Die Komplexe der Hexamine «penten» und «ptetraen» Thermodynamik ihrer Bildung in wässeriger Lösung

The two hexamines (H₂N? CH₂? CH_{2? )2}N? (CH_2)n? N(? CH₂? CH₂? NH₂₎₂, «penten» (n = 2) and «ptetraen» (n=3) have been investigated as chelating agents for COIII (preparative Study) and some of the divalent metal ions (potentiometric and calorimetric studies). Both amines function as sexadentate ligands for Co^III, Co^II and Ni^II, but one of the terminal aminogroups is much easier detached from the metal in case of M (penten)^v+ than in case of M(ptetraen)^v+, thus revealing more strain in the fivemembered chelate rings of the girdle plane of the «penten» complexes. On the other hand, the sixmembered chelate ring in M(ptetraen)^v+ is more strained than the five-membered ring comprising the tertiary nitrogen atoms of M(penten)^v+ Cu^II and Zn^II coordinate with both ligands only 5 of the 6 basic nitrogen atoms present. Both hexaamines function as sexadentates again with Mn^II, but the metal is coordinated with a molecule of water in addition to the 6 nitrogen atoms in the «penten» complex in contrast to the «ptetraen» complex. The thermodynamic functions for the protonation of the hexamines and for the addition of metal ions in aqueous solution are understood in almost every detail. The dielectric shielding of the charges of the reactants exerted by the solvent has to be taken into account; it is reduced by electrostriction as well as by an increase in temperature. It is shown that the approach of charges of equal sign often is an exothermic process.