Mononuclear, dinuclear, and polynuclear dioxomolybdenum(VI)-tridentate Schiff base complexes: crystal structures and properties

Dioxomolybdenum(VI)-tridentate Schiff base complexes, [MoO2{nap-(R)-btol}(py)] (1), [ (MoO2{nap-(R)-btol}),(4,4'-bpy)] (2), and [MoO2{nap-(R) -btol}]. CH2Cl2 (3) (H(2)nap-(R)-btol = (R)-2-[(2-hydroxy-1-naphthyl) methylideneamino] butanol, py = pyridine, 4,4'-bpy = 4,4'-bipyridine) were prepared and their structures determined by the X-ray method. In 1-3, the geometry around molybdenum is a distorted octahedron with one oxide ligand and the Schiff base ligand in the equatorial positions. The other oxide ligand occupies the axial position, and the nitrogen atom of pyridine or 4,4'-bipyridine coordinates at the sixth site of the molybdenum center for 1 or 2 respectively. In 3, the axial oxide ligand of one molecule coordinates to the sixth site of the molybdenum atom in an adjacent molecule to give an infinite linear Mo=O ... Mo=O ... chain. 1 contains only one of the four possible isomers, while 2 and 3 are composed of two isomers. The H-1 NMR spectra suggest rapid isomerization between the isomers in CD,CI, even at low temperatures. The isomerization would proceed via a five coordinate intermediate where rotation of the cis-MoO2 moiety takes place. (C) 1998 Elsevier Science S.A. All rights reserved.