COORDINATION TENDENCY OF [3K]ANENK POLYAZACYCLOALKANES - THERMODYNAMIC STUDY OF SOLUTION EQUILIBRIA

Equilibria between polyazacycloalkanes of the series [3k]aneN(k) (k = 3-11) and the bivalent metal ions of Mn through Zn have been studied. The stability constants (log K) for the complexes of Mn2+, Cu2+ and Fe2+ with 1,4,7,10,13,16-hexaazacyclooctadecane (L4), 1,4,7,10,13,16,19-heptaazacyclohenicosane (L5) and 1,4,7,10,13,16,19,22-octaazacyclotetracosane (L6) have been determined potentiometrically in 0.15 mol dm-3 NaClO4 at 25-degrees-C: [MnL4]2+, 10.50; [MnL6]2+, 6.27; [CuL4]2+, 24.40; [CuL5]2+, 19.48; [Cu2L5]4+, 30.49; [Cu2L6]4+, 35.25; and [FeL5]2+, 12.09. The enthalpy changes (-DELTA-H-degrees/kcal mol-1) for the formation of [CuL4]2+ (23.9), [CuL5]2+ (19.7) and [NiL5]2+ (11.7) have been measured by means of microcalorimetric techniques. The results are discussed in terms of the increasing number of donor atoms and size of the macrocycles. As the size increases the co-ordination features of the metal complexes largely depend on the metal ion.