Issue 22, 2020

Probing the limits of linker substitution in aluminum MOFs through water vapor sorption studies: mixed-MOFs instead of mixed-linker CAU-23 and MIL-160 materials

Abstract

We report a systematic study on the possibility of forming mixed-linker metal–organic frameworks (MOFs) spanning between the aluminum MOFs CAU-23 and MIL-160 with their 2,5-thiophenedicarboxylate (TDC) and 2,5-furandicarboxylate (FDC) linkers, respectively. The planned synthesis of a mixed-linker MOF, combining TDC and FDC in the framework turned out to yield a rather largely intricate mixture of CAU-23 and MIL-160. This is due to the different opening angles of 150° for TDC versus 120° for FDC and the concomitant cistrans versus cis-only OH-bridges in the infinite secondary building unit {Al(μ-OH)(O2C–)} chains. At the same time, the CAU-23 phase is accompanied by the polymorphic MIL-53-TDC phase with trans-only OH-bridges. The measurement of water vapor sorption isotherms was the method of choice to confirm the formation of mixed MOFs instead of mixed-linker phases. Thereby, the water sorption isotherms indicate the simultaneous formation of both MOF phases, albeit they do not exclude mixed-linker MOFs which may have formed at low levels of substitution. The differentiation via powder X-ray diffractometry (PXRD), IR-spectroscopy and nitrogen sorption was either not conclusive enough or impossible, due to similarities of the neat MOF phases. The synthesized MOF mixtures within the TDC : FDC ratios of 38 : 62 up to 82 : 18 exhibit two or three uptake steps in the water sorption isotherm, with the first two corresponding to an overlay from the individual water sorption isotherm of CAU-23 and MIL-160 and a third one from the additional MIL-53-TDC.

Graphical abstract: Probing the limits of linker substitution in aluminum MOFs through water vapor sorption studies: mixed-MOFs instead of mixed-linker CAU-23 and MIL-160 materials

Supplementary files

Article information

Article type
Paper
Submitted
19 mrt 2020
Accepted
04 mei 2020
First published
05 mei 2020

Dalton Trans., 2020,49, 7373-7383

Probing the limits of linker substitution in aluminum MOFs through water vapor sorption studies: mixed-MOFs instead of mixed-linker CAU-23 and MIL-160 materials

C. Schlüsener, D. N. Jordan, M. Xhinovci, T. J. Matemb Ma Ntep, A. Schmitz, B. Giesen and C. Janiak, Dalton Trans., 2020, 49, 7373 DOI: 10.1039/D0DT01044H

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