Cytosine as a root to a nonconventional layered hydroxide nanostructure

A self-assembled layered compound of formula {[Cu5(OH)8Cyt2]·2ClO4} n (1) was obtained from the direct reaction between copper perchlorate and cytosine. Thanks to its peculiar structural features, this coordination compound can be classified as an intermediate nonconventional analog of Layered Simple Hydroxides (LSHs) and Layered Double Hydroxides (LDHs), two fascinating classes of inorganic materials with variable chemical composition and structures. Like LDHs, 1 consists of positively charged layers of metal hydroxides and non-framework charge-balancing anions located between the layers. However, the hydroxide layers, similar to LSHs, contain only divalent copper(II) metal ions, supported by cytosine molecules with long contacts. Cytosine coordinates to the metal centers adopting an unusual µ3 coordination mode, the exocyclic oxygen atom simultaneously binding to three adjacent copper(II) centers. This coordination mode has not been observed with transition metal ions. This work further demonstrates that nucleobases and their derivatives, despite presenting a limited pool of molecules, can potentially afford a significantly expanded set of compounds with diverse nanostructures, owing to their multiple metal binding sites of different coordination properties and their ability to direct assembly of highly ordered structures. Their potential as building blocks should be further explored for the preparation of new bio-inorganic hybrid materials.