Trinuclear Carboxylate Complexes of First Row Transition Metals

Abstract

Trinuclear carboxylate complexes have been studied for well over a century. Since the advent of X-ray crystallography and the first application on this system in the 1960's, the interest in their peculiar magnetic and electronic properties has increased enormously and so has the number of published crystal structures. In these compounds, three metal ions are arranged in a triangular fashion around a central oxygen atom. The metal ions are held in place by carboxylate bridging ligands. Apart from the nature of the metal ions and carboxylate ions involved, the number of variables in this system is increased by the presence of a terminal ligand which completes the coordination sphere of each of the metal ions. In the example below, this is the pyridine molecule. 19 such complexes have been synthesised and characterised by single crystal X-ray crystallography and are discussed in detail. The Cambridge Structural Database was employed to collect structural information of all published structures of this type. Conclusions as to the structural function of the various determinants of these materials are drawn on the basis of a large amount of data gathered from the CSD as well as the new and previously unpublished structures presented here: 1. The distances between the central oxide ion and the metal ions in the core of these materials is largely independent from the nature of either the metal ions, the carboxylate bridges or the terminal ligands. 2. Distances between the metal ions and the terminal ligands as well as between the metal ions and bridging carboxylate ligands are on the whole as expected from the nature of the metal ions. 3. Single crystal X-ray structural analysis cannot, on the whole, determine the site of the heteroatom in heteronuclear complexes but is frequently able to identify the site of the heteroatom in heterovalent systems. 4. No clear relationship was found between structural parameters and the relative orientation of terminal ligands and the plane of the core. 5. A database of all crystallographic parameters relating to these compounds has been established and will provide a good source of information to probe further into the chemistry of these interesting and fascinating compounds.