Periodates and periodato-complexes of aluminium, gallium and indium

Abstract

Crystallisation of aluminium or gallium salts with periodic acid at low pH forms [M(H2O)6][IO2(OH)4]3 (M = Al or Ga) which have by characterised by elemental analysis, IR, MAS NMR spectroscopy and X-ray crystallography. Single crystal studies on both revealed disordered structures. The compound [Ga(H2O)6][IO2(OH)4]3 has also been characterised by gallium and iodine K-edge EXAFS studies. Indium(III) nitrate and H5IO6 at pH < 1 produced crystalline H11I2InO14 which contains indium(III) bound to two trans H2O ligands and two chelating [H2I2O10]4– groups, the latter bridging neighbouring indiums to produce an infinite chain. This is the first example of I2O10 groups functioning as chelates and co-ordination is via vertex- rather than the usual edge-linking. At higher pH, gallium and indium produced amorphous insoluble materials of composition M5(IO6)3·nH2O (M = Ga or In) and H3In4(IO6)3·nH2O. Multi-edge EXAFS studies showed that these have structures based upon edge-shared MO6 and IO6 groups and it is proposed that they are Anderson type heteropolyanions A[M4(IO6)3(H2O)6]·nH2O (A = H3, M = In; A and M = Ga or In). The solution behaviour of these three metals in periodate media has been probed by 27Al, 71Ga and 115In NMR spectroscopy, and thermal decomposition of the solid periodate compounds explored by a combination of TGA, IR spectroscopy and PXRD.