MCD Spectra for Metal-Centered Transitions in the Hg(3)(dppm)(3)(4+) Cluster Complex

The magnetic circular dichroism (MCD) spectrum for Hg(3)(dppm)(3)(SO(4))(2), dppm = bis(diphenylphosphino)methane, in 5:3:2 v/v ethanol-methanol-ether solvent in the range 2.5-3.7 &mgr;m(-)(1) (1 &mgr;m(-)(1) = 10(4) cm(-)(1)) at 295 K (solution) shows two minima at 2.99 and 3.41 &mgr;m(-)(1), which resolve into a positive A term at 3.12 &mgr;m(-)(1) and a negative B term at 3.40 &mgr;m(-)(1) at 80 K (rigid glass). The absorption spectrum shows an intense band at 3.05 &mgr;m(-)(1) at 295 K which sharpens and shifts slightly to 3.09 &mgr;m(-)(1) at 80 K. The 80 K spectrum also reveals a lower intensity band maximum clearly resolved at 3.40 &mgr;m(-)(1). The MCD and absorption spectra are interpreted in terms of 6s 6s sigma --> sigma and 6s 6p sigma --> pi metal-centered transitions. The A term in the region of the lowest energy band is ascribed to the sigma --> pi transition to the spin-orbit E' state of (3)A(2)" origin.