Synthesis, spectral and X-ray structural studies of a NO donor Schiff base ligand and its Ni(II) complexes

The Schiff base ligand, 4-isopropylbenzaldehyde[N-(3-oxo-3,4-dihydro-2-quinoxalinyl)hydrazone] (Ipbh), the 1:1 condensation product of 4-isopropylbenzaldehyde and 2-hydroxy-3-hydrazinoquinoxiline, has been synthesized and characterized by X-ray crystallography. A series of complexes of Ipbh with Nickel(II), viz., [Ni(Ipbh)2]Cl2 (1), [Ni(Ipbh)2]Br2 (2), [Ni(Ipbh)2]I2 (3), [Ni(Ipbh)2·(CH3OH)2](NO3)2·(CH3OH)2 (4) and [Ni(Ipbh)2ClO4]ClO4 (5) have been synthesized. All the complexes were characterized by elemental analysis, molar conductivity, CHN analysis, spectroscopic studies, magnetic susceptibility measurements and TG/DTA methods. The solid-state structure of the complex 4 was established by single crystal X-ray crystallography. In all the complexes, Ipbh acts as a bidentate NO chelating agent, coordinated to the metal ion through the imine nitrogen and quinoxaline oxygen. In complex 4, Nickel(II) is in a distorted octahedral environment with an identical set of donor atoms, N2O4, coming from two imine nitrogen and two quinoxaline oxygen atoms of two Ipbh moieties as well as two oxygen atoms of the two methanol molecules. The crystal packing of Ipbh and the complex 4 exhibits 1D and 2D supramolecular networks, respectively through different intermolecular hydrogen-bonding interactions.