Remote stereocentres do not disrupt the stereochemical coupling in homochiral [M2L3] helicates and [M4L6] tetrahedra.

Despite the use of achiral ligands, the vast majority of metallosupramolecular assemblies containing octahedral tris-bidentate metal centres show strong stereochemical communication between metal centres, generally resulting in homochiral assemblies even though they are statistically disfavoured. Here we show that when resolved stereocentres are attached to the central part of a quaterpyridine ligand, the stereochemical coupling from this centre is insufficient to disrupt the strong stereochemical communication between metal centres in both [M2L3] helicates and [M4L6] tetrahedra.

Diastereomer Resolution of M4 L6 Coordination Cages by Ultra-High-Resolution Ion-Mobility Mass Spectrometry.

Coordination cages can be used for enantio- and regioselective catalysis and for the selective sensing and separation of isomeric guest molecules. Here, stereoisomers of a family of coordination cages are resolved using ultra-high-resolution cyclic ion-mobility mass spectrometry (cIM-MS). The observed ratio of diastereomers is dependent on both the metal ion and counter ion. Moreover, the point groups can be assigned through complementary NMR experiments. This method enables the identification and interrogation of the individual isomers in complex mixtures of cages which cannot be performed in solution. Furthermore, these techniques allow the stability of individual isomers within the mixture to be probed, with the T-symmetric isomers in this case shown to be more robust than the C3 and S4 analogues.

Crystals of Aliphatic Derivatives of [Cu(acac)2 ] have Distinct Atomic-Scale Mechanisms of Bending.

Molecular crystals displaying elastic flexibility have important applications in the fields of optoelectronics and nanophotonic technologies. Understanding the mechanisms by which these materials bend is critical to the design of future materials incorporating these properties. Based on the known elastic properties of bis(acetylacetonato)copper(II), a series of 14 aliphatic derivatives are synthesized and crystallized. All those which grew in a needle morphology display noticeable elasticity, with 1D chains of π-stacked molecules parallel to the long metric length of the crystal a consistent crystallographic feature. Crystallographic mapping is used to measure the mechanism of elasticity at an atomic-scale. Symmetric derivatives with ethyl and propyl side chains are found to have different mechanisms of elasticity, which are further distinguished from the previously reported mechanism of bis(acetylacetonato)copper(II). While crystals of bis(acetylacetonato)copper(II) are known to bend elastically via a molecular rotation mechanism, the elasticity of the compounds presented is facilitated by expansion of their π-stacking interactions.

Plastic Deformation in a Molecular Crystal Enables a Piezoresistive Response.

Organic materials are promising candidates for the development of efficient sensors for many medicinal and materials science applications. Single crystals of a small molecule, 4-trifluoromethyl phenyl isothiocyanate (4CFNCS), exhibit plastic deformation when bent, twisted, or coiled. Synchrotron micro-focus X-ray diffraction mapping of the bent region of the crystal confirms the mechanism of deformation. The crystals are incorporated into a flexible piezoresistive sensor using a composite constituting PEDOT: PSS/4CFNCS, which shows an impressive performance at high-pressure ranges (sensitivity 0.08 kPa-1 above 44 kPa).

Exploring the Gas-Phase Formation and Chemical Reactivity of Highly Reduced M8 L6 Coordination Cages.

Coordination cages with well-defined cavities show great promise in the field of catalysis on account of their unique combination of molecular confinement effects and transition-metal redox chemistry. Here, three coordination cages are reduced from their native 16+ oxidation state to the 2+ state in the gas phase without observable structural degradation. Using this method, the reaction rate constants for each reduction step were determined, with no noticeable differences arising following either the incorporation of a C60 -fullerene guest or alteration of the cage chemical structure. The reactivity of highly reduced cage species toward molecular oxygen is "switched-on" after a threshold number of reduction steps, which is influenced by guest molecules and the structure of cage components. These new experimental approaches provide a unique window to explore the chemistry of highly-reduced cage species that can be modulated by altering their structures and encapsulated guest species.

Reactions of sulfoxides with reactive oxygen species to reveal the radical chemistry of pollution-derived particulate matter.

The radical reactions of dimethylsulfoxide (DMSO) and tetrahydrothiophene-1-oxide (THTO) with reactive oxygen species (ROS) in the presence of a nitroxide radical scavenger have been evaluated both synthetically and in analytical practice. Fenton-mediated generation of oxygen-centred radicals produced several unusual products that reflect the fragmentation and ring-opening radical mechanisms of DMSO and THTO respectively. Addition of pollution-derived ROS to DMSO/THTO nitroxide solutions produced LC-MS detectable amounts of the same products isolated from the larger-scaled Fenton reactions. For air pollution analysis, these results highlight the complexity surrounding DMSO reactivity and fragmentation, and indicate that THTO produces simpler outcomes that should facilitate analysis of the processes involved.

Sterics and metal-ion radius control the self-assembly of [M2L3] helicates.

The interplay of many factors influences the outcomes of self-assembly reactions. Using an acetylene-appended quaterpyridine ligand we show that both the size of the metal ion and the presence of steric repulsion between the acetylene groups result in the exclusive formation of [M2L3] helicates rather than a helicate/tetrahedron equilibrium.

Controlling the Complexity and Interconversion Mechanisms in Self-Assembled [Fe2 L3 ]4+ Helicates and [Fe4 L6 ]8+ Cages.

Self-assembled coordination cages and metal-organic frameworks have relied extensively on symmetric ligands in their formation. Here we have prepared a relatively simple system employing an unsymmetric ligand that results in two distinct self-assembled structures, a [Fe2 L3 ]4+ helicate and a [Fe4 L6 ]8+ cage composed of 10 interconverting diastereomers and their enantiomers. We show that the steric profile of the ligand controls the complexity, thermodynamics and kinetics of interconversion of the system.

Unconventional, Gram-Scale Synthesis of a Molecular Dimer Organic Luminogen with Aggregation-Induced Emission.

Organic luminogens have been widely used in optoelectronic devices, bioimaging, and sensing. Conventionally, the synthesis of organic luminogens requires sophisticated, multistep design, reaction, and isolation procedures. Herein, the products of the melt-phase condensation of benzoguanamine (BG; 2,4-diamino-6-phenyl-1,3,5-triazine) at 370-410 °C display interesting reaction-condition-dependent luminescence properties, including photoluminescence (PL) at a variety of wavelengths in the visible spectrum and quantum efficiencies (PLQE) of up to 58% in the powder form. With a simple and straightforward solvent washing procedure, the prominent blue luminescent component BG dimer was obtained in gram scale with >93% purity (96.5% purity after fractional sublimation). The BG dimer exhibited distinct aggregation-induced emission (AIE) properties. PL measurements indicate that the electronically excited state of the BG dimer undergoes efficient intramolecular nonradiative deactivation in room-temperature solution, leading to a significantly reduced PLQE (<0.1%) in solution. These nonradiative processes are substantially inhibited when the dimer existed in the form of crystals, solid aggregates in solution or being fixed in a rigid polymer film, resulting in a significant increase in the PLQE and lifetime. This work not only provided a new understanding for PL properties of self-condensation luminescent products but also represented an unconventional strategy for large-scale preparation of organic luminogens with high purity.

A Self-Catalyzed Visible Light Driven Thiol Ligation.

We introduce a highly efficient ligation system based on a visible light-induced rearrangement affording a thiophenol which rapidly undergoes thiol-Michael additions. Unlike conventional light-triggered thiol-ene/yne systems, which rely on the use of photocaged bases/nucleophiles, (organo)-photo catalysts, or radical photoinitiators, our system provides a light-induced reaction in the absence of any additives. The ligation is self-catalyzed via the pyridine mediated deprotonation of the photochemically generated thiophenol. Subsequently, the thiol-Michael reaction between the thiophenol anion and electron deficient alkynes/alkenes proceeds additive-free. Hereby, the underlying photoinduced rearrangement of o-thiopyrinidylbenzaldehyde (oTPyB) generating the free thiol is described for the first time. We studied the influence of various reactions conditions as well as solvents and substrates. We exemplify our findings in a polymer end group modification and obtained macromolecules with excellent end group fidelity.

Supramolecular Modulation of Spin Crossover in an Fe(II) Dinuclear Triple Helicate.

A spin-crossover (SCO) active dinuclear Fe(II) triple helicate of the form [Fe2L3]4+ was combined with additional supramolecular components in order to manipulate the interhelical separation and steric congestion and to study the magneto-structural effects on the ensuing composite materials. A more separated array of SCO units produced more extensive spin-transitions, while a tightly arranged lattice environment stabilized the low-spin state. This study highlights the important interplay between crystal packing, intermolecualr interactions, and the magentic behavior of SCO materials.

Comment on "Trimorphs of 4-bromophenyl 4-bromobenzoate. Elastic, brittle, plastic" by S. Saha and G. R. Desiraju, Chem. Commun., 2018, 54, 6348.

A re-refinement of the published but chemically implausible, crystal structure of "Form III" of 4-bromophenyl 4-bromobenzoate shows that it is not a polymorph, but instead a co-crystal containing both 4-bromophenyl 4-bromobenzoate (≈25%) and likely 4-bromophenyl 4-nitrobenzoate (≈75%).

The kinetics and mechanism of interconversion within a system of [Fe2L3]4+ helicates and [Fe4L6]8+ cages.

Nature builds simple molecules into highly complex assemblies, which are involved in all fundamental processes of life. Some of the most intriguing biological assemblies are those that can be precisely reconfigured to achieve different functions using the same building blocks. Understanding the reconfiguration of synthetic self-assembled systems will allow us to better understand the complexity of proteins and design useful artificial chemical systems. Here we have prepared a relatively simple system in which two distinct self-assembled structures, a [Fe2L3]4+ helicate and a [Fe4L6]8+ cage that are formed from the same precursors, coexist at equilibrium. We have measured the rates of interconversion of these two species and propose a mechanism for the transformation.

Wavelength-Gated Photochemical Synthesis of Phenalene Diimides.

Herein, we pioneer a wavelength-gated synthesis route to phenalene diimides. Consecutive Diels-Alder reactions of methylisophthalaldehydes and maleimides afford hexahydro-phenalene-1,6-diol diimides via 5-formyl-hexahydro-benzo[f]isoindoles as the intermediate. Both photoreactions are efficient (82-99 % yield) and exhibit excellent diastereoselectivity (62-98 % d.r.). The wavelength-gated nature of the stepwise reaction enables the modular construction of phenalene diimide scaffolds by choice of substrate and wavelength. Importantly, this synthetic methodology opens a facile avenue to a new class of persistent phenalenyl diimide neutral radicals, constituting a versatile route to spin-active molecules.

The mechanism of bending in a plastically flexible crystal.

Mechanically adaptable molecular crystals have potential applications in flexible smart materials and devices. Here, we report the mechanism of plastic deformation in single crystals of a small organic molecule (N-(4-ethynylphenyl)-3-fluoro-4-(trifluoromethyl)benzamide) that can be repeatedly irreversibly bent and returned to its original shape without concomitant delamination or loss of integrity. Along with the quantification of the crystals' local and bulk mechanical properties (hardness, indentation modulus and Young's modulus), micro-focus synchrotron X-ray diffraction mapping show that upon deformation, molecular layers lined with trifluoromethyl groups cooperatively slip past one another resulting in their impressive plastic malleability.

Elastically Flexible Crystals have Disparate Mechanisms of Molecular Movement Induced by Strain and Heat.

Elastically flexible crystals form an emerging class of materials that exhibit a range of notable properties. The mechanism of thermal expansion in flexible crystals of bis(acetylacetonato)copper(II) is compared with the mechanism of molecular motion induced by bending and it is demonstrated that the two mechanisms are distinct. Upon bending, individual molecules within the crystal structure reversibly rotate, while thermal expansion results predominantly in an increase in intermolecular separations with only minor changes to molecular orientation through rotation.

A three-dimensional cubic halogen-bonded network.

The rational, deliberate design of supramolecular architectures is of great importance for the discovery of complex materials. A three-dimensional cubic halogen-bonded network has been prepared by combination of an octahedral metal-containing halogen bond acceptor and a linear ditopic donor. This material displays α-Po pcu topology and is seven-fold interpenetrated. This is the first neutral, metal-containing three-dimensional halogen-bonded network to be reported.