Interconvertable Modular Framework and Layered Lanthanide(III)-Etidronic Acid Coordination Polymers

Isostructural modular microporous Na2[Y(hedp)(H2O)0.67] and Na4[Ln2(hedp)2(H2O)2]·nH2O (Ln
= La, Ce, Nd, Eu, Gd, Tb, Er) framework-type, and layered orthorhombic [Eu(H2hedp)(H2O)2]·H2O and
Na0.9[Nd0.9Ge0.10(Hhedp)(H2O)2], monoclinic [Ln(H2hedp)(H2O)]·3H2O (Ln = Y, Tb), and triclinic [Yb(H2hedp)]·H2O coordination polymers based on etidronic acid (H5hedp) have been prepared by hydrothermal
synthesis and characterized structurally by (among others) single-crystal and powder X-ray diffraction and
solid-state NMR. The structure of the framework materials comprises eight-membered ring channels filled
with Na+ and both free and lanthanide-coordinated water molecules, which are removed reversibly by
calcination at 300 °C (structural integrity is preserved up to ca. 475 °C), denoting a clear zeolite-type behavior.
Interesting photoluminescence properties, sensitive to the hydration degree, are reported for Na4[Eu2(hedp)2(H2O)2]·H2O and its fully dehydrated form. The 3D framework and layered materials are, to a certain extent,
interconvertable during the hydrothermal synthesis stage via the addition of HCl or NaCl:  of the 3D
framework Na4[Tb2(hedp)2(H2O)2]·nH2O, affords layered [Tb(H2hedp) (H2O)]·3H2O, whereas layered [Tb(H2hedp)(H2O)2]·H2O reacts with sodium chloride yielding a material similar to Na4[Tb2(hedp)2(H2O)2]·nH2O.
In layered [Y(H2hedp)(H2O)]·3H2O, noncoordinated water molecules are engaged in cooperative water-to-water hydrogen-bonding interactions, leading to the formation of a (H2O)13 cluster, which is the basis of
an unprecedented two-dimensional water network present in the interlayer space.