ArticlePDF Available

Abstract

The effective crystal field method for calculating the magnetic and optical properties of transition metal complexes is extended to take into account the electrons that fill the ligand molecular orbitals whose occupancy changes during chemical transformations. An effective Hamiltonian is constructed for a system of strongly correlating d-shell electrons and electrons on ligand orbitals that intersect each other during a reaction. Taking into account complete configuration interaction for this subsystem makes it possible to determine the structure of the ground and excited electronic states. The suggested calculation procedure is applied to isomerization of quadricyclane to norbornadiene in the coordination sphere of Co-tetraphenylporphyrin.
Article
The theory of catalytic activity of transition-metal compounds is a fascinating problem especially if a comparison of different catalysts is necessary. The isomerization of quadricyclane (QC) to norbornadiene (NB) catalyzed by transition-metal porphyrins is a challenge and incidentally a suitable benchmark for various theories of catalysis. We analyze this process in detail using a valence bond-like scheme adjusted for the description of reaction centers containing transition-metal atoms. A qualitative explanation of contrasting catalytic behavior of Mn-phthalocyanine and Co-tetraphenylporphyrin is obtained from the analysis of the spectra of local many electron states of free catalysts and their complexes with the reactant/product. This picture is supported by the numerical analysis of potential energy profiles for the QC to NB isomerization in the presence of a catalyst performed in the effective Hamiltonian approximation. This exemplary reaction is put in a more general perspective of theories of catalytic activity of transition-metal complexes and in relation with oxygenation reactions. V C 2013 Wiley Periodicals, Inc.
Article
The application of an effective electron Hamiltonian approach to the description of the electronic structure of transition metal complexes with chemically active ligands is analyzed. This approach is implemented in a computational code. The evolution of the electronic structure along a path of isomerization of quadricyclane to norbornadiene in the coordination sphere of Co-tetraphenylporphyrin is considered. In addition, the electronic states of atomic oxygen coordinated to transition metal oxides and metal porphyrins are studied. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 84: 99–109, 2001
Article
Publisher Summary This chapter presents the specific catalytic functions of the transition metal in the various types of transformations, and discusses the associated chemistry. Molecular orbital symmetry conservation constrains all molecular systems to specific paths of transformation. Symmetry conservation principles have proven to be powerful tools for understanding a large body of complex organic chemistry. These concepts further bear on molecular stability. A molecule in one bonding configuration transforms into other configurations primarily through allowed paths. The thermal stability enjoyed by simple olefins to a certain extent rests on orbital symmetry restraints. Both olefin cyclobutanation and double-bond isomerization (through a 1,3-hydrogen shift), involving forbidden passages, are not observed at moderate temperatures. Simple olefins are fixed in their bonding configurations and cannot interconvert through the sterically-preferred paths. The thermal interconversion of olefins is necessarily a high-temperature process involving predominantly the higher energy, allowed transformations incorporating free radical intermediates.
Article
Aus den nach bekannten Verfahren hergestellten Quadricyclanen (I), (III), (V) und (VII) entstehen bei der Behandlung mit Rhodium(I)-Komplexen in einer thermodynamisch kontrollierten Reaktion die Norbornadien-Derivate (II), (IV), (VI) bzw. (VIII), während aus dem Oxa-quadricyclan (IX) in einer kinetisch kontrollierten Reaktion das thermodynamisch stabilere Hydroxyfulven (X) erhalten wird.
Article
A spin-averaged Hartree–Fock (SAHF) procedure is examined within the framework of the configuration-averaged methodology proposed earlier. The SAHF method produces reasonable total energies and can be successfully used for the calculation of electronic spectra, especially in the cases of marked energy separation between the spin states. An example is given with the spectroscopy of Mn2+ ions in the ZnS crystal where the SAHF procedure provides a more accurate interpretation of the electronic spectrum than that obtained by other self-consistent-field methods. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 65: 877–884, 1997
Article
The mechanism of the catalytic activity of transition metal complexes is discussed in terms of an effective Hamiltonian of a reactant-catalyst system. The potential energy surface has been constructed for the reaction of catalytic isomerization of quadricyclane to nonbornadiene. The properties of the catalyst are found to affect strongly the activation energy of the reaction.
Article
A general scheme for theoretical treatment of organometallic reactivity is proposed. It is based upon the notion that the reactivity of a molecule is strongly affected by its coordination to metal-containing fragments. Based upon this idea we describe the large-scale organometallic reactions as reactions of the ligands in the coordination spheres of transition metal complexes. We propose here a quantum mechanical framework for analysis of effects of coordination on the reactivity and give several examples of qualitative energy profiles for reactions in the ligand spheres of transition metal complexes. © 1996 John Wiley & Sons, Inc.
Article
(Porphinato)iron(III) complexes can exist as low-spin doublets, high-spin sextets, and intermediate-spin quartets. While the experimental ground state depends on the nature and number of axial ligands, INDO calculations on the five-coordinate (porphinato)iron(III) chloride of this study suggests a high-spin sextet and an intermediate-spin quartet to be nearly degenerate in energy. The lowest doublet is calculated some 8000 cm-1 above the sextet. The calculated UV/visible spectra of each of these states are reported and compared to experimental spectra and ab initio calculated spectra.
Article
Restricted Hartree-Fock plus configuration interaction and generalized molecular orbital plus configuration interaction calculations are reported for several structural models of the dioxygen complexes of manganese(II) porphyrins. An analysis of the results suggests a ground-state structure with a side-on (Griffith) dioxygen and oxygen atoms eclipsing the ring nitrogens. The calculation predicts three singly occupied metal orbitals (t22e1 in pseudocubic symmetry; σ1π1β1 in pseudolinear symmetry) in agreement with the ESR results. In contrast to previous ab initio calculations, the CI results also predict a ground-state end-on (Pauling) structure with three unpaired electrons in metal orbitals that would be consistent with the ESR. On the basis of our calculations alone, this structure could not be eliminated as a possibility.
Article
Magnetic and optical properties of transition-metal complexes are governed by the ground state and the low-energy excitation spectrum of the d-shell of the central transition metal ion. These spectra are successfully fit to the crystal field theory. We present here an account of the effective Hamiltonian method recently developed to calculate the ground state and the excitations of the d-shells of transition-metal complexes and report the results of its application to some complexes of particular interest. © 1996 John Wiley & Sons, Inc.