A Calixarene‐Based Metal–Organic Framework for Highly Selective NO 2 Detection

A calixarene‐based metal–organic framework (Zr‐cal, [Zr 6 O 4 (OH) 4 (FA) 6 ] 2 (cal) 3 ], FA=formate, cal=1,3‐alt‐25,26,27,28‐tetrakis[(carboxy)methoxy]calixarene) was synthesized and characterized by single‐crystal X‐ray diffraction. The three‐dimensional framework is a 4,6‐connected network of gar topology and exhibits two equal but nonintersecting three‐dimensional pore systems. It has a specific BET surface area of 670 m 2  g −1 , and the calixarene cavities are accessible through the pore systems. The exposed calixarenes can be used for the visual detection and encapsulation of NO 2 through the formation of deeply colored charge–transfer complexes inside the MOF. The highly selective complexation was analyzed by UV/Vis and IR spectroscopy, and the stability of the material was confirmed by powder X‐ray diffraction and 1 H NMR spectroscopy. Finally, the MOF was used as a sensor material in a home‐made sensor cell and showed high sensitivity for NO 2 .