR spectra of the title complex (polymorph 2) are illus-
ꢀ1
trated in Figs. 5 and 6, in the regions 4000–500 cm and 700–
ꢀ1
5
0 cm , respectively. The theoretical IR spectrum has been calcu-
ꢀ1
The very strong band at 1065 cm
lated for the model consisting of four imidazole ligands and the
chloride ion bonded to copper. The unrestricted B3LYP method
was used with the combined basis sets (LanL2DZ for copper and
ꢀ1
1
IR spectrum of imidazole the corresponding bands are observed
ꢀ1
at 1057 and 1084 cm , respectively [27].
6
-311++G(3df,3pd) for the remaining atoms). All the calculated fre-
quencies and IR intensities (108 normal modes for 38 atoms of the
+
[
4
Cu(ImH) Cl] cation) are listed in Table 3S (Supplementary mate-
rial). Table 4 collects the experimental bands observed in the infra-
red spectra and the corresponding theoretical results. The
vibrational assignments have been made on the basis of visualiza-
tion of the atomic displacements in each calculated normal mode
and by comparison with the assignments reported earlier for imid-
azole [27,28] and other similar systems [14,15,29–34].
Table 4
4
Comparison of the experimental data for polymorph 2 of [Cu(ImH) Cl]Cl and the
theoretical wavenumbers (
ion calculated by the B3LYP method with the 6-311++G(3df,3pd)/LanL2DZ basis sets.
ꢀ1
ꢀ1
+
4
m, cm ) and IR intensities (A, km mol ) for [Cu(ImH) Cl]
FT-IR
Calculated
m
A
Assignments
As is seen in Fig. 5, the bands in the range from 3500 to about
ꢀ1
2
500 cm are very strong and broad, which confirms the presence
of hydrogen bonding in crystal. According to the X-ray data (Table
), the NAH groups are engaged in the NAHꢁ ꢁ ꢁCl intermolecular
3384 vs
3649
3253
3272
97
63
4
m
m
m
NH
CH
CH
a
3
2
2
1
122 vs
973 w
845 m
580 s
3
Overtone (2ꢁ1429)
interactions with the Nꢁ ꢁ ꢁCl distances ranging from 3.190(5) to
1578
1523
1517
1450
1368
1296
1293
1292
1189
1186
1151
1119
1116
1116
1081
1078
957
939
937
933
924
908
905
872
867
830
768
755
659
603
592
269
258
254
206
171
151
150
129
110
93
45
53
9
15
9
6
2
13
1
8
d NH,
m
m
m
m
CC,
CN
CN
CC,
CN
m
CN
ꢀ1
3
.264(4) Å. Thus, a broad band with the maximum at 3384 cm
1536 m
m
m
CC,
CC,
1490 m
1429 m
1328 m
1262 m
arises from the
m (NAH) stretching vibrations. This assignment is
d NH,
d CH,
m
CN
supported by our earlier spectroscopic and structural studies on
indolecarboxylic acids and its metal complexes [29–32]. For exam-
ple, in the IR spectrum of crystalline indole-2-carboxylic acid
m
m
m
m
m
m
m
m
m
m
m
m
CN, d CH
CN, d CH
CN, d CH
1256 m
1246 w
1175 w
(
3
I2CA) the corresponding
m
(NAH) vibration was assigned at
ꢀ1
CC,
CC,
CC,
CN,
CN,
CN,
CN,
CN,
m
m
m
m
m
m
m
m
CN, d CH
CN, d CH
CN, d CH
CC
CC
CC
350 cm
[29,30]. It should be mentioned that in I2CA the
1
1
1
164 w
140 w
127 w
NAHꢁ ꢁ ꢁO intermolecular hydrogen bond is somewhat stronger
than the NAHꢁ ꢁ ꢁCl hydrogen bond in the title complex, as indicated
by a slightly shorter Nꢁ ꢁ ꢁO distance, 3.118(11) Å in the former com-
27
46
7
1113 w
110 w
1094 m
1
5
pound [29].
In Fig. 5, the broad bands at 3122 and 2973 cmꢀ1 are assigned to
90
171
2
6
5
4
6
6
CC, d CH
CC, d CH
1
9
065 vs
53 w
ꢀ
ꢀ
1
1
the
m (CAH) stretching vibrations, while a band at 2845 cm
d ring, d CH
d ring, d CH
d ring, d CH
d ring, d CH
CH, d ring
CH, d ring
CH, d ring
arises, most probably, from an overtone of a band at 1429 cm
943 w
937 w
(
this overtone gains IR intensity via Fermi resonance with the
neighboring (CAH) fundamental transition). For comparison, in
the IR spectrum of imidazole in the gas phase the (CAH) vibra-
tions were observed in the range 3159–3132 cm , while
920 w
904 w
896 w
890 w
m
p
p
p
p
p
p
p
p
s
m
ꢀ1
m
12
11
4
ꢀ1
(
NAH) was assigned at 3517 cm [27].
845 s
CH,
CH,
CH,
CH
s
s
s
ring
ring
ring
8
8
7
7
6
6
6
2
2
2
2
26 s
06 s
29
24
98
75
116
72
42
45
20
11
9
1
1
18
16
2
73 vs
57 vs
66 vs
23 m
11 s
85 s
59 m
29 s
90
CH
ring
NH
NH
80
p
p
70
m
m
m
m
m
s
as CuN
as CuN
4
4
60
s
CuN
CuCl
4
05 w
50
161 s
53w
145w
25 s
113 w
CuCl, ms CuN4
1
ring,
p
p
CuN
CuN
4
40
s
ring,
4
1
p
p
s
ClCuN
4
30
ClCuN
4
98 w
74 w
61 w
54 w
ring, das CuN
4
73
60
6
1
m
s
CuCl,
ring
4
p ClCuN , s ring
20
45
1
s
ring
10
700
600
500
400
300
200
100
Abbreviations: m, medium; s, strong; w, weak; v, very;
bending; , out-of-plane bending; , torsion; subscripts as and s denote asymmetric
and symmetric modes, respectively.
m, stretching; d, in-plane
-1
p
s
Wavenumber [cm ]
a
4
Fig. 6. FT-IR spectrum of [Cu(ImH) .
Cl]Cl (polymorph 2), in the range 700–50 cm 1
ꢀ
Reordered theoretical wavenumbers.

B. Morzyk-Ociepa et al. / Journal of Molecular Structure 1028 (2012) 49–56
55
ꢀ1
+
As shown in Table 4, strong bands in the range 845–757 cm
4
ular geometry of the [Cu(ImH) Cl] complex cation and the
are generated mainly by the out-of-plane
the copper complex.
p
(CAH) vibrations, in
patterns of intermolecular hydrogen bonding, in the crystal
structures of two polymorphs.
Fig. 6 illustrates the spectrum where the torsion modes of the
ligands and the Cu-ligand stretching and bending vibrations should
(4) The detailed assignments of the experimental infrared spec-
trum of the title compound have been made on the basis of
ꢀ1
+
be observed. The distinct band at 666 cm (and a shoulder at
the theoretical calculations of the [Cu(ImH)
4
Cl] complex
ꢀ
1
6
55 cm ) arise from the torsion vibrations of the imidazole rings.
cation using the unrestricted density functional B3LYP
method and the combined basis set: 6-311++G(3df,3pd) for
non-metal atoms and LanL2DZ for Cu. The calculated
ꢀ1
The next two bands, at 623 and 611 cm , are assigned to the out-
of-plane (NH) vibrations. Due to intermolecular hydrogen bonds
in the title complex, the frequencies of (NH) modes show an up-
p
p
(unscaled) frequencies show good agreement with experi-
ꢀ1
ꢀ1
ward shift, in comparison to the corresponding mode at 509 cm
ment, in the range below 1600 cm
.
ꢀ1
in the IR spectrum of imidazole in the gas phase [27].
(5) The bands at 285 and 259 cm in the IR spectrum of the
title complex are assigned to the asymmetric as (CuAN)
+
According to the theoretical calculations for [Cu(ImH)
4
Cl] , the
m
ꢀ1
ꢀ1
bands at 285 and 259 cm are generated by the asymmetric
m
as
stretching vibrations, while the band at 229 cm is due to
ꢀ
1
(
CuAN) stretching vibrations, while that at 229 cm should be as-
signed to the symmetric (CuAN) stretching vibration of the
CuAN skeleton. This assignment is supported by the results from
the spectroscopic studies of the histamine complex, Cu(hm)Cl
containing the Cu-imidazole bond, where the (CuAN) stretching
on the basis of the
the symmetric (CuAN) stretching vibration of the CuAN
m
s
4
m
s
skeleton. The identification of CuAN (imidazole) vibrations
provides valuable information about the bonding in copper
enzymes.
4
2
,
m
ꢀ1
frequency was determined at 270 cm
6
3
65
Cu/ Cu substitution [33]. It is interesting that the corresponding
Acknowledgements
m
(CuAN) stretching vibration in the Cu-pyridine complex,
ꢀ1
Cu(py)
2
Cl
2
, was assigned at very similar frequency, 268 cm [34].
(CuACl) stretching vibration, in the title
complex, is less certain since the CuACl bond is weak and very long
about 2.62 Å). The theoretical results indicate that (CuACl)
vibration contributes mainly to the bands observed at 205 and
The authors are grateful to reviewer for valuable suggestions.
The Wrocław Centre for Networking and Supercomputing is
acknowledged for generous computer time. This work was par-
tially supported by the Grant No. S10064 from the Department of
Chemistry, Wroclaw University of Technology.
The assignment of the
m
(
m
ꢀ1
1
61 cm . The assignments of the remaining bands in the FT-IR
spectrum are shown in Table 4.
Appendix A. Supplementary material
It should be mentioned that Otieno et al. [10] listed the charac-
teristic IR bands of polymorph 1, in the range from about 3300 to
Supplementary data associated with this article can be found,
in the online version, at http://dx.doi.org/10.1016/j.molstruc.
ꢀ1
ꢀ1
6
00 cm . Two strong bands at 3384 and 1580 cm are missing
in their list (probably are overlooked), however, the reported
wavenumbers for 1 are very close to these measured for 2 in this
work. This shows that infrared spectroscopy cannot be used to dis-
2
012.06.028.
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