Structures, Sorption Characteristics, and Nonlinear Optical Properties of a New Series of Highly Stable Aluminum MOFs

Abstract

Employing high-throughput methods, the synthesis conditions for a series of six new MOFs based on aluminium ions and the V-shaped linker molecule 1,3-benzene dicarboxylic acid, denoted as CAU-10-X (CAU = Christian-Albrechts-University) with the sum formula [Al(OH)(C 8 H 3 O 4 X)]•solvent, were established (X = functional group in 5-position of the aromatic ring; X = H (1), CH 3 (2), OCH 3 (3) NO 2 (4), NH 2 (5), or OH (6)). Due to the absence of macroscopic crystals, the obtained compounds were structurally characterized employing XRPD-methods. The crystal structures of 1, 2 and 3 were refined using Rietveld methods. Although the described MOFs are isoreticular, they crystallize in several, sometimes non-centrosymmetric space groups (1, 4, 6), due to slight structural changes induced by the functionalization. These space groups were confirmed with second-harmonic generation measurements. All compounds are highly stable as confirmed by temperature-dependent XRPD-and IR-experiments and decompose at temperatures above 350 °C. The stabilities of all compounds in aqueous solutions of varying pH were confirmed by XRPD-measurements and their sorption properties towards nitrogen, hydrogen, carbon dioxide and water vapor at low pressures are reported. A drastic influence of the functional group on affinity, capacity and accessibility of the pores for these gases is observed. These properties depend on the polarity and size of the functional group as well as on subtle structural differences between the CAU-10-X compounds.

Synthesis, Structure, and Selected Properties of Aluminum-, Gallium-, and Indium-Based Metal-Organic Frameworks

“…In contrast to the chains in MIL-53, the use of isophthalic acid leads to chains of cis-corner-sharing AlO 6 polyhedra, as it is observed in the framework of CAU-10 (Table 5.1) [99]. The IBUs in this framework are 4 1 -and 4 3 -helices of AlO 6 polyhedra.…”

“…Thus square-shaped channels are formed. This framework structure is much more rigid in comparison to the MIL-53 framework but still allows for a phase transition upon removal of water molecules from the pores [99]. The CAU-10 structure can also be obtained with various functional groups (e.g., -NO 2 , -CH 3 , -OCH 3 ) or mixtures of linker molecules [50].…”

Screening of mixed-linker CAU-10 MOF materials for humidity sensing by impedance spectroscopy

“…The single-linker compound CAU-10-H shows a permanent porosity of a s,BET ¼ 635 m 2 g À1 and a micropore volume of V mic ¼ 0.25 cm 3 g À1 and is accessible for H 2 and CO 2 gas as well as H 2 O vapour. [9] The characteristic S-shape of the water vapour isotherm as well as exceptional hydrothermal stability, which was shown by Fr€ ohlich et al by multi-cycle water vapour measurements open the possibility for an application in the field of heat transformation processes of this material [10]. In addition, it was possible to grow this compound directly on galumina and metallic alumina without any loss of performance in repeated water vapour adsorption measurements, which is advantageous for industrial use [11].…”

“…With CAU-10, [Al(OH)(1,3-BDC-H)], we chose a recent type of functionalized MOF, which was first described by Reinsch et al [9] The structure of CAU-10 is built up by cis-corner-sharing AlO 6 octahedra to form a helix (Fig. 1).…”

Design of Porous Metal-Organic Frameworks for Adsorption Driven Thermal Batteries

“…The hydrophilicity of CAU-10 can be improved during post-syntheses treatment by grafting functional groups such as -OH and -NH 2 on the organic linkers [9]. This method allows the enhancement of the material affinity for water, however this drastically drops the water uptake since the grafting leads to a decrease of the pore volume.…”