Reduction of OsO4 by some imidazolidine-2-thiones. X-ray crystal structure of trans- dichlorotetrakis(NN′-diethylimidazolidine-2-thione)osmium(IV) diperchlorate

Abstract

Osmium tetroxide is reduced to an Os^III complex by reaction with some N-monosubstituted Imidazolidine-2-thiones in H₂O–EtOH in the presence of HClO₄. In order to clarify the mechanism of this reduction, NN′-dimethyl- and NN′-diethyl-Imidazolidine-2-thiones (L), with low reducing power, were employed. Intermediate species of Os^VI and Os^IV with formulae [OsO₂L₄][ClO₄]₂ and [OsCl₂L₄][ClO₄]₂ were isolated. The title compound crystallizes in the triclinic space group P with unit-cell dimensions a= 11.845(2), b= 10.451(2), c= 9.376(3)Å, α= 70.659(9), β= 86.670(9), γ= 86.708(5)°, and z= 1. The structure was solved by the heavy-atom method and refined by least-squares calculations to a conventional R factor of 0.023 for 4 087 counter data. It consists of discrete trans-dichlorotetrakis(NN′-dimethylimidazolidine-2-thione)osmium(IV) dications, in which the metal atom is bonded in a nearly idealized octahedral geometry to four S and two trans CI atoms, and of disordered C1O₄^– anions. The i.r.-active v_asym.(OsCI₂) is assigned at ca. 300 cm^–1 for the [OsC1₂L₄][ClO₄]₂ complexes.