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

Four new porous CAU-1 derivatives CAU-1-NH2 ([Al-4(OH)(2)(OCH3)(4)(BDC-NH2)(3)]center dot xH(2)O, BDC-NH22- = aminoterephthalate), CAU-1-NH2(OH) ([Al-4(OH)(6)(BDC-NH2)(3)]center dot xH(2)O), CAU-1-NHCH3 ([Al-4(OH)(2)(OCH3)(4)(BDC-NHCH3)(3)]center dot xH(2)O) and CAU-1-NHCOCH3 ([Al-4(OH)(2)(OCH3)(4)(BDC-NHCOCH3)(3)]center dot xH(2)O) all containing an octameric [Al-8(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 H-1-N-15, H-1-C-13 and homonuclear H-1-H-1 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 degrees C in air. Solid-state NMR spectra unequivocally demonstrate the presence of the amino groups, as well as the successful post-synthetic modification. Furthermore H-1 H-1 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 H-1 liquid-state NMR and IR spectroscopy.