Fluorescence excitation spectra of quadruply bonded M_2X_4L_4 complexes

Abstract

Fluorescence excitation spectra have been obtained by monitoring the emissive ^1(δδ*) excited states of Mo_2X_4(PMe_3)_4 (X= CI, Br, I), Mo_2CI_4(AsMe_3)_4), and W_2Cl_4(PMe_3)_4 in solution at 300 and 77 K. The polarization ratios of these transitions, and their shifts in energy arising from substitution of the metal and ligand, have been correlated with predictions derived from available theoretical calculations and photoelectron spectroscopic data to yield self-consistent assignments of all observed bands in the UV region. These bands, with the exception of a poorly characterized one at the edge of the vacuum-UV region, are assigned to singlet excitations from metal-metal (δ, σ, π) and ligand (σ(MP), σ(MX), π(X)) orbitals to the δ* orbital.