Studies on copper(II) complexes of some polyaza macrocycles derived from 1,2-diaminoethane

Abstract

Syntheses of copper(II) complexes of 20-membered and 15-membered aza macrocycles 1,3,6,8,11,13,16,18-octaaza-2,7,12,17-tetrachlorocycloeicosane (OTCE, [20]-N8) and 1,3,6,8, 11,13-hexaazacyclopentadecane (HCPD, [15]-N6) involving metal template condensation between 1,2-diaminoethane, trichloromethane and dichloromethane, respectively, are reported. Formulation of [Cu4(OTCE)(H2O)8]Cl8 and [Cu3(HCPD)(H2O)6]Cl6 · 2H2O and the ligand hydrochlorides OTCE · 8HCl and HCPD · 6HCl are supported by elemental analyses, conductivity measurements, and spectral studies. For a comparative cavity size effect on the stability constant, potentiometric measurements on the copper complexes of the generated macrocycles [15]-N6 and [20]-N8 and the structurally related larger macrocycle 1,3,6,8,11,13,16,18,21,23-decaaza-2,2,7,7,12,12,17,17,22,22-decachlorocyclopentacosane (DDCP, [25]-N10, prepared recently) have been performed in aqueous solution at 25°C (μ = 0.1 M KNO3). Very high stability constants obtained for reaction Cu2+ + A ⇌ CuA2+ (A = ligand, log K = 20.51 and 25.87, respectively, for OTCE and DDCP systems) are a reflection on the folding of the ligand to provide a small cavity suitable for fitting of the copper ion. Further, a high equilibrium constant value for CuA2+ + Cu2+ ⇌ Cu2A4+ (OTCE system, log K = 14.59) or Cu2A4+ + Cu2+ ⇌ Cu3A6+ (DDCP system, log K = 16.69) is due to suitable fitting of two and three copper ions in the 20-membered and 25-membered ring cavity of OTCE and DDCP, respectively.