Electrochemical Generation of an Open-Shell Gold(III)-Dithiolene Porous Coordination Polymer

<p indent="0mm">Host-guest chemistry, distinguished by its involvement in the self-assembly of molecular systems into well-organized functional assemblies through supramolecular interactions, remains a fundamental concept within the field of supramolecular chemistry. Porous coordination polymers (PCPs) represent a fascinating and distinctive category of porous crystalline materials that have increasingly captured the attention of researchers. Owing to the modularized design and construction features of PCPs, they could exhibit highly tunable framework structures and properties, which have been developed as an exciting realm for exploration. The remarkable tunability of micro-nano confined space in PCPs, stemming from their versatile structures and components, make them a highly versatile host platform for the construction of functional host-guest systems through the introduction of various guest species. The highly tunable size and geometry of the confined space in the host framework of PCPs allow the manipulation of the distribution and arrangement of guest species, and the diversity of PCPs hosts and guest species endows the corresponding host-guest systems with distinctive host-guest interactions. The interaction between hosts and guests may induce new features such as electron/energy transfer, redox reactions, or other processes, resulting in emergent properties different from those of the individual hosts or guests. Accordingly, the functionalization of micro-nano confined space in PCPs could be achieved to give rise to a vast array of functional materials. The resulting host-guest PCPs can exhibit a wealth of properties and potential applications, and their performance can be optimized by adjusting the host, guest, and host-guest interactions. Therefore, host-guest PCPs have attracted much attention in the current research, and have gradually become a research hotspot. However, the research on the strategy and method of functionally oriented construction of micro-/nano-confined space in PCPs is still going deep, so it is indispensable to review the rational construction and regulation of PCPs system and its application of functionally oriented research. This paper aims to provide a comprehensive review of recent advancements in the construction and properties regulation of the functional micro-/nano-confined space in coordination polymers focusing on the luminance and electricity properties. The comprehensive understanding and analysis of host-guest PCPs, encompassing the components of host-guest systems and the diverse interactions between species have been reviewed and discussed. Based on this, the design and fine-tuning principles for the construction of micro-/nano-confined space in PCPs have been highlighted. Additionally, the review offers an overview of recent exemplary cases wherein host-guest PCPs have been purposefully constructed to optimize a range of properties, including optical and electrical characteristics. In addition, the further development direction and challenges needed to be addressed are raised, including the controllable orientation and ordered arrangement of guest species, understanding the interactions between PCPs and guests, exploring the combination of different guest species and developing host-guest PCPs-based devices. The insights derived from this comprehensive review will serve as invaluable guidelines, offering researchers and innovators a solid reference for shaping the future of this rapidly evolving field.

ConspectusThe precise and effective separation of similar mixtures is one of the fundamental issues and essential tasks in chemical research. In the field of gas/vapor separation, the size difference among the molecular pairs/isomers of light hydrocarbons and aromatic compounds is generally 0.3-0.5 Å, and the boiling-point difference is generally 6-15 K. These are necessary industrial raw materials and have great separation demands. Still, their separation mainly relies on energy-intensive distillation technology. On the other hand, remarkably similar substances such as oxygen/argon and isotopologues usually exhibit size differences of only 0-0.07 Å and boiling-point differences of only 1-3 K. Although their industrial separation can be realized, their efficiency is considerably low. Therefore, effectively separating remarkably similar mixtures is crucial in fundamental chemistry and industry, but it remains a significant challenge. Porous coordination polymers (PCPs) or metal-organic frameworks (MOFs) are emerging materials platforms for designing adsorbents for separating similar mixtures. However, the reported PCPs did not work well for separating remarkably similar substances. The framework structures of the mainstream PCPs remain unchanged (rigid) or significantly change (globally flexible) upon adsorption. However, rigid and globally flexible PCPs find controlling the pore aperture in subangstrom precision challenging, a prerequisite for distinguishing remarkably similar substances. Thus, novel mechanisms and materials design principles are urgently needed to realize PCPs-based adsorptive separation of remarkably similar mixtures.To confront the obstacles in separating remarkably similar mixtures, our group started contributing to this field in 2017. We employed locally flexible PCPs as the materials designing platform, whose local motions of the side substituent groups potentially regulate the pore apertures to design and control the gas/vapor diffusion in PCPs. Specifically, we encoded dynamic flipping molecular motions into the diffusion-regulatory gate functionality. The ligands were designed by integrating carboxylic coordination groups with nonplanar fused-ring moieties, with the latter moieties exhibiting flipping motion around their equilibrium positions with small energy increases. Such local motions of ligands lead to the dynamic opening and blocking of PCP channels, thus termed flipping dynamic crystals (FDCs). FDCs feature distinctive temperature-responsive adsorption behaviors due to the competition of thermodynamics and kinetics under diffusion regulation, enabling differentiation of remarkably similar mixtures by each gate-admission temperature much higher than the boiling-point temperature of each component. Even when the molecular sizes are the same in the water isotopologue mixtures, FDCs can separate each isotopologue by amplifying their diffusion-rate differences. Finally, by combining the thermodynamic and kinetic factors, FDCs achieve temperature-switched recognition of CO2/C2H2 and diffusion-rate sieving of C3H6/C3H8. Therefore, our work provides a platform for designing locally flexible PCPs by introducing subangstrom precision in flexibility. This opens up the feasibility of separating remarkably similar mixtures on scientific principles. In this Account, we summarize our above ongoing research contributions, including (i) the design of flipping ligands and FDCs, (ii) the characterization of flipping motions, (iii) the gas/isotopologue sorption behaviors, and (iv) the separation of gases and isotopologues. Overall, our studies offer a new aspect of soft porous crystals and provide future opportunities for relevant researchers in this field.

Absorption of CO2 and CS2 molecules into the Hofmann-type three-dimensional porous coordination polymer (PCP) {Fe(Pz)[Pt(CN)4]}n (Pz = pyrazine) was theoretically explored with the ONIOM(MP2.5 or SCS-MP2:DFT) method, where the M06-2X functional was employed in the DFT calculations. The binding energies of CS2 and CO2 were evaluated to be -17.3 and -5.2 kcal mol(-1), respectively, at the ONIOM(MP2.5:M06-2X) level and -16.9 and -4.4 kcal mol(-1) at the ONIOM(SCS-MP2:M06-2X) level. It is concluded that CS2 is strongly absorbed in this PCP but CO2 is only weakly absorbed. The absorption positions of these two molecules are completely different: CO2 is located between two Pt atoms, whereas one S atom of CS2 is located between two Pz ligands and the other S atom is between two Pt atoms. The optimized position of CS2 agrees with the experimentally reported X-ray structure. To elucidate the reasons for these differences, we performed an energy decomposition analysis and found that (i) both the large binding energy and the absorption position of CS2 arise from a large dispersion interaction between CS2 and the PCP, (ii) the absorption position of CO2 is mainly determined by the electrostatic interaction between CO2 and the Pt moiety, and (iii) the small binding energy of CO2 comes from the weak dispersion interaction between CO2 and the PCP. Important molecular properties relating to the dispersion and electrostatic interactions, which are useful for understanding and predicting gas absorption into PCPs, are discussed in detail.

Sol−gel polycondensation of tetramethoxysilane was performed in nanochannels of porous coordination polymers (PCPs), resulting in the formation of nanosized silica dispersed homogeneously inside the channels. In this system, the growth of silica was highly constrained, which increases the hydrophilic silanol moieties on the surface of silica particles. Deposition of silica particles into the nanochannels of PCPs could allow the remarkable alternations of the porous properties of the PCPs. Compared to the original PCP systems, adsorption of water was greatly enhanced because of the strong interaction between silica and water. The PCP−silica nanocomposites preferred to adsorb 1,4-dioxane rather than cyclohexane, showing the remarkable affinity of PCP−silica hybrids to hydrophilic molecules. It is noteworthy that pore dimensionality of PCPs have large effects on the adsorption properties of PCP−silica hybrids. Compared to a PCP with three-dimensional interconnecting nanochannels, a PCP with one-dimensional porous system showed more significant gate effects on selectivity for the adsorbates.

The design of monomer sequences in polymers has been a challenging research subject, especially in making vinyl copolymers by free-radical polymerization. Here, we report a strategy to obtain sequence-regulated vinyl copolymers, utilizing the periodic structure of a porous coordination polymer (PCP) as a template. Mixing of Cu2+ ion and styrene-3,5-dicarboxylic acid (S) produces a PCP, [Cu(styrene-3,5-dicarboxylate)]n, with the styryl groups periodically immobilized along the one-dimensional channels. After the introduction of acrylonitrile (A) into the host PCP, radical copolymerization between A and the immobilized S is performed inside the channel, followed by decomposing the PCP to isolate the resulting copolymer. The predominant repetitive SAAA sequence in the copolymer is confirmed by monomer composition, NMR spectroscopy and theoretical calculations. Copolymerization using methyl vinyl ketone also provides the same type of sequence-regulated copolymer, showing that this methodology has a versatility to control the copolymer sequence via transcription of PCP periodicity at the molecular level.

Porous coordination polymers (PCPs), constructed from organic linkers and metal ions, can provide special pore environments for selective CO2 capture. Although many PCPs have been reported, a rational design for identifying PCPs that adsorb CO2 molecules with a low binding energy, high separation ability and high chemical stability remains a great challenge. Here, we propose and validate, experimentally and computationally, a new PCP, [La(BTN)DMF]·guest (PCP-1⊃guest), that has a large aromatic organic surface and a low binding energy for high CO2 separation from four-gas mixtures (CO2–N2–O2–CO) at ambient temperature. In addition, it shows good water and chemical stability; in particular, it is stable from pH = 2 to 12 at 100 °C, which is unprecedented for carboxylate-based PCPs.

Three new coordination polymers, namely, {[Cu2(bcpmba)(μ4-OH)]·2H2O}n (1), [Mn(Hbcpmba)]n (2), and [Co2(bcpmba)(μ3-OH)·H2O]n (3) (H3bcpmba = 3,5-bi(4-carboxy-phenylene-methylene-oxy)-benzoic acid) have been prepared under solvothermal conditions. The complexes were characterized by physico-chemical and spectroscopic methods. All of the compounds 1–3 contain one-dimensional (1D) chains extended via the bcpmba3− bridge to generate 2D porous layers which are further connected by bcpmba3− ligands to form 3D porous coordination polymers. The result shows configurations of the ligand have an important influence on the structure. Magnetic susceptibility measurements indicate that compounds 1–3 exhibit antiferromagnetic coupling between adjacent metal ions, with the corresponding J value of − 2.76 cm−1 for compound 2. Three porous coordination polymers, namely, {[Cu2(bcpmba)(μ4-OH)]·2H2O}n (1), [Mn(Hbcpmba)]n (2) and [Co2(bcpmba)(μ3-OH)·H2O]n (3) have been synthesized by employing a semi-rigid aromatic multicarboxylate acid (3,5-bi(4-carboxy-phenylene-methylene-oxy)-benzoic acid, H3bcpmba) under solvothermal conditions. Porous coordination polymers 1–3 consisted of 1D chain extended via the bridge of bcpmba3– to generate 2D porous layers and further connected by bcpmba3– to provide a 3D porous frameworks. The results reveal that different coordination modes of the ligand play an important role in the self-assembly processes to form metal-organic frameworks with different structures. Moreover, compounds 1–3 exhibited antiferromagnetic properties.

Porous coordination polymer synthesized from a polydentate 8-hydroxyquinoline ligand via interface reaction

Photochemical [2+2] cycloaddition of 1,4-bis[2-(4-pyridyl)ethenyl]benzene, carried out in a CdII porous coordination polymer (PCP), produces different isomeric products depending on the guest solvent present in the PCP during irradiation. The nature of the included guest influences the conformation of the ligand, and thus the outcome of the cycloaddition reaction. We demonstrate controlled production of the two isomers from the same PCP by simple exchange of solvent.

Nonspherical polymer particles have been efficiently prepared in different morphological crystals of porous coordination polymers (PCPs) by in situ radical polymerization of styrene and methylmethacrylate, followed by removal of the host PCP frameworks in aqueous tetrasodium ethylenediaminetetraacetate (Na-EDTA) solution. In this replication process, the isolated vinyl polymer particles retained the size and morphologies of the original PCP particles, although the polymer chains were not stabilized by cross-linking. This morphological retention of vinyl polymers after the isolation from the PCP matrixes was ensured by the rigidity and porosity of the polymers, which was confirmed by DSC and adsorption measurements. The unconventional assembly of polymer chains in the particles is of interest from the viewpoints of functional properties of the polymer particles.

The design of inexpensive and less toxic porous coordination polymers (PCPs) thatshow selective adsorption or high adsorption capacity is a critical issue inresearch on applicable porous materials. Although use of Group II magnesium(II) andcalcium(II) ions as building blocks could provide cheaper materials and lead toenhanced biocompatibility, examples of magnesium(II) and calcium(II) PCPs areextremely limited compared with commonly used transition metal ones, because neutralbridging ligands have not been available for magnesium(II) and calcium(II) ions.Here we report a rationally designed neutral and charge-polarized bridging ligand asa new partner for magnesium(II) and calcium(II) ions. The three-dimensionalmagnesium(II) and calcium(II) PCPs synthesized using such a neutral ligand arestable and show selective adsorption and separation of carbon dioxide over methane at ambient temperature. Thissynthetic approach allows the structural diversification of Group II magnesium(II)and calcium(II) PCPs.

Either of two different isomeric products can be selectively obtained by photochemical [2+2] cycloaddition of 1,4-bis[2-(4-pyridyl)ethenyl]-benzene within a porous coordination polymer (PCP). The cycloaddition product obtained depends on the temperature at which irradiation occurs. A rare temperature-induced phase transition alters the conformation of the photoactive ligand in the PCP, and thereby the positions at which cycloaddition occurs. We show that the multistimulus responsive nature of this particular PCP is due to the flexibility of the ligands employed.

In this work, 5, 10, 15, 20‐Tetra‐(4‐aminophenyl) porphyrin (TAPP) was used as gelator to prepare metal‐porphyrin porous coordination polymer (PCP) via solvothermal process, Soxhlet extraction and supercritical CO2 extraction. Firstly, the metal‐porphyrin organic gel (MOG) was prepared as intermediate with solvothermal method. The generation of gels is associated with many factors. When four acetates [Co(Ac)2•4H2O, Zn(Ac)2•2H2O, Mn(Ac)2•4H2O and Ni(Ac)2•7H2O] reacted with TAPP, only the reaction between Co(Ac)2•4H2O and TAPP could form desired metal‐porphyrin organic gel. The influences of solvent, concentration and anions were investigated in the gelation process. Secondly, the residual reactants and solvent molecules in MOG were removed through Soxhlet extraction and supercritical CO2 extraction. The Co‐PCP is an amorphous material with a hierarchical porous structure can effectively catalyze the oxidation of ethylbenzene and also exhibits a strong adsorptive capacity for the strong‐polar solvent molecules.

Adsorptions of CO, N2, NO, and CO2 in a paddle-wheel-type porous coordination polymer (PCP) [Cu(aip)]n (aip = 5-azidoisophthalate) were investigated with ONIOM[MP4(SDQ):ωB97XD] method using a model system consisting of two [Cu2(O2CC6H4-R)4] units (R = H and Me) and one [Cu2(O2CC6H4–R)4] unit, namely, dimer and monomer models. The experimental CO adsorption position was reproduced well by the present calculation with the dimer model. For adsorptions of CO, N2, NO, and CO2 in the dimer model, the position of gas molecule deviates from the normal one that is found in the monomer model and becomes more distant from the surrounding phenyl group(s) of the neighbor [Cu(aip)] unit. For all of these gas molecules, the calculated binding energy (BE) at the deviating adsorption position is larger than that at the normal one against our expectation that the normal position is the best for the gas adsorption. The deviation of gas adsorption position arises from the interaction between the organic linker (O2CC6H4–R moiety) and gas molecule. For all cases, the exchange repulsion with the organic linker decreases to a larger extent than the attractive electrostatic and dispersion interactions decrease when going from the normal position to the deviating one. To enhance the binding energy of gas molecule, the introduction of electron-donating substituent on phenyl moiety is computationally recommended for this PCP.

Starting from a chiral building block--α-cyclodextrin--and rubidium salts, the crystallization of a complex of chiral helices, which constitute a "green" porous coordination polymer, has been realized. Cyclodextrin molecules coordinated by rubidium ions form porous, infinitely long left-handed helical channels, interdigitated with each other. A theoretical examination of the potential of this new material to act as a medium for chiral separation is presented.