Coordinating tendencies of a 14-membered tetraaza macrocycle which forms a seven-membered chelate ring

1,4,7,10-Tetraazacyclotetradecane (L) was prepd., and the basicity and stability consts. of [CuL]2+ and [Cu(HL)]3+ were detd. by potentiometry at 25° in 0.5 mol/dm3 KNO3. The heats of formation of the Cu(II) and Ni(II) complexes were detd. by batch and flow microcalorimetry, resp. The coordination of L to Cu and Ni to form a system with a (5,5,5,7) chelate ring is less exothermic than that of 1,4,8,11-tetraazacyclotetradecane and 1,4,7,11-tetraazacyclotetradecane, which form (5,6,5,6) and (5,5,6,6) chelate sequences, resp. [CuL]2+ is more stable than [Cu(trien)]2+ (trien = triethylenetetramine) due to a favorable entropy contribution. The stability of [Cu(HL)]3+ was compared to that of protonated complexes formed by other tetraaza macrocycles.