Xianhui Bu

Induction of chiral porous solids containing only achiral building blocks.

In many areas of chemistry the synthesis of chiral compounds is a target of increasing importance. They play a vital role in biological function and in many areas of society and science, including biology, medicine, biotechnology, chemistry and agriculture. Many pharmaceutical molecules, like their biological targets, are chiral and it is therefore easy to understand the growing demand for efficient methods of producing enantiomerically pure compounds. This is equally true for the preparation of chiral solids, which have potential applications in asymmetric catalysis, chiral separations and the like. In this Review we will consider recent progress and future potential in the development of methods for the preparation of chirally pure solids, in particular where the building blocks of the structure are achiral themselves. We will discuss strategies for the synthesis of both inorganic (for example, zeolites) and inorganic-organic hybrid (for example, metal organic framework) chiral porous solids.

Hydrothermal syntheses and structural characterization of zeolite analogue compounds based on cobalt phosphate

Zeolite analogues containing transition metals are highly desirable for industrial processes. A generalized synthesis method has been developed and demonstrated to have the potential to generate many transition-metal-rich zeolite-type structures. The method has been used to make zeolite analogues based on cobalt phosphate with diverse chemical compositions and structure types, including some analogues never previously synthesized and some zeolite-like structures only previously known theoretically. The concentrations of transition-metal atoms in the frameworks can be controlled by varying the charge and geometry of the structure-directing amine molecules.

Homochiral Crystallization of Microporous Framework Materials from Achiral Precursors by Chiral Catalysis

While it is not uncommon to form chiral crystals during crystallization, the formation of bulk porous homochiral materials from achiral building units is rare. Reported here is the homochiral crystallization of microporous materials through the chirality induction effect of natural alkaloids. The resulting material possesses permanent microporosity and has a uniform pore size of 9.3 A.

Synthetic design of crystalline inorganic chalcogenides exhibiting fast-ion conductivity

Natural porous solids such as zeolites are invariably formed with inorganic cations such as Na+ and K+ (refs 1, 2). However, current research on new porous materials is mainly focused on the use of organic species as either structure-directing or structure-building units; purely inorganic systems have received relatively little attention in exploratory synthetic work. Here we report the synthesis of a series of three-dimensional sulphides and selenides containing highly mobile alkali metal cations as charge-balancing extra-framework cations. Such crystalline inorganic chalcogenides integrate zeolite-like architecture with high anionic framework polarizability and high concentrations of mobile cations. Such structural features are particularly desirable for the development of fast-ion conductors. These materials demonstrate high ionic conductivity (up to 1.8 × 10-2 ohm-1 cm-1) at room temperature and moderate to high humidity. This synthetic methodology, together with novel structural, physical and chemical properties, may lead to the development of new microporous and open-framework materials with potential applications in areas such as batteries, fuel cells, electrochemical sensors and photocatalysis.

Pore Space Partition and Charge Separation in Cage-within-Cage Indium−Organic Frameworks with High CO2 Uptake

The integration of negatively charged single-metal building blocks {In(CO2)4} and positively charged trimeric clusters {In3O} leads to three unique cage-within-cage-based porous materials, which exhibit not only high hydrothermal, thermal, and photochemical stability but also attractive structural features contributing to a very high CO2 uptake capacity of up to 119.8 L/L at 273 K and 1 atm.

Selective anion exchange with nanogated isoreticular positive metal-organic frameworks

Crystalline porous materials, especially inorganic porous solids such as zeolites, usually have negative frameworks with extra-framework mobile cations and are widely used for cation exchange. It is highly desirable to develop new materials with positive frameworks for selective anion exchange and separation or storage and delivery. Recent advances in metal-organic framework synthesis have created new opportunities in this direction. Here we report the synthesis of a series of positive indium metal-organic frameworks and their utilization as a platform for the anion exchange-based separation process. This process is capable of size- or charge-selective ion-exchange of organic dyes and may form the basis for size-selective ion chromatography. Ion-exchange dynamics of a series of organic dyes and their selective encapsulation and release are also studied, highlighting the advantages of metal-organic framework compositions for designing host materials tailored for applications in anion separation and purification.

Multiroute synthesis of porous anionic frameworks and size-tunable extraframework organic cation-controlled gas sorption properties.

Under diverse and dramatically different chemical environments, including organic solvents, an ionic liquid, and a deep eutectic solvent, a series of porous anionic framework materials that contain size-tunable, ion-exchangeable extraframework organic cations have been prepared. Even though a large fraction of the pore space is occupied with charge-balancing cations, some of these materials exhibit a very high gas uptake capacity (e.g., 70.6 cm(3)/g for CO(2) at 1 atm and 273 K), suggesting that the charged anionic framework and extraframework cations may help to enhance the gas adsorption.

Synthesis and organization of zeolite-like materials with three-dimensional helical pores

The increasing demand for enantiomerically pure chemicals has stimulated extensive research into the preparation of heterogeneous chiral catalysts or separation media that combine both shape selectivity and enantioselectivity. Helical pores in inorganic materials might be able to perform such functions, but their occurrence is rare. Attempts have been reported to synthesize a specific enantiomorph of the chiral zeolite beta, and chiral metal complexes have been used to assemble inorganic precursors into chiral frameworks,. Materials with a fully three-dimensional array of helical structural units are particularly rare, because helical structures (such as quartz) are commonly generated by a uni-dimensional symmetry element acting on an achiral structural subunit,. Here we report on a family of zeolite-type materials (which we call UCSB-7) that possess two independent sets of three-dimensional crosslinked helical pores, separated by a gyroid periodic minimal surface. We have synthesized the UCSB-7 framework for various compositions (zinc and beryllium arsenates, gallium germanate) using either inorganic cations or amines as structure-directing agents. The helical-ribbon motif that we identify might be exploited more widely for developing useful chiral solid-state structures.

Zeolitic Boron Imidazolate Frameworks

B-hive? A family of crystalline materials analogous to porous AlPO(4) but based on boron imidazolate frameworks (BIFs) can be formed by the crosslinking of various presynthesized boron imidazolates with monovalent cations (Li(+) and Cu(+), see picture). This synthetic method is capable of generating a large variety of open frameworks, ranging from the four-connected zeolitic sodalite type to the three-connected chiral (10,3)-a type.

Luminescent MTN-type cluster-organic framework with 2.6 nm cages.

From a basic tetrahedral Cu(4)I(4) cluster, a new MTN-type cluster-organic framework (COZ-1) containing giant 6(4)5(12) and 5(12) cages was successfully constructed. The 6(4)5(12) cage has an inner diameter of 2.6 nm and a large pore volume of 9.2 nm(3); these tetrahedral Cu(4)I(4) clusters with bulky size offer new opportunities for not only the formation of 4-connected zeotype structures but also the integration of porosity and photoluminescent properties from both the cluster and the framework.