Hydrothermal synthesis and structural characterization of the aluminogermanate analogues of JBW, montesommaite, analcime and paracelsian

Four aluminogermanates (AlGes), Na-AlGe-JBW (CsAlGe₂O₆) and Rb-AlGe-Para (RbAlGe₃O₈) were synthesized hydrothermally from gels containing GeO₂, Al₂O₃, tetramethyl ammonium hydroxide (TMAOH), alkali metal cation and H₂O. Although TMAOH was not found as an extra-framework species in any of these compounds, synthesis carried out in its absence resulted in the formation of dense phases and other open frameworks, suggesting that it suppresses the crystallization of competing phases. Single crystal X-ray diffraction studies indicate that Na-AlGe-JBW crystallizes in the orthorhombic space group (Pmn2₁, a = 15.445(3), b = 8.357(2), c = 5.307(1) Å, Z = 4). A strictly alternating array of corner-connected AlO₄ and GeO₄ tetrahedra similar to Na₂RbAl₃Ge₃O₁₂-H₂O is observed. There is no evidence of a superlattice in the AlGe in contrast to the aluminosilicate analogue. K-AlGe-MON, the first synthetic analogue of montesommaite, crystallizes in the tetragonal space group (14̄2d, a = 7.373(1), c = 17.513(4) Å, Z = 4). The framework, Ge and Al atoms, share the same crystallographic site with Ge/Al = 1.63. Cs-AlGe-ANA, with the zeolite analcime topology, crystallizes in space group (14̄3d, a = 13.945(2) Å, Z = 16) with Ge and Al disordered over the same crystallographic site and Ge/Al = 2. In Rb-AlGe-Para, with paracelsian topology, disordering in the framework T sites results in a change of symmetry from the monoclinic, P2₁/a, observed in aluminosilicates to orthorhombic (Pnma, a = 8.848(2), b = 9.550(2), c = 10.010(2) Å, Z = 4). The general trend of low Ge/Al ratio is also observed in the four AlGes along with a wider range of values of T-O-T angles compared with their aluminosilicate counterparts.