The ability to suppress the yield for a solid-state [2 + 2] cycloaddition reaction for a halogen-bonded co-crystals is reported. The decline was influenced by simply heating the cocrystal while...

The synthesis, crystal structure, and [2+2] cycloaddition photoreactivity of a halogen-bonded mixed cocrystal is reported. The cocrystal solid solution contains two isosteric donors, namely, 1,4-diiodoperchlorobenzene (C6I2Cl4) and iodoperchlorobenzene (C6ICl5), along with trans-1,2-bis(pyridin-4-yl)ethylene (BPE, C12H10N2) which behaves as a ditopic reactant molecule. The mixed cocrystal, namely, (C6I2Cl4)0.75·(C6ICl5)0.25·(BPE), is achieved since both halogen-bond donors are similar in shape and are interchangeable at equivalent crystallographic positions. The combination of I...N and Cl...N halogen bonds generates one-dimensional chains that engage in homogeneous π-stacks, thereby positioning a pair of reactant molecules in a suitable location to photoreact. Notably, the overall yield for the solid-state photoreaction is influenced by the initial molar ratio of the isosteric halogen-bond donors within the mixed cocrystal.

The cocrystallization of either 2,3,5,6-tetrachloroaniline (C6H3Cl4N) or 2,4,6-trichloroaniline (C6H4Cl3N) with trans-1,2-bis-(4-pyridyl)-ethylene (BPE) results in a pair of three-component hydrogen-bonded cocrystals, namely 2-(C6H3Cl4N)·(BPE) and 2-(C6H4Cl3N)·(BPE). These cocrystals undergo up to a quantitative [2 + 2] cycloaddition reaction in the organic solid state upon exposure to ultraviolet light. Utilizing the ability of these chlorinated anilines to engage in both N-H···N hydrogen bonds along with homogeneous and face-to-face π-π stacking interactions ultimately positions BPE in a suitable location to photoreact and generate the stereoselective photoproduct rctt-tetrakis-(4-pyridyl)-cyclobutane (TPCB). The tendencies for these chlorinated anilines to form homogeneous π-stacks were investigated by means of density functional theory calculations with the goal to determine not only the overall strength but also the preference for this stacking pattern. In addition, a series of isostructural cocrystals were also achieved by incorporating two isosteric hydrogen-bond acceptors, namely 1,2-bis-(4-pyridyl)-acetylene (BPA) and azobipyridine (Azo), with these chlorinated anilines.

The ability to tune the thermomechanical properties of organic solids by utilizing a mixed cocrystal approach is described. The components of each solid are self-assembled through hydrogen bonds, and changing the composition of the solid at the molecular level provides control over the solid-state property. Specifically, two binary solids are prepared using the same hydrogen-bond donor molecule and an unsymmetrical, isosteric hydrogen-bond acceptor. The mixed cocrystal is realized by incorporating both acceptors into the solid material. The thermomechanical response of the mixed cocrystal lies numerically in between the two binary systems along all three principal directions of the solid. Mixed cocrystals are underexplored when compared to their binary counterparts, and this work demonstrates the tunability in solid-state material properties that can be achieved using the mixed approach.

The ability to achieve a series of photoreactive solids using dry-vortex grinding that contains trans-1,2-bis(2-pyridyl)ethylene along with 2,4,6-trifluorophenol at different molar ratios is reported. In all cases, mechanochemical grinding generates a three-component hydrogen-bonded co-crystal that undergoes a [2 + 2] cycloaddition reaction. Curiously, the solids formed with a substoichiometric ratio of the template also reached a nearly quantitative yield, since the formation of the photoproduct causes a cascade-like reaction within the solid which shifts the remaining reactant molecules into a suitable position to photoreact.

The ability to achieve a catalytic [2 + 2] cycloaddition reaction involving trans-1,2-bis(4-pyridyl)ethylene (BPE) within a halogen-bonded cocrystal formed via a dry vortex grinding approach is reported. The donor, namely 1,4-diiodoperchlorobenzene (C6I2Cl4), behaves as a catalytic supramolecular template at both substoichiometric and stoichiometric ratios to achieve a nearly quantitative photoreaction in the organic solid state. The mechanochemical grinding not only generates the initial photoreactive cocrystal (C6I2Cl4 )(BPE) but subsequently facilitates dynamic turnover that releases the photoproduct rctt-tetrakis(4-pyridyl)cyclobutane (TPCB) and regenerates the reactive cocrystal. Importantly, additional grinding-photolysis sequences increase the yield, which ultimately returns a near quantitative value for the solid-state cycloaddition reaction. Lastly, this dry vortex grinding approach also increases the yield for the photoreaction previously reported for the cocrystal (C6I2Cl4 )(BPE) formed from a stoichiometric ratio of the components. After photoreaction, the resulting equal molar solid is ground a second time and exposed to ultraviolet light to increase the yield to a near quantitative level matching that for the substoichiometric solid.

The thermal expansion behavior of a series of halogen-bonded cocrystals containing 1,4-diiodoperchlorobenzene as the donor is described. Two of the solids are polymorphs and contain 4-stilbazole as the acceptor, while the third solid contains 4-(phenylethynyl)pyridine as the acceptor, and this solid is isostructural with one of the polymorphs. All solids are sustained by IN halogen bonds, and the least thermal expansion occurs along this direction in all solids. The polymorphs exhibit significant differences in pi stacking, and we show that electronically similar face-to-face stacked rings undergo more expansion compared to electronically different stacked rings. Moreover, in the two polymorphs, the directions of moderate expansion and most expansion are reversed, demonstrating how cocrystal polymorphism can affect material properties.

The preference in the type of halogen bond accepted by anthraquinone (C14H8O2) from two isosteric donors, namely 1,4-diiodoperfluorobenzene (C6I2F4) and 1,4-diiodoperchlorobenzene (C6I2Cl4), is reported. The two co-crystals, (C6I2F4)·(C14H8O2) and (C6I2Cl4)·(C14H8O2), are sustained primarily by I···O rather than π-type halogen bonds to form these multicomponent solids. The ability for each component to engage in two divergent halogen-bonding interactions generates a one-dimensional chain structure for each co-crystal. The bias in the halogen-bonding type is due to the difference in electrostatic potential between the carbonyl oxygen and the aromatic surface on the anthraquinone. To support this observed preference, the binding energies of the I···O halogen bond were quantified for both co-crystals by using density functional theory calculations and then compared to the interaction energy for related π-type halogen bond from previously reported structures.

The formation of a halogen-bonded co-crystal based upon 1,2-bis(2-pyridyl)ethylene along with iodoperchlorobenzene is reported. The co-crystal undergoes a nearly quantitative [2 + 2] cycloaddition reaction in the organic solid state.

A series of [2+2] cycloaddition reactions involving trans-1,2-bis(2-pyridyl)ethylene that is templated by three 2,4,6-trihalophenols is reported. In each case, the co-crystal undergoes a quantitative and stereoselective photoreaction to generate the corresponding cyclobutane, namely rctt-tetrakis(2-pyridyl)cyclobutane. The reliability of these phenols to engage in the combination of homogenous and face-to-face pi-pi stacking interactions along with O-H & ctdot;N hydrogen bonds places the carbon-carbon double bond within the reactant in a suitable position to photoreact. In addition, density functional theory calculations supported the occurrence of the homogeneous stacking pattern which is required to form these photoreactive co-crystals. The formation of a series of hydrogen-bonded co-crystals that contain 1,2-bis(2-pyridyl)ethylene along with one of three trihalophenols is reported. Each co-crystal undergoes a quantitative [2+2] cycloaddition reaction in the organic solid state.

The formation and crystal structure of a co-crystal based upon 1,4-diiodoperchlorobenzene (C6I2Cl4) as the halogen-bond donor along with naphthalene (nap) as the acceptor is reported. The co-crystal [systematic name: 1,2,4,5-tetrachloro-3,6-diiodobenzene–naphthalene, (C6I2Cl4)·(nap)] generates a chevron-like structure that is held together primarily by π-type halogen bonds (i.e. C—I...π contacts) between the components. In addition, C6I2Cl4 also interacts with the acceptor via C—Cl...π contacts that help stabilize the co-crystal. Within the solid, both aromatic components are found to engage in offset and homogeneous face-to-face π–π stacking interactions. Lastly, the halogen-bond donor C6I2Cl4 is found to engage with neighboring donors by both Type I chlorine–chlorine and Type II iodine–chlorine contacts, which generates an extended structure.

The ability of 1,2,4,5-tetrachloro-3-iodobenzene to act as a template to form a pair of polymorphic cocrystals with trans-1,2-bis(4-pyridyl)ethylene is reported. After exposure to ultraviolet light, a nearly quantitative yield for the [2 + 2] cycloaddition reaction was observed for both concomitant cocrystals. These crystalline solids engage in both I center dot center dot center dot N halogen bonds along with nontraditional C-H center dot center dot center dot N hydrogen bond which results in a one-dimensional chain. In addition, the components homogeneous pi-pi stack which positions the carbon-carbon double bond on the reactant molecule in a suitable orientation to undergo a photoinduced cyclization reaction.

The formation and crystal structure of a zigzag network held together by I⋯N halogen bonds is reported. In particular, the halogen-bond donor is 1,3-di-iodo-perchloro-benzene (C6I2Cl4 ) while the acceptor is the photoproduct rtct-tetra-kis-(pyridin-4-yl)cyclo-butane (TPCB). Curiously, within the resulting co-crystal (C6I2Cl4 )·(TPCB), the photoproduct accepts only two halogen bonds between neighbouring 4-pyridyl rings and as a result behaves as a bent two-connected node rather than the expected four-connected centre. In addition, the photoproduct, TPCB, is also found to engage in C-H⋯N hydrogen bonds, forming an extended zigzag chain.

The formation of a series of isostructural three-component co-crystals between 1,2,4,5-tetrachloro-3-iodobenzene and each of three isosteric bipyridines is reported.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

The formation of a pair of co-crystals based upon isosteric halogen-bond donors, namely 1,4-diiodoperchlorobenzene and iodoperchlorobenzene, along with the acceptor 4,4-bipyridine is reported. As expected, the components in each co-crystal engage in halogen bonding interactions resulting in a one-dimensional chain-like structure. In particular, the co-crystal containing 1,4-diiodoperchlorobenzene is primarily held together by I···N halogen bonds while the solid based upon iodoperchlorobenzene forms both I···N and Cl···N interactions. Structural diversity is achieved between these co-crystals based upon the type of secondary interactions involving the chlorine atoms on each halogen-bond donor even though they are isosteric in nature.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

The formation and crystal structure of a zigzag molecular network held together by I...N halogen bonds is reported. In particular, the halogen-bond donor is 1,2-diiodoperchlorobenzene (1,2-C6I2Cl4) while the acceptor is a head-to-tail photoproduct, namely rctt-1,3-bis(pyridin-4-yl)-2,4-diphenylcyclobutane (ht-PP). In this co-crystal (1,2-C6I2Cl4)·(ht-PP), the donor acts as a bent two-connected node while the acceptor behaves as a linear linker to form the extended solid. Neighbouring chains pack in a tongue-and-groove-like pattern that engage in various Cl...π interactions to both the phenyl and pyridyl rings resulting in a supramolecular two-dimensional sheet.

We designed a series of metal-organic solids using ligands with similar molecular structures that were expected to afford coordination complexes with similar solid-state structures. The metal component is silver(I) p-toluenesulfonate, and the ligands differ in their ability to undergo dynamic molecular motion. Although the ligands are similar in their molecular structure, the metal complexes exhibit different solid-state structures because of differences in pi-stacking arrangements and the presence or lack of AgmiddotmiddotmiddotAg interactions. The coordination units (ligand-Ag-ligand) in each complex respond differently to temperature changes, which results in thermal expansion behaviors ranging from negative to zero to positive within the series. Two unique complexes were obtained with the azo-containing ligand, and preparation of each complex in bulk was controlled by synthetic conditions. Two polymorphs were obtained with the olefin-containing ligand, and both complexes undergo dynamic molecular motion, although the supramolecular structures differed dramatically. Overall, we show that simple modifications to the ligand structure can significantly affect solid-state structure, crystal form, and subsequent thermal expansion behavior.