Structural isomerism among octanuclear oxomolybdenum(V) coordination compounds with pyridines. Two isomers of [Mo8O16(OCH3)8(RPy)4]

The condensation of dinuclear {Mo2O4}2+ leads, under conditions of the solvothermal synthesis, to two distinct architectures: (i) the cluster species of [Mo8O16(OCH3)8Py4]·2CH3OH (Py=pyridine, C5H5N) (1·2CH3OH) whose four building blocks, {Mo2O4}2+ units, are linked through doubly or triply bridging oxo and methoxo groups into a compact array; and (ii) [Mo8O16(OCH3)8(4-MePy)4] (4-MePy=4-methylpyridine, C6H7N) (2) which displays an open, bent cyclic structure made of four building blocks linked to each other by pairs of methoxo bridges. The MoMo distances within dinuclear units, 2.5638(12) and 2.6012(13) Å in 1, and 2.5661(3) Å in 2, are characteristic for single metal–metal bonds. All metal atoms of 1 are in a distorted octahedral coordination; each octahedron shares several edges (two, three or four) with its neighbors. Compound 2 displays two types of coordination polyhedra, square pyramids and octahedra (four of each) that are connected through common edges. Each polyhedron shares two edges with the adjacent polyhedra.