Rare Sandwich-Type Polyoxomolybdates Constructed from Di-/Tetra-Nuclear Transition-Metal Clusters and Trivacant Keggin Germanomolybdate Fragments

Two types of rare sandwich-type germanomolybdates [Na-12(H2O)(36)][Cu-2(beta-Y-GeMo9O33)(2)]center dot 3H(2)O (1), [N(CH3)(4)](4) [Na-6(H2O)(24)][Cr-2(beta-Y-GeMo9O33)(2)]center dot 7H(2)O (2), and [Na-11(H2O)(25)]H[M-4(H2O)(2)(alpha-B-GeMo9O34)(2)]center dot 6H(2)O (M = Ni for 3, M = Mn for 4 and M = Co-II for 5) have been synthesized and characterized by elemental analyses, ICP spectra, IR spectroscopy, UV spectroscopy, thermogravimetry (TG) analyses (for 1-3), X-ray photoelectron spectroscopy (XPS) (for 1 and 3), X-ray powder diffraction (XRPD) (for 1 and 3) and single-crystal X-ray diffraction. To our knowledge, 1-5 represent the first sandwich-type germanomolybdates containing both {beta-Y-GeMo9O33}/ {alpha-B-GeMo9O34} fragments and transition-metal clusters. Interestingly, 1 and 2 display the rare dinuclear transition-metal substituted sandwich-type structures with unusual trivacant {beta-Y-GeMo9O33} germanomolybdate units whereas 3-5 exhibit the first tetranuclear transition-metal substituted sandwich-type structures with familiar trivacant {alpha-B-GeMo9O34} germanomolybdate units. Surface photovoltage spectroscopy (SPS) and electric field induced surface photovoltage spectroscopy (EFISPS) measurements reveal that 1 and 3 bear the behavior of the n-type semiconductor. Magnetic measurements indicate 1 and 3 demonstrate antiferromagnetic exchange interactions and ferromagnetic exchange interactions, respectively.