Towards guest-zeolite interactions: an NMR spectroscopic approach

Guest(metal)-zeolite interactions in a two component heterogeneous catalyst have been investigated by high-field and high-speed (27)Al MAS NMR, and two-dimensional (27)Al MQ MAS NMR experiments as well as ab initio DFT methods. It was established that strong interactions between guest and zeolite occur in a metal/zeolite system, with the metal anchored to the tetrahedral aluminum framework site through two oxygen bridges. It disturbs the tetrahedral environment of associated aluminum framework, changing AlO(4) geometry from near T(d) to C(2v); this enables us to resolve this species from the undisturbed aluminum framework species in high-field (27)Al MAS NMR and two-dimesional (27)Al MQ MAS NMR experiments.     

A heterobimetallic metal-organic framework with tunable reactive metal sites: synthesis, characterization, and reactivity

A technique for preparing heterobimetallic frameworks with tunable metal sites is demonstrated by the synthesis of a new two-dimensional metal-organic framework that is constructed from tetra(4-carboxyphenyl)porphyrin and Cd(II) species. The solid can be prepared in the presence of other divalent transition metals to yield the same framework with the smaller metal ions occupying the porphyrin ligands.     

金属离子调控IRMOF3-sal的发光性质

通过后合成修饰将水杨醛(Salicylaldehyde, sal)锚装在金属-有机框架化合物IRMOF-3上, 捕获不同金属离子得到系列化合物IRMOF3-M_sal(M=Mg, Zn, Co, Cd, Ni, Eu, Nd, Pr, Tb); 采用红外光谱、元素分析和X射线粉末衍射对其进行表征, 并对其荧光性质进行了对比研究. 结果表明, IRMOF3-M_sal的荧光峰均发生较大蓝移且IRMOF3-Mg_sal的荧光强度最大.     

从头算分子动力学模拟Pd团簇负载UiO-66材料结构及稳定性

采用从头算分子动力学模拟与密度泛函理论相结合的方法,计算模拟了不同尺寸的Pdn(n=1~32)金属团簇在UiO-66孔道中的稳定构型,并对金属团簇与材料骨架之间的作用方式、结合能及骨架形变能等进行了讨论.采用Bader电荷分析方法对该体系的电荷转移情况进行了计算分析.结果表明,Pdn团簇稳定负载于UiO-66材料的四面体笼中,且均呈堆积型构型.当Pd原子个数为28时体系的热力学稳定性最好,这与金属团簇和有机配体的成键方式相关,是金属团簇内部结合能和骨架形变能综合作用的结果.     

Generalized synthesis of zeolite-type metal-organic frameworks encapsulating immobilized transition-metal clusters

Zeolites are generally made from tetrahedral nodes and ditopic linkers. Reported here is a versatile method based on trifunctional ligands. With this method, two functional groups are used to form zeolitic nets, while the third one serves to immobilize metal clusters within the channels. The process is driven by the coexistence of multiple inorganic building blocks generated in the heterometallic system. The generality of this method is shown by three distinct metal-organic frameworks mimicking AlPO(4)-5 (AFI) and BCT zeotypes as well as the cubic lcs topology. The correlation between the framework topology and trapped metal species reveals the unique bidirectional control (framework topology ? confined metal species) that may be exploited to create a large family of zeotypes with channels modified by different metal ions and clusters.     

Complete Transmetalation in a Metal–Organic Framework by Metal Ion Metathesis in a Single Crystal for Selective Sensing of Phosphate Ions in Aqueous Media

A complete transmetalation has been achieved on a barium metal–organic framework (MOF), leading to the isolation of a new Tb‐MOF in a single‐crystal (SC) to single‐crystal (SC) fashion. It leads to the transformation of an anionic framework with cations in the pore to one that is neutral. The mechanistic studies proposed a core–shell metal exchange through dissociation of metal–ligand bonds. This Tb‐MOF exhibits enhanced photoluminescence and acts as a selective sensor for phosphate anion in aqueous medium. Thus, this work not only provides a method to functionalize a MOF that can have potential application in sensing but also elucidates the formation mechanism of the resulting MOF.     

活化温度对CuBTC催化CO氧化反应性能的影响(英文)

考察了金属有机骨架材料CuBTC(BTC为均苯三酸)催化CO氧化的反应性能,发现CuBTC对CO氧化反应表现出良好的催化活性,且CuBTC样品的活化温度对其催化活性的影响很大.原位漫反射红外光谱、粉末X射线衍射、扫描电镜、热重分析和差示扫描量热结果表明,CO在CuBTC骨架中不饱和金属位点上的配位是加速CO氧化的主要原因,且这种不饱和金属位点越多,其催化活性越高.     

高度隔离过渡金属催化剂及其烯烃环氧化研究

 介绍了过渡金属杂原子分子筛的骨架杂原子表征、用离子注入法和化学嫁接法制备高度隔离过渡金属催化剂及其催化烯烃环氧化研究的结果．基于共振拉曼原理,用紫外共振拉曼光谱明确鉴别了TS－1,Fe－ZSM－5和V－MCM－41等分子筛中的骨架杂原子．用离子注入法和化学嫁接法制得具有高度隔离过渡金属离子的非杂原子分子筛催化剂．烯烃环氧化反应结果表明,所制得的催化剂显示出优良的催化性能．     

Epoxidation of olefins catalyzed by novel Mn(III) and Mo(IV) Salen complexes immobilized on mesoporous silica gel: Part I. Synthesis and characterization of homogeneous and immobilized Mn(III) and Mo(IV) Salen complexes

New ways of the covalent immobilization of Mn(III) and Mo(IV) Salen complexes on a mesoporous silica support to produce a stable heterogeneous catalyst for epoxidation reactions are reported. Peptide and ester interactions were employed to anchor the metal Salen complex on the organo-modified silica framework. Electrospray MS, FTIR, TGA, ICP-OES and elemental analysis were used for quantitative and qualitative analyses of the immobilized Salen complexes. The results confirm the location of the metal Salen complex inside the mesopores covalently attached to the silica framework.     

Electronic origin of the structural versatility in linear trichromium complexes of dipyridylamide

Spin unrestricted DFT calculations on Cr3(dpa)4Cl2 (dpa = dipyridylamide) suggest that the linear (Cr3)6+ metal framework could adopt either a symmetric conformation, or a strongly nonsymmetric one, depending on the nature of the spin coupling between the localized metal electrons.     

Metal–organic framework ZIF-8 loaded with rhodium nanoparticles as a catalyst for hydroformylation

Porous metal–organic framework ZIF-8 materials containing incorporated rhodium (Rh@ZIF-8) and rhodium chloride (RhCl₃@ZIF-8) nanoparticles were obtained and tested as a catalytic reaction vessel in the reactions of hydroformylation of 1-decene and styrene. Catalytic tests with Rh@ZIF-8 showed that the selectivity and conversion of the hydroformylation reaction depended on the size of the substrate molecule. The incorporation of catalytic nanoparticles into the pores of a metal–organic framework opens up new possibilities for regioselective hydroformylation.     

Oxidation reactions catalysed by molybdenum(VI) complexes grafted on UiO‐66 metal–organic framework as an elegant nanoreactor

A heterogeneous catalyst was synthesized by immobilizing Mo(CO)₃ in a UiO‐66 metal–organic framework. The benzene ring of the organic linker in UiO‐66 was modified via liquid‐phase deposition of molybdenum hexacarbonyl, Mo(CO)₆, as starting precursor to form the (arene)Mo(CO)₃ species inside the framework. The structure of this catalyst was characterized using X‐ray diffraction, and chemical integrity was confirmed using Fourier transform infrared and diffuse reflectance UV–visible spectroscopic methods. The metal content was analysed with inductively coupled plasma. Field emission scanning electron microscopy was used to measure particle size and N₂ adsorption measurements to characterize the specific surface area. This catalytic system was efficiently applied for epoxidation of alkenes and oxidation of sulfides. The Mo‐containing metal–organic framework was reused several times without any appreciable loss of its efficiency.     

Structural identification of multidimensional metal–organic frameworks using soft x-ray tomography

This paper mainly discusses the applicability of using soft x-ray tomography technology to examine the multidimensional structure of metal–organic frameworks, such as their core-shell and hollow framework, by visually observing their corresponding images in different energy bands by different excitation energies for different elements. The results show that the use of soft x-ray tomography (SXT) can effectively observe the distribution of metals in the structure, as well as observe the type of hollow pores the metal – organic framework (MOF) possesses. This pioneering evaluation of MOFs via SXT shows excellent performance in the structure identification of multidimensional metal–organic frameworks.     

A closed molecular cube and an open book: two different products from assembly of the same metal salt and bridging ligand

Reaction of the bis-bidentate bridging ligand L1 with Co(ClO4)2 or Zn(BF4)2 affords a mixture of complexes [M8(L1)12]X16 and [M6(L1)9]X12 having the same metal : ligand ratio: the former is a molecular cube with a metal ion at each vertex and a bridging ligand spanning each edge, whereas the latter has a metal framework like that of an 'open book' containing cross-linked double helical metal-ligand subunits.     

Versatile Tailoring of Paddle‐Wheel ZnII Metal–Organic Frameworks through Single‐Crystal‐to‐Single‐Crystal Transformations

A new tetracarboxylate ligand having short and long arms formed 2D layer Zn^II coordination polymer 1 with paddle‐wheel secondary building units under solvothermal conditions. The framework undergoes solvent‐specific single crystal‐to‐single crystal (SC‐SC) transmetalation to produce 1_Cu . With a sterically encumbered dipyridyl linker, the same ligand forms non‐interpenetrated, 3D, pillared‐layer Zn^II metal–organic framework (MOF) 2 , which takes part in SC‐SC linker‐exchange reactions to produce three daughter frameworks. The parent MOF 2 shows preferential incorporation of the longest linker in competitive linker‐exchange experiments. All the 3D MOFs undergo complete SC‐SC transmetalation with Cu^II, whereby metal exchange in different solvents and monitoring of X‐ray structures revealed that bulky solvated metal ions lead to ordering of the shortest linker in the framework, which confirms that the solvated metal ions enter through the pores along the linker axis.     

A hybrid metalloarsenate 3D framework-1D interrupted metal oxide

Complex metal arsenates of the stoichiometry M(1)(-)(x)()M'(6)(OH)(3)(AsO(4)H(2)(x)()(/3))(3)(HAsO(4)), M = M' = Co, Ni, have been synthesized under hydrothermal conditions. The two compounds display a very similar structural topology to that of the mineral dumortierite, an uncommon complex oxyborosilicate of aluminum. The hybrid structures consist of well separated, vacancy interrupted chains of face sharing MO(6) octahedra, with short M.M distances near 2.5 A, embedded in a metalloarsenate 3D framework having the topology of the aluminosilicate cancrinite. The framework also contains a quadruply bridging hydroxide ion. Magnetic susceptibility measurements reveal a strong antiferromagnetic interaction and magnetic transition to low temperature spin canted phases below 51 K (Co) and 42 K (Ni). The material may be considered as a zeotype framework structure templated by an interrupted one-dimensional metal oxide.     

Carborane-based metal-organic frameworks as highly selective sorbents for CO(2) over methane

Separation of CO(2)/CH(4) mixtures was studied in carborane-based metal-organic framework materials with and without coordinatively unsaturated metal sites; high selectivities for CO(2) over CH(4) ( approximately 17) are obtained, especially in the material with open metal sites.     

A series of isostructural mesoporous metal-organic frameworks obtained by ion-exchange induced single-crystal to single-crystal transformation

A series of metal-organic frameworks representing a non-interpenetrated framework analogue of MOF-14 have been synthesized by using two different linkers, 4,4',4'-benzene-1,3,5-triyl-benzoic acid (H(3)BTB) and 4,4'-bipyridine (Bpy). Interestingly, the transition metal ions in the paddle-wheel metal clusters could be exchanged by other transition metal ions via a direct single-crystal to single-crystal transformation. This post-synthesis route can be used for synthesis of isomorphous metal-organic frameworks that cannot be obtained by direct synthesis.     

Understanding the Anion-Templated,OSDA-Free,Interzeolite Conversion Synthesis of High Silica Zeolite ZK-5**

High silica zeolite ZK-5 (framework Si/Al=4.8) has been prepared by interzeolite conversion from ultrastable zeolite Y via a co-templating route using alkali metal cations and nitrate anions but without organic structure directing agents. The mechanism, which involves zeolite framework – alkali metal cation – nitrate anion ordering, has been established by a combination of chemical and thermal analyses, Raman spectroscopy, computational modelling, and X-ray powder diffraction. Ammonium exchange gives ZK-5 with occluded ammonium nitrate and subsequent heating gives microporous zeolite ZK-5.     

Unsymmetrical (R)PNP(R') pincer ligands and their group 10 complexes

Two new unsymmetrical (R)PNP(R')-type pincer ligands based on a bis(tolyl)amine framework have been synthesized and characterized by a variety of techniques, including X-ray crystallography. These ligands have been coordinated to Ni, Pd, and Pt precursors to provide a number of well-characterized group 10 halides. Conversion of these metal halides to metal hydrides was accomplished using borohydride reagents, or by direct interaction of the ligand with the zerovalent metal precursor. The insertion of oxygen into these hydrides in an attempt to prepare metal hydroperoxides has been examined; however, we were unable to obtain stable and isolable hydroperoxide species.