Le nitrate double NaRb 2 (NO 3 ) 3 , composé intermédiaire du système binaire isobare NaNO 3 + RbNO 3 : études thermiques et cristallographiques

• Published in: Acta crystallographica. Section E, Crystallographic communications Crystallographic communications, 2015-05, Vol.71 (5), p.455-458
• Main Authors: Ksiksi, Nesrine, Driss, Mohamed, Hellali, Dalila, Guesmi, Abderrahmen, Zamali, Hmida
• Format: Article
• Language: English
• ISSN: 2056-9890; 2056-9890
• DOI: 10.1107/S2056989015006532

Crystallographic and thermodynamic investigations of the binary (NaNO 3 + RbNO 3 ) phase diagram at atmospheric pressure reveal the existence of an intermediate compound NaRb 2 (NO 3 ) 3 (sodium dirubidium trinitrate) previously predicted and now reported experimentally for the first time. According to a DSC analysis, the compound exhibits three allotropic forms. In its low-temperature allotropic form (α form, orthorhombic) there are two Rb ( m .. site symmetry) and one Na ( m ..) independent crystallographic positions and three planar nitrate groups. The bond-valence-sum calculations for all atoms agree well with their oxidation states. The Rb cations are located in the (100) plane at x = ½ with 11 oxygen coordination. The Na ones are in the same plane at x = 0 and are coordinated to eight O atoms from six nitrate groups. The charge-distribution method has been used to evaluate the degree of distortion of the alkali polyhedra.