Analysis of the Interaction between Adenine Nucleobase and Metal‐Malonato Complexes

Abstract

AbstractThe synthesis, crystal structure and variable‐temperature magnetic measurements of compounds [M2(μ‐Hade)2(μ‐mal)2(H2O)2]·2H2O [M = Ni (1), Co (2)], [Co2(μ‐Hade)2(μ‐mal)2(H2O)2] (3), {(H2ade)2[Cu(μ‐mal)2]·2H2O}n (4) and (H2ade)2[Cu(mmal)2(H2O)] (5; H2ade = adeninium, Hade = adenine, mal = malonato, mmal = methylmalonato) are reported. Compounds 1–3 contain neutral paddle‐wheel [M2(μ‐Hade)2(μ‐mal)2(H2O)2] [M = Ni (1), Co (2 and 3)] units where the 7H‐tautomeric form of the nucleobase and the malonate dianion act as μ‐κN3:κN9 and μ‐κ2O1,O2:κO1 bridging ligands, respectively. The supramolecular crystal structures of 1–3 are essentially maintained by hydrogen‐bonding interactions involving the nucleobases, the carboxylate groups and crystallisation water molecules (in compounds 1 and 2). Compounds 4 and 5 show a hybrid inorganic‐organic lamellar structure containing layers of anionic metal‐malonato complexes and supramolecular aggregates of the 1H,9H‐adeninium cation. Their overall three‐dimensional architectures are controlled, in addition to electrostatic forces, by supramolecular recognition processes between the inorganic and organic frameworks. Compound 4 contains one‐dimensional anionic copper‐malonato chains in which the copper atoms are doubly bridged by μ‐κ2O1,O2:κO2′ malonato ligands and the cationic nucleobases form dimeric entities sustained by Hoogsteen‐Hoogsteen hydrogen‐bonding interactions. Compound 5 is built up of anionic [Cu(mmal)2(H2O)]2– monomeric entities and planar, hydrogen‐bonded, one‐dimensional, ribbon‐like aggregates of protonated adenine. Variable‐temperature magnetic susceptibility measurements of compounds 1–4 show the preponderance of ferromagnetic interactions between the paramagnetic centres. DFT calculations have been performed to evaluate the magnetic behaviour of these compounds and to analyze the interaction between two adeninium cations in compound 4. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)