Crystal structure of K[PtCl₃(caffeine)] and its interactions with important nitrogen-donor ligands

Abstract

The crystal structure of K[PtCl₃(caffeine)] was determined. The coordination geometry around platinum is square-planar formed by N9 of the caffeine ligand and three Cl⁻ ions. The bond lengths and angles of K[PtCl₃(caffeine)] were compared with those reported for [PtCl₃(caffeine)]⁻ and K[PtCl₃(theobromine)]. At the level of the statistical significance of the data we have compared, no differences in the bond distances and angles for any of these compounds were noticed. Weak interactions between K⁺ and Cl⁻ are responsible for the formation of 1-D polymeric chains in the crystal structure of the complex. The interactions of K[PtCl₃(caffeine)] with inosine (Ino) and guanosine-5′-monophosphate (5′-GMP) were studied by ¹H NMR spectroscopy at 295 K in D₂O in a molar ratio of 1 : 1. The results indicate formation of the reaction product [PtCl₃(Nu)] (Nu=Ino or 5′-GMP) with the release of caffeine from the coordination sphere of the starting complex. The higher stability of the bond between the Pt(II) ion and Ino or 5′-GMP compared to the stability of the platinum–caffeine bond is confirmed by density functional theory calculations (B3LYP/LANL2DZp) using as models 9-methylhypoxanthine and 9-methylguanine.

Keywords:

• Crystal structure
• Pt(II) complex
• caffeine
• substitution

Acknowledgments

We would like to thank Prof. Dr. h.c. mult. Rudi van Eldik for continued kind support, Prof. Tim Clark for hosting this work in the CCC and the Regionales Rechenzentrum Erlangen (RRZE) for a generous allotment of computer time.

Funding

The authors gratefully acknowledge financial support of the Ministry of Education, Science and Technological Development, Republic of Serbia [grand number 172011].