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Designing materials to have three unique but predictable thermal expansion axes represents a major challenge. Inorganic materials and hybrid frameworks tend to crystallize in high-symmetry space groups, which necessarily limits this by affording isotropic behavior. On the other hand, molecular organic materials tend to crystallize in lower-symmetry space groups, offering significant opportunity to achieve anisotropic properties. The challenge arises in self-assembling the organic components into a predictable arrangement to afford predictable thermal expansion properties. Here, we demonstrate a design strategy for engineering organic solid-state materials that exhibit anisotropic thermomechanical behaviors. Presented are a series of multicomponent solids wherein one component features a BODPIY core strategically decorated with orthogonal hydrogen- and halogen-bond donor groups. A series of size-matched halogen-bond acceptors are used as the second component in each solid. By matching the molecular dimensions with the interaction strength, we obtained good control over the anisotropic thermal expansion of the molecular materials. Moreover, using shape-size mimicry and propensity for molecular motion, a rare ternary molecular system that is isostructural to the two binary solids was successfully achieved. The diiodo-functionalized BODIPY core in this study has been previously used in photocatalysts, and halogen bonding was hypothesized as a driving force; here, we provide corroborating solution and solid-state evidence of intermolecular halogen bonding in multicomponent solids featuring a 2,6-diiodo BODIPY. 

The solution phase anion binding behavior of a water-stable bidentate pnictogen bond donor was studied. A modest change in the visible absorption spectrum allowed for the determination of the binding constants. High binding constants were observed with cyanide, cyanate, and acetate, and these were corroborated with density functional theory (DFT) calculations. The receptor could be recovered free from the anion following treatment with methyl triflate, confirming that it remains intact. The tight binding of cyanide and water stability were exploited to use this system as a supramolecular catalyst in a phase-transfer Strecker reaction, further demonstrating the utility of pnictogen bonding as a tool in noncovalent catalysis. 

The structure of the simplest stibatrane has been a mystery since it was first prepared in 1966. This study reports the preparation and characterization of two stibatranes from triethanolamine and triisopropanolamine. Solid state structures reveal macrocycles that contain favourable inter- and intramolecular pnictogen bonds. Solution studies, corroborated by DFT analysis, reveal an equilibrium mixture assigned to monomer and pnictogen-bonded dimer. This allowed for the determination of an enthalpy associated with pnictogen bond formation of −27 kJ mol −1 , in line with the supramolecular nature of these interactions. 

A new air and moisture stable antimony thiolate compound has been prepared that spontaneously forms stable hollow vesicles. Structural data reveals that pnictogen bonding drives the self-assembly of these molecules into a reversed bilayer. The ability to make these hollow, spherical, and chemically and temporally stable vesicles that can be broken and reformed by sonication allows these systems to be used for encapsulation and compartmentalisation in organic media. This was demonstrated through the encapsulation and characterization of several small organic reporter molecules. 

Pnictogen bonding is beginning to emerge as a useful supramolecular interaction. The design strategies for these systems are still in the early stages of development and much attention has been focused on the lighter pnictogens. Pnictogen bond donors can have up to three independent sites for binding which can result in triple pnictogen bonding. This has been observed in the self-assembly of antimony alkoxide cages, but not with the lighter congeners. This work reports structural characterization of an analogous arsenic alkoxide cage that engages in a single pnictogen bond and synthetic explorations of the bismuth congener. DFT calculations are used to evaluate the differences between the structures. Ultimately the partial charge on the pnictogen and the energy of the pnictogen lone pair dictate the strength, orientation and number of pnictogen bonds that these cages form. Antimony cages strike the best balance between strength and directionality, allowing them to achieve triple pnictogen bonding where the other congeners do not.