Crystal structure of rubidium pentabromodistannate(II)

Abstract

The crystal structure of rubidium pentabromodistannate(II) (RbSn 2Br 5) is determined. The crystals are tetragonal and contain four formula units in a cell of dimensions α = 8.442(2) Å, and c = 14.754(3) Å with D c = 4.54 g cm −3, and D m = 4.44 g cm −3. The structure was solved in the space group I4 mcm . Unlike NaSn 2F 5, which contains discrete [Sn 2F 5] − ions, the structure is a layered lattice consisting of two-dimensional polymeric (Sn 2Br 5) n− n layer units separated by Rb ions. The Sn and bridging Br atoms lie in planes perpendicular to the c-axis at c = 0 and c = 1 2 . Each Sn atom is surrounded by two bridging Br atoms, at 3.105(1) Å, in the plane of the polymer network and by two terminal Br atoms, at 2.755(3) Å, symmetrically above and below the network plane. The bridging Br atoms are surrounded by four equatorial Sn atoms and by two axial Rb atoms in the direction of the c-axis at 3.688(1) Å. The positions of the non-bonding orbitals on the Sn(II) atoms suggest that the lone pairs could be partly delocalized within the polymeric network. The 119Sn Mössbauer data for RbSn 2Br 5 are interpreted in the light of its structural data.