Phase Diagram Measuring Of AlCl₃-H₂O-Al（OH）₃ At 120℃ And Structure Solving Of [（OH）₂（H₂O）_0.5]₂-Al₃₀

The hydrolysis morphology study of aluminum salts is vital important for many fields of science.One of the most effective way for speculating the hydrolysis route of aluminum salt is to obtain more pure polyaluminum compounds and solve their crystal structures.The hydrolysis of aluminum in aqueous solutions is extremely complex.Due to the influences of many factors,it is difficult to isolate pure polyaluminum compounds or capture the preponderant polyaluminum species from a hydrolyzed Al solution,and the more difficult thing is to grow several single crystals large enough for structure analysis.Up to now,only 20（or more）exact Al species structures were obtained based on the crystal diffraction method.To find an effective control method,so that every Al species can be crystallized as a pure compound isolated from the hydrolyzed solution in turn,after several years of exploring and innovating,a control theory,that was regarded as the most effective method by ourselves,was found by our group,that is the solid-liquid equilibrium phase diagram.Under the direction of the phase diagram,as long as the chemical composition of the hydrolyzed Al solution was controlled to an area that is near by the single phase crystalline region of a target polyaluminum compound,pure crystals even single crystals of the target compound can be isolated by a slow evaporation,of course,if a proper catcher was added into the solution,the polyaluminum species can also be captured and then crystallized from the solution.Therefore,in this paper,a solid-liquid equilibrium diagram of AlCl₃-H₂O-Al（OH）₃ ternary system at 120℃ was successfully drawn by using the wet slag method.It is clear that only three solid phases were included in the phase diagram at this temperature only Except for the starting material,AlCl₃·6H₂O,and the final product,Al（OH）₃,only Al₅（OH）₁₂Cl₃·7H₂O exists and covers a wide crystalline region,So it is esay to obtain..In order to improve the solubility of polyaluminum compound,our group also study the Al species and their structures got from a spontaneously hydrolyzed solution of Al₁₃.In this paper,a polyaluminum stock solution was first prepared basing on the phase diagram,and after 2,6-naphthalene disulfonate（NDS）was added,a novel polyaluminum compound was obtained,and the result of structural analysis shows that the structural formula is[Al₃₀O₈（OH）₅₆（H₂O）₂₂（OH）₄（H₂O）][NDS]₇·2N₂·49H₂O(expressed as[（OH）₂（H₂O）_0.5]₂-Al₃₀).The structure of the polycation can be regarded as the result after two pair of H₂O molecules coordinated for the two pair of neighbor Al nuclei（in which their local basification degrees are the most unbalanced on the symmetry）in the two sides of the Al₃₀ were replaced by two semi-hydrated di-hydroxyls(OH^--（H₂O）_0.5-OH^-),it is firstly discovered that water molecule was associated on Al30,and the positions where the two quarter-water molecules associated to are the same positions where the two quarter-aluminum nuclei,the two semi-aluminum nuclei and the two aluminum nuclei combined to in Al_30.5,Al₃₁ and Al₃₂,respectively.It is expected that[（OH）₂（H₂O）_0.5]₂-Al₃₀ should be the most adjacent derivative of Al30 in the evolution process of Al₃₀→Al_30.5→Al₃₁→Al₃₂.The discovery of this novel construction manner not only proves that the local basification degree symmetrical equalization（LBDSE）principle can correctly predict the active sites in further hydrolyzing once again,but also enriches the construction manners of polyaluminum species,and provides a new evidence for the further improvement of the polymerization model and theory of polyaluminum species.