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

Abstract

Several mercury(II) complexes of 2-quinaldic acid (quinH; IUPAC name: quinoline-2-carboxylic acid) were synthesized and characterized. [Hg(quin) 2(OH 2)] ( 1) was obtained as the reaction product of mercury(II) chloride and 2-quinaldic acid in an aqueous media, while a mixture of 1, [(quinH 2)(HgCl 3)]·2quinH·H 2O ( 2), and [Hg(quin) 2(EtOH)]·H 2O ( 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 Hg 2+ ion as a N,O-chelating quinaldate ion in structures 1, 3 and 4. In the structure of 2 polymeric [ HgCl 3 ] n n - 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, quinH 2 + . 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.