Experimental and theoretical study of N1-hexylcytosine and N1-hexylcytosinium nitrate: the crucial role of hydrophobic and anion–π interactions

We report the synthesis and X-ray characterization of N1-hexylcytosine (1) and N1-hexylcytosinium nitrate (2). N1-hexylcytosine (1) does not follow the same behaviour previously described for N1-hexylthymine and N1-hexyluracil in the solid state. This different behavior has been analyzed by means of density functional theory (DFT) calculations including the latest available correction for dispersion (D3). In addition hydrophobic and anion–π noncovalent interactions play a key role in stabilizing the 3D architectures of the compounds, which have been energetically studied using theoretical calculations and compared with similar structures retrieved from the Cambridge Structural Database (CSD). The anion–π–anion binding mode observed for nitrate in compound 2 is also observed in several crystal structures involving cytosine ring coordinated to transition metals.