Exploring Multifunctional Hydrogen-Bonded Organic Framework Materials

Abstract

Metrics & MoreArticle Recommendations CONSPECTUS: Hydrogen-bonded organic framework (HOF) materials have provided a new dimension and bright promise as a new platform for developing multifunctional materials. They can be readily self-assembled from their corresponding organic molecules with diverse functional sites such as carboxylic acid and amine groups for their hydrogen bonding and aromatic ones for their weak π•••π interactions to stabilize the frameworks.Compared with those established porous materials such as zeolites, metal−organic frameworks (MOFs), and covalent−organic frameworks (COFs), it is much more difficult to stabilize HOFs and thus establish their permanent porosities given the fact that hydrogen bonds are typically weaker than ionic, coordination, and covalent bonds. But it provides the uniqueness of HOF materials in which they can be easily recovered and regenerated through simple recrystallization. HOF materials can also be easily and straightforwardly processed and very compatible with the biomolecules, making them potentially very useful materials for industrial and biomedical applications. The reversible and weak bonding nature of the hydrogen bonds can be readily utilized to construct flexible porous HOF materials in which we can tune the temperature and pressure to control their porosities and, thus, their diverse applications, for example, on gas separations, gas storage, drug delivery, and sensing. Some specific organic functional groups are quite directional for the hydrogen bond formations; for example, carboxylic acid prefers to form a directional dimer, which has enabled us to readily construct reticular porous HOF materials whose pores can be systematically tuned. In this Account, we outline our journey of exploring this new type of porous material by establishing one of the first porous HOFs in 2011 and thus developing its diverse applications. We have been able to use organic molecules with different functional sites, including 2,4-diaminotriazine (DAT), carboxylic acid (COOH), aldehyde (CHO), and cyano (CN), to construct porous HOFs. Through tuning the pore sizes, introducing specific binding sites, and making use of the framework flexibility, we have realized a series of HOF materials for the gas separations of C

Metalo Hydrogen-Bonded Organic Frameworks Self-Assembled by Charge-Assisted Synthons for Ultrahigh Proton Conduction

“…These results provide another strong proof to support the high thermal stability of the MOFs, and suggest no phase transformation during the measured temperature range. To our knowledge, high-temperature single crystal measurements for HOFs, MHOFs, and supramolecular frameworks are extremely rare. − Consequently, together with the cobalt HOF, the present results provide a family of rare HOFs having single crystal structures at 373 K.…”

“…In addition, the development of proton-conducting materials is also important for understanding the physiological activity of living systems . Over the last decades, molecule-based proton conductors have been well developed due to the fast evolution of crystalline framework materials, such as covalent organic frameworks (COFs) and metal–organic frameworks (MOFs), which provide a versatile platform for building a highly efficient proton transfer pathway, switched proton conductivity behaviors, and multifunctional proton-conducting materials. − Recently, hydrogen-bonded organic frameworks (HOFs), including metalo hydrogen-bonded organic–inorganic frameworks (MHOFs), are emerging as a class of new supramolecular platforms for material studies. − Generally, HOFs are constructed by organic or metal–organic molecules via hydrogen bonding with the assistance of other noncovalent interactions, such as π–π stacking interactions and van der Waals forces. Though these supramolecular materials are less stable in comparison with materials constructed by covalent or coordination bonds, HOFs have great advantages in synthesis, processing, and recyclability, etc., which have motivated renewed interest in the design of functional molecular materials, especially the proton-conducting materials. − To date, some HOFs/MHOFs have been reported to show proton conductivity over a wide range of operating temperatures. − However, there have been only a limited number of HOFs/MHOFs that exhibit high proton conduction with excellent water stability.…”

Immobilization of the Polar Group into an Ultramicroporous Metal–Organic Framework Enabling Benchmark Inverse Selective CO2/C2H2 Separation with Record C2H2 Production

“…Extensive endeavors have been devoted to exploring porous solid adsorbents including but not limited to zeolites, activated carbons, metal–organic frameworks (MOFs), hydrogen-bonded organic frameworks (HOFs), covalent–organic frameworks (COFs), and hybrid ultramicroporous materials (HUMs). − Especially, MOFs, also called porous coordination polymers (PCPs), as novel porous organic–inorganic hybrid materials, are constructed from the self-assembly of metal ions or clusters and organic ligands, which become promising adsorbents for gas mixture separation owing to their tunable pore size and pore chemistry. ,, The rational design of the pore shape/size and pore chemistry based on the modular feature of MOFs in reticular chemistry and crystal engineering has enabled some MOF adsorbents to exhibit unprecedented adsorption and separation performance for hydrocarbons, including but not limited to C 2 H 2 /C 2 H 4 , C 2 H 6 /C 2 H 4 , and C 3 H 6 /C 3 H 8 . − However, the almost same kinetic diameter of CO 2 and C 2 H 2 makes it greatly challenging for MOFs to differentiate these gases. Recently, a large number of MOF adsorbents have been reported to be used for CO 2 /C 2 H 2 separation, with almost all of them exhibiting a C 2 H 2 -selective adsorption behavior.…”

Controllable Synthesis and Ultrahigh Anisotropic Single-Crystal Proton Conduction of a Hydrogen-Bonded Organic Framework

“…In the past decades, the crystalline porous materials of metal–organic frameworks (MOFs) and covalent organic frameworks (COFs) which are built up from coordinated and covalent bonds, have been popularly explored in the field of proton conduction owing to their tunable structures and functional channels. − In contrast to MOFs and COFs, hydrogen-bonded organic frameworks (HOFs) are highly porous and inherently present well-defined intermolecular noncovalent hydrogen-bonding interactions, − more favorable for the proton transfer, making them versatile platforms as outstanding solid-state proton conduction materials. − Another notable characteristic of HOFs is their typically simplistic structural components. This simplicity enables a precise analysis of the relationship between structure and properties, specifically based on single-crystal proton conduction.…”