Six Flexible and Rigid Co(II) Coordination Networks with Dicarboxylate and Nicotinamide-Like Ligands: Impact of Noncovalent Interactions in Retention of Dimethylformamide Solvent

Six mixed-ligand Co (II) coordination polymers, {[Co (adi) (iso-nia)(2)]center dot dmf}(n) (1), [Co (adi) (iso-nia)(2)](n) (2), {[Co-2(suc)(ac)(2)(iso-nia)(4)] [Co-2(suc)(SUCH)(2)(iso-nia)(4)]center dot 2dmf} (3), [Co(adi)(nia)(2)] (4), {[Co(bdc)(nia)(2)]center dot dmf}(n) (5), and {[Co(mal)(S-nia)(H2O)]center dot dmf}(n) (6), were synthesized and characterized by single crystal X-ray analysis. They are based on four dicarboxylic acids, namely, malonic (H(2)mal), succinic (H(2)suc), adipic (H(2)adi), and 1,4-benzenedicarboxylic (H(2)bdc) acids, as well as three nicotinamide-like ligands, isonicotinamide (iso-nia), nicotinamide (nia) and thionicotinamide (S-nia). Compounds 1, 2, and 3 represent one-dimensional coordination polymers, whereas 4, 5, and 6 exhibit two-dimensional structures. The coordination arrays in 1-5 are built from the similar [Co-2(COO)(2)] binuclear clusters, while framework 6 is based on mononuclear metal nodes. All crystal lattices are supported by hydrogen bonding with nicotinamide-like ligands acting as pillars or dangling terminal ligands. Four crystal lattices 1, 3, 5, and 6 host dmf solvent via NH center dot center dot center dot O hydrogen bonding and pi-pi stacking interactions with the coordination networks. Details of the reversible dmf release-uptake by 1 and 2, and contribution of hydrogen bonding in stabilization of the solvent-free structures 2 and 4 are discussed. All new solids were characterized by IR spectroscopy and thermogravimetric analysis, while magnetic measurements are reported for compounds 1, 5, and 6. The magnetic data show the typical behavior of Co(II) ions originating from pronounced zero-field splitting within the ground state with contributing effects from weak antiferromagnetic exchange interactions.