THE GROUND-STATE IN TRIS(ACETYLACETONATO)RUTHENIUM(III) FROM LOW-TEMPERATURE SINGLE-CRYSTAL MAGNETIC-PROPERTIES

The magnetic susceptibilities of tris(acetylacetonato)ruthenium(III) h ave been measured between 2.5 and 300 K along the a, b, c; and a axis directions, together with the magnetizations along the same direction s up to a magnetic field of 5 T. There is a small amount of magnetic e xchange interaction apparent below 10 K: with Weiss constants up to -0 .35 K and the magnetization is fitted with exchange integrals up to -0 .38K 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 i nterpreted in terms of a four-parameter ligand field model (CF1) Opera ting on the ground T-2(2g), term of the d(5) configuration. The t(2g); orbitals are found to be split by 475 cm(-1) by a dominant trigonal s ymmetry component and then by -50 cm(-1) by a subsidiary rhombic compo nent. The single-electron spin-orbit coupling constant is 875 cm(-1) a nd the orbital angular momentum reduction parameter is 0.7. The g-valu es deduced for the ground Kramers doublet are not in good agreement wi th those from e.s.r. experiments, but rather better agreement is found for closely allied ligand field parameter sets (CF2) which can fit th e susceptibilities at particular temperatures but do not reproduce the ir temperature dependence well. Consideration of the variation of stru ctural details with temperature indicate that, in fact;, the CF2 sets may be more realistic.