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Issue 12, 2012
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Controlled modification of the inorganic and organic bricks in an Al-based MOF by direct and post-synthetic synthesis routes

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Abstract

Four new porous CAU-1 derivatives CAU-1–NH2 ([Al4(OH)2(OCH3)4(BDC–NH2)3xH2O, BDC–NH22− = aminoterephthalate), CAU-1–NH2(OH) ([Al4(OH)6(BDC–NH2)3xH2O), CAU-1–NHCH3 ([Al4(OH)2(OCH3)4(BDC–NHCH3)3xH2O) and CAU-1–NHCOCH3 ([Al4(OH)2(OCH3)4(BDC–NHCOCH3)3xH2O) all containing an octameric [Al8(OH)4+y(OCH3)8−y]12+ cluster, with y = 0–8, have been obtained by MW-assisted synthesis and post-synthetic modification. The inorganic as well as the organic unit can be modified. Heteronuclear 1H–15N, 1H–13C and homonuclear 1H–1H connectivities determined by solid-state NMR spectroscopy prove the methylation of the NH2 groups when conventional heating is used. Varying reaction times and temperatures allow controlling the degree of methylation of the amino groups. Short reaction times lead to non-methylated CAU-1 (CAU-1–NH2), while longer reaction times result in CAU-1–NHCH3. CAU-1–NH2 can be modified chemically by using acetic anhydride, and the acetamide derivative CAU-1–NHCOCH3 is obtained. Thermal treatment permits us to change the composition of the Al-containing unit. Methoxy groups are gradually exchanged by hydroxy groups at 190 °C in air. Solid-state NMR spectra unequivocally demonstrate the presence of the amino groups, as well as the successful post-synthetic modification. Furthermore 1H–1H correlation spectra using homonuclear decoupling allow the orientation of the NHCOCH3 groups within the pores to be unravelled. The influence of time and temperature on the synthesis of CAU-1 was studied by X-ray powder diffraction, elemental analyses, and 1H liquid-state NMR and IR spectroscopy.

Graphical abstract: Controlled modification of the inorganic and organic bricks in an Al-based MOF by direct and post-synthetic synthesis routes

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Publication details

The article was received on 02 Dec 2011, accepted on 26 Jan 2012 and first published on 16 Feb 2012


Article type: Paper
DOI: 10.1039/C2CE06620C
CrystEngComm, 2012,14, 4126-4136

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    Controlled modification of the inorganic and organic bricks in an Al-based MOF by direct and post-synthetic synthesis routes

    T. Ahnfeldt, D. Gunzelmann, J. Wack, J. Senker and N. Stock, CrystEngComm, 2012, 14, 4126
    DOI: 10.1039/C2CE06620C

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