Search for: All records

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 I···N halogen bonds, and the least thermal expansion occurs along this direction in all solids. The polymorphs exhibit significant differences in π 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 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-diiodoperchlorobenzene ( C 6 I 2 Cl 4 ) while the acceptor is the photoproduct rtct -tetrakis(pyridin-4-yl)cyclobutane ( TPCB ). Curiously, within the resulting co-crystal ( C 6 I 2 Cl 4 )·( 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. 

Methods to form cyclobutane rings by an intermolecular [2 + 2] cross-photoreaction (CPR) with four different substituents are rare. These reactions are typically performed in the liquid phase, involve multiple steps, and generate product mixtures. Here, we report a CPR that generates a cyclobutane ring with four different aryl substituents. The CPR occurs quantitatively, without side products, and without a need for product purification. Generally, we demonstrate how face-to-face stacking interactions of aromatic rings can be exploited in the process of cocrystallization and the field of crystal engineering to stack and align unsymmetrical alkenes in CPRs to afford chiral cyclobutanes with up to four different aryl groups via binary cocrystals. Overall, we expect the process herein to be useful to generate chiral carbon scaffolds, which is important given the presence of four-membered carbocyclic rings as structural units in biological compounds and materials science.

 

A halogen-bonded supramolecular ladder comprised of a novel pyrimidine-based cyclobutane photoproduct synthesized in the organic solid state via a [2 + 2] photoreaction is reported. The photoproduct rctt -tetrakis(5′-pyrimidyl)cyclobutane functions as rungs while the linear divergent halogen-bond donor 1,4-diiodoperchlorobenzene acts as the rails. Our report also confirms the structure and stereochemistry of the tetrapyrimidyl cyclobutane ring system. 

The formation of a photoreactive cocrystal based upon 1,2-diiodoperchlorobenzene ( 1,2-C 6 I 2 Cl 4 ) and trans -1,2-bis(pyridin-4-yl)ethylene ( BPE ) has been achieved. The resulting cocrystal, 2( 1,2-C 6 I 2 Cl 4 )·( BPE ) or C 6 Cl 4 I 2 ·0.5C 12 H 10 N 2 , comprises planar sheets of the components held together by the combination of I...N halogen bonds and halogen–halogen contacts. Notably, the 1,2-C 6 I 2 Cl 4 molecules π-stack in a homogeneous and face-to-face orientation that results in an infinite column of the halogen-bond donor. As a consequence of this stacking arrangement and I...N halogen bonds, molecules of BPE also stack in this type of pattern. In particular, neighbouring ethylene groups in BPE are found to be parallel and within the accepted distance for a photoreaction. Upon exposure to ultraviolet light, the cocrystal undergoes a solid-state [2 + 2] cycloaddition reaction that produces rctt -tetrakis(pyridin-4-yl)cyclobutane ( TPCB ) with an overall yield of 89%. A solvent-free approach utilizing dry vortex grinding of the components also resulted in a photoreactive material with a similar yield. 

A halogen-bonded eight-fold interpenetrated diamondoid net was constructed employing a node generated in the solid state. Specifically, co-crystallization of a tetrahedral-like tecton, rctt -tetrakis(4-pyridyl)cyclobutane (4,4′-TPCB), combined with a rigid halogen-bond donor, 1,4-diiodoperchlorobenzene, achieved a diamondoid architecture. In the co-crystal, 4,4′-TPCB is found to form three types of linkages based on one cis - and two trans -orientations enabled by the intrinsic rctt -stereochemisty of the central cyclobutane ring. Thus, 4,4′-TPCB is able to adapt to the constraints of the diamondoid net owing to the flexibility of the pendant 4-pyridyl groups. 

The realization of a pair of photoreactive polymorphic co-crystals that are held together by the combination of I⋯N halogen bonding interactions and C–H⋯Cl contacts is reported. The reactant molecule within these co-crystals is based upon an unsymmetrical olefin, namely 4-stilbazole, that results in a regioselective solid-state [2 + 2] cycloaddition reaction in both polymorphic forms. Each solid undergoes a quantitative photoreaction which yields exclusively the head-to-tail photoproduct.