Microporous Metal‐Phosphonates with a Novel Orthogonalized Linker and Complementary Guests: Insights for Trivalent Metal Complexes from Divalent Metal Complexes

Abstract

The reliable self‐assembly of microporous metal‐phosphonate materials remains a longstanding challenge. This stems from, generally, more coordination modes for the functional group allowing more dense structures, and stronger bonding driving less crystalline products. Here, a novel orthogonalized aryl‐phosphonate linker, 1,3,5‐tris(4’‐phosphono‐2’,6’‐dimethylphenyl) benzene (H6L3) has been used to direct formation of open frameworks. The peripheral aryl rings of H6L3 are orthogonalized relative to the central aromatic ring giving a tri‐cleft conformation of the linker in which small aromatic molecules can readily associate. When coordinated to magnesium ions, a series of porous crystalline metal‐organic, and hydrogen‐bonded metal‐organic frameworks (MOFs, HMOFs) are formed (CALF‐41 (Mg), HCALF‐42 (Mg), ‐43 (Mg)). While most metal‐organic frameworks are tailored based on choice of metal and linker, here, the network structures are highly dependent on the inclusion and structure of the guest aromatic compounds. Larger guests, and a higher stoichiometry of metal, result in increased solvation of the metal ion, resulting in networks with connectivities increasingly involving hydrogen‐bonds rather than direct phosphonate coordination. Upon thermal activation and aromatic template removal, the materials exhibit surface areas ranging from 400–600 m2/g. Self‐assembly in the absence of aromatic guests yields mixtures of phases, frequently co‐producing a dense 3‐fold interpenetrated structure (1). Interestingly, a series of both more porous (530–900 m2/g), and more robust solids is formed by complexing with trivalent metal ions (Al, Ga, In) with aromatic guest; however, these are only attainable as microcrystalline powders. The polyprotic nature of phosphonate linkers enables structural analogy to the divalent analogues and these are identified as CALF‐41 analogues. Finally, insights to the structural transformations during metal ion desolvation in this family are gained by considering a pair of structurally related Co materials, whose hydrogen‐bonded (HCALF‐44 (Co)) and desolvated (CALF‐44 (Co)) coordination bonded networks were fully structurally characterized.

Performance of ionic liquid functionalized metal organic frameworks in the adsorption process of phenol derivatives

“…The hexyl group in IL brings about somewhat greater flexibility in the linker in a conformation in which the aromatic rings are oriented outwards and which leads to an increase in the number of adsorption sites. 54 In this manner, the methyl imidazole-based ionic liquid blocks access to the active sites, whereas the hexyl imidazole-based ionic liquid has more access to the active sites. Since the structure is more open, the access of the pollutant will be facilitated.…”

Measuring Diffusion Kinetics with Zero-Length Chromatography in Isomorphous and Ultramicroporous Phosphonate Metal–Organic Frameworks

“…52,53 Indeed, the observation of isomorphous phosphonate network made with either Al(III) or Ti(IV) has been observed by Serre et al 54 The trigonal linker, 1,3,5-tris(4-phosphonophenyl)benzene (H 6 L1, Figure 1) has been studied to form open structures 53 but often, π−π stacking of the linker compromises porosity. 55 Recently, we have reported the synthesis of networks composed of orthogonalized tris-phosphonate linkers 56,57 including 1,3,5-tris(4-phosphonophenyl)-2,4,6-trime-thylbenzene (H 6 L2, Figure 1) coordinated to Sr 2+ ions ([Sr(H 4 L2)], CALF-35 (Sr) (CALF = Calgary Framework). 56 CALF-35 (Sr) has parallel 1-D channels lined with methyl groups, with calculated pore apertures that are similar in size to some strategic molecular adsorptives; 58 however, this structure was not highly stable to moisture.…”

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

“…With the linear 1,4diphosphonobenzene linker, 28 dehydration of the Cr HMOF simply led to a dense solid as the linear linker was easily able to balance favorable aromatic interactions with metal coordination. To promote the formation of a multidimensional porous HMOF, we synthesized 1,3,5-tris(4′-phosphono-2′,6′dimethylphenyl)benzene (H 6 L), 32 a trigonal phosphonate ligand with orthogonalized peripheral aryl rings to inhibit close packing. Here, we report H-CALF-50 (H = hydrogenbonded, CALF = Calgary framework), a HMOF composed of hexaaquachromium(III) L complexes and its subsequent dehydration to a tremendously stable MOF.…”