American Chemical Society
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Three Transition-Metal Substituted Polyoxotungstates Containing Keggin Fragments: From Trimer to One-Dimensional Chain to Two-Dimensional Sheet

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journal contribution
posted on 2011-05-04, 00:00 authored by Lijuan Chen, Dongying Shi, Junwei Zhao, Yulong Wang, Pengtao Ma, Jingping Wang, Jingyang Niu
Three novel transition-metal substituted polyoxotungstates based on Keggin fragments, Cs3K3[Co(H2O)6]2[Co(H2O)3(α-GeW11CoO38)3]·30H2O (1), K18{[Mn(H2O)3]2[Mn(H2O)2][(B-β-SiW9O33(OH))Mn3(H2O)(B-β-SiW8O30(OH))]2}·16H2O (2), and K8[Cd(H2O)3]2[Cd4(H2O)2(B-α-SiW9O34)2]·20H2O (3), have been synthesized by reaction of dilacunary Keggin precursors K8[γ-GeW10O36]·6H2O/K8[γ-SiW10O36]·12H2O with transition-metal salts at ambient temperature and characterized by inductively coupled plasma (ICP) analyses, IR spectra, UV spectra, and single-crystal X-ray diffraction. The polyoxoanion of 1 is a novel trimer constructed from three mono-CoII substituted Keggin fragments [α-GeW11CoO38]4− linked by six W−O−Co/W bridges and a capping [Co(H2O)3]2+ bridge. 2 displays the one-dimensional chain built by tetrameric {[Mn(H2O)3]2[Mn(H2O)2][(B-β-SiW9O33(OH))Mn3(H2O)(B-β-SiW8O30(OH))]2}18− units, which is the first one-dimensional silicotungstate containing asymmetric sandwich-type moieties constructed from [B-β-SiW9O34]10− and [B-β-SiW8O31]10− fragments. 3 utilizes the two-dimensional sheet established by tetra-CdII substituted sandwich-type [Cd4(H2O)2(B-α-SiW9O34)2]12− units and [Cd(H2O)3]2+ linkers, representing the first two-dimensional (3,6)-topological network with a Schläfli symbol of 364653 built by sandwich-type Keggin units in polyoxometalate chemistry. Magnetic susceptibility measurements indicate antiferromagnetic exchange interactions within CoII ions in 1 and within MnII ions in 2. The best least-squares fitting values for 2 are J = −1.16 cm−1 and g = 2.13 based on the isostropic spin model. Furthermore, the room-temperature solid-state photoluminescence of 3 displays two emission bands, which are derived from O → Cd ligand-to-metal charge transfer transitions and O → W ligand-to-metal charge transfer transitions, respectively.