COMPLEXES OF TRI-PROTONATED AND TETRA-PROTONATED FORMS OF 1,4,8,12-TETRAAZACYCLOPENTADECANE WITH CHLORIDE, NITRATE, IODATE, AND SULFATE-IONS IN AQUEOUS-MEDIA .1. FORMATION-CONSTANTS, THERMODYNAMIC PROPERTIES, AND BONDING MECHANISMS

Complexation stoichiometries and formation constants of tri- and tetra-protonated forms of 1,4,8,12-tetraazacyclopentadecane with NO3-, Cl-, IO3- and SO4(2)- ions are determined by pH potentiometric and C-13 NMR spectrometric measurements. Estimates of DELTA-H and DELTA-S are obtained from the values of the temperature dependent formation constants and acid dissociation constants. All four anions form only 1:1 complexes with the triprotonated amine species. NO3- and Cl- form 1:1 complexes only with the tetraprotonated amine, while IO3- and SO4(2)- form both 1:1 and 2:1 complexes. The complexation behavior is interpreted in terms of solvation and internal hydrogen bonding interactions.