Polyamines XV. Thermodynamics of Metal Complex Formation of Linear Tetraamines Containing Two Ethylenediamine Residues

The complex formation of Co2+, Ni2+, Cu2+, Zn2+, Pb2+ and Hg2+ with three tetraamines of type H2N(CH2)2NH(CH2)nNH(CH2)2NH2 (= 2, n, 2‐tet) for n = 2. 3 and 4, and with N‐methylethylenediamine (= nmen) have been investigated at 25° and I = 1(KNQ3). The stability constants and the heat evolved by formation of the (1:1)‐complexes ML have been determined. It is shown that the more stable complexes are normally formed by 2,3,2‐tet‐ligands. These results are discussed relating the thermodynamic data obtained to the stereochemistry of the complexes and using the visible spectra of the complexes in solution. The change in enthalpy is found to be the dominant factor and the measure of the steric strain whereas the entropy of complex formation decreases slowly.