Magnetic circular dichroism spectra of the octahedral niobium and tantalum subhalide clusters [M6X12]n+

Abstract

The magnetic circular dichroism (m.c.d.) spectra of the octahedral niobium and tantalum subchloride clusters, [M₆Cl₁₂]ⁿ⁺(n= 2, 3, and 4) have been measured in solution at room temperature. The m.c.d. spectra provide for the first time an unambiguous assignment of the electronic spectra of the clusters within a LCAO bonding scheme. The assignment shows that all previous bonding schemes give rise to an incorrect ordering of one-electron levels. Spin-orbit coupling in these cluster systems is considered for the first time, and a revised bonding scheme is proposed on the basis of the new assignment. This is rationalised with the aid of a simple crystal-field model.