The crystal structure of sodium pentafluorodistannate(II), NaSn₂F₅

The crystal structure of sodium pentafluorodistannate(II), :NaSn2Fs, has been determined from single-crystal X-ray data. The compound is tetragonal, space group P42/nbc , with a =9-020 and c = 13-685 A, and there are eight formula units per unit cell. Anisotropic least-squares refinement was made with a final R of 5.6%. Discrete Sn2F ~" groups are observed. These complex ions consist of two SnF~. groups bridged by a fluorine atom lying on a twofold axis. The Sn2F ~-groups are linked by two Sn-F bonds of 2.53 /~ so that infinite chains of these groups lie parallel to c. The Sn-F distance in the bridge is 2.22 0.01 A and the other Sn-F distances are 2.07 0.02 and 2.08 i 0.02 A. Sodium atoms have both six and eightfold coordination with fluorine atoms.