Studies on Zinc(II) perchlorate complex with tripod ligand tris(N-methylbenzimidazol-2-ylmethyl)amine and salicylate

Article abstract of DOI:10.1080/15533170903129240

A novel five-coordinate zinc(II) complex with the tripod ligand tris(N-methylbenzimidazol-2-ylmethyl)amine (Mentb) and salicylate, with the composition [Zn(Mentb)(salicylate)](ClO4) 1.5DMF, was synthesized and characterized by means of elemental analyses,

Full text of DOI:10.1080/15533170903129240

Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 39:361–366, 2009
Copyright © Taylor & Francis Group, LLC
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533170903129240
Studies on Zinc(II) Perchlorate Complex with Tripod Ligand
Tris(N-methylbenzimidazol-2-ylmethyl)Amine
and Salicylate
Huilu Wu, Kaitong Wang, Xingcai Huang, Ruirui Yun, Tao Sun, Ke Li,
and Xuyang Fan
School of Chemical and Biological Engineering, Lanzhou Jiaotong University, Lanzhou, China
helminthics amongst others.[5] Tripodal ligands have long been
used in both coordination and organometallic chemistry,[6−7]
typically polypyrazolylborate and tris(2-pyridyl) tripodal lig-
ands. However, their potential use in supramolecular chemistry
for the construction of various cagelike or boxlike complexes
has not been fully realized until quite recently.[8−10] In particular,
the use of C3-symmetric tripodal ligands in crystal engineering
has been reviewed.[11] The tetradentate tripodal ligand, tris(N-
methylbenzimidazol-2-ylmethyl)amine (Mentb) (Figure 1), is
similar to the imidazole in terms of its mode of coordination.[12]
Since the three arms of this type of ligand can each rotate
freely around an N(apical)-C bond, multicomponent complexes
or coordination polymeric networks may be expected to form
the assembly of this ligand by metal ions of low coordination
number.[13−17] In this paper, we have prepared and investigated
the properties and crystal structure of the zinc(II) complex with
Mentb and salicylate as an exogenous ligand. The zinc(II) in the
complex adopts a distorted trigonal-bipyramidal coordination
geometry with the N4O ligand donor set.
A novel five-coordinate zinc(II) complex with the tripod ligand
tris(N-methylbenzimidazol-2-ylmethyl)amine (Mentb) and salicy-
late, with the composition [Zn(Mentb)(salicylate)](ClO4) · 1.5DMF,
was synthesized and characterized by means of elemental analy-
ses, electrical conductivities, thermal analyses, i.r., u.v. and 1H-
n.m.r. spectra. The crystal structure of the complex has been de-
termined by a single-crystal X-ray diffraction method, and shows
that the ZnII atom is bonded to a tris(N-methylbenzimidazol-2-
ylmethyl)amine (Mentb) ligand and a salicylate molecule through
four N atoms and one O atom, giving a distorted trigonal-
bipyramidal coordination geometry [τ(Zn) = 0.78], with approxi-
mate C3 molecular symmetry.
Keywords Crystal structure, synthesis and characterization, tris(N-
methylbenzimidazol-2-ylmethyl)amine, zinc(II) complex
INTRODUCTION
Imidazole is a typical heterocyclic ligand with nitrogen as
the donor atom. It is also a component of biologically im-
portant molecules.[1] Because of this, the coordination chem-
istry of related ligands has been the subject of numerous
investigations.[1] Amongst them, the coordinating behavior of
chelating benzimidazolic ligands has been studied by several
research groups, some of them with an interest in mimick-
ing biological activities.[2−4] Benzimidazoles exhibit a wide
variety of pharmacological activities like fungicides or anti-
EXPERIMENTAL
Materials and Physical Measurements
All chemicals were reagent grade and were used without
further purification. C, H and N elemental analysis were de-
termined using a Carlo Erba 1106 elemental analyzer. Metal
contents were determined by EDTA titration. Thermal stud-
ies of the complex was made in the 25–800◦C range us-
ing a ZRY-2P thermal analyser with a heating rate of 10◦C
min−1. The IR spectra were recorded in the 4000–400 cm−1
region with a Nicolet FI-IR AVATAR 360 spectrometer us-
ing KBr pellets. Electronic spectra were taken on a TU-
Received 10 February 2009; accepted 10 March 2009.
The authors acknowledge the financially support and grant from
‘Qing Lan’ Talent Engineering Funds and Students’ Science and Tech-
nology Innovation Funds (grant no. DXS2008-041) by Lanzhou Jiao- Visible spectrophotometer. Electrolytic conductance measure-
tong University. The grant from the Middle-Young Age Science Foun-
ments were made with a DDS-11A type conductivity bridge
dation (grant no. 3YS061-A25-023) and ‘Long Yuan Qing Nian’ of
using a 10−3 mol L−1 solution in DMF at room temperature.
Gansu Provinceis also acknowledged.
Address correspondence to Dr. Hui-Lu Wu School of Chemical
and Biological Engineering, 88 West Anning Rd., Lanzhou Gansu,
1H NMR spectra were recorded on a Bruker AM200A NMR
spectrometer with TMS as internal standard and d6-DMSO as
Lanzhou 730070, China. E-mail: wuhuilu@163.com
solvent.
361

362
H. WU ET AL.
TABLE 1
Crystal data and structure refinement for
[Zn(Mentb)(salicylate)] (ClO4)· 1.5DMF
Formula
C38.5H42.5ClZnN8.5O8.50
861.13
monclinic
Molecular weight (g mol−1
Crystal system
)
Space group
C2/c
Unit cell dimensions
˚
a (A)
27.7110 (7)
11.4499 (3)
25.1395 (6)
102.829 (1)
7777.3 (3)
8
˚
b (A)
FIG. 1. Structure of Mentb.
˚
c (A)
β (◦)
Preparation of Tris(N-methylbenzimidazol-2-ylmethyl)
amine (Mentb) and the Zinc Complex
3
˚
Vol (A )
Z
Tris(N-methylbenzimidazol-2-ylmethyl)amine
(Mentb).
T (K)
153 (2)
1.471
0.77
3584
This compound was synthesized by the literature method.[12]
Yield: 4.6 g (51%); m.p.: 215–217◦C (m.p.: 215◦C in the
literature [12]). The infrared spectra and 1H NMR spectra of the
Mentb were consistent with the literature.[12]
D (calculated) (g· cm−3
)
Absorption coefficient (mm−1
F(000)
)
Crystal size (mm)
0.78 × 0.59 × 0.52
[Zn(Mentb)(salicylate)](ClO4)·1.5DMF. To a stirred solu-
tion of tris(N-methylbenzimidazol-2-ylmethyl)amine (0.0899 g,
0.2 mmol) in hot MeOH (10 mL) was added Zu(ClO4)2·6H2O
(0.0745 g, 0.2 mmol), followed by a solution of Na(salicylate)
(0.0320 g, 0.2 mmol) in MeOH (5 mL). A colorless crystalline
product formed rapidly. The precipitate was filtered off, washed
with MeOH and absolute Et2O, and dried in vacuo. The dried
precipitate was dissolved in DMF to a colorless solution that
was allowed to evaporate at room temperature. colorless crys-
tals suitable for X-ray diffraction studies were obtained after two
weeks. Yield, 0.085 g (49%). (found: C, 53.74; H, 5.01; N,13.66;
Zn, 7.24. Calcd. for C38.5H42.5ClZnN8.5O8.50 (MW 861.16):
C, 53.70; H, 4.97; N, 13.83; Zn, 7.59%). ꢀM(DMF, 297 K):
θ range for data collection (◦) 3.02 to 27.48
Index ranges
−35 ≤ h ≤ 34, −14 ≤ k ≤
14, −32 ≤ l ≤ 32
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Full-matrix least-squares on
F2
8893[R(int) = 0.0242]/
8/600
1.002
Finial R1 and wR2 [I > 2σ(I)] 0.0363, 0.1060a
R1 and wR2 indices (all data)
0.0425, 0.1113
aw = 1/[σ2F20 + (0.0680P)2 + 9.5996P], where P = (F02 + 2F2c)/3.
64.7 S cm2 mol−1
.
atoms of this molecule are refined with isotropic displacement
parameters. The largest peak in the residual electron density
is associated with the perchlorate anion. The crystal data and
experimental parameters relevant to the structure determination
are listed in Table 1 and the final positional and thermal param-
eters are available as supplementary material.
X-ray Structure Determination of [Zn(Mentb)(salicylate)]
(ClO4)· 1.5DMF
All data were mounted using a Rigaku R-axis Spider diffrac-
tometer with the graphite-monochromated MoKα radiation
(λ = 0.071073 nm) at 153 (2) K. Data reduction and cell re-
finement were performed using Rapid Auto programs.[18] The
absorption corrections were carried out by the multi-scan. The
structure was solved by direct methods (Bruker Shelxtl) using
RESULTS AND DISCUSSION
The zinc complex is soluble in DMF and DMSO, but insol-
all unique data.[19] All H atoms associated with the cation were uble in water and organic solvents, such as methanol, ethanol,
visible in difference Fourier maps but were placed geometri- benzene, petroleum ether, trichloromethane etc. The elemental
˚
cally with C–H distances ranging from 0.95 to 0.99 A and O–H analyses show that the composition is [Zn(Mentb)(salicylate)]
˚
= 0.82 A. They were allowed to ride during subsequent refine- (ClO4)·1.5DMF. A comparsion of molar conductance value,
ment with Uiso(H) = 1.2 or 1.5 Ueq(C/O). The DMF molecule shows the 1:1 electrolytes of the complex in DMF with those
on the general position is refined in two coplanar orientation, previously reported in the literature.[20]
each with 50% site occupancy. The DMF molecule lying on the
Thermogravimetric analysis (TGA) curve of the zinc(II)
twofold rotation axis is modelled as one molecule with 50% complex shows that the initial mass loss within the 163–167◦C
site occupancy, with bond distancees tightly resrtained (C40– range is attributed to elimination of the DMF molecules. Dif-
O9 = 1.200 (5), C40–N9 = 1.320 (5), N9–C37/C38 = 1.420 ferential thermal analysis (DTA) curve indicates that the pro-
˚
(5) A) and the whole molecule restrained to be plainar. The cess appears an endothermic peak. The decomposition of the

STUDIES ON ZINC(II) PERCHLORATE COMPLEX
363
FIG. 2. The [Zn(Mentb)(salicylate)]+ cation with displacement ellipsoids drawn at the 50% probability level. H atoms are omitted.
complex starts at 242◦C and is completed at ca 575◦C, yielding consists of a discrete [Zn(Mentb)(salicylate)] cation, a perchlo-
ZnO as the final product.
rate anion, 1.5 molecules of DMF molecules. One dimethylfor-
mamide molecule lies on a general position and is disordered
over two coplanar orientations with equal occupancy. A second
dimethylformamide molecule is disordered about a twofold ro-
tation axis. The ZnII atom is five-coordinate with a ZnN4O chro-
mophore. The Mentb ligand acts as a tetradentate N-donor, and
an O atom of carboxylate groups of the salicylate complete the
Crystal Structure of [Zn(Mentb)(salicylate)]
(ClO4)·1.5DMF
The molecular structure and crystal packing of the zinc(II)
complex are shown in Figures 2 and 3; selected bond dis-
tances and angles are shown in Table 2. The asymetric unit
FIG. 3. Packing diagram. H atoms are omitted for clarity.

364
H. WU ET AL.
coordination. The coordination geometry of the ZnII atom is best
TABLE 2
◦
˚
Selected bond distances (A) and bond angles ( )
described as distorted trigonal-bipyramid (τ = 0.84), with ap-
proximate molecular symmetry C3. The parameter τ is defined
as (β – α)/60 [where β = N(7)–Zn–O(1), α = N(1)–Zn–N(5)]
and its value varies from 0 (in regular square-based pyramidal) to
1 (in regular trigonal bipyramidal).[21] The coordination geome-
try around the ZnII atoms appears to relieve the steric crowding.
The equatorial plane is occupied by three N atoms of three
benzimidazolyl groups, while the ZnII atom protrudes towards
Bond distances
Zn–O(1)
Zn–N(1)
Zn–N(3)
Bond angles
1.9970 (16) Zn–N(5)
2.0780 (16) Zn–N(7)
2.0521 (17)
2.4361 (18)
3.135 (2)
. . .
2.0463 (18) Zn O(2)
O(1) Zn N(1) 92.78 (7) N(1) Zn N(7)
O(1) Zn N(3) 113.72 (7) N(3) Zn N(7)
O(1) Zn N(5) 110.70 (7) N(5) Zn N(7)
N(1) Zn N(3) 112.91 (7) C(28) O(1) Zn
N(3) Zn N(5) 110.35 (7) O(1) C(28) O(2)
73.14 (6)
74.68 (7)
74.91 (6)
123.95 (14)
123.6 (2)
˚
O(1) and is 0.560(2) A from the plane of atoms N(1)/N(3)/N(5).
The axial positions are occupied by N(7) and O(1), with Zn-
˚
˚
N(7) 2.4361(18) A, Zn-O(1) 1.9966(14) A and N(7)-Zn-O(1)
is 165.79(6)◦. The three benzimidazole ring arms of the Mentb
ligand form a cone-shaped cavity. The angles N(3)–Zn–N(1),
N(5)–Zn–N(1) and N(5)–Zn–N(3) are 112.96(6), 115.33(6) and
110.38(6)◦, respectively. The N(7)–Zn–N(1) 73.13(6), N(7)–
Zn–N(3) 74.72(6) and N(7)–Zn–N(5), 74.86(6)◦ angles, which
are all ca 16◦ less than the ideal 90◦, are imposed by the geome-
try of the Mentb ligand. The distance between ZnII and O(2) is
N(5) Zn N(1) 115.42 (6) O(1) C(28) C(29) 117.67 (19)
O(1) Zn N(7) 165.80 (6) O(2) C(28) C(29) 118.76 (19)
TABLE 3
◦
˚
˚
3.135(2) A, so O(2) is not coordinated. The angles and distance
Selected hydrogen bonding distances (A) and angles ( )
in the Mentb and salicylate are within the normal ranges. Weak
supramolecular π · · · π , OH–O hydrogen-bonding interactions
play important roles in the crystal packing modes in the complex
(Figure 3). The selected hydrogen bonds are listed in Table 3.
. . .
D H
. . .
. . .
. . .
D H A
A
D H
0.84
D
A
H
A
. . .
O3 H3 O2
2.556 (3)
1.82
146
TABLE 4
I.r. spectral data for the Zn complex and their relative assignments (cm−1
)
Compounda
νasCOO
νsCOO
ꢁν
ν Ar O
ν C N
ν C N C C
ν ClO−4
NaL
Mentb
Zn complex
1523 s
—
1594 s
1374 s
—
1367 s
149
—
227
1228 m
—
1245 m
—
1515 m
1499 m
—
1475 s
1458 s
—
—
1085 bs
aL = salicylate; b = broad; s = strong; m = mediun.
TABLE 5
1H-N.M.R. data for the Mentb and Zn complex (solvent d6-DMSO)a
δ Ha1
δHa2
δHb
δCH2
δCH3
δOH
Compound
(m)
(m)
(m)
(s)
(s)
(bs)
Mentb
Zn complex
7.66
8.13
7.24
7.72
7.22
7.36
4.22
4.71
3.45
3.93
—
9.23
am = multiple, s = singlet, bs = broad singlet.

STUDIES ON ZINC(II) PERCHLORATE COMPLEX
365
SUPPORTING INFORMATION AVAILABLE
I.r. and Electronic Spectra
Crystallographic data (excluding structure factors) for the
structure in this paper have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication
CCDC 669530 Copies of the data can be obtained, free of charge,
on application to the CCDC, 12 Union Road, Cambridge CB2
1EZ, UK.
The i.r. spectra data for the zinc complex along with their rel-
ative assignments are given in Table 4. In the free ligand Mentb,
a strong band is found at ca 1475 cm−1 together along with a
weak band at 1515 cm−1. By analogy with the assigned bands
of imidazole, the former can be attributed to ν (C N Cd C),
while the latter can be attributed to ν (C N).[12,22−23] They shift
to the higher frequency ca 16–17 cm−1 in the complex, which
implies direct coordination of all four imine nitrogen atoms to
zinc(II). This is the preferred nitrogen atom for coordination as
found for other metal complexes with benzimidazoles.[24] Infor-
mation regarding the possible bonding modes of the perchlorate
may also be obtained from the i.r. spectra. The strong, fairly
broad absorption band at 1085 cm−1 indicate that the ionic per-
chlorate groups (Td) are present.[25] Since the carboxylate group
can coordinate to the metal ion in a bidentate or a monodentate
fashion, the ‘ꢁ criterion’, which is based on the difference be-
tween the νas (O C O) and νs (O C O) values, compared to
the corresponding value in sodium carboxylate, is currently em-
ployed to determine the coordinating mode of the carboxylate
group.[26,27] The data in Table 4 suggests that the carboxylate
group of salicylate in the complex behaves as a monodentate
ligand. This conclusion is confirmed by the result of the crystal
structure analysis.
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