Hydrogen-Bonded Frameworks of Mercury(II) Complexes with Pyridinedicarboxylic Acids

Abstract

Three novel mercury(ii) coordination compounds, [HgCl(2,4-pydcH2)(2,4-pydcH)]·2H2O (1) and [HgCl(2,6-pydcH)(H2O)]·3H2O (2) that exhibit hydrogen-bonded 3D frameworks, and [Hg(2,6-pydcH)2]·2H2O (3), exhibiting only hydrogen-bonded 1D chains (2,4-pydcH2 = pyridine-2,4-dicarboxylic acid; 2,6-pydcH2 = pyridine-2,6-dicarboxylic acid), were prepared in the reactions of the corresponding pyridinedicarboxylic acid with mercury(ii) chloride or mercury(ii) acetate. Compounds 1–3 were prepared by conventional solution synthesis. Only the hydrogen-bonded 1D chain of 3 was robust enough to be prepared by mechanochemical synthesis. The crystal structures of 1–3 were determined by the single-crystal X-ray diffraction method. Neutral 2,4-pydcH2 and partially deprotonated 2,4-pydcH− act as N,O-bidentate ligands in the structure of 1 whereas crystal structure analysis reveals O,N,O′-tridentate 2,6-pydcH− ligand in the structures of 2 and 3. Compounds 1–3 were characterised by IR spectroscopy in the solid state, and compounds 1 and 2 were also characterised by 1H and 13C NMR spectroscopy in DMSO solution. Thermal properties of 1–3 were also investigated. NMR data support a collapse of the hydrogen-bonded frameworks of 1 and 2 in DMSO solution, and the existence of monomeric species in DMSO solutions.