Coordination polymers with adjustable dimensionality based on CuII and bis-imidazolyl bridging ligand

Article abstract of DOI:10.1007/s11172-016-1677-4

1,4-Bis(imidazol-1-yl)butane was synthesized from imidazole and 1,4-dibromobutane in an alkaline medium. A variation of the molar ratio of reagents in the system copper(II) chloride dihydrate and 1,4-bis(imidazol-1-yl)butane (bImB) upon heating in N,N-dimethylformamide resulted in the synthesis of two new coordination polymers [Cu(bImB)Cl₂] (1) and [Cu(bImB)₂Cl₂] (2), which were structurally characterized. Product 1 was found to possess a chain structure, while structure 2 is built of neutral layers, with the dimensionality of the extended coordination structures being determined by the reaction conditions. The new compounds were characterized by IR spectroscopy, elemental analysis, and powder X-ray diffraction data.

Full text of DOI:10.1007/s11172-016-1677-4

Russian Chemical Bulletin, International Edition, Vol. 65, No. 12, pp. 2914—2919, December, 2016
2914
Coordination polymers with adjustable dimensionality
based on CuII and bisꢀimidazolyl bridging ligand*
M. O. Barsukova,a D. G. Samsonenko,a,b T. V. Goncharova,c A. S. Potapov,c,d
S. A. Sapchenko,a,b D. N. Dybtsev,a,b and V. P. Fedina,b

aA. V. Nikolaev Institute of Inorganic Chemistry,
Siberian Branch of the Russian Academy of Sciences,
3 prosp. Akad. Lavrent´eva, 630090 Novosibirsk, Russian Federation.
Fax: +7 (383) 330 9489. Eꢀmail: cluster@niic.nsc.ru
bNovosibirsk State University, Department of Natural Sciences,
2 ul. Pirogova, 630090 Novosibirsk, Russian Federation
cI. I. Polzunov Altai State Technical University,
46 prosp. Lenina, 656038 Barnaul, Russian Federation
dNational Research Tomsk Polytechnic University,
30 prosp. Lenina, 634050 Tomsk, Russian Federation
1,4ꢀBis(imidazolꢀ1ꢀyl)butane was synthesized from imidazole and 1,4ꢀdibromobutane in an
alkaline medium. A variation of the molar ratio of reagents in the system copper(II) chloride
dihydrate and 1,4ꢀbis(imidazolꢀ1ꢀyl)butane (bImB) upon heating in N,Nꢀdimethylformamide reꢀ
sulted in the synthesis of two new coordination polymers [Cu(bImB)Cl2] (1) and [Cu(bImB)2Cl2]
(2), which were structurally characterized. Product 1 was found to possess a chain structure, while
structure 2 is built of neutral layers, with the dimensionality of the extended coordination structures
being determined by the reaction conditions. The new compounds were characterized by
IR spectroscopy, elemental analysis, and powder Xꢀray diffraction data.
Key words: coordination polymer, copper, bis(imidazolyl)alkanes, Xꢀray diffraction.
Imidazole is a part of many biological molecules such
properties. In the present work, we describe the synthesis
of the organic ligand 1,4ꢀbis(imidazolꢀ1ꢀyl)butane
(bImB), as well as the preparation, crystal structure, and
spectral analysis of two coordination polymers on its basis
with copper(II) cations.
It was found that the
dimensionality of coorꢀ
dination compounds can
be varied on demand
as histidine. The chemistry of copper(II) imidazolyl comꢀ
plexes is closely related to the presence of such fragments
in the nature as active sites of different enzymes.1
From the point of view of coordination chemistry,
copper(II) imidazolyl complexes are of interest due to the
structural diversity, redox,2 luminescent,3 as well as magꢀ
netic properties,4 which arouse from the paramagnetic
nature of Cu2+ cations. An additional impulse to the
studies of chemistry of copper imidazolyl complexes was
given after discovery of their antitumor activity.5,6 At
the same time, organic bridging ligands with imidazolyl
functional groups are actively used for the design of coorꢀ
dination polymers. Such compounds possess a number
of unique properties, including ionꢀexchange, sensor,
and sorption properties, which frequently are conjugated
with the structural transformations of the metalꢀorganic
framework.7 In this connection, the use of structurally
flexible bis(imidazolyl)alkane bridging ligands in the synꢀ
thesis of coordination polymers is promising for the studꢀ
ies of possible structural transitions and related functional
from oneꢀdimensional (chain) to twoꢀdimensional (netꢀ
work) depending on the conditions of the synthesis.
Results and Discussion
The organic ligand 1,4ꢀbis(imidazolꢀ1ꢀyl)butane
(bImB) was synthesized using a suggested by us new methꢀ
od, namely, by the reaction of imidazole with 1,4ꢀdibroꢀ
mobutane in a superbasic medium DMSO—KOH. Earlier,
this reaction was carried out either by using phaseꢀtransfer
catalysis,8 or generating an imidazolate anion upon treatꢀ
ment with sodium hydride.9 Our method does not require
expensive phaseꢀtransfer catalysts or metal hydrides and
provides higher, nearly quantitative yield.
* Dedicated to Academician of the Russian Academy of Sciences
R. Z. Sagdeev on the occasion of his 75th birthday.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2914—2919, December, 2016.
1066ꢀ5285/16/6512ꢀ2914 © 2016 Springer Science+Business Media, Inc.

1D and 2D coordination polymers
Russ.Chem.Bull., Int.Ed., Vol. 65, No. 12, December, 2016
2915
In the synthesis of coordination polymers
[Cu(bImB)Cl2] (1) and [Cu(bImB)2Cl2] (2), we used
copper(II) chloride dihydrate as a source of copper, which
was involved in the reaction with different amounts of the
organic bridging ligand bImB upon heating in a mixture
of N,Nꢀdimethylformamide (DMF) and methanol. Deꢀ
pending on the molar ratio of the starting reagents
CuCl2•2H2O : bImB = 1 : 1 or 1 : 3, we obtained single
crystals of two coordination polymers, the structure of
which was established by Xꢀray diffraction.
The single crystal Xꢀray diffraction data showed that
the asymmetric unit of structure 1 contains one copper(II)
cation, two chloride anions, and one molecule of
1,4ꢀbis(imidazolꢀ1ꢀyl)butane, which occupy general poꢀ
sitions. The coordination environment of copper(II) conꢀ
sists of two nitrogen atoms of the imidazole rings and two
chloride anions (Fig. 1). The distances Cu—N are 1.950(3)
and 1.952(3) Å, the distances Cu—Cl are 2.2600(10) and
2.2702(10) Å. The coordination polyhedron can be reꢀ
garded as a strongly distorted (flattened along the axis C2)
tetrahedron. The angles N—Cu—N and Cl—Cu—Cl are
149.97(13)° and 142.84(4)°, respectively. The molecule of
1,4ꢀbis(imidazolꢀ1ꢀyl)ꢀbutane acts as a bridging ligand
coordinated to the two copper(II) cations. Each copper(II)
cation coordinates two organic ligands, forming a zigzagꢀ
like polymeric chain (see Fig. 1). The polymeric chains are
laid in layers parallel to the plane ac, which, in turn, form
a doubleꢀlayer packing. The polymeric chains are parallel
inside the layer, the chains from the neighboring layers
form crossed straight lines at an angle of ~74.4° (Fig. 2).
The polymeric chains are linked to each other by the van
der Waals interactions.
The asymmetric unit of structure 2 contains one
copper(II) cation, one chloride anion, and one molecule
of 1,4ꢀbis(imidazolꢀ1ꢀyl)butane. The copper(II) cations
occupy position 2a (one of the systems of inversion cenꢀ
ters: 0, 0, 0; 0, 1/2, 1/2). The coordination environment
of the copper(II) cation consists of four nitrogen atoms of
the imidazole rings and two chloride anions. The coordiꢀ
nation polyhedron is an octahedron elongated along the
axis C4, where the nitrogen atoms of the imidazole rings
are located in the equatorial plane, while the axial posiꢀ
tions are occupied by the chloride anions (Fig. 3). The
distances Cu—N are 2.022(2) and 2.030(2) Å, the disꢀ
tance Cu—Cl is 2.9247(6) Å. The molecule of 1,4ꢀbisꢀ
(1ꢀimidazolyl)butane acts as a bridging ligand coordiꢀ
nated to the two copper(II) cations. Each copper(II)
cation, in turn, coordinates four organic ligands, forming
Cl(2)i
N(4)ii
Cu(2)i
Cl(1)i
N(1)i
N(2)i
N(3)i
N(4)i
Cl(2)
Cu(1)
N(1)
Cl(1)
N(2)
Cl(2)iii
N(3)
N(4)
Cl(1)iii
Cu(1)iii
N(1)iii
Fig. 1. A fragment of the polymeric chain in structure 1 (displacement ellipsoids at 50% probability). Hydrogen atoms are omitted.
The coordinates of symmetrically equivalent atoms were obtained by the following symmetry operations: i) 1/2 + x, 3/2 – y, 1 + z; ii) 1 + x,
y, 2 + z; iii) –1/2 + x, 3/2 – y, –1 + z.

2916 Russ.Chem.Bull., Int.Ed., Vol. 65, No. 12, December, 2016
Barsukova et al.
c
a
Fig. 2. The packing of the polymeric chains in structure 1. Hydrogen and chlorine atoms are omitted. Positions of copper(II) cations are shown
as spheres. The chains of the neighboring layers are shown in different shades of grey.
a polymeric layer of the sql topology (Fig. 4). The layers
form a threeꢀlayer close packing, being placed on the
system of (102) planes. The polymeric layers are linked to
each other by the van der Waals interactions.
C—C. The C—N stretching vibrations of the imidazolyl
ring were found at 1093 and 1110 cm–1 for compounds 1
and 2, respectively.
Note that the formation of the chain structure 1 or the
layered structure 2 takes place under absolutely identical
reaction conditions, except the concentration of the orꢀ
ganic ligand bImB. The use of the lower concentration
(the molar ratio metal : ligand = 1 : 1) leads to the formaꢀ
tion of the chain product 1 with a similar formula ratio
Cu : bImB = 1. When an excess of the ligand is used
(metal : ligand = 1 : 3), product 2 with the layered strucꢀ
ture and a formula ratio Cu : bImB = 0.5 crystallizes from
the reaction mixture. The literature data show that the
formation of the chain coordination polymers similar to
The phase purity of the samples of compounds 1 and 2
was confirmed by powder Xꢀray diffraction. The experiꢀ
mental diffractograms of compounds 1 and 2 are in good
agreement with those calculated from the single crystal
Xꢀray diffraction data (Fig. 5). The IR spectra of comꢀ
pounds 1 and 2 showed absorption bands attributed to the
stretching vibrations ν(O—H) of the adsorbed water molꢀ
ecules at 3467 and 3424 cm–1, respectively. The vibrations
in the region of 2950—3124 cm–1 correspond to the asymꢀ
metric and symmetric vibrations of the ligand fragments

1D and 2D coordination polymers
Russ.Chem.Bull., Int.Ed., Vol. 65, No. 12, December, 2016
2917
N(4)i
N(3)i
N(2)i
N(1)ii
Cl(1)
N(1)i
N(2)ii
N(4)iii
N(4)ii
Cu(1)
N(3)iii
N(2)iii
N(1)iii
N(3)ii
Cl(1)i
N(1)
N(2)
N(3)
N(4)
Fig. 3. Coordination environment of the copper(II) cation in structure 2 (displacement ellipsoids at 50% probability). Hydrogen atoms are
omitted. The coordinates of symmetrically equivalent atoms were obtained by the following symmetry operations: i) –x, 1 – y, 1 – z; ii) –1 + x,
3/2 – y, 1/2 + z; iii) 1 – x, –1/2 + y, 1/2 – z.
b
a
c
Fig. 4. A fragment of the polymeric layer in structure 2. Hydrogen atoms are omitted. Positions of copper(II) cations are shown as spheres.

2918 Russ.Chem.Bull., Int.Ed., Vol. 65, No. 12, December, 2016
Barsukova et al.
Experimental
a
1
The starting compounds, i.e., copper(II) chloride dihydrate,
N,Nꢀdimethylformamide, and methanol, were at least of reagent
grade and used without additional purification. IR spectra were
recorded on a Scimitar FTS 2000 Fourierꢀtransform spectrometer
in the 4000—400 cm–1 range in KBr pellets. NMR spectra were
recorded on a Bruker AVꢀ300 spectrometer (300 MHz for protons,
75 MHz for 13C). Elemental analysis was carried out on a Euro EA
3000 analyzer in the Analytical Laboratory of the A. V. Nikolaev
Institute of Inorganic Chemistry, Siberian Branch of the Russian
Academy of Sciences. Powder Xꢀray diffraction data were recorded
2
b
1´
2´
on
a
Shimadzu XRD 7000S powder diffractometer
(CuꢀKα radiation).
10
15
20
25
30
2θ
1,4ꢀBis(imidazolꢀ1ꢀyl)butane (bImB). A mixture of imidazole
(1.36 g, 20 mmol), powdered KOH (1.68 g, 30 mmol), and DMSO
(5 mL) was stirred at 80 °C for 30 min and cooled, then 1,4ꢀdibroꢀ
mobutane (2.16 g, 10 mmol) in DMSO (5 mL) was added dropwise
and the stirring was continued for another 8 h at 80 °C. Then, the
reaction mixture was diluted with water (200 mL) and a mixture of
water and DMSO was removed in vacuo. A solid residue was
treated with boiling ethyl acetate to extract an organic product, the
extract was distilled in vacuo. The yield was 95%, colorless crystals,
m.p. 81—83 °C. Found (%): C, 63.2; H, 7.5; N, 29.5. C10H14N4.
Calculated (%): C, 63.3; H, 7.4; N, 29.5. IR, ν/cm–1: 1577, 1461,
Fig. 5. Comparison of experimental (1, 1´) and simulated (2, 2´)
Xꢀray diffraction patterns for compound 1 (a) and compound 2 (b).
structure 1 in the system copper—bis(imidazolꢀ1ꢀyl)ꢀ
butane was observed when copper(I) chloride and broꢀ
mide were used in the solvothermal synthesis,10,11 as
well as under conditions of slow diffusion from the methꢀ
anolic solution of the ligand to the aqueous solution of
copper(II) chloride,12 with the halide ions being includꢀ
ed in the coordination environment of copper cations.
The formation of the layered coordination polymer with
a squareꢀtype topology of the polymeric layer was obꢀ
served in the case of a slow diffusion from a methanolic
solution of 1,4ꢀbis(imidazolꢀ1ꢀyl)butane to the aqueous
solution of copper(II) bromide.12 Apart from that, the
formation of layered coordination polymers was observed
upon standing of aqueous solutions containing copper(II)
chloride, nitrate, or sulfate, with the indicated counteriꢀ
ons not being included in the coordination sphere of the
copper(II) cation.13 To sum up, according to the analysis
of the published data, the formation of either
oneꢀdimensional or twoꢀdimensional structure of a givꢀ
en coordination polymer depends simultaneously on many
difficultꢀtoꢀsystematize parameters, which include the
nature of anion used in the synthesis of copper salts, the
metal oxidation state, solvent, and method of synthesis.
In the present work, we showed that a controlled formaꢀ
tion of a layered or a chain coordination polymer can
occur depending on only one parameter of the reaction
mixture, namely, the ratio of reagents.
In conclusion, we optimized a procedure for the synꢀ
thesis of the flexible bridging ligand 1,4ꢀbis(imidazolꢀ
1ꢀyl)butane and obtained two coordination polymers on
its basis with copper(II) chloride. The composition, the
structure, and the phase purity of the products were esꢀ
tablished by singleꢀcrystal Xꢀray diffraction and confirmed
by elemental analysis, IR spectroscopy, and powder Xꢀ
ray diffraction. The ratio of the reagents in the reaction
mixture was found to influence the dimensionality of the
coordination compound, that leads to the formation of
chain or layered structure.
1
1431 (Im). H NMR (DMSOꢀd6), δ: 1.33 (t, 2 H, ImCH2CH2,
J = 8 Hz); 3.95 (t, 4 H, ImCH2CH2, J = 8 Hz); 6.85 (d, 2 H,
HIm(4), J = 2 Hz); 7.01 (d, 2 H, HIm(5), J = 2 Hz); 7.61 (s, 2 H,
H
Im(2)). 13C NMR (DMSOꢀd6), δ: 27.7 (ImCH2CH2); 45.3
(ImCH2CH2); 119.3 (CIm(5)); 128.4 (CIm(4)); 137.2 (CIm(2)).
catenaꢀDichloroꢀ1,4ꢀbis[(imidazolꢀ1ꢀyl)butane]copper
[Cu(bImB)Cl2] (1). A mixture of CuCl2•2H2O (17 mg, 0.1 mmol),
1,4ꢀbis(imidazolꢀ1ꢀyl)butane (19 mg, 0.1 mmol), N,Nꢀdimethylꢀ
formamide (2 mL), and methanol (2 mL) was heated in a glass vial
with a screw cap at 100 °C for 24 h. The crystals formed were
washed with N,Nꢀdimethylformamide (5×1 mL) and dried in air.
The yield was 26 mg (80% calculated on Cu). Found (%): C, 36.5;
H, 4.7; N, 17.0. C10H14Cl2CuN4. Calculated (%): C, 37.0; H, 4.4;
N, 17.3. IR (KBr), ν/cm–1: 3468 (w), 3124 (s), 2932 (m), 1638
(m), 1520 (s), 1448 (s), 1409 (m), 1369 (m), 1279 (m), 1236 (s),
1093 (s), 956 (m), 863 (m), 757 (m), 656 (s), 629 (m), 572 (w),
438 (w).
catenaꢀDichloroꢀbis[1,4ꢀbis(imidazolꢀ1ꢀyl)butane]copper
[Cu(bImB)2Cl2] (2). A mixture of CuCl2•2H2O (17 mg, 0.1 mmol),
1,4ꢀbis(imidazolꢀ1ꢀyl)butane (57 mg, 0.3 mmol), N,Nꢀdimethylꢀ
formamide (2 mL), and methanol (2 mL) was heated in a glass vial
with a screw cap at 100 °C for 24 h. The crystals formed were
washed with N,Nꢀdimethylformamide (5×1 mL) and dried in air.
The yield was 37 mg (72% calculated on Cu). Found (%): C, 46.0;
H, 5.8; N, 21.4. C20H28Cl2CuN8. Calculated (%): C, 46.6; H, 5.5;
N, 21.8. IR (KBr), ν/cm–1: 3424 (w), 3122 (s), 2941 (m), 1639
(m), 1518 (s), 1467 (m), 1441 (m), 1380 (m), 1271 (s), 1237 (s),
1110 (s), 1036 (m), 943 (s), 886 (s), 846 (s), 738 (s), 660 (s), 624
(m), 452 (w).
Xꢀray diffraction study. Single crystal Xꢀray diffraction data for
1 and 2 were measured at 130 K on an Agilent Xcalibur automated
diffractometer equipped with an AtlasS2 2D detector (graphite
monochromator, λ(MoꢀKα) = 0.71073 Å, ωꢀscan technique). The
integration, correction for absorption, and determination of the unit
cell parameters were carried out using the CrysAlisPro software.14
The structure was solved by direct methods and refined by the fullꢀ

1D and 2D coordination polymers
Russ.Chem.Bull., Int.Ed., Vol. 65, No. 12, December, 2016
2919
Table 1. Crystallographic parameters and details of Xꢀray diffraction experiment
Parameter
1
2
Empirical formula
M/g mol–1
Crystal system
Space group
a/Å
C10H14Cl2CuN4
324.69
Orthorhombic
Pna21
14.9245(4)
9.5062(3)
9.7578(3)
C20H28Cl2CuN8
514.94
Monoclinic
P21/c
7.6061(5)
17.6047(6)
8.9119(5)
114.965(7)
1081.83(11)
2
b/Å
c/Å
β/deg
V/Å3
1384.39(7)
4
Z
dcalc/g cm–3
1.558
1.947
1.581
1.283
μ/mm–1
F(000)
660
534
Crystal size/mm
θ Range for data collection
Range of indices hkl
0.20×0.12×0.09
3.29—28.99
–21 < h < 13,
–12 < k < 13,
–13 < l < 9
4284/2433
0.39×0.16×0.07
3.42—28.43
–8 < h < 11,
–23 < k < 16,
–7 < l < 12
3205/1988
Number of reflections
collected/unique
Rint
0.0176
2312
1.090
0.0180
1749
1.066
Nhkl с I > 2σ(I)
Goodness of fit on F2
Rꢀfactors (I > 2σ(I))
R1
wR2
0.0264
0.0636
0.0342
0.0956
Rꢀfactors (based on all reflections)
R1
wR2
0.0289
0.0650
0.592/–0.359
0.0395
0.0995
0.532/–0.602
Residual electron density (max/min), e/Å3
matrix least squares method with anisotropic displacement paramꢀ
eters (except hydrogen atoms) using the SHELXꢀ2014 software.15
The hydrogen atoms of the organic ligands were positioned geometꢀ
rically and refined using a riding model. The crystallographic data
and the details of diffraction experiments are given in Table 1. The
full tables of interatomic distances and bond angles, atomic coordiꢀ
nates, and atomic displacement parameters were deposited with the
Cambridge Crystallographic Data Center (CCDC 1482782 and
1482783), as well as can be requested from the authors.
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This work was financially supported by the Russian
Science Foundation (Project No. 15ꢀ13ꢀ10023).
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Received June 3, 21016;
in revised form July 15, 2016