Metal Complexes of Ethane and Propane Frame-Substituted Oligophosphonic and Oligophosphonocarboxylic Acids

Abstract

The stability constants of the complexes of one oligophosphonic acid (ethane-1,1,2-triphosphonic acid 1), five phosphonocarboxylic acids (ethane-1,2-diphospho-no-1-carboxylic acid 2, propane-1,1-diphosphono-2,3-dicarboxylic acid 3, ethane-1,2-diphosphono-1,2-dicarboxylic acid 4, ethane-1-phosphono-1,2-dicarboxylic acid 5, and propane-1-phosphono-1,2,3-tricarboxylic acid 6), and ethane-1,1,2-tricarboxylic acid 7 with Cu^{2 +}, Ni^{2 +}, Zn^{2 +}, Cd^{2 +} and Ca^{2 +} were determined by pH-metric titrations. The six ligands of type H_NL (N = 4 – 6) form mononuclear MLH_n (n = 0, 1, …, N–1) complexes with chelate structure. The calcium complexes seem to be less stable than the transition metal complexes.

Keywords:

• Oligophosphonates
• phosphonocarboxylates
• protonated metal complexes
• stability constant

Acknowledgments

Currently at KFKI Research Institute for Particle and Nuclear Physics, Budapest, Hungary.

Cs. Bogdán is indebted to Prof. Ferenc Gaizer (Prof. Emeritus of the Institute of Chemistry, Eötvös Loránd University, Budapest, Hungary), whose help, hints and stimulating suggestions contributed to the current work.

Notes

^a –P and –C denote –PO₃H₂ and –COOH groups, respectively;

^b number of measured points per titration curve.