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Singlet fission is a photophysical process that provides a pathway for more efficient harvesting of solar energy in photovoltaic devices. The design of singlet fission candidates is non-trivial and requires careful optimization of two key criteria: (1) correct energetic alignment and (2) appropriate intermolecular coupling. Meanwhile, this optimization must not come at the cost of molecular stability or feasibility for device applications. Cibalackrot is a historic and stable organic dye which, although it has been suggested to have ideal energetics, does not undergo singlet fission due to large interchromophore distances, as suggested by single crystal analysis. Thus, while the energetic alignment is satisfactory, the molecule does not have the desired intermolecular coupling. Herein, we improve this characteristic through molecular engineering with the first synthesis of an aza-cibalackrot and show, using ultrafast transient spectroscopy, that singlet fission is successfully "turned on."

Atomic force microscopy is used as a characterisation tool to investigate cocrystal dissociation under high relative humidity. Caffeine–glutaric acid as a model system showed possible role of crystal surface defects in the process of cocrystal dissociation.

Crystal engineering has, so far, exclusively focused on the development of advanced materials based on small organic molecules. We demonstrate how the cocrystallization of a polymer significantly enhances its thermal stability without compromising its mechanical flexibility, while isomorphous replacement of one of the cocrystal components enables the formation of solid solutions with melting points that can be readily fine-tuned over a practically wide temperature range. The results of this study credibly extend the scope of crystal engineering and cocrystallization from small molecules to polymers.

The one-dimensional (1-D) coordination polymer [Ni(bdc)(pico)2(H2O)2] (where bdc = terephthalate, pico = 4-picoline) is hosted within a two-dimensional (2-D) hydrogen-bonded grid [Ni(bdc)(pico)2(H2...

Intermolecular interactions play a fundamental role on the performance of conjugated materials in organic electronic devices, as they heavily influence their optoelectronic properties. Synthetic control over the solid state properties of organic optoelectronic materials is crucial to access real life applications. Perylene diimides (PDIs) are one of the most highly studied classes of organic fluorescent dyes. In the solid state, π-π stacking suppresses their emission, limiting their use in a variety of applications. Here, we report the synthesis of a novel PDI dye that is encapsulated by four alkylene straps. X-ray crystallography indicates that intermolecular π-π stacking is completely suppressed in the crystalline state. This is further validated by the photophysical properties of the dye in both solution and solid state and supported by theoretical calculations. However, we find that the introduction of the encapsulating "arms" results in the creation of charge-transfer states which modify the excited state properties. This article demonstrates that molecular encapsulation can be used as a powerful tool to tune intermolecular interactions and thereby gain an extra level of control over the solid state properties of organic optoelectronic materials.

We demonstrate that liquid additives can exert inhibitive or prohibitive effects on the mechanochemical formation of multi-component molecular crystals, and report that certain additives unexpectedly prompt the dismantling of such solids into physical mixtures of their constituents. Computational methods were employed in an attempt to identify possible reasons for these previously unrecognised effects of liquid additives on mechanochemical transformations., Liquid additives can exert catalytic, inhibitive or prohibitive effects on the mechanochemical formation of multi-component molecular crystals.

A structural study of two-dimensional inverted metal–organic frameworks demonstrates that the interior cavities of the framework structures can be systematically modified by changing the organic anion of a Cu(II)-paddlewheel unit. Changing the anion allows modifications to the shapes and sizes of the cavities in a series of isoreticular frameworks. The construction of the frameworks is based on the application of a tetrafunctional organic cyclobutane ligand synthesized in the organic solid state.

Co‐crystallisation is widely explored as a route to improve the physical properties of pharmaceutical active ingredients, but little is known about the fundamental mechanisms of the process. Herein, we apply a hyphenated differential scanning calorimetry—X‐ray diffraction technique to mimic the commercial hot melt extrusion process, and explore the heat‐induced synthesis of a series of new co‐crystals containing isonicotinamide. These comprise a 1:1 co‐crystal with 4‐hydroxybenzoic acid, 2:1 and 1:2 systems with 4‐hydroxyphenylacetic acid and a 1:1 crystal with 3,4‐dihydroxyphenylactic acid. The formation of co‐crystals during heating is complex mechanistically. In addition to co‐crystallisation, conversions between polymorphs of the co‐former starting materials and co‐crystal products are also observed. A subsequent study exploring the use of inkjet printing and milling to generate co‐crystals revealed that the synthetic approach has a major effect on the co‐crystal species and polymorphs produced., Co‐crystallisation is widely explored as a route to improve the physical properties of pharmaceutical active ingredients, but little is known about the fundamental mechanisms of the process. In this study, X‐ray diffraction was used to provide an unprecedented insight into pharmaceutical co‐crystallisation processes (see figure).

An introduction to the virtual special issue in honor of Prof. William Jones, wherein the authors reflect on his scientific career and his many outstanding contributions to organic solid-state chemistry.

The Strecker reaction is thought to offer a prebiotically plausible synthesis of amino acids, but is reversible at the high or low pH ranges needed to promote reactivity. Here the reaction of hydrogen cyanide and diamidophosphate is shown to provide stable phosphorylated amino acid precursors at neutral pH, which can be hydrolysed to amino acids or thiolysed to thioamides.

This Tutorial Review, aimed at both the novice and the seasoned solid-state chemist, provides a succinct overview of key findings that have, over the last half century, advanced our ability to make molecular crystals with targeted structures and desired properties. The article critically evaluates the efficiency and reliability of the well-established guidelines used by experimentalists in crystal engineering and highlights statistical and computational tools that are both advantageous to crystal design and accessible to experimental solid-state chemists.

A personal account of the hurdles encountered when studying each of the aspects of crystal engineering, namely, designing, building, and using crystal structures. Examples are given to illustrate the “backbreaking” nature of the crystal engineering endeavor, as well as the limitations of our current abilities to understand, engineer, and maintain molecular crystals.

The inability to obtain a crystal form that has previously been reliably prepared is an important concern for industrial solid-state scientists. In the present study, we extend further the evidence that such a phenomenon also applies to cocrystals. Specifically, we report further on the apparent "disappearing polymorphs" of a cocrystal composed of caffeine and citric acid. This study commenced at the University of Cambridge with the initial aim of gaining insight into the mechanisms associated with the mechanochemical formation of the known caffeine-citric-acid cocrystal, namely, Form I. A second polymorph, Form II, was later prepared mechanochemically through neat grinding, making it seemingly impossible to reproduce Form I in the same laboratory. Subsequent studies also resulted in the mechanochemical formation of another polymorph, Form III, for which no structural characterization has yet been possible. We therefore also focus on the understanding of the factors contributing to the inability to reproduce Form I after another polymorph has been obtained. Experiments were then extended to two other laboratories within different UK universities (De Montfort University Leicester and University College London) and revealed that, depending on the "apparent" level of contamination of a specific laboratory, different polymorphs can be obtained, but only one of them at any period of time. The inability to predict, control, and understand disappearing polymorphs remains a frustrating experience - even 25 years after Dunitz and Bernstein first stated that "we are far from being able to present a theory of disappearing polymorphs". In this context, we reason that a first step forward would consist of reporting comprehensive and detailed accounts for every example of apparently disappearing polymorphs, with the hope of finding similarities that can subsequently result in a better understanding and possible rationalization of the puzzling phenomenon of disappearing polymorphs. We here report what we know so far of the intriguing caffeine-citric-acid cocrystal system.

A central problem for the prebiotic synthesis of biological amino acids and nucleotides is to avoid the concomitant synthesis of undesired or irrelevant by-products. Additionally, multistep pathways require mechanisms that enable the sequential addition of reactants and purification of intermediates that are consistent with reasonable geochemical scenarios. Here, we show that 2-aminothiazole reacts selectively with two- and three-carbon sugars (glycolaldehyde and glyceraldehyde, respectively), which results in their accumulation and purification as stable crystalline aminals. This permits ribonucleotide synthesis, even from complex sugar mixtures. Remarkably, aminal formation also overcomes the thermodynamically favoured isomerization of glyceraldehyde into dihydroxyacetone because only the aminal of glyceraldehyde separates from the equilibrating mixture. Finally, we show that aminal formation provides a novel pathway to amino acids that avoids the synthesis of the non-proteinogenic α,α-disubstituted analogues. The common physicochemical mechanism that controls the proteinogenic amino acid and ribonucleotide assembly from prebiotic mixtures suggests that these essential classes of metabolite had a unified chemical origin.

A crystal growth technique, interfacial cocrystallization, is demonstrated to be a simple and effective method for preparing multicomponent crystal forms. The technique is based on the generation of a liquid–liquid interface between two immiscible solutions of cocrystal-forming compounds, and its utility is demonstrated through the preparation of polymorphs and hydrates of caffeine cocrystals, involving three different hydroxy-2-naphthoic acids, including the formation of some with unexpected compositions.

A correlation between Young's modulus, as determined by using nanoindentation atomic force microscopy (AFM), and atomic polarizability is observed for members of a series of cocrystals based on systematic changes to one cocrystal component. Time domain spectroscopy over terahertz frequencies (THz-TDS) is used for the first time to directly measure the polarizability of macro- and nanosized organic solids. Cocrystals of both macro- and nanodimensions with highly polarizable atoms result in softer solids and correspondingly higher polarizabilities.

L-Arabinose is an abundant resource available as a waste product of the sugar beet industry. Through use of a hydrazone-based strategy, L-arabinose was selectively dehydrated to form a chiral tetrahydrofuran on a multi-gram scale without the need for protecting groups. This approach was extended to other biomass-derived reducing sugars and the mechanism of the key cyclization investigated. This methodology was applied to the synthesis of a range of functionalized chiral tetrahydrofurans, as well as a formal synthesis of 3R-3-hydroxymuscarine.

We present the synthesis and characterization of a series of encapsulated diketopyrrolopyrrole red-emitting conjugated polymers. The novel materials display extremely high fluorescence quantum yields in both solution (>70%) and thin film (>20%). Both the absorption and emission spectra show clearer, more defined features compared to their naked counterparts demonstrating the suppression of inter and intramolecular aggregation. We find that the encapsulation results in decreased energetic disorder and a dramatic increase in backbone colinearity as evidenced by scanning tunnelling microscopy. This study paves the way for diketopyrrolopyrrole to be used in emissive solid state applications and demonstrates a novel method to reduce structural disorder in conjugated polymers.

The [4+2] cycloaddition of 3-alkoxyfurans with N-substituted maleimides provides the first general route for preparing endo-cantharimides. Unlike the corresponding reaction with 3H furans, the reaction can tolerate a broad range of 2-substitued furans including alkyl, aromatic, and heteroaromatic groups. The cycloaddition products were converted into a range of cantharimide products with promising lead-like properties for medicinal chemistry programs. Furthermore, the electron-rich furans are shown to react with a variety of alternative dienophiles to generate 7-oxabicyclo[2.2.1]heptane derivatives under mild conditions. DFT calculations have been performed to rationalize the activation effect of the 3-alkoxy group on a furan Diels–Alder reaction.

Herein, we report a silver-free Pd(II)-catalyzed C(sp

Theophylline, a pharmaceutical model compound, was screened for cocrystal formation using nine (di)hydroxybenzoic acids as cocrystal formers, namely, 2-, 3-, 4-hydroxybenzoic- and 2,3-, 2,4-, 2,5-, 2,6-, 3,4-, and 3,5-dihydroxybenzoic acids. The experiments were conducted using an efficient, reliable, and fast screening method based on thermodynamically driven solution-mediated phase transformation and revealed the formation of eight cocrystals and one salt. The theophylline-based solids were identified using powder and structurally characterized via single-crystal X-ray diffraction. The obtained solids are sustained by theopylline-carboxylic acid heterosynthons, in addition to both theophylline and carboxylic acid homosynthons. The results are a part of a systematic study of xanthine-alkaloid cocrystals that aims to establish synthon hierarchies in cocrystals comprised of molecules with multiple hydrogen-bonding functional groups. Structural features and synthon hierachies are discussed and compared to t...

Photoreactive Ag(I) organosulfonate complexes involving (E)-methyl-3-(pyridin-3-yl)prop-2-enoate (3-PAMe) are reported. Argentophilic interactions stack 3-PAMe to undergo a head-to-head intermolecular [2+2] photodimerisation to generate (rctt)-dimethyl-3,4-bis(pyridine-3-yl)cyclobutane-1,2-dicarboxylate (3,3′-MeBPCD) in the solid state regioselectively and in quantitative yield. The organosulfonate participates in C–H…O interactions with the coordinated 3-pyridyl groups to effectively aid in crystal engineering of the reactivity.

Two new palladium-catalysed reactions have been developed for the synthesis of stable 4-substituted benzooxaborinin-1-ols. A palladium-catalysed cyclisation of ortho-alkenylbenzene boronic acids can be used to access 4-chlorobenzooxaborinin-1-ols via a Wacker-type oxidation and chlorination. Alternatively, ortho-alkynylbenzene boronic acids undergo a palladium-catalysed oxyallylation reaction to provide 4-allylbenzooxaborinin-1-ols.

We apply crystal engineering principles to prepare organic co-crystals and salts of sulfadiazine and pyridines. Pyridines are molecular building blocks utilized in crystal engineering that can disrupt the hydrogen bonded (amidine) N–H···N (pyrimidine) dimer within the parent sulfa drug (SD) crystals, while providing access to both co-crystals and salts. We have synthesized four co-crystals and three salts of sulfadiazine involving N,N-dimethyl-4-aminopyridine, 4-aminopyridine, 4-picoline, 4,4′-bipyridine, (E)-1,2-bis(4-pyridyl)ethylene, 1,2-bis(4-pyridyl)acetylene, and 4-(pyridin-4-yl)piperazine. Single-crystal X-ray analyses reveal three hydrogen-bond motifs, namely, dyads, rings, and chains based involving either (amidine/aniline) N–H···N (pyridine/pyrimidine), (pyridinium) +N–H···N– (amidide), (aniline/piperazine) N–H···O2S (sulfoxide) interactions, or a combination thereof. The hydrogen-bond motifs are assigned as D11(2), R22(8), R22(20), C22(17), and C22(13) graph sets. An analysis of the Cambridge S...

We describe a conceptually novel “accelerated aging” approach for the synthesis of metal–organic materials. This approach, inspired by natural mineral weathering processes, enables the synthesis of metal–organic structures from simple and inexpensive solid reactants upon exposure to catalytic amounts of an ammonium salt under conditions of high humidity and mild temperatures (up to 45 °C). Accelerated aging exploits the inherent mobility of molecules and is entirely different from solution-based (precipitation, solvothermal synthesis) or other solvent-free (mechanochemical synthesis) approaches to metal–organic materials that require either bulk solvent and/or thermo- or mechanochemical intervention. The present proof-of-principle study of accelerated aging demonstrates the catalysed and topologically specific transformation of ZnO into unusual close-packed varieties of zeolitic imidazolate frameworks (ZIFs) in a static, non-agitated reaction mixture. The reactivity is readily scaled up, as demonstrated by performing selected syntheses of quartz- and diamondoid-topology close-packed ZIFs in ten gram amounts. The latter framework, previously obtained only by using a large excess of reagents under hydrothermal conditions, is transformed into the well-known open framework ZIF-8 by exposure to methanol vapours at room temperature, suggesting an alternative to both solvothermal and mechanochemical approaches to these materials. A tentative proton-transfer mechanism underpinning the catalytic effect in accelerated aging is proposed, involving protonated imidazole as an intermediate.

A supramolecular protecting group strategy has been applied to achieve solid-state photodimerizations of olefins lined with a combination of hydrogen-bond-donor and -acceptor groups. Esters were used as protecting groups to generate head-to-head photodimers that were readily converted into diacids. A protected olefin equipped with a stilbene unit exhibits enhanced reactivity that is ascribed to pedal motions in the solid state (orange hexagons: template: blur circles: recognition sites). Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Treatment of an achiral molecular ladder of C 2 h symmetry composed of five edge-sharing cyclobutane rings, or a [5]-ladderane, with acid results in cis - to trans -isomerization of end pyridyl groups. Solution NMR spectroscopy and quantum chemical calculations support the isomerization to generate two diastereomers. The NMR data, however, could not lead to unambiguous configurational assignments of the two isomers. Single-crystal X-ray diffraction was employed to determine each configuration. One isomer readily crystallized as a pure form and X-ray diffraction revealed the molecule as being achiral based on C i symmetry. The second isomer resisted crystallization under a variety of conditions. Consequently, a strategy based on a cocrystallization was developed to generate single crystals of the second isomer. Cocrystallization of the isomer with a carboxylic acid readily afforded single crystals that confirmed a chiral ladderane based on C 2 symmetry. The chiral ladderane and acid self-assembled to generate a five-component hydrogen-bonded complex that packs to form large solvent-filled homochiral channels of nanometer-scale dimensions. Whereas cocrystallizations are frequently applied to structure determinations of proteins, our study represents the first application of a cocrystallization to confirm the relative configuration of a small-molecule diastereomer generated in a solution-phase organic synthesis.

The fac -M (CO) 3 + (M = Re, 99m Tc) moiety was investigated with a known bidentate ligand, acetylacetone (acac) and imidazole based ligands in a 2 + 1 and tridentate approach. In the 2 + 1 approach, the fac -Re(CO) 3 (acac)(OH 2 ) was reacted with imidazole or 1-methylimidazole to yield a unique anionic μ-bridging imidazol-1-ide dimer fac -[(imidazol-1-ide)-bis-( fac -acetylacetonatotricarbonylrhenium (I)], 1 , or the monomer version fac -M(CO) 3 (acac)(1-methylimidazole), 2 , respectively. Based on the Schiff base condensation of a ketone and a primary amine, a tridentate ligand approach for fac -M ( OH 2 ) 3 (CO) 3 + utilizing the reactivity of acac and histamine was explored in a didactic manner: (1) an in situ ligand synthesis approach reacting fac -M(CO) 3 (acac)(OH 2 ) with histamine (2 + 2 = 3) that led to the formation of an unexpected dimer μ-acachistimine, compound, 3 , or (2) direct complexation of fac -M ( OH 2 ) 3 (CO) 3 + with the prepared ligand acachistimine, 4 , to yield the monomer product fac -M(CO) 3 (acachistimine), 5 . The results observed with rhenium complexes characterized by standard chemical analysis and X-ray analysis correlated with the radioactive experiments conducted with 99 m Tc (CO) 3 + .

A cocrystal of caffeine (caf) and 2-hydroxy-1-naphthoic acid (2H1NA), namely, (caf)·(2H1NA), was discovered via a screening method based on solution-mediated phase transformation (SMPT). The components crystallize as a two-component hydrogen-bonded assembly involving both an intermolecular O–H···N and intramolecular O–H···O hydrogen bond. The assemblies stack parallel and offset. Crystal data: monoclinic P 21/n space group, a = 7.909(2) A, b = 15.275(5) A, c = 14.704(5) A, β = 103.66(1)°, Z = 4, V = 1726.1(9) A3, D c = 1.471 g/cm3 and R 1 = 0.081, wR 2 = 0.163. The cocrystal (caf)·(2H1NA) was also subjected to polymorph screening using 15 different solvents, with all resulting solids being identified as the original form. A cocrystal of caffeine and 2-hydroxy-1-naphthoic acid was discovered via a screening method and is shown to form a two-component hydrogen-bonded molecular assembly based on an intermolecular O–H⋯N and intramolecular O–H⋯O hydrogen bond.

[Figure Presented] Chemical mechanics: Hydrogen-bonddriven self-assembly and mechanochemistry are used to facilitate supramolecular catalysis in the solid state. Mortar-andpestle grinding proves to be an efficient means to achieve co-crystal formation and turnover using a physical mixture composed of an olefin and catalytic amounts of a ditopic template (see scheme). © 2010 Wiley-VCH Verlag GmbH &. Co. KGaA.

A bridge-substituted [2.2]paracyclophane obtained from the organic solid state exhibits a dramatic red shift in fluorescence relative to [2.2]paracyclophane. A further red shift occurs upon alkylation of the pyridylcyclobutyl bridges. Our results demonstrate that [2.2]cyclophanes substituted at the bridge, despite not being attached via the extended pi-system, are promising building blocks in the development of optical materials.

Development of new ligands for fac-M(OH(2))(3)(CO)(3)(+) (M = Re, (99m)Tc) led the investigation with S-(pyridin-2-ylmethyl)-l-cysteine, 1. The ligand 1 has potential to coordinate with the metal through three different tridentate modes: tripodal through cysteine (O,N,S) and two linear involving the S-pyridyl and cysteine (O,S,N(Py), N,S,N(Py)). From the reaction with 1, two species were observed in the (1)H NMR, where the primary product was the linear fac-Re(N,S,N(Py)-1)(CO)(3)(+), 2a, complex. To identify the coordination mode of the minor product, functionalized analogues of 1 were prepared from S-(pyridin-2-ylmethyl)-Boc-l-cysteine-methyl ester, 3, with orthogonal protecting groups on the C terminus (methyl ester) in S-(pyridin-2-ylmethyl)-l-cysteine methyl ester, 4, or N terminus (Boc) in S-(pyridin-2-ylmethyl)-Boc-l-cysteine, 6, that specifically directed the coordination mode of fac-M(H(2)O)(3)(CO)(3)(+) to either N,S,N(Py) or O,S,N(Py), respectively. Two diastereomers [fac-Re(CO)(3)(N,S,N(Py)-4)](+), 5a and 5b, were observed and independently characterized by X-ray structure analysis and NMR in high yield with 4. Surprisingly, the O,S,N(Py) Re complex with ligand 6 was not observed and simplified versions, 3-(pyridin-2-ylmethylthio) propanoic acid, 7, and 2-(pyridin-2-ylmethylthio)acetic acid, 8, were investigated. Ligand 7 did not yield the desired linear tridentate O,S,N(Py) product. However, the shorter ligand 8 formed fac-Re(CO)(3)(O,S,N(Py)-8), 9, in high yield. (99m)Tc labeling studies were conducted and yielded similar results to the rhenium complex and effective (>99%) at 10(-5) M ligand concentration.

Caffeine, a pharmaceutical model compound, generally forms cocrystals with carboxylic acids that involve an O−H···N hydrogen bond between the carboxylic acid group of the acid and the caffeine imidazole moiety. Such solids are typically based on a single heterosynthon. To examine the facility of introducing additional supramolecular heterosynthons to the caffeine-carboxylic-acid cocrystal system, structural isomers of aromatic carboxylic acids (i.e., hydroxy- and dihydroxybenzoic acids) with additional hydrogen-bonding functional groups (i.e., hydroxy group) were screened for cocrystal formation. For this purpose, a highly efficient screening method based on thermodynamically driven solution-mediated phase transformation was utilized. This method enabled the rapid discovery of nine new solid phases involving caffeine. These caffeine phases were identified using single-crystal X-ray diffraction and FT-IR spectroscopy as cocrystals based on 2-, 3-, 4-hydroxybenzoic- and 2,3-, 2,4-, 2,5-, 3,4-, and 3,5-dihyd...

We describe how reactivity can be controlled in the solid state using molecules and self-assembled metal-organic complexes as templates. Being able to control reactivity in the solid state bears relevance to synthetic chemistry and materials science. The former offers a promise to synthesize molecules that may be impossible to realize from the liquid phase while also taking advantage of the benefits of conducting highly stereocontrolled reactions in a solvent-free environment (i.e., green chemistry). The latter provides an opportunity to modify bulk physical properties of solids (e.g., optical properties) through changes to molecular structure that result from a solid-state reaction. Reactions in the solid state have been difficult to control owing to frustrating effects of molecular close packing. The high degree of order provided by the solid state also means that the templates can be developed to determine how principles of supramolecular chemistry can be generally employed to form covalent bonds. The paradigm of synthetic chemistry employed by Nature is based on integrating noncovalent and covalent bonds. The templates assemble olefins via either hydrogen bond or coordination-driven self-assembly for intermolecular [2 + 2] photodimerizations. The olefins are assembled within discrete, or finite, self-assembled complexes, which effectively decouples chemical reactivity from effects of crystal packing. The control of the solid-state assembly process affords the supramolecular construction of targets in the form of cyclophanes and ladderanes. The targets form stereospecifically, in quantitative yield, and in gram amounts. Both [3]- and [5]-ladderanes have been synthesized. The ladderanes are comparable to natural ladderane lipids, which are a new and exciting class of natural products recently discovered in anaerobic marine bacteria. The organic templates function as either hydrogen bond donors or hydrogen bond acceptors. The donors and acceptors generate cyclobutanes lined with pyridyl and carboxylic acid groups, respectively. The metal-organic templates are based on Zn(II) and Ag(I) ions. The reactivity involving Zn(II) ions is shown to affect optical properties in the form of solid-state fluorescence. The solids based on both the organic and metal-organic templates undergo rare single-crystal-to-single-crystal reactions. We also demonstrate how the cyclobutanes obtained from this method can be applied as novel polytopic ligands of metallosupramolecular assemblies (e.g., self-assembled capsules) and materials (e.g., metal-organic frameworks). Sonochemistry is also used to generate nanostructured single crystals of the multicomponent solids or cocrystals based on the organic templates. Collectively, our observations suggest that the organic solid state can be integrated into more mainstream settings of synthetic organic chemistry and be developed to construct functional crystalline solids.

L-Arabinose is an abundant resource available as a waste product of the sugar beet industry. Through use of a hydrazone-based strategy, L-arabinose was selectively dehydrated to form a chiral tetrahydrofuran on a multi-gram scale without the need for protecting groups. This approach was extended to other biomass-derived reducing sugars and the mechanism of the key cyclization investigated. This methodology was applied to the synthesis of a range of functionalized chiral tetrahydrofurans, as well as a formal synthesis of 3R-3-hydroxymuscarine.

In this microreview, we show how principles of coordination-driven self-assembly can be used to direct chemical reactivity in the organic solid state. We also show how products obtained from the templated solid-state reactions can be used as organic building units of metal–organic frameworks and coordination capsules. Self-assembled structures based on dinuclear ZnII and AgI complexes are used to direct stereocontrolled [2+2] photodimerizations of vinylpyridines in the solid state in up to quantitative yield. The products are used as bi- and polytopic ligands of self-assembled coordination capsules and metal–organic frameworks. We also describe emerging metal-based approaches to conduct mechanochemical reactions in organic solids. In addition to the field of supramolecular coordination chemistry, these observations impact the field of green chemistry.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

This article outlines the benefits of using 'Design of Experiments' (DoE) optimisation during the development of new synthetic methodology. A particularly important factor in the development of new chemical reactions is the choice of solvent which can often drastically alter the efficiency and selectivity of a process. Whilst solvent optimisation is usually done in a non-systematic way based upon a chemist's intuition and previous laboratory experience, we illustrate how optimisation of the solvent for a reaction can be carried out by using a 'map of solvent space' in a DoE optimisation. A new solvent map has been developed specifically for optimisation of new chemical reactions using principle component analysis (PCA) incorporating 136 solvents with a wide range of properties. The new solvent map has been used to identify safer alternatives to toxic/hazardous solvents, and also in the optimisation of an S(N)Ar reaction.

Cycloaddition of 3-alkoxyfurans with N-substituted maleimides provides the first general route towards endo-cantharimide analogs.

We show that a molecule constructed from an organic solid-state synthesis, namely, rctt-1,3-bis(2-pyridyl)-2,4-bis(4-pyridyl)cyclobutane (ht-2,4′-tpcb) upon reaction with Cu(II) and Zn(II) ions gives one- (1D) and two-dimensional (2D) metal–organic frameworks (MOFs) of composition [Cu(hfac)2(2,4′-tpcb-ht)]∞ (where: hfac=hexafluoroacetylacetonate) (1) and [ Zn ( 2 , 4 ′ ‐ tpcb ‐ ht ) 2 ( H 2 O ) 2 ] ∞ 2 + (2). Each MOF possesses uncoordinated, or free, 2-pyridyl groups that decorate the walls of each extended structure.

The hydrogen-bond-acceptor (HBA) templates 2,3-bis(4-methylenethiopyridyl)naphthalene (2,3-nap) and 1,8-bis(4-pyridyl)naphthalene (1,8-dpn) are used to assemble (E,E)-2,5-dimethylmuconic acid (dmma) in the solid state for an intermolecular [2 + 2] photocycloaddition. Co-crystallisation of 2,3-nap with dmma affords an 1D hydrogen-bonded polymer that is photostable while 1,8-nap affords a 0D hydrogen-bonded assembly that is photoactive. The diene stacks in-phase and reacts to give a syn monocyclobutane in up to 55% yield.

A bicyclobutyl that bears six carboxylic acid groups results from a trimerisation of a diene diacid in the solid state. Powder X-ray diffraction and a co-crystallisation are used to solve the structure of the diene and elucidate the stereochemistry of the bicyclobutyl, respectively.

Nearly twenty years ago, Dunitz and Bernstein described a selection of intriguing cases of polymorphs that disappear. The inability to obtain a crystal form that has previously been prepared is indeed a frustrating and potentially serious problem for solid-state scientists. This Review discusses recent occurrences and examples of disappearing polymorphs (as well as the emergence of elusive crystal forms) to demonstrate the enduring relevance of this troublesome, but always captivating, phenomenon in solid-state research. A number of these instances have been central issues in patent litigations. This Review, therefore, also highlights the complex relationship between crystal chemistry and the law.