The ground state in tris(acetylacetonato)ruthenium (III) from low-temperature single-crystal magnetic properties

The magnetic susceptibilities of tris(acetylacetonato)ruthenium(III) have been measured between 2.5 and 300 K along the a, b, c, and a* axis directions, together with the magnetizations along the same directions up to a magnetic field of 5 T. There is a small amount of magnetic exchange interaction apparent below 10 K, with Weiss constants up to -0.35 K and the magnetization is fitted with exchange integrals up to -0.38 K in magnitude. A pathway for magnetic exchange in terms of a pair of symmetry-related Ru(acac) rings lying parallel and close is obvious from the structure. The susceptibility results above 10 K have been interpreted in terms of a four-parameter ligand field model (CF1) operating on the ground 2T2g term of the d5 configuration. The t2g orbitals are found to be split by 475 cm-1 by a dominant trigonal symmetry component and then by 50 cm-1 by a subsidiary rhombic component. The single-electron spin-orbit coupling constant is 875 cm-1 and the orbital angular momentum reduction parameter is 0.7. The g-values deduced for the ground Kramers doublet are not in good agreement with those from e.s.r. experiments, but rather better agreement is found for closely allied ligand field parameter sets (CF2) which can fit the susceptibilities at particular temperatures but do not reproduce their temperature dependence well. Consideration of the variation of structural details with temperature indicate that, in fact, the CF2 sets may be more realistic. Copyright (1998) CSIRO Australia