Synthesis, crystal structure, optical absorption study, and electronic structure of Cs3FeCl5

Abstract

The single crystals of Cs3FeCl5 were synthesized at 973 K using the sealed tube solid-state molten flux method using CsCl as a reactive flux. The polycrystalline sample of Cs3FeCl5 was obtained by the stoichiometric reaction of CsCl and FeCl2 powders at 823 K by the sealed tube solid-state method. The crystal structure of Cs3FeCl5 was determined by single-crystal X-ray diffraction study at 298 (2) K. This ternary halide crystallizes in the body-centered tetragonal crystal system in I4/mcm space group with cell constants of a = b = 9.279 (1) Å and c = 14.824 (3) Å with four formula units per cell. The asymmetric unit of Cs3FeCl5 contains five crystallographically independent atomic sites: Cs1 (site symmetry: m.2 m), Cs2 (422), Fe1 (4¯2 m), Cl1 (..m), and Cl2 (4/m..). Each Fe atom in Cs3FeCl5 structure is bonded to four Cl1 atoms in a slightly distorted tetrahedral fashion to form isolated FeCl42− units. These FeCl42− units are separated by the Cs+ cations and infinite [CsCl] linear chains. Charge balance in this closed-shell compound can be achieved by 3 × Cs+, 1 × Fe2+, and 5 × Cl−. Bond valence sum (BVS) calculation also supports this assignment of formal oxidation states of elements in Cs3FeCl5 structure. The electronic structure calculation for Cs3FeCl5 performed within a density functional theoretical framework predicts a band gap of 3.5 eV, which is in good agreement with the experimental band gap of 3.71 (2) eV, that was estimated from the UV–vis absorption edge study of polycrystalline Cs3FeCl5.