Abstract of Publication No. 388
Ralph Schenker, Høgni Weihe, Hans U. Güdel and Berthold Kersting
From polarized optical absorption and emission spectra of the tris-m-thiolato
(L = 2,6-Bis(aminomethyl)-4-tert-butyl-thiophenolate) 1
in the visible and near UV, the exchange splittings of the 4A2
ground and the 2E and 2T1
excited states are determined. In view of the large Cr-Cr
distance of 3.01Å, the antiferromagnetic ground state splitting
with J = 78cm–1 (H = J(SA·SB))
is large compared to other triply bridged Cr3+ dimers.
This can be rationalized using a model based on a valence bond
approach, in which the exchange splittings are derived from
configuration interactions between the ground electron
configuration and ligand-to-metal (LMCT) as well as
metal-to-metal (MMCT) charge-transfer configurations. It allows
us to distinguish the interactions via ligand orbitals from the
direct interactions between the metal-centered orbitals. We
compare our results with those obtained for the tri-m-hydroxo-bridged
(tmtame = N,N',N''-trimethyl-1,1,1-tris(aminomethyl)ethane) 2.
In the latter the interactions via the ligands are negligible,
whereas they play an important role in 1, due to the
softness of the sulfur ligand atoms.