Coordination modes of 3-hydroxypicolinic acid: Synthesis and structural characterization of polymeric mercury(II) complexes

Novel mercury(II) compounds of 3-hydroxypicolinic acid (HpicOH; IUPAC name: 3-hydroxy-2-pyridinecarboxylic acid) were synthesized and characterized. HgCl(picOH) (1) and HgBr2(HpicOH) (2) were obtained as reaction products from the reaction of the corresponding mercury(II) halide with HpicOH, irrespective of the molar ratio of the reactants. From the reaction of HpicOH and mercury(II) acetate, Hg(picOH)2 (3) was obtained, while mercury(II) nitrate monohydrate gave the 1/1 solvate with water Hg(picOH)2 · H2O (3a). Infrared, 1H and 13C NMR spectroscopic data were analyzed for complexes 1, 2 and 3. X-ray crystal structure analysis of 1 and 2 revealed their polymeric nature and different coordination modes of HpicOH. In 1 the deprotonated picolinic acid is N,O-chelating and bridging, while in 2 HpicOH is a O-monodentate weakly bound ligand. Compound 1 consists of HgCl(picOH) moieties with two linear covalent bonds, Hg–N 2.143(4) and Hg–Cl 2.298(1) Å, and four additional Hg⋯O contacts (2.460(3)–2.904(3) Å) in which both oxygen atoms from the carboxylic group are bridging and involved in coordination to three neighboring mercury atoms, thus forming infinite layers. The coordination of mercury is 2 + 4. 2 consists of {HgBr2(HpicOH)} moieties, which are linked into chains by means of mercury to bromine secondary long range interactions. The coordination sphere of mercury can be described as irregular 2 + 3 formed by two covalently bonded bromine atoms (Hg–Br 2.277(1) and 2.366(1) Å), two bridging bromine atoms (Hg⋯Br 3.309(1) and 3.247(1) Å) and by the HpicOH ligand attached to mercury in the zwitterionic form via the carboxylic oxygen atom (Hg⋯O 2.602(7) Å).

Novel polymeric mercury complexes, HgCl(picOH), HgBr2(HpicOH), Hg(picOH)2 and Hg(picOH)2 · H2O (HpicOH = 3-hydroxypicolinic acid) were obtained. Crystal structure analysis of the halogeno-derivatives confirmed two different coordination modes of HpicOH. In DMSO solutions these complexes exist in the identical form as in the solid state.Figure optionsDownload as PowerPoint slide