Synthesis and Characterization of New Polyaza Non-macrocyclic and Macrocyclic Nickel(II) Complexes Containing One 1,3-Diazacyclohexane Ring

A new nickel(II) complex [NiL1]2+ (L1 = 1-(2-aminoethyl)-3-(N-{2-aminoethyl}aminomethyl-1,3-diazacyclo-hexane) containing one 1,3-diazacyclohexane ring has been prepared selectively by the metal-template condensation of formaldehyde with N-(2-aminoethyl)-1,3-propanediamine and ethylenediamine at room temperature. The complex reacts with nitroethane and formaldehyde to yield the pentaaza macrocyclic complex [NiL2]2+ (L2 = 8-methyl-8-nitro-1,3,6,10,13-pentaazabicyclo[13.3.1]heptadecane) bearing one C-NO2 pendant arm. The reduction of [NiL2]2+ by using Zn/HCl produces [NiL3(H2O)] 2+ (L3 = 8-amino-8-methyl-1,3,6,10,13-pentaazabicyclo[13.3.1]heptadecane) bearing one coordinated C-NH2 pendant arm that is readily protonated in acid solutions. The hexaaza macrocyclic complex [NiL4]2+ (L4 = 8-phenylmethyl-8-nitro-1,3,6,8,10,13-hexaazabicyclo[13.3.1]heptadecane) bearing one N-CH2C6H5 pendant arm has also been prepared by the reaction of [NiL1]2+ with benzylamine and formaldehyde. The nickel(II) complexes of L1, L2, and L4 have square-planar coordination geometry in the solid states and in nitromethane. However, they exist as equilibrium mixtures of the square-planar [NiL]2+ (L = L1, L2, or L4) and octahedral [NiL(S)2] 2+ species in various coordinating solvents (S); the proportion of the octahedral species [NiL(S)2] 2+ is strongly influenced by the ligand structure and the nature of the solvent. Synthesis, spectra, and chemical properties of the nickel(II) complexes of L1-L4 are described