Synthesis of sodium and potassium aluminogermanate inorganic polymers

Synthesis of aluminogermanate inorganic polymers containing sodium as the charge-balancing ion was attempted by reacting NaAlO₂ solution with GeO₂ 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 GeO₂ and a trace of Na₃HGe₇O₁₆·4H₂O, 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 NaAlO₂ in the above synthesis with KAlO₂ produced only crystalline K(AlGeO₄)H₂O and K₃HGe₇O₁₆·4H₂O 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(GaGeO₄)₆·7H₂O and K₃HGe₇O₁₆·4H₂O. 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.