Abstract
A series of Ni(Ⅱ)-ternary complexes have been synthesised by the reactions of Ni(Ⅱ) complexes of 1,4,7,10-tetraazacyclododecane (cyclen) and tris(2-aminoethyl)amine (tren) with different diamines such as, en, 1,1-Me2en, pn, 2,2-Me2pn. The X-ray crystal structures confirmed the compositions and geometry of complexes. They possess distorted octahedral geometry. The crystal structures of [Ni(tren)(pn)](ClO4)2 and [Ni(tren)(1,1-Me2en)](ClO4)2 are under study. The bond lengths of diamines nitrogens with Ni(Ⅱ) are different, because they faced different environments. The thermodynamic properties of all Ni(Ⅱ)-ternary complexes were studied by protonation titration method and spectroscopic method. The stability constants of the ternary complexes were determined by potentiometrically and spectrophotometrically in aqueous solution. The ionic strength hold at 0.1M NaClO4 at 25.0±0.1℃. In aqueous solution Ni(Ⅱ), cyclen or tren and diamine in 1:1:1 ratio was subjected for reaction with increase of pH, at first Ni(Ⅱ) form complexes with cyclen or tren and further increase of pH ternary Ni(Ⅱ)-diamines complexes were obtained. The stability of chelate ring size, steric effect and inductive effect of ternary complexes of Ni(Ⅱ)-cyclen/tren with diamines could be infered from the stability constants. The experimental data revealed that the Ni(tren)2+-ternary complexes are more stable than Ni(cyclen)2+-ternary complexes.The most important fact is the stability of chelate ring size, en and 1,1-Me2en form five membered chelate ring whereas pn and 2,2-Me2pn form six membered chelate ring with Ni(Ⅱ)-cyclen/tren. It has been found that five membered chelate rings are more stable than six membered chelate rings. The steric effect of the diamines containing methyl groups on their skeleton is more important than inductive effect on the stability constants.