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

Abstract

The crystal and molecular structures of potassium ( I), ammonium ( II) and dicyclohexylammonium ( III) (2-oxopropyl) phosphonates were determined by X-ray methods. For all three compounds the monoionized anion has a similar conformation, with the phosphonate group projected out of the ketone backbone. The crystals of I and II contain two symmetry-independent anions and cations in the asymmetric unit, the anions are arranged in tetramers by strong hydrogen bonds. In the crystals of III the anions are arranged in hydrogen-bonded dimers. The anions differ mostly in the orientation of the hydroxyl group, being + gauche for Ia, IIb and III, nearly antiperiplanar for Ib, and — gauche for IIa, with regard to the C(CO) atom. In all cases the hydrogen bonds between phosphonate groups are strong. The hydrogen bonds between anions and ammonium and dicyclohexylammonium cations display normal strength. In all crystals the carbonyl O atom is an acceptor of hydrogen from the methyl or methylene group. The K-cations in I are hexaccordinated and four of them are arranged in a cubane-like structure connected through four phosphonate O atoms.