Determination of Formation Constants of Calcium Complexes of Difluoromethylenediphosphonic Acid and Related Diphosphonates

Tekum Fonong, Donald J. Burton, Donald J. Pietrzyk

Research output: Contribution to journalArticle

Abstract

Formation constants for the 1:1 and 2:1 complexes formed between Ca2+ and difluoromethylenedlphosphonate (F2MDP), dichloromethylenediphosphonate (Cl2MDP), and 1-hydroxy-ethane-1,1-diphosphonate (EHDP) were determined by a Potentiometrie titration procedure where the Indicator electrode Is a Ca Ion selective electrode and the titrant is a CaCl2 solution. Measurements were made in the absence of Ionic strength control and in 0.10 M NaCl and 0.10 M NH4Cl solution. Logarithm formation constants, although similar for the 1:1 complex, change In the order EHDP > Cl2MDP > F2MDP which is opposite to the acid strength exhibited by the ligands. For the 2:1 Ca2+:llgand complex the EHDP complex formation constant is similar to the 1:1 complex and the complex is significantly more stable than either of the 2:1 Ca2+:Cl2MDP or Ca2+:F2MDP complexes. This Is probably the result of coordination Involving the hydroxyl group In EHDP. Weak 1:1 Na+:ligand complexes were also detected.

Original languageEnglish (US)
Pages (from-to)1089-1094
Number of pages6
JournalAnalytical chemistry
Volume55
Issue number7
DOIs
StatePublished - Jun 1983

ASJC Scopus subject areas

  • Analytical Chemistry

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