New double formates Na3M(HCOO)6 (M = Ga, In) with diamond-like metal framework: Synthesis, structure and coordination modes

Two new double formates, Na3M(HCOO)6 (M = Ga, In), have been synthesized by using quasi-solvothermal method. Both compounds are isostructural, crystallizing in orthorhombic space group Pccn, with lattice parameters a = 14.6279(5) Å, b = 6.2607(1) Å, and c = 13.5132(4) Å for Na3Ga(HCOO)6 and a = 14.6054(5) Å, b = 6.4160(1) Å, and c = 13.9444(3) Å for Na3In(HCOO)6. The structure takes a three-dimensional framework consisting of MO6 and NaO6 octahedra which are connected in edge- and corner-sharing modes. Regarding to the linkage of octahedra, the framework could be considered as a diamond net. The formates in the structure bridge the metal octahedra in an unusual 4.22 connection mode. IR spectroscopy and elemental analysis support the structure characterization. Thermal decomposition process was also studied by TG and X-ray diffraction.