EPR spectroscopic and theoretical study chromium(I) carbonyl phosphine and phosphonite complexes

isotropic and frozen-solution EPR spectra are reported for several Cr(I) carbonyl complexes of the type cis-[Cr(CO)(4)L-2](+), mer- and fac-[Cr(CO)(3)L-3](+), and trans-[Cr(CO)(2)L-4](+), where L is a monodentate (or L-2 a bidentate) phosphine or phosphonite ligand. Extended Huckel molecular orbital theory calculations were performed for cis-and trans-[Cr(CO)(4)L-2], mer- and fac-[Cr(CO)(3)L-3], and cis-and trans-[Cr(CO)(2)L-4] (L = PH3, P(OH)(3)). The EPR results are discussed in light of the electronic structure predictions, which also provide some insights on the oxidation potentials and the isomerization reaction energetics of these complexes. Isotropic P-31 hyperfine couplings can be understood in terms of spin densities in the Cr 3d, P 3s, and P 3p orbitals.