The Effect of N-alkyl Substitution on Binding of Polycarboxylic Anions by Linear Polyammonium Cations |
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Authors: | Stefania Cascio Alessandro De Robertis Concetta De Stefano Silvio Sammartano |
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Institution: | (1) Dipartimento di Chimica Inorganica, Chimica Analitica, e Chimica Fisica, dell'Università, Salita Sperone 31, I-98166 Messina (Vill. S. Agata), Italy |
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Abstract: | The interaction between three N-alkyl-substituted polyamines1,1,4,4-tetramethylethylenediamine, 1,1,4,7,7,-pentamethyldiethylenetriamine,and 1,1,4,7,10,10-hexamethyltriethylenetetramine; general formula C3nNnH(7n+2)] with fourpolycarboxylic ligands (malonate, citrate, 1,2,3-propanetricarboxylate, and1,2,3,4-butanetetracarboxylate) has been studied potentiometrically in aqueous solution at25°C. For all the systems, the species ALHr (r = 1, 2 ... n + m – 1;n and m are the maximum degrees of protonation for the amine A and the carboxylicligand L, respectively) are formed. The stability of these species is quite high(in particular, that of species with r = n and r = n + 1) and is a linear functionof the charges involved in the formation reaction. The effect of N-alkyl substitutionis quite small: comparison with the analogous unsubstituted polyamines C(2n–2)NnH(5n–2) shows only a small decrease in stability. On average we have– G
o/n = 5.9 kJ-mol–1 for N-alkyl-substitutedamines and 6.6 kJ-mol–1 for unsubstituted ones (ndenoting the number of possible salt bridges). Other linear charge—stabilityrelationships are considered. |
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Keywords: | anion coordination amines carboxylic ligands effects of N-alkyl substitution on coordination aquatic chemistry |
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