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 so lvothermal synthesis, to two distinct architectures: (i) the cluster specie s of [Mo8O16(OCH3)(8)Py-4]. 2CH(3)OH (Py=pyridine, C5H5N) (1 . 2CH(3)OH) wh ose four building blocks, {Mo2O4}(2+) units, are linked through doubly or t riply bridging oxo and methoxo groups into a compact array; and (ii) [Mo8O1 6(OCH3)(8)(4-MePY)(4)] (4-MePy = 4-methylpyridine, C6H7N) (2) which display s an open, bent cyclic structure made of four building blocks linked to eac h other by pairs of methoxo bridges. The Mo-Mo distances within dinuclear u nits, 2.5638(12) and 2.6012(13) Angstrom in 1, and 2.5661(3) Angstrom in 2, are characteristic for single metal-metal bonds. All metal atoms of I are in a distorted octahedral coordination; each octahedron shares several edge s (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 t he adjacent polyhedra. (C) 2001 Elsevier Science BN. All rights reserved.