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.

Keywords:

• Copper(II) and nickel(II) complexes
• Tetraaza ligands
• Cage ligands
• Potentiometric study

Acknowledgements

The authors are thankful to Regional Sophisticated Instrumentation Centres, Punjab University, Chandigarh, and Central Drug Research Institute, Lucknow, for recording various spectra and microanalyses, respectively. The authors wish to thank Professor Ashok Mahan, University of Allahabad for helpful discussions.