Toward the Next Generation of Permanently Porous Materials: Halogen-Bonded Organic Frameworks

Abstract

Halogen bonding has emerged as a reliable and intuitive handle in crystal engineering, providing predictable, noncovalent interactions capable of directing supramolecular assembly into networks with varying degrees of dimensionality. Conceptually similar to hydrogen bonding, halogen bonding represents a virtually untapped space for realizing new low-density porous architectures with large, highly crystalline domains. With the foundational understanding gained from almost two decades of computational and empirical supramolecular investigations, we believe that halogen bonding is on the precipice of enabling a new class of noncovalently linked permanently porous materials, aptly called halogen-bonded organic frameworks (XOFs). This perspective focuses on defining the criteria for the classification of XOFs and highlights seminal works in both halogen and hydrogen bonding that play an integral role toward understanding the key strategies in both synthon and tecton design that will lead to assembly of materials with accessible void space and observable porosity. Finally, solvent activation procedures and desorption mechanisms are discussed toward the goal of achieving permanently porous frameworks and thrusting halogen bonding into the realm of porous materials.

Open Frameworks Formed from Iodoalkyne∙∙∙Halide Halogen Bonds

“…[16,22,23] An alternative to using hydrogen bonds to assemble frameworks would be to use "-hole" interactions, [24] such as halogen [25][26][27] or chalcogen bonding, [28,29] as these are far more directional than typical hydrogen bonds. Numerous 2D and 3D frameworks have been assembled using halogen bonding and chalcogen bonding interactions, [30][31][32][33][34][35][36][37][38][39][40][41][42][43] although perhaps surprisingly, very few permanently porous frameworks [44][45][46] have been reported, particularly when compared with the large number of permanently porous hydrogen bonded frameworks.…”

Open Networks Formed from Iodoalkyne···Halide Halogen Bonds

“…An alternative to using hydrogen bonds to assemble frameworks would be to use “σ-hole” interactions, such as halogen − or chalcogen bonding, , as these are far more directional than typical hydrogen bonds. Numerous 2D and 3D networks have been assembled using halogen-bonding and chalcogen-bonding interactions, − although perhaps surprisingly, very few permanently porous frameworks − have been reported, particularly when compared with the large number of permanently porous hydrogen-bonded frameworks.…”