Hydrothermal Syntheses and Structural Characterizations of Polyoxometalate (Mo/W) Compounds Consisting of M-L Cations, (M = Mn, Co, Ni, Cu, Zn; L=3-(2-Pyridyl)pyrazole)

A series of molybdenum/tungsten polyoxometalate compounds, namely, 1 1, M-II(HL)(2)Mo3O10] (M = Mn (1), Co (2), Ni (3)), [Cu-2(II)(L)(2)(HL)(2)](2)(Mo8O26) (4), [Zn(HL)(2)(MoO4)](2)center dot HL center dot 4H(2)O (5), [Cu-4(II)(L)(6)WO4)]center dot 3H(2)O (6) (HL = 3-(2pyridyl)pyrazole), were designed and synthesized under hydrothermal conditions. X-ray diffraction analyses reveal that compounds 1-3 have an isostructural wavelike chain structure consisting of the asymmetric building blocks Of [Mo3O10], in which the ratio of octahedron {MoO6} and square pyramid {MoO5} is 1:2. The hexacoordinated transitional metal cation, just like one "anchor" to fix the above wavelike chain, is linked by two terminal oxygen atoms belonging to two edged asymmetric molybdate [Mo3O10](2-) units, and further chelated by two 3-(2-pyridyl)pyrazole ligands. Although a similar synthetic method in preparation of 1-5 was employed, compounds 4 and 5 show a completely different structure compared to compounds 1-3. Compound 4 is composed of two separate parts of the [Cu-2(II)(L)(2)(HL)(2)](2+) dimer and the epsilon-[Mo8O26](4-) unit. Compound 5 consists of a bimetallic tetranuclear cluster that is constructed from corner-sharing {MoO4} tetrahedra and {ZnN4O2} distorted octahedron forming a cyclic {Zn2Mo2O4} core. For compound 6, a one-dimensional structure is composed Of WO42-, linked by the centrosymmetric tetranuclear copper grids, in which two approximately planar [Cu-II(L)](2) units with an inversion center stack parallel and face-to-face linked by two additional deprotonated ligands of L-1 perpendicularly.