Coordination chemistry of molybdenum and tungsten—VIII. Oxomolybdenum(V) complexes of 8-hydroxyquinoline and relevance of EPR spectra to binding sites in flavoenzymes

MoOCl₃(THF)₂ (THF = tetrahydrofuran) reacts with 8-hydroxyquinoline (QH) to form [MoOCl₃(QH)₂], which contains neutral monodentate ligands, [MoOCl(Q)₂], and anionic bidentate ligands, and the dimeric [Mo₂O₃(Q)₄], which contains anionic bidentate ligands and both terminal and bridging oxo donors. In dichloromethane [MoOCl₃(QH)₂] dissolves to give three species, and epr measurements identify these as unchanged [MoOCl₃(QH)₂], [MoOCl(Q)₂] and a third species characterised by a value of 1.979. No g value of this magnitude has previously been obtained for molybdenum(V) complexes which do not contain sulphur donors, and the significance of epr measurements as an indication of the nature of molybdenum coordination in flavoenzymes must be questioned. These complexes have also been characterised by vibrational and electronic spectral measurements.