Nickel(II) and copper(II) complexes of aza macrocycles derived from trichloromethane

Abstract

Syntheses of nickel(II) complexes of the tetraaza macrocycles 2,7-dichloro-1,3,6,8-tetraazacyclodecane (DCCD) and 2,8-dichloro-1,3,7,9-tetraazacyclododecane (DICD) and a copper(II) complex of 2,6,8,12,13,17-hexaazabicyclo[5.5.5]heptadecane (HBCH) are reported in the template condensation of trichloromethane with 1,2-diaminoethane or 1,3-diaminopropane. Formulation of the synthesized products [Ni(DCCD)(H2O)2]Cl2, [Ni(DICD)(H2O)2]Cl2 · H2O, and [Cu3(HBCH)(H2O)6]Cl6, and the metal-free ligand hydrochloride HBCH · 6HCl has been confirmed by elemental analyses, conductivity measurements, and spectral studies. Potentiometric studies of nickel(II) and copper(II) complexes of HBCH and structurally similar 2,5,8,10,13,16,17,20,23-nonaazabicyclo[7.7.7]tricosane (NACT, earlier derived from trichloromethane and diethylenetriamine) have also been performed in the structural support of HBCH. In 1 : 1, metal : HBCH solution, copper(II) is coordinated to four N-donors of two-HN(CH2)3NH– groups of the ligand in a non-planar tetraaza cavity. The equilibrium constant value (log K = 15.41) for the reaction Cu2+ + A ⇔ CuA2+ (A = HBCH) is in favor of the cyclic structure of the ligand. A high value (log K = 23.27) for corresponding reaction in the NACT system is due to conformational change in the ligand, where copper(II) organizes the macrocycle to form a nearly planar cavity in which the cation fits well.