Individual Nickel Research Articles

A molecular butterfly: Self-assembly of an imidazolate bridged tetranuclear nickel(II) compound from Ni(II) and 3-(4-methylimidazol-5-yl)methylene-hydrazonobutan-2-one oxime

Reaction of the Schiff-base ligand, 3-(4-methylimidazol-5-yl)methylenehydrazonobutan-2-one oxime (H2L) with nickel(II) perchlorate hexahydrate in 1:1 molar proportion in methanol gives rise to a tetranuclear nickel(II) compound, Ni4L4 (1) in moderate yield. The compound has been characterized by C, H, N microanalyses, FT-IR, UV–Vis spectra and room temperature magnetic susceptibility measurements. The X-ray crystal structure of the title compound has been determined. The structure reveals that it is an imidazolate bridged neutral tetranuclear nickel(II) compound. The nickel(II) centers in 1 adopt a rare ‘butterfly-like’ topology. The compound crystallizes in the monoclinic space group P21/c with a=17.648 (4), b=23.209 (5), c=14.418 (3) Å, β=108.708 (2)°, V=5593 (2) Å3 and Z=4. Individual nickel(II) center is in square-planar ‘N4’ coordination chromophore. Electrochemical studies show Ni(II) to Ni(III) oxidation along with Ni(II) to Ni(I) reduction in dichloromethane solution. Bond-Valence Sum (BVS) model calculation was performed to assign the oxidation state of each nickel center in 1.

Thermodynamics of formation of urea complexes with manganese(II), nickel(II) and zinc(II) ions in N, N-dimethylformamide

The complexation of urea (ur) with manganese(II), nickel(II) and zinc(II) ions has been studied by titration calorimetry in N, N-dimethylformamide (DMF) containing 0.4 M (C 2H 5) 4 NBF 4 as a constant ionic medium at 25°C. The calorimetric data were well explained in terms of the formation of [Mn(ur)] 2+, [Mn(ur) 2] 2+ and [Mn(ur) 4] 2+ for manganese(II), [Ni(ur)] 2+ for nickel(II) and [Zn(ur)] 2+ and [Zn(ur) 2] 2+ for zinc(II), and their formation constants, reaction enthalpies and entropies were determined. The complexation of the nickel(II)-urea system in DMF has also been studied by means of spectrophotometric titration and electronic spectra of individual nickel(II) complexes were determined. On the basis of the stepwise thermodynamic quantities and the individual electronic spectra of the complexes, it is revealed that the [Mn(ur)] 2+, [Mn(ur) 2] 2+, [Ni(ur)] 2+, [Zn(ur)] 2+ and [Zn(ur) 2] 2+ complexes have a six-coordinate octahedral structure, while the [Mn(ur) 4] 2+ complex has a four-coordinate tetrahedral structure.