John E. Warren

Flexible (Breathing) Interpenetrated Metal-Organic Frameworks for CO2 Separation Applications

A breathing 2-fold interpenetrated microporous metal-organic framework was synthesized with a flexible tetrahedral organic linker and Zn(2) clusters that sorb CO(2) preferably over N(2) and H(2).

Flexible metal–organic supramolecular isomers for gas separation

Three interpenetrated metal-organic supramolecular isomers were synthesised using a flexible tetrahedral organic linker and Zn(2) clusters that sorb CO(2) preferably over N(2), H(2) and methane at room temperature.

Heme-like coordination chemistry within nanoporous molecular crystals

Iron Exposure The macrocyclic heme motif coordinates iron ions in proteins and plays a widespread role in biochemical oxidative catalysis. Bezzu et al. (p. 1627) prepared crystals in which analogous iron-centered macrocycles were aligned in pairs. The outer faces of the pairs exposed the iron ions to vacant cavities, where ligand exchange could take place; the inner faces were bound together by rigid bridging ligands lending the crystals structural integrity. The stability and high porosity of these crystals lend themselves to potential catalytic applications. Metal-organic framework compounds expose iron atoms for reactions in a manner analogous to heme sites in proteins. Crystal engineering of nanoporous structures has not yet exploited the heme motif so widely found in proteins. Here, we report that a derivative of iron phthalocyanine, a close analog of heme, forms millimeter-scale molecular crystals that contain large interconnected voids (8 cubic nanometers), defined by a cubic assembly of six phthalocyanines. Rapid ligand exchange is achieved within these phthalocyanine nanoporous crystals by single-crystal–to–single-crystal (SCSC) transformations. Differentiation of the binding sites, similar to that which occurs in hemoproteins, is achieved so that monodentate ligands add preferentially to the axial binding site within the cubic assembly, whereas bidentate ligands selectively bind to the opposite axial site to link the cubic assemblies. These bidentate ligands act as molecular wall ties to prevent the collapse of the molecular crystal during the removal of solvent. The resulting crystals possess high surface areas (850 to 1000 square meters per gram) and bind N2 at the equivalent of the heme distal site through a SCSC process characterized by x-ray crystallography.

Stellated polyhedral assembly of a topologically complicated Pd4L4 'Solomon cube'

Metallosupramolecular chemistry relies on self-assembly processes in which complicated species form through labile dative-covalent interactions. Two remarkable areas of this chemistry are the synthesis of topologically complicated threaded assemblies and of three-dimensional (3D) polyhedral assemblies. Very few polyhedral 3D metallosupramolecular assemblies show threaded motifs within them. Here we report an example of a new type of threaded 3D metallosupramolecular assembly built from four organic ligands and four palladium ions, a Pd4L4 so-called ‘Solomons cube’ in which interweaving and twisting of the ligands form both Solomons links and figure-of-eight ring motifs. In the solid state, six of these Pd4L4 tetramers assemble into a hollow spheroid that closely resembles a stellated truncated hexahedron. A topologically non-trivial metallosupramolecular structure is formed by a Pd4L4 complex in which interweaving and twisting of the ligands results in both Solomons Link and figure-of-eight ring motifs. In the solid state, six of these complexes assemble into a hollow spheroid that closely resembles a stellated truncated hexahedron.

CO2 selectivity of a 1D microporous adenine-based metal–organic framework synthesised in water

The coordination of adenine to Ni(2+) forms a dimer unit which can be linked by 3,5-pyrazoledicarboxylic acid into chains which assemble under hydrothermal conditions via hydrogen bonding into a robust porous network. The material displays selectivity for CO(2) over CH(4) and an isosteric heat which increases with guest loading.

Large Self‐Assembled Chiral Organic Cages: Synthesis, Structure, and Shape Persistence

Keep the cage filled: Two large organic cages (see example) with void diameters of 1.2 nm were synthesized through [8+12] imine condensation reactions. The materials become amorphous upon solvent removal and show little permanent porosity. Molecular dynamics simulations give an insight into the mechanism of these processes, suggesting strategies for synthesizing larger shape-persistent organic cages in the future.

Incorporation of a new design of backing seat and anvil in a Merrill–Bassett diamond anvil cell

A modification to the Merrill–Bassett miniature diamond anvil cell is reported here, with the inclusion of tungsten carbide backing seats with Boehler–Almax-cut diamonds to replace the previously used beryllium seats and (typically) modified brilliant-cut anvils. This has led to the removal of troublesome beryllium powder lines from diffraction images, while maintaining the pressure range and opening angle of the original design.

Control of Porosity Geometry in Amino Acid Derived Nanoporous Materials

Substitution of the pillaring ligand in the homochiral open-framework [Ni(2)(L-asp)(2)(bipy)] by extended bipy-type ligands leads to a family of layer-structured, homochiral metal-organic frameworks. The 1D channel topology can be modified by the nature of the organic linker, with shape, cross-section and the chemical functionality tuneable. In addition, the volume of these channels can be increased by up to 36 % compared to the parent [Ni(2)(L-asp)(2)(bipy)]. The linker 1,4-dipyridylbenzene (3rbp) gives access to a new layered homochiral framework [Ni(2)(L-asp)(2)(3rbp)] with channels of a different shape. In specific cases, non-porous analogues with the linker also present as a guest can be activated to give porous materials after sublimation. Their CO(2) uptake shows an increase of up to 30 % with respect to the parent [Ni(2)(L-asp)(2)(bipy)] framework.

Chemical and Structural Stability of Zirconium‐based Metal–Organic Frameworks with Large Three‐Dimensional Pores by Linker Engineering

The synthesis of metal–organic frameworks with large three-dimensional channels that are permanently porous and chemically stable offers new opportunities in areas such as catalysis and separation. Two linkers (L1=4,4′,4′′,4′′′-([1,1′-biphenyl]-3,3′,5,5′-tetrayltetrakis(ethyne-2,1-diyl)) tetrabenzoic acid, L2=4,4′,4′′,4′′′-(pyrene-1,3,6,8-tetrayltetrakis(ethyne-2,1-diyl))tetrabenzoic acid) were used that have equivalent connectivity and dimensions but quite distinct torsional flexibility. With these, a solid solution material, [Zr6O4(OH)4(L1)2.6(L2)0.4]⋅(solvent)x, was formed that has three-dimensional crystalline permanent porosity with a surface area of over 4000 m2 g−1 that persists after immersion in water. These properties are not accessible for the isostructural phases made from the separate single linkers.

Cellular confocal fluorescence studies and cytotoxic activity of new Zn(II) bis(thiosemicarbazonato) complexes

We report the synthesis and characterisation of new, highly fluorescent, zinc complexes of bis(thiosemicarbazone) ligands incorporating extended aromatic backbones which are cytotoxic at levels comparable to cisplatin; cellular fluorescence imaging studies suggest these cause cell death by disruption of mitochondria.