Nusrallah Jubran

Stabilization of monovalent nickel in aqueous solutions by complexation with the β-isomer of C-5,12-racemic-1,4,5,7,7,8,11,12,14,14-decamethyl-1,4,8,11-tetraazacyclotetradecane

Abstract The monovalent nickel complex formed by the reduction of the β-isomer of the complex of C-5,12- racemic-1,4,5,7,7,8,11,12,14,14-decamethyl-1,4,8,11- tetraazacyclotetradecane nickel(II), NiL12+ in 0.1 M HCO2Na, pH 7.6, has a half-life longer than 90 h. The redox potential of the couple NiL1+/NiL12+ is −0.94 V vs. Ag/AgCl. The absorption spectrum of NiL1+ consists of a band with λmax = 335 nm and ϵmax = 2200 M−1 cm−1. For the analogous complex with C-5,12-racemic-5,7,7,12,14,14-hexamethyl-1,4, 8,11-tetraazacyclotetradecane, L2, the half-life time of NIL2+ is less than 1 min and the redox potential is −1.44 V vs. Ag/AgCl. These results are similar to those reported earlier for the analogous nickel complexes with the meso-isomers of the ligands. The results thus indicate that both the kinetic and thermodynamic stabilization of monovalent nickel by N-methylation of tetraazamacrocyclic ligands is not significantly affected by the configuration of the ligand.

Determination of the equilibrium constant for binding hydroxide to tetraazamacrocyclic—Nickel(II) complexes

Abstract The p K b for the equilibria NiL(OH) + ⇄ NiL 2+ + OH − for L1,4,7,10-tetraazacyclotridecane, 1,4,8, 12-tetraazacyclopentadecane, C-β-racemic-5,7,7,12, 14,14-hexamethyl-l,4,8,11-tetraazacyclotetradecane and C-β-racemic-1,4,5,7,7,8,11,12,14,14,-decamethyl- 1,4,8,112-tetraazacyclotetradecane are 0.95, 1.9, 0.2 and 0.65 respectively. The results are compared with data for analogous complexes reported earlier. The results indicate that the main factors affecting these equilibrium constants are the in plane ligand field strengths of the square planar complexes and steric factors.

The thermal behavior of dithiooxamide ligands and their nickel complexes

Abstract The thermal behavior of substituted dithiooxamide ligands and their nickel complexes has been studied with differential scanning calorimetry and thermogravimetry. The thermal products were analyzed by mass spectral and IR techniques. The mechanism of the thermal decomposition of both the free ligands and metal complexes precludes the clean thermal formation of the polymeric nickel complexes from the neutral ligand derivatives, Ni(LH 2 ) 2 Br 2 .

Ring size effects on the chemical properties of tervalent nickel complexes with tetra-aza macrocyclic ligands in aqueous solutions. An electrochemical and pulse radiolytic study

Electrochemical oxidation and oxidation by hydroxyl radicals of the divalent nickel complexes of 1,4,7,10-tetra-azacyclotetradecane and 1,4,8,12-tetra-azacyclopentadecane in acidic aqueous solutions containing perchlorate or sulphate anions are reported. The properties of the tervalent complexes thus formed are described. The results are compared with those reported earlier for other tervalent nickel complexes with tetra-aza macrocyclic ligands. The results indicate that neither the redox potentials nor the half-lives of the tervalent complexes are directly related to the cavity size of the ligand or its ligand-field strength. It is suggested that the detailed conformation of the macrocyclic ligands has a profound effect on the properties of the tervalent complexes. The difference in the factors affecting the chemical properties of the mono- and ter-valent complexes is discussed.

Stabilization of copper(I) in aqueous solutions by ligation with the saturated tetra-aza macrocyclic ligand 1,4,5,7,7,8,11,12,14,14,-decamethyl-1,4,8,11-tetra azacyclotetradecane

The title perchlorate complex is stable in air-saturated aqueous solutions and is reversibly oxidized to the divalent complex at +0.47 V vs. Ag/Agcl.

Stabilization of monovalent nickel in aqueous solutions by a saturated tetra-aza-macrocyclic ligand

The planar form of the complex C-meso-1,4,5,7,7,8,11,12,14,14-decamethyl-1,4,8,11-tetra-azacyclotetradecanenickel(I){[Ni(L1)]+}is shown to be stable in aqueous solutions, with t½ > 100 h and the formal potential of the couple [Ni(L1)]2+/[Ni(L1)]+ is – 0.98 V vs. standard calomel electrode; redox reactions involving this couple were studied and compared with those of the couple [Ni(L2)]2+/[Ni(L2)]+(L2=C-meso-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetra-azacyclotetradecane).