Metal−Ligand Coupling Elements and Antiferromagnetic Superexchange in Ruthenium Dimers

Antiferromagnetic exchange constants were calculated by using the Mulliken−Hush treatment for metal−ligand coupling elements ( J. Photochem. Photobiol. A: Chem. 1994, 82, 47) and the valence bond model of antiferromagnetic exchange ( Inorg. Chem. 1993, 32, 2850), from the spectral data of the solvent-dependent ligand-to-metal charge-transfer bands of [{(NH 3 ) 5 Ru} 2 (μ-L)] 4+ complexes, where L is a substituted 1,4-dicyanamidobenzene dianion derivative. These calculated values were compared to the corresponding experimental exchange constants that were estimated from the complexes' solvent-dependent room-temperature magnetic moments. The correlation between these values is quite good, and this in turn implies that a relatively unsophisticated level of theory in conjunction with spectroscopy may be all that is necessary to predict trends in molecular properties derived from frontier orbitals.