Synthesis of sodium and potassium aluminogermanate inorganic polymers

Synthesis of aluminogermanate inorganic polymers containing sodium as the charge-balancing ion was attempted by reacting NaAlO(2) solution with GeO(2) in an adaption of a sol-gel synthesis for aluminosilicate inorganic polymers. XRD and (27)Al MAS NMR suggested that only a small degree of reaction had occurred, based on the presence of unreacted GeO(2) and a trace of Na(3)HGe(7)O(16)center dot 4H(2)O, with only a small amount of the tetrahedral aluminium characteristic of a true inorganic polymer. The addition of KOH markedly enhanced the reaction, producing a (Na,K) product with properties characteristic of a true inorganic polymer (an amorphous X-ray powder pattern and predominantly tetrahedral aluminium). An attempt to synthesise the potassium end-member aluminogermanate compound by replacement of the NaAlO(2) in the above synthesis with KAlO(2) produced only crystalline K(AlGeO(4))H(2)O and K(3)HGe(7)O(16)center dot 4H(2)O containing solely tetrahedral aluminium. Attempts to extend these syntheses to the gallium analogues of these aluminogermanate compounds were unsuccessful, producing only the crystalline products K(GaGeO(4))(6)center dot 7H(2)O and K(3)HGe(7)O(16)center dot 4H(2)O. Thus, the most successful sol-gel synthesis of a germanate compound with the properties of an inorganic polymer was of an aluminogermanate containing Na(+) and K(+) as the exchangeable cations. (C) 2011 Elsevier B.V. All rights reserved.