PERIODATES AND PERIODATO-COMPLEXES OF ALUMINUM, GALLIUM AND INDIUM

Crystallisation of aluminium or gallium salts with periodic acid at lo w pH forms [M(H2O)(6)][IO2(OH)(4)](3) M = Al or Ga) which have by char acterised by elemental analysis, IR, MAS NMR spectroscopy and X-ray cr ystallography. Single crystal studies on both revealed disordered stru ctures. The compound [Ga(H2O)(6)][IO2(OH)(4)](3) has also been charact erised by gallium and iodine K-edge EXAFS studies. Indium(III) nitrate and H5IO6 at pH < 1 produced crystalline H11I2InO14 which contains in dium(III) bound to two trans H2O ligands and two chelating [H2I2O10](4 -) groups the latter bridging neighbouring indiums to produce an infin ite chain. This is the first example of I2O10 groups functioning as ch elates and co-ordination is via vertex- rather than the usual edge-lin king. At higher pH, gallium and indium produced amorphous insoluble ma terials of composition M-5(IO6)(3). nH(2)O (M = Ga or In) and H3In4(IO 6)(3). nH(2)O. Multi-edge EXAFS studies showed that these have structu res based upon edge-shared MO, and IO6 groups and it is proposed that they are Anderson type heteropolyanions A[M-4(IO6)(3)(H2O)(6)]. nH(2)O (A = H-3, M = In; A and M = Ga or In). The solution behaviour of thes e three metals in periodate media has been probed by Al-27,Ga- 71 and In-115 NMR spectroscopy, and thermal decomposition of the solid period ate compounds explored by a combination of TGA, IR spectroscopy and PX RD.