The new isomeric pendent arm macrocyclic hexaamines trans- and cis-6,13-diethyl-1,4,8,11-tetraazacyclotetradecane-6, 13-diamine (L(5) and L(6)) and their hexadentate coordinated cobalt(III) complexes are reported. X-ray crystal structural analyses of [H(4)L(5)](ClO4)(4) . 2H(2)O (triclinic, , a = 7.840(1) Angstrom, b = 13.6206(9) Angstrom, c = 14.246(1) Angstrom, alpha 77.141(6)degrees, beta = 86.539(9)degrees, gamma = 86.465(9)degrees, Z = 2) and [CoL(5)](ClO4)(3) (monoclinic, C2/c, a = 14.461(6) Angstrom, b = 11.580(2) Angstrom, c = 15.865(5) Angstrom, beta 111.96(1)degrees, Z = 4) were performed. Cation disorder in the structure of [CoL(5)](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 [H(4)L(5)](4+) is unusually ordered, by comparison with other closely related ligand systems.