Calculation of Zero-Field Splittings, g-Values, and the Relativistic Nephelauxetic Effect in Transition Metal Complexes. Application to High-Spin Ferric Complexes
- 1 December 1998
- journal article
- research article
- Published by American Chemical Society (ACS) in Inorganic Chemistry
- Vol. 37 (26), 6568-6582
- https://doi.org/10.1021/ic980948i
Abstract
Equations are derived and discussed that allow the computation of zero-field splitting (ZFS) tensors in transition metal complexes for any value of the ground-state total spin S. An effective Hamiltonian technique is used and the calculation is carried to second order for orbitally nondegenerate ground states. The theory includes contributions from excited states of spin S and S ± 1. This makes the theory more general than earlier treatments. Explicit equations are derived for the case where all states are well described by single-determinantal wave functions, for example restricted open shell Hartree−Fock (HF) and spin-polarized HF or density functional (DFT) calculation schemes. Matrix elements are evaluated for many electron wave functions that result from a molecular orbital (MO) treatment including configuration interaction (CI). A computational implementation in terms of bonded functions is outlined. The problem of ZFS in high-spin ferric complexes is treated at some length, and contributions due to low-symmetry distortions, anisotropic covalency, charge-transfer states, and ligand spin−orbit coupling are discussed. ROHF-INDO/S-CI results are presented for FeCl4- and used to evaluate the importance of the various terms. Finally, contributions to the experimentally observed reduction of the metal spin−orbit coupling constants (the relativistic nephelauxetic effect) are discussed. B3LYP and Hartree−Fock calculations for FeCl4- are used to characterize the change of the iron 3d radial function upon complex formation. It is found that the iron 3d radial distribution function is significantly expanded and that the expansion is anisotropic. This is interpreted as a combination of reduction in effective charge on the metal 3d electrons (central field covalence) together with expansive promotion effects that are a necessary consequence of chemical bond formation. The 〈r-3〉3d values that are important in the interpretation of magnetic data are up to 15% reduced from their free-ion value before any metal−ligand orbital mixing (symmetry-restricted covalency) is taken into account. Thus the use of free-ion values for spin−orbit coupling and related constants in the analysis of experimental data leads to values for MO coefficients that overestimate the metal−ligand covalency.Keywords
This publication has 69 references indexed in Scilit:
- Electronic Structural Contributions togValues and Molybdenum Hyperfine Coupling Constants in Oxyhalide Anions of Molybdenum(V)Inorganic Chemistry, 1996
- Accurate empirical spin-orbit coupling parameters .zeta.nd for gaseous ndq transition metal ions. The parametrical multiplet term modelInorganic Chemistry, 1993
- Electronic structures and d—d spectra of vanadium(IV) and VO2+complexes: discrete variational Xα calculationsJ. Chem. Soc., Dalton Trans., 1991
- Variable photon energy photoelectron spectroscopy on FeCl4-. An unusual electronic structure for high-spin d5 complexesJournal of the American Chemical Society, 1990
- A configuration‐averaged Hartree–Fock procedureInternational Journal of Quantum Chemistry, 1989
- Variable photon energy photoelectron spectroscopic studies of copper chlorides: an experimental probe of metal-ligand bonding and changes in electronic structure on ionizationJournal of the American Chemical Society, 1988
- A generalized restricted open-shell Fock operatorTheoretical Chemistry Accounts, 1987
- Spin–orbit coupling and inelastic transitions in collisions of O(1D) with Ar, Kr, and XeThe Journal of Chemical Physics, 1979
- Spin Hamiltonian for Cr III Complexes. Calculation from Crystal Field and Molecular Orbital Models and ESR Determination for Some Ethylenediammine ComplexesThe Journal of Chemical Physics, 1964
- The Physical Nature of the Chemical BondReviews of Modern Physics, 1962