Crystal and molecular structure of potassium, ammonium and dicyclohexylammonium salts of (2-oxopropyl)phosphonic acid in monoionized state

The crystal and molecular structures of potassium (I), ammonium (II) and di cyclohexylammonium (III) (2-oxopropyl) phosphonates were determined by X-ra y methods. For all three compounds the monoionized anion has a similar conf ormation, with the phosphonate group projected out of the ketone backbone. The crystals of I and II contain two symmetry-independent anions and cation s in the asymmetric unit, the anions are arranged in tetramers by strong hy drogen bonds. In the crystals of III the anions are arranged in hydrogen-bo nded dimers. The anions differ mostly in the orientation of the hydroxyl gr oup, being + gauche for Ia, nb and III, nearly antiperiplanar for Ib, and - gauche for IIa; with regard to the C(CO) atom. In all cases the hydrogen b onds between phosphonate groups are strong. The hydrogen bonds between anio ns and ammonium and dicyclohexylammonium cations display normal strength. I n all crystals the carbonyl O atom is an acceptor of hydrogen from the meth yl or methylene group. The K-cations in I are hexacoordinated and four of t hem are arranged in a cubane-like structure connected through four phosphon ate O atoms. (C) 1998 Elsevier Science B.V. All rights reserved.