Zinc(II) complexes with saturated and unsaturated tetraazamacrocyclic ligands: enthalpy contribution to their solution stability

Heats of complexation of Zn2+ with I (2 tautomeric forms) and its satd. analog were detn. in MeCN-74 wt.% CHCl3 or MeOH-50 wt.% Me2CO (both solns. contg. 0.15 M Et4NBr) at 25°. The overall reaction is ZnBr42- + L → ZnLBrn(2-n) + (4-n)Br-. Heats of soln. and molar conductivities were detd. for (Et4N)2ZnBr4, Et4NBr, ligands (L), and the Zn complexes.