Supramolecular Behavior of Adenine with Succinic, Fumaric, and Maleic Acids: Tautomerism, Cocrystallization, Salt Formation, and Solvation

The powerful hydrogen bonding capability
of adenine makes it a
key component of the DNA double helix, while as a crystalline molecular
material, these hydrogen bond donors and acceptors make it a good
potential cocrystal component possessing distinct physical properties.
Here, we report the preparation and structure determination of four
adenine-based multicomponent adducts formed with a number of dicarboxylic
acids: an anhydrous cocrystal with succinic acid (1),
anhydrous salts with fumaric acid (2) and maleic acid
(3), and a methanolated salt with maleic acid (4). The supramolecular behavior of adenine in these materials
is discussed in terms of strong hydrogen-bonded bidentate motifs formed
between the adenine and acid components and the homomeric adenine
synthons retained in these structures. The additional formation of
a CH···N interaction on the Watson–Crick site
in (3) enables the stabilization of the unusual 3H,7H adeninium tautomer within a purely
molecular material.