Directing the Formation of Adenine Coordination Polymers from Tunable Copper(II)/Dicarboxylato/Adenine Paddle-Wheel Building Units

Abstract

Coordination polymers containing paddle-wheel shaped building units of general formula [Cu2(μ-adeninato)2(μ-carboxylato)2] (1–3) and [Cu2(μ-carboxylato)4(methyladenine)2] (4–6) are reported. The copper(II) centers of the compounds {[Cu2(μ3-adeninato)2(μ-Hglut)2]·2H2O}n (1), {[Cu2(μ3-adeninato)2(μ-Hadip)2]}n (2), and {[Cu2(μ3-adeninato)2(μ-Hpime)2]}n (3) (where glut: glutarato; adip: adipato; and pime: pimelato) are bridged by tridentate N3,N7,N9-adeninato ligands to give a similar covalent three-dimensional network in which the dicarboxylate anions act as bidentate μ-κO1:κO2 ligands with a free hydrogencarboxylic group placed within the channels present in the crystal structures. In 2–3, the −COOH group of the pendant aliphatic chain is hydrogen bonded to the Watson–Crick face (N6H/N1) of an adenine nucleobase placed at the opposite side of the channel, whereas in 1, the shorter aliphatic chain precludes this interaction and crystallization water molecules are placed between the hydrogencarboxylic group and the nucleobase. Compounds {[Cu2(μ4-glut)2(3Meade)2]·4H2O}n (4), {[Cu2(μ4-glut)2(9Meade)2]}n (5), and {[Cu2(μ4-pime)2(9Meade)2]·2H2pime}n (6) (where 3Meade: 3-methyladenine and 9Meade: 9-methyladenine) contain neutral chains where the paddle-wheel motifs are doubly bridged by tetratopic dicarboxylate anions. The supramolecular architecture of 4 and 5 is essentially knitted by hydrogen bonding interactions between the Watson–Crick faces of adjacent adenines, whereas compound 6 shows the inclusion of guest pimelic molecules which are anchored to the polymeric chains through fork-like hydrogen bonding interactions between one of the carboxylic groups and the peripheral adenine moieties, affording a supramolecular layered structure. The magnetic data of all the compounds show the occurrence of an antiferromagnetic behavior which is dominated by the orbital complementarity of the adenine and carboxylato bridging ligands in compounds 1–3.