La struttura cristallina della kernite, Na2B4O6(OH)2·3 H2O

Cialdi, Gloria ; Corazza, Egizio ; Sabelli, Cesare

Atti della Accademia nazionale dei Lincei. Rendiconti della Classe di scienze fisiche, matematiche e naturali, Série 8, Tome 42 (1967) no. 2, pp. 236-251

Résumé

The crystal structure of kernite, Na2B4O6(OH)2·3 H2O has been determined by means of x-ray diffraction, using the Weissenberg equiinclination technique. The structure was solved from direct methods, giving the signs to 25% of the observed structure factors, and from a three-dimensional Fourier synthesis. Least squares refinement with 951 independent reflections yielded a reliability index of 0.083, based on the observed reflections only. The approximate positions of the hydrogen atoms could be deduced from stereochemical considerations. The monoclinic cell has dimensions, a = 7.022, b = 9.151, c = 15.676 Å; ß = 108.8°. The space group is P 21/c. For a cell containing four units of Na2B4O6(OH)2·3 H2O, the calculated density is 1.904 g·cm-3. The atoms within the square brackets are interconnected along the y axis so as to form an infinite chain complex [B4O6(OH)2]n-2n. Both sodium atoms coordinate five oxygens according to a distorted trigonal bipyramid. The Na(1) and Na(2) coordination polyhedra are connected by a corner, and Na(1) shares an edge with its centro-symmetrical one, to form a four-membered group. The boron-oxygen chains, two per cell, are linked three-dimensionally by the Na polyhedra groups and by hydrogen bonds.