![(a-e) Crystal structure, determined by synchrotron X-ray diffraction, of the Pd8@MOF 2: (a) View along c crystallographic axis of crystal structure of 2 (a) featuring channels filled by [Pd II 2(-OH2)2(NH3)4)] 4+ and [Pd II 8(-OH2)8(NH3)8(L1)4] 16+ SCCs [L1 = 1,2-di(pyridn-4-yl)ethyne]. (b-c) Views of one single channel: Perspective views of a portion of single pores along the [111] direction showing the [Pd II 8(-OH2)8(NH3)8(L1)4] 16+ SCCs (b) and [Pd II 2(-OH2)(NH3)4] 4+ dimers (c) and related structural parameters, stabilized by symmetric NH3 ···O interactions. The heterobimetallic CuNi 3D anionic network is depicted as grey sticks. Pd(II) cations in the pores and ligands forming the squares and cages, are represented by purple spheres and blue sticks, respectively. Hydrogen-bonds are represented as purple dashed lines. (d-e) Details of [Pd II 8(-OH2)8(NH3)8(L1)4] and [Pd II 2(-OH2)2(NH3)4)] structures built within pores. Palladium, oxygen, carbon and nitrogen atoms are represented as violet, red, blue and pastel cyan colors. Crystal structure. The SCXRD data of 2-4 evidences that the 3D network remained crystalline during the MOFtemplated in-situ heterogeneous self-assembled process. The anionic Ni II 4Cu II 6 open-framework structure in 2-4 retains the known pillared square/octagonal layer architecture of 1 (Figure 2, 3 and Figures S1-S10). Both, the biggest hydrophobic octagonal channels and the square smallest pores, accommodate Pd(II) (2-3) and Pd(II)/Au(III) (4) complexes as result of L1-L3 binding to either mononuclear, [Pd II (NH3)4] 2+ , or dinuclear complexes, [Pd II 2(-O)(NH3)6] 2+ , of 1 (Figures 2, 3 and Figures S1-S10). The confined assemblies in 2-4, stabilized by mechanical-bonds with the MOF network, are strictly related to nature of the ligands (L) employed in terms of size, shape and imposed symmetry (see crystallographic section in Supplementary Information for structure refinement details and in-depth analysis of X-ray data). In 2, half of the Pd 2+ ions from the mononuclear and dinuclear entities in 1 are self-assembled by L1 giving [Pd II 8(-OH2)8(NH3)8(L1)4] 16+ square polygons, with [Pd II 2(-OH2)2(NH3)4] dimers residing at the corners of the quadrangular SCC (Figures 2, 3a left, 3b and Figures S1-S5) and stabilized by H-bonds to the MOF. Each Pd(II) exhibits regular square planar geometry, with Pd-N [2.02(2) and 2.09(2) Å for Pd-NL1 and Pd-NH3, respectively] and Pd-OH2 [1.99(2)](https://www.researchgate.net/profile/Emilio-Pardo/publication/333769652/figure/fig1/AS:870444399865862@1584541525902/a-e-Crystal-structure-determined-by-synchrotron-X-ray-diffraction-of-the-Pd8MOF-2_Q320.jpg)
![Figure S1. View along c crystallographic axis of crystal structures of 2 (a) and 3 (b) featuring channels filled by {[Pd II 2(-OH2)2(NH3)4)] 4+](https://www.researchgate.net/profile/Emilio-Pardo/publication/333769652/figure/fig2/AS:870444404064256@1584541526056/Figure-S1-View-along-c-crystallographic-axis-of-crystal-structures-of-2-a-and-3-b_Q320.jpg)
![Figure S3. A portion of crystal structures of 2 obtained by SCXRD. (a-b) Perspective views of a channel of 2 along the c or b axes showing, in detail, the Pd II 8 and Pd II 2 complexes. (c) Perspective view of a Pd II 8 SCC underlining the intra-assembly structural parameters related to Pd II ···Pd II separations. (d) Perspective view of propagation within [101] direction of a single channel underlining the inter-assembly structural parameters related to Pd II ···Pd II separations. Color scheme: Cu and Ni atoms from the network are represented by cyan and blue polyhedra, respectively, whereas organic ligands are depicted as yellow and purple sticks (in a-b) for ligand of the whole net and L1 ligand, respectively. Purple spheres represent Pd 2+ , whereas red, blue and grey sticks represent oxygen, nitrogen and carbon atoms, respectively (in c-d).](https://www.researchgate.net/profile/Emilio-Pardo/publication/333769652/figure/fig4/AS:870444404076550@1584541526387/Figure-S3-A-portion-of-crystal-structures-of-2-obtained-by-SCXRD-a-b-Perspective_Q320.jpg)
![Figure S4. Perspective views of a portion of a pore of the crystal structure of 2 along the b axis and the [111] direction (a and b) showing the [Pd II 8(-OH2)8(NH3)8(L1)4] 16+ SCCs and related structural parameters, stabilized by symmetric NH3 ···O interactions [H3N···Ooxamate of 2.913(9) Å]. Color scheme: palladium, violet sphere; carbon and nitrogen atoms of the ligands L1 are depicted as purple and blue sticks, respectively; nitrogen atoms, blue sticks, whereas ligands atoms and metal ions of the whole net have been depicted as yellow sticks.](https://www.researchgate.net/profile/Emilio-Pardo/publication/333769652/figure/fig5/AS:870444404064263@1584541526650/Figure-S4-Perspective-views-of-a-portion-of-a-pore-of-the-crystal-structure-of-2-along_Q320.jpg)
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Self-Assembly of Catalytically-Active Supramolecular Coordination Compounds within Metal-Organic Frameworks
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Supramolecular Coordination Compounds (SCCs) represent the power of Coordination Chemistry methodologies to self-assemble discrete architectures with targeted properties. SCCs are generally synthesised in solution, with isolat-ed fully-coordinated metal atoms as structural nodes, thus severely limited as metal-based catalysts. Metal-Organic Frameworks (MOFs) show unique features to act as chemical nanoreactors for the in-situ synthesis and stabilization of otherwise not accessible functional species. Here, we present the self-assembly of PdII SCCs within the confined space of a preformed MOF ([email protected]) and its post-assembly metalation to give a PdII-AuIII supramolecular assembly, crys-tallography underpinned. These [email protected] catalyse the coupling of boronic acids and/or alkynes, representative multisite metallic-catalysed reactions in which traditional SCCs tend to decompose, and retain its structural integrity as consequence of the synergetic hybridization between SCCs and MOF. These results open new avenues in both the synthesis of novel SCCs and their use on heterogeneous metal-based Supramolecular Catalysis.
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... The design, synthesis and development of coordination complexes of transition metals have attracted significant attention from researchers not only due to their myriad potential applications in various fields but also due to their intriguing structural topologies [1][2][3][4]. Organization of the molecular building blocks via a self-assembly process plays a decisive role in the structural topology and network architectures of coordination compounds [5,6]. However, it is challenging to develop network architectures of the desired dimensionalities as various synthetic factors such as the coordination behavior of the metal centers, organic moieties as ligands, pH, temperature, etc. can effectively influence the design and synthesis of the desired structural topologies [7][8][9]. ...
Two coordination compounds of Cu(II), namely, [Cu (phen)2Cl](NO3)·H2O (compound 1) and [Cu2(µ-Cl2)Cl2(Hdmpz)4] (compound 2), where phen = 1,10-phenanthroline and Hdmpz = 3,5-dimethylpyrazole, were synthesized at room temperature and characterized using elemental analysis, TGA, spectroscopic techniques (FT-IR and electronic) and single-crystal X-ray diffraction studies. The cooperative anion–π/π–π/anion–π assemblies involving the coordinated phen, along with the uncoordinated nitrate moieties, played pivotal roles in the stabilization of the crystal structure of compound 1. Unconventional type I Cl· · · Cl interactions involving the coordinated Cl atoms provided reinforcement to the crystal structure of compound 2. We theoretically explored the supramolecular assemblies observed in the crystal structures of compounds 1 and 2 using DFT calculations, MEP surface analysis and combined NCI plot/QTAIM computational tools. Theoretical analysis revealed that the antiparallel π-stacking interactions in compound 1 and the N–H···Cl H-bonds in compound 2 were the strong structure-guiding non-covalent synthons which stabilized the compounds. In the anion–π/π–π/anion–π assembly observed in compound 1, the anion–π interaction reinforced the π-stacking by reducing the electrostatic repulsion between the metal-coordinated electron-deficient phen rings
... Transition-metal-based coordination compounds involving organic ligands have attracted researchers because of their wide potential applications in catalysis, non-linear optics, semiconductor devices and in biology [1][2][3][4]. The intriguing self-assemblies of metal-organic compounds have also gained remarkable interest because of their interesting structural topologies and network architectures [5,6]. Metal-organic co-crystals, involving metal centers having a minimum of two components with lattice water molecules, have also received emphasis owing to their wide practical utilities in the pharmaceutical industry, electronic devices as well as in synthetic chemistry [7,8]. ...
Two new Ni(II) and Co(II) coordination compounds,viz., [Ni(H2O)5(DMAP)](IPhth)·2H2O (1) and [Co(Hdmpz)4(H2O)2]Cl2 (2) (where DMAP = 4-dimethylaminopyridine, IPhth = Isophthalate, Hdmpz = 3,5-dimethylpyrazole),were synthesized and characterized using elemental analysis, TGA, spectroscopic (FTIR and electronic) and single crystal X-ray diffraction techniques. Compound 1 crystallizes as a co-crystal hydrate of Ni(II), whereas compound 2 is a mononuclear compound of Co(II). The crystal structure analysis of compound 1 reveals the presence of various non-covalent interactions such as anion-π, π-π, C-H···π, C-H···C, etc., which stabilize the layered assembly of the compound. In compound 2, en-clathration of counter chloride ions within the supramolecular trimeric host cavity plays a crucial role in the stabilization of the compound. The non-covalent interactions observed in the crystal structures were further studied theoretically, focusing on the cooperative π-stacking interactions between the DMAP and IPhth counter-ions in 1. To identify the non-covalent interactions of the compounds, Hirshfeld surfaces and their associated two-dimensional fingerprint regions were analyzed. Theoretical calculations confirm that H-bonding interactions combined with the π-stacking contacts are crucial synthons for the solid-state stability of compound 1.
... Metal-organic frameworks (MOFs) are formed by the coordination of metal ions with organic ligands, and have the advantages of high specific surface area, large porosity, variable structure, and adjustable channel [24][25][26]. MOFs have become the attractive antimicrobial materials for applications in which a tunable antibacterial agent is required. Different from the action mechanism of small molecular antibacterial agents, the antibacterial performance of MOFs is mainly due to release of metal ions (such as Ag + , Cu 2+ , Zn 2+ , and Co 2+ ) from structure collapse, which destroy the cell membrane, lipid peroxidation, and DNA degradation to kill bacteria [27][28][29][30]. ...
Developing degradable filter membranes that inhibit bacterial infection for preventing particle matter and infectious disease has been a research hotspot. Here, the fiber membranes of polylactic acid (PLA)/HKUST-1 with porous structure through the entire fiber matrix were prepared by electrospinning method. Due to the HKUST-1 incorporation and the presence of pore through fiber, the hydrophobicity of prepared membranes had been improved. The PLA/HKUST-1 membranes exhibited the good antibacterial activity against Escherichia coli and Staphylococcus aureus, and the antibacterial rate for S. aureus reached 99.99%. The filtration performance of PLA/HKUST-1 membranes was better than that of the melt-blown fabric although their thickness was only about one-third of the thickness of the currently commercial polypropylene melt-blown fabric.
Metal-organic framework (MOF) materials have broad application prospects in catalysis because of their ordered structure and molecular adjustability. However, the large volume of bulky MOF usually leads to insufficient exposure of the active sites and the obstruction of charge/mass transfer, which greatly limits their catalytic performance. Herein, we developed a simple graphene oxide (GO) template method to fabricate ultrathin Co-metal-organic layer (2.0 nm) on reduced GO (Co-MOL@r-GO). The as-synthesized hybrid material Co-MOL@r-GO-2 exhibits highly efficient photocatalytic performance for CO2 reduction, and the CO yield can reach as high as 25,442 μmol/gCo-MOL, which is over 20 times higher than that of the bulky Co-MOF. Systematic investigations demonstrate that GO can act as a template for the synthesis of the ultrathin Co-MOL with more active sites and can be used as the electron transport medium between the photosensitizer and the Co-MOL to enhance the catalytic activity for CO2 photoreduction.
Since the emergence of metal-organic frameworks (MOFs), a myriad of thrilling properties and applications, in a wide range of fields, have been reported for these materials, which mainly arise from their porous nature and rich host-guest chemistry. However, other important features of MOFs that offer great potential rewards have been only barely explored. For instance, despite the fact that MOFs are suitable candidates to be used as chemical nanoreactors for the preparation, stabilization and characterization of unique functional species, that would be hardly accessible outside the functional constrained space offered by MOF channels, only very few examples have been reported so far. In particular, we outline in this feature recent advances in the use of highly robust and crystalline oxamato- and oxamidato-based MOFs as reactors for the in situ preparation of well-defined catalytically active single atom catalysts (SACS), subnanometer metal nanoclusters (SNMCs) and supramolecular coordination complexes (SCCs). The robustness of selected MOFs permits the post-synthetic (PS) in situ preparation of the desired catalytically active metal species, which can be characterised by single-crystal X-ray diffraction (SC-XRD) taking advantage of its high crystallinity. The strategy highlighted here permits the always challenging large-scale preparation of stable and well-defined SACs, SNMCs and SCCs, exhibiting outstanding catalytic activities.
Palladium-based metal-organic frameworks (Pd-MOFs) are an emerging class of heterogeneous catalysts extremely challenging to achieve due to the facile leaching of palladium and its tendency to be reduced. Herein, Pd(ii) was successfully incorporated in the framework of a MOF denoted as MUV-22 using a solvent assisted reaction. This stable MOF, with square-octahedron (soc) topology as MIL-127, and a porosity of 710 m2 g-1, is highly active, selective, and recyclable for the Suzuki-Miyaura allylation of aryl and alkyl boronates as exemplified with the coupling between cinnamyl bromide and Me-Bpin, a typically reluctant reagent in cross-coupling reactions.
Exploration of high-order multiphoton-excited fluorescent (H-MPEF) material for bioimaging with deeper tissue penetration and higher spatial resolution has attracted great interest but remains a challenge. Herein, a H-MPEF-responsive metal-organic framework-based material, ZLPH, was rationally fabricated by the pore confinement of a two-photon active unit (ZL) using the "ship-in-bottle" strategy. It demonstrated that the judicious selection effectively avoided the annoying weakened/quenched H-MPEF behavior due to the instability of ZL in the molecular state. Moreover, the obtained material, ZLPH, exhibited bright four-photon-excited fluorescence (4PEF) under the excitation of a 1550 nm femtosecond laser. In view of deep-tissue biological applications, it is envisioned that this work provides a promising platform for bright H-MPEF imaging.
Metal–organic frameworks (MOFs) as a class of unique porous crystalline materials have developed rapidly in the past decades. The unique features of component diversities, structural designability, and tunable porosities of MOFs endow them inherent superiorities as hosts to accommodate diverse species of guests. The resulting host–guest MOFs reveal a variety of properties and applications, which could be readily modulated through the tuning of the host, the guest, and the host–guest interactions. Therefore, the host–guest MOFs have attracted much attention and become a hot topic for research. This review will concentrate on the recent progress of host–guest MOFs. The achievements and understanding of host–guest MOF, including the components of host–guest systems, the types of species interactions, and the characterization methods have been reviewed and discussed. Based on this, the design and tuning principles for the construction of host–guest MOFs have been highlighted. The recently typical examples of function-oriented construction of host–guest MOF for various properties including optical, electrical, and catalytic properties have been overviewed. Furthermore, the challenges and perspectives of developing host–guest MOF materials have been generalized.
Two new coordination compounds of Zn(II) involving cyanopyridine ligands viz. [Zn(2,6-PDC)(3-CNpy)(H2O)2] (1) and [Zn(4-CNpy)2Cl2] (2) (2,6-PDC = 2,6-pyridinedicarboxylate, 3-CNpy = 3-cyanopyridine, 4-CNpy = 4-cyanopyridine) have been synthesized and characterized using elemental analysis, TGA, spectroscopic (FT-IR, electronic and ¹H-NMR) techniques and single crystal XRD. Crystal structure analyses of 1 and 2 unfold the presence of unusual π(CN)-π interactions which provide stability to the layered assemblies of the compounds. Anion-π with parallel nitrile-nitrile interactions in 1 and unconventional anion-π(nitrile) with antiparallel nitrile-nitrile interactions in 2 also contribute to the stability of the crystal structures. Antiparallel CO⋯CO interactions give additional reinforcement to the crystal structure of 1. DFT calculations in combination with MEP surface and NCI plot/QTAIM analyses on different self-assembled supramolecular dimers of the compounds revealed that the unusual CN···π interactions in 1 and Chlorine-π(nitrile) in 2 are energetically significant. The studies also reveal that both H-bonding and π-stacking interactions are energetically important for the stability of the compounds. Compounds 1 and 2 mediated anticancer evaluation on Dalton's lymphoma (DL) cancer cells has been explored considering cytotoxicity and apoptosis assays. The compounds induce significant concentration dependent cytotoxicity in DL cells with negligible effects on normal PBMC cells. Molecular docking studies reveal that the compounds effectively interact with the active sites of antiapoptotic proteins which are actively involved in cancer progression. Pharmacophore features of the structures of the compounds have been finally identified to establish the structure activity relationships (SAR).
A newly lower rim functionalized octa-substituted resorcin[4]arene based supramolecular compounds variable alkoxy side chain (-OC4H9, -OC6H13, -OC8H17, -OC10H21) has been synthesized by simple two step procedure method. The propose method...
Herein we describe the topological influence of zigzag ligands in the assembly of Zr(IV) metal-organic frameworks (MOFs). Through a transversal design strategy using reticular chemistry, we were able to synthesize a family of isoreticular Zr(IV)-based MOFs exhibiting the bcu – rather than the fcu – topology. Our findings underscore the value of the transversal parameter in organic ligands for dictating MOF architectures.
Nitrogen dioxide (NO2) is a major air pollutant causing significant environmental1,2 and health problems3,4. We report reversible adsorption of NO2 in a robust metal-organic framework. Under ambient conditions, MFM-300(Al) exhibits a reversible NO2 isotherm uptake of 14.1 mmol g-1, and, more importantly, exceptional selective removal of low-concentration NO2 (5,000 to <1 ppm) from gas mixtures. Complementary experiments reveal five types of supramolecular interaction that cooperatively bind both NO2 and N2O4 molecules within MFM-300(Al). We find that the in situ equilibrium 2NO2 ↔ N2O4 within the pores is pressure-independent, whereas ex situ this equilibrium is an exemplary pressure-dependent first-order process. The coexistence of helical monomer-dimer chains of NO2 in MFM-300(Al) could provide a foundation for the fundamental understanding of the chemical properties of guest molecules within porous hosts. This work may pave the way for the development of future capture and conversion technologies.
Self-assembly of a cis-blocked Pd(II) 90 ditopic acceptor [cis-(tmeda)Pd(NO3)2] (M) with a tetradentate donor L1 [benzene-1,4-di(4-terpyridine)] in 2:1 molar ratio yielded two isometric molecular barrels MB1 and MB3 in DMSO [tmeda = N,N,NN-tetramethylethane-1,2-diamine]. Exclusive formation of the symmetrical tetrafacial barrel (MB1) was achieved when the self-assembly was performed in aqueous medium. The presence of a large confined cavity makes MB1 as a potential molecular container. Spiropyran (SP) compounds exist in stable closed spiro-form in visible light and converts to transient open merocyanine (MC) form upon irradiation with UV-light or upon strong heating. The transient MC form readily converts to the stable closed SP form in visible light. MB1 has been employed as a safe container to store the planar and unstable merocyanine isomers (MC1/2) of different spiropyran molecules (SP1/2) [SP1/2 = 6-bromo-spiropyran and 6-nitrospiropyran] for several days. The transient MC forms (MC1 and MC2) were found to be stable inside the molecular container MB1 under visible light and even in presence of different stimuli such as heat and UV-light for long time. Such stabilization of MC forms inside the confined cavity of MB1 is noteworthy. This phenomenon was generalized by utilizing a carbazole based molecular barrel (MB2) as a host, which also showed a similar stabilization of transient MC form in visible light at room temperature. Moreover, reverse thermochromism was observed as a result of heating of the MC1⊂MB2 complex, which de-encapsulates the guest in the form of SP1 to give a colourless solution. Moreover, both the host molecules (MB1, MB2) were capable of stabilizing transient MC2 even in solid state. Such stabilization of transient MC forms in solid state and transformation of SP forms to MC forms in solid state in presence of molecular barrel are remarkable; and these properties have been employed in developing a magic ink.
A series of platinum (II) metallacycles were prepared via the coordination-driven self-assembly of a phenazine-cored dipyridyl donor with a 90° Pt(II) acceptor and various dicarboxylate donors in a 1:1:2 ratio. While the metallacycles dis-play similar absorption profiles, they exhibit a trend of blue-shifted fluorescence emission with the decrease in the bite angles between the carboxylate building blocks. Comprehensive spectroscopic and dynamic studies, as well as a computational approach were conducted, revealing that the difference in the degree of constraint imposed on the ex-cited-state planarization of the phenazine core within these metallacycles results in the distinct photophysical behav-iors. As such, a small initial difference in the dicarboxylate building blocks is amplified into distinct photophysical properties of the metallacycles, which is reminiscent of the efficient functional tuning observed in natural systems. In addition to the pre-assembly approach, the photophysical properties of a metallacycle can also be modulated using a post-assembly modification to the dicarboxylate building block, suggesting another strategy for functional tuning. This research illustrated the potential of coordination-driven self-assembly for the preparation of materials with precisely tailored functionalities at the molecular level.
Metal-organic frameworks (MOFs) based on edge-transitive 6-c acs nets are well-developed and can be synthesized from trinuclear metal clusters and ditopic ligands, i.e., MOF-235 and MIL-88. The rational design of noncatenated acs-MOFs by symmetry-matching between trigonal prismatic organic ligands and trinuclear clusters, however, remains a great challenge. Herein, we report a series of acs-MOFs (NU-1500) based on trivalent trinuclear metal (Fe ³⁺ , Cr ³⁺ , and Sc ³⁺ ) clusters and a rigid trigonal prismatic ligand courtesy of reticular chemistry. The highly porous and hydrolytically stable NU-1500-Cr can be activated directly from water and displays an impressive water vapor uptake with small hysteresis.
The field of supramolecular chemistry has its foundation in molecular recognition and selective binding of guest molecules, often with remarkably strong binding affinities. The field evolved to leverage these favorable interactions between the host and its guest to catalyze simple, often biomimetic transformations. Drawing inspiration from these early studies, self-assembled supramolecular hosts continue to capture a significant amount of interest toward their development as catalysts for increasingly complex transformations. Nature often relies on microenvironments, derived from complex tertiary structures and a well-defined active site, to promote reactions with remarkable rate acceleration, substrate specificity, and product selectivity. Similarly, supramolecular chemists have become increasingly intrigued by the prospect that self-assembly of molecular components might generate defined and spatially segregated microenvironments that can catalyze complex transformations.
Metal–organic frameworks (MOFs) and porous coordination polymers (PCPs) have been well-recognized as emerging porous materials that afford highly tailorable and well-defined nanoporous structures with three-dimensional lattices. Because of their microporous nature, MOFs can accommodate small molecules in their lattice structure, thus discriminating them on the basis of their size and physical properties and enabling their separation even in the gas phase. Such characteristics of MOFs have attracted significant attention in recent years for diverse applications and have ignited a worldwide race toward their development in both academic and industrial fields. Most recently, new challenges in porous materials science demand processable liquid, melt, and amorphous forms of MOFs. This trend will provide a new fundamental class of microporous materials for further widespread applications in many fields. In particular, the application of flexible membranes for gas separation is expected as an efficient solution to tackle current energy-intensive issues. To date, amorphous MOFs have been prepared in a top-down approach by the introduction of disorder into the parent frameworks. However, this new paradigm is still in its infancy with respect to the rational design principles that need to be developed for any approach that may include bottom-up synthesis of porous soft materials.
A combined experimental and computational approach has been used to shed light on the mechanism of the Pd-catalyzed oxidative homocoupling of alkynes using oxygen as oxidant. Mechanistic understanding is important because of the synthetically relevant direct involvement of oxygen in the oxidative coupling, and because of the presence of related processes as undesired side reactions in cross-coupling reactions involving terminal alkynes. A low-ligated [Pd(PPh3)(alkyne)] complex is key in the process and it can be conveniently generated from allylic palladium(II) complexes in the presence of a base or from Pd(I) allylic dimers as precatalysts. The catalytic coupling occurs by alkyne metalation to give an anionic [Pd(PPh3)(alkynyl)]– complex that is then oxidized by oxygen. The interaction of oxygen occurs only on this electron rich Pd(0) anionic species and leads to a κ²-peroxo palladium(II) singlet intermediate that undergoes subsequent protonolysis to a κ¹-hydroperoxide palladium(II) complex. The second alkyne metalation occurs on the Pd(II) hydroperoxo derivative, this ligand acting as an internal base, to give a bis(alkynyl)Pd(II) complex that evolves to the product by reductive elimination as the product-forming step. This reaction is an oxidase-type process that, in contrast to most Pd-catalyzed oxidative processes, occurs without separation of the substrate transformation and the catalyst oxidation, both processes being intertwined and dependent of one another.
It is a general and common practice to carry out single crystal X-ray diffraction experiments at cryogenic temperatures in order to obtain high resolution data. In this report, we show that this practice is not always applicable to MOFs especially when these structures are highly porous. Specifically, two new MOFs are reported here (MOF-1004 and 1005) where the collection of the diffraction data at lower temperature (100 K) was not of sufficient quality to allow structure solution. Indeed, collection of data at higher temperature (290 K) gave atomic resolution data allowing for structure solution. We find that this inverse behavior contrary to normal practice is also true for some well-established MOFs (MOF-177 and UiO-67). Close examination of the X-ray diffraction data obtained for all four MOFs at various temperatures led us to conclude that disordered guests-framework interactions play a profound role in introducing disorder at low temperature, and the diminishing strength of these interactions at high temperature reduces the disorder and gives high resolution diffraction data. We believe our finding here is more widely applicable to other highly porous MOFs and crystals containing highly disordered molecules.
Rational design and construction of MOFs with intricate structural complexity are of prime importance in reticular chemistry. We report our latest addition to the design toolbox in reticular chemistry, namely the concept of merged-nets based on merging two edge-transitive nets into a minimal edge-transitive net for the rational construction of intricate mixed-linker MOFs. In essence, a valuable net for design enclosing two edges (not related by symmetry) is rationally generated by merging two edge-transitive nets, namely (3,6)-coordinated spn and 6-coordinated hxg. The resultant merged-net, (3,6,12)-coordinated sph net with net transitivity [32] enclosing three nodes and two distinct edges, offers potential for deliberate design of intricate mixed-linker MOFs. We report the implementation of the merged-net approach for the construction of isoreticular RE mixed-linker MOFs, sph-MOF-1 to 4, based on the assembly of 12-c hexanuclear carboxylate-based MBBs, displaying cuboctahedral building units, 3-c tritopic ligands, and 6-c hexatopic ligands. The resultant sph-MOFs represent the first examples of MOFs where the underlying net is merged from two 3 periodic edge-transitive nets, spn and hxg. Distinctively, the sph-MOF-3 represents the first example of a mixed-linker MOF to enclose both trigonal and hexagonal linkers. The merged-nets approach allowed the logical practice of isoreticular chemistry by taking into account the mathematically correlated dimensions of the two ligands to afford the deliberate construction of a mixed-linker mesoporous MOF, sph-MOF-4. Merged-net equation and two key parameters, ratio constant and MBB constant, are disclosed. Merged-net strategy for design of mixed-linker MOFs by strictly controlling the size ratio between edges is introduced.