Crystal Structures Of （H₂O）₃-Al₃₀-NDS And P-Al₁₃-I And The Phase Diagram Of AlCl₃·6H₂O-H₂o-Al（OH）₃ System At 75℃

The solution chemistry of Al,especially the structural chemistry of hydrolyzed species of aluminum salts,is significantly important for many academic fields such as geochemistry,biochemistry,environmental science,etc.So as more as possibly synthesizing different kinds of polyaluminum compounds and solving their structures is the most direct and effective method to study the hydrolyzation and polymerization mechanism of aluminum salts and the formation and transformation law of polyaluminum species.However,since the hydrolysis reaction process is actually quite complex,only 20 or more structures of polyaluminum species have been unambiguously identified so far.In order to obtain more structural information about polyaluminum compounds,our group has formed a systematic research method,that is,solely isolating each crystalline phase by phase diagram controlling combined with capturing the dominant polyaluminium species by adding crystallization reagents to prepare the polyaluminum compounds,single crystal diffraction method combined with powder diffraction technique to solve the crystal structures,and structural information induction combined with theoretical model deduction to speculate the evolution mechanisms of polyaluminum species.In this paper,a suitable phase point for feeding was selected according to the phase diagram of AlI₃-H₂O-Al₂O₃ system at 25℃ to conduct a spontaneous hydrolysis reaction,after the reaction was completed,two crystallization methods were adopted,one is adding the capturing reagents of 2,6-naphthalenedisulfonic acid disodium salt（NDS）to the hydrolyzed solution then keeping slowly evaporation,the other is slowly evaporating the hydrolyzed solution directly without adding any reagents,by this way,two new polyaluminum compounds with completely different compositions and structures were obtained.The structural analysis results of single-crystal X-ray diffraction show that the structural formulas of them are{Al₃₀O₈（OH）₅₆（H₂O）₂₂[HO（H₂O）_1.5OH]₂}[NDS]₇·31H₂O(（H₂O）₃-Al₃₀-NDS)and[Al₁₃（OH）₂₄（H₂O）₂₄]I₁₅·24H₂O(P-Al₁₃-I),respectively.Both of them belong to triclinic system and P^—1^—space group.The structure of aluminum polycation in the former can be regarded as a result that the reported Al₃₀ are linked by a couple of[HO（H₂O）_1.5OH]^2-groups with replacement of four unsharedm₁-H₂O molecules located on the two pair of edge-shared AlO₆ octahedra that show the most unequalized local basification degree in the two sides of its middle.And that the four linked positions on Al₃₀ exactly are the same where two aluminum nuclei with 1/4,1/2,and 1 occupancy are combined on Al_30.5,S-Al₃₁ and S-Al₃₂reported by our group,respectively,and are also the most active sites in further hydrolyzing of Al₃₀ as predicted by the local basification degree symmetrical equalization principle summed up by our group.The discovery of the novel（H₂O）₃-Al₃₀-NDS species not only explained the diversity of hydrolyzing modes and the flexibility of bonding manners in Al₃₀ species series but also verified the accuracy of the active sites in further hydrolyzing predicted by the local basification degree symmetrical equalization principle once more.The structure of aluminum polycation[Al₁₃（OH）₂₄（H₂O）₂₄]¹⁵⁺in the latter is similar to those appearing in Al₁₃ chloride and nitrate reported by literatures and in Al₁₃ bromide synthesized by our group,an AlO₆octahedral core is surrounded by a“hexameric ring”that are composed by sixedge-shared AlO₆octahedraformed a“seven Alplank”through a edge-sharing manner,and then another six octahedral AlO₆ units are suspended onto the perihery of the hexameric ring upper and lower alternately by sharing two neighboring corners forming a“Plank-suspengding”structure(P-Al₁₃),the six suspended AlO₆ octahedra have an average inward turn angle of 26.0°in this iodide.It was found that as the size of anions increases,the turn angle of the suspended octahedra becomes bigger when comparing with those in P-Al₁₃ chloride（21.1°）,bromide（21.4°）,iodide（26.0°）,and nitrate（26.2°）,which indicates that the spatial orientation of the suspended octahedra in P-Al₁₃ structure can be adjusted“flexibly”by changing the turn angle according to the size of the counter ion.Also,the discovery of P-Al₁₃ iodide proves the universality of existing this kind of“Plank-suspending”Al₁₃ again.And two new structures were added to the crystallographic database.In addition,the phase diagram of AlCl₃·6H₂O-H₂O-Al（OH）₃ system at 75℃ has been completed with a combination of wet slag method and synthesis system method.In this paper,the previous static evaporation was changed as dynamic evaporation with continuously stirring and the solid-liquid equilibrium time was extended,moreover,whether a solid-liquid equilibriumis really reached,it was judged by a criterion that the composition of liquid is no longer changed with time.As a result,the problem of insufficient solid-liquid equilibrium existed in drawing phase diagrams in the past was solved.A large number of experimental data have confirmed that the phase diagram determined in this paper is more accurate and reasonable,and it provides a more reliable basis for designing the synthesis routes and preparing Al₉Cl₆（OH）₂₁·18H₂O and Al₅Cl₃（OH）₁₂·7H₂O in a single-phase isolation manner at this temperature.