Thermochemistry of metal complexes from first principles calculations

José R. B. Gomes and Manuel A. V. Ribeiro da Silva

Centro de Investigação em Química, Department of Chemistry,

Faculty of Science, University of Porto, R. Campo Alegre, 687,

P-4169-007 Porto, Portugal   [email protected]

  Acylchalcogenothioureas are used as metal complexing agents with interesting applications such as metal separation by selective extraction of the corresponding stable neutral metal chelates, or determination of transition metal (TM) traces by means of normal phase chromatography [1].

  It is known that the chelating mechanismo dependes greatly on ligand structure, on number and size of substituents at the terminal nitrogen atoms, and on ligand PI delocalization. Despite their interest in many important applications, little is known about the structure and energetics of these metal chelates [2]. In fact, few studies are found in the literature devoted to the coordination of metal atoms with acylchalcogenothioureas ligands and their main objective was the oxidation state and the local geometry of the metal atoms. From these studies and for some metal atoms, different authors have proposed different coordination polyhedra for these metal complexes. Recently, we have used density functional theory to obtain more information about the local geometry of copper complex with the 1,1-diethyl-3-benzoyl-thiourea ligand [3]. An energy gap of only 5 kJ/mol for three different geometries of the corresponding copper complex was found and this may explain why different coordination polyhedra were proposed based on experimental work.

  The energetics of the metal-ligand binding is even less studied and so, theoretical studies are welcome. In the present communication some preliminary results will be presented which show how computational chemistry may be used to obtain thermodynamic information about the stability and the metal-ligand binding in metal complexes.

[1] K. R: Koch, Coord. Chem. Rev. 216-217, 473-488 (2001).

[2] M. A. V. Ribeiro da Silva, M. D. M. C. Ribeiro da Silva, L. C. M. Silva, F. Dietze, E. Hoyer, Thermochim. Acta 378, 45-50 (2001); M. A. V. Ribeiro da Silva, M. D. M. C. Ribeiro da Silva, L. C. M. Silva, J. R. B. Gomes, A. M. Damas, F. Dietze, E. Hoyer, Inorg. Chim. Acta, in press, and references therein.

[3] J. R. B. Gomes, M. A. V. Ribeiro da Silva, Inorg. Chem. Comm. 6, 149-153 (2003).

Thanks are due to Fundação para a Ciência e a Tecnologia (FCT) for financial support given to Centro de Investigação em Química of University of Porto. JRBG thanks FCT for the award of a post-doc (BPD/11582/2002) research grant.