Synthesis, Characterization, Crystal Structure and Supramolecular Interactions of a New Ni(II) Compound Based on l-Histidine and Dipicolinic Acid; New Solid State Precursor for NiO Nanoparticles and Its Catalytic Activity for Nitrophenol Reduction

Abstract

New discrete supramolecular coordination compound of Ni(II) namely (H2Lh)[Ni(pydc)2]·5H2O (1), where pydc = pyridine-2,6-dicarboxylic acid and Lh = l-histidine has been fabricated and characterized by elemental analysis, spectral (IR, UV–Vis), thermal (TG/DTG) analysis and single crystal X-ray diffraction (XRD). The asymmetric unit of the title compound containing two halves of [Ni(pydc)2]2− anions, one (H2Lh)2+ counter cation and five uncoordinated water molecules. The building units of this coordination compound connected via complicated strong and weak intermolecular interactions and made fascinating a 3D supramolecular architecture. In compound 1 two Ni1II and Ni2II ions are located at the center of distorted octahedrons. NiO nanoparticles were prepared using thermal decomposition of the (H2Lh)[Ni(pydc)2]·5H2O complex at 450 °C and well characterized by Fourier transform infrared, XRD, scanning electron microscopy, and energy dispersive X-ray spectroscopy techniques, to examine the structure, morphology, particle size and phase composition. The XRD patterns proved that the nanosized NiO particles had high purity and crystallinity. So, the Ni(II) complex could be used as a good precursor for the fabrication of NiO nanoparticles as a result of its low temperature of decomposition. After that, this nanosize nickel oxide used as heterogeneous catalyst for the reduction of nitrophenols (NPs) in aqueous solution in the presence of excess NaBH4 at room temperature. The reduction of 4-NP by NaBH4 and catalyst has been extensively used as a model reaction for reduction of nitroarene, since it is easy to monitor with simple and fast UV–Vis technique, and there are no by-products. This reaction is also valuable in the view of green chemistry because 4-NP, one of the toxic materials in the wastewater, is transformed into a commercially important substance, 4-aminophenol (4-AP). NiO nanoparticles indicated excellent performance in the reduction of NP to corresponding AP within 21 min with rate constant about 0.15 min−1. The effect of catalyst dosage also evaluated on the efficiency of reduction process. The NiO nanoparticles could be reused upon multipel cycles without changing in its structure and activity.