In the last decades, inorganic chemist has faced the need to mimic the properties of metal sites in metalloproteins to synthesize new catalytic materials with advantageous properties [1].  However, one of the mayor difficulties in the synthesis of these materials has been to prepare pro-ligands with structural conformations and chemical properties close enough to the ligands around the metal in the protein to avoid problems associated with molecular recognition in the catalytic process. In this work, we have attempted to study the molecular and crystalline structure by means of X-ray powder diffraction and theoretical calculations using density functional tight-binding methods (DFTB) of two new pro-ligands  of the type [NS] bidentate and [N₂S₂] tetradentate: iso-butyl 2,4-bis(cyclohexane)dispiro-[1,2,3,4,4a,5,6,7]-octahydro-(1H,3H)quinazoline-8-carboxydithioate (compound I)  and methyl N,N'-buthyl-bis(2-amino-1-cyclopentendi-thiocarboxidithioate (compound II) [2-4]. Powder diffraction experiments were carried out in the diffractometer of beam line ID31, ESRF, France. DFTB calculations were carried out using the computer facilities of the Theoretical Chemistry Group: Dynamical Processes, ULA, Venezuela. The structural solution was achieved using the program FOX. The Rietveld refinement of the models used the program GSAS. The molecular conformation for both compounds, which are subjected to internal hydrogen bonds and electron charge delocalization in the carboxydithioate group, and the crystal packing of the compounds are thoroughly discussed here. Finally, the molecular structures obtained by X-ray powder diffraction are compared with the ones optimized by DFTB calculations.

Acknowledgement: This study was supported by the CDCHT-ULA, FONACIT-Venezuela (Lab-97000821, Subvention-200500703) and beam line ID31, ESRF (France).

References

1. Solomon, E. I., Szilagyi, R. K., DeBeer, G. S. & Basumallick, L., 2004, Chem. Rev. 104, 419-458.
2. Avila, E.E., Mora, A.J., Delgado, G.E., Contreras, R.R., Fitch, A.N. & Brunelli, M. 2008, Acta Crystal. B64, 217-222.
3. Contreras, R. R., Fontal, B., Romero. I., Briceño, A. & Atencio, R., 2006, Acta Cryst. E62, o205-o208.
4. Contreras, R. R., Fontal, B., Bahsas, A., Reyes, M., Suárez, T. & Bellandi, F. 2001, J. Heterocycles Chem. 38, 1223-1225.

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