Synthesis, Characterization, and Properties of Supported Tungstozincate Bridged by Co(II) Complex Fragment

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CHEW RES. CHINESE UNIVERSITIES 2008,24(6). 668-671 Article ID 1005-9040(2008)-06-668-04

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Synthesis, Characterization, and Properties of Supported Tungstozincate Bridged by Co(I1) Complex Fragment LIU Kun', Ll Jia', LIU Hong-bo1.2and CHEN Ya-guang'* I. Key Laboratory of Polyoxometalates Science of Ministry of Education. Northeast Normal Vniversiw, Changchun 130024, P R. China; 2. Department of Pharmaceutics, Changchun Medical College, Changchun 130031. P R. China Abstract [Coil( hen)^]*[ { (ZnW 1204,,)Co'i(phen)2( H 2 0 ) ) 2Coii(trien)2(NaH20)2].3 H 2 0 was synthesized via hydrothermal technique and characterized with elemental analyses, IR spectroscopy, TGA-DTA, and variable temperature magnetic susceptibiiky. The compound crystallized in the monoclinic system with the space group P211n. a=1.8210 nm, b=2.3592 nm, c=2.2932 nm, /?-I 10.31°, 1'29.239 nm3, Z=2. R1-0.0827. The compound consists of two coordination cations, three lattice water molecules, and a macroanion [ { (ZnWi2040)C~(phen)2(H20)J2Co(C,HigN4)~. (NaHz0),l4- in which each supported Keggin anion [(ZnWi2040Co'i(phen)2(H20)]4acts as a ligand to coordinatc to central bridging Co2' ion via a terminal oxygen atom. Hydrogen bonds are responsible for the construction of 3D architecture of the compound. The compound is paramagnetic with a weak antiferromagnetic interaction(&-46.796 K). Keywords Hydrothermal synthesis; Organic-inorganic hybrid; Supported Keggin structure; Cobalt complex: Tungstozincate

1 Introduction

2 Experimental

Polyoxometalates(POMs), including POM-based 2.1 General Procedures organic-inorganic hybrids, are of great interest not only because of their various structures but also beAll chemicals purchased were of reagent grade and were used without further purification. Elemental cause of their potential application in different areas analyses(C, H, and N) were performed on a Perkinsuch as catalysis, materials science, and medicine''-51. Elmer 2400 CHN Elemental Analyzer. Amounts of Zn, As we know, the Keggin-type of POMs is one of the Co, and W were determined with a Prodigy 1CP important building blocks in this field and is used for atomic emission spectrometer. 1R spectrum( KBr the preparation of sandwiching-type, capped or suppellets; 4000-400 cm-')was recorded on a Magnaported compounds. In most cases, these Keggin clus560 FTIR Spectrophotometer. Thermal analysis was ters supporting metal complexes are found in the inoic performed on a Perkin-Elmer TGA7 instrument in compoundsib"' or in the polymer constructed from flowing air at a heating rate of 20 "C/min. Variable Keggin units as building blocks and metal complexes temperature magnetic susceptibilities were measured as bridging u n i t ~ ' ' ~ - ' ~Although ~. many kinds of on a Quantum Design XL-5 magnetic property meahybrids with Keggin-type clusters supporting metal surement system in a temperature range of 2-300 K complexes have been synthesized, the discrete at 8 X 105A/m. macroanions with supported Keggin units linked by a metal complex fragment are still very rare. The 2.2 Synthesis of Compound 1 synthesis and characterization of ionic organic-inorA mixture of 1 g(3 mmol) of Na2W04.2H20, ganic hybrid compound [Co"(phen)&[ { (ZnW 12040). 0.0724 g(0.3 mmol) of CoCI2.6H20, 0.1514 g(0.6 Co"(phen)~(H~O))~Co"(trien)2(NaH20)~]~3H20( 1) mmol) of C O ( C H ~ C O O ) ~ . ~ 0.041 H ~ O ,g(0.3 mmol) of (trien-triethylenetetraarnine) is reported in this article.

* Corresponding author. E-mail: [email protected] Received April 9, 2008; accepted April 30,2008. Supported by the National Natural Science Foundation of China(No.33970842) and the Analysis and Testing Foundation of Northeast Normal University, China. Copyright 0 2008, Jilin University. Published by Elsevier Limited. All rights reserved.

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ZnCl2, 0.066 g(0.3 mmol) of Zn(CH$00)2.2H20, 0.1 mL(0.6 mmol) of trien, 0.0589 g(0.3 mmol) of phen(phen=l,lO-phenanthro line), and 16.2 mL(900 mmol) of H2O was stirred, and the pH value of the above mixture was adjusted to 5 with 2 mol/L'HCl. The mixture was sealed in a 25 cm3 Teflon-lined autoclave and heated to 160 "C for 120 h. Green tube crystals of 0.206 g(yie1d cu. 20% based on W) were collected by filtration. Elemental anal.(%) calcd. for C132H1&05N28Na2087W~~Zn2(found):W 53.0(52.63), Co 3.7(3.51), Zn 1.5(1.56), Na 0.51(0.55), C 18.8 (18.91), N 4.21(4.68), H 1.34(1.4). FTIR(KBr pellets), Wcm-': 935, 870, 759, 448 for Keggin anion and 1642, 1550, 1514, 1462, 1428, 1145, 1101 for organic ligands. 2.3 X-ray Crystallography

A single crystal with dimensions 0.39 mmx0.19 mmx0.18 mm of compound 1 was used for X-ray diffraction data collection on a Smart Apex CCD diffractometer at 293(2) K with graphite monochromated Mo Ku radiation(L=0.071069 nm). A total of 85828 reflections were collected in a range of 3.02"68<

27.48"(-236h621, -276kG30, -2961S29). Empirical absorption correction(mu1tiscan) was carried out. The structure of compound 1 was solved by direct method and refined by the full-matrix least squares on 2 with the SHELXTL-97 ~oftware"~"~'. All the nonhydrogen atoms were refined anisotropically. Hydrogen atoms were added according to theoretical models. A summary of the crystallographic data and structural refinement of compound 1 is shown in Table 1.

3

Results and Discussion

3.1 Aspects About Formation of Compound 1

Many factors including starting materials, stoichiometry, acidity, temperature, pressure, and time of reaction exert a great influence on the formation and yield of the product and crystal quality. In our work, the crystalline product could not be obtained in the absence of acetate. The most reasonable explanation for this is that the acetate anion played a role of buffer in the reaction system and therefore restrained the acidity from a wide range of change, which benefited the formation and crystallization of compound 1. Both the two kinds of nitrogen-containing ligands, phen and trien, have coordinated to Co atoms as we expected, but only two trien molecules appear in compound 1, although its amount in the starting material was double of the amount of phen; and the coqrdination fragment of c o 3 ion with n(Co):n(trien)=l:2 rather than 1:1(in which four nitrogen atoms of trien coordinate to one cobalt ion) was formed. The best explanation for these phenomena should be the nonrigidity of trien and asymmetric configuration of the 1:l coordination fragment of trien. 3.2

Structural Description

Compound 1 consists of one macroanion [{znw12040Co(phen)2(H20) )ZCO(C6HlEN4)2. (NaH20)2]4-, two cations [Co(phen)3I2+, and three lattice water molecules. Fig. 1 shows the asymmetric unit of compound 1 in which Ow2 has a half site occupancy. The macroanion is composed of two a-Keggin units [ZnW1204~]6-, two cobalt(I1) complex Table 1 Crystal data and structure refinement of fragments [C0(phen)2(H~O)]~'supported on the Kegcompound 1 gin units through the terminal oxygen coordination Empirical formula CI?~HI,OC~SN~~N~~~S~WZ~Z~~ and one complex fragment [CO(C~H~~N~)Z(N~H~O)~]~', M 8384.43 Cxystal system, space group a, b, c/nm

PI(") Z, Unm' Calculated density/(Mgm-') p/mm-'

Independent reflections(R,,,) Completeness to e27.48" Dat~restraints/parameters Goodness-of-fit on F' RI, wR2 P2dl)l R I ,wR2(all data)

Monoclinic, P2lln 1.8210(4),2.3592(5), 2.2932(5) 1l0.31(3) 2,9.239(3) 3.039 15.659 21 194(0.0897) 0.994 2 1073/5599/1228 I .024 0.0827,0.1541 0.1166,0.1682

Crystallographic data for the structural analysis have been deposited in the Cambridge Crystallographic Data Center with CCDC reference number 275145.

Fig.1 ORTEP drawing of asymmetric unit of compound 1 50% probability ellipsoids. All hydrogen atoms are omitted for clarity.

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which acts as a bridging unit and connects two Keggin units through terminal oxygen atoms(see Fig.2). Like other Keggin anions, the [ZnW12040]6-unit consists of a central tetrahedron Zn04 and 12 octahedra W 0 6 in the form of four w3013groups, which surround Zn04 tetrahedrally. According to their different coordination environments in the unit, the oxygen atoms can be divided into five groups: Oa(oxygen atoms connecting the central Zn atom and W atoms), Oh(oxygen atoms shared by two w3013 groups), O,(oxygen atoms shared by two W 0 6 octahedra of a W3OI3 group), O,(terminal oxygen atoms connecting to one W atom), and O,'(terminal oxygen atoms coordinating to Co atom). The W-0 bonds are then categorized into four classes: (1) W-0, with an average bond length of 0.2190 nm; (2) w-ob,, with a mean bond length of 0.192 1 nm; (3) W-0, with an average bond length of 0.1686 nm, and (4) W-0; bond lengths in a range of 0.1729-0.1734 nm. However, 0- W-0 bond angles vary from 70.3' to 163.0'. In comparison with those of [Zn(2,2'-bipy)3]2[ZnW12040Zn(2,2'-bipy)2]. HZO'~',the W-Ob,, lengths do not obviously change, but W-0, lengths increase a little and W 4 , lengths decrease, showing that there is a weak interaction between the macroanons and complex cations. The lengthening of W-Ot' bonds results from the coordination of 0,'to Co atom.

Fig.2

Vo1.24

longer than Co2-0,' bond. Co3 is the symmetry center of the macroanion, it links two Keggin units via terminal oxygen atoms[Co-0,' 0.2002( 13) nm] and is also coordinated by four nitrogen atoms from two trien 'molecules. Col, C02, and Co3 are all in a distorted octahedral environment. As seen in Fig.3, in compound 1, there exist n-n interactions between neighboring phen molecules a1 and b l , c2 and d l of vicinal macroanions in b axis direction with the shortest C-C distance 0.3418 nm, between b2 and c l of diagonally vicinal macroanions with a C-C distance of 0.3483 nm, and between b2 and e l , c l and fl of macroanion and coordination cations with a C-C distance of 0.3490 nm. The macroanions arrange via the n-n interaction into 2D waved layers parallel to the ab plane. The coordination cation is at the center of the quadrilateral formed by four Keggin units of four discrete macroanions on the ac plane. At the same time, some intermolecular hydrogen bonds are formed between the coordinated water molecules of the supported complex fragment in one layer and the terminal oxygen atoms of Keggin units of neighboring layers and between the terminal 0 atoms of anions from vicinal layers and lattice H20 molecules with short 0-0 separation, as well as between nitrogen atoms of trien and oxygen atoms of POM(Tab1e 2). Via these molecular interactions, a 3D supramolecular architecture of compound 1 is constructed.

Polyhedral and ball-stick representation of the macroanion Hydrogen atoms are omitted for clarity.

Transition metal atoms in compound 1 lie in different coordination environments. Znl atom lies in the center of the Keggin unit. The Zn-0 bond lengths in a range of 0.1839-0.1889 nm indicate that the Zn04 is almost a normal tetrahedron. Col connects to six N atoms of three phen ligands, forming the coordination cation. C02 atoms are supported by the terminal oxygen atoms 0,' in the Keggin unit and are coordinated by two phen molecules and one water molecule. The Co2-0,' bond length is 0.2075 nm, consistent with that of other POM cluster-supported metal complexes'6-81. Co2-OW bond[0.2151(14) nm] is a little

Fig3

m r stacking interaction in compound 1

a, b, c and d represent macroanions, e and f represent coordi-

nation cations. The numbers label the phen molecules in the same macroanion.

Sodium ion that resides in the center of the distorted tetrahedron, which is defined by one oxygen atom of water molecule, one oxygen atom of Keggin unit, and two nitrogen atoms from trien. The sodium ion plays an important role in the stabilization of trien

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ligands. Table 2 Hydrogen " - bonds in conmound 1 D-H

d(H...A)/ L D W d(D...A)/ (7 nm nm

Atom

OW-H 1 1B Nll-H71A N12-H72A NIl-H71B OIW-HI11 02W-H21L 02W-H21J N14-H74A N14-H74B

0 12(~+1/2,-yC 1/2, Z+ 112) 0.1886 03W(-x, -+l, -r+2) 0.2396 N13 0.2405 02W 0.2508 027 0.1964 038 0.1822 0 3 W ( ~r,+ l , ~ + 2 ) 0.2551 0 5 ( ~ + 1 / 2-yt1/2, , ~ + 1 / 2 ) 0.2140 0 6 ( ~ + 1 / 2-j+1/2, , r+1/2) 0.2474

140.62 153.70 112.38 125.63 179.88 154.91 120.45 139.35 135.58

0.2698 0.3284 0.2909 0.3165 0.2835 0.2722 0.3148 0.2935 0.3231

67 1

suggesting an antiferromagnetic interaction. The temperature dependence of l/xmin a range of 50-300 K is in good agreement with the Curie-Weiss law with C=0.9332 emu.K.mol-', 8=-46.796 K. 3.0

1 350

F

300 h

I 2.6 -

250

2-

5f

200 -

2.2 -

.

150

2

v

<

1.8

-

100 50

1.4 --

3.3 Thermal Property

0 0

50

100

150

200

250

300

TIK

The thermal decomposition of compound 1 with a total mass loss of 26.8% in a range of 70-900 "C is divided roughly into three stages(Fig.4). In the first stage, a mass loss of 1.64%, in a range of 70- 302 "C is due to the loss of crystallization and coordination of water molecules(ca1cd. 1.50%). The second mass loss of 3.61% from 302 to 398 "C corresponds to the loss of trien(ca1cd. 3.49%). The third mass loss of 21.5% in the temperature range 407.7-900 "C is attributed to the decomposition of phen molecules (21.49%). The DTA curve has an exothermic peaks resulted from combustion of phen in air and phase transition of the Keggin framework to oxide.

Fig.5 XmT-TandXm-l-Tplotsof compound 1

Acknowledgements We especially acknowledge Pro$ Gao Song of Beijing University for his discussion about magnetic properties. References Pope M. T., Muller A,, Polyoxometalates: From Platonic Solids to Anti-Retroviral AcriviQ, Kluwer Academic, Dordrecht, 1994

Kozhevnikov I. V., Chem. Rev., 1998, 98(1), 171 Coronado E., Gomez-Garcia C. J., Chem. Rev., 1998, 98(1), 273 Rhule J. T., Hill C. L., Judd D. A,, et al., Chem. Rev., 1998, 98(1), I327 Besserguenev A. V., Dickman M. H., Pope M. T., et al., Inorg. Chem., 2001,40,2582

Xu Y.,Xu J. Q., Zhang K. L., et al., Chem. Commun., 2000, 153 Devi R. N., Burkholder E., Zubieta J., Inorg. Chim. Acta, 2003,348, 150 Wang Z. L., Wang J. P., Inorg. Chem. Commun.,2003, 6, Niu J. Y., I272 Reinoso S., Vitoria P., Felices L. S., et al., fnorg. Chem., 2006, 45, 108

I

I

1

0

200

400

I

I

600

800

d 1000

t / r

Fig.4

TG and DTA curves of compound 1

3.4 Magnetic Property The magnetic susceptibilities of compound 1 were measured in the 2-300 K temperature range and are shown as x,T vs. T and l/xm vs. T plots in Fig.5. At 300 K, the xmTvalue is 2.883 emu.K.mol-', which is higher than that expected(0.625 emu.K.mol-') for the spin-only value of five low-spin octahedral Co(I1) atoms. The high xmT value is attributed to orbital contribution and spin-orbital coupling interaction for a system with 2Egbasic term"". The x,T continuously decreases with the lowering of temperature,

Liu K., Meng F. X., Chen Y. G., Chem. Res. Chinese Universities, 2007,23(4). 391 Meng F. X., Sun Y., Liu K., et al., J. Coord. Chem., 2007, 60(4), 40 1 Lisnard L., Dolbecq A,, Mialane P., et al., fnorg. Chim. Acta, 2004, 357, 845 Reinoso S., Vitoria P., Lezama L., et al., fnorg. Chem., 2003, 42, 3 709 Liu F. X., Marchal-Roch C., Bouchard P., et al., Inorg. Chem Commun., 2004,43,2240

Niu J. Y.,Zhao J. W., Wang J. P., et al., J. Mol. Struct., 2004, 699, 85 Sheldrick G. M., SHELXS 97, Program for Crystal Structure Solution, University of Gdttingen, Gdttingen, 1997

Sheldrick G. M., SHELXL 97, Program f o r Crystal Structure Refinement, University of Gbttingen, Gdttingen, 1997

YOUX. Z., Structure and Properties of Coordination Compoundr, Science Press, Beijing, 1992