BINDING OF INORGANIC AND ORGANIC POLYANIONS BY PROTONATED OPEN-CHAIN POLYAMINES IN AQUEOUS-SOLUTION

The stability constants of complexes between protonated open chain pol yamines (with pyridine and imidazole as well) and organic or inorganic polyanions (16 amines, 16 anions, 87 systems, 435 complexes), have be en collected and compared. The main characteristic of these systems (b oth with organic and inorganic polyanions) is the high number of speci es that can be formed, ie., m+n-1 species, with m = maximum value of i in AH(i)(j+) and n = maximum value of j in HjL(z-j-). All the data sh owed that the stability of these complexes is strongly dependent on th e charges involved in the formation reaction. Less important, but sign ificant, factors affecting the stability of these complexes are the di stance between the charges and the number of aminogroups in the polyam ines, and the difference between the charges of the reactants. Moreove r, it has been found that inorganic polyanions form more stable mixed complexes with respect to those of organic polyanions. A general equat ion, log K = f(z(cat), z(an), z) (z(cat) = charge of protonated amine, z(an) = charge of anion, z = \z(cat) + z(an)\), has been found for pr oton-amine-inorganic anions and for proton-amine-organic anions comple xes: log K = -2.3 + 1.42 z(cat) + bxz(an) - 0.45 z (b = 1.44(5) and 1. 09(5) for inorganic and organic anions, respectively), with a mean dev iation of similar to 0.5 log units. Though this deviation is quite gre at, the predictive value, when analysing multicomponent systems, may b e very important. A simple linear free energy relationship gives -Delt a G degrees = 7.5 +/- 0.3 and 6.4 +/- 0.4 kJ mol(-1) n(-1) for inorgan ic and organic anions, respectively (n = number of possible salt bridg es). T Delta S degrees also depends an charges and, for some systems, T Delta S degrees = 5.5 x z(cat) x z(an) J mol(-1) has been found. Mor eover, spectroscopic evidence (UV/CD) for the formation of these compl exes is reported. These species are generally not very stable (if comp ared with transition metal complexes), but they are not negligible in a correct modelling and speciation of ionic multicomponent solutions.