Contribution of Neutron Diffraction to the Crystal Structure Determination of 1-Hydroxy-1-Phosphono-Pentyl-Phosphonic Acid Dimethyl Ammonium Salt

Abstract

The crystal structure of 1-hydroxy-1-phosphono-pentyl-phosphonic acid dimethylammonium salt has been determined by neutron diffraction measurements on single crystals at room temperature (triclinic, space group P-1, a=11.419(23) Å, b=10.447(18) Å, c=6.211(9) Å, α=92.041(2)°, β=95.870 (3)°, γ=110.408(2)°, V=689(2) Å 3). Refinements of the structure using 1195 observed structure factors converged to the final R=0.068. Results have put in evidence that acids of the hydroxybisphosphonic family can protonate volatile alkaline species like dimethylamine to give particularly stable crystals. The hydrogen bonds formed by the dimethylammonium cation link columns of hydroxybisphosphonate groups parallel to the [010] direction. The structure is built up by alternated hydrophobic/polar layers parallel to the (100) plane.