Investigation of the Polymorphism of Osmium Tetrachloride

Abstract

Depending on the method of preparation, osmium tetrachloride may be obtained in two different crystalline modifications, namely the high-temperature and the low-temperature forms. Both these species have been identified by elemental analysis and characterised by their respective x-ray powder photographs and magnetic susceptibilities. The x-ray powder data of the high-temperature form are tentatively rationalized in terms of an orthorhombic unit cell with the following dimensions: a = 12.08 A, b = 11.96 Å and c = 11.68 A. From the x-ray powder digram of the lowtemperature form the cubic lattice constant a = 9.95 Å is deduced. Reflection conditions for hkl and h00 are indicative of the space groups 06(P4332) and 07(P4132). Both compounds are paramagnetic and display low magnetic susceptibilities as a consequence of strong spin-orbit coupling. The high-temperature form exhibits the temperature-independent magnetic susceptibility χmole = +1080 × 10-6 c.g.s. units, whereas for the low-temperature form the value is χmole = +880 × 10-6 c.g.s. units (at 300°K). The latter susceptibility is temperature dependent. Some regularities between the uptake of chlorine by second- and third-row transition metals and the first ionization potential of the metals involved are discussed.