The Crystal Structure of Trichloroamminebis(triphenylphosphine)osmium(III), OsCl₃(NH₃)(P(C₆H₅)₃)₂

The yellow-orange product obtained from the reaction of oxotrichlorobis(triphenylphosphme)osmium(V) with hydrazine dihydrochloride in refluxing ethanol-water solutions and recrystallized from acetonitrile is shown, on the basis of a diffraction study, to be trichloroamminebis(triphenylphosphine)osmium(III), OsCl₃(NH₃)(P(C₅H₅)₃)₂. The crystal structure has been determined from three-dimensional X-ray data collected by counter methods and has been refined using least-squares techniques to a final R factor, on F, of 3.2% for the 1554 independent reflections above background. The material crystallizes in the monoclinic space group C_2h⁶-I2/a in a cell of dimensions a = 22.429 (8), b = 9.519 (3), c = 15.852 (5) Å, and β = 102.80 (2)°. The density of 1.69 g/cm³ calculated for four formula units in the cell agrees well with the observed density of 1.68 ± 0.01 g/cm³. The well-separated individual molecules are required crystallographically to possess C₂ symmetry. Imposition of C₂ symmetry requires that the ammine hydrogens be disordered, and an NH₃ group freely rotating about the Os-N bond was used as an approximation to this disorder. The configuration about the osmium atom is distorted octahedral with P atoms trans to one another and Cl atoms trans to one another in the basal plane and with the third Cl atom at the one vertex and the ammine group at the other. The only large deviation from an ideal octahedral configuration is a movement of the Cl atoms cis to N toward the nitrogen atom. The Os-N distance is 2.136 (9) Å, and the Os-P distance is 2.411 (2) Å. The Os-Cl distance cis to the N atom is not significantly different from the Os-Cl distance trans to the N atom, and the mean value of these distances is 2.362 (1) Å. The geometric details on this molecule are compared with previous results on aryl- and alkylimino complexes of Re and found to be explicable in terms of intramolecular nonbonded interactions.