Creating Order in Ultrastable Phosphonate Metal–Organic Frameworks via Isolable Hydrogen-Bonded Intermediates

Abstract

The stability presented by trivalent metal−organic frameworks (MOFs) makes them an attractive class of materials. With phosphonate-based ligands, crystallization is a challenge, as there are significantly more binding motifs that can be adopted due to the extra oxygen tether compared to carboxylate counterparts and the self-assembly processes are less reversible. Despite this, we have reported charge-assisted hydrogen-bonded metal−organic frameworks (HMOFs) consisting of [Cr(H 2 O) 6 ] 3+ and phosphonate ligands, which were crystallographically characterized. We sought to use these HMOFs as a crystalline intermediate to synthesize ordered Cr(III)-phosphonate MOFs. This can be done by dehydrating the HMOF to remove the aquo ligands around the Cr(III) center, forcing metal−phosphonate coordination. Herein, a new porous HMOF, H-CALF-50, is synthesized and then dehydrated to yield the MOF CALF-50. CALF-50 is ordered, although it is not single crystalline. It does, however, have exceptional stability, maintaining crystallinity and surface area after boiling in water for 3 weeks and soaking in 14.5 M H 3 PO 4 for 24 h and 9 M HCl for 72 h. Computational methods are used to study the HMOF to MOF transformation and give insight into the nature of the structure and the degree of heterogeneity.

Photochromic Ln-Phosphonates Assembled by an Imidazole Derivative: Construction, Crystal Structures, and Light-Enhanced Proton Conductivity

“…The first approach is to reduce the activation energy of proton transfer or/and increase the number of proton carriers (such as H 2 O, NH 4 + , H 3 O + ). , However, it still confronts challenges in the current situation due to the fact that this method needs to comprehensively consider various factors that may affect the performance of proton conduction. The other approach is to introduce more acidic functional groups such as carboxylic acids, , sulfonic acids, , or phosphonic acids to enhance their acidity and hydrophilicity, thereby enriching the presence of hydrogen-bonding networks. − Evidently, the second method is more meaningful for improving proton conductivity owing to its chemical stability and structural diversity accompanied by the simple and facile operation procedure.…”

Arylsulfonate Ionic Hydrogen-Bonded Organic Frameworks Enable Highly Stable and Superprotonic Conductivity for Enhancing Direct Methanol Fuel Cells

“…Proton-conducting materials have potential in electrochemical devices, where superprotonic conductivity can accelerate the proton transport rate in PEMs and enhance the performance of DMFCs. , Metal–organic frameworks (MOFs) , and covalent organic frameworks (COFs) are characterized by their perfect crystallinity, porosity, and ease of functionalization, which makes them exhibit ultrahigh superprotonic conductivity of 10 –1 S cm –1 or beyond. Hydrogen-bonded organic frameworks (HOFs) are emerging crystalline materials with unique properties, constructed from organic molecular units through noncovalent hydrogen bonding interactions. − , Traditional single-component HOFs are constructed from single molecules, which may not contain high concentrations of protons in the structure, leading to less research on proton conducting. , We introduce two differently charged organic molecules with hydrogen bonding to build ionic HOFs (iHOFs).…”