Exchange pathways in tris-mu-thiolato-bridged [Cr(2)L(3)](ClO(4)2Cl*H2O*MeOH (L=2,6-bis(aminomethyl)-4-tert-butyl-thiophenolate).
From polarized optical absorption and emission spectra of the tris-mu-thiolato bridged [Cr(2)L(3)](ClO(4))(2)Cl.H(2)O.MeOH (L = 2,6-bis(aminomethyl)-4-tert-butyl-thiophenolate) 1 in the visible and near UV, the exchange splittings of the (4)A(2) ground and the (2)E and (2)T(1) excited states are determined. In view of the large Cr-Cr distance of 3.01 A, the antiferromagnetic ground state splitting with J = 78 cm(-1) (H = J(S(A).S(B))) is large compared to other triply bridged Cr(3+) 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-mu-hydroxo-bridged [Cr(2)(OH)(3)(tmtame)(2)](NO(3))(3) (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.
Schenker
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Departement für Chemie und Biochemie, Universität Bern, Freiestrasse 3, CH-3000 Bern 9, Switzerland.
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Kersting
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