A density functional based first-principles study of the Jahn−Teller (JT) distortion of VCl4 is presented. The method used in this study includes an exploration of the adiabatic energy surface along the JT active mode as well as a full total energy relaxation along the path of minimal energy. The two approaches are shown to agree extremely well. A calculation of the JT stabilization energy with either method yields 51 cm-1 for the flattened tetrahedron and 40 cm-1 for the elongated conformation. For the JT-distortion a value of 0.08 Å is predicted. The results obtained in this work demonstrate once more the good ability of DFT calculations to predict the state energies as well as the corresponding structural parameters with a reasonable accuracy.

The new DFT based ligand field (LF) model is proposed to calculate the g-and A-tensors of [Co(acacen)] that is known to be a difficult case. The results obtained are compared with the ZORA approach implemented in ADF as well as with the experimental values. The calculations are in good agreement with the experimental data and demonstrate the ability of the method to reproduce the large anisotropy typical for this type of complexes. The ligand field -density functional theory method is therefore not simply a method to calculate multiplet structure, ligand field splittings and UV-Vis transitions, but is also appropriate to compute magnetic properties.

As observed by variable temperature and pressure (13)C NMR, the intramolecular scrambling of carbonyl ligands in Rh(4)(CO)(12) and IrRh(3)(CO)(12) is due to a merry-go-round process (3 &mgr;(2)-CO <--> 3 eta(1)-CO) about any triangular face of the metal tetrahedron. Both cluster compounds have a negative activation volume on going from the bridged ground-state structure of C(3)(v)() symmetry to an unbridged transition state, suggesting that bridged M-M distances are longer than unbridged M-M distances. Site exchange is faster in Rh(4)(CO)(12) than in IrRh(3)(CO)(12) where the apical position is occupied by an iridium atom. Density functional calculations on the bridged and unbridged forms of both cluster compounds have been made at two levels of approximation (LDA and GGA) including relativistic effects for Ir and Rh. LDA reproduces best the experimental distances and shows that opening bridges shortens the M-M bonds. The difference in volume of the bridged and unbridged forms of Rh(4)(CO)(12), as calculated from Connoly surfaces, agrees fairly well with the experimental activation volume. Calculations at the GGA level give the correct trends in energies. ELF maps and overlap population analysis indicate that iridium is more electropositive than rhodium, as suggested by the experimental results.

Jahn−Teller parameters have been calculated for a macrobicyclic cage complex of copper(II) having a CuN6 chromophore by using the density functional theory. Comparison of the calculated values with the corresponding experimental data shows an excellent agreement. The lowest energy on the adiabatic potential surface for the CuN6 chromophore of this complex corresponds to C 2 symmetry resulting from a tetragonally elongated D 3 symmetry with a2b1 occupation.