27Al NMR Study of Al-Speciation in Aqueous Alumina-Sols

A new method of preparing concentrated alumo-sols, the hydrolysis of Al-tri-sec-butylate in acidic aqueous media at 85°C, was studied in detail by varying the H₂O/Al- and NO₃ ⁻/Al-ratios in wide ranges. The components of the sols were characterized by ²⁷Al NMR spectroscopy. The pH-value depends on both the chosen H₂O/Al- and NO₃ ⁻/Al-ratio and on the aging time of the sols and reflects the composition of the sols. Al₁₃ polycations were detected in sols with a pH-value between 3.0 and 3.7. As a new result its presence was shown by NMR below 3.4. The Al₁₃ content of the sols increased with pH and the maximum fraction of Al₁₃ polycations was detected in the sol with the highest pH (3.7). Nearly 65% of the entire aluminium content of this solution is bound in the Al₁₃ polycations. Hence, a new synthetic method for the preparation of Al₁₃ ions containing sols was developed. Aging studies of the sols showed, that the Al₁₃ polycations were more stable in solutions with higher pH-value. Al₁₃ polycations were detected after an aging time of four months only in sols with a pH-value of 3.7. Tempering the aged sols at 40° to 80°C caused formation of Al₁₃ and also of Al₃₀ polycations.     

The aluminum ordering in aluminosilicates: a dipolar 27Al NMR spectroscopy study

The spatial ordering of aluminum atoms in CsAl(SiO3)2 and 3Al2O3.2SiO2 was probed by 27Al dipolar solid-state NMR spectroscopy. The 27Al response to a Hahn spin-echo pulse sequence in a series of aluminum-containing model crystalline compounds demonstrates that quantitative 27Al homonuclear dipolar second moments can be obtained to within +/-20% of the theoretical values, if evaluation of the spin-echo response curve is limited to short evolution periods (2t1 < or = 0.10 ms). Additionally, selective excitation of the central transition m = 1/2 --> -1/2 is necessary in order to ensure quantitative results. Restriction of spin exchange affecting the dephasing of the magnetization may decelerate the spin-echo decay at longer evolution periods. Considering these restraints, the method was used to probe the spatial distribution of aluminum atoms among the tetrahedral sites in two aluminosilicate materials. Experimental 27Al spin-echo response data for the aluminosilicates CsAl(SiO3)2 (synthetic pollucite) and 3Al2O3.2SiO2 (mullite) are compared with theoretical data based on (I) various degrees of aluminum-oxygen-aluminum bond formation among tetrahedrally coordinated aluminum atoms (Al(T(d) )-O-Al(T(d) )) and (II) the maximum avoidance of Al(T(d) )-O-Al(T(d) ) bonding. Analysis of the second moment values and resulting echo decay responses suggests that partial suppression of spin exchange among aluminum atoms in crystallographically distinct sites may contribute to the 27Al spin echo decay in 3Al2O3.2SiO2, thus complicating quantitative analysis of the data. Silicon-29 and aluminum-27 magic angle spinning (MAS) NMR spectra of 3Al2O3.2SiO2 are consistent with those previously reported. The experimental 27Al spin-echo response behavior of CsAl(SiO3)2 differs from the theoretical response behavior based on the maximum avoidance of Al-O-Al bonding between tetrahedral aluminum sites in CsAl(SiO3)2. A single unresolved resonance is observed in both the silicon-29 and aluminum-27 MAS spectra of CsAl(SiO3)2.     

Characterization of the malate-aluminum(III) complex using 1H and 27Al NMR spectroscopy

Structural elucidation of a malate-aluminum(III) complex has been carried out using 1H and 27Al NMR spectroscopy. The 1H chemical shift perturbation clearly indicated the interaction between malate and Al(III) ion. The measurements of 27Al NMR and 1H-13C HSQC spectra demonstrated that the major form of a complex comprised two equivalent malate ions and two unequivalent Al(III) ions. With this constraint, an equilibrium geometry of the complex was proposed by a semi-empirical molecular orbital calculation.     

New synthesis of mullite. Structural evolution study by 17O, 27Al and 29Si MAS NMR spectroscopy

Mullite has been prepared from a new combination of precursors. An aluminum alkoxide, aluminium isopropoxide, and silicon tetrachloride, are hydrolysed in tetrahydrofuran solution by ¹⁷O enriched water. The resulting powder is chemically homogeneous, crystallizing into mullite at 980°C. The structural evolution has been studied by DTA, TGA, XRD and ¹⁷O, ²⁷Al and ²⁹Si MAS NMR spectroscopy.     

1H NMR spectroscopic study of theert-butyl chloride—aluminum bromide cationic initiating system

The interaction oftert-butyl chloride with aluminum bromide in methylene dibromide at −30°C leads to the formation of two types of adducts, which give signals with δ 2.4 and 3.2 in the¹H NMR spectra in addition to that of free alkyl halide. these signals are attributed to a polarized complex (PC) and ion pair (IP), respectively. An excess of AlBr₃ shifts the equilibria toward IP. The latter contains more AlBr₃ than the polarized complex. Based on the spectral data, we calculated the limiting values of some equilibrium constants. The ability of AlBr₃ to solvate counterions is consistent with the results of isobutylene polymerization under the action of the initiating Bu^tCl−AlBr₃ system at different ratios of the starting concentrations [AlBr₃]₀/[Bu^tCl]₀. An increase in this ratio results in both the acceleration of polymerization and an increase in the relative role of chain transfer reactions. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2217–2222, November, 1998.     

Coordination Structure of Aluminum in Magnesium Aluminum Hydroxide Studied by ^27Al NMR

The coordination structure of aluminum in magnesium aluminum hydroxide was studied by ^27Al NMR.The result showed that tetrahedral aluminum (Al^IV) existed in magnesium aluminum hydroxide,and the contents of Al^TV increased with the increase of the ratio of Al/Mg and with the peptizing temperature.Al^IV originated from the so-called Al13 polymer with the structure of one Al tetrahedron surrounded by twelve Al octahedrons.     

Aluminum Solvate Complexes Forming in Acidic Methanol-Acetone Mixtures Studied by <Superscript>27</Superscript>Al NMR Spectroscopy

²⁷Al NMR spectroscopy is a powerful tool for the study of coordination and solvation in both aqueous and nonaqueous solutions. In this study, the complexes coexisting upon dissolution of AlCl₃ in acidic acetone + methanol solutions are shown to consist essentially of mixed hexacoordinated species of the general formula [Al(CH₃OH)_6−n (CH₃COCH₃) _n ]³⁺ (n=1,2 and 3), all exhibiting distinctly different ²⁷Al shielding effects. The relative populations of the various mixed species are found to be highly dependent upon the acetone:methanol mole ratio that in the more acetone-rich mixtures with aluminum become appreciably coordinated by acetone. The results demonstrate that the key factor for the formation of acetone-containing species in acidic methanolic solutions is having the CH₃COCH₃:CH₃OH mole ratio at 3:1.     

27Al NMR diffusometry of Al13 Keggin nanoclusters

Although nanometer-sized aluminum hydroxide clusters (i.e., ϵ-Al₁₃, [Al₁₃O₄(OH)₂₄(H₂O)₁₂]⁷⁺) command a central role in aluminum ion speciation and transformations between minerals, measurement of their translational diffusion is often limited to indirect methods. Here, ²⁷Al pulsed field gradient stimulated echo nuclear magnetic resonance (PFGSTE NMR) spectroscopy has been applied to the AlO₄ core of the ϵ-Al₁₃ cluster with complementary theoretical simulations of the diffusion coefficient and corresponding hydrodynamic radii from a boundary element-based calculation. The tetrahedral AlO₄ center of the ϵ-Al₁₃ cluster is symmetric and exhibits only weak quadrupolar coupling, which results in favorable T₁ and T₂ ²⁷Al NMR relaxation coefficients for ²⁷Al PFGSTE NMR studies. Stokes–Einstein relationship was used to relate the ²⁷Al diffusion coefficient of the ϵ-Al₁₃ cluster to the hydrodynamic radius for comparison with theoretical simulations, dynamic light scattering from literature, and previously published ¹H PFGSTE NMR studies of chelated Keggin clusters. This first-of-its-kind observation proves that ²⁷Al PFGSTE NMR diffusometry can probe symmetric Al environments in polynuclear clusters of greater molecular weight than previously considered.     

27Al核磁共振波谱法测定环境生物样品中铝研究进展

近二十年来,高分辨率²⁷Al核磁共振(²⁷Al NMR)广泛应用于研究Al(Ⅲ)离子水解过程,Al(Ⅲ)与环境生物配体的配位化学,环境与生物样品中铝含量测定和形态分析,监测铝在植物、动物、酵母菌等微生物中的转运过程,具有快速、直接、非破坏性等优点。²⁷Al NMR不仅适用于高浓度的溶液,也可应用于低浓度(10^-6mol·L^-1)的实际环境、生物样品。应用²⁷Al MASNMR可直接对固态样品中铝的存在状态和含量进行表征和测量。本文中对²⁷Al NMR的应用进展作一评述,并总结了近二十年来文献发表的²⁷Al化学位移数据。引用文献70余篇。     

硅铝酸钠溶液中27Al和29Si的核磁共振研究

本文采用原位核磁共振方法检测不同碱度硅铝酸钠溶液中²⁷Al的信号, 在比较了文献实验结果的基础上, 明确了体系中的不同铝物种的化学位移, 进一步提出了硅铝酸钠溶液中的硅铝物种的归属.     

NMR invisible" aluminum species in dealuminated mordenite zeolite:a ~1H/~(27)Al TRAPDOR NMR study

Ｈｉｇｈｃａｔａｌｙｔｉｃａｃｔｉｖｉｔｙｏｆｓｔｅａｍｅｄｆｏｒｍｓｏｆｍｏｒｄｅｎｉｔｅ,Ｙｚｅｏｌｉｔｅ,ａｎｄＺＳＭ5ｉｎｃａｔａｌｙｔｉｃｃｒａｃｋｉｎｇｉｓｍａｉｎｌｙａｔｔｒｉｂｕｔｅｄｔｏｔｈｅｉｒｐｏｓｓｅｓｓｉｎｇａｃｉｄｃａｔａｌｙｚｅｄａｃｔｉｖｉｔｙ[1].ＴｈｅｒｅａｒｅｍａｎｙＮＭＲｒｅｐｏｒｔｓｏｎｔｈｅｎａｔｕｒｅｏｆｄｅａｌｕｍｉｎａｔｅｄＹａｎｄＺＳＭ5ｚｅｏｌｉｔｅｓ.Ｈｏｗｅｖｅｒ,ｆｅｗａｒｅｋｎｏｗｎａｂｏｕｔａｌｕｍｉｎｕｍｓｐｅｃｉｅｓｉｎｄｅａｌｕｍｉｎ…     

Polymerization Reactions in an Al(OBus)3-(COOH)2 System

Reactions in an Al(OBu^s)₃-(COOH)₂ (OA)-tetrahydrofuran (THF)/(CD₃)₂SO (DMSO-d₆) system (Al(OBu^s)₃: THF : DMSO-d₆: OA = 1 : 5 : 5 : x, x = 0.01 –3) were studied, without the addition of water and the process was monitored by NMR. When x 0.3, homogeneous solutions were obtained, whereas white precipitates formed with x 0.7. The formation of sec-butyl alcohol was evident with x 0.6, indicating that oxalate groups coordinate to aluminum to release sec-butyl alcohol. ¹³C NMR spectra of the solutions after 1 day suggest the presence of polymeric species if 0.03 x 0.6. The addition of a small amount of water resulted in the formation of a white precipitate (Al(OBu^s)₃: THF : DMSO-d₆ : OA : H₂O = 1 : 5 : 5 : 0.3 : y,y = 0.03–0.3), indicating that water, possibly formed by esterification in the Al(OBu^s)₃-OA-THF/DMSO-d₆ system, does not take a major role in the present system.     

Solid-state Al NMR investigation of thermal decomposition of LiAlH4

Solid-state nuclear magnetic resonance is used to study the thermal decomposition of lithium tetrahydroaluminate into metallic aluminum, hydrogen and trilithium hexahydroaluminate. Aluminum sites in LiAlH₄ and Li₃AlH₆ were characterized using static, magic angle spinning (MAS) and multiple-quantum MAS NMR. By applying the in situ NMR method, it has been demonstrated that melting is not a prerequisite for the decomposition of LiAlH₄. Based on the observed data, a decomposition path has been established that is consistent with the concentrations of observed Al species at various stages of the thermally induced reaction.     

“NMR invisible” aluminum species in dealuminated mordenite zeolite: a1H/27 AI TRAPDOR NMR study

Various kinds of aluminum species in dealuminated mordenite were investigated in detail, and the quadrupole coupling constants (QCCs) for aluminum atoms associated with these species were obtained by means of the newly introduced¹H/²⁷ AI TRAPWR method as well as²⁷Al magic angle spinning (MAS) nuclear magnetic resonance (NMR). QCC values of 11.3, 15.3, 13.3 and (14.0± 0.6) MHz were determined from the TRAPDOR profiles for Lewis acid sites, Bronsted acid sites (SiOHAl) and two kinds of non-framework aluminum species Al(OH) _n , respectively. The source of the “invisible Al” is discussed on the basis of the NMR experimental results.     

利用27Al NMR研究茶多酚与铝形成配合物的形态

采用27Al NMR技术,研究了不同茶叶中茶多酚与铝形成配合物的形态。考察了在不同pH值和配体/金属(L/M)下铝的存在形态,系统地研究了焦性没食子酸、儿茶酚等官能团模拟化合物与铝的配位体系中铝的形态,探讨了配体取代基的个数与焦性没食子酸-铝配合物的δ27Al的关系,获得了非常有意义的规律,并确定了茶多酚与铝配合物的结构。     

Direct Observation of Various Al Sites in SAPO-34by ^27Al Multiquantum(MQ) Magic Angle Spinning (MAS)NMR

The elegant 2D multiquantum (MQ) MAS NMR has been applied to investigate the coordination of Al atoms in SAPO-34.The results show that the effects of the template and /or water on the coordination of Al atoms are significant,which lead to the formation of various Al species.Up to four kinds of Al species are distinctly resolved.     

The evidence for complex formation between N-acetyl-l-tyrosine methyl ester and N-acetylprocainamide hydrochloride using NMR spectroscopy

In order to reveal the possible mechanism of the recognition of antiarrhythmic agents class I and class III by the amino acid residues, which are responsible for drug binding to the selectivity filters either in the sodium or potassium ion channels, co-crystallizations of procainamide hydrochloride and N-acetylprocainamide hydrochloride with N-acetyl-l-tyrosine methyl ester and N-acetyl-l-phenylalanine methyl ester were performed using various conditions. Because the crystallization of the complexes failed, the intermolecular interactions between the components were evidenced using NMR spectroscopy. Exclusively, in the case of N-acetylprocainamide hydrochloride and N-acetyl-l-tyrosine methyl ester, two-dimensional NMR experiments and Job Plot analysis indicated the formation of the 1:1 complex in DMSO-d ₆  solution (with the association constant of 16 M⁻¹), whereas for the mixture of procainamide hydrochloride with N-acetyl-l-tyrosine methyl ester, the complex formation was not confirmed. The NMR results were discussed using crystal structure data obtained for N-acetylprocainamide hydrochloride, procainamide hydrochloride, as well as procainamide dihydrochloride, and were compared with the known pharmacological activity of the antiarrhythmic agents.     

Synthesis,structure, and 77Se NMR study of the (PPh4)2[Re6Se6Br8] complex

The octahedral cluster anion [Re₆Se₆Br₈]^2– was prepared by high-temperature synthesis from elementary substances in the presence of KBr. This cluster anion was isolated and structurally characterized by single-crystal X-ray diffraction analysis as the (PPh₄)₂[Re₆Se₆Br₈] complex (1). Refluxing of polymeric rhenium selenide bromide Re₆Se₆Br₆ in DMF in the presence of Bu₄NBr led to the cleavage of the Re—Br—Re bridges to form the complex (Bu₄N)₂[Re₆Se₆Br₈]. Comparative analysis of the interatomic distances in the octahedral rhenium(iii) selenide bromide clusters was carried out.     

Study of ion exchange selectivity of organic ions by using (31)P NMR spectroscopy

Ion exchange distribution of the phenylphosphoric acid has been studied on various types of chloride form strong base resins as a function of pH at 25 °C, at 0.1 M ionic strength. Equilibrium measurements were supplemented by the study of pH dependence of the ³¹P NMR spectra of the resin-phase phenylphosphate species. Equations were derived to describe the pH dependence of the overall distribution coefficient and the chemical shift of the resin-phase solute species. Experimental data were evaluated by using these model equations and the values of the individual distribution coefficients, ion exchange selectivity coefficients and the resin-phase ³¹P chemical shifts of the mono- and divalent ions have been calculated. Comparison of distribution data of the individual species corroborated the significance of the role of hydrophobic interaction in the selectivity of organic ion exchange processes. A well-defined correlation between the ion exchange selectivity and the resin-phase ³¹P NMR chemical shift data has been pointed out.