A comparison of the electronic structure of some Group 6A dimetal tetracarboxylates using photoelectron spectroscopy

He(I) and He(II) photoelectron spectra are presented for [Cr2(O2CR)4](R = Me or Et), [CrMo(O2CMe)4], and [Mo2(O2CR)4](R = H, Me, CMe3, or CF3). Ionization energies and intensities are discussed in relation to ab initio and SCF–Xα-SW calculations. A σ2π4δ2 configuration for the metal electrons gives the most plausible explanation for all spectra, but the 2Σ, 2Π and 2Δ ion states lie much closer in energy for the dichromium tetracarboxylates than for the molybdenum analogues.