Synthesis, X-ray and spectroscopic characterisation of chromium(III) coordination compounds with benzimidazolic ligands

Article abstract of DOI:10.1016/S0277-5387(00)00458-7

The syntheses and characterisation of chromium(III) complexes with tris(2-benzimidazolylmethyl)amine (ntb), 2-guanidinobenzimidazole (2gb), 2,6-bis(2-benzimidazolyl)pyridine (bbimpy) and 2-(2-pyridyl)benzimidazole (2pb), of composition [Cr(ntb)Cl₂]Cl·4.5H₂O (1), [Cr(2gb)₃]Cl[ZnCl₄]·CH₃OH (2), [Cr(2gb)₃]Cl₃·4H₂O (3), [Cr₂(2gb)₄(μ-OH)₂](ClO₄)₄·5H₂O (4), [Cr(b-bimpy)Cl₃] (5) and [Cr(2pb)₂Cl₂]Cl·C₂H₅OH·0.5H₂O (6) are presented. The compounds are obtained from Cr(III)in alcoholic solution, or a Cr(II) aqueous acidic solution. The latter were carried out under air-free conditions. The reaction of 2gb with Cr(II) in aqueous solution yielded a dinuclear compound. The X-ray crystal structures of 1 and 4 are discussed. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0277-5387(00)00458-7

www.elsevier.nl/locate/poly
Polyhedron 19 (2000) 1821–1827
Synthesis, X-ray and spectroscopic characterisation of
chromium(III) coordination compounds with benzimidazolic
ligands
Agueda E. Ceniceros-Go´mez a, Nora´h Barba-Behrens a, M. Elba Quiroz-Castro a,
Sylvain Berne`s b, Heinrich No¨th c, Silvia E. Castillo-Blum a,*
a Departimento de Qu´ımica Inorga´nica, Facultad de Qu´ımica, UNAM, Ciudad Uni6ersitaria, 04510 Mexico D.F., Mexico
b USAI, Facultad de Qu´ımica, UNAM, Ciudad Uni6ersitaria, 04510 Mexico D.F, Mexico
c Institute of Inorganic Chemistry, Uni6ersity of Munich, Bu¨tenandtstraße 5-13, Haus D, D-81377 Munich, Germany
Received 6 June 2000; accepted 7 June 2000
Abstract
The syntheses and characterisation of chromium(III) complexes with tris(2-benzimidazolylmethyl)amine (ntb), 2-guanidinobenz-
imidazole (2gb), 2,6-bis(2-benzimidazolyl)pyridine (bbimpy) and 2-(2-pyridyl)benzimidazole (2pb), of composition
[Cr(ntb)Cl2]Cl·4.5H2O (1), [Cr(2gb)3]Cl[ZnCl4]·CH3OH (2), [Cr(2gb)3]Cl3·4H2O (3), [Cr2(2gb)4(m-OH)2](ClO4)4·5H2O (4), [Cr(b-
bimpy)Cl3] (5) and [Cr(2pb)2Cl2]Cl·C2H5OH·0.5H2O (6) are presented. The compounds are obtained from Cr(III) in alcoholic
solution, or a Cr(II) aqueous acidic solution. The latter were carried out under air-free conditions. The reaction of 2gb with Cr(II)
in aqueous solution yielded a dinuclear compound. The X-ray crystal structures of 1 and 4 are discussed. © 2000 Elsevier Science
Ltd. All rights reserved.
Keywords: Chromium(III) complexes; Tris(2-benzimidazolylmethyl)amine; 2-Guanidinobenzimidazole; 2,6-Bis(2-benzimidazolyl)pyridine; 2-(2-
Pyridyl)benzimidazole; Crystal structures
about the coordination chemistry of benzimidazolic
ligands have been carried out mainly on labile metal
1. Introduction
ions [1,8–10]. It is worth mentioning that there are only
Imidazole is a typical heterocyclic ligand with nitro-
a limited number of reports on chromium(III) com-
gen as the donor atom. It is also a component of
plexes containing imidazoles [11–14] or benzimidazoles
biologically important molecules [1]. Because of this,
[14,15]. The synthesis, reactivity and magnetic proper-
the coordination chemistry of related ligands has been
ties of dinuclear chromium(III) species containing OH−
the subject of numerous investigations [1]. Amongst
bridges have been studied for the last two decades
them, the coordinating behaviour of chelating benzimi-
[16,17]. However, none of them contained imidazolic or
dazolic ligands has been studied by several research
benzimidazolic ligands.
groups, some of them with an interest in mimicking
We have been interested in the coordinating ability
biological activities [2–6]. Benzimidazoles exhibit a
of benzimidazolic ligands towards transition metal
wide variety of pharmacological activities like fungi-
ions [8,18,19]. Here we describe the synthesis and char-
cides or anti-helminthics amongst others [7]. Studies
acterisation of substitution inert chromium(III) coordi-
nation compounds with four benzimidazolic ligands.
The X-ray crystal structures of [Cr(ntb)Cl2]Cl·2H2O·
C2H5OH and [Cr2(2gb)4(m-OH)2](ClO4)4·4.67H2O are
discussed.
* Corresponding author. Tel.: +52-5-622-3812; fax: +52-5-622-
3724.
E-mail address: blum@servidor.unam.mx (S.E. Castillo-Blum).
0277-5387/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved.
PII: S0277-5387(00)00458-7

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A.E. Ceniceros-Go´mez et al. / Polyhedron 19 (2000) 1821–1827
2. Experimental
2.1. Materials
which were filtered off (0.635 g, 48.1%). (Found: C,
28.74; H, 3.41; N, 20.85. C32H48O23N20Cr2Cl4 requires
C, 28.97; H, 3.65; N, 21.12%).
Metallic chromium, zinc and mercury, anhydrous
CrCl3, CrCl2, CrCl3·nH2O, 2-guanidinobenzimidazole
(2gb), 2,6-bis(2-benzimidazolyl)pyridine (bbimpy), 2-(2-
pyridyl)benzimidazole (2pb) and tris(2-benzimidazolyl-
methyl)amine (ntb), methanol, ethanol and HClO4 were
used as analytical reagents and obtained from Aldrich.
They were used without further purification.
2.2.4. [Cr(bbimpy)Cl3] (5)
Anhydrous CrCl3 (0.158 g, 1.00 mmol) was placed in
the filter thimble of a Soxhlet extractor together with
ZnꢀHg amalgam (1 cm3). A solution of bbimpy (0.622
g, 2.00 mmol) in anhydrous ethanol (60 cm3) was
placed into the reservoir flask. N2 was bubbled through
the ligand solution for 10 min before heating and
chromium chloride was then extracted as a green solu-
tion that reacted with the bbimpy ligand. A green solid
precipitated and was isolated by vacuum filtration
(0.435 g, 92.6%). (Found: C, 48.77; H, 2.95; N, 14.82.
C19H13N5CrCl3 requires C, 48.59; H, 2.80; N, 14.90%).
2.2. Syntheses
2.2.1. [Cr(ntb)Cl2]Cl·4.5H2O (1)
Anhydrous CrCl3 (0.158 g, 1.00 mmol) was placed in
the filter thimble of a Soxhlet extractor together with
ZnꢀHg amalgam (1 cm3), and a solution of ntb (0.407
g, 1.00 mmol) in anhydrous methanol (50 cm3) was
added to the reservoir flask. N2 was bubbled through
the ntb solution for 10 min before heating and
chromium chloride was then extracted as a green solu-
tion that reacted with ntb. A green precipitate formed
and was isolated by vacuum filtration (0.270 g, 42.3%).
(Found: C, 44.65; H, 4.20; N, 14.90. C24H20N7CrCl3·
4.5H2O requires C, 44.56; H, 4.67; N, 15.16%). Green
crystals of 1 (minimum formula C26H31O3N7CrCl3)
were obtained simply by mixing the solutions of
CrCl3·nH2O and ntb in ethanol and leaving the solution
to stand for few days.
2.2.5. [Cr(2pb)2Cl2]Cl·C2H5OH·0.5H2O (6)
Anhydrous CrCl3 (0.158 g, 1.0 mmol) was placed in
the filter thimble of a Soxhlet extractor together with
ZnꢀHg amalgam (1 cm3) and a solution of 2pb (0.585 g,
3.0 mmol) in anhydrous ethanol (60 cm3) was added to
the reservoir flask. N2 was bubbled through the ligand
solution for 10 min before heating and the chromium
chloride was then extracted as a green solution that
reacted with the 2pb ligand. A green precipitate formed
and was isolated by vacuum filtration (0.294 g, 49.5%).
(Found: C, 51.65; H, 4.02; N, 13.99. C24H18N6CrCl3·
C2H5OH·0.5H2O requires C, 51.71; H, 4.17; N,
13.92%).
2.2.2. [Cr(2gb)3]Cl[ZnCl4]·CH3OH (2),
2.3. Physical measurements
[Cr(2gb)3]Cl3·4H2O (3)
Anhydrous CrCl3 (1.0 g, 6.3 mmol) and Zn powder
(10 mg) were stirred together in anhydrous methanol
(50 cm3). A solution of 2gb (3.31 g, 18.9 mmol) in hot
anhydrous methanol was added with stirring. The mix-
ture was heated (40°C) with stirring for 3 h. A pink
solid precipitated immediately 2, which was filtered off.
The red solution deposited small red crystals of 3 by
slow evaporation. Compound 2: (0.128 g, 2.4%).
(Found: C, 35.20; H, 4.47; N, 25.38. C25H31ON15-
CrZnCl5 requires C, 35.23; H, 3.68; N, 24.65%). Com-
pound 3: (4.50 g, 95.2%). (Found: C, 38.13; H, 4.15; N,
27.16. C24H35O4N15CrCl3 requires C, 38.13; H, 4.67; N,
27.79%).
An FT-IR spectrometer (Perkin–Elmer 1600) was
used for obtaining IR spectra of solid samples in KBr
pellets (4000–400 cm−1). The UV–Vis spectra (diffuse
reflectance) were recorded on a Cary-5E (Varian) spec-
trometer (250–2500 nm). Elemental analyses were car-
ried out with a Fisons EA 1180 analyser. Magnetic
susceptibility measurements of powdered samples were
recorded on a Johnson–Matthey DG8 5HJ balance
using the Gouy method. Magnetic susceptibilities were
measured on powdered samples of 4 in the temperature
range 17–280 K using a Vibrating Sample Magnetome-
ter Model 4500 from EG & G PARC.
2.4. Crystallography
2.2.3. [Cr2(2gb)4(v-OH)2](ClO4)4·5H2O (4)
A solution of 2gb (0.525 g, 3.00 mmol) in methanol
(30 cm3) was deoxygenated with N2 in a vacuum line.
Chromium metal (0.32 g, 6.00 mmol), or CrCl2 (0.737
g, 6.00 mmol), was dissolved in 6 cm3 of deoxygenated
2.0 M HClO4. 1.0 cm3 of this chromium(II) solution
was injected into the 2gb solution. Air was allowed into
the flask, and 2.0 g of NaClO4 was added. X-ray
quality purple crystals deposited from the solution,
Pertinent crystal data for 1 and 4 are given in Table
1. The diffraction data for 4 were collected at 298 K on
a Siemens P4 diffractometer in the 2q range 3–50°
,
(u=0.71073 A) at variable scan speed in ꢀ (4–60°
min−1). Data were corrected for absorption using 12
„-scans with  close to 90° (min=0.712, max=0.758).
Data for 1 were collected at 183 K with the crystal
mounted on a glass fibre coated with perfluorpolyether

A.E. Ceniceros-Go´mez et al. / Polyhedron 19 (2000) 1821–1827
1823
Table 1
Crystallographic data for compounds 1 and 4
1
4
Formula
[Cr(C24H21N7)Cl2]Cl
(C2H5OH)(H2O)2
647.93
[Cr2(C8H9N5)4(OH)2]
(ClO4)4(H2O)4.67
1320.70
M
Crystal system
Space group
monoclinic
P21/c
10.3057(2)
13.4632(3)
21.5037(3)
triclinic
(
P1
,
a (A)
12.156(2)
14.035(2)
16.733(3)
90.04(1)
110.18(1)
106.96(1)
2546.7(6)
2
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
103.103(1)
3
,
U (A )
2905.91(9)
4
1.481
1340
0.711
Z
Dcalc (Mg m−3
F(000)
)
1.722
1353
0.738
v(Mo Ka) (mm−1
)
Crystal dimensions (mm)
Total reflections measured
Number of unique reflections
Number of observed reflections [Fo\4|(Fo)]
Number of variables
0.32×0.25×0.18
16 066
5802
3791
362
0.6×0.4×0.4
10 303
8917
6646
739
Goodness of fit a
1.501
1.034
R1 (observed data) a
6.62
5.91
wR2 (all data) a
12.64 b
18.24 c
a R1=SꢀꢀFoꢀ−ꢀFcꢀꢀ/SꢀFoꢀ, wR2=ꢁSw(Fo2−Fc2)2/Sw(Fo2)2, S=ꢁSw(Fo2−Fc2)2/m−n.
b w=[|2(Fo2)+(0.0210P)2+7.6749P]−1
.
c w=[|2(Fo2)+(0.0959P)2+4.42P]−1
.
oil. 1200 frames were measured on a Siemens P4 diffrac-
tometer equipped with an area detector in the hemi-
sphere scan mode (ƒ=0–360°, 10 s exposure per
frame), which corresponds to the 2q range 3–58° (u=
and SHELX-97-2 [22], without constraints or restraints
for non-H atoms. Most of the H atoms were placed on
idealised positions and refined using a riding model with
a fixed isotropic U factor. H atoms for the OH groups
in 4 and for the water molecules in 1 were found on
difference maps and refined as remaining H. In the case
of 4, H atoms were omitted for the water molecules.
,
0.71073 A). Absorption correction was applied using
SADABS [20] (min=0.804, max=0.883). Both struc-
tures were solved and refined using SHELXTL 5.03 [21]
Fig. 1. Structures of the benzimidazolic ligands.

1824
A.E. Ceniceros-Go´mez et al. / Polyhedron 19 (2000) 1821–1827
Table 2
Spectroscopic UV–Vis, IR and magnetic data for 1–6
Compound
Uv–Vis
IR
veff
w1
(cm−1
w2
w3
w(NꢀH)
w(CꢁC)+w(CꢁN)
l(NꢀH)
l(CꢀH)
)
(cm−1
)
M.B.
3.9
ntb
3384
3384
3140
3190
3190
3194
3055
3068
3056
3072
1622, 1536
1622, 1594
1438
1450
1450
1486
1486
1466
1459
1467
742
744
740
744
744
749
741
753
743
752
1 [Cr(ntb)Cl2]Cl·4.5H2O
2gb
2 [Cr(2gb)3]Cl(ZnCl4)·CH3OH
3 [Cr(2gb)3]Cl3·4H2O
4 [Cr2(2gb)4(m-OH)2](ClO4)4·5H2O
bbimpy
5 [Cr(bbimpy)Cl3]
2pb
6 [Cr(2pb)2Cl2]Cl·0.5H2O·C2H5OH
16 650
23 050
28 580
1648 a, 1598 a, 1540
1666 a, 1634 a, 1556
1668 a, 1634 a, 1556
1667 a, 1560
20 050
19 723
17 360
25 050
25 320
24 570
28 650
28 010
36 100
3.9
3.9
4.96 b
1599, 1588, 1571
1607, 1590, 1575
1593, 1567,
16 660
17 240
20 000
20 490
25 000
25 970
3.8
3.9
1442, 1400
1457, 1445
1608, 1593
a There is also contribution from l(NH2) and w(CꢁN) from the guanidine group.
b Calculated for the dinuclear compound.
3. Results and discussion
basicity of 2gb is responsible for the formation of the
hydroxo bridges. The same method of synthesis gave
mononuclear species when ntb, bbimpy or 2pb were
reacted with an acidic aqueous Cr(II) solution, indicat-
ing that they are less basic than 2gb.
3.1. Synthesis and characterisation of the
coordination compounds
Six coordination compounds with the benzimidazolic
ligands: ntb, 2gb, bbimpy and 2pb Fig. 1, were synthe-
sised and characterised by spectroscopic and analytical
methods.
Table 2 shows some of the main IR vibrational
frequencies, UV–Vis absorption bands and magnetic
moments.
Two different synthetic routes were used for prepar-
ing the coordination compounds. In the first technique,
chromium(III) is extracted, in anhydrous methanol or
ethanol, from CrCl3 by means of a Soxhlet and then
reacted with the ligand, as previously reported for
chelating ligands [23]. For the second method, a chromi-
um(II) acidic aqueous solution is reacted with the ligand
under oxygen-free conditions, followed by air oxidation
[24]. The solution of chromium(II) is made from CrCl2
or chromium metal in HClO4 under a nitrogen atmo-
sphere.
Compounds 1, 5 and 6 can be prepared by either of
these techniques, i.e. from Cr(II) or CrCl3; however,
yields are better when using the Soxhlet method.
The reactions with the 2gb ligand yielded two differ-
ent types of chromium(III) compound, i.e. two mononu-
clear compounds 2 and 3, and a dinuclear species 4. The
dinuclear compound is bridged by two hydroxo moieties
and was obtained when a chromium(II) acid aqueous
solution was reacted with a methanolic solution of 2gb.
The coordination sphere of each chromium(III) con-
tains two chelating 2gb molecules. It is known that the
synthesis of the chromium(III) dinuclear species con-
taining hydroxo bridges requires the addition of a base;
however, in some instances this is not necessary, de-
pending on the basicity of the ligand and the molar ratio
of ligand to metal ion [16,17]. We here suggest that the
3.2. Spectroscopy
The main vibrational frequencies observed for the
benzimidazolic ring are those due to the w(NꢀH),
w(CꢁC)+w(CꢁN) vibrations, l(NꢀH) and l(CꢀH) benz-
imidazolic ring out of plane [8,10,25,26]. All the IR
spectra of the coordination compounds show these
vibrations, however in all cases the bands are shifted
towards higher energy as compared with the position in
the free ligand, Table 2. These results are indicative of
ligand coordination through the imidazolic nitrogen.
For the 2gb complexes the band due to w(NH···N) from
the guanidine group in the ligand [8] is shifted from 3444
to 3300 cm−1 for 2 and 3, and to 3341 cm−1 for 4.
The strong band at 1317 (bbimpy) and 1314 cm−1
(2pb) in the spectra of the ligands is shifted towards
higher energy and splitted upon chelation, indicating
coordination through the pyridinic nitrogen [27,28]. The
split band appears at 1321 and 1310 cm−1 for 5 and at
1323 and 1302 cm−1 for 6. In the low-frequency in-
frared spectra of 1, 5 and 6 the vibrational bands at 360,
343 and 361 cm−1, respectively, were assigned as
w(CrꢀCl) [29], corroborating the presence of coordi-
nated chlorides.
For Cr(III) hexacoordinated complexes there are
three spin-allowed transitions in the electronic spectrum,
w1 T2g’4A2g, w2 T1g(F)’4A2g and w3 T1g(P)’4A2g
4
4
4

A.E. Ceniceros-Go´mez et al. / Polyhedron 19 (2000) 1821–1827
1825
[30]. The diffuse reflectance spectra of compounds 1–6,
show three absorption bands, the first one in the region
from 16 600 to 20 050 cm−1, the second band from
20 000 to 25 400 cm−1 and the third from 25 000 to
36 100 cm−1, where w1 correspond to 10 Dq for each
complex (Table 2). The third band for compounds 1, 3,
4, 5 and 6 appears as a shoulder obscured by CT bands.
The electronic spectra of the compounds reported here
are in reasonable agreement with those in the literature
[30,31].
The magnetic moments at room temperature for
compounds 1, 2, 3, 5 and 6 correspond to the expected
values for mononuclear chromium(III) compounds.
Compound
4 has a magnetic moment at room
temperature of 4.96 MB, smaller than the expected
value (5.43 MB spin only) for a Cr(III) dinuclear
species [32]. Studies of the variable temperature
magnetic susceptibility of 4 were made at 3500 Oe and
in the temperature range 17–280.15 K. Least-squares
analysis was used to fit the data to a susceptibility
expression based on the isotropic spin Hamiltonian
[33]:
Fig. 2. Geometry for the cation [CrCl2ntb]+ in complex 1. Thermal
ellipsoids are at 50% probability level.
Table 3
,
Selected bond lengths (A) and angles (°) with s.u. in parentheses for
compound 1
Cr1ꢀN2
Cr1ꢀN3
Cr1ꢀCl2
2.047(3)
2.062(3)
2.2909(13)
Cr1ꢀN4
Cr1ꢀN1
Cr1ꢀCl1
2.050(3)
2.154(3)
2.3180(13)
H= −2J(S1·S2)
The best fit of the susceptibility data reveals that the
dinuclear compound has weak antiferromagnetic
coupling (J= −2.05 cm−1). This value is within the
range of those for other dinuclear di-v-hydroxo-
chromium(III) complexes [17].
N2ꢀCr1ꢀN4
N4ꢀCr1ꢀN3
N4ꢀCr1ꢀN1
N2ꢀCr1ꢀCl2
N3ꢀCr1ꢀCl2
N2ꢀCr1ꢀCl1
N3ꢀCr1ꢀCl1
Cl2ꢀCr1ꢀCl1
88.26(13)
157.18(14)
78.30(13)
95.75(10)
99.52(10)
172.76(11)
91.80(10)
91.45(5)
N2ꢀCr1ꢀN3
N2ꢀCr1ꢀN1
N3ꢀCr1ꢀN1
N4ꢀCr1ꢀCl2
N1ꢀCr1ꢀCl2
N4ꢀCr1ꢀCl1
N1ꢀCr1ꢀCl1
87.82(13)
82.95(13)
78.91(13)
103.23(10)
177.98(10)
89.30(10)
89.88(10)
3.3. Description of the structures
3.3.1. Complex 1
The cation [CrCl2ntb]+ is depicted in Fig. 2. Ntb acts
as a tetradentate ligand coordinating through the amine
N atom and the three benzimidazole N atoms to the
metal ion, as reported for a number of ntb complexes
[2]. Two Cl atoms in a cis configuration complete the
coordination sphere, yielding an hexacoordinated ar-
rangement for the metal. It should be mentioned that
only two related ntb-containing complexes with an
hexacoordinated metal environment have been reported
up to now, with Fe(II) [34] and Ni(II) [9]. On the other
hand, 1 is the first reported X-ray characterised
Cr(III)ꢀntb complex.
As expected, the tertiary N atom presents a bond
,
length about 0.10 A longer than those for the benzimi-
dazole N atoms (see Table 3). The tripodal ntb ligand is
forced to adopt a planar geometry in order to retain the
octahedral geometry on the metal–dihedral angle be-
tween the aromatic moieties containing the rings [N3,
N7] and [N4, N5] is 10.1°, while angles of these planes
with the third moiety [N2, N6] are 89.6 and 79.6°. This
uncommon spatial arrangement for ntb reflects the great
versatility of this tripodal ligand in order to take in the
preferred geometry of the metal ion. On the other
Fig. 3. Geometry for the cation [Cr2(2gb)4(m-OH)2]4+ in complex 4.
Thermal ellipsoids are at 30% probability level.

1826
A.E. Ceniceros-Go´mez et al. / Polyhedron 19 (2000) 1821–1827
Table 4
,
range 0.040–0.048 A. This point confirms that the
,
Selected bond lengths (A) and angles (°) for compound 4
coordinated 2gb ligand in 4 is the same as the free ligand
depicted in Fig. 1. However, deviations from an ideal
octahedral geometry are smaller than in the case of 1,
because 2gb acts as a bidentate ligand while ntb is
tetradentate: cis and trans angles for Cr1 are from
75.83(11) to 95.54(13)° and from 168.30(14) to
169.29(14)°, respectively, and ranges are similar for Cr2.
This distortion is reflected in the dihedral angles be-
tween the benzimidazolic rings for two 2gb coordinated
on the same metal centre: 29.0° between planes [N1, N3]
and [N21, N23] and 29.6° between planes [N41, N43]
and [N61, N63]. In spite of the parallel arrangement of
the benzimidazolic rings in the complex, no intramolec-
ular interactions are observed: the shortest calculated
separation between the centroids of the benzene rings is
Cr1ꢀO2
Cr1ꢀN12
Cr1ꢀN3
Cr2ꢀO1
Cr2ꢀN72
Cr2ꢀN63
1.960(3)
2.021(3)
2.045(3)
1.953(3)
2.019(3)
2.056(3)
Cr1ꢀO1
1.961(3)
2.023(4)
2.052(3)
1.955(3)
2.020(4)
2.060(3)
Cr1ꢀN32
Cr1ꢀN23
Cr2ꢀO2
Cr2ꢀN52
Cr2ꢀN43
O2ꢀCr1ꢀO1
O1ꢀCr1ꢀN12
O1ꢀCr1ꢀN32
O2ꢀCr1ꢀN3
N12ꢀCr1ꢀN3
O2ꢀCr1ꢀN23
N12ꢀCr1ꢀN23
N3ꢀCr1ꢀN23
75.83(11)
168.30(14)
92.86(13)
93.25(13)
84.10(14)
95.31(13)
89.10(14)
169.29(14)
O2ꢀCr1ꢀN12
O2ꢀCr1ꢀN32
N12ꢀCr1ꢀN32
O1ꢀCr1ꢀN3
N32ꢀCr1ꢀN3
O1ꢀCr1ꢀN23
N32ꢀCr1ꢀN23
92.50(14)
168.65(13)
98.82(15)
95.54(13)
88.72(14)
92.78(13)
84.14(14)
O1ꢀCr2ꢀO2
76.12(11)
169.49(14)
93.30(14)
92.25(13)
83.81(14)
95.06(13)
90.25(14)
170.85(14)
O1ꢀCr2ꢀN72
O1ꢀCr2ꢀN52
N72ꢀCr2ꢀN52
O2ꢀCr2ꢀN63
N52ꢀCr2ꢀN63
O2ꢀCr2ꢀN43
N52ꢀCr2ꢀN43
93.49(14)
169.32(14)
97.13(15)
94.87(13)
90.01(14)
92.23(13)
83.82(14)
O2ꢀCr2ꢀN72
O2ꢀCr2ꢀN52
O1ꢀCr2ꢀN63
N72ꢀCr2ꢀN63
O1ꢀCr2ꢀN43
N72ꢀCr2ꢀN43
N63ꢀCr2ꢀN43
,
4.13 A.
As in the previous case, numerous hydrogen bonds
which involve five water molecules, m-OH groups, NH
of imidazole, NH and NH2 of 2gb stabilise, the crystals
,
(H···A separations from 1.971 to 2.624 A).
Cr2ꢀO1ꢀCr1
104.03(12)
Cr2ꢀO2ꢀCr1
104.01(12)
4. Supplementary data
Supplementary data are available from the CCDC on
request, quoting the deposition numbers CCDC 140724
(1) and 140725 (4). The information can be obtained
free of charge from The Director, Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge, CB2
1EZ, UK (Fax: +44-1223-336033; e-mail: deposit@
ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
hand, the Cr ion lies in the plane formed by N1, N3, N4
,
and Cl2 (calculated maximal deviation: 0.025 A). As a
result of these features, the deviations from an ideal
octahedral geometry around the Cr ion are the follow-
ing: trans angles range from 157.18(14) to 177.98(10)°
and cis angles from 78.30(13) to 99.52(10)°.
Ethanol and water molecules included in the cell form
a complex tri-dimensional network of hydrogen bonds
using benzimidazolic N atoms and chlorine atoms as
acceptors (H···A separations in the range 1.854–2.468
Acknowledgements
,
A), which probably greatly stabilises the crystal.
We acknowledge grant DGAPA-UNAM IN 222096
for financial support. S.B. is grateful to Dr Cecilia
Rodr´ıguez de Barbar´ın (Monterrey, Me´xico) for diffrac-
tometer time and UNAM for financial support. A.E.C.-
G. thanks CONACyT and DGEP for a scholarship. We
thank M. Franco-Gutie´rrez, R.P. Fierro and Antonio
Morales for technical support.
3.3.2. Complex 4
Complex 4 is the first X-ray characterised Cr(III)
complex including 2gb as ligand. The dinuclear cation
[Cr2(2gb)4(m-OH)2]4+ is depicted in Fig. 3. It should be
mentioned that the charge of the cation is in line with
the four ClO4− anions present in the asymmetric unit
and with the fact that the H atoms of the OH groups
were found on difference Fourier maps. The (m-OH)2
bridge is symmetric, with CrꢀO bond lengths in the
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