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

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.