научная статья по теме A 2D ORGANIC-INORGANIC HYBRID [CU(EN)2(H2O)]2[CU(EN)2]4[SI2CU2W22O78] · 7H2O ASSEMBLED FROM MONOCOPPER(II)-SUBSTITUTED KEGGIN SILICOTUNGSTATE DIMERS Химия

УДК 541.49

A 2D ORGANIC-INORGANIC HYBRID [Cu(En)2(H2O)]2[Cu(En)2]4[Si2Cu2W22O78] • 7H2O ASSEMBLED FROM MONOCOPPER(II)-SUBSTITUTED KEGGIN SILICOTUNGSTATE DIMERS © 2012 J. Luo1, 2, L. J. Chen1, 2, *, D. Y. Shi1, Y. Y. Li1, and J. W. Zhao1, *

1 Institute of Molecular and Crystal Engineering, College of Chemistry and Chemical Engineering, Henan University,

Kaifeng, Henan, 475004 P.R. China 2Basic Experiment Teaching Center, Henan University, Kaifeng, Henan 475004, P.R. China *E-mail: ljchen@henu.edu.cn; zhaojunwei@henu.edu.cn Received August 10, 2011

The reaction of Na10L4-a-SiW9O34] • 18H2O with CuCl2 • 2H2O in the participation of ethylenediamine (En) under hydrothermal conditions resulted in a 2D organic-inorganic hybrid monocopper(II)-substituted Keggin silicotungstate [Cu(En)2(H2O)]2[Cu(En)2]4[Si2Cu2W22O78] • 7H2O (I), which was structurally characterized by elemental analyses, IR spectrum, UV spectrum, powder X-ray diffraction (PXRD), and single-crystal X-ray diffraction. Single crystal structural analysis shows that adjacent monocopper(II)-substituted Keggin silicotungstate [Si2Cu2W22O78]12- dimeric subunits are interconnected by sharing terminal oxygen atoms to make the 1D polymeric linear chain and neighboring chains are combined with each other through [Cu(En)2]2+ connectors giving rise to an interesting 2D organic-inorganic hybrid sheet architecture with a 4-connected topology. To our knowledge, I is the rare organic-inorganic hybrid 2D polyoxometate constructed by mono-transition-metal substituted Keggin silicotungstate dimeric subunits. The photocatalytic measurement illustrates that I can to some extent inhibit the photodegradation of rhodamine-B.

INTRODUCTION

Polyoxometalates (POMs), as a unique class of fascinating metal-oxygen cluster species with enormous structural varieties and interesting properties, have been extensively studied due to their actual and potential applications in diverse fields, such as catalysis, material science and magnetism [1—4]. It has been long recognized that the incorporation of transition-metal complexes (TMCs) to the lacunary POM matrixes or surfaces provides a very effective approach for the design and preparation of novel inorganic-organic hybrid POM-based materials that bear both features of inorganic and organic components [5]. The in-situ formed TMCs can function as charge compensation cations, modify inorganic POM surfaces and frameworks, or join discrete clusters into extended architectures [6]. Recently, we have concentrated on the exploration on the hydrothermal reactivity of lacunary POM precursors with electrophilic transition-metal (TM) cations in the participation of organic ligands with aim of discovering novel TMCs-containing POMs with unexpected structures and properties. Thus, a family of unique TMCs-containing POMs have been prepared in our lab, such as a CdSO4-like 3D framework [Cu(En)2]3[a-AsW11NaO39] • 2H2O [7], three multi-nickel substituted arsenotungstates [EnH2]2[Ni(H2O)4]2[Ni(En)2]2[Ni(En)]2{[(a-AsW6O26) Ni6(OH)2(H2O)3(En)CB-a-AsW9O34)yW4Oi6]

[Ni3(H2O)2(En)]2} • I6H2O [8], [Ni(H2O)(En)2]2 [Ni(H2O)3(En)][Ni(H2O)(En)]{[(a-AsW6O26)Ni6(OH)2

(En)2.5(£-a-AsW9O34)]2H4[W4Oi6][Ni4(H2O)2(En)2]2} •

• 13H2O [8], and [Na(H2O)3]2[Ni(H2O)6]2[Ni(H2O)5] {[Ni3(Dap)(H2O)2]2(H2W4Oi6)}{(a-H2AsW6O26) [Ni6(OH)2(H2O)(Dap)2]CB-a-HAsW9O34)}2 • 7^O (Dap = 1,2-diaminopropane) [9] and a dimer [EnH2]4{[Cu(En)2][(4-p-H2AsW9O34)Cu(En)2]2} •

• 8H2O containing [A-P-AsW9O34]9- fragments [10]. As a part of our ongoing work, the hydrothermal reaction of Na10[A-a-SiW9O34] • 18H2O with CuCl2 • 2H2O in the presence of En led to a 2D organic-inorganic hybrid monocopper(II)-substituted Keggin silicotungstate [Cu(En)2(H2O)]2[Cu(En)2]4[Si2Cu2W22O78] • 7H2O (I). Interestingly, adjacent monocopper(II)-substitut-ed [Si2Cu2W22O78]12- dimeric subunits are interconnected by sharing terminal oxygen atoms to make the 1D polymeric linear chain and neighboring chains are combined with each other through [Cu(En)2]2+ connectors giving rise to an interesting 2D organic-inorganic hybrid sheet architecture with a 4-connected topology. Although several 0D and 1D monocop-per(II)-substituted Keggin silicotungstates, such as K5[Cu(Ac)(Pmdien)][SiW11CuO39] • 12H2O (Ac = = acetate, Pmdien = N,N,N',N'',N"-pentamethyldi-ethylentriamine) [11], K14[{Cu2(Bipy)2(^-Ox)} {SiW11O39Cu(H2O)}]2[SiW11O39Cu(H2O)] • ~55H2O

859

3*

(Bipy = 2,2'-bipyridine, Ox = oxalate) [12], K4[{SiW11O39Cu(H2O)}{Cu2(Ac)2(Phen)2(H2O)}] • • 14H2O (Phen = phenanthroline) [13], and {[Cu(De-ta)(H2O)2]2[Cu(Deta)(H2O)][a-XCuWnO39]} • 5H2O (Deta = diethylenetriamine) [5] have been reported. To our knowledge, I is a rare organic-inorganic hybrid 2D POM constructed by mono-TM substituted Keggin silicotungstate dimeric subunits. By means of UV-visible spectra, we examined the degradation of the rhodamine-B by the 500 W Hg lamp irradiation in the presence of I as the photocatalyst.

EXPERIMENTAL

Materials and methods. Na10[4-a-SiW9O34] • 18H2O was prepared according to the literature [14] and confirmed by IR spectrum. All other chemicals used for synthesis were reagent grade and used without further purification. Elemental analyses (C, H, and N) were performed on a Perkin-Elmer 240C elemental analyzer. The IR spectrum was recorded from a sample powder palletized with KBr on a Nicolet FT-IR 360 spectrometer in the range of 4000—400 cm-1. The UV-vis-ible spectrum was obtained with a U-4100 spectrometer at room temperature. PXRD measurement was performed on a Philips X'Pert-MPD instrument with CuZ"a radiation (A = 1.54056 A) in the angular range 29 = 10°-45° at 293 K.

Synthesis of I. Na10[4-a-SiW9O34] • 18H2O (0.300 g, 10.788 mmol) and Cu(CH3COO)2 • H2O (0.063 g, 31.555 mmol) were suspended in H2O (5 mL), to which En (0.050 mL, 0.740 mmol) was added under stirring. The resulting mixture was stirred for 3 h, sealed in a 25 mL Teflon-lined stainless steel autoclave, kept for 5 days at 160°C and then cooled to room temperature. Purple prismatic crystals were filtered, washed with distilled water and dried in air at ambient temperature. The yield was ~41% (based on Na10[^-a-SiW9O34] • 18H2O).

For C24HmN24O87Si2Cu8W22

anal. calcd., %: C, 4.28; H, 1.70; N, 4.99. Found, %: C, 4.35; H, 1.86; N, 4.90.

As I contains the monovacant Keggin [a-SiW11O39]8- fragments, when the precursor [a-SiW11O39]8- in place of [^-a-SiW9O34]10- was used to react with Cu(CH3COO)2 • H2O under similar conditions, we failed to obtain I. The result indicates that [^-a-SiW9O34]10- plays an important role in the formation of I. Interestingly, the transformation of the trivacant [^-a-SiW9O34]9- to the monovacant [a-SiW11O39]8- occurred, which is very similar to the evolution of [^-a-PW9O34]9- ^ [a-PW11O39]7- in the preparation of the 3d-4f heterometallic POM

[Cu(Dap)2(H2O)][Cu(Dap)2]4.5[Gd(a-PWnO39)2] • • 5H2O reported by us [15].

X-ray crystal determination. A purple prismatic crystal was carefully selected under an optical microscope and glued at the tip of a thin glass fiber with cy-anoacrylate adhesive. Intensity data were collected on a Bruker APEX-II CCD detector at 296(2) K with a Mo!a radiation (A = 0.71073 A). Direct methods were used to solve the structures and to locate the heavy atoms using the SHELXTL-97 program package [16]. The remaining atoms were found from successive full-matrix least-squares refinements on F2 and Fourier syntheses. Lorentz polarization and empirical absorption corrections were applied. In I, the W(3), W(12), W(13), and W(22) positions are simultaneously statistically occupied by copper(II) and tungsten(VI) elements with half occupancy for each, resulting in one expected Cu2+ ion per Keggin cage on the charge balance and crystallographic considerations, which is very common in POM chemistry [5, 17]. All of the non-hydrogen atoms were refined anisotropically. All hydrogen atoms were placed in the idealized positions and refined with a riding model using default SHELXL parameters. The hydrogen atoms attached to lattice water molecules were not located. The weighting detail: w = 1/[ct 2 (Fo2) + (0.0599P)2 + 448.2024P], where

P = (Fo2 + 2Fc2 )/3. The crystallographic data are listed in table. The atomic coordinates and other parameters of structure I have been deposited with the Cambridge Crystallographic Data Centre (no. 838105; deposit@ccdc.cam.ac.uk or http://www.ccdc.cam. ac.uk).

RESULTS AND DISCUSSION

In order to characterize the purity of I, the PXRD has been measured. The experimental PXRD pattern of the bulk product of I is in good consistent with the simulated PXRD pattern from single-crystal X-ray diffraction, showing that the phase of the sample is pure (Fig. 1). Both differences in intensity are related to the variation in preferred orientation of the powder sample during collection of the experimental PXRD. X-ray single-crystal structure analysis indicates that the molecular structural unit of I (Fig. 2a) consists of a monocopper(II)-substituted Keggin silicotungstate [Si2Cu2W22O78]12- dimeric subunit, one discrete [Cu(En)2(H2O)]2+ cation, three supporting [Cu(En)2]2+ cations, one supporting [Cu(En)2(H2O)]2+ cation and one bridging [Cu(En)2]2+ cation and seven lattice water molecules. Notably, there are six crystallographically unique Cu2+ cations (Cu(1), Cu(2), Cu(3), Cu(4), Cu(5), and Cu(6)) in I. The supporting [Cu(1)(En)2]2+, [Cu(3)(En)2]2+, and [Cu(6)(En)2]2+ cations inhibit in the square pyramid geometry established by four nitrogen atoms from two En ligands

KOOP^HH^HOHHAtf XHMHfl TOM 38 № 12 2012

A 2D ORGANIC-INORGANIC HYBRID [Cu(En)2(H2O)]2[Cu(En)2]4[Si2Cu2W22O78] • 7H2O 861

(Cu—N 1.95(2)—2.07(2) A) and one terminal oxygen atom from the [Si2Cu2W22O78]12- dimeric subunit (Cu-O 2.30(2)—2.53(2) A). The supporting [Cu2(En)2(H2O)]2+ cation adopts the six-coordinate octahedral geometry, in which four nitrogen atoms from two En ligands build the basal plane (Cu—N 1.99(3)—2.05(3) A) and a terminal oxygen atom from the

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