Cobalt(II) complexes of 4-(1-H-1,3-benzimidazole-2-yl)-1,5-dimethyl-2-phenyl-1-2-dihydro-3-H-pyrazol-3-one incorporating various anions: Synthesis, characterization and crystal structures

The structure of 4-(1-H-1,3-benzimidazole-2-yl)-1,5-dimethyl-2-phenyl-1-2-dihydro-3-H-pyrazol-3-one (Opdac) derived from the condensation of O  -phenylenediamine and 4-antipyrine carboxaldehyde has been confirmed by X-ray crystallography. The free ligand, Opdac, crystallizes into a triclinic lattice with the space group P1¯. Reaction of Opdac with salts of Co(II) affords five novel mononuclear complexes [Co(Opdac)Cl2] (1), [Co(Opdac)Br2] (2), [Co(Opdac)I2] (3), [Co(Opdac)2NO3]NO3 (4) and [Co(Opdac)2ClO4]ClO4 (5). All the reaction products were characterized by a variety of physicochemical techniques, viz. elemental analysis, molar conductivity, CHNS analysis, magnetic susceptibility measurements and spectroscopic studies. The solid-state structures of complexes 1, 2 and 4 were established by Single Crystal X-ray crystallography. The complex 1 crystallize in the monoclinic space group C2/c, where as complex 2 crystallizes in the orthorhombic space group Pbca. In complexes 1 and 2, the ratio of metal to ligand is 1:1 and both the anions are coordinated to the metal ion, in which central metal ion adopts a distorted tetrahedral geometry. The mononuclear units in 1 and 2 are engaged in weak intermolecular C–H···X and N–H···X (X = Cl or Br) hydrogen bonds to give a 2D structure. The complex 4 crystallized in monoclinic space group C2/c forming six membered chelate ring. The structural analysis show that Co(II) ion in 4 adopts a distorted octahedral geometry with a CoN2O2 chromophore, ligated through two imine nitrogen and two pyrazolone oxygen atoms from two Opdac units; the hexacoordination is completed by O atom of the nitrate ion in a bidentate fashion. The hydrogen gas sorption isotherms at 77 K confirmed the permanent porosities of the complex 1.

Graphical abstractThe present investigation reports the novel synthesis of mononuclear Cobalt(II) complexes [Co(Opdac)Cl2] (1), [Co(Opdac)Br2] (2), [Co(Opdac)I2] (3), [Co(Opdac)2NO3]NO3 (4) and [Co(Opdac)2ClO4]ClO4 (5) with the Schiff base ligand, 4-(1-H-1,3benzimidazole-2-yl)-1,5-imethyl-2-phenyl-1-2-dihydro-3-H-pyrazol-3-one (Opdac) and their characterization. In all the complexes Opdac acts as neutral bidentate ligand forming six membered chelate ring around the central metal ion. X-ray study of complexes 1, 2 and 4 indicates that intermolecular hydrogen bonding interactions play an important role in the different dimensional assembly of these complexes because of the presence of organic ligand and various anions.Figure optionsDownload full-size imageDownload as PowerPoint slide