title: A new crystalline phase of nitric acid dihydrate.
abstract: The crystal structure of a new high-temperature phase of nitric acid dihydrate, HNO(3).2H(2)O, has been determined at 225 K by single-crystal X-ray diffraction. The H atom of the nitric acid is delocalized to one water molecule, leading to an association of equimolar NO(3)(-) and H(5)O(2)(+) ionic groups. The asymmetric unit contains two molecules of HNO(3).2H(2)O. The two independent molecules are related by a pseudo-twofold c axis, by a translation of 0.54 (approximately (1/2)) along b, with a mean atomic distance difference of 0.3 A, except for one H atom of the water molecules (1.5 A), because of their different orientations in the two molecules. The two independent molecules, linked by strong hydrogen bonds, are arranged in layers. These layers are linked by weaker hydrogen bonds oriented approximately along the c axis. A three-dimensional hydrogen-bond network is observed.
authors.affiliation: Laboratoire de Dynamique et Structure des Matériaux Moléculaires (ESA 8024), UFR de Physique, Bâtiment P5, 59655 Villeneuve d'Ascq Cedex, France. nathalie.lebrun@univ-lille1.fr
authors.forename: N
authors.initials: N
authors.lastname: Lebrun
authors.forename: F
authors.initials: F
authors.lastname: Mahe
authors.forename: J
authors.initials: J
authors.lastname: Lamiot
authors.forename: M
authors.initials: M
authors.lastname: Foulon
authors.forename: J C
authors.initials: JC
authors.lastname: Petit