Synthesis, characterisation and crystal structure of molybdenum and molybdenum–copper hydroxy-rich Schiff-base complexes

Abstract

The reaction of hydroxy-rich Schiff bases [H₃L = XC₆H₃(OH)CHNC(R)(CH₂OH)₂ where X = H, 5-Cl or 5-Br and R = Me or Et] with [MoO₂(acac)₂](acac = acetylacetonate) gave mononuclear complexes [MoO₂(HL)(MeOH)]. The complexes were characterised by spectroscopic methods and by a single-crystal structure determination. Reaction of the mononuclear complexes with Ph₂PCH₂PPh₂ in methanol or acetonitrile led to five-co-ordinate polymeric compounds of the type [MoO(L)]_n in which the fifth position of the distorted square pyramid is occupied by the oxygen atom of a CH₂O^– moiety of a neighbouring repeat unit. The complex [MoO₂(HL³)(MeOH)][H₃L³= 2-(5-chlorosalicylideneamino)-1,3-dihydroxy-2-methylpropane] reacted with Cu(O₂CMe)₂ in methanol–acetonitrile to yield the mixed-metal cluster [Cu₂Mo₂O₄L³₂(OMe)₂] with a Cu₂Mo₂O₄ cubane-like core. Reflux of this complex with an excess of 2,2′-bipyridine in acetonitrile yielded pale blue-green crystals of the tetranuclear cluster [CuMo₃O₈(HL³)₂(bipy)₂] the structure of which has been determined by X-ray crystallography. The molybdenum part may be described in terms of three oxo-bridged centres, one tetraoxomolybdate [MoO₄]^2– and two six-co-ordinated MoO₂(Schiff base) moieties. The magnetic properties of this compound have been studied in the temperature range 5–300 K.