Theoretical and Experimental Insights into the Spatial Distribution of Functional Groups in a Multivariate Flexible Metal–Organic Framework

Dynamic multicomponent metal–organic frameworks, comprising numerous functional groups attached to a flexible backbone, expedite the complexity of coordination chemistry. Both factors, stimuli responsiveness and nonhomogeneous environments, are pivotal for creating complex systems that bring scientists closer to understanding biological structures; nevertheless, comprehension of such systems remains largely unexplored. Inspired by this concept, we prepared a series of flexible multivariate JUK-8­(NO2)x(Br)1–x (0 x 1H NMR was employed to determine the molar fraction of the linker in the bulk sample, whereas single-crystal X-ray diffraction verified this value for single crystals. CO2 adsorption studies at 195 K revealed that the monosubstituted JUK-8­(NO2) transitioned from a less porous to a porous phase at p/p0 ∼ 0.20, while for JUK-8­(Br), this process occurred at p/p0 ∼ 0.58. For the MTV MOFs, in contrast to the anticipated steady increase in transformation pressure with the molar fraction of Br-pip, xBr, we observed a constant gate-opening pressure, p/p0 ∼ 0.33, across a broad range of xBr, 0.27–0.63, and then its gradual increase up to p/p0 ∼ 0.48 for xBr up to 0.96. Resolving the crystal structure of the closed phases of JUK-8­(Br) and JUK-8­(NO2) allowed us to identify the crucial interactions governing this phenomenon. Finally, by constructing theoretical models of a multivariate structure and employing solid-state NMR crystallography supported by DFT simulation, we shed light on the possible spatial arrangement of functional groups in JUK-8­(NO2)0.50(Br)0.50. Overall, our report introduces a methodology that could potentially be utilized for investigating multicomponent flexible MOFs.