Cu(II) coordination polymers stabilized by pyridine-2,6-dicarboxylate anion and pyrazole derivatives through ligand hydrolysis

2,6-Pyridinedicarbonyldichloride (PDD) was treated with pyrazole, 3-methylpyrazole, and 3,5-dimethylpyrazole in the presence of trimethylamine at room temperature. Reactions afforded 2,6-bis(pyrazolyl-1-carbonyl)pyridine (1), 2,6-bis(3-methylpyrazolyl-1-carbonyl)pyridine (2) and 2,6-bis(3,5-dimethylpyrazolyl-1-carbonyl)pyridine (3). 1-3 were treated with copper ion under ambient conditions in open air. Such coupling of 1 and 2 with copper led to coordination polymers 6 and 7, bearing 1D architectures, of general formulas [Cu(C7H3NO4)(C3H4N2)]n and [Cu(C7H3NO4)(C4H7N2)]n (C7H3NO4 = 2,6-pyridinedicarboxylate ion, C3H4N2 = pyrazole and C4H7N2 = 3-methylpyrazole), respectively. Under the same experimental conditions, 3 instead forms a mononuclear Cu(II) complex (8). Structures of 1-3 and 6-8 were determined with X-ray diffraction. The solid state structures reveal that short-range intermolecular interactions in the ligands afford 1D (1) and 2D (2 and 3) supramolecular chains, respectively. 6 and 7 both crystallize in the orthorhombic system, space group P212121. 1–3 were also characterized with elemental analysis and NMR spectroscopy. The magnetic susceptibility measurements indicate that both complexes are paramagnetic with effective moments of 1.75 (6) and 1.90 (7) µB at 300 K. The voltammetric signatures of 6 and 8 show two steps reversible redox behavior as evidenced by the appearance of two cathodic waves with corresponding anodic peaks in the backward scan.