Spontaneous enanti-omorphism in poly-phased alkaline salts of tris-(oxalato)ferrate(III): crystal structure of cubic NaRb[Fe(CO)].

We show here that the phenomenon of spontaneous resolution of enanti-omers occurs during the crystallization of the sodium and rubidium double salts of the transition metal complex tris-(oxalato)ferrate(III), namely sodium penta-rubidium bis-[tris-(oxalato)ferrate(III)], NaRb[Fe(CO)]. One enanti-omer of the salt crystallizes in the cubic space group 432 with = 4 and a Flack absolute structure parameter = -0.01 (1) and its chiral counterpart in the space group 432 with = -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 RbO coordination. The sodium ion is at a site of point group symmetry in a trigonal-anti-prismatic NaO coordination.