About crystalline sodium hydroxogallates

Article abstract of DOI:10.1002/zaac.19976230925

Two crystalline sodium hydroxogallates 4,5Na₂O · Ga₂O₃ · 13,5 H₂O (I) and 5 Na₂O · Ga₂O3 · 8 H₂O (II), as well as a crystalline phase of the composition Na₂O · Ga₂O₃ · 4 H₂O · 2NaCl (III) are described. (I) crystallizes from sodium gallate solutions in a wide concentration field; 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 structure contains water of crystallization and further hydroxide ions. (I) has to be formulated as nonasodium bis(hexahydroxogallate) trihydroxide hexahydrate Na₉[Ga(OH)₆]₂(OH)₃ · 6H₂O; it is isotypic with the corresponding sodium hydroxoaluminate [2, 3]. 5 Na₂O · Ga₂O₃ · 8 H₂O (II) was obtained from (I) in presence of sodium hydroxide by dehydration over P₄O₁₀ in an inert atmosphere (N₂) at room temperature. (II) crystallizes tetragonally and is isotypic with Na₁₀[Al(OH)₆]₂(OH)₄ [4]. Accordingly it could be described as a decasodium bis(hexahydroxogallate) tetrahydroxide, Na₁₀[Ga(OH)₆]₂(OH)₄. Na₂O · Ga₂O₃ · 4H₂O · 2NaCl (III) was obtained by addition of sodium chloride to sodium gallate solutions. (III) crystallizes also tetragonally and is isotypic with (Na₂[Al(OH)₄]Cl [5]. Correspondingly, it has to be formulated as disodium tetrahydroxogallate chloride Na₂[Ga(OH)₄]Cl. The results of ⁷¹Ga and ²³Na MAS NMR investigations of the compounds (I) to (III) and their thermal behaviour are discussed.