Ligand-field theory

Abstract

THE chemical and physical properties which we think of as characteristic of transition metals, for example their variable valencies and the colours of their compounds, are almost all associated with the presence of an incomplete shell of d electrons. I n this Review we shall consider, qualitatively, two closely related theories which deal with the effect of the neighbours of a transition-metal ion on the behaviour of the d electrons of the metal, and hence on the properties of the ion. The first theory, usually called the crystal field or electrostatic theory, was developed by Bethe, Van Vleck, 2 and many others 39 4, t i in connection with studies on magnetism. The second theory, the molecular-orbital theory, was also discussed a t an early date by Van More recently each theory has been used to discuss the optical and chemical properties of a variety of compounds. We regard them both as expressing certain aspects of a more complete theory which we call ligand-field theory.

The electronic structure and spectra of octacyanide complexes

“…This leaves one non-bonding d orbital which is occupied by two electrons. Griffith and Orgel [3] have tentatively arranged the d orbitals in order of energy on the basis of the electrostatic crystal field theory but a quantitative calculation of the d orbital energies has not been carried out. In this paper we describe such a calculation and use the resulting energy level diagram for discussing the electronic absorption spectra of these ions.…”

Orbital Constructions and Electron Populations in the Transition Elements

“…This cannot be thought of as simply a regular increase in the stability of the d orbital as the d subshell fills, for energy is also contributed to the system in a non-linear way. Because of a lower electrostatic repulsive energy and a more favorable exchange energy among single electrons with parallel spins, states with the maximum number of singly filled orbitals are favored, as is well known from Hund's rule (4). As the magnitude of this energy term depends directly on the number of singly filled states, the d orbitals will be stabilized by increasing amounts as the number of valence electrons increases from one to six.…”

“…I , which is not in the direction of maximum extension. The band will be called the bcc de band to conform with usage in the ligand-field theory (4 whereas ccp d y is virtually non-bonding. The bcc d y will therefore support bcc de when fewer than five d electrons arc present, but will weaken bcc de when more than five electrons are prcserlt.…”

“…Indeed, precisely because of a general lack of emphasis on the directive properties of the orbitals it has not been possible up till now to answer the simple structural question, "Why should a particular metal have one lattice rather than another?" I t would seem that a solution to the problem is implicit in the molecular orbital theory, particularly in view of recent developments in the ligand-field theory (4), and the work: of Jaffe ( 5 ) and of Craig, Maccoll, Nyholm, Orgel, and Sutton (6, 7) on orbital pairs.…”

The structure of ammonium copper sulphate (NH4)2Cu(SO4)2.6H2O7

“…It is so short, that not only is it unlikely that a hydrogen bond will form but there is probably some repulsion between the two atoms. The authors suggest that this tighter packing and resultant strain is one of the reasons for the much poorer stability of the copper salt than that of the nickel salt to dehydration (Caven & Ferguson, 1922) even though the heats of hydration of the hexahydrated copper and nickel ions are practically identical (Griffith & Orgel, 1957). The close approach of H20(1) and 0(4) does not, in this case, lead to extra stability since it is imposed by the packing of sulphate group tetrahedra and Cu(H20)6 octahedra and is not due to attractive forces between H20(1) and 0(4).…”