DENSITY-FUNCTIONAL STUDY OF FIRST ROW TRANSITION-METAL DIHALIDES

In contrast to former ligand held predictions, the standard energetic order of the metal 3d orbitals, delta< pi < sigma, is not reproduced h ere. Throughout, the 3d sigma molecular orbital (MO) level is found ra ther low lying because of sigma-donating ligand induced 3d-4s hybridiz ation in these linear dicoordinated compounds, while the 3d pi is rath er high due to the pronounced rr-donor character of the halogen ligand s at the short distances of the digonal halides. This results in an un expected electron distribution for the ground state and in an unusual order of electronic states. The calculations are in general consistent with recent experimental findings. The approach yields semiquantitati vely correct geometric parameters and vibrational frequencies, and qua litatively correct trends for the dissociation energies. Those propert ies show a secondary periodicity, similar to the one known for octahed ral high-spin complexes, though for different electronic reasons. Unkn own structures, vibrational frequencies, and dissociation energies are predicted. (C) 1998 American Institute of Physics. [S0021-9606(98)301 39-7].