Synthesis and X-ray crystal structures of the new, three-dimensional ethylenediphosphonates [A{HO<inf>3</inf>P(CH<inf>2</inf>)<inf>2</inf>PO <inf>3</inf>H<inf>2</inf>}] (A = alkali metal, Tl, or NH<inf>4</inf>): Solid Brönsted acids that exhibit topotactic intercalation and deintercalation of ammonia

Seven new ethylenediphosphonates with the formula [A{HO 3P(CH2)2PO3H2}] [A = Li (1), Na (2), K (3), Rb (4), Cs (5), Tl (6), and NH4 (7)], have been synthesized and characterized by single-crystal X-ray diffraction, infrared spectroscopy, and thermal studies. They have four types of three-dimensional structures, with variations in the coordination of the A+ ions. All of them are solid Brönsted acids that undergo room-temperature, acid-base intercalation reactions with ammonia. © Wiley-VCH Verlag GmbH & Co. KGaA, 2006.