Chiral Motifs in Highly Interpenetrated Metal-Organic Frameworks Formed from Achiral Tetrahedral Ligands

Formation of highly interpenetrated frameworks is demonstrated. An interesting observation is the presence of very large adamantane-shaped cages in a single network, making these crystals new entries in the collection of diamondoid-type metal-organic frameworks (MOFs). The frameworks were constructed by assembling tetrahedral pyridine ligands and copper dichloride. Currently, the networks' degree of interpenetration is among the highest reported and increases when the size of the ligand is increased. Highly interpenetrated frameworks typically have low surface contact areas. In contrast, in our systems, the voids take up to 63 % of the unit cell volume. The MOFs have chiral features but are formed from achiral components. The chirality is manifested by the coordination chemistry around the metal center, the structure of the helicoidal channels, and the motifs of the individual networks. Channels of both handednesses are present within the unit cells. This phenomenon shapes the walls of the channels, which are composed of 10, 16, or 32 chains correlated with the degree of interpenetration 10-, 16-, and 32-fold, respectively. By changing the distance between the center of the ligand and the coordination moieties, we succeeded in tuning the diameter of the channels. Relatively large channels were formed, having diameters up to 31.0 Å×14.8 Å.

Iodine‐Chemisorption, Interpenetration and Polycatenation: Cationic MOFs and CPs from Group 13 Metal Halides and Di‐Pyridyl‐Linkers

Eight cationic, two‐dimensional metal‐organic frameworks (MOFs) were synthesized in reactions of the group 13 metal halides AlBr₃, AlI₃, GaBr₃, InBr₃ and InI₃ with the dipyridyl ligands 1,2‐di(4‐pyridyl)ethylene (bpe), 1,2‐di(4‐pyridyl)ethane (bpa) and 4,4’‐bipyridine (bipy). Seven of them follow the general formula ²_∞[MX₂(L)₂]A, M=Al, In, X=Br, I, A⁻=[MX₄]⁻, I⁻, I₃⁻, L=bipy, bpa, bpe. Thereby, the porosity of the cationic frameworks can be utilized to take up the heavy molecule iodine in gas‐phase chemisorption vital for the capture of iodine radioisotopes. This is achieved by switching between I⁻ and the polyiodide I₃⁻ in the cavities at room temperature, including single‐crystal‐to‐single‐crystal transformation. The MOFs are 2D networks that exhibit (4,4)‐topology in general or (6,3)‐topology for ²_∞[(GaBr₂)₂(bpa)₅][GaBr₄]₂⋅bpa. The two‐dimensional networks can either be arranged to an inclined interpenetration of the cationic two‐dimensional networks, or to stacked networks without interpenetration. Interpenetration is accompanied by polycatenation. Due to the cationic character, the MOFs require the counter ions [MX₄]⁻, I⁻ or I₃⁻ counter ions in their pores. Whereas the [MX₄]⁻, ions are immobile, iodide allows for chemisorption. Furthermore, eight additional coordination polymers and complexes were identified and isolated that elaborate the reaction space of the herein reported syntheses.

Exploiting a C-N Bond Forming Cytochrome P450 Monooxygenase for C-S Bond Formation

C-S bond formation reactions are widely distributed in the biosynthesis of biologically active molecules, and thus have received much attention over the past decades. Herein, we report intramolecular C-S bond formation by a P450 monooxygenase, TleB, which normally catalyzes a C-N bond formation in teleocidin biosynthesis. Based on the proposed reaction mechanism of TleB, a thiol-substituted substrate analogue was synthesized and tested in the enzyme reaction, which afforded the unprecedented sulfur-containing thio-indolactam V, in addition to an unusual indole-fused 6/5/8-tricyclic product whose structure was determined by the crystalline sponge method. Interestingly, conformational analysis revealed that the SOFA conformation is stable in thio-indolactam V, in sharp contrast to the major TWIST form in indolactam V, resulting in differences in their biological activities.

In vitro biological properties and predicted DNA–BSA interaction of three new dicyanidoargentate(i)-based complexes: synthesis and characterization

The synthesis, characterization and biological activity of three novel dicyanidoargentate(i)-based complexes are reported. The in vitro results show that these complexes may be potent antiproliferative drug candidates.

Semiconducting Coordination Polymers Based on the Predesigned Ternary Te-Fe-Cu Carbonyl Cluster and Conjugation-Interrupted Dipyridyl Linkers

A series of semiconducting cluster-incorporated Cu-based coordination polymers, namely, 1D zigzag polymers [{TeFe₃ (CO)₉ Cu₂ }(L)]_n (L=1,2-bis(4-pyridyl)ethane (bpea), 1; L=1,2-bis(4-pyridyl)ethylene (bpee), 5), 2D honeycomb-like polymers [{TeFe₃ (CO)₉ Cu}Cu(L)_2.5 ]_n (L=bpea, 2; L=bpee, 6), and 2D wave-like cation-anion polymer [{Cu₂ (L)₄ }({TeFe₃ (CO)₉ Cu}₂ (L))]_n (L=1,3-bis(4-pyridyl)propane (bpp), 4), as well as the macrocycle [{TeFe₃ (CO)₉ Cu₂ }₂ (bpp)₂ ] (3) have been quantitatively synthesized via the liquid-assisted grinding from the pre-designed cluster [TeFe₃ (CO)₉ Cu₂ (MeCN)₂ ] with conjugated or conjugation-interrupted dipyridyl linkers. Notably, the most conjugation-interrupted bpp-bridged polymer 4 exhibited extraordinary semiconducting characteristics with an ultra-narrow bandgap of 1.43 eV and a DC conductivity of 1.5×10^-2 Ω^-1  cm^-1 , which violates our knowledge, mainly attributed to the through-space electron transport via non-classical C-H⋅⋅⋅O(carbonyl) hydrogen bonds and aromatic C-H⋅⋅⋅π interactions. The incorporated Te-Fe-CO anions can not only provide numerous possibilities for secondary interactions within these Cu-based polymers but also serve as a redox-active coordination ligand to promote their conductivities. The intriguing structure-property relationships were studied by X-ray and DFT analyses and further demonstrated by significant change in the oxidation state of Cu atoms by XPS and Cu K-edge XANES.

An Unprecedented Two-Fold Nested Super-Polyrotaxane: Sulfate-Directed Hierarchical Polythreading Assembly of Uranyl Polyrotaxane Moieties

The hierarchical assembly of well-organized submoieties could lead to more complicated superstructures with intriguing properties. We describe herein an unprecedented polyrotaxane polythreading framework containing a two-fold nested super-polyrotaxane substructure, which was synthesized through a uranyl-directed hierarchical polythreading assembly of one-dimensional polyrotaxane chains and two-dimensional polyrotaxane networks. This special assembly mode actually affords a new way of supramolecular chemistry instead of covalently linked bulky stoppers to construct stable interlocked rotaxane moieties. An investigation of the synthesis condition shows that sulfate can assume a vital role in mediating the formation of different uranyl species, especially the unique trinuclear uranyl moiety [(UO2 )3 O(OH)2 ](2+) , involving a notable bent [O=U=O] bond with a bond angle of 172.0(9)°. Detailed analysis of the coordination features, the thermal stability as well as a fluorescence, and electrochemical characterization demonstrate that the uniqueness of this super-polyrotaxane structure is mainly closely related to the trinuclear uranyl moiety, which is confirmed by quantum chemical calculations.

X-ray Crystallography in Open-Framework Materials

Open-framework materials, such as metal-organic frameworks (MOFs) and coordination polymers have been widely investigated for their gas adsorption and separation properties. However, recent studies have demonstrated that their highly crystalline structures can be used to periodically organize guest molecules and non-structural metal compounds either within their pore voids or by anchoring to their framework architecture. Accordingly, the open framework can act as a matrix for isolating and elucidating the structures of these moieties by X-ray diffraction. This concept has broad scope for development as an analytical tool where obtaining single crystals of a target molecule presents a significant challenge and it additionally offers potential for obtaining insights into chemically reactive species that can be stabilized within the pore network. However, the technique does have limitations and as yet a general experimental method has not been realized. Herein we focus on recent examples in which framework materials have been utilized as a scaffold for ordering molecules for analysis by diffraction methods and canvass areas for future exploration.

Catenanes: fifty years of molecular links

Half a century after Schill and Lüttringhaus carried out the first directed synthesis of a [2]catenane, a plethora of strategies now exist for the construction of molecular Hopf links (singly interlocked rings), the simplest type of catenane. The precision and effectiveness with which suitable templates and/or noncovalent interactions can arrange building blocks has also enabled the synthesis of intricate and often beautiful higher order interlocked systems, including Solomon links, Borromean rings, and a Star of David catenane. This Review outlines the diverse strategies that exist for synthesizing catenanes in the 21st century and examines their emerging applications and the challenges that still exist for the synthesis of more complex topologies.

Structural Transformation of ZnII -Dipyridylamide-Based Coordination Frameworks: Hybrid-Ligand and Metal Effects

A series of one-dimensional (1D) double-zigzag ({[Zn(papx)₂ (H₂ O)₂ ](ClO₄ )₂ }_n (x=so 1, sc 3, oc 5, and soc 7) and 2D polyrotaxane ([Zn(papx)₂ (ClO₄ )₂ ]_n (x=so 2, sc 4, oc 6, and soc 8) frameworks are synthesized by the reactions of Zn(ClO₄ )₂ with equimolar amounts of papx (i.e., papso=1/2paps+1/2papo, papsc=1/2paps+1/2papc, papoc=1/2papo+1/2papc, and papsoc=1/3paps+1/3papo+1/3papc; paps=N,N'-bis(pyridylcarbonyl)-4,4'-diaminodiphenyl thioether, papo=N,N'-bis(pyridylcarbonyl)-4,4'-diaminodiphenyl ether, papc=N,N'-(methylenedi-p-phenylene)bispyridine-4-carboxamide). The new frameworks are isolated and characterized by single-crystal and powder X-ray diffraction studies, elemental analysis, and ¹ H NMR spectroscopy. In addition, synthesis and structural characterization of 2D polyrotaxane frameworks of [Cu(papx)₂ (ClO₄ )₂ ]_n (x=s 9, o 10, and c 11) by the reaction of Cu(ClO₄ )₂ with the respective dipyridylamide ligands are carried out. Based on the PXRD experiments, upon heating, the double-zigzag frameworks of 1, 3, 5, and 7 undergo structural transformation to give the respective polyrotaxane frameworks of 2, 4, 6, and 8. Moreover, grinding the solid samples of 2, 4, 6, and 8 in the presence of moisture also result in the total conversion back into the double-zigzag frameworks of 1, 3, 5, and 7, respectively. Remarkably, grinding the solid samples of polyrotaxane frameworks of 9 and 10 in the presence of moisture fails to induce a structural transformation process.

Stitching 2D polymeric layers into flexible interpenetrated metal-organic frameworks within single crystals

A 2D coordination polymer prepared with bulky diethylformamide solvates exhibits channels which allow dipyridyl bridging ligands to diffuse into the crystal lattice. The absorbed dipyridyls thread through the pores of one layer and substitute the surface diethylformamide molecules on the neighboring layers to stitch alternate layers to form flexible interpenetrated metal-orgaic frameworks. The threading process also results in exchange of the bulky diethylformamide solvates for aqua to minimize congestion and, more strikingly, forces the slippage of two-dimensional layers, while still maintaining crystallinity.