Aluminium trimellitate [Al(OH)(BDC–COOH)]
?
0.9H
2
O(
1
), the Al-MIL-53–COOH derivative, was
discovered under solvothermal conditions using a high-throughput set-up suitable for microwave
(MW)-assisted heating. The compound shows high structural flexibility. The large-pore (lp) form of
the framework is obtained under large excess of H
2
O or after solvothermal treatment with
N
,
N
-dimethylformamide upon which [Al(OH)(BDC–COOH)]
?
0.7DMF (
2
) is obtained. Exposure of
the water rich lp form of
1
to ambient conditions leads to the transformation to the narrow-pore (np)
form. Thermal activation of both compounds results in the formation of the empty lp form and the
activation of
1
was studied in detail by
in situ
IR-spectroscopy. Depending on the activation
temperature and time two post-synthetic modification (PSM) processes are observed: the partial
decarboxylation and the formation of acid anhydride groups. Thus at high temperatures and long
activation times [Al(OH)(BDC–OCOCO–BDC)
x
/2
(BDC)
y
](
x
+
y
= 1) is formed. Upon cooling in air
the anhydride functionality still remains intact, but the np form is obtained in air due to the
adsorption of H
2
O molecules. Sorption measurements of
1
confirm a preference for polar gases like
H
2
O and CO
2
in comparison to N
2
,H
2
, and CH
4
. The N
2
capacity depends strongly on the degree of
decarboxylation.