The Extra‐Framework Sub‐Lattice of the Metal–Organic Framework MIL‐110: A Solid‐State NMR Investigation

Abstract

A changeable character: Differences in the dynamics of occluded moieties within the large pores (see graphic) of aluminium 1,3,5-benzene tricarboxylate framework solid MIL-110 are a function of the synthesis pH. Host-guest proton-transfer processes lead to a reversible change in the character of the framework from cationic to neutral, depending on the nature of the extra-framework moieties.The aluminium 1,3,5-benzene tricarboxylate framework solid MIL-110, which crystallises either at pH approximately 0 or at pH approximately 4, has been investigated by solid-state NMR spectroscopy. At pH approximately 0 the solid (MIL-110{pH0}) is the unique stable thermodynamic product, whereas at pH approximately 4 MIL-110{pH4} is observed as a kinetic product in competition with the MIL-96 phase. Diffraction studies and (27)Al NMR spectroscopy prove that the framework is identical in both cases. The nature and dynamics of occluded moieties within the large pores look quite different for the two compounds. MIL-110{pH4} and MIL-110{pH0} both show the presence of occluded 1,3,5-benzene tricarboxylate (btc), with additional nitrates and water molecules. However, the proportions of btc, nitrates and water are functions of the pH, leading to an identical framework and a quite different extra-framework. With the extra-framework moieties, the framework undergoes a proton transfer which is a function of the synthesis pH. Washing the MIL-110{pH0} phase with water produces a different extra-framework structure, richer in water and poorer in btc and nitrates. The hydroxyl groups of the inorganic aluminium cluster of the framework are involved in a proton transfer, which leads for all cases to a cationic framework and an anionic extra-framework. (1)H-(1)H DQ 2D NMR spectra (DQ=double quantum) give evidence for the interaction of extra-framework btc with the terminal water carried by Al(2,3) and shows their proximity to the closest hydroxyl groups. A structure for the non-diffracting extra-framework is proposed as the most plausible topology. It provides an efficient picture for the creation of many substituted MIL-110 compounds that would have a large number of applications.

Synthesis and characterization of porous Al(III) metal-organic framework nanoparticles as a new precursor for preparation of Al2O3 Nanoparticles

“…Acceptable match were observed between the simulated and experimental powder X-ray diffraction pattern. This indicates that the compound obtained in this work is identical to that reported by Ferey et al [33,34].…”

“…The resulting powder was filtered off, washed with water and dried at ambient temperature (noted as MIL-110{pH7}). For the second synthesis method MIL-110 (Al) obtained at controlled pH (initial pH = 4) from reaction of mixture containing Al(NO 3 ) 3 .9H 2 O (0.874 mmol, 328 mg)/ Me 3 btc (0.436 mmol, 110 mg)/H 2 O (270 mmol,5 mL)/NaOH (2 mmol, 0.5 mL 4 M), but the 23 mL Teflon-lined steel Parr autoclave was operated at 210°C for only 3 h (noted as MIL-110{pH4}) [33,34].…”

“…The structure of MIL-110 (Al) has been reported [33,34] and it shows that this compound was made from aluminum octameric clusters, linked through the trimesate (btc) ligand. The inorganic clusters (Fig.…”

“…In the result, the structure is hexagonal channels 1.7 nm wide. Interestingly the powder of MIL-110 is consisting of hexagonal needle-like single crystals [33,34].…”

“…The resulting powder was filtered off, washed with water and dried at ambient temperature (noted as MIL-110{pH7}). For the second synthesis method MIL-110 (Al) obtained at controlled pH (initial pH = 4) from reaction of mixture containing Al(NO 3 ) 3 .9H 2 O (0.874 mmol, 328 mg)/ Me 3 btc (0.436 mmol, 110 mg)/H 2 O (270 mmol,5 mL)/NaOH (2 mmol, 0.5 mL 4 M), but the 23 mL Teflon-lined steel Parr autoclave was operated at 210°C for only 3 h (noted as MIL-110{pH4}) [33,34].For preparation of Al 2 O 3 , about 50 mg of MIL-110{pH7} was heated for 12 h at 500°C and 750°C MIL-110{pH4} heated at 500°C for 3 h. After cooling the weight precipitate was obtained and washed with EtOH and dried under nitrogen. IR spectrum shows that calcination was completed and all of the organic compounds were…”