Structural chemistry and magnetic properties of copper pyromellitate coordination polymers containing pyridylnicotinamide ligands

A series of divalent copper pyromellitate (1,2,4,5-benzenetetracarboxylate, pyro) coordination polymers containing either 3-pyridylnicotinamide (3-pna) or 4-pyridylnicotinamide (4-pna) was hydrothermally prepared and structurally characterized by single-crystal X-ray diffraction. [Cu2(pyro)(pyroH2)(3-pnaH)2(H2O)2]n (1) is a 2-D coordination polymer built from {Cu2O2(OCO)2} dimeric units, while {[Cu(pyro)(3-pnaH)2(H2O)2]·4H2O}n (2) is a simple neutral 1-D chain polymer. {[Cu(pyroH2)(4-pnaH)2(H2O)2](pyroH2)·2H2O}n (3) possesses cationic 1-D chain motifs and unligated pyroH2 dianions. {[Cu2(pyroH2)3(4-pnaH)2]·6H2O}n (4) is also a 1-D coordination polymer, but built from the linkage of {Cu2(pyroH2)} dimeric units. {[Cu3(pyroH)2(4-pna)2(H2O)2]·2H2O}n (5) manifests a 3-D coordination polymer network with rare frl topology, containing embedded {Cu3(OCO)2} linear trimers. Moderately strong antiferromagnetic coupling (J = −76.4(3) cm−1) was observed within the {Cu2O2(OCO)2} dimeric units in 1, while very weak ferromagnetic coupling (J = 0.8(2) cm−1) was observed within the {Cu3(OCO)2} linear trimers in 5. Thermal degradation behavior of the five new materials is also presented.