Hydrothermal synthesis and crystal structure of a sulfur-bridged

binuclear copper(II) coordination polymer generated

by a spontaneous reduction

Xiaojun Gua, Zhenyu Shia, Jun Penga,*, Yanhui Chena, Enbo Wanga, Ninghai Hub

aDepartment of Chemistry, Institute of Polyoxometalate Chemistry, Northeast Normal University, Changchun 130024, ChinabChangchun Institute of Applied Chemistry, Chinese Academy of Science, Changchun 130022, China

Received 28 February 2004; revised 26 March 2004; accepted 26 March 2004

Abstract

A simultaneous reduction of SO422 to S22 by 2,5-pyridinedicarboxylate under hydrothermal conditions produced a new binuclear

copper(II) coordination polymer [CuS(4,40-bipy)]n (4,40-bipy ¼ 4,40-bipyridine) (1). Single crystal X-ray analysis revealed that compound 1

consisted of sulfur-bridged binuclear copper(II) units with Cu–Cu bonding which were combined with 4,40-bipy to generate a three-

dimensional network constructed from mutual interpenetration of two-dimensional (6,3) nets. Crystal data for 1: C10H8CuN2S, tetragonal

I41=acd; a ¼ 14:0686ð5Þ A, b ¼ 14:0686ð5Þ A, c ¼ 38:759ð2Þ A, Z ¼ 32: Other characterizations by elemental analysis, IR, EPR and TGA

analysis were also described in this paper.

q 2004 Elsevier B.V. All rights reserved.

Keywords: Coordination polymer; Hydrothermal synthesis; Simultaneous reduction; Interpenetration

1. Introduction

The design and synthesis of new coordination polymers

have attracted great attention in recent years due to their

intriguing structural features and potential applications in

catalysis, ion-exchange, non-linear optics, chemical

adsorption and magnetism [1–7]. Particular interest has

been directed towards binuclear copper coordination

polymers because they play an important role in biological

metalloenzymes, industrial catalysis [8,9] and especially

magneto-structural correlations [10]. However, the great

majority of these studies are mainly concentrated on

carboxylate or halogen-bridged copper(II) complexes

[11–13], and a minority on sulfur-bridged species because

the latter are relatively rare. On the other hand, sulfur-

bridged copper(II) coordination polymers are attracting a

great deal of attention owing to their relevance to

biological, rich structural chemistry, non-linear optic and

special reactive properties [14–18]. Therefore, it would be

of interest to synthesize and study the magnetic properties

copper(II)-sulfur coordination polymers. To date, sulfur-

bridged copper coordination polymers are synthesized

usually by conventional solution methodology, while

hydrothermal technique is less exploited. Many fascinating

structures and unexpected reactions can be achieved under

hydrothermal conditions [19–24]. Although, in most cases,

the reaction mechanisms under hydrothermal conditions

are not clear and the control and prediction of crystal

structures are difficult, the architecture of the final product

directly depends on the interplay of the characteristics of

metal ion, ligand and reaction conditions [25]. It is well

accepted that pyridine derivatives can act as good

reductants under hydrothermal conditions [26,27], whereas

a simultaneous reduction of SO422 to S22 by pyridine

derivatives during a self-assembly process has never been

observed. In this paper, we report synthesis and crystal

structure of a novel coordination polymer: [CuS(4,40-

bipy)]n (1). Compound 1 exhibits a three-dimensional

network constructed from mutual interpenetration of two-

dimensional (6,3) nets, in which sulfur-bridged binuclear

copper(II) units are combined with 4,40-bipy to form sheets

of [CuS(4,40-bipy)]-containing cavities with dimensions of

ca. 28 £ 20 A.

0022-2860/$ - see front matter q 2004 Elsevier B.V. All rights reserved.

doi:10.1016/j.molstruc.2004.03.036

Journal of Molecular Structure 694 (2004) 219–222

www.elsevier.com/locate/molstruc

* Corresponding author. Tel.: þ86-431-5269765; fax: þ86-431-

5684009.

E-mail address: jpeng@nenu.edu.cn (J. Peng).

2. Experimental

2.1. General procedures

All reagents were purchased commercially and used

without further purification. Elemental analyses (C, H and

N) were performed on a Perkin – Elmer 2400 CHN

Elemental Analyzer. IR spectrum was obtained on Alpha

Centaurt FT/IR spectrometer with KBr pellet in the

400–4000 cm21 region. The EPR spectrum was recorded

on a Japanese JES-FE3AX spectrometer at room tempera-

ture. The TG analysis was performed on a Perkin–Elmer

TGA7 instrument in flowing N2 with a heating rate of

10 8C min21.

2.2. Synthesis

The title compound was hydrothermally synthesized

from the reaction mixture of CuSO4·5H2O (0.5 mmol),

4,40-bipy (0.5 mmol), 2,5-pyridinedicarboxylic acid

(0.5 mmol), NaOH (1 mmol) and H2O (8 ml) at 190 8C for

3 days, followed by slowly cooling (5 8C/h) to room

temperature. Dark red block crystals of 1 were recovered in

30% yield based on 4,40-bipy. C10H8CuN2S (251.8): Calcd

C, 47.66; H, 3.18; N, 11.12 (%). Found C, 47.58; H, 3.24;

N, 11.04 (%).

2.3. X-ray crystallography

The crystal structure of compound 1 was determined by

single-crystal X-Ray diffraction. Crystal data: C10H8CuN2S,

tetragonal I41=acd; a ¼ 14:0686ð5Þ A, b ¼ 14:0686ð5Þ A,

c ¼ 38:759ð2Þ A, Z ¼ 32: The crystal determination for

compound 1 was performed on a Bruker Smart-CCD

diffractometer with Mo Ka Monochromated radiation

(l ¼ 0:71073 A�) at 293 K in the range of 2:078 , u ,

27:458: The structure was solved by direct methods using the

program SHELXL-97 and refined by full-matrix least-

squares methods on F2 using the SHELXL crystallographic

software package. All of the non-hydrogen atoms were

refined anisotropically. Hydrogen atoms were located from

difference Fourier maps. The crystal data and structure

refinement, atomic coordinates, and selected bond lengths

and angles of compound 1 were listed in Tables 1–3.

3. Results and discussion

3.1. Crystal structure

The X-ray single-crystal analysis reveals that compound

1 is a three-dimensional network constructed from mutual

interpenetration of two-dimensional (6,3) nets. The funda-

mental unit is shown in Fig. 1. There is only one

crystallographically unique Cu(II) center in the crystal

structure. The Cu(II) center is coordinated by two nitrogen

atoms from two different 4,40-bipy groups and two sulfurTable 1

Crystallographic data for compound 1

Empirical formula C10H8CuN2S

Formula weight 251.78

T (K) 293(2)

Crystal system Tetragonal

Space group I41=acd

a (A) 14.0686(5)

b (A) 14.0686(5)

c (A) 38.759(2)

V (A3) 7671.4(6)

Z 32

l (A) 0.71073

Crystal size (mm) 0.256 £ 0.157 £ 0.072

Absorption coefficient (mm21) 2.449

u range 2.10–27.468

Limiting indices 0 # h # 18; 0 # k # 12; 1 # l # 50

F(000) 4064

Reflections collected 2204

Independent reflections 2204 ðRint ¼ 0:0000Þ

GOF 1.026

R1; wR2½I . 2sðIÞ� 0.0299, 0.0562

R1; wR2 (all data) 0.0755, 0.0828

Table 2

Selected bond lengths (A) and angles (deg) for compound 1

Cu–N(1) 1.982(3) Cu–N(2) 1.985(3)

Cu–S 2.4212(14) Cu–S#1 2.4524(14)

Cu–Cu#1 2.7585(11) N(1)–C(4) 1.337(6)

N(1)–C(3) 1.327(6) N(2)–C(8) 1.332(5)

N(2)–C(9) 1.358(5)

N(1)–Cu–N(2) 127.43(14) N(1)–Cu–S 108.30(12)

N(2)–Cu–S 103.46(12) N(1)–Cu–S#1 111.17(12)

N(2)–Cu–S#1 99.69(12) S–Cu–S#1 104.48(4)

N(1)–Cu–Cu#1 101.04(10) N(2)–Cu–u#1 131.49(10)

S–Cu–Cu#1 56.06(4) Cu–S–Cu#1 68.94(4)

S#1–Cu–Cu#1 55.00(4)

Table 3

Atomic coordinates ( £ 104) and equivalent isotropic displacement

parameters (A2 £ 103) for compound 1

x y z U(eq)

Cu 674(1) 8212(1) 167(1) 34(1)

S 1007(1) 6572(1) 314(1) 31(1)

N(1) 890(3) 8379(3) 2334(1) 24(1)

N(2) 1268(3) 8937(3) 550(1) 27(1)

C(1) 935(3) 8427(3) 21061(1) 20(1)

C(2) 469(3) 9118(3) 2870(1) 27(1)

C(3) 472(3) 9069(3) 2512(1) 27(1)

C(4) 1357(4) 7723(3) 2518(1) 30(1)

C(5) 1392(4) 7727(3) 2875(1) 31(1)

C(6) 2113(3) 9911(3) 1106(1) 19(1)

C(7) 2246(3) 10,190(3) 769(1) 24(1)

C(8) 1817(3) 9699(3) 505(1) 28(1)

C(9) 1128(3) 8668(4) 883(1) 29(1)

C(10) 1520(3) 9124(3) 1158(1) 25(1)

U(eq) is defined as one third of the trace of the orthogonalized Uij

tensor.

X. Gu et al. / Journal of Molecular Structure 694 (2004) 219–222220

bridged-ligands to form binuclear copper(II) units with

Cu–Cu distance of 2.759 A. The Cu–N bond lengths vary

from 1.982(3) to 1.985(3) A, and the Cu–S bond lengths

range from 2.4212(14) to 2.4524(14) A. The N(S)–Cu–

S(N) bond angles range from 99.69(12) to 127.43(14)8.

Thus, all Cu centers display distorted tetrahedral coordi-

nation geometry. Each 4,40-bipy adopts a bismonodentate

bridging mode to link two sulfur-bridged binuclear

copper(II) units (Cu2S2). It should be noted that the two

pyridine rings in the two independent 4,40-bipy are twisted

by 22.7(6) and 16.5(4)8, respectively. Based on this

connection mode, all Cu2S2 units are combined by 4,40-

bipy to form hexagonal rings (size ca. 28 £ 20 A), which

form a two-dimensional (6,3) net (see Fig. 2).

In the packing arrangement of compound 1, there are

four crystallographically identical yet topologically inde-

pendent (6,3) nets that can be grouped into two sets, one

with two vertical and parallel nets and the other with two

horizontal and parallel nets. These networks interpenetrate

with mutual interlocking of the hexagons to result in

a three-dimensional framework (see Fig. 3). However,

there does not exist bond interaction among the interlock-

ing two-dimensional (6,3) nets. Interpenetration in nature is

a space-filling effect to produce dense framework, but,

surprisingly, the interpenetrating two-dimensional net-

works do not fill up all the pore space formed by one

independent two-dimensional network. A perspective view

of compound 1 clearly shows there are one-dimensional

channels (size ca. 2 £ 4 A) along the c axis (see Fig. 4).

It is interesting to note that SO422 ions were reduced to

S22 by 2,5-pyridinedicarboxylate under hydrothermal

conditions, at the same time, 2,5-pyridinedicarboxylate

transforms into pyridine. To the best of our knowledge, this

reduction reaction in constructing coordination polymers is

unique. To verify this deduction, we repeated the reaction

without adding 2,5-pyridinedicarboxylic acid and did not

Fig. 1. ORTEP drawing of 1 showing the local coordination environment of

Cu(II) with thermal ellipsoids at 50% probability. Hydrogen atoms are

omitted for clarity.

Fig. 2. Perspective view of the 2D (6,3) net in 1.

Fig. 3. The independent interlocking planar nets in 1. The S atoms are

omitted for clarity.

Fig. 4. Plots of the 3D structure of 1 along the c axis.

X. Gu et al. / Journal of Molecular Structure 694 (2004) 219–222 221

obtain compound 1.

SO224 þ C5H3NðCOOÞ222 !

Cu2þþ4;40-bipy

190 8C

S22 þ C5H5N þ CO2

3.2. IR spectrum

In the infrared spectrum of compound 1, absorption

bands from 1608.5 to 1411.7 cm21 are attributed to the

pyridine ring breathing bands of 4,40-bipy.

3.3. EPR spectrum

The EPR spectrum of compound 1 exhibits the Cu2þ

signal at 293 K with g ¼ 2:0332; which is consistent with

the result of valence sum calculations.

3.4. Thermal analysis

Thermogravimetric (TG) analysis was carried out under

N2 with a heating rate of 10 8C min21. The TG curve of

compound 1 (shown in Fig. 5) indicates three steps of

weight loss. The first two stages of weight loss are 61.89%

(calcd: 62.15%) in the temperature range 190–320 8C,

corresponding to the release of the 4,40-bipy ligands. The

third weight loss occurs from 320 to 520 8C, due to the

release of part of sulfur. After decomposition of compound

1 at high temperature, the weight of the residue (,31.29%)

is responded to Cu2S (calcd: 31.90%).

4. Conclusion

In summary, we have successfully synthesized a novel

coordination polymer consisting of two-dimensional (6,3)

nets under hydrothermal conditions. The result reveals that

SO422 ions are reduced to S22 ions by 2,5-pyridinedicarboxy-

late under hydrothermal conditions. This provides a possible

method to in situ generate sulfur-contained coordination

polymers.

Acknowledgements

This research was financially supported by the National

Science Foundation of China (20271011).

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X. Gu et al. / Journal of Molecular Structure 694 (2004) 219–222222