ABOUT CRYSTALLINE-SODIUM HYDROXOGALLATES

Two crystalline sodium hydroxogallates 4,5 Na2O . Ga2O3 . 13,5 H2O (I) and 5 Na2O . Ga2O3 . 8H(2)O (II), as well as a crystalline phase of t he composition Na2O . Ga2O3 . 4H(2)O . 2 NaCl (III) are described. (I) crystallizes from sodium gallate solutions in a wide concentration fi eld; from the X-ray single crystal diffraction analysis [1] results a three dimensional network structure, consisting of monomeric [Ga(OH)(6 )](3-) anions connected by NaO6 octahedra groups. Furthermore the stru cture contains water of crystallization and further hydroxide ions. (I ) has to be formulated as nonasodium bis(hexahydroxogallate) trihydrox ide hexahydrate Na-9[Ga(OH)(6)](2)(OH)(3) . 6H(2)O; it is isotypic wit h the corresponding sodium hydroxoaluminate [2, 3]. 5 Na2O . Ga(2)O3 . 8H(2)O (II) was obtained from (I) in presence of sodium hydroxide by dehydration over P4O10 in an inert atmosphere (N-2) at room temperatur e. (II) crystallizes tetragonally and is isotypic with Na-10[Al(OH)(6) ](2)(OH)(4) [4]. Accordingly it could be described as a decasodium bis (hexahydroxogallate) tetrahydroxide, Na-10[Ga(OH)(6)](2)(OH)(4). Na2O . Ga2O3 . 4H(2)O . 2NaCl (mi) was obtained by addition of sodium chlor ide to sodium gallate solutions. (III) crystallizes also tetragonally and is isotypic with (Na-2[Al(OH)(4)]Cl [5]. Correspondingly, it has t o be formulated as disodium tetrahydroxogallate chloride Na-2[Ga(OH)(4 )]Cl. The results of Ga-71 and Na-23 MAS NMR investigations of the com pounds (I) to (III) and their thermal behaviour are discussed.