Substituents Effect on the Kinetics and Mechanisms of Formation of Copper (II) and Nickel (II) Complexes of Some Β-Diketones

Chelates of β – diketones (R1COCH2COR2) with transition metals have been found to possess a wide range of properties and application, some of which are dependent on the substituents (R1 and R2).  Copper(II) and Nickel(II) complexes of β – diketones in which R1= C6H5 and R2 = C6H5 (dbm), R2 = CH3 (bza) R2 = CF3 (tfpbd) and R1 = C4H3S, R2 = CF3(tta) were synthesised and characterised using UV, IR, elemental analysis and magnetic susceptibility. The probable influence of the substituents on the kinetics and mechanisms of formation of the complexes were investigated with the aid of a Thermostated Schimadu 1800 uv-visible spectrophotometer. The reactions were studied at wavelengths characteristics of each complex. Results show the six coordinate copper(II) and nickel(II) complexes have probable distorted octahedral geometry while the four coordinate Ni(dbm)2 is tetrahedral. The kinetics data suggests an influence of the diketonate substituents on the copper(II) and nickel(II) complexes in solution is in the order C6H5 > CH3 >CF3 > C4H3S and CF3 > C6H5 > CH3 > C4H3S respectively. Solvent influence (k-1) was constant in the range 0.007 – 0.008 for fluorosubstituted complexes and least at 0.004 – 0.005 mol-1s-1 in the alkyl substituted complexes. The steady state approximation gave solvent independent rates k1k2 at 25oC, in the copper(II) complexes, k2 is greater than k1 (k2 > k1) , with k2 constant while in the nickel(II) complexes, the values of k2 was less than k1 and ascribed to rate determining and varies with the nickel(II) - ligand systems studied. Keywords: β-diketones, Copper II and Nickel II Complexes, Substituents effect, Kinetics

Synthesis, characterization, electrochemical studies and X-ray structures of mixed-ligand polypyridyl copper(II) complexes with the acetate

[Cu(phen)2(CH3COO)](ClO4).2H2O (1) and [Cu(bipy)2(CH3COO)]-(ClO4).H2O (2) {phen = 1,10-phenanthroline, bipy = 2,2’-bipyridine}were synthesized and characterized. The complexes were characterized by employying elemental analyses, infrared and UV-Visible spectroscopy, room temperature magnetic measurements and the crystal structures elucidated using X-ray diffraction experiment. The redox properties of the complexes were also investigated. Both structures have a square pyramidal CuN4O chromophore which exhibit significant distortions due to long Cu-O [2.217(3) Å for (1) and 2.179 (1) for (2)] and Cu-N [2.631(2) Å for (1) and 2.714(1) Å for (2)] bonds. This distortion if further shown by the O-Cu-N bond angles [147.71(8) o for (1) and 153.40(5) o for (2)]. The elemental analyses further support the structural details unveiled by the single crystal X-ray diffraction analysis. The infrared spectra shows the acetate vibrational frequencies at 1587 cm-1,1428 cm-1, 1314 cm-1 for (1) and 1571 cm-1, 1441 cm-1, 1319c m-1 for (2) and the perchlo-rate bands at 1059 cm-1, 720 cm-1 (1) and 1080 cm-1,768 cm-1 (2). The broad d-d bands for the copper ion at 14,514 cm-1(1) and 14,535 cm-1(2) support the adoption of square pyramid geometries. The magnetic moments for the two complexes are 1.83 B.M for (1) and 1.72 B.M for (2). The peak to peak values of the two complexes show that the electrode reactions are quasi-reversibile with ΔEp = 0.023V (1) and 0.025V for (2). In both structures, there are π-π intermolecular interactions in addition to hydrogen bonding between the units