Polyoxometalate clusters as building blocks for oxide materials: Synthesis and structure of a three-dimensional copper-pyrazinetetrazolate/Keggin assembly

The hydrothermal reaction of pyrazinetetrazole, copper(II) acetate monohydrate, molybdenum(VI) oxide and 1,2-ethylenediphosphonic acid yields the bimetallic oxide [{Cu4(pyztet)4(Hpyztet)(H2O)2}{Mo12O36(PO4)}]·2H2O (1·2H2O). The framework structure is constructed from {Mo12O36(PO4)}3 − clusters sandwiched between and linking {Cu4(pyztet)5(Hpyztet)(H2O)2}n3n + networks. The Cu(II)-pyrazinetetrazolate substructure contains both ‘4 + 2’ axially distorted and square planar Cu(II) sites. The six-coordinate sites are of two types: the first exhibits {CuN6} coordination to four tetrazolate and two pyrazine nitrogen donors, while the second enjoys {CuN4O2} coordination defined by three tetrazolates and one pyrazine nitrogen donor, an aqua ligand and an oxo-group bridging to the Keggin cluster.