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 < 1) compounds (MTV MOFs) and introduced experimental and theoretical methodologies for their investigation. 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, x_Br, we observed a constant gate-opening pressure, p/p₀ ∼ 0.33, across a broad range of x_Br, 0.27-0.63, and then its gradual increase up to p/p₀ ∼ 0.48 for x_Br 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.