First Iridium(IV) Chloride–Dimethyl Sulfoxide Complex [H(dmso)(2)][IrCl(5)(dmso-κO)]: Synthesis and Structure along with Novel Polymorph Modifications of [H(dmso)(2)][trans-IrCl(4)(dmso-κS)(2)] and [H(dmso)][trans-IrCl(4)(dmso-κS)(2)]

[Image: see text] As evidenced by UV–Vis and EPR spectroscopies, the reaction of H(2)IrCl(6)·6H(2)O or Na(2)[IrCl(6)]·nH(2)O with DMSO results in a slow reduction of Ir(IV) avoiding the formation of Ir(IV) dimethyl sulfoxide complexes in measurable quantities. More specifically, we successfully isolated and solved the crystal structure of a sodium hexachloridoiridate(III), Na(3)[IrCl(6)]·2H(2)O, as a product of Na(2)[IrCl(6)]·nH(2)O reduction in an acetone solution. Furthermore, it was shown that [IrCl(5)(Me(2)CO)](−) species is gradually formed in an acetone solution of H(2)IrCl(6)·6H(2)O upon storage. The reaction of DMSO with aged acetone solution of H(2)IrCl(6)·6H(2)O dominated by [IrCl(5)(Me(2)CO)](−) affords a novel iridium(IV) chloride-dimethyl sulfoxide salt [H(dmso)(2)][IrCl(5)(dmso-κO)] (1). The compound was characterized by various spectroscopies (IR, EPR, UV–Vis) and X-ray diffraction techniques applied both to single-crystal and polycrystalline powder. The DMSO ligand is coordinated to the iridium site via the oxygen atom. New polymorph modifications of known iridium(III) complexes [H(dmso)(2)][trans-IrCl(4)(dmso-κS)(2)] and [H(dmso)][trans-IrCl(4)(dmso-κS)(2)] were isolated and structurally elucidated as byproducts of the above reaction.