Magnetic exchange and zero-field splitting in the d3[OsVCl6]– ion

Abstract

The principal magnetic susceptibilities, and magnetisations, of [PPh₄][Os^VCl₆] are reported for temperatures between 4.5 and 300 K at 1.0 T, and between 2.5 and 20 K at 0.25 to 5.0 T respectively. The data are interpreted in terms of zero-field splitting of the ground ⁴A_2g term [D=–16.5(1.5) cm^–1], large because of the high spin-orbit coupling constant for the Os⁵⁺ ion, with smaller Ising antiferromagnetic exchange [J=–8(2) cm^–1], probably of one-dimensional nature, given the constraints of the crystal structure. This appears to be the first observation of one-dimensional magnetic exchange in a heavy transition-metal complex. A DV-Xα calculation on the [OsCl₆]^– ion in its experimental tetragonal geometry is included, which estimates, inter alia, the overall d-orbital splitting, 10Dq, the low-symmetry energy splitting of the t_2g orbitals, and the orbital angular momentum reduction factor, k. Crystal-field calculations, using similar values of these parameters, together with reasonable values for spin-orbit coupling and Racah parameters, agree with the magnetic behaviour and optical spectrum. In particular the large negative, zero-field splitting parameter, D, is reproduced.