Synthesis of sodium and potassium aluminogermanate inorganic polymers

Abstract

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 27Al 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 3HGe 7O 16·4H 2O, 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 2O and K 3HGe 7O 16·4H 2O 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) 6·7H 2O and K 3HGe 7O 16·4H 2O. 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.