(NH_4)_2GeF_6·H_2O is obtained as light-green single crystal from the low-temperature solvothermal reaction of GeO_2, NH_4VO_3 and HF in pyridine-water and characterized by the IR, elemental analysis, TG-DTA and single crystal X-ray diffraction. It crystallizes into cubical system, space group Fm3m, a = 0.9118(2) nm, β = 90 °, V = 0.7580 (3) nm~3, Z = 1, D_c = 2.021 g/cm~3, F(000) = 432, R_1 = 0.0612, wR_2 = 0. 1510 for 357 reflections. The structure of the title compound consists of four GeF_6~(2-) units, four crystal H_2O and eight NH_4~+ cations. It is interesting that there exit GeF_6~(2-) octahedra with high O_h symmetry. Moreover, the GeF_6~(2-) and H_2O connected 3-D grid-shaped network through F…H-O hydrogen bonds. NH_4~+ cations locate in the center of the grids and the electrostatic interactions between NH_4~+ and GeF_6~(2-) further stabilize the supramolecular network.

Key words: GERMANATE, AMMONIUM COMPOUND, FLUORINE COMPOUNDS, CRYSTAL STRUCTURE, SUPERMOLECULAR STRUCTURE, HYDROFLUORIC ACID, PYRIDINE