Pg. Daniele et al., BINDING OF INORGANIC AND ORGANIC POLYANIONS BY PROTONATED OPEN-CHAIN POLYAMINES IN AQUEOUS-SOLUTION, Annali di chimica, 87(7-8), 1997, pp. 415-447
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.