Density functional calculations of 19-electron organometallic molecules.: A comparison of calculated and observed anisotropic hyperfine coupling constants for the CpCo(CO)2- anion.: Implications for determining orbital spin populations from EPR data

The anisotropic hyperfine coupling constants for a 19-electron organometallic complex, CpCo(CO)(2)(-), were calculated using the B3LYP density functional in conjunction with several all-electron basis sets. The calculated hfc constants are generally within 10% of the experimental values as determined by EPR. The calculated wave function indicates that the unpaired electron has a much lower occupancy of the cobalt d(yz) orbital (0.17-0.31) than the value of 0.56 obtained from the EPR data. It is concluded that the traditional method of calculating atomic orbital spin populations from EPR hyperfine coupling constants, which neglects spin polarization and covalency effects, should be used with caution when applied to organometallic systems, No significant structural changes occur in the ligands of CpCo(CO)(2)(-) as a result of having to accommodate an extra electron.