Spontaneous enanti-omorphism in poly-phased alkaline salts of tris-(oxalato)ferrate(III)

Abstract

We show here that the phenomenon of spontaneous resolution of enanti­omers occurs during the crystallization of the sodium and rubidium double salts of the transition metal complex tris­(oxalato)ferrate(III), namely sodium penta­rubidium bis­[tris­(oxalato)ferrate(III)], NaRb₅[Fe(C₂O₄)₃]₂. One enanti­omer of the salt crystallizes in the cubic space group P4₃32 with Z = 4 and a Flack absolute structure parameter x = −0.01 (1) and its chiral counterpart in the space group P4₁32 with x = −0.00 (1). All metal ions are at crystallographic special positions: the iron(III) ion is on a threefold axis, coordinated by three oxalate dianions in a propeller-like conformation. One of the two independent rubidium ions is on a twofold axis in an eightfold coordination with neighbouring oxalate oxygen atoms, and the other one on a threefold axis in a sixfold RbO₆ coordination. The sodium ion is at a site of D₃ point group symmetry in a trigonal–anti­prismatic NaO₆ coordination.