ELECTRONIC-STRUCTURES OF TETRACHLOROBIS(PHOSPHINE)NIOBIUM(IV) COMPLEXES

Previous interpretation of the EPR spectra of the d1 pseudo-D4h NbCl4(PR3)2 complexes assumed that the unpaired electron resides in the b2g(d(xy)) orbital. In contrast, simple molecular orbital considerations suggest that the unpaired electron resides in the Jahn-Teller unstable e(g)(d(xy)d(yz)) orbital. Ab initio self-consistent field calculations, which should be reasonably accurate for the relative energies of these various d1 states, predict the ground state to be a Jahn-Teller-distorted 2E(g). Although the predicted geometry of this state is in agreement with the X-ray structure, the calculated g values for this and other possible states are incompatible with the experimental g values. We conclude that the observed spectra are due to some other species.