A Diazo Linker Ligand Promotes Flexibility and Induced Fit Binding in a Microporous Copper Coordination Network

Abstract Flexible organic linkers represent an intuitive and effective strategy to design flexible metal–organic materials. We report herein a systematic study concerning the effect of varying the central bond of mixed pyridyl‐benzoate linkers, L, upon the flexibility of three isostructural kdd topology microporous coordination networks (CNs) of formula ML 2 : X‐kdd‐1‐Cu , 1 = L = ( E )‐4‐(pyridin‐4‐yldiazenyl)benzoate; X‐kdd‐2‐Cu , 2 = L = ( E )‐4‐(2‐(pyridin‐4‐yl)vinyl)benzoate; the previously reported X‐kdd‐3‐Cu , 3 = L = 4‐(pyridin‐4‐ylethynyl)benzoate. As revealed by single crystal x‐ray diffraction (SCXRD) and gas sorption studies, X‐kdd‐1‐Cu , exhibited gate‐opening during CO 2 and hydrocarbon (C2 and C8) sorption experiments whereas the other two CNs did not. Insight into these phase transformations was gained from in situ variable‐pressure and variable temperature powder X‐ray diffraction (PXRD), SCXRD, and modeling. Rotation of ligand 1 around the diazo bond, torsion angle changes between phenyl and carboxylate moieties, and deformation of the Cu‐based rod building blocks enabled activated X‐kdd‐1‐Cu to form new phases with C8 isomers and CH 2 Cl 2 , CH 2 Cl 2 inducing contraction of the activated phase. Computational studies suggest that 1 enables flexibility thanks to its lower barrier of deformation versus 2 or 3 . This study teaches that diazo moieties could offer a general strategy to enhance the flexibility of CNs.