STRUCTURAL STUDIES INTO POLYOXOMETALATE DERIVATIVES OF THE KEGGIN STRUCTURE
R.A.Coxall, W.Clegg, R.J.Errington, M.N. Mohamed, R.Bakri
Department of Chemistry, Bedson Building, University of Newcastle upon Tyne, Newcastle upon Tyne, NE1 7RU, U.K.
Keywords: Polyoxometalates, Keggin structure, Heterometallic.
Polyoxometalates are extremely robust and stable against oxidants and this, coupled with the fact that many highly oxidised metal centres are present in these species, makes them good candidates for a range of applications. Thus research into polyoxometalates has increased over recent years with applications in such diverse areas as analytical chemistry,1 catalysis and photocatalysis2 and solid state applications such as electronic and protonic conductors.3 The technique of X - ray crystallography has been essential in understanding the structure and reactivity of such complexes.
The Keggin structure,4 [(XO4)(M12O36)] is adopted by many heteropolyanions and is based on a central XO4 tetrahedron surrounded by twelve MO6 octahedra arranged in four groups of three edge - shared octahedra, M3O13.
Structural studies of two Keggin derivatised complexes [PMo12V2O42]3- and [PNaW11O39]6- have been carried out using a Bruker AXS SMART CCD diffractometer at 160K. We are particularly interested in the coordination of the sodium and vanadium atoms and their attachment to the polyoxometalate cage. In the case of the anion of [PNaW11O39]6-, it was found that the sodium atom is disordered over eight of the twelve tungsten sites whilst in the anion of [PMo12V2O42]3- the polyoxometalate cage is capped by two VO units in a trans disposition. Both complexes were obtained as [nBu4N]+ salts.