Structures of Metal-Organic Frameworks with Rod Secondary Building Units.

Rod MOFs are metal-organic frameworks in which the metal-containing secondary building units consist of infinite rods of linked metal-centered polyhedra. For such materials, we identify the points of extension, often atoms, which define the interface between the organic and inorganic components of the structure. The pattern of points of extension defines a shape such as a helix, ladder, helical ribbon, or cylinder tiling. The linkage of these shapes into a three-dimensional framework in turn defines a net characteristic of the original structure. Some scores of rod MOF structures are illustrated and deconstructed into their underlying nets in this way. Crystallographic data for all nets in their maximum symmetry embeddings are provided.

Two Principles of Reticular Chemistry Uncovered in a Metal-Organic Framework of Heterotritopic Linkers and Infinite Secondary Building Units.

Structural diversity of metal-organic frameworks (MOFs) has been largely limited to linkers with at most two different types of coordinating groups. MOFs constructed from linkers with three or more nonidentical coordinating groups have not been explored. Here, we report a robust and porous crystalline MOF, Zn3(PBSP)2 or MOF-910, constructed from a novel linker PBSP (phenylyne-1-benzoate, 3-benzosemiquinonate, 5-oxidopyridine) bearing three distinct types of coordinative functionality. The MOF adopts a complex and previously unreported topology termed tto. Our study suggests that simple, symmetric linkers are not a necessity for formation of crystalline extended structures and that new, more complex topologies are attainable with irregular, heterotopic linkers. This work illustrates two principles of reticular chemistry: first, selectivity for helical over straight rod secondary building units (SBUs) is achievable with polyheterotopic linkers, and second, the pitch of the resulting helical SBUs may be fine-tuned based on the metrics of the polyheterotopic linker.

A family of porous lonsdaleite-e networks obtained through pillaring of decorated kagomé lattice sheets.

A new and versatile class of metal-organic materials (MOMs) with augmented lonsdaleite-e (lon-e-a) topology is presented herein. This family of lon-e nets are built by pillaring of hexagonal two-dimensional kagomé (kag) lattices constructed from well-known [Zn2(CO2R)4] paddlewheel molecular building blocks (MBBs) connected by 1,3-benzenedicarboxylate (bdc(2-)) linkers. The pillars are [Cr3(µ3-O)(RCO2)]6 trigonal prismatic primary MBBs decorated by six pyridyl moieties (tp-PMBB-1). The three-fold symmetry (D3h) of tp-PMBB-1 is complementary with the alternating orientation of the axial sites of the paddlewheel MBBs and enables triple cross-linking of the kag layers by each pillar. These MOMs represent the first examples of axial-to-axial pillared undulating kag layers, and they are readily fine-tuned because the bdc(2-) moieties can be varied at their 5-position without changing the overall structure. This lon-e platform possesses functionalized hexagonal channels since the kag lattices are necessarily eclipsed. The effects of the substituent at the 5-positions of the bdc(2-) linkers upon gas adsorption, particularly the heats of adsorption of carbon dioxide and methane, were studied.

Why Design Matters: From Decorated Metal Oxide Clusters to Functional Metal-Organic Frameworks.

The opportunity to generate functional solids with defined properties by deliberate design has not been materialized in traditional solid-state chemistry over many decades. The emergence of metal-organic frameworks (MOFs), permanently porous, crystalline solids with defined metrics, has allowed for studying design, synthesis, and properties, which then translated into new applications. Aggregates of metal ions stitched together by multidentate functional groups form such metal oxide clusters and represent the nodes of MOFs. These clusters, termed secondary building units (SBUs), are decorated with organic moieties that provide directionality and can be linked through geometric principles into extended nets using organic molecules (spacers). This concept of reticular chemistry has afforded permanently porous MOFs, and has resulted in over 20,000 structures over the past 20 years. However, there are still only a limited number of symmetric, discrete SBUs commonly used to design and synthesize MOFs. We herein introduce the most important SBUs that have emerged over time together with prototypal MOF structures and their fundamental applications. Both the discovery and the scientific impact will be highlighted alongside advantages and/or drawbacks. In addition, an outlook will be given on how the combination of multiple SBUs can lead to heterogeneous but ordered materials with higher complexity and functionality.

Two Dimensional Host-Guest Metal-Organic Framework Sensor with High Selectivity and Sensitivity to Picric Acid.

A dye-sensitized metal-organic framework, TMU-5S, was synthesized based on introducing the laser dye Rhodamine B into the porous framework TMU-5. TMU-5S was investigated as a ratiometric fluorescent sensor for the detection of explosive nitro aromatic compounds and showed four times greater selectivity to picric acid than any state-of-the-art luminescent-based sensor. Moreover, it can selectively discriminate picric acid concentrations in the presence of other nitro aromatics and volatile organic compounds. Our findings indicate that using this sensor in two dimensions leads to a greatly reduced environmental interference response and thus creates exceptional sensitivity toward explosive molecules with a fast response.