Other than one carbonyl Os(CO)5 2 , and two carbo-nyl halides of the type [OsX(CO)4]2 (X = Br,I) 3 , described by HIEBER and STALLMANN, there has been no reported evidence of compounds containing osmium in oxidation states lower than II. For the carbonyl mono-halides, [OsX(CO)4]2, the authors propose the conventional halogen-bridged configuration, but no physical measurements are given to support this assumption and thus the univalency of osmium. This communication reports a new series of osmium complexes, with triphenylphosphine and triphenyl-arsine, in which the central atom displays the oxidation state I, and an apparent quadricovalency which marks a pronounced departure from all previously known complexes of osmium. The compounds [OsCl (Ph3P) 3], [OsBr (Ph8P) 3], [OsCl(Ph3As)3] and [OsBr(Ph3As)3] are prepared directly from the corresponding hexahalo-genoösmate (IV) and the appropriate ligand which is the sole reducing agent for osmium in the system. (NH4) 20s IV Cl6-f 4.5 Ph3P->• [Os T Cl (Ph3P) 3] +1.5 Ph3PCl2 + 2 NH4C1. Extensive reduction of Os(IV) is achieved by employing relatively high temperatures (120°-150°) and reaction media which prevent compounds of intermediate valencies from precipitating. Ethylene glycol mono-methyl ether (b. p. 124°) and various mixtures of ethanol and ethylene glycol (b. p. 196°) have proved useful solvents in these preparations. The crystals of these complexes are colorless or nearly so and stable in air (decomp. temperatures range from 156° to 198°). They can be considered as essentially diamagnetic (at 25°, // = 0.3 to 0.5 B. M.) which suggests exchange interaction between two neighboring osmium (I) atoms of d 7 configuration. As a conse-1 Presented in part at the International Conference on Coordination Chemistry, London, April, 1959 (Special Publication No. 13, The Chemical Society). 2 W. HIEBER and H. STALLMANN, Z. Elektrochem., 49, 288 [1943]. quence, the spatial arrangements of ligands ought to provide for a relatively short Os-Os distance. A dimeric structure, derived from two parallel square planes (each comprising a quadricovalent formula unit), appears to fulfill this requirement and is not inconsistent with the chemical evidence 4. From precession and Weissenberg photographs a crystal of OsBr(Ph3P)3 was found to be orthorhombic with a= 19.5 Ä, b = 18.7 Ä, and c = 25.6 Ä. It belongs to space group Pbca (No. 61) and has eight formula units per unit cell. The crystal is centrosymmetric and has a calculated density of 1.50. The X-ray powder diffraction patterns of OsBr(Ph3P)3, OsCl(Ph3P)3, OsBr(Ph3As)3 and OsCl(Ph3As)3 are all very similar, which suggests that these complexes are isomorphous. The stereochemistry of OsBr(Ph3P)3 is being studied by X-rays by Dr. P. ORIOLI The osmium (I) complexes are non-electrolytes in nitrobenzene. The observed values for their molecular weights in chloroform fall in the range expected for monomeric species. These results, however, are inconclusive , for they may equally well reflect dissocia-tion of phosphine or arsine ligands from...
