Porous coordination polymers with ubiquitous and biocompatible metals and a neutral bridging ligand

Insight into the Gas-Induced Phase Transformations in a 2D Switching Coordination Network via Coincident Gas Sorption and In Situ PXRD

Switching coordination networks (CNs) that reversibly transform between narrow or closed pore (cp) and large pore (lp) phases, though fewer than their rigid counterparts, offer opportunities for sorption-related applications. However, their structural transformations and switching mechanisms remain underexplored at the molecular level. In this study, we conducted a systematic investigation into a 2D switching CN, [Ni(bpy)2(NCS)2]n, sql-1-Ni-NCS (1 = bpy = 4,4'-bipyridine), using coincident gas sorption and in situ powder X-ray diffraction (PXRD) under low-temperature conditions. Gas adsorption measurements revealed that C2H4 (169 K) and C2H6 (185 K) exhibited single-step type F-IVs sorption isotherms with sorption uptakes of around 180-185 cm3 g-1, equivalent to four sorbate molecules per formula unit. Furthermore, parallel in situ PXRD experiments provided insight into sorbate-dependent phase switching during the sorption process. Specifically, CO2 sorption induced single-step phase switching (path I) solely between cp and lp phases consistent with the observed single-step type F-IVs sorption isotherm. By contrast, intermediate pore (ip) phases emerged during C2H4 and C2H6 desorption as well as C3H6 adsorption, although they remained undetectable in the sorption isotherms. To our knowledge, such a cp-lp-ip-cp transformation (path II) induced by C2H4/6 and accompanied by single-step type F-IVs sorption isotherms represents a novel type of phase transition mechanism in switching CNs. By virtue of Rietveld refinements and molecular simulations, we elucidated that the phase transformations are governed by cooperative local and global structural changes involving NCS- ligand reorientation, bpy ligand twist and rotation, cavity edge (Ni-bpy-Ni) deformation, and interlayer expansion and sliding.

Synthesis, Structural Versatility, Magnetic Properties, and I- Adsorption in a Series of Cobalt(II) Metal-Organic Frameworks with a Charge-Neutral Aliphatic (O,O)-Donor Bridge

Four new metal-organic frameworks based on cobalt(II) salts and 1,4-diazabicyclo[2.2.2]octane N,N'-dioxide (odabco) were obtained. Their crystallographic formulae are [Co3(odabco)2(OAc)6] (1, OAc- = acetate), [Co(H2O)2(HCOO)2]·odabco (2), [Co2(H2O)(NO3)(odabco)5](NO3)3·3.65H2O (3), and [Co2(DMF)2(odabco)4](NO3)4·3H2O (4; DMF = N,N-dimethylformamide). Crystal structures of 1-4 were determined by single-crystal X-ray crystallography. Coordination polymer 1 comprises binuclear and mononuclear metal-acetate blocks alternating within uncharged one-dimensional chains, in which odabco acts as a bridging ligand. A layered Co(II) formate 2 contains odabco only as guest molecules located in the interlayer space. Layered compound 3 and three-dimensional 4 have cationic coordination frameworks with 26% and 34% specific void volumes, respectively, unveiling high structural diversity of Co(II)-odabco MOFs based on quite a rare aliphatic moiety. Magnetization measurements were performed for 1, 3, and 4 and the obtained data were interpreted on the basis of their crystal structures. A strong (J/kB~100 K) antiferromagnetic coupling was found within binuclear metal blocks in 1. Ion exchange experiments revealed a considerable iodide uptake by 3 resulting in an up to 75% guest nitrate substitution within the voids of a coordination framework, found by capillary zone electrophoresis data and confirmed by single-crystal XRD. A preservation of 3 crystallinity during the exchange allowed for the guest I- positions within a new adduct with the formula [Co2(H2O)(NO3)(odabco)5]I2(NO3)·1.85H2O (3-I) to be successfully determined and the odabco aliphatic core to be revealed as a main adsorption center for quite large and easily polarizable iodide anions. In summary, this work presents a comprehensive study for a series of 1,4-diazabicyclo[2.2.2]octane N,N'-dioxide-based MOFs of cobalt(II) within the framework of magnetic properties and reports the first example of anion exchange in odabco-based coordination networks, supported by direct X-ray structural data. The reported results unveil promising applications of such frameworks bearing ligands with an aliphatic core in the diverse structural design of selective adsorbents and other types of functional materials.

Vinylimidazole-Based Polymer Electrolytes with Superior Conductivity and Promising Electrochemical Performance for Calcium Batteries

Calcium batteries are next-generation energy storage technologies with promising techno-economic benefits. However, performance bottlenecks associated with conventional electrolytes with oxygen-based coordination chemistries must be overcome to enable faster cation transport. Here, we report an imidazole-based polymer electrolyte with the highest reported conductivity and promising electrochemical properties. The polymerization of vinylimidazole in the presence of calcium bis(trifluoromethanesulfonyl)imide (Ca(TFSI)₂) salt creates a gel electrolyte comprising a polyvinyl imidazole (PVIm) host infused with vinylimidazole liquid. Calcium ions effectively coordinate with imidazole groups, and the electrolytes present room temperature conductivities of >1 mS/cm. Reversible redox activity in symmetric Ca cells is demonstrated at 2 V overpotentials, stable cycles at 0.1 mA/cm², and areal capacities of 0.1 mAh/cm². Softer coordination, polarizability, and closer coordinating site distances of the imidazole groups can explain the enhanced properties. Hence, imidazole is a suitable chemical benchmark for the future design and advancement of polymer electrolytes for calcium batteries.

Fe-Based Metal-Organic Frameworks for the Controlled Release of Fertilizer Nutrients

Due to the controlled-delivery function of metal-organic frameworks (MOFs) for gases, drugs, and pesticides, iron-based MOFs (Fe-MOFs) were explored in the laboratory as a novel fertilizer, which showed potential for use in the fertilizer industry; the challenge in the industrial scale application of Fe-MOFs in practical crop production was mainly the impact of scaling-up to energy and heat transfer, as well as the reaction yield. In this study, Fe-MOFs were hydrothermally synthesized both in the laboratory scale and in the pilot scale, their structure and components were characterized using various spectroscopic techniques, and then their nutrient release and degradation behaviors were investigated. The results showed that Fe-MOFs were successfully synthesized in both scales with similar yields around 27%, and the Fe-MOFs showed a similar structure with the molecular formula of C₂H₁₅Fe₂N₂O₁₈P₃. The nutrients N, P, and Fe were present in the Fe-MOFs with the average contents of 6.03, 14.48, and 14.69%, respectively. Importantly, the nutrient release rate and pattern of Fe-MOFs well matched with the crop growth, which greatly promoted the rice yield. Therefore, the environmentally friendly compounds of Fe-MOFs could be industrially produced and used as an innovative fertilizer with unique features of varied nutrients and controlled release.

Considerations on Gated CO2 Adsorption Behavior in One-Dimensional Porous Coordination Polymers Based on Paddlewheel-Type Dimetal Complexes: What Determines Gate-Opening Temperatures?

Low-dimensional coordination polymers such as one-dimensional chains often exhibit gated guest sorption accompanying structural transition at a temperature (T_G), which is associated with an external pressure of the guest (P_G) characteristic to the material and guest used. This phenomenon can be evaluated using the Clausius-Clapeyron relationship with the equation d(ln P_G)/d(1/T_G) = ΔH_G/R, where ΔH_G and R are the transition enthalpy and gas constant, respectively. In this study, gated CO₂ adsorption behavior was investigated in a one-dimensional chain based on a benzoate-bridged paddlewheel diruthenium(II,II) complex with a phenazine (phz) linker, [Ru₂(p-MeOPhCO₂)₄(phz)] (1; p-MeOPhCO₂^- = p-anisate). Surprisingly, 1 underwent gate opening (GO)/closing (GC) at a much higher T_G, e.g., 385 K for GC, under P_CO2 = 100 kPa than those previously reported for such chain compounds, which usually appeared in the temperature range of 200-270 K. The transition entropy ΔS_G in each system plays a key role in shifting T_G; 1 results in a much smaller |ΔS_G| in the series. Only 1 produced a CO₂-accessible two-dimensional topological pore in its CO₂-adsorbed phase 1⊃CO₂, whereas the others reported previously produced one-dimensional or discrete topological pores for CO₂ accommodation, strongly reflecting the degree of freedom of CO₂ molecules in pores, which is related to ΔS_G.

The mechanochemical synthesis of polymers

Mechanochemistry - the utilization of mechanical forces to induce chemical reactions - is a rarely considered tool for polymer synthesis. It offers numerous advantages such as reduced solvent consumption, accessibility of novel structures, and the avoidance of problems posed by low monomer solubility and fast precipitation. Consequently, the development of new high-performance materials based on mechanochemically synthesised polymers has drawn much interest, particularly from the perspective of green chemistry. This review covers the constructive mechanochemical synthesis of polymers, starting from early examples and progressing to the current state of the art while emphasising linear and porous polymers as well as post-polymerisation modifications.

A two-dimensional calcium (II) coordination polymer constructed from 2,2'-[terephthaloylbis(azanediyl)]diacetate: synthesis, structure and properties

A new two-dimensional (2D) coordination polymer, namely, poly[[diaqua-[μ₄-2,2'-[terephthaloylbis(azanediyl)]diacetato]calcium(II)] monohydrate], {[Ca(C₁₂H₁₀N₂O₆)(H₂O)₂]·H₂O}_n, (I), has been synthesized by the reaction of CaCl₂ with 2,2'-[terephthaloylbis(azanediyl)]diacetic acid (H₂L). The title compound was structurally characterized by single-crystal X-ray diffraction analysis, elemental analysis and IR spectroscopy. In the crystal structure of (I), each Ca^II cation binds to six carboxylate groups from four symmetry-related L^2- dianions. The hexadentate L^2- ligand links four symmetry-related calcium cations into a 2D layer-like structure, which can be simplified as a uninodal SP 2-periodic (3,6)III net with the point symbol (4³·6³). In the lattice, all layers pack in parallel arrays through weak interlayer hydrogen bonding and π-π interactions. The thermal stability and photoluminescence properties of (I) have been investigated. Thermogravimetric analysis reveals the different thermal stabilities of the two coordinated water molecules due to their different hydrogen-bonding interactions. The title coordination polymer exhibits an excitation-wavelength-dependent fluorescence in the solid state.

Calcium-Based Metal-Organic Frameworks and Their Potential Applications

Metal-organic frameworks (MOFs) built on calcium metal (Ca-MOFs) represent a unique subclass of MOFs featuring high stability, low toxicity, and relatively low density. Ca-MOFs show considerable potential for molecular separations, electronic, magnetic, and biomedical applications, although they are not investigated as extensively as transition metal-based MOFs. Compared to MOFs made of other groups of metals, Ca-MOFs may be particularly advantageous for certain applications such as adsorption and storage of light molecules because of their gravimetric benefit, and drug delivery due to their high biocompatibility. This review intends to provide an overview on the recent development of Ca-MOFs, including their synthesis, crystal structures, important properties, and related applications. Various synthetic methods and techniques, types of building blocks, structure and porosity features, selected physical properties, and potential uses will be discussed and summarized. Representative examples will be illustrated for each type of important applications with a focus on their structure-property relations.

A redetermination of the structure and Hirshfeld surface analysis of poly[di-aquadi-μ-hydroxido-tetra-kis-(μ-nicotinato N-oxide)tricopper(II)]

The product obtained from the reaction of pyridine-2,3-di-carb-oxy-lic acid and hydrated copper(II) chloride in hot aqueous NaOH solution was determined by low temperature X-ray diffraction to be [Cu3(C6H4NO3)4(OH)2(H2O)2] n or [Cu3(μ-OH)2(μ-nicNO)4(H2O)2] n (nicNO is pyridine-3-carboxyl-ate N-oxide), a structure obtained from room temperature data and reported previously. The present determination is improved in quality and treatment of the H atoms. A Hirshfeld surface analysis of the inter-molecular inter-actions is presented.

Metal-Assisted and Solvent-Mediated Synthesis of Two-Dimensional Triazine Structures on Gram Scale

Covalent triazine frameworks are an emerging material class that have shown promising performance for a range of applications. In this work, we report on a metal-assisted and solvent-mediated reaction between calcium carbide and cyanuric chloride, as cheap and commercially available precursors, to synthesize two-dimensional triazine structures (2DTSs). The reaction between the solvent, dimethylformamide, and cyanuric chloride was promoted by calcium carbide and resulted in dimethylamino-s-triazine intermediates, which in turn undergo nucleophilic substitutions. This reaction was directed into two dimensions by calcium ions derived from calcium carbide and induced the formation of 2DTSs. The role of calcium ions to direct the two-dimensionality of the final structure was simulated using DFT and further proven by synthesizing molecular intermediates. The water content of the reaction medium was found to be a crucial factor that affected the structure of the products dramatically. While 2DTSs were obtained under anhydrous conditions, a mixture of graphitic material/2DTSs or only graphitic material (GM) was obtained in aqueous solutions. Due to the straightforward and gram-scale synthesis of 2DTSs, as well as their photothermal and photodynamic properties, they are promising materials for a wide range of future applications, including bacteria and virus incapacitation.

Building a robust 3D Ca-MOF by a new square Ca4O SBU for purification of natural gas

For the first time, a new square Ca4O SBU is introduced into a 3D Ca-MOF, ([MeNH2]2[Ca4O(MTB)2(EtOH)4])·(solvent)n (1), to generate a (4,8)-connected flu-topology structure. Compound 1 exhibits selective adsorption of C3 and C2 hydrocarbons and CO2 over CH4 with especially high IAST selectivities for C3 hydrocarbons over CH4 (at 15/85 and 50/50 ratio) at 298K and 1 bar.

Combined experimental and computational studies on preferential CO2 adsorption over a zinc-based porous framework solid

Synthesis, characterization and study of selective CO₂ adsorption over other small gas molecules on a Zn-based porous framework compound.

Immobilization of N-oxide functionality into NbO-type MOFs for significantly enhanced C2H2/CH4 and CO2/CH4 separations

Two NbO-type MOFs with N-oxide functionality immobilized in the pore surface display significantly enhanced C₂H₂/CH₄ and CO₂/CH₄ separation performance.

Unexpected discovery of calcium cryptates with exceptional stability

A 2,2′-bipyridine-N,N′-dioxide-based cryptand has been found to exhibit exceptional apparent complex stability for Ca²⁺and unusually shows very high selectivity for Ca²⁺over trivalent lanthanoid cations.

Assembly of metal–organic frameworks based on 4-connected 3,3′,5,5′-azobenzenetetracarboxylic acid: structures, magnetic properties, and sensing of Fe3+ ions

Three complexes based on 3,3′,5,5′-azobenzenetetracarboxylic acid were synthesized, showing potential applications in magnetism and excellent sensing properties towards Fe³⁺.

Multifunctional Efficiency: Extending the Concept of Atom Economy to Functional Nanomaterials

Green chemistry, in particular, the principle of atom economy, has defined new criteria for the efficient and sustainable production of synthetic compounds. In complex nanomaterials, the number of embedded functional entities and the energy expenditure of the assembly process represent additional compound-associated parameters that can be evaluated from an economic viewpoint. In this Perspective, we extend the principle of atom economy to the study and characterization of multifunctionality in nanocarriers, which we define as "multifunctional efficiency". This concept focuses on the design of highly active nanomaterials by maximizing integrated functional building units while minimizing inactive components. Furthermore, synthetic strategies aim to minimize the number of steps and unique reagents required to make multifunctional nanocarriers. The ultimate goal is to synthesize a nanocarrier that is highly specialized but practical and simple to make. Owing to straightforward crystal engineering, metal-organic framework (MOF) nanoparticles are an excellent example to illustrate the idea behind this concept and have the potential to emerge as next-generation drug delivery systems. Here, we highlight examples showing how the combination of the properties of MOFs ( e.g., their organic-inorganic hybrid nature, high surface area, and biodegradability) and induced systematic modifications and functionalizations of the MOF's scaffold itself lead to a nanocarrier with high multifunctional efficiency.

Hydrated and dehydrated Ca-coordination polymers based on benzene-dicarboxylates: mechanochemical synthesis, structure refinement, and spectroscopic characterization

Hydrated Ca-CPs were synthesized by milling. Dehydrated phases were obtained by thermal treatments in reversible processes.

Geometry variation in porous covalent triazine polymer (CTP) for CO2 adsorption

Covalent triazine-based organic polymers (CTPs), a sub class of covalent organic polymers (COPs), are promising materials for CO₂ adsorption although the impact of their dimensionality on the trapping process is not well-understood.

2D and 3D mixed MII/CuIImetal–organic frameworks (M = Ca and Sr) withN,N′-2,6-pyridinebis(oxamate) and oxalate: preparation and magneto-structural study

Heterobimetallic coordination polymers with either antiferro- of ferromagnetic interactions are described herein.

Phosphorescence emission and fine structures observed respectively under ambient conditions and at ca. 55 K in a coordination polymer of lead(ii)-thiophenedicarboxylate

Under solvothermal conditions, a robust Pb²⁺-based coordination polymer (CP), [Pb(TDC)]_n (1), where H₂TDC is thiophenedicarboxylic acid, has been achieved.

Dimensionality of luminescent coordination polymers of magnesium ions and 1,1′-ethynebenzene-3,3′,5,5′-tetracarboxylic acid modulated by structural inducing agents

Crystal structure diversity and dimensionality of three Mg²⁺-based CPs, which emit bright ligand-based luminescence at ambient conditions, are modulated by reaction temperature and structural induction agents.

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.