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This article gives a review of complexes in which a dioxygen ligand is bonded to a transition metal. Three aspects of these complexes are discussed in detail: the structure, the electronic structure, and the reactivity. The structural section summarises the recent X-ray crystal structure determinations, and the structural data obtained by other methods. The electronic structure is first considered in qualitative terms which allow the rationalisation of the different structures observed, and this qualitative model is compared with the results of calculations and with spectroscopic data. The reactivity of the complexes is discussed separately for each structural class in terms of the electronic structure. An attempt is made to compare the results obtained in historically different areas of research. Our objective is to give a clear summary of current knowledge of these compounds for workers interested in their application to catalysis and in their rôle in biochemical systems. [ABSTRACT FROM AUTHOR]

The aim of the present article is to review several biomolecules, the spectroscopic and structural properties of which have been so far interpreted in the light of the Jahn-Teller effect. Indeed the importance of the vibronic coupling in the interpretation of physical properties of molecules and crystals is widely recognized now, but only a desultory attention has been paid to the role played by such a coupling in biological systems. After a brief outline of the Jahn-Teller effect, the whole problem is critically re-examined separating the systems for which the experimental evidence of the Jahn-Teller effect is clear, from those where its effectiveness is still debated. Furthermore some suggestions are given for a proper inclusion of the vibronic coupling in future analysis on biomolecules. [ABSTRACT FROM AUTHOR]

This review shows that the growing interest aroused by phospholes in coordination chemistry can be attributed to three main reasons: 1. The influence of the partial delocalization of the phosphorus lone pair upon the complexing ability of phospholes. 2. The discovery of phosphametallocenes. 3. The tremendous variety of complexing modes found for the phosphole nucleus. For a given phosphole, no less than ten different types of complexes can be obtained. [ABSTRACT FROM AUTHOR]

The ability of coordination polyhedra of different central atoms in the solid state to undergo distortions has often been discussed. These distortions are also correlated with the nature of the central atom. This paper deals with the conception of crystal structure non-rigidity for central atoms of some selected complexes by the using of statistical distributions of interatomic distances central atom-nearest ligand atom (M-L; M=Mn(II), Fe(II), Fe(III), Co(II), Co(III), Ni(II), Cu(II) and Zn(II)). Based on the vector equilibrium principle the dispersion of these empirical distributions has been introduced as a measure of non-rigidity of central atoms, decreasing in the order: Cu(II) > Fe(II)HS > Mn(II)HS > Ni(II)LS > Zn(II) > Fe(III)HS ≈ Co(II)HS > Ni(II)HS > Co(III)LS, where LS and HS denote low-spin and high-spin states, respectively. Starting from the distribution of M-L distances for certain types of central and ligand atoms, the contribution of atoms of the inner coordination sphere to the vector equilibrium of crystal structures is discussed. The structures of complexes with all M-L bond lengths of at least one symmetrically independent central atom in the interval of maximum frequency exhibit in the appropriate set the most stable inner coordination sphere. These compounds are classified both with respect to the geometry of their inner coordination sphere fulfilling the above condition and to their crystal structure aspect. The square-planar geometry is found to be the most stable for Cu(II) and Ni(II)LS complexes, tetragonal-pyramidal for Zn(II) complexes, while for Fe(II)HS, Mn(II)HS, Fe(III)HS, Co(II)HS, Ni(II)HS and Co(III)LS complexes it is the regular octahedral geometry. Except for one Mn(II)HS complex, in the discussed structures chromophores with the most stable geometry of the coordination polyhedron form part of the final relatively isolated structural unit (island) with expressively chemical bonds between atoms. These facts are illustrated by the stabilization effected by the crystal field and by the properties of the ligands. [ABSTRACT FROM AUTHOR]