| Morphological chemistry of Aluminum salt hydrolyzates has played a very important role in many academic fields such as geochemistry,soil chemistry and environmental chemistry,but due to the complexity of the aluminum salt hydrolysis process and the distribution of various polyaluminum species in solution,making it difficult to isolate pure polyaluminum compounds and it is more difficult to grow a single crystal large enough for structural analysis,which leads to a serious shortage of polyaluminum species structures,therefore,an unified understanding for the formation and evolution process of aqueous aluminum species has still not been reached.To prepare more polyaluminum compounds and to obtain more structural information of polyaluminum species,after several years of exploration,our group formed a distinctive research idea,that is,phase diagram control combined with Al species capture to prepare polyaluminum compounds,single crystal diffraction combined with powder diffraction to solve crystal structures,and structural information induction combined with theoretical model deduction to speculate evolution mechanisms.The successful synthesis of more than 30 kinds of polyaluminum compounds,the crystal structure analyses of more than 10 polyaluminum species,the extraction of two evolution mechanisms of polyaluminum species,and the discovery of the local basification degree symmetrical equalization(LBDSE)principle,have proved the correctness and validity of this research idea.In this paper,AICl3 solution was forcedly hydrolyzed by NaOH solution and experienced a thermal aging,then Na2S04 solution was added to capture the dominant polyaluminum species,after a slow evaporating and crystallizing at room temperature,two kinds of single crystal with different crystal forms(tetrahedron and rectangular plate)were found in the same beaker.The crystal structure analysis results show that the composition and structure of the two crystals are completely different.The stoichiometric formula of the former is Na2O·13Al2O3·8SO3·76H2O,its structure belongs to the cubic F43m space group,a = 17.838A,V = 5675.9A3,is similar to the result reported by Johansson in 1960,but the existing form of the polyaluminum cation[Al04Al12(OH)24(H20)12]7+(?-K-Al13)is not a separated finite structure as reported,it is characterized by the fact that each ?-K—Al13 is connected to four symmetrically split Na(H20)4+ units and each Na(H2O)4+ tetrohedron is connected to four ?-K—Al13,so the exact structure is that the Na(H20)4+unit and the e-K—Al13 species connected each other in a ratio of 1:1 and formed a basic repeat unit of[Na(H2O)4AlO4Al12(OH)24(H20)12]8+(Na-?-K-Al13),then developed continuously and finally form a three-dimensional infinite frame structure.Therefore,compound Na2O13A12O3·8S03·76H20 with a structural formula of[na(H2O)4Al13O4(OH)24(H2O)12][SO4]4·10H2O is not the earliest source of?-K—Al13.This discovery of the infinite structure of Nar-?-K—Al13 also provides a direct evidence for the formation mechanism of finite Na-?-K—Al13 species.In this paper,the absolute structures mirrored each other of compound[Na(H2O)4Al3O4(OH)24(H2O)12][SO4]4·10H20 was obtained by using the Cs2S04 solution to capture the dominant polyaluminum species form NaOH solution forcedly hydrolyzed AlC13 solution.The.stoichiometric formula for the latter is 13Al2O3·6S03·79H20,its structure belongs to monoclinic system,a = 14.023A,b =11.480 A,c = 20.166 A,? = 120.917°,V= 2785.3A3,is similar to the result reported by Johansson in 1963,but it was found that the polyaluminum cations are still normal[AlO4Al12(OH)24(H2O)12]7+(s-K-A113)rather than[Al04Al12(OH)25(H2O)11]6+ as he reported,The 25th hydroxyl is actually associated with a SO42-anion that was split in half due to closing to a symmetrical center,formed a[(HOSO4)0.5-(SO40H)0.5]3-structure to balance the charge.And the space group is P2/c instead of the reported Pn.Thereby,compound 13Al2O3·6S03·79H20 with a structural formula of[AlO4Al12(OH)24(H2O)12][HOSO4][SO4]2·15H2O is really the original source of the finite ?-K—Al13.Correctly understand the existence and coordination relationship of Al13 species in the two polyaluminum compounds,is undoubtedly important for removing the misunderstanding and updating the results of various application studies based on the incorrect structures in the past half of century.In the process of drawing the phase diagram of AlI3-H2O-Al2O3 system at 25?,AlI3 solution was spontaneously hydrolyzed by adding aluminum powder,a sheet-like single crystal is grown under low basification condition.Structural analysis results show that the stoichiometric formula is A1I3·9H20,the structural formula is Al(H2o)6I3·3H20,the cationic structure is similar to the results in Al(H20)6C13 and Al(H20)6Br3,which are separated[Al(H2O)6]3+ octahedron,the difference is that each Al(H2O)6I3·3 H2O molecule has three interstitial water than its homologues,indicating that when the anion radius increases to a certain extent require solvent molecules to be filled into the larger voids formed between[Al(H20)6]3+ and I-ions.The powder XRD analysis showed that the compound is a new phase that is not present in the PDF powder diffraction database and the ICSD inorganic crystal structure database,the species of hydrated aluminum halide and the powder diffraction and single crystal structure databases can be enriched.By using the experience of our group,the single-phase crystallization regions of Al(PH)2Br·2H20 and Al5(OH)12Br3·6H20 as well as the co-saturation point between them were determined by wet slag method,a ternary system solid-liquid equilibrium phase diagram of AlBr3-H2O-Al2O3 system at 75? is basically completed,the pure crystallization of the two polyaluminum compounds can be prepared at this temperature by controlling the evaporation crystallization route. |
PDF Full Text Request