Hydrothermal Synthesis and Characterization of New Pillared Layered Ethylenediphosphonates of Molybdenum(VI), A<sub>2</sub>[Mo<sub>2</sub>O<sub>5</sub>(O<sub>3</sub>PCH<sub>2</sub>CH<sub>2</sub>PO<sub>3</sub>)] (A = NH<sub>4</sub>, Tl, Cs, Rb) and K(H<sub>3</sub>O)[Mo<sub>2</sub>O<sub>5</sub>(O<sub>3</sub>PCH<sub>2</sub>CH<sub>2</sub>PO<sub>3</sub>)]

New ethylenediphosphonates of molybdenum, A<sub>2</sub>[Mo<sub>2</sub>O<sub>5</sub>(O<sub>3</sub>PCH<sub>2</sub>CH<sub>2</sub>PO<sub>3</sub>)] (A = NH<sub>4</sub> (<b>1</b>), Tl (<b>2</b>), Cs (<b>3</b>), Rb (<b>4</b>)), and K(H<sub>3</sub>O)[Mo<sub>2</sub>O<sub>5</sub>(O<sub>3</sub>PCH<sub>2</sub>CH<sub>2</sub>PO<sub>3</sub>)] (<b>5</b>), have been synthesized by a hydrothermal method and structurally characterized by X-ray diffraction, spectroscopic, and thermal studies. These compounds consist of pillared anionic layers [Mo<sub>2</sub>O<sub>5</sub>(O<sub>3</sub>PCH<sub>2</sub>CH<sub>2</sub>PO<sub>3</sub>)]<sup>2-</sup>, with A<sup>+</sup>, K<sup>+</sup>, and H<sub>3</sub>O<sup>+</sup> ions in the interlayer region as well as in the cavities within the anionic layers. Single-crystal X-ray structures of compounds <b>1</b> and <b>5</b> have been determined. They crystallize in the orthorhombic space group <i>Cmca</i> with <i>Z</i> = 8 and have the following unit cell parameters. For <b>1</b>, <i>a</i> = 25.60(1), <i>b</i> = 10.016(4), and <i>c</i> = 9.635(3) Å and for <b>5</b>, <i>a</i> = 25.63(1), <i>b</i> = 10.007(2), and <i>c</i> = 9.512(1) Å.