The chemistry of molybdenum and tungsten. Part 7. Oxomolybdenum(V) and oxotungsten(V) complexes of neutral aromatic Schiff-base ligands

Abstract

A series of oxomolybdenum(V) and oxotungsten(V) complexes of potentially quadridentate (N₂O₂ donor set) and quinquedentate (N₃O₂ donor set) Schiff-base ligands, [MOCl₃(H₂L)](M = Mo or W), has been prepared in which the ligands bind only via the imine nitrogens, acting as neutral N₂ donors in contrast to the usual binding of these ligands as dianionic N₂O₂ or N₃O₂ species. With small chelate backbones between the imine groups the resulting [MOCl₃(H₂L)] complexes appear to be monomeric, and whilst i.r. spectra do not enable a choice to be made between mer and fac structures we have employed e.s.r. results, notably using a series of specially synthesised model complexes, to deduce that these complexes have a mer configuration. With long chelate backbones (six carbon atoms) between the imine groups it is suggested that the [MOCl₃(H₂L)] complexes are dimeric and contain at least two isomeric forms. The molybdenum(V) complexes exhibit g_iso values in fhe range 1.934–1.945 and the tungsten(V) complexes in the range 1.72–1.80.