Various coordination modes in mercury(II) complexes with quinoline-2-carboxylic acid: Preparation and structural characterization

Several mercury(II) complexes of 2-quinaldic acid (quinH; IUPAC name: quinoline-2-carboxylic acid) were synthesized and characterized. [Hg(quin)2(OH2)] (1) was obtained as the reaction product of mercury(II) chloride and 2-quinaldic acid in an aqueous media, while a mixture of 1, [(quinH2)(HgCl3)]·2quinH·H2O (2), and [Hg(quin)2(EtOH)]·H2O (3) was obtained from a 96% ethanol solution. Pure [HgCl(quin)(quinH)] (4) was obtained as the first reaction product when the reaction was performed in absolute alcohol. After isolation of 4 from the filtrate the mixture of 1–3 was again obtained. The X-ray single-crystal structure analysis reveals that the ligand, 2-quinaldic acid is coordinated to the Hg2+ ion as a N,O-chelating quinaldate ion in structures 1, 3 and 4. In the structure of 2 polymeric [HgCl3]nn- anions are formed with a very deformed trigonal-bipyramidal 3 + 2 mercury coordination sphere while the ligand, 2-quinaldic acid exists in the zwitterionic form as quinH, and as a cation, quinH2+. The coordination polyhedron in 1 and 4 can be described as 2 + 3 and 4 + 1 deformed trigonal-bipyramidal and square-pyramidal geometry with the water molecule and chlorine atom at the fifth site in 1 and 4, respectively. The coordination sphere in 3 is square-pyramidal with the ethanol molecule at the vertex, however through additional Hg···O contacts centrosymmetric dimers are formed resulting in a 5 + 1 effective octahedral mercury coordination.The crystal structures of 1–4 are characterized by O–H···O and N–H···O intermolecular hydrogen bonds forming various packing motifs, which are discussed in details.

In this work we report the synthesis, IR, 1H and 13C NMR spectroscopy, and crystal and molecular structures determined by X-ray single crystal diffraction of several mercury(II) complexes with quinaldic acid: [Hg(quin)2(OH2)], aquabis(quinoline-2-carboxylato-κ2N,O)mercury(II), [(quinH2)(HgCl3)]·2quinH·H2O, quinolinium-2-carboxylic acid trichloromercurate(II) bis(quinolinium-2-carboxylate) monohydrate, [Hg(quin)2(EtOH)]·H2O, bis(ethanol-κO)bis(quinoline-2-carboxylato-κ2N,O)mercury-(II) monohydrate, [HgCl(quin)(quinH)], chloro(quinoline-2-carboxylato-κ2N,O)(quinoline-2-carboxylic acid-κ2N,O)mercury(II).Figure optionsDownload as PowerPoint slide