Heterogeneity of functional groups in a metal–organic framework displays magic number ratios

Abstract

Multiple organic functionalities can now be apportioned into nanoscale domains within a metal-coordinated framework, posing the following question: how do we control the resulting combination of "heterogeneity and order"? Here, we report the creation of a metal-organic framework, MOF-2000, whose two component types are incorporated in a 2:1 ratio, even when the ratio of component types in the starting solution is varied by an order of magnitude. Statistical mechanical modeling suggests that this robust 2:1 ratio has a nonequilibrium origin, resulting from kinetic trapping of component types during framework growth. Our simulations show how other "magic number" ratios of components can be obtained by modulating the topology of a framework and the noncovalent interactions between component types, a finding that may aid the rational design of functional multicomponent materials.metal-organic framework | out of equilibrium | polycrystalline | Monte Carlo simulationT he assembly of multiple types of component offers a potential route to the precise control of component heterogeneity within ordered 3D frameworks. Metal-organic frameworks (MOFs) (1-5) possessing well-defined connectivities (6, 7) and tunable pore sizes (8-10) can assemble from a variety of building blocks (11)(12)(13)(14)(15)(16)(17). Recently, a MOF harboring two components distributed in a heterogeneous fashion on an ordered framework was demonstrated (1, 2). There exists no framework, however, whose component heterogeneity remains controlled in the face of changes of environment. Here, we report the creation of a material with exactly this property. MOF-2000 is assembled from two types of organic struts, called L r and L b (Fig. 1A). These struts have identical rigid backbones but bear either a crown ether (L r ) or [2] catenane (L b ) side chain attached at their center. X-ray diffraction of MOF-2000 single crystals revealed that struts form a twofold interpenetrated cubic framework of pcu-c topology (Fig. 1A, Right, and SI Appendix, section S1.3; structure available in Dataset S1). As a result of optical investigations, we confirmed that the two struts are distributed in the crystalline framework in an isotropic manner (Fig. 1B), suggesting that the two components are not distributed in a simple periodic way throughout the framework (because such arrangements would give rise to optical anisotropy; SI Appendix, section S1.5).Even though the arrangement of the two components in MOF-2000 is indiscernible by X-ray crystallography, presumably as a result of the positional disorder of the two strut types within the framework, and the rotational (11, 18) and conformational (11) disorder of the side chains, the presence of the two organic struts can be clearly determined by 1 H-NMR (SI Appendix, section S1.4). Strikingly, MOF-2000 displays a 2:1 ratio of L r and L b struts, even when the ratios of components in the parent solution are varied by over an order of magnitude (Fig. 1C). This feature makes MOF-2000 unique among multicomponent extended framework...

Design principles for nonequilibrium self-assembly

“…We anticipate that our results will find important applications in studies of crystal nucleation (17), self-assembly of metal organic frameworks (27), nonequilibrium roughening transitions, and the synthesis of nanocrystals using DNA and other biopolymers as building materials. In all these instances, the assembly process can occur far from equilibrium depending on the effective chemical potentials imposed.…”

Enhancing Multicomponent Metal–Organic Frameworks for Low Pressure Liquid Organic Hydrogen Carrier Separations

“…Multicomponent MOFs have emerging applications in catalysis, luminescence and gas storage . In order to form multicomponent MOFs judicious selection of the linkers is essential (Figure , Scheme S1) .…”

Synthetic Strategies and Structural Arrangements of Isoreticular Mixed‐Component Metal–Organic Frameworks

“…Afterwards, the growth of the crystallites continued with both types of linkers resulting in at erephthalate rich core and ah ydroxyterephthalate rich shell. Another parameter that influences the outcomeo fa are different space requirements of the linker species, which can favor the formation of D. [30,34] Furthermore, if one type of linker molecules is preferably incorporated next to al inker of the same kind due to strong interactions with each other, B will be obtained in the product. [23] In addition, the incorporation of the second linker might not be achieved even though it is present in the reactionsolution.…”