Mono- and di-nuclear tris(pyrazolyl)borato-oxo-tungsten(V) complexes with phenolate ligands: syntheses and structures, and magnetic, electrochemical and UV/Vis/NIR spectroscopic properties

A series of oxo-tungsten(v) complexes of the type [W(Tp*)(O) Cl(OAr)] (mononuclear) and [{W(Tp*)(O)Cl}(2) (mu-OO)] (dinuclear, where 'OO' denotes a para-substituted bis-phenolate bridging ligand) has been prepared and many members structurally characterised. The complexes have been studied by a variety of physical techniques (electrochemistry; EPR spectroscopy; magnetic susceptibility; UV/Vis/NIR spectroelectrochemistry) in order to evaluate the electronic and magnetic interactions between the redox-active, paramagnetic metal centres and to compare the magnitudes of these interactions with those observed for the Mo(v) analogues. It was found that both electronic interactions (as measured by the separation between successive metal-centred redox processes) and magnetic exchange interactions (as determined from variable-temperature magnetic susceptibility studies) are reduced in the W(v) dinuclear complexes compared to their Mo(v) analogues, which we ascribe to a poorer d(pi)-p(pi) overlap between metal and bridging ligand orbitals. In addition the complexes have been fully characterised by UV/ Vis/NIR spectroscopy in all accessible oxidation states, as well as by EPR spectroscopy.