Crystal structure and temperature-dependent properties of Na2H4Ga2GeO8 – a novel gallogermanate

Abstract

Abstract Synthesis, crystal structure and temperature-dependent behavior of Na2H4Ga2GeO8 are reported. This novel gallogermanate crystallizes in space group I41/acd with room-temperature powder diffraction lattice parameters of a = 1298.05(1) pm and c = 870.66(1) pm. The structure consists of MO4 (M = Ga, Ge) tetrahedra in four-ring chains, which are connected by two different (left- and right-handed) helical chains of NaO6 octahedra. Protons coordinating the oxygen atoms of the GaO4 tetrahedra not linked to germanium atoms ensure the charge balance. Structure solution and refinement are based on single crystal X-ray diffraction measurements. Proton positions are estimated using a combined approach of DFT calculations and NMR, FTIR and Raman spectroscopic techniques. The thermal expansion was examined in the range between T = 20(2) K and the compound’s decomposition temperature at 568(5) K, in which no phase transition could be observed, and Debye temperatures of 266(11) and 1566(65) K were determined for the volume expansion.