First Keto-Functionalized Microporous Al-Based Metal–Organic Framework: [Al(OH)(O₂C‑C₆H₄‑CO‑C₆H₄‑CO₂)]

Abstract

Based on the V-shaped linker molecule 4,4′-benzophenonedicarboxylic acid, the new carbonyl-functionalized metal–organic framework (MOF) [Al­(OH)­(O₂C-C₆H₄-CO-C₆H₄-CO₂)], denoted as CAU-8, was discovered employing high-throughput methods. The compound is obtained from 4,4′-benzophenonedicarboxylic acid, Al₂(SO₄)₃·18H₂O in a mixture of <i>N</i>,<i>N</i>-dimethylformamide (DMF) and water under solvothermal conditions. The structure was determined from single-crystal X-ray diffraction data (<i>I</i>4₁/<i>a</i>, <i>a</i> = <i>b</i> = 13.0625(5), <i>c</i> = 52.565(2) Å). The framework is based on infinite inorganic building units of <i>trans</i>-connected, corner-sharing AlO₆-polyhedra. Parallel Al–O-chains are arranged in layers perpendicular to [001]. Within a layer an interchain distance of ∼1.1 nm is observed. The orientation of the Al–O-chains within neighboring layers is perpendicular to each other, along [100] and [010], respectively, and an ABCDA stacking of these layers is observed. The interconnection of these orthogonally oriented chains by the V-shaped dicarboxylate ions results in the formation a three-dimensional framework structure containing one-dimensional channels with a diameter of about 8 Å. The pore walls are lined by the keto-groups. CAU-8 was thoroughly characterized by X-ray powder diffraction (XRPD), thermogravimetric measurements, IR- and Raman-spectroscopy, elemental analysis, and gas sorption experiments using N₂ and H₂ as adsorptives. CAU-8 is stable up to 350 °C in air and exhibits a moderate porosity with a specific surface area of <i>S</i>_BET = 600 m²/g and a micropore volume of 0.23 cm³/g. Moreover, a detailed topological analysis of the framework was carried out, and an approach for the topological analysis of MOFs based on infinite 1-periodic building units is proposed