Synthesis, X-ray characterization, and DFT calculations of gold–nucleobase complexes: on the importance of regium bonds and anion–π interactions

Abstract

In this manuscript, we report the synthesis and X-ray characterization of two new Au(III)–cytosine systems: AuCl₃(CytC₆) (1) and (HCytC₆)₂[AuCl₄]Cl (2), where CytC₆ is N1-hexylcytosine. Compound 1 is an inner sphere complex where the AuCl₃ unit is coordinated to N3, while compound 2 is an outer sphere complex (salt) where two N1-hexylcytosinium cations are charge compensated by one chloride anion and one tetrachloroaurate anion. Inner sphere complexes of Au(III) with cytosine and nucleobases, in general, are scarcely found in the CSD. In fact, compound 1 is only the third example of a cytosine derivative coordinated to Au(III). Such complexes remain elusive for other nucleobases. The formation of regium bonds in the solid state of compound 1 has been analysed using DFT calculations and characterized with several computational tools, including molecular electrostatic potential (MEP), energy decomposition analysis (EDA), quantum theory of atoms in molecules (QTAIM), and noncovalent interaction plot (NCIplot).