Spectroscopic Studies of Some Iron-Sulfur Systems

Abstract

<p>Transition metal complexes bonded to sulfur are of interest both from the theoretical standpoint of the bonding involves and from their chemical and biochemical properties. Iron is by far the most widespread and important transition metal with a functional role in living systems. Current interests in nonheme iron proteins containing iron-sulfur bonds and in complexes of nitric oxide with hemoglobin and related substances have received increasing attention and it was the purpose to investigate various aspects of the coordination chemistry of iron with sulfur ligands.</p> <p>Mössbauer spectroscopy is a very useful probe with which to obtain information about the immediate iron environment. This technique gives information about the s-electron density at the Fe nucleus which is related to the oxidation state of the metal and in addition provides information about the symmetry of the electronic distribution around the nucleus. Electron spin resonance spectroscopy is also invaluable in providing structural information on paramagnetic transition metal complexes. In this work, some iron-sulfur complexes have been studied by means of these and other spectroscopic techniques.</p> <p>Spectroscopic evidence has shown that the structures of iron-nitrosyl complexes with thioamide ligands should be formulated as Fe(NO)2LX rather than [Fe(NO)2L]+X‾. The crystal structure of Fe(NO)2(thiobenzamide)Br shows that it is a covalent compound where bromine is coordinated to the iron atom and thioamide being attached as a monodentate ligand.</p> <p>A series of iron-dithiooxalate complexes have been shown to be distorted from a cubic symmetry due to the effect of cations and/or solvent of crystallisation. The usefulness of Mössbauer spectroscopy to study the behaviour of complexes in solution has been demonstrated by a study of aqueous solutions of the thiooxalate and ferric (or ferrous) ions.</p> <p>The orientation of [C5H5Fe(CO)2]2 in liquid crystals was studied by Mössbauer spectroscopy. A similar study on the Fe(NO)2LX complexes in liquid crystals was not successful.</p>