КООРДИНАЦИОННАЯ ХИМИЯ, 2014, том 40, № 8, с. 468-475
УДК 541.49
TWO NOVEL FOUR-COORDINATED ZINC(II) POLYMERS: SYNTHESIS, STRUCTURES, AND PROPERTIES
© 2014 W. M. Tian1, C. Y. Wei2, C. H. Peng1, P. Liang1, H. Xiao1, and X. H. Yin1, *
1College of Chemistry and Chemical Engineering, Guangxi University for Nationalities, Nanning, 530006 P.R. China 2School Marine Science and Biotechnology, Guangxi University for Nationalities, Nanning, 530006 P.R. China
*E-mail: yxhphd@163.com Received December 2, 2013
The synthsis, crystal structure, thermal analysis and spectroscopic studies of two novel zinc(II) coordination polymers Zn4(NA)4Dpa)2 (I) and Zn(Inic)(Bpdc)0.5 (II) (NA = niacin, Inic = isonictinic acid, Dpa = 2,2'-biphenyldicarboxylate, Bpdc = 4,4'-biphenyldicarboxylate) are presented here. The crystal structure of I is a two-dimensional network whose tetranuclear unit is a slightly distorted square. Two kinds of ligand connect adjacent zinc(II) ions, respectively, in a coordinate direction. The structure of II is a three-dimensional and it consist of corrugated square layers of isonictinic acid—bridged zinc(II) ions which are pillared by 4,4'-bi-phenyldicarboxylate. The rod-ligands in II appear as useful tools to control the interlayer metal—metal separation. Each zinc(II) ion in I and II is four-coordinated with three oxygen atoms and one nitrogen atom building distorted tetrahedron environments.
DOI: 10.7868/S0132344X14080118
INTRODUCTION
The construction of coordination polymers has attracted remarkable interest. These polymers become a quite active research field in recent years, not only due to their fascinating structural diversities such as molecular cage, honeycomb, grid, ladder, polyrotaxanes, and multidimensional frameworks [1, 2], but also because of their interesting properties and potential applications as functional materials in optical, electronic, magnetic fields, gas storage, catalysis, ionic/molecular recognition and drug delivery [3, 4].
Up to now, a great number of inorganic-organic hybrid coordination polymers have been synthesized based on strong covalent bonds or weak supramolecu-lar connections, such as hydrogen bonds and/or n—n interactions [5]. It has been documented that the geometries of the organic ligands have a great effect on the structural framework of such coordination polymers; thus, much effort has been devoted to modifying the building blocks and to controlling the assembled motifs for required products through the selection of different organic ligands. Previous studies have shown that rigid bridging ligands to afford moderately robust networks of variable dimensionality and porosity [6, 7].
We report two novel four-coordinated zinc(II) polymers Zn4(NA)4Dpa)2 (I) and Zn(Inic)(Bpdc)05 (II) (NA = niacin, Inic = isonictinic acid, Dpa = 2,2'-biphe-nyldicarboxlate, Bpdc = 4,4'-biphenyldicarboxylate) not only due to their infrequent four-coordinated mode, but
also because of their fascinating structural motifs and interesting properties. Herein we reported the syntheses, elemental analysis, IR spectrum, TGA, single-crystal X-ray diffraction analysis and powder X-ray diffraction analysis.
EXPERIMENTAL
Materials and instrumentation. All chemicals were commercial materials of analytical grade and used without purification. Elemental analysis for C, H, and N was carried out on a PerkinElmer 2400 II elemental analyzer. Infrared spectrum was recorded in KBr pellets using a PE Spectrum One FT-IR Spectrometer Fourier transform infrared spectroscopy in the 4000—400 cm-1 regions. PerkinElmer Diamond TG/DTA thermal analyzer was used to record simultaneous TG curves in the static air atmosphere at a heating rate of10 K min-1 in the temperature range 25-1000° C using platinum crucibles. Powder X-ray diffraction patterns of all samples were recorded on a Rigaku D/M-2200 T automated diffractometer (Ultima+) using CuZ"a radiation (k = 1.5406 Ä). Graphite monochromator was used and the generator power settings are at 40 kV and 40 mA.
Synthesis of complex I. A mixture of ZnSO4 • 7H2O (0.1438 g, 0.5 mmol), H2Dpa (0.1213 g, 0.5 mmol), NA (0.0616 g, 0.5 mmol), Py (0.5 mL), H2O (10 mL), methanol (5 mL), and DMF (2.5 mL) was stirred for 20 min in the beaker. Then an aqueous solution of
NaOH was added dropwise in the stirring condition to adjust the pH value of the mixture to 6. After keeping on stirring for another 1 h, the resulting mixture was transferred to a 30 mL Teflon-lined stainless steel reactor, kept under ordinary pressure at 160°C for 72 h in the oven, and then slowly cooled to room temperature at a rate of 10°C per hour. The colourlessblock crystals which were suitable for X-ray diffraction were isolated directly, washed with methanol and dried in the air (the yield was 86.7%).
For C52H32N4Oi6Zn4
anal. calcd., %: C, 50.72; H, 2.60; O, 20.81; N, 4.52. Found, %: C, 50.68; H, 2.63; O, 20.86; N, 4.46.
IR data (KBr; v, cm-1): 3071 s, 1608 v.s, 1451 m 1389 v.s, 1219 m, 1147 m, 849 m, 749 s, 697 s.
Synthesis of complex II. A solution of ZnSO4 • 7H2O (0.1438 g, 0.5 mmol) and Inic (0.0615 g, 0.5 mmol), which are dissolved in the mixed solvent of 5 mL DMF and 5 mL methanol, was added dropwise with stirring at room temperature to a mixture of H2Bpdc (0.1213 g, 0.5 mmol) and 10 mL DMF. Then an aqueous solution of sodium hydroxide was dropwise added with stirring to adjust the pH value of the solution being 6. After keeping on stirring for another 1 h, the resulting mixture was transferred to a 30 mL Teflon-lined stainless steel reactor, kept under ordinary pressure at 145°C for 72 h in the oven, and then slowly cooled to room temperature at a rate of10°C per hour. The purple block crystals which were suitable for X-ray diffraction were isolated directly, washed with methanol and dried in the air (the yield was 81.5%).
For C13H8NO4Zn
anal. calcd., %: C 50.72; H 2.60; N 4.55; O 20.81. Found, %: C 50.68; H 2.68; N 4.47; O 20.91.
IR data (KBr; v, cm-1): 3083 s, 2359 w, 1590 v.s, 1542 s, 1421 s, 1057 m, 1023 m, 769 s, 704 s.
X-ray structure determination. A high-quality crystal of complex was slected and mounted on the top of a glass fiber. The data was measured by a Bruker SMART CCD area detector using graphite-mono-chromated MoZa radiation (X = 0.71073 A) at 296 K. Absorption correction were applied using SADABS program [8]. The crystal structure was solved by the direct method and refined with a full-matrix least-squares technique using SHELXTL program [9]. All non-hydrogen atoms were refined anisotronically. Hydrogen atoms were generated geometrically. The crystal data and structure refinement details for two complexes are shown in Table 1. Selected bond lengths and angles of the complexes are listed in Table 2.
Crystallographic data for the structures I and II have been deposited with the Cambridge Crystallographic
Data Centre (№ 945429 (I), 945430 (II); deposit @ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).
RESULTS AND DISCUSSION
The coordination environment around the Zn(II) center in I is presented in Fig. 1a with atom numbering scheme. Each Zn(II) atom is tetracoordinated by three oxygen atoms with one coming from ^1,n1-car-boxylate groups and one coming from ^2,n1,n1-car-boxylate groups, which come from the same Dpa ligand. The last oxygen atom and nitrogen come from NA ligand. The coordination polyhedron around Zn(II) atoms are arranged in a 2D network plane composed of ZnNO3 tetrahedra which could be best described as trigonal pyramid. The Zn-N bond distances are in the range from 2.014(5) to 2.054(5) A while the Zn-O bond distances are in the range from 1.927(4) to 2.008(5) A (Table 2). The molecular structure of I exists as a slightly distorted rectangle cluster (Fig. 2), which contains Zn(II) centres in four different environments. Adjacently nobonding distances of Zn(1)-Zn(4) are 4.5778(15) and 4.7523(15) A, respectively, while adjacently nobonding distances of Zn(2)-Zn(3) are 4.6030(14) and 4.7068(15) A, respectively. Adjacently nobonding distances of Zn(1)-Zn(2) and Zn(3)-Zn(4) are constant and are 7.3379(18) and 7.2396(18) A, respectively (Fig. 3).
Colorless block-shaped crystals of II were grown solvothermally. Study by single crystal X-ray diffraction disclosed a 3D framework structure. The Zn shows slightly distorted tetrahedral coordination geometry. It is defined by three oxygen atoms with two (O(3), O(3)') coming from ^1,n1-carboxylate groups of two Bpdc ligands and the other two coordinated atoms (O(2), N(1)') coming from two different Inic ligands (Fig. 1b). The overall structure can be viewed as Bpdc ligands pillaring the undulating charge-neutral [Zn2(Inic)4] layers. Two bidentate carboxylate groups from two centrosymmetrically related Bpdc ligands coordinate to two zinc(II) centres to form the [Zn2(COO)2]2+corrugated eight-membered cross-type secondary building unit (SBU, Fig. 4). Two mon-odentate carboxylates from a pair of centrosymmetri-cally related Inic ligands coordinate to the two Zn(II) centers, balancing the charges on the SBU. Another pair of nitrogen atoms coming from centrosymmetri-cally adjacent Inic ligands coordinate to the two Zn(II) centers to form the four-coordinated mode. Thus each SBU becomes a four connecting node, which is linked by Inic ligands to four other SBUs to form the two-dimensional 44 (brick-like) net [10] (Fig. 5). The Bpdc ligands coordinate to the Zn(II) centers in two neighboring layers, connecting the layers into the overall 3D structure (Fig. 6). Interestingly, polymer II allows three such identical frameworks to interpenetrate each
Table 1. Crystal data and structure refinements for complexes I and II
Parameter Value
I II
Formula weight 1230.30 307.57
Temperature, K 293(2) 296(2)
Crystal system Triclinic Monoclinic
Space group p1 P2x/n
a, A 9.235(2) 6.489(4)
b, A 14.267(3) 18.016(10)
c, A 18.787(4) 10.704(6)
a, deg 99.729(4) 90
ß, deg 97.296(4) 103.744(6)
Y, deg 90.040(3) 9
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