Elastically flexible molecular crystals are an emerging class of advanced materials, driving innovation in fields ranging from electronics to medicinal applications. At the fundamental level, bulk material elasticity is governed by the nature of the intermolecular forces found in the material, which are not directly probed using structural (crystallographic) measurements. Low-frequency vibrational spectroscopy, on the other hand, directly interrogates these interactions, and is applied here to directly measure strain in the intermolecular coordinate in mechanically-bent crystals of copper (II) acetylacetonate (Cu(acac)2). This represents the first instance of a direct measurement of the modulation of intermolecular forces through bending strain, enabling identification of the particular coordinates involved in bulk elastic phenomena without the need for large-scale instrumentation such as synchrotrons. From such observations, it is possible to derive a thermodynamic picture of the forces that govern elastic crystals, which highlights the delicate interplay between stabilizing and destabilizing interactions within the material that promote the elastic phenomena in these crystals.

Solute binding proteins can capture strongly hydrated substrates from water with high affinity. Notable examples are the sulfate binding proteins (SBPs), which use neutral NH and OH groups to stabilize highly charged sulfate anions without salt-bridge formation. Synthetic receptors are yet to achieve comparable capabilities solely by hydrogen bonds or other ion-dipole interactions. Here we report charge-neutral urea cages which have strong affinities for CrO42–, SO42– and Cl– up to micromolar and sub-micromolar levels in water, with tunable anion selectivity based on size match. This is despite the fact that these urea cages are much smaller than proteins and have their anion binding sites exposed to water, demonstrating synthetic receptors’ hydrogen bonding potency that emulates nature’s anion binders.

Starting in the Australian 2015 summer, the Australian supramolecular chemistry community has held annual student-focused conferences. These started as very informal gatherings but over time have become more established and very slightly more formal. Spurred in part by these meetings, The Royal Australian Chemical Institute (RACI)'s Supramolecular Division was established in 2022 to recognise and support the growing supramolecular chemistry community in Australia. This article describes the genesis of these student-focused conferences, the founding of the RACI Supramolecular Division, and summarises the recent Supramol25 conference held in Canberra.

Elasticity is ubiquitous and produces a spontaneously reversible response to applied stress1. Despite the utility and importance of this property in regard to scientific and engineering applications, the atomic-scale location of the force that returns an object to its original shape remains elusive in molecular crystals. Here we use a series of density functional theory calculations to locate precisely where the energy is stored when single crystals of three molecular materials are placed under elastic stress. We show for each material that different intermolecular interactions are responsible for the restoring force under both expansive and compressive strain. These findings provide insight into the elastic behaviour of crystalline materials that is needed for more efficient design of flexible technologies and future smart devices.

In biological systems, enzymes and transport proteins can bind anions in aqueous media solely by forming hydrogen bonds with charge-neutral motifs. Reproducing this functionality in synthetic systems presents challenges and incurs high costs, particularly when targeting strongly hydrated anions such as sulfate. Here we report a [2.2.2]urea cryptand (cage), synthesized in one pot, that selectively binds sulfate in a mixture of dimethyl sulfoxide and water and in water with affinities in the micromolar to millimolar range. The neutral cage bearing six urea groups donates 12 strong hydrogen bonds to encapsulate a sulfate anion, showing favourable enthalpy even in pure water. Sulfate binding can be further enhanced by using micelles to provide a low-polarity microenvironment. The cage finds utility in analysing divalent anions in water and beverage samples or in removing sulfate. The work demonstrates the achievability of robust and selective anion binding in water with minimal synthetic efforts, by using neutral NH hydrogen bonds akin to those found in biology.

Three new complexes of a tetrabenzotetraza-crown ether macrocyclic ligand (L) with Cd(II) chloride (1), iodide (2), and acetate (3) salts were synthesized and characterized by FT-IR, H-1 NMR spectroscopy, elemental microanalysis, and single crystal X-ray diffraction. Complex 1 has the formula [Cd(L)Cl](2) [CdCl4] with two square pyramidal [Cd(L)Cl](+) subunits interconnected through the CdCl42- counter anion. Meanwhile, the reaction with CdI2 produces the discrete complex [Cd(L)I]I (2) with an octahedral geometry about the Cd(II) center. A distorted six-coordinated asymmetric unit was observed for [Cd(L)OAc](2)(OAcH2O)(2) (3), wherein two [Cd(L)OAc](+) subunits are held together by a flat (OAcH2O)(2) acetate-water cluster. Hirshfeld Surface calculations were applied to confirm the dominant interactions in 1-3, namely pi-pi, and X & ctdot;H/H & ctdot;X (X-H, C, O, and halogen) interactions as the main factors for their structural differences. At the same time, the structure of [Cd(L)L '](+) (L ' = Cl, I, and OAc) core remained almost unchanged. The Cd(II) coordination with L in the presence of different Cd(II) salts was followed by H-1 NMR spectroscopy. All three Cd(II) salt displays 1:1 stoichiometry, with binding constants in the order CdCl2 < CdI2 < Cd(OAc)(2).

Unequivocally establishing chemical connectivity and ultimately chemical identity is of central importance to all branches of science and particularly chemistry. Accordingly, the determination of a crystal structure is often considered the "gold standard" as this technique can unambiguously establish both the connectivity and identity of a compound. Crystal structure data, however, are prone to misinterpretation, and the increasing development of automatic data processing and verification has the potential to result in an epidemic of incorrectly modeled crystal structures. Here, we present a series of case studies where structures were modeled to current publication standards with the incorrect chemical composition. It is essential that researchers, referees, editors, and the scientific community be vigilant in upholding the scientific method.

Through coordination-driven self-assembly, aesthetically captivating structures can be formed by tuning the length or flexibility of various components. The self-assembly of an elongated rigid terphenyl-based tetra-pyridyl ligand ( L1 ) with a cis-Pd(II) acceptor produces an [M 12 L1 6 ] 24+ triangular orthobicupola structure ( 1 ). When flexibility is introduced into the ligand by the incorporation of a -CH 2 - group between the dipyridylamine and terphenyl rings in the ligand ( L2 ), anunique [M 8 L2 4 ] 16+ water-soluble ‘intertwined cubic structure’ ( 2 ) results. The inherent flexibility of ligand L2 might be the key factor behind the formation of the thermodynamically stable and ′intertwined cubic structure′ in this scenario. This research showcases the ability to design and fabricate novel, topologically distinctive molecular structures by a straightforward and efficient approach.

Catalytic transfer hydrogenation of furfural is an environmentally friendly approach for the production of biofuels such as 2-methylfuran (2-MF). The presence of both metallic and Lewis acid sites in the catalyst is required to produce 2-MF by this process. However, the inherent unstable nature of these catalytic sites poses a significant challenge to controlling their stoichiometry. Herein, we report the preparation of a highly active and robust catalyst through the pyrolysis of a Cu-BTC metal-organic framework under controlled conditions. This catalyst exhibits outstanding performance in furfural transfer hydrogenation using isopropyl alcohol as the hydrogen donor. Under optimized conditions of 250 degrees C and 5 bar, we achieved 100% furfural conversion with a 77% selectivity toward 2-MF after 6 h reaction time by using Cu-BTC pyrolyzed at 310 degrees C as a catalyst. The observed superior activity could be attributed to the presence of both Cu(I) and Cu(0) sites in the catalyst, in combination with high acidic site concentrations. This work introduces a facile method for establishing a stable coexistence of metallic and acid sites in Cu-based catalysts, showcasing its potential for advancing sustainable biofuel production. Notably, this strategic catalyst design opens avenues for broader applications in sustainable catalysis.

Molecular hosts with functional cavities can emulate enzymatic behavior through selective encapsulation of substrates, resulting in high chemo-, regio-, and stereoselective product formation. It is still challenging to synthesize enzyme-mimicking hosts that exhibit a narrow substrate scope that relies upon the recognition of substrates based on the molecular size. Herein, we introduce a Pd-4 self-assembled water-soluble molecular capsule [M4L2] (MC) that was formed through the self-assembly of a ligand L (4 ',4 & tprime;'-(1,4-phenylene)bis(1 ',4 '-dihydro-[4,2 ':6 ',4 ''-terpyridine]-3 ',5 '-dicarbonitrile)) with the acceptor cis-[(en)Pd(NO3)(2)] [en = ethane-1,2-diamine] (M). The molecular capsule MC showed size-selective recognition towards xylene isomers. The redox property of MC was explored for efficient and selective oxidation of one of the alkyl groups of m-xylene and p-xylene to their corresponding toluic acids using molecular O-2 as an oxidant upon photoirradiation. Employing host-guest chemistry, we demonstrate the homogeneous catalysis of alkyl aromatics to the corresponding monocarboxylic acids in water under mild conditions. Despite homogeneous catalysis, the products were separated from the reaction mixtures by simple filtration/extraction, and the catalyst was reused. The larger analogues of the alkyl aromatics failed to bind within the MC's hydrophobic cavity, resulting in a lower/negligible reaction outcome. The present study represents a facile approach for selective photo-oxidation of xylene isomers to their corresponding toluic acids in an aqueous medium under mild conditions.

In order to bind guest molecules with exquisite selectivity, biological host molecules often employ low symmetry binding pockets. The majority of metallosupramolecular assemblies, however, rely on symmetrical ligands to form high-symmetry assemblies that enclosing similarly symmetrical cavities. Here we employ an unsymmetrical quaterpyridine ligand in combination with cobalt(ii) to form a mixture of low-symmetry [M2L3] helicates and [M4L6] tetrahedra and their subsequent oxidation to Co(iii)-containing assemblies.

A facile route to spiro-γ-lactams containing fused seven- and five-membered rings is showcased here in a multicomponent reaction harnessing glycine. Four spiro-γ-lactams were characterised, including by X-ray diffraction techniques, showing them to be trapped unstable intermediates of the Strecker degradation. This hitherto unknown reaction pathway was investigated with mass spectrometry, revealing a plausible reaction mechanism.

Research on the synthesis of catenated cages has been a growing field of interest in the past few years. While multiple types of catenated cages with different structures have been synthesized, the application of such systems has been much less explored. Specifically, the use of catenated cages in the separation of industrially relevant molecules that are present in coal tar has not been explored before. Herein, we demonstrate the use of a newly synthesized interlocked cage 1 [C184H240N76O48Pd6] (M6L4), formed through the self-assembly of ligand L.HNO3 (tris(4-(1H-imidazole-1-yl)benzylidene)hydrazine-1-carbohydrazonhydrazide) with acceptor cis-[(tmchda)Pd(NO3)(2)] [tmchda = +/- N,N,N ',N '-tetramethylcyclohexane-1,2-diamine] (M). The interlocked cage 1 was able to separate the isomers (anthracene and phenanthrene) using a simple solvent extraction technique. Using the same technique, the much more difficult separation of structurally and physiochemically similar compounds acenaphthene and acenaphthylene was performed for the first time with 1 as the host. Other noninterlocked hexanuclear Pd-6 cages having a wider cavity proved inefficient for such separation, demonstrating the uniqueness of the interlocked cage 1 for such challenging separation.

The structural dynamics involved in the mechanical flexibility of molecular crystals are not well understood yet. Here, we report an elastically bending lipidated molecular crystal that shows systematic shifts in characteristic vibrational frequencies across the bent crystal region - revealing the nature of structural changes during bending and the local internal stress distribution. The elastic flexibility is rendered by intermolecular N-H∙∙∙O hydrogen-bonded chains along with strong yet flexible alkyl-chain hydrophobic interactions in this crystal structure. The blue shifts in the bond stretching modes (such as C=O and C-H modes) in the inner arc region and red shifts in the outer arc region of the bent crystals observed via micro-Raman mapping are counterintuitive to the bending models based on intermolecular hydrogen bonds. Correlating these shifts with the trends observed from high-pressure Raman studies on the crystal reveals the local stress difference between the inner arc and outer arc regions of the bent crystal to be ~2 GPa, more than an order of magnitude higher than the previously proposed value in elastically bending crystals. High local internal stress can have direct ramifications on the properties of molecular piezoelectric energy harvesters, actuators, semiconductors, and flexible optoelectronic materials.

The production of 2-methylfuran (2-MF) through catalytic transfer hydrogenation of furfural is a promising avenue in biomass-derived chemical synthesis. This process offers an environmentally friendly and cost-effective alternative to the conventional furfural hydrogenation processes, which are burdened by high operational costs, safety concerns and environmental impacts. Despite substantial research advances, the commercialization of transfer hydrogenation faces complexities requiring a systematic exploration for practical implementation. This comprehensive review examines the multifaceted factors influencing 2-MF synthesis from furfural. A primary focus lies in juxtaposing catalyst and H-donor properties, process conditions and reactor configurations on the production of 2-MF. Catalyst properties, including surface area, acidic site concentration, oxophilicity and isoelectric point, emerge as pivotal determinants of the efficiency of the process. Concurrently, the hydrogen release capacity of H-donors emphasises the contributions of redox potential, polarity and carbon chain length, amongst other properties. Reactor configurations and operational conditions such as temperature, duration, and substrate quantity wield considerable influence over 2-MF yield and furfural conversion. Challenges with regard to scalability, economics and sustainability are highlighted, underscoring the need for innovative catalyst designs, efficient reactor setups, and strategic process establishment to enable industrial adoption. The intricate interplay of these factors necessitates in-depth exploration to produce innovative solutions to unlock the full potential of 2-MF synthesis via catalytic transfer hydrogenation of furfural for industrial-scale implementation.

Strongly hydrated anions are challenging targets for molecular receptors. In nature, sulfate binding proteins use multiple neutral NH hydrogen bonds to surround the guest, resulting in sub-millimolar to sub-micromolar sulfate affinities. Synthetic receptors, however, have not yet achieved comparable efficiency and selectivity for sulfate solely by relying on hydrogen bonds or other ion-dipole interactions. Here we report charge-neutral macrotricyclic hexa-urea cages which exhibit strong sulfate affinities (6000 to 9000 M–1) in water with exceptional selectivity over hydrophobic anions. Unlike sulfate binding proteins where a low-polarity microenvironment enhances sulfate binding, the urea cages achieve high sulfate affinities with the urea binding sites exposed to water. The work demonstrates that synthetic receptors operating solely by neutral hydrogen bond donors can emulate the efficiency and selectivity of naturally occurring systems.

The majority of reported metallo-supramolecules are highly symmetric homoleptic assemblies of M x L y type, with a few reports on assemblies that are obtained using multicomponent self-assembly or using ambidentate ligands. Herein, we report the use of an unsymmetrical tetratopic ligand (Lun) containing pyridyl and imidazole donor sites in combination with a cis-protected Pd(ii) acceptor for the formation of a low-symmetry M8Lun 4 molecular barrel (UNMB). Four potential orientational isomeric (HHHH, HHHT, HHTT, and HTHT) molecular barrels can be anticipated for the M8Lun 4 type metallo-assemblies. However, the formation of an orientational isomer (HHTT) of the barrel was suggested from single-crystal X-ray diffraction and 1H NMR analysis of UNMB. Two large open apertures at terminals and the hydrophobic confined space surrounded by four aromatic panels of Lun make UNMB a potential host for bigger guests. UNMB encapsulates fullerenes C70 and C60 favoured by non-covalent interactions between the fullerenes and aromatic panels of the ligand molecules. Experimental and theoretical studies revealed that UNMB has the ability to bind C70 more strongly than its lower analogue C60. The stronger affinity of UNMB towards C70 was exploited to separate C70 from an equimolar mixture of C70 and C60. Moreover, C70 can be extracted from the C70⊂UNMB complex by toluene, and therefore, UNMB can be reused as a recyclable separating agent for C70 extraction.

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).

In this work, a detailed Hammett structure-structure correlation was applied to a range of chalcogen bonded co-crystals prepared by combining 4′-substituted derivatives of the selenium-based drug ebselen with three different 4-amino-substituted pyridine based chalcogen bond acceptors of differing basicities. This established that the N · · · Se chalcogen bond distance is well within the sum of the van der Waals radii of Se and N and is sensitive to the electronic nature of the substituent. Thus N · · · Se distances ranging from 2.2424(5)–2.4496(9) Å were observed with the shorter distances being observed in co-crystals of ebselen substituted with electron withdrawing groups. Associated with trends of the N · · · Se distance as a function of the 4′-substituent was lengthening of the internal Se−N bond distance consistent with a significant covalent contribution to N · · · Se chalcogen bonding in these derivatives. We define a covalency quotient for the chalcogen bond as the negative slope of the plot of the internal Se−N bond distance vs the external N · · · Se chalcogen bond distance. A value of 0.31 was obtained implying a significant covalent contribution to N · · · Se chalcogen bond. A similar result was obtained by an analysis of chalcogen bonded selenium containing molecules harvested from the Cambridge Crystallographic Database. The covalency quotient is extended to the general case for sigma-hole interactions including halogen bonding and hydrogen bonding, and we show that the covalent component of such interactions can be inferred from the lengthening of the donor bond. The degree of charge transfer in a smaller number of chalcogen bonded co-crystals of ebselen was established by measuring experimental electron density using high-resolution x-ray diffraction to more accurately measure the degree of electron transfer and hence covalency. This showed that in the most strongly bound systems, up to 1 electron worth of charge is transferred from the Lewis base to the Ch-bond donor, which again clearly points to significant covalent character.