The crystal structure of tricaesium tetrabromocobaltate(II) bromide, Cs₃CoBr₅, at 4.2 K by neutron diffraction

Abstract

The crystal structure of Cs₃CoBr₅ [I4/mcm, a 946(1), c 1504(2) pm, U 1.346(7) nm³, Z 4] has been determined at 4.2 K by single-crystal neutron diffraction methods. The Co-Br bond length is 239.8(2) pm, and the Br-Co-Br angles of the distorted tetrahedral cobalt environment are 107.58(9) and 110.43(9)º. The neutron scattering lengths of cobalt and bromine were found, by least-squares refinement, to be 2.46(2) × 10^-15 and 6.78(2) × 10^-15 m respectively, relative to a caesium scattering length of 5.38 × 10^-l5 m. The contact distances and thermal parameters of Cs₃CoBr₅, when compared with those from Cs₃CoCl₅, provide further evidence on the stability of M₃CoX₅ salts. The metal ion must be sufficiently large to adequately fill the large holes in the lattice whose size is determined by X^-...X^- contacts.