engleski

Structural study of picolinamide complexes of Ni(II), Zn(II), Cd(II) and Hg(II) nitrates in solid state and solution

Three picolinamide complexes of nickel(II) (1), zinc(II) (2) and cadmium(II) (3), have been prepared and their solid state structures determined by single crystal X-ray diffraction analysis. Their structures in DMSO solutions as well as the structure of similar mercury(II) complex, [Hg(NO3)(pia)2](NO3) (4), have been elucidated by 1H and 13C NMR spectra. The picolinamide is bound through the N, O-donor set of atoms in all four complexes in solid state, but in solution only in mercury complex 4. In nickel (1), zinc (2) and cadmium (3) complexes pia-N coordination in solution is suggested. The X-ray analysis revealed that isomorphous nickel (1) and zinc (2) crystal structures comprise the centrosymmetrical trans-[M(H2O)2(pia)2]2+ complex cations (M = Ni, Zn ; pia = picolinamide) and the nitrate ions. The crystal lattices also contain two non-coordinated H2O molecules. In cadmium complex 3, each cadmium(II) ion is N, O-chelated by two cis-oriented pia ligands, while remaining coordination sites of the capped pentagonal bipyramid are occupied by three oxygen atoms from two nitrate ions. Crystal structures are dominated by O/N/C—H•••O hydrogen bonds. The carboxamide moieties in 1 and 2 do not form any of head-to-head or catemeric supramolecular synthons, but participate in the formation of R44(12) motifs with solely the amide nitrogen atoms as double hydrogen bond donors. In 3, neighbouring molecules are linked into head-to-head amide dimmers. The biological effect of picolinamide and [Zn(pia)2(H2O)2](NO3)2 on ingestion and intracellular microbicidal capacities of human peripheral blood phagocytes was also assessed.

Picolinamide complexes ; NMR ; Crystal structure ; Hydrogen bonding ; Phagocytosis

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