Crystal-field splittings and optical spectra of transition-metal mixed-ligand complexes by effective Hamiltonian method

✍ Scribed by A. V. Soudackov; A. L. Tchougreeff; I. A. Misurkin

• Publisher: John Wiley and Sons
• Year: 1996
• Tongue: English
• Weight: 818 KB
• Volume: 57
• Category: Article
• ISSN: 0020-7608
• DOI: 10.1002/(sici)1097-461x(1996)57:4<663::aid-qua13>3.0.co;2-1

✦ Synopsis

Many of the important properties of transition-metal complexes depend on the low-energy excitation spectrum formed by d-electrons of the central transition-metal atom. The spectra of this type are usually fit to the well-known crystal field theory or to the angular overlap model. The result of the fitting is a set of parameters which are considered as characteristics of the electronic structure of the complex such as strength of the ligand field or types and extent of metal-ligand bonding. We present here a short account of the effective Hamiltonian method recently developed to calculate the splitting of the d-levels by the ligands and the resulting d-d spectra of transition-metal complexes together with some results of its application to the mixed-ligand complexes with the general formula ML,Z,, where M = V, Co, Ni; L = H20, NH3, Py; and Z = H,O, N C S , C1-. Particular attention is paid to the V(H,O),Cl, and CdH,O),Cl, compounds. The former seems to have tetragonal structure, whereas for the latter, our method predicts a spatially degenerate ground state for the tetragonal arrangement of the ligands. That must lead to the Jahn-Teller distortion, which is actually observed. 0 1996 John Wiley & Sons, Inc. great interest for chemistry. For the direct quantum chemical calculation of the energies of the d-d excitations, both semiempirical [l-51 and ab initio [6-131 methods based upon the Hartreealculations on the electronic structure of Fock-Roothaan approximation have been applied. transition-metal complexes (TMC) present a

In the case of ab initio calculations with large CI expansions 16-10] or with a special selection of configurations in the MCSCF wave function [ l l , 121, a reasonable agreement of the calculated transition energies with experiment can be obtained.