Calorimetric and laser induced fluorescence investigation of the complexation geometry of selected europium-gem-diphosphonate complexes in acidic solutions

Journal Article · Wed May 10 04:00:00 EDT 1995 · Inorganic Chemistry

DOI:https://doi.org/10.1021/ic00114a038· OSTI ID:458756

Nash, K L ^[1]; Rao, L F; Choppin, G R ^[2]

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1. Argonne National Lab., IL (United States)
2. Florida State Univ., Tallahassee, FL (United States)

Details of the coordination chemistry of europium complexes with methanediphosphonic acid (MDPA), vinylidene-1,1-diphosphonic acid (VDPA), and 1-hydroxyethane-1,1-diphosphonic acid (HEDPA) in acidic aqueous solutions have been investigated by titration calorimetry and laser-induced fluorescence. For the 1:1 complexes, thermodynamic parameters and complex hydration are consistent with those previously reported for europium complexes with the carboxylate structural analog malonate. In the 1:2 complexes, markedly different thermodynamic parameters and cation dehydration are observed. The second diphosphonate ligand adds to the 1:1 complex displacing four additional water molecules from the primary coordination sphere (as compared with two for the addition of a second malonate). This reaction is also characterized by a nearly zero entropy change. The results are rationalized using molecular mechanics to suggest an unusual geometry in which the diphosphonate ligands and bound water molecules are appreciably segregated in the europium coordination sphere. Intramolecular hydrogen bonding and second hydration sphere ordering are suggested to explain the low complexation entropies.

• OSTI ID: 458756
• Journal Information: Inorganic Chemistry, Journal Name: Inorganic Chemistry Journal Issue: 10 Vol. 34; ISSN 0020-1669; ISSN INOCAJ
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
CALORIMETRY
CHEMICAL REACTIONS
ENTROPY
EUROPIUM COMPLEXES
FLUORESCENCE
MATHEMATICAL MODELS
PHOSPHONATES
THERMODYNAMIC PROPERTIES
TITRATION