Interconvertable Modular Framework and Layered Lanthanide(III)-Etidronic Acid Coordination Polymers ShiF. N. Cunha-SilvaL. MafraL. TrindadeT. CarlosL. D. A. Almeida PazF. RochaJ. 2008 Isostructural modular microporous Na<sub>2</sub>[Y(hedp)(H<sub>2</sub>O)<sub>0.67</sub>] and Na<sub>4</sub>[Ln<sub>2</sub>(hedp)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>]·<i>n</i>H<sub>2</sub>O (Ln = La, Ce, Nd, Eu, Gd, Tb, Er) framework-type, and layered orthorhombic [Eu(H<sub>2</sub>hedp)(H<sub>2</sub>O)<sub>2</sub>]·H<sub>2</sub>O and Na<sub>0.9</sub>[Nd<sub>0.9</sub>Ge<sub>0.10</sub>(Hhedp)(H<sub>2</sub>O)<sub>2</sub>], monoclinic [Ln(H<sub>2</sub>hedp)(H<sub>2</sub>O)]·3H<sub>2</sub>O (Ln = Y, Tb), and triclinic [Yb(H<sub>2</sub>hedp)]·H<sub>2</sub>O coordination polymers based on etidronic acid (H<sub>5</sub>hedp) 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<sup>+</sup> and both free and lanthanide-coordinated water molecules, which are removed reversibly by calcination at 300 °C (structural integrity is preserved up to ca<i>.</i> 475 °C), denoting a clear zeolite-type behavior. Interesting photoluminescence properties, sensitive to the hydration degree, are reported for Na<sub>4</sub>[Eu<sub>2</sub>(hedp)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>]·H<sub>2</sub>O 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 Na<sub>4</sub>[Tb<sub>2</sub>(hedp)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>]·<i>n</i>H<sub>2</sub>O, affords layered [Tb(H<sub>2</sub>hedp) (H<sub>2</sub>O)]·3H<sub>2</sub>O, whereas layered [Tb(H<sub>2</sub>hedp)(H<sub>2</sub>O)<sub>2</sub>]·H<sub>2</sub>O reacts with sodium chloride yielding a material similar to Na<sub>4</sub>[Tb<sub>2</sub>(hedp)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>]·<i>n</i>H<sub>2</sub>O. In layered [Y(H<sub>2</sub>hedp)(H<sub>2</sub>O)]·3H<sub>2</sub>O, noncoordinated water molecules are engaged in cooperative water-to-water hydrogen-bonding interactions, leading to the formation of a (H<sub>2</sub>O)<sub>13</sub> cluster, which is the basis of an unprecedented two-dimensional water network present in the interlayer space.