Six
mixed-ligand Co(II) coordination polymers, {[Co(adi)(iso-nia)2]·dmf}
n
(1),
[Co(adi)(iso-nia)2]
n
(2), {[Co2(suc)(ac)2(iso-nia)4][Co2(suc)(sucH)2(iso-nia)4]·2dmf}
n
(3), [Co(adi)(nia)2]
n
(4), {[Co(bdc)(nia)2]·dmf}
n
(5), and {[Co(mal)(S-nia)(H2O)]·dmf}
n
(6), were synthesized and characterized by single crystal X-ray analysis.
They are based on four dicarboxylic acids, namely, malonic (H2mal), succinic (H2suc), adipic (H2adi),
and 1,4-benzenedicarboxylic (H2bdc) 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 [Co2(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···O hydrogen bonding and π–π
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.
