CRYSTAL-STRUCTURE OF L-HISTIDINIUM PHOSPHITE AND A STRUCTURE REINVESTIGATION OF THE MONOCLINIC FORM OF L-HISTIDINE

L-histidinium phosphite, [C6N3O2H10]+ . [HPO3H]- is monoclinic P2(1), with crystal data: a = 8.497(7), b = 11.999(10), c = 4.967(3) angstrom , beta = 104.15(6)-degrees, V = 491(1) angstrom3 and Z = 2. The crysta l structure was solved with a final R value of 0.030 for 1780 independ ent reflections. The organic and phosphoric entities build layers para llel to the (100) plane. The [HPO3H]- groups, not held together by H-b onds, are linked by O - H ... O and N - H - O bonds to the histidine g roups. The latter are laced together by N - H ... O bonds to form chai ns running parallel to b. In addition to this study, the atomic arrang ement of the monoclinic form Of L-histidine was reinvestigated, this t ime with an untwinned crystal. The space group is P2(1), with a = 5.16 6(6), b = 7.385(5), c = 9.465(4) angstrom, beta = 98.16(5)-degrees, V = 357.4(9) angstrom3 and Z = 2. The new refinement, based on 1182 inde pendent reflections, led to a final R value of 0.039. A description of the structure, including the H-bond scheme, is given. In addition to an improvement of the experimental accuracy, some H atoms, not found i n the first study were located. The main structure is in general agree ment with that from the previous investigation.