Two-point halogen bonding between 3,6-dihalopyromellitic diimides

The syntheses of several 3,6-dihalopyromellitic diimides have been achieved. Two-point intermolecular halogen–oxygen interactions—reminiscent of carboxylic acid dimers—are observed in the solid-state superstructures of (i) these molecules and (ii) their charge-transfer complexes with electron-rich naphthalenes.

CO2 selective 1D double chain dipyridyl-porphyrin based porous coordination polymers

Two CO₂ selective 1D double chain dipyridyl-porphyrin-based porous coordination polymers, Co₃(DPyP)₃·4DMF (I) and Zn₃(DPyP)₃·2DMF·4H₂O (II) are prepared from thermal reactions of MnCl(DPyP) with Co^II and Zn^II ions in DMF.

Linear bilateral extended 2,2′:6′,2′′-terpyridine ligands, their coordination complexes and heterometallic supramolecular networks

Combination of five- and six-membered rings allows creation of 2,2′:6′,2′′-terpyridine derivatives mimicking the topology of 5,5′-functionalized 2,2′-bipyridine. This molecular design led to the assembly of heterometallic supramolecular networks.

Stable encapsulation of acrylate esters in networked molecular capsules

Reactive acrylate esters were encapsulated in the cavity of networked molecular capsules in a single-crystal-to-single-crystal fashion. Owing to the encapsulation effect, acrylates inside the capsules do not undergo polymerization upon irradiation with UV light or heating, while the guest molecules can be quantitatively extracted by treatment with toluene.

The Chemistry and Applications of Metal-Organic Frameworks

Crystalline metal-organic frameworks (MOFs) are formed by reticular synthesis, which creates strong bonds between inorganic and organic units. Careful selection of MOF constituents can yield crystals of ultrahigh porosity and high thermal and chemical stability. These characteristics allow the interior of MOFs to be chemically altered for use in gas separation, gas storage, and catalysis, among other applications. The precision commonly exercised in their chemical modification and the ability to expand their metrics without changing the underlying topology have not been achieved with other solids. MOFs whose chemical composition and shape of building units can be multiply varied within a particular structure already exist and may lead to materials that offer a synergistic combination of properties.

Post‐synthetic Modification of MOFs

Post‐synthetic modification is increasingly recognised as an important and versatile tool in the preparation of functionalised metal organic frameworks (MOFs). The process involves one or more reactions on a pre‐formed MOF, and it can be used to prepare MOFs that are not accessible by direct combination of metal and linker. This review explores the methods and strategies that have been developed for post‐synthetically modifying MOFs, concentrating on four classes of reaction: covalent transformations of the linker, coordination of a metal centre to a linker, modification of the inorganic part of the MOF and exchange of counter‐ions. Examples of the use of the modified MOFs are given, with a focus on their utility in catalysis.

Three-dimensional architectures incorporating stereoregular donor-acceptor stacks

We report the synthesis of two [2]catenane-containing struts that are composed of a tetracationic cyclophane (TC(4+)) encircling a 1,5-dioxynaphthalene (DNP)-based crown ether, which bears two terphenylene arms. The TC(4+) rings comprise either 1) two bipyridinium (BIPY(2+)) units or 2) a BIPY(2+) and a diazapyrenium (DAP(2+)) unit. These degenerate and nondegenerate catenanes were reacted in the presence of Cu(NO3)2⋅2.5 H2O to yield Cu-paddlewheel-based MOF-1050 and MOF-1051. The solid-state structures of these MOFs reveal that the metal clusters serve to join the heptaphenylene struts into grid-like 2D networks. These 2D sheets are then held together by infinite donor-acceptor stacks involving the [2]catenanes to produce interpenetrated 3D architectures. As a consequence of the planar chirality associated with both the DNP and hydroquinone (HQ) units present in the crown ether, each catenane can exist as four stereoisomers. In the case of the nondegenerate (bistable) catenane, the situation is further complicated by the presence of translational isomers. Upon crystallization, however, only two of the four possible stereoisomers--namely, the enantiomeric RR and SS forms--are observed in the crystals. An additional element of co-conformational selectivity is present in MOF-1051 as a consequence of the substitution of one of the BIPY(2+) units by a DAP(2+) unit: only the translational isomer in which the DAP(2+) unit is encircled by the crown ether is observed. The overall topologies of MOF-1050 and MOF-1051, and the selective formation of stereoisomers and translational isomers during the kinetically driven crystallization, provide evidence that weak noncovalent bonding interactions play a significant role in the assembly of these extended (super)structures.

A rationally designed nitrogen-rich metal-organic framework and its exceptionally high CO(2) and H(2) uptake capability

On the way towards a sustainable low-carbon future, the design and construction of chemical or physical adsorbents for CO₂ capture and clean energy storage are vital technology. The incorporation of accessible nitrogen-donor sites into the pore walls of porous adsorbents can dramatically affect the CO₂ uptake capacity and selectivity on account of the dipole-quadrupole interactions between the polarizable CO₂ molecule and the accessible nitrogen site. In the present work, a nitrogen-rich rth-type metal-organic framework (MOF) was constructed based on rational design and careful synthesis. The MOF presents exceptionally high uptake capacity not only for CO₂ but also for H₂, which is attributed to favorable interactions between the gas molecules and the nitrogen-rich triazole units of the MOF proved by both experimental measurements and theoretical molecular simulations.

Redox-switchable tetra-copper assembly of N,N-, N,O-phenolate-phenanthroimidazolate bridging ligands

A redox-active dianionic N,O-phenolate-imidazolate/N,N-phenanthroline bridging ligand is used to form unique square-like neutral tetra-Cu(II) assemblies, the structural, magnetic, electronic and redox properties of which are herein described.

Facile route to an all-organic, triply threaded, interlocked structure by templated dynamic clipping

Encaged! Three-terminal interlocked molecular species were obtained by dynamic (2+3) assembly of a cagelike macro-bicycle around a trifurcated trispyridinium π guest. The complex is stabilized by π-π interactions and multiple [C-H⋅⋅⋅O] and [C-H⋅⋅⋅N] interactions. Uncomplexed guest molecules cocrystallize alongside the threaded complexes in the solid state, thus giving extended π-stacked columns.

Thermally-induced phase transition of pseudorotaxane crystals: changes in conformation and interaction of the molecules and optical properties of the crystals

This paper presents a pseudorotaxane that acts as a thermally driven molecular switch in the single-crystal state. Crystals of the cationic pseudorotaxane consisting of dibenzo[24]crown-8 (DB24C8) and N-(xylylammonium)-methylferrocene as the cyclic and axle component molecules, respectively, undergo crystalline-phase transition at 128 °C with heating and 116 °C with cooling, according to differential-scanning-calorimetry measurements. X-ray crystallographic analyses revealed that the phase transition was accompanied by rotation of the 4-methylphenyl group of the axle component molecule and a simultaneous shift in the position of the PF(6)(-) counteranion. Crystalline phase transition changes the conformation and position of the DB24C8 molecule relative to the ammonium cation partially; the interaction between the cyclic component and the PF(6)(-) anion in the crystal changes to a greater extent. Moreover, there are changes in the vibration angle (θ) and birefringence (Δn) on the (001) face of the crystal transitionally; θ is rotated by +12°, and Δn is decreased from 0.070 to 0.059 upon heating across the phase transition temperature. The phase transition and accompanying change in the optical properties of the crystal occur reversibly and repeatedly upon heating and cooling processes. The switching rotation of the aromatic plane of the molecule induces a change in the optical anisotropy of the crystal, which is regarded as a demonstration of a new type of optical crystal. Partial replacement of the PF(6)(-) anion with the bulkier AsF(6)(-) anion forms crystals with similar crystallographic parameters. An increase in the AsF(6)(-) content decreases the reversible-phase-transition temperature gradually down to 99 °C (T(end)) and 68 °C (T(exo)) ([AsF(6)(-)]:[PF(6)(-)] = 0.4:0.6).

Mechanostereochemistry and the mechanical bond

The chemistry of mechanically interlocked molecules (MIMs), in which two or more covalently linked components are held together by mechanical bonds, has led to the coining of the term mechanostereochemistry to describe a new field of chemistry that embraces many aspects of MIMs, including their syntheses, properties, topologies where relevant and functions where operative. During the rapid development and emergence of the field, the synthesis of MIMs has witnessed the forsaking of the early and grossly inefficient statistical approaches for template-directed protocols, aided and abetted by molecular recognition processes and the tenets of self-assembly. The resounding success of these synthetic protocols, based on templation, has facilitated the design and construction of artificial molecular switches and machines, resulting more and more in the creation of integrated functional systems. This review highlights (i) the range of template-directed synthetic methods being used currently in the preparation of MIMs; (ii) the syntheses of topologically complex knots and links in the form of stable molecular compounds; and (iii) the incorporation of bistable MIMs into many different device settings associated with surfaces, nanoparticles and solid-state materials in response to the needs of particular applications that are perceived to be fair game for mechanostereochemistry.

Molecular recognition: from solution science to nano/materials technology

In the 25 years since its Nobel Prize in chemistry, supramolecular chemistry based on molecular recognition has been paid much attention in scientific and technological fields. Nanotechnology and the related areas seek breakthrough methods of nanofabrication based on rational organization through assembly of constituent molecules. Advanced biochemistry, medical applications, and environmental and energy technologies also depend on the importance of specific interactions between molecules. In those current fields, molecular recognition is now being re-evaluated. In this review, we re-examine current trends in molecular recognition from the viewpoint of the surrounding media, that is (i) the solution phase for development of basic science and molecular design advances; (ii) at nano/materials interfaces for emerging technologies and applications. The first section of this review includes molecular recognition frontiers, receptor design based on combinatorial approaches, organic capsule receptors, metallo-capsule receptors, helical receptors, dendrimer receptors, and the future design of receptor architectures. The following section summarizes topics related to molecular recognition at interfaces including fundamentals of molecular recognition, sensing and detection, structure formation, molecular machines, molecular recognition involving polymers and related materials, and molecular recognition processes in nanostructured materials.

Stimuli-responsive supramolecular polymeric materials

Supramolecular materials, dynamic materials by nature, are defined as materials whose components are bridged via reversible connections and undergo spontaneous and continuous assembly/disassembly processes under specific conditions. On account of the dynamic and reversible nature of noncovalent interactions, supramolecular polymers have the ability to adapt to their environment and possess a wide range of intriguing properties, such as degradability, shape-memory, and self-healing, making them unique candidates for supramolecular materials. In this critical review, we address recent developments in supramolecular polymeric materials, which can respond to appropriate external stimuli at the fundamental level due to the existence of noncovalent interactions of the building blocks.

Chiral porous metal-organic frameworks with dual active sites for sequential asymmetric catalysis

Metal-organic frameworks (MOFs) are a class of organic–inorganic hybrid materials built from metal-connecting nodes and organic-bridging ligands. They have received much attention in recent years owing to the ability to tune their properties for potential applications in various areas. Properly designed MOFs with uniform, periodically aligned active sites have shown great promise in catalysing shape-, size-, chemo-, regio- and stereo-selective organic transformations. This study reports the synthesis and characterization of two chiral MOFs (CMOFs 1 and 2 ) that are constructed from Mn-salen-derived dicarboxylic acids [salen is ( R , R )- N , N ′-bis(5- tert -butylsalicylidene)-1,2-cyclohexanediamine], bis(4-vinylbenzoic acid)-salen manganese(III) chloride (H 2 L 4 ) or bis(benzoic acid)-salen manganese(III) chloride (H 2 L 3 ) and [Zn 4 (μ 4 -O)(O 2 CR) 6 ] or [Zn 5 (H 2 O) 2 (μ 3 -OH) 2 (O 2 CR) 8 ] secondary building units (SBUs), respectively. The SBUs in CMOF- 1 are connected by the linear ditopic Mn-salen-derived linkers to construct a fourfold interpenetrated isoreticular MOF (IRMOF) structure with pcu topology. In CMOF- 2 , the Mn-salen centres dimerize in a cross-linking way to form a diamondoid structure with threefold interpenetration. CMOF- 1 was examined for highly regio- and stereo-selective tandem alkene epoxidation/epoxide ring-opening reactions by using the Mn-salen andZn 4 (μ 4 -O)(carboxylate) 6 active sites, respectively. Our work demonstrated the potential utility of chiral MOFs with multiple active sites in the efficient synthesis of complex molecules with excellent regio- and stereo-controls

Metal-organic frameworks incorporating copper-complexed rotaxanes

MOFs on the move: A copper coordinated [2]pseudorotaxanate which reacts with zinc nitrate to form an extended structure, consisting of three-fold interpenetrated networks, retains most of its solution-state chemistry including its ability to undergo electronic switching of some of the copper(I) ions under redox control.