Towards understanding the magnetism of Os(iv) complexes: an ab initio insight

Abstract

The magnetism of a recently synthesizedtrans-[OsIVCl4(κN1-Hind)2] complex (5d4-system), where Hind = 2H-indazole, was studied experimentally and theoretically. Relativistic CASSCF/CASPT2 calculations for this and model [OsIVCl6]2−complexes were employed to understand the nature of the low-lying multiplets. It is found that despite strong metal-ligand covalency they are basically characterized by the total angular pseudo-momentumJ̃originating from the spin-orbit coupling of the ground-state spinS= 1 with the orbital pseudo-momentumL̃= 1 of the OsIVion. The strong spin-orbit interaction also preserves the dominantJ̃= 0 character of the non-magnetic ground state in thetrans-[OsIVCl4(κN1-Hind)2] complex despite significant deviation of the ligand environment of OsIVfrom octahedral symmetry. At the same time the spin-orbit admixture of all multiplets arising from the t2g4strong-field electronic configuration is indispensable for the correct description of magnetic properties of OsIVcomplexes. Moreover, based onab initiocalculations, we argue that the charge-transfer states play an important role in the magnetism of the present and probably other 5d complexes, a situation never encountered for 3d and 4f compounds.