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.