Preparation and characterisation of [M(CN)(4)O(pz)](2-) complexes (M = Mo or W) and their reactivity towards molecular oxygen

The synthesis and characterisation of (PPh4)(2)[M(CN)(4)O(pz)]. 3H(2)O (M = Mo or W; pz = pyrazine) are presented. The salts are reactive towards mole cular oxygen, both in solution and in the solid state, with formation of (P Ph4)(2)[M(CN)(4)O(O-2)]. The X-ray crystal structure of the molybdenum comp ound confirmed the presence of a peroxo ligand cis to the M=O bond; the O-O bond distance is 1.41 Angstrom. The IR spectra exhibit two absorption band s in the 950-850 cm(-1) region assigned to the terminal M=O group [917 (Mo) and 933 (W) cm(-1)] and the peroxo group [893 (Mo) and 871 (W) cm(-1)]. Th e possible mechanism of molecular oxygen uptake by pyrazine complexes is di scussed. (C) 2000 Elsevier Science Ltd. All rights reserved.