Solid–Solid Synthesis, Crystal Structure and Thermal Decomposition of Copper(II) Complex of 2-Picolinic Acid

The copper(II) complex [Cu(pic)2]·2H2O was synthesized with 2-picolinic acid (Hpic) and copper acetate as reactants by room temperature solid-solid reaction. The composition and structure of the complex was characterized by elemental analyses, single crystal X-ray diffraction, X-ray powder diffraction, FT-IR spectroscopy and thermogravimetry-differential scanning calorimetry. The crystal structure of the copper(II) complex belongs to triclinic system and space group , with cell parameters of a = 5.1274(16) Å, b = 7.641(2) Å, c = 9.209(2) Å,α = 74.91(2)°, β = 84.56(2)°, γ = 71.58(3)°, V = 338.48(15) Å3, Z = 1, F(000) = 175, R1 = 0.0530, and wR2 = 0.1141. The Cu(II) ion is six-coordinated through two nitrogen atoms from two pyridine rings and four carboxyl oxygen atoms from four different 2-picolinic acid anions, forming an elongated octahedral geometry. The interaction of carboxylate O and Cu(II) forms an one-dimensional chain structure, and the complex exhibits a two-dimensional layered structure by hydrogen bonds. The thermal decomposition processes of the complex under air include dehydration and pyrolysis of the ligand, and the final residue at about 400 °C is copper oxide.