научная статья по теме SYNTHESIS, CRYSTAL STRUCTURE, AND MAGNETIC PROPERTIES OF BINUCLEAR COBALT(II) COMPLEX WITH 2-(5-{6-[5-(PYRAZIN-2-YL)-1H-1,2,4-TRIAZOL-3-YL]- PYRIDIN-2-YL}-1H-1,2,4-TRIAZOL-3-YL)PYRAZINE Химия

Текст научной статьи на тему «SYNTHESIS, CRYSTAL STRUCTURE, AND MAGNETIC PROPERTIES OF BINUCLEAR COBALT(II) COMPLEX WITH 2-(5-{6-[5-(PYRAZIN-2-YL)-1H-1,2,4-TRIAZOL-3-YL]- PYRIDIN-2-YL}-1H-1,2,4-TRIAZOL-3-YL)PYRAZINE»

КООРДИНАЦИОННАЯ ХИМИЯ, 2015, том 41, № 3, с. 183-187

УДК 541.49

SYNTHESIS, CRYSTAL STRUCTURE, AND MAGNETIC PROPERTIES OF BINUCLEAR COBALT(II) COMPLEX WITH 2-(5-{6-[5-(PYRAZIN-2-YL)-1H-1,2,4-TRIAZOL-3-YL]-PYRIDIN-2-YL}-1H-1,2,4-TRIAZOL-3-YL)PYRAZINE © 2015 X. Y. Huang1, Q. Q. Jiang1, J. S. Zhao1, *, S. C. Zhang2, *, and J. L. Wang3

1Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of Education, Shaanxi Key Laboratory of Physical-Inorganic Chemistry, College of Chemistry & Material Science, Northwest University, Xi'an, 710069 P.R. China 2School of Material Science and Engineering, Beihang University, XueYuan Road No. 37, HaiDian District, Beijing,

100191 P.R. China

3Composites Research Institute, Weinan Normal University, Weinan, 714000 P.R. China *E-mail: jszhao@nwu.edu.cn; csc@buaa.edu.cn Received August 16, 2014

The synthesis and crystal structure of a new Co(II) compound with 2-(5-{6-[5-(pyrazin-2-yl)-1H-1,2,4-tri-azol-3-yl]-pyridin-2-yl|-1H-1,2,4-triazol-3-yl)pyrazine (H2Ptptp) are reported. The new compound [Co2(Ptptp)Cl2(H2O)2] • H2O (I) has been determined by single-crystal X-ray diffraction (CIF file CCDC no. 1010785) and characterized by elemental analyses and infrared spectrum. The structure I consists of two independent Co2+ ions, one Ptptp2- anion, two Cl- anions, two coordinated H2O molecules and one lattice H2O molecule. The three-dimensional (3D) supramolecular architecture is formed through the hydrogen bonds among adjacent units. Moreover, magnetic susceptibility measurements indicate that the compound exhibits weak antiferromagnetic coupling interaction.

DOI: 10.7868/S0132344X15030032

INTRODUCTION

In the past decades, the studies on intriguing structures and potential applications of functional coordination polymers made significant achievements. It improved the development of magnetism, photochemical areas, ion exchange, catalysis and porous materials [1—7].

The 1,2,4-triazole compounds are considered as an interesting heterocycles because of their effective biological importances and applications [8, 9]. Its derivatives constitute an interesting type of ligands, which can be coordinated to a metal atom in different ways, depending on the position and the nature of the substituent [10]. A part of the complexes containing 1,2,4-triazole ligands possess rather peculiar structures and specific magnetic properties [11, 12]. The ligands can adopt multiple coordination modes, such as bidentate, tridentate or tetradentate, to meet the different requirements on the metal centers' coordination [13, 14]. The 1,2,4-triazole and its pyrazine derivatives have many advantages: (i) strong coordination ability; (ii) more coordination points and more patterns; (iii) can be bridging in various ways with metal ions and other bridging ligand; (iv) widely used in the construction of the functional complexes. Heterocyclic H2Ptptp can rotate around the central C—C bond

and adopt different conformations, no matter which conformation it adopts, H2Ptptp will provide potential tridentate and bidentate binding sites [15].

In this study, a new compound [Co2(Ptptp)Cl2(H2O)2 • H2O (I) has been prepared by hydrothermal synthesis. 2-(5-{6-[5-(Pyrazin-2-yl)-1H-1,2,4-triazol-3-yl]-pyridin-2-yl}-1H-1,2,4-triaz-ol-3-yl)pyrazine (H2Ptptp) was selected as ligand for the synthesis of the new compound. It has been well characterized by elemental analysis, infrared spectroscopy, X-ray single crystal diffraction and variable-temperature magnetic susceptibility.

H2Ptptp

EXPERIMENTAL

Materials and physical measurements. H2Ptptp was purchased from Jinan Camolai Trading Company. Tetrahydrofuran was commercially available from Ainopharm Chemical Reagent Co., Ltd. All starting

Table 1. Crystallographic data and experimental details for structure I

Parameter Value

Formula weight 610.16

Crystal system Monoclinic

Space group C2/c

a, A 10.5833(18)

b, A 13.4832(18)

c, A 15.740(2)

ß, deg 95.644(4)

V, A3 2235.2(6)

T, K 296(2)

Z 4

P calcd mg m-3 1.813

p., mm-1 1.771

/(000) 1224

Crystal size, mm 0.30 x 0.27 x 0.24

9 Range, deg 2.45-25.00

Reflections collected/unique 5484/1970

Rint 0.0540

R indices (I > 2a(T)) R1 = 0.0636 WR2 = 0.1501

R indices (all data) Rx = 0.1097 wR2 = 0.1771

GOOF on F 2 1.029

Largest diff. peak and hole, e/A3 1.275 and -1.083

Table 2. Selected bond distances (A) and angles (deg) for I*

Bond d, A Bond d, A

Co(1)-N(1) Co(1)-N(2) Co(1)-Cl(1) 2.031(8) 2.216(5) 2.247(3) Co(2)-N(4) Co(2)-N(5) Co(2)-O(1w) 2.045(5) 2.144(5) 2.189(5)

Angle ro, deg Angle ro, deg

N(1)Co(1)N(2) N(2)#1Co(1)N(2) N(1)Co(1)Cl(1) N(2)Co(1)Cl(1) N(2)Co(1)Cl(1)#1 77.58(15) 155.2(3) 118.88(15) 95.16(16) 96.77(15) Cl(1)#1Co(1)Cl(1) N(4)Co(2)N(5) N(5)Co(2)O(1w) N(4)Co(2)O(1w) 122.2(3) 78.1(2) 91.5(2) 89.0(2)

* Symmetry operations: #1 -x + 1, y, -z + 1/2.

materials were of analytical grade and were used without further purification.

The IR spectra were recorded as KBr pellets on a Bruker Vectorm 22 spectrometer in the range of 4000 to 400 cm-1. Elemental analyses for C, H, and N were obtained on a Vario EL III elemental analyzer. Variable-temperature magnetic susceptibility measure-

ments (2-300 K) were carried out on a Quantum Design PPMS60000 in a magnetic field of 2000 Oe, and the diamagnetic corrections were evaluated by using Pascal's constants.

Synthesis of I. A mixture of CoCl2 • 6H2O (0.0476 g, 0.2 mmol), H2Ptptp (0.0369 g, 0.1 mmol), 6 mL tet-rahydrofuran and 2 mL H2O was sealed in a 25 mL Teflon-lined autoclave and heated at 160 °C for 3 days, and then cooled at a rate of 2°C min-1 to room temperature. Black block crystals were obtained. The yield was 40%.

For C17H15NnO3Cl2Co2

anal. calcd., %: C, 33.46; H, 2.48; N, 25.25. Found, %: C, 33.47; H, 2.85; N, 25.91.

IR for complex I (KBr; v, cm-1): 3386 m, 3063 w, 1615 w, 1568 m, 1517 m, 1434 s, 1285 w, 1149 m, 1033 m, 866 w, 798 w, 670 w.

X-ray crystallography. Diffraction intensities for complex I were collected on a Bruker Smart APEX II CCD diffractometer equipped with graphite-mono-chromated Mo^a radiation (X = 0.71073 A) by using the 9-® scan technique at room temperature. Absorption corrections were based on symmetry equivalent reflections using the SADABS program. The crystal structure was solved by direct methods with program SHELXL-97 and followed by successive Fourier and difference Fourier syntheses and refined by full-matrix least-squares on F2 [16]. Non-hydrogen atoms were refined anisotropically. The hydrogen atoms on carbon atoms were generated geometrically. Experimental details of the X-ray analyses are provided in Table 1. The selected bond lengths and bond angles are listed in Table 2.

Supplementary material for structure I has been deposited with the Cambridge Crystallographic Data Centre (CCDC no. 1010785; deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).

RESULTS AND DISCUSSION

The crystallographic analysis of I presents that each unit consists of two independent Co2+ ions, one Ptptp2- anion, two Cl- anions, two coordinated H2O molecules and one lattice H2O molecule. As exhibited in Fig. 1, the coordination geometries of Co(1) and Co(2) in the crystallographically unique unit are slightly different. The Co(1) center is five-coordinated with geometry of distorted trigonal bipyramid by coordination with three N atoms (N(1), N2, N(2)#1 from one Ptptp2- ligand) and two Cl atoms (Cl(1) and Cl(1)#1), while Co(2) center is coordinated by four N atoms (N(4), N(5) from the Ptptp2- ligand and N(4)#2, N(5)#2 from the adjacent binuclear unit) and two O atoms (O(1w) and O(1w)#2 from the H2O mole-

KOOP,3HHAUHOHHAH XHMH3 tom 41 № 3 2015

Fig. 1. The dinuclear unit of [Co2(Ptptp)Cl2(H2O)2] • H2O (a); view of the coordination environment of the Co(2) in complex I (b). Symmetry operations: #1 —x + 1, y, —z + 1/2; #2 —x, —y + 1, —z.

H(15) H(L4) Co(2)

u

Fig. 2. The 1D chain of I.

x

cules) but in a slightly distorted octahedral geometry. The Co—N bond lengths range from 2.031 to 2.216 A, the Co—Cl bond length is 2.247 A, and the Co—O bond length is 2.189 A. The angles of N(5)#2Co(2)N(4)#2, N(4)#2Co(2)N(5),

N(5)Co(2)N(4), and N(4)Co(2)N(5)#2 added up to 360°, indicating that the Co(2) ion and the four N atoms are on the identical plane.

As show in Fig. 2, the Ptptp2— anion, acting as a connector, links the Co(II) centers to form a one-dimensional (1D) chain. Each Ptptp2— ligand connects one Co(1) and two Co(2) atoms; Co(1) is only coordinated with N atoms from one ligand, while Co(2) is coordinated by N(4), N(5) from one Ptptp2— ligand and N(4)#2, N(5)#2 from the adjacent Ptptp2— ligand, resulting in [Co2(Ptptp)]B 1D belts with the

Co(1)...Co(2), Co(1)...Co(1)#2 and Co(2)...Co(2)#1 distances of 6.3004(8), 12.6008(16), and 12.5523(16) A, respectively. The distances between Co—Co also tell us the Co(II) centers are not in an absolutely straight line.

The 1D chains are connected through the intermolecular hydrogen bonds between the coordinated water molecules and lattice water molecules (2.925 Á for O(1w)-"O(2w)#3). There are just one type H-bond in this complex. The angle of O(1w)—H(1$)."O(2w)#3 is 154.086°. Every oxygen atom of the lattice water molecules is all in part connecting adjacent two units of [Co2(Ptptp)Cl2(H2O)2]. Thus, 3D supramolecular structure of this compound is formed (Fig. 3).

We investigated the variable temperature magnetic susceptibilities of this compound, which were measured on the field of 2000 Oe in the temperature range of2.0—300 K as shown in Fig. 4. The xMTvalues at 300 K is 2.57 cm3 mol-1 K, which is higher than the expected spin-only value for isolated Co2+ ion (1.86 cm3 K mol-1, S = 3/2), indicating an orbital contribution to the spin-orbital coupling of the Co2+ions [17]. As the temperature is lowered, the %MT value decreases continuously and falls rapidly in the lower temperature region, which is 0.517 cm3 K mol-1 at 2 K. This behavior

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