Abstract.A copper(II) complex with 6-hydroxypicolinic acid (6-OHpicH) and 3-picoline (3-pic), [Cu(6-OHpic) 2 (3-pic) 2 ] (1), was prepared by recrystallization of [Cu(6-OHpic) 2 (H 2 O) 2 ] from 3-picoline and characterized by IR spectroscopy and thermal methods (TGA/DTA and DSC). The molecular and crystal structure of 1 was determined by single-crystal X-ray structural analysis. The copper(II) ion in 1 has a tetragonally compressed octahedral coordination environment, achieved by two N,O-bidentate 6-hydroxypicolinate ligands and by two 3-picoline molecules in trans positions. The crystal structure of 1 exhibits one strong intermolecular O-HO hydrogen bond, one weak intermolecular C-HO hydrogen bond and one C-Hπ interaction. Molecules of 1 are assembled into a 2D network in the (1 0 -1) plane, giving rise to C 1 1 (8) graph-set motif. These 2D networks are further assembled into 3D architecture only by weak Van der Waals interactions. A thermogravimetric study showed the initial loss of two coordinated 3-picoline molecules in 1, followed by a complete decomposition of the compound.

A few novel metal complexes of chelidonic acid (chelH2), namely [Ca(chel)(H2O)3] (1), [Cu(chel)(H2O)5] ⋅ 2H2O (2) and [VO(chel)(H2O)3] ⋅ 2H2O (3) were prepared, identified by elemental analysis and characterized by electrochemical methods. IR‐spectra and thermal stability in solid state are discussed as well. The electrochemical characteristics of the free chelidonic acid and its complexes 1–3 were studied by (cyclic) square‐wave voltammetry, on static mercury drop electrode (SMDE) and paraffin‐impregnated graphite electrode (PIGE), in aqueous media over a wide pH range. The reduction of chelidonic acid on SMDE is a kinetically controlled electrode reaction, occurring with the transfer of one electron and two protons for 1