Anion and cation disorder in [CN_3H_6] centre dot (TaF_6)

摘要

A new guanidinium fluoride tantalate, [CN_3H_6] centre dot (TaF_6), crystallises at 50 deg C from a solution of Ta_2O_5 in 40 percent aqueous HF and of guanidinium chloride. The structure is rhombohedral, R3m space group, with the equivalent hexagonal cell a_H = 8.647(1) A, C_H = 8.507(2) A, Z = 3 and R = 0.029, R_w = 0.077 for 312 reflections. The three-dimensional network is built up from parallel (0001)_H layers propor. to ([CN_3H_6]F_6)~(5-) between which tantalum atoms are inserted. These tantalum atoms, in 3a sites, adopt an octahedral coordination with = 1.894(7) A. (TaF_6)~- anions are disordered over (0001)_H mirror plane related positions while guanidinium cations are disordered over centrosymmetric positions; site occupancy of fluoride and nitrogen sites is fifty per cent.