The Potentially Hexadentate Isomeric Macrocycles <i>trans- </i>and <i>cis-</i>6,13-Diethyl-1,4,8,11-tetraazacyclotetradecane-6,13-diamine and Their Cobalt(III) Complexes: Unexpected Conformational Behavior

The new isomeric pendent arm macrocyclic hexaamines trans- and cis-6,13-diethyl-1,4,8,11-tetraazacyclotetradecane-6,13-diamine (L5 and L6) and their hexadentate coordinated cobalt(III) complexes are reported. X-ray crystal structural analyses of [H4L5](ClO4)4·2H2O (triclinic, P1̄, a = 7.840(1) Å, b = 13.6206(9) Å, c = 14.246(1) Å, α = 77.141(6)°, β = 86.539(9)°, γ = 86.465(9)°, Z = 2) and [CoL5](ClO4)3 (monoclinic, C2/c, a = 14.461(6) Å, b = 11.580(2) Å, c = 15.865(5) Å, β 111.96(1)°, Z = 4) were performed. Cation disorder in the structure of [CoL5](ClO4)3 is interpreted with the aid of molecular mechanics calculations, and solution conformational behavior is analyzed by NMR spectroscopy. It is found that the aqueous solution structure of [H4L5]4+ is unusually ordered, by comparison with other closely related ligand systems.