Abstrakt
The ligand, 4-chloro-2,6-dipicolinic acid (H(2)PDA-Cl), and its two heavy metal complexes, [Ag(HDPA-Cl)(H(2)DPA-Cl)·2H2O] (1) and {[Cd(μ(2)-H2O)(H2O)(PDA-Cl)]}(n) (2), were prepared and then characterized by single-crystal X-ray diffraction. In addition, spectral and thermal correlations with structural results complete their solid-state description and facilitate complex 3 ([Pb(DPA-Cl)]) composition determinations.
Complex 1 crystallizes in a monoclinic space group C2/c and each DPA-Cl ligand is tridentate to Ag(I) through the pyridine N and two monodentate carboxyl O atoms. The carboxy group with carbonyl C1 is semideprotonated and forms a symmetric hydrogen bond with a carboxy group of a neighboring complex.
Complex 2 crystallizes in a triclinic lattice with space group P The Cd(II) ions are seven-coordinate and the coordination polyhedra can be described as a distorted pentagonal bipyramid. IR data are consistent with monodentate coordination of the carboxylate to Ag(I), Cd(II), and Pb(II) and observed wavenumber shifts confirm PDA-Cl ligand coordination to Pb(II) in 3.
Thermal stability of anhydrous complexes indicates the metal-ligand interactions. The thermal stability of prepared compounds is reflected by the strength of interaction between metal-ligand and hydrogen bonds.