LANTHANIDE COMPLEXES WITH 1-HYDROXYETHANE-1,1-DIPHOSPHONIC ACID - SOLVENT ORGANIZATION AND COORDINATION GEOMETRY IN CRYSTALLINE AND AMORPHOUS SOLIDS

In has been suggested in an earlier report that a 1:2 complex between europium(III) and 1-hydroxyethane-1,1-diphosphonic acid, Eu(H3HEDP)(2) (+), adopts an unexpected coordination geometry in aqueous solution. T hermodynamic and spectroscopic results were interpreted to indicate ex tensive hydrogen bonding within the complex, and between the complex a nd the water molecules in its second coordination sphere. In an attemp t to confirm some of these features, samples of six amorphous and ten crystalline 1:2 complexes of selected lanthanides with HEDP have been prepared and characterized by single crystal X-ray diffraction,FT IR s pectroscopy and thermogravimetric analysis, For the heavy lanthanides (To-Lu plus Y) the crystals are polymeric chains in which the metal io ns are seven-coordinate, five water molecules are dispersed in interla mellar spaces, and the fifth hydrogen ion is bound to a free phosphona te oxygen on HEDP. The structure parameters for To(H3HEDP)(H2HEDP). 5H (2)O (representative of the heavy lanthanides) are a = 10.465, b = 11. 415, c = 17.252 Angstrom, alpha = 90, beta = 94.22, gamma = 90 degrees and the crystal system is monoclinic. In the corresponding crystallin e complexes of the light lanthanides (Eu and Nd), the metal ion is eig ht-coordinate and the hydration numbers are higher. The fifth hydrogen ion is not closely associated with the phosphonate group in the Eu co mplex but is bound in the Nd crystal. The crystal indices for [H3O][Eu (H2HEDP)(2)]. 12H(2)O are a = 10.0988, b = 11.4846, c = 11.9303 Angstr om, alpha = 99.637, beta = 91.277, gamma = 95.828 degrees. The corresp onding values for Nd(H3HEDP)(H2HEDP). 7H(2)O are a = 9.318, b = 10.272 , c = 11.766 Angstrom, alpha = 91.09, beta = 111.24, gamma = 98.50 deg rees, Both crystallize in the triclinic crystal system. Thr amorphous analogs for both light and heavy lanthanides are more strongly hydrate d (Ln(H3HEDP)(H2HEDP). 18H(2)O). FT-IR spectra confirm that there are no inner sphere water molecules in either the crystalline or amorphous solids, but the water stretching and bending frequencies are proporti onal to the cation radius in the amorphous species (though not in the crystalline analogs). The crystal position parameters indicate extensi ve hydrogen bonding between the interstitial water molecules and the b ound ligands, and a hydrogen bonding interaction between the bound lig ands, Though the polymeric nature of the solids is different from that in solution, the solvent organization features are consistent with th e previously postulated structure of the 1:2 complex between Eu(III) a nd HEDP in aqueous solution. (C) 1998 Elsevier Science S.A.