Infrared and MAS NMR Spectroscopic Studies of Al18B4O33

IntroductionAllsB.O,, is a refractory compound with the melting point of 1 713 K. It has a low density of 2. 94 g/cm' and tends to form a needle--shaped crystal. These characteristics lead to itspotential application in reinforced plastics or metal alloys['j. The investigationL'] in the crystalstructure Of Al,SB,O,, by X-ray study has reve.aled that the material has a 10Al,O,. BZO3type structure. This structure contains AIO.--tetrahedra, AIO,-octahedra, five-oxygen-coordinated Al ato…     

用固体核磁共振研究Al/P>1的磷酸铝分子筛AlPO4-5

用固体高分辩核磁共振（ＮＭＲ）方法对一系列Ａｌ／Ｐ＞１的新型磷酸铝分子筛ＡｌＰＯ４－５中磷和铝的结构状态及联结方式进行了研究，＾２７Ａｌ和＾３１Ｐ ＮＭＲ都给出了在分子筛骨架中存在有Ａｌ－Ｏ－Ａｌ联结方式的实验证据，寓示着在该体系中Ｐ和Ａｌ的排布不再遵循Ｌｏｅｗｅｎｓｔｅｉｎ规则。     

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.     

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.     

^29Si（^27Al）MAS NMR考察镧离子在LaDAlY型沸石中的作用

用~(29)Si(~(27)Al)MAS NMR和辅加乙酰丙酮(acac)处理样品的静态~(27)Al NMR研究了镧离子对脱铝Y型沸石(DAIY)骨架硅、铝和非骨架铝(EFAL)的影响.结果表明,~(29)Si MAS谱的化学位移及其形状不仅取决于连接[SiO_4]四面体的[AlO]-四面体数目,而且还与引入镧离子的量有关.镧离子的引入导致~(27)Al MAS谱的明显宽化和不对称形变.另外,还讨论了镧离子对非骨架铝的影响.     

Studies on Natural CXN Zeolite： Modification, Framework De-alumination and Ion-exchange

A natural CXN zeolite (stilbite, type code-STI) discovered in China was modified with NH4^ exchange by using ammonium salt and calcinations (procedure Ⅰ), or with NH4 exchange followed by treatment with acid (procedure Ⅱ). The coordination state of Si and A1 atoms in the framework, the property of ion exchange, and the adsorption of the H-STI zeolite samples prepared by different modification procedure were investigated with XRD,EDX,^29Si and ^27Al MAS NMR, Ag^ ion exchange and Ne adsorption. The results of the investigations indicate that different procedure of the modification made variety on the distribution of the framework Si atoms and A1 atoms,the content of non-framework aluminum, and the blocking channels and the shielding effect to the positions of the exchangeable cations. The H-STI zeolite prepared by the procedure Ⅱ possesses high ion exchange capacity, open and perfect pore system, and high thermal stability.     

Si-VPI-5分子筛的多核固体NMR研究

磷酸铝类分子筛是近年来继Y型和ZSM七分子筛之后的第三代合成分子筛材料，其骨架由A10。和P0。四面体均匀交替地组成问．由于带负电行的A10。和带正电荷的PO。四面体数目相等，整个骨架呈电中性，所以这类分子筛本身无离子交换能力和催化活性．当用硅或某些金属离子（如Mg、Fe、Co、Zn等）对磷酸铝分子筛进行同晶取代，就会在骨架上造成电行不平衡，从而使这类分子筛具有一定的离子交换能力和酸性【习．因而对硅或金属离子在磷酸错类分子筛中取代机理的研究一直是人们感兴趣的问题问．Vpl－5是最近才合成出来的具有18圆环一维孔结构的…     

Methane dehydrogenation and aromatization in the absence of oxygen on Mo/HZSM-5: A study on the interaction between Mo species and HZSM-5 by using Al and Si MAS NMR

By using a high-resolution solid state nuclear magnetic resonance spectrometer with ²⁷Al and ²⁹Si probes, the interaction between Mo species and HZSM-5 of frsol|Mo/HZSM-5 catalysts has been studied. The results show that there is a strong interaction between Mo species and HZSM-5 zeolite. The framework aluminum in the zeolite can be easily extracted by the introduction of Mo species. The extractability of framework aluminum by Mo species increases with increasing Mo loading and the calcination temperature. The extraction process leads to the formation of non-framework Al at first and then a new crystalline phase of Al₂(MoO₄)₃. The dealumination of the catalyst having a Mo loading of 15% and had been calcined at 973 K is so severe that all the aluminum in the framework are extracted and no framework Al could be detected by ²⁷Al MAS NMR. The catalyst, therefore, lost its catalytic activity for methane dehydrogenation and aromatization in the absence of oxygen. The Si/Al ratio measured from ²⁹Si MAS NMR further confirms the dealumination process observed by ²⁷Al MAS NMR. The MAS NMR results give us an evidence that Al₂(MoO₄)₃ crystallites are much less active for the reaction.     

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.     

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.     

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。     

铝在MCM-22分子筛骨架上分布的27Al MQ MAS NMR研究

利用二维多量子魔角旋转（2D MQ MAS）技术并结合量子化学计算，研究了铝在MCM-22分子筛骨架上的分布，并对铝的不等价四面体位进行了归属.在27Al 2D 5Q MAS NMR谱中骨架四配位铝的范围内观察到3个信号，证明MCM-22分子筛有3种骨架铝.经计算这3种骨架四配位铝的各向同性化学位移和四极作用常数分别为：δ 50.5、δ 57.3、δ 62.4和1.74、1.68、1.92 MHz. MCM-22分子筛结构中有8种结晶学不等价四面体（T）位.我们通过模拟MCM-22分子筛的27Al 2D 5Q MAS NMR谱，认为8种不等价T位分为3组. T2、T6位上的铝分别与δ 61、δ 49处的信号相关， T1、T3、T4、T5、T7、T8位上的铝对δ 56处的共振峰有贡献.当硅铝原子数比(Si/Al)在10～15之间变化时，铝在MCM-22分子筛的骨架上是无规占据的.     

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.     

Nonanatrium-bis(hexahydroxoaluminat)-trihydroxid-hexahydrat (Na9[Al(OH)6]2(OH)3 · 6H2O) – Kristallstruktur,NMR-Spektroskopie und thermisches Verhalten

Nonasodium Bis(hexahydroxoaluminate) Trihydroxide Hexahydrate (Na₉[Al(OH)₆]₂(OH)₃ · 6H₂O) – Crystal Structure, NMR Spectroscopy and Thermal Behaviour The crystal structure of the nonasodium bis(hexahydroxoaluminate) trihydroxide hexahydrate Na₉[Al(OH)₆]₂(OH)₃ · 6H₂O (4.5 Na₂O Al₂O₃ · 13.5 H₂O) (up to now described as 3 Na₂O · Al₂O₃ · 6H₂O, 4Na₂O · Al₂O₃ · 13 H₂O and [3 Na₂O · Al₂O₃ · 6H₂O] [xNaOH · yH₂O], respectively) was solved. The X-ray single crystal diffraction analysis (triclinic, space group P1 , a = 8.694(1) Å, b = 11.344(2) Å, c = 11.636(3) Å, α = 74.29(2)°, β = 87.43(2)°, γ = 70.66(2)°, Z = 2) results in a structure, consisting of monomeric [Al(OH)₆]^3? aluminate anions, which are connected by NaO₆ octahedra groups. Furthermore the structure contains both, two hydroxide anions only surrounded by water of crystallization and OH groups of [Al(OH)₆]^3? aluminate anions and a hydroxide anion involved in three NaO₆ coordination octahedra directly and moreover connected with a water molecule by hydrogen bonding. The results of ²⁷Al and ²³Na-MAS-NMR investigations, the thermal behaviour of the compound and possible relations between the crystal structure and the conditions of coordination in the corresponding sodium aluminate solution are discussed as well.     

低熔点晶体叠氮二乙基铝的合成和证明

叠氮二乙基铝（DEAA)是叠氮有机铝化合物中比较重要的一个化合物,但对DEAA的合成报道很少,还没有分离出纯的DEAA的报道。对它的研究有着重要的理论意义和应用价值。DEAA用作叠氮化试剂可用于多种叠氮化反应^[1-3];作为MOCVD前体物,由DEAA可制得性能优良的纳米级AIN材料,如AIN微晶薄膜^[4-6]和AIN粉末材料;DEAA是高含能材料,在国防和空间技术领域有着潜在的应用前景。文献报道的DEAA的合成方法按原料可分为三种^[7-10],其中以叠氮化钠和氯化二乙基铝（DEAC）为原料的合成方法应用较广,得到的DEAA为无色透明液体,熔点为－130℃^[11]。但笔者曾和到过固体DEAA^[12]。因此,本文将主要就DEAA的形态问题展开研究。     

Precursor structure and hydrolysis-gelation process of Al(O-sec-Bu)3 modified with ethylacetoacetate

The precursor structure and hydrolysis-gelation process of aluminum-sec-butoxide, Al(O-sec-Bu)₃, modified with ethylacetoacetate (EAcAc) were investigated using IR, UV and high magnetic field (11.7 T) ²⁷Al NMR spectra. ²⁷Al NMR showed that the reaction of EAcAc with Al(O-sec-Bu)₃ led to the formation of six-coordinated structural units and most of the precursors were assumed to be present as linear trimer containing a four- and two six-coordinated Al atoms. It was found that EAcAc formed the strong chelating bonds with Al(O-sec-Bu)₃, which were hardly hydrolyzed by the attack of water molecules in the gelation process.     

Factor analysis of 27Al MAS NMR spectra for identifying nanocrystalline phases in amorphous geopolymers

Nanostructured materials offer enhanced physicochemical properties because of the large interfacial area. Typically, geopolymers with specifically synthesized nanosized zeolites are a promising material for the sorption of pollutants. The structural characterization of these aluminosilicates, however, continues to be a challenge. To circumvent complications resulting from the amorphous character of the aluminosilicate matrix and from the low concentrations of nanosized crystallites, we have proposed a procedure based on factor analysis of ²⁷Al MAS NMR spectra. The capability of the proposed method was tested on geopolymers that exhibited various tendencies to crystallize (i) completely amorphous systems, (ii) X‐ray amorphous systems with nanocrystalline phases, and (iii) highly crystalline systems. Although the recorded ²⁷Al MAS NMR spectra did not show visible differences between the amorphous systems (i) and the geopolymers with the nanocrystalline phase (ii), the applied factor analysis unambiguously distinguished these materials. The samples were separated into the well‐defined clusters, and the systems with the evolving crystalline phase were identified even before any crystalline fraction was detected by X‐ray powder diffraction. Reliability of the proposed procedure was verified by comparing it with ²⁹Si MAS NMR spectra. Factor analysis of ²⁷Al MAS NMR spectra thus has the ability to reveal spectroscopic features corresponding to the nanocrystalline phases. Because the measurement time of ²⁷Al MAS NMR spectra is significantly shorter than that of ²⁹Si MAS NMR data, the proposed procedure is particularly suitable for the analysis of large sets of specifically synthesized geopolymers in which the formation of the limited fractions of nanocrystalline phases is desired. Copyright © 2013 John Wiley & Sons, Ltd.     

Solid-state nuclear magnetic resonance investigation of synthetic phlogopite and lepidolite samples

In the present work, our aim is to decipher the cationic ordering in the octahedral and tetrahedral sheets of two Al-rich synthetic materials, namely, phlogopites of nominal composition K(Mg_3-xAl_x)[Al_1+xSi_3-xO₁₀](OH)_yF_2-y and lepidolites in the system trilithionite–polylithionite with composition K (Li_xAl_3-x)[Al_4-2xSi_2xO₁₀](OH)_yF_2-y, by directly probing the aluminium distribution through ²⁷Al and ¹⁷O magic-angle spinning, multiple-quantum magic-angle spinning, and ²⁷Al-²⁷Al double-quantum single-quantum nuclear magnetic resonance (NMR) experiments. Notably, ²⁷Al-²⁷Al double-quantum single-quantum magic-angle spinning NMR spectra, recorded at 9.34 and/or 20.00 T, show the spatial proximity or avoidance of the Al species inside or between the sheets. In both studied minerals, the ensemble of NMR data suggests a preference for ^[4]Al in the tetrahedral sheet to occupy position close to the ^[6]Al of the octahedral sheets.     

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.     

Interactions of Al(III) with a neurofilament heptapeptide fragment: AcLysSerProValValGluGly

The solution state of the neurotoxic Al(III) in biological systems is discussed briefly, and the importance of the Al(III)-peptide and Al(III)-protein interactions in the various neurodegeneration processes is emphasised and evaluated. The possible involvement of Al(III) in the formation of Alzheimer's disease marker senile plaques and neurofilament tangles is discussed in light of the solution speciation of the Al(III)-AcLysSerProValValGluGly system and the structural features of the complexes formed.