Macrocyclic amines as structure-directing agents for the synthesis of three-dimensional antimony-sulfide frameworks

A new family of antimony sulfides, incorporating the macrocyclic tetramine 1,4,8,11-tetraazacyclotetradecane (cyclam), has been prepared by a hydrothermal method. [C10N4H26][Sb4S7] (1), [Ni(C10N4H24)][Sb4S7] (2), and [Co(C10N4H24)]x[C10N4H26](1-x)[Sb4S7] (0.08 < or = x < or = 0.74) (3) have been characterized by single-crystal X-ray diffraction, elemental analysis, thermogravimetry, and analytical electron microscopy. All three materials possess the same novel three-dimensional Sb4S7(2-) framework, constructed from layers of parallel arrays of Sb4S8(4-) chains stacked at 90 degrees to one another. In 1, doubly protonated macrocyclic cations reside in the channel structure of the antimony-sulfide framework. In 2 and 3, the cyclam acts as a ligand, chelating the divalent transition-metal cation. Analytical and X-ray diffraction data indicate that the level of metal incorporation in 2 is effectively complete, whereas in 3, both metalated and nonmetalated forms of the macrocycle coexist within the structure.     

在无有机导向剂条件下采用乙醇为助剂合成高硅沸石

高硅沸石具有优异的热稳定性、水热稳定性、大的微孔体积、高表面积和均匀的微孔孔道,因而广泛应用于催化领域.然而,高硅沸石的合成往往需要使用有机结构导向剂,不但增加了沸石合成成本,而且还产生了大量的三废排放.为了解决这个问题,我们发展了在无有机导向剂存在条件下采用沸石晶种诱导合成沸石的方法,但是该方法合成的沸石产物骨架富铝...     

Solvothermal synthesis of new open-framework metal phosphites with structure-directing agents generated in situ

By using amide molecules and a urea derivative as the source of structure-directing agents (SDAs), three open-framework metal phosphites, (CH₃NH₃)₂·[Be₃(HPO₃)₄] (1), (CH₃CH₂NH₃)₂·[Be₃(HPO₃)₄] (2), and [(CH₃)₂NH₂]_1.5·(H₃O)_0.5·[Al₄(HPO₃)₇(H₂O)₃]·(H₂O)_0.5 (3), have been synthesized under solvothermal conditions. Compound 1 has left- and right-handed helical channels running along the [001] directions. Compound 2 possesses zigzag 12-ring channels running along the [001] direction. Compound 3 contains multidirectional 12-ring channels running along the [100], [010], and [110] directions. It is noteworthy that the direct use of methylamine, ethylamine and dimethylamine as SDAs can't produce corresponding single crystals of compounds 1–3, demonstrating the slow release of amines from amide molecules and urea derivative is a key process for the crystal growth.     

Monomers that form conducting polymers as structure-directing agents: synthesis of microporous molecular sieves encapsulating poly-para-phenylenevinylene

We have developed a novel concept that uses monomers required for making conducting polymers as organic structure-directing agents, for the synthesis of microporous molecular sieves. We show that these monomers facilitate the formation of crystalline and amorphous molecular sieves depending on the synthesis procedure. The monomers filling the pores of the silicates can be polymerized under certain conditions, resulting in a polymer immobilized and protected inside the matrix. The concept was exemplified with para-phenylenemethylene-bis(1-tetrahydrothiophenium) and para-phenylenemethylene-bis(trimethylammonium) that were used to template microporous molecular sieves and subsequently to obtain poly-para-phenylenevinylene (PPV) inside the matrix. The organic self-assembled organic-inorganic material was extensively characterized and the implication on electrical conductivity is presented.     

A study of piperidinium structure-directing agents in the synthesis of silica molecular sieves under fluoride-based conditions

This study is a continuation of our efforts to understand the interplay in the self-assembly chemistry for formation of molecular sieves from guest organocations and inorganic silicon oxide. In this particular study we focus on the competitive interplay of the organocations and the synthesis cofactor fluoride anion. The anions play a key role in structure determination, as a function of net solution concentration. They compete with the role for the space-filling organocation in determining which molecular sieve host structure will be specified. In this study we look at this competition in the synthesis for a series of 33 different organocations derived from the piperidine ring system. Derivatives were prepared which both fixed substituents on the carbon and nitrogen centers on the ring. Results were discussed in terms of product selectivity from synthesis as a function of solution concentration for the reactants. A total of 17 different host topologies were found in this series, and a correlation was seen for (a) open-framework lattices (low framework densities) under the most concentrated reaction conditions and then (b) high framework density products once the conditions were more dilute. Some surprising synthesis differences are seen in comparing the performance of these structure directing agents (SDAs) in fluoride media vs hydroxide media (the more conventional environment for zeolite/molecular sieve syntheses involving silicate chemistry). Finally molecular modeling was used to understand some of the trends in product selectivity for closely related guest (SDA) candidates.     

Multi-objective de novo molecular design of organic structure-directing agents for zeolites using nature-inspired ant colony optimization

Organic structure-directing agents (OSDAs) are often employed for synthesis of zeolites with desired frameworks. A priori prediction of such OSDAs has mainly relied on the interaction energies between OSDAs and zeolite frameworks, without cost considerations. For practical purposes, the cost of OSDAs becomes a critical issue. Therefore, the development of a computational de novo prediction methodology that can speed up the trial-and-error cycle in the search for less expensive OSDAs is desired. This study utilized a nature-inspired ant colony optimization method to predict physicochemically and/or economically preferable OSDAs, while also taking molecular similarity and heuristics of zeolite synthesis into consideration. The prediction results included experimentally known OSDAs, candidates having structures closely related to known OSDAs, and novel ones, suggesting the applicability of this approach.

Inspired by the exploratory methods of ant colonies, adaptive optimization was employed to explore the chemical space for organic molecules that guide zeolite crystallization, giving both physicochemically and economically promising molecules.     

Molecular simulations of host-guest interactions between zeolite framework STW and its organic structure-directing agents

Zeolites have been widely applied in many chemical processes owing to their featured microporous framework structures. Organic structure-directing agents (OSDAs) play an important role during of the formation of zeolite frameworks via non-bonding host-guest interactions. Understanding these interactions is crucial to the design of OSDAs and the synthesis of target zeolites. Here, we report a molecular simulation study in the host-guest interactions between zeolite framework STW and 21 alkylated imidazolium and pyrazolium cations that have been used as the OSDAs for the synthesis of STW-type zeolites. We find that OSDAs that have successfully directed the formation of STW exhibit stronger host-guest interactions than unsuccessful ones. Furthermore, we find all successful OSDAs possess relatively more negative atomic charges on nitrogen atoms and smaller dipole moments. According to this finding, we have designed seven new alkylated imidazolium and pyrazolium cations that may be suitable for zeolite STW, and verified their structure-directing capability by molecular simulation calculations.     

Supramolecular chemistry in the structure direction of microporous materials from aromatic structure-directing agents

A combination of fluorescence spectroscopy, thermogravimetric analysis, and molecular mechanics calculations has been used to study the structure-directing effect of the aromatic benzylpyrrolidine (BP) molecule (and its monofluorinated derivatives), and (S)-(-)-N-benzylpyrrolidine-2-methanol (BPM) in the synthesis of the microporous AFI structure. The results clearly show that, while all molecules form supramolecular aggregates in concentrated water solution, BPM molecules have a much more pronounced trend to aggregate as dimers within the AFI structure due to the development of interdimer H-bond interactions. Instead, BP (and its ortho- and meta-fluorinated derivatives) SDAs tend to incorporate in the AFI structure as monomers but with the simultaneous occlusion of water molecules, while para-fluorinated BP derivatives do not form compact dimers able to be accommodated in the AFI structure. We propose a crystallization mechanism where the presence of dimers is required for the nucleation step to occur, while crystal growth takes place through the simultaneous occlusion of SDA monomers and water (when the synthesis is performed with BP and derivatives) or through the occlusion of SDA dimers (in the synthesis with BPM).     

Design and synthesis of readily degradable acyloxysilane dendrimers

Two types of dendrimers with AB₂ branching, one with acyloxysilanes at the branching position (V type) and the other at the non-branching position (Y type), were synthesized using hydrosilylation with chlorosilanes followed by heterofunctional condensation with olefin-functional carboxylic acids, and examined as readily degradable template materials. The V type dendrimer was much more susceptible to ligand redistribution with chlorosilanes during preparation, whereas the Y type was less. The acyloxysilane linkages in these dendrimers could be cleaved readily by alcoholysis or hydrolysis on demand, making for suitable templates.     

One-pot synthesis of MWW zeolite nanosheets using a rationally designed organic structure-directing agent

A new material MIT-1 comprised of delaminated MWW zeolite nanosheets is made in a one-pot synthesis using a rationally designed organic structure-directing agent (OSDA). The OSDA consists of a hydrophilic head segment that resembles the OSDA used to synthesize the zeolite precursor MCM-22(P), a hydrophobic tail segment that resembles the swelling agent used to swell MCM-22(P), and a di-quaternary ammonium linker that connects both segments. MIT-1 features high crystallinity and surface areas exceeding 500 m² g^–1, and can be synthesized over a wide synthesis window that includes Si/Al ratios ranging from 13 to 67. Characterization data reveal high mesoporosity and acid strength with no detectable amorphous silica phases. Compared to MCM-22 and MCM-56, MIT-1 shows a three-fold increase in catalytic activity for the Friedel–Crafts alkylation of benzene with benzyl alcohol.     

A nonacid degradable linker for solid-phase synthesis

Synthesis and applications of two new nonacid degradable linkers as an alternative to the Wang linker for solid-phase synthesis are described. Resin from linker 2 looks superior to linker 1 in terms of yields for both anchoring of the first building block and cleavage and in terms of higher purity of the final product. Use of linker 2 avoids side reactions associated with the use of Wang resin due to an undesired cleavage during final acid treatment.     

P-derived organic cations as structure-directing agents: synthesis of a high-silica zeolite (ITQ-27) with a two-dimensional 12-ring channel system

Recently, efforts have been made to synthesize large-pore, multidimensional zeolite frameworks as a basis for new catalysts to improve various hydrocarbon conversions. A new aluminosilicate zeolite, ITQ-27, has been prepared using the phosphorus-containing structure-directing agent, dimethyldiphenylphosphonium. Its crystal structure was determined in its calcined form by direct methods (FOCUS) on synchrotron powder diffraction data (lambda = 0.8702 A) after the unit cell and space group were determined from tilt electron diffraction experiments on individual microcrystals. The material crystallizes in space group Fmmm, where a = 27.7508(5) A, b = 25.2969(7) A, and c = 13.7923(4) A. The final model, refined by Rietveld methods, comprises seven unique T-sites forming a framework with straight 12-MR channels that are connected by 14-MR openings between them. (Corresponding 12-ring pore dimension is 6.94 A x 6.20 A.) Since access from one 14-MR opening to the next is through the 12-MR channel, the structure is best described as a two-dimensional, 12-MR framework.     

高硅沸石合成中四氢呋喃模板作用的初步研究

在四氢呋喃(THF)-Na~2O-SiO~2-Al~2O~3-H~2O体系中,水热条件下合成出的沸石相,随配料硅铝比提高,依次为MOR(丝光沸石),ZSM-35,ZSM-5和ZSM-39,1^3^CCP/MASNMR谱,TG/DTG/DTA和EDX成分分析方法对沸石中的THF进行表征,1^3^C谱化学位移的显著变化,以及THF高的脱除温度,证明作为模板剂的THF分子进入所合成的沸石结构,并与骨架发生强的相互作用。     

Highly elastic and degradable vitrimeric elastomers using polycondensation

Introducing covalently crosslinked network to polymer matrix can merge the advantages in reprocessing and durability of polymers. In this contribution, a series of high-performance vitrimeric elastomers were achieved via polycondensation. The topological structures of polymers were tuned by varying the feeding ratios of bisacetoacetate, hex–substituted bisacetoacetate, bisamine and tris(2-aminoethyl)amine.With these structural manipulations, the vitrimeric elastomers presented great elastic reco...     

Zeolite catalysed synthesis of coumarin derivatives

The direct synthesis of coumarin derivatives from m-substituted phenols and α,β-unsaturated carboxylic acids catalysed by solid-acid catalysts, such as zeolite H-Beta or Amberlyst-15, in toluene as solvent was studied. The conversion involves esterification followed by alkylation (ring closure). Ring closure of the ester is promoted both by an appropriate substituent on the aromatic ring and by Michael activation of the β-carbon of the ester. These influences were studied by variation of the reactants. 7-Hydroxy-3,4-dihydrocoumarin is formed in high yield when resorcinol and propenoic acid are used as reactants.     

Zeolite synthesis from tetraalkylammonium silicate gels

Siliceous zeolite synthesis gels containing tetraalkylammonium (TAA⁺) and sodium cations were studied using X-ray diffraction, elemental analysis, ion exchange, ²⁹Si magic-angle spinning nuclear magnetic resonance spectroscopy, and scanning electron microscopy. The TAA⁺ cations are encapsulated in silicate cages, and silicalite is formed via the rearrangement of these cages by the breaking and reformation of siloxane bonds. Tetrabutylammonium (TBA⁺) cations promote silicalite growth, but not as effectively as tetrapropylammonium (TPA⁺) because the larger TBA⁺ cations do not conform as well to the silicalite lattice, thus forming an intergrowth of the silicalite-1 and silicalite-2 structures. The time to nucleate silicalite is not affected by the TBA⁺ content of the gel, but the rate of silicalite crystal growth increases with increasing TBA⁺ in the gel. The TBA⁺ occupies all the channel intersections of the silicalite formed. Tetraethylammonium (TEA⁺) cations are encapsulated in silicate cages, but not to the same extent as TPA⁺ and TBA⁺, because TEA⁺ is not as hydrophobic. No silicalite forms in the TEA⁺ silicate gel. The addition of tripropylamine (TriPA) to a TPA⁺ silicate gel has no effect on the kinetics of silicalite formation. TriPA does not incorporate into the gel because it is neutral and, therefore, does not experience a coulombic attraction to the negatively charged surface of the gel.     

Zeolite synthesis: an energetic perspective

Taking |D(H(2)O)(x)|[AlSiO(4)] based materials (where D is Li, Na, K, Rb or Cs) as an archetypal aluminosilicate system, we use accurate density functional theory calculations to demonstrate how the substitution of silicon cations in silica, with pairs of aluminium and (alkali metal) cations, changes the energetic ordering of different competing structure-types. For large alkali metal cations we further show that the formation of porous aluminosilicate structures, the so-called zeolites, is energetically favored. These findings unequivocally demonstrate that zeolites can be energetic preferred reaction products, rather than being kinetically determined, and that the size of the (hydrated) cations in the pore, be it inorganic or organic, is critical for directing zeolite synthesis.     

无有机模板剂体系水热合成Beta沸石中晶种的导向机理(英文)

在无有机模板剂体系中研究了不同硅铝比和晶粒度Beta沸石晶种的结构导向行为,采用X射线衍射、X射线荧光光谱、扫描电镜、透射电镜、紫外-拉曼光谱、红外光谱和N2物理吸附等方法对不同晶化时间固相产物和Beta沸石产物进行了表征.结果表明,不同Beta沸石晶种,包括全硅晶种,均能够导向合成Beta沸石,而且晶种在晶化诱导期都发生溶解.但是,晶种的硅铝比、晶粒度、预处理(焙烧)以及晶种加入的时间对晶种的溶解行为、Beta沸石晶化过程和产物都有重要影响.形貌研究还发现,含铝晶种不仅溶解后的残体通过提供晶核聚集的"固载化"表面导向了新生Beta沸石小晶体的密集生长,而且溶解下来的结构片段也提供了分散的晶核导向形成相对分散的Beta沸石小晶体;全硅晶种则仅通过溶解下来的结构片段提供分散的晶核.在无模板体系中,使用适当高硅铝比、小晶粒和经过焙烧处理的Beta沸石作为晶种有利于合成得到高结晶度的Beta沸石纯相.