Exploring the Structure and Intermolecular Interactions in a Novel Copper-Cytosine Supramolecular Polymer Using Density Functional Theory

Abstract

In this work, we report the synthesis and structure of a new complex containing the [Cu(C₄H₅N₃O)₄]²⁺ cationic unit where the N₃ nitrogen atoms of the four cytosine are coordinated to the equatorial positions of the central copper atom. There exist bifurcated intramolecular hydrogen bonds among the amine and keto groups of the cytosines which reinforce the molecular structure of the complex entity. The expected cytosine-cytosine base pairing is hindered by the sulphate counterion that interacts with the sugar edge of the nucleobase. As a result, the interactions between adjacent cytosines follow a nonconventional hydrogen bonding pattern giving rise to supramolecular ribbons of [Cu(C₄H₅N₃O)₄]²⁺ discrete entities. It is noteworthy to observe the presence of an, otherwise repulsive, close contact between keto•••keto groups of cytosine molecules of adjacent units. Geometry optimization calculations are performed on a finite structural model consisting of two interacting monomers by using dispersion corrected density functional theory calculations with the code DMOL3, which gives evidence on the structural features that stabilizes the supramolecular array even in the presence of the shorter oxygen•••oxygen distances.