Calculation of the electronic structures and spectra of several organic and inorganic radicals containing aluminum

Electronic structure calculations were performed for AlH⁺, AlH₂, AlH₃^-, AlF⁺, AlF₂, AlH(OH), Al(OH)₂, AlFO⁺, AlCH₂, AlH(CH₃), Al(CO)₂, Al(C₂H₂) and Al(C₂H₄). Isotropic hyperfine coupling constants were predicted from unrestricted, MP2-spin-density-matrix-derived Fermi contact integrals and compared with experimental data. This relatively rapid, correlated method appears to be quite consistent and, after application of a roughly 10% scaling factor, reasonably accurate (±0-20 G depending partly on the magnitude of the coupling constant). The method performs poorly, however, when the expected doublet molecular wavefunctions exhibit significant contamination from spin states of higher multiplicity. Based on these results, the spectral assignment of AlFO⁺ is questioned. The Al(CO)₂ complex is shown to have a remarkably small central bond angle and to require consideration of correlation energy to exhibit a bound ground state. Commentary on the aluminum-acetylene and aluminum-ethylene complexes is offered. Theoretical IR data for AlF₂, Al(OH)₂, AlFO⁺ and A1(CO)₂ are additionally provided.