The chemistry of metal phosphonates has been progressing fast with the addition of new materials that possess novel structural features and new properties, occasionally in a cooperative manner. In this paper, we report a new family of functional lanthanide-carboxyphosphonate materials. Specifically, the lanthanide is La, Ce, Pr, Sm, Eu, Gd, Tb, or Dy and the carboxyphosphonate ligand is 2-hydroxyphosphonoacetic acid ( H 3 H P A ) . A l l r e p o r t e d L n H P A c o m p o u n d s , Ln 3 (H 0.75 O 3 PCHOHCOO) 4 •xH 2 O (x = 15−16), crystallize in the orthorhombic system. Two types of structures were isolated: series I and II polymorphs. For both series, the three-dimensional (3D) open frameworks result from the linkage of similar organo-inorganic layers, in the ac-plane, by central lanthanide cations, which yield trimeric units also found in other metal-HPA hybrids. Large oval-shaped 1D channels are formed by the spatial separation of the layers along the b-axis and filled with lattice water molecules. LnHPA materials undergo remarkable crystalline-to-amorphous-to crystalline transformations upon dehydration and rehydration cycles, as confirmed by thermodiffraction and NMR spectroscopy. The highest proton conductivity was observed for GdHPA (series II), 3.2 × 10 −4 S cm −1 at 98% RH and T = 21°C. The dehydration−rehydration chemistry was also followed by photoluminescence spectroscopy. It was shown that loss and reuptake of water molecules are accompanied by clear changes in the photoluminescence spectra and lifetimes of the Eu analog (series II). Our present results reveal a wide family of wellcharacterized, multifunctional lanthanide-based phosphonate 3D-structured metal−organic frameworks (MOFs) that show reversible crystalline-to-amorphous-to-crystalline transformations and, at the same time, exhibit high proton conductivity.

Syntheses and structures of alkaline earth metal ions and EDTMP, ethylenediamine-tetrakis(methylenephosphonate), are reported. The isostructural Ca 2+ and Sr 2+ analogs have 1D topologies, with EDTMP acting as both chelating and bridging ligand. The M-EDTMP compounds act as Fe-oxide removers from corroded surfaces.

available: powder XRD patterns for bulk samples of all materials reported, detailed experimental strategy, crystallographic cif files for Ca-PMIDA (CCDC 870777), Ca-HEDP (CCDC 870776), Ca-AMP (CCDC 870775), and Mg-PMIDA (CCDC 877820).

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The tetra-acid 2-hydroxyethylimino-bis(methylenephosphonic acid) (HEIBPH, 1) and its ring condensation product, the triacid 2-hydroxy-2-oxo-4-phosphonemethyl-1,4,2-oxazaphosphorinane (2), were investigated for determination of protonation constants using (31)P, (1)H, and (13)C NMR spectroscopy in a wide pH range. As for other alpha-amino-phosphonic acids, the first protonation of 1 is straightforward and occurs at the nitrogen, while for 2 the first protonation occurs simultaneously at the exo phosphonate group, allowing estimation of the microscopic protonation constants. The complexation of Ca(2+) with 1 in a 1:1 molar ratio in aqueous solutions and in the presence of a 5-fold excess Na(+) is rationalized by the products LCaH(2), LCaH, LCaNaH, LCa, and LCa(2) (L = 1). Only the phosphonate groups are involved in Ca(2+) binding at pH > 3, while the phosphonate, hydroxyl, and amine functionalities coordinate to Ca(2+) at pH > 6-7, as soon as the proton at N is lost. Probable conformation states of ions of 1 and 2 are estimated by means of the dependence of vicinal coupling constants (3)J(HH) and (3)J(PC) from dihedral angles.