Anionic Framework Research Articles

Anionic Ni-Based Metal-Organic Framework with Li(I) Cations in the Pores for Efficient C2H2/CO2 Separation.

Acetylene (C2H2) is widely used as a raw material for producing various downstream commodities in the petrochemical and electronic industry. Therefore, the acquisition of high-purity C2H2 from a C2H2/CO2 mixture produced by partial methane combustion or thermal hydrocarbon cracking is of great significance yet highly challenging due to their similar physical and chemical properties. Herein, we report an anionic metal-organic framework (MOF) named LIFM-210, which has Li+ cations in the pores and shows a higher adsorption affinity for C2H2 than CO2. LIFM-210 is constructed by a unique tetranuclear Ni(II) cluster acting as a 10-connected node and an organic ligand acting as a 5-connected node. Single-component adsorption and transient breakthrough experiments demonstrate the good C2H2 selective separation performance of LIFM-210. Theoretical calculations revealed that Li+ ions strongly prefer C2H2 to CO2 and are primary adsorption sites, playing vital roles in the selective separation of C2H2/CO2.

Structural Tuning Strategy to Improve Ionic Conductivity of Eco, Cost-Effective Zr-Based Halide Solid Electrolyte

Lithium-ion conductors based on halide anion frameworks have garnered significant attention as optimal ceramic conductors for composite cathodes due to their high oxidation stability and deformability. Recently, a cost-effective halide electrolyte, Li2ZrCl6, has been reported as a promising alternative to rare-metal-based halide solid electrolytes which are not suitable for manufacturing. Despite the economic advantage of using Zr, its ionic conductivity remains relatively low (0.36 mS cm-1), which could limit its applicability in high C-rate applications.To enhance the ionic conductivity of Zr-based solid electrolytes, various structural tuning strategies have been employed. However, challenges persist, such as unstable cycling due to the redox reactions of metal ion and the uneconomical aspects of incorporating rare metals like Yttrium, Indium, and Lanthanides. In this study, we propose economical and rational strategies for tuning Li2ZrCl6 to achieve higher ionic conductivity without compromising stability and affordability.By introducing zero-valent dopants, vacancies, we were able to increase the ionic conductivity of the Zr-based solid electrolyte to nearly twice its original value (0.8 mS cm-1). Our detailed analysis reveals that the enhanced conductivity and reduced activation energy are primarily due to the activation of local diffusion paths, resulting from the alleviated repulsion between transition metal ions and Lithium ions. Furthermore, we establish the relationship between the Lithium-ion content and Li diffusivity in the Zr-based solid electrolyte, uncovering a new aspect for structural tuning in Zr-based solid electrolytes.Consequently, we optimized the content of Lithium ions and dopants in the solid electrolyte, synthesizing a super-ionic conductive Zr-based solid electrolyte with an impressive ionic conductivity of approximately 1.6 mS cm-1 and highest Zr percentage reported to date. Our findings offer a rational and economical design strategy for developing stable hcp-LZC structures with faster ionic conduction. This breakthrough has the potential to facilitate the widespread adoption of Zr-based solid electrolytes in lithium-ion batteries.

Fabrication of an anionic layered metal-organic framework for the efficient removal of Sr2+

Efficient removal of radioactive 90Sr from solutions is of vital importance due to its radioactive nature and high mobility. Herein, a 2D anionic metal-organic framework (MOF) [Me2NH2][KZn(pydc)2(H2O)2]∙H2O (K-Zn-MOF; pydc = 2,6-pyridinedicarboxylic acid) was synthesized and characterized. The prepared K-Zn-MOF was in turn applied for the removal of Sr2+ ions and various experimental conditions including contact time, initial concentration, and temperatures were optimized. Experimental findings revealed that the adsorption of Sr2+ on K-Zn-MOF reached equilibrium within 60 min at room temperature with Re = 95.39%. K-Zn-MOF exhibited ultra-high adsorption capacity (878.3 mg g−1), remarkable affinity (Kd = 5.8 × 105 mL g−1) in solutions and super-high selectivity in the presence of interfering coexisting ions (Na+, K+, Mg2+, and Ca2+). Mechanistic investigation suggested that free exchangeable [Me2NH2]+ ions and strong interactions between uncoordinated oxygens from COO− groups with target ions significantly contributed to the rapid adsorption of Sr2+ ions.

Isolation of an Anionic Dicarbene Embedded Sn2 P2 Cluster and Reversible CO2 Uptake.

Decarbonylation of a cyclic bis-phosphaethynolatostannylene [(ADC)Sn(PCO)]2 based on an anionic dicarbene framework (ADC=PhC{N(Dipp)C}2 ; Dipp=2,6-iPr2 C6 H3 ) under UV light results in the formation of a Sn2 P2 cluster compound [(ADC)SnP]2 as a green crystalline solid. The electronic structure of [(ADC)SnP]2 is analyzed by quantum-chemical calculations. At room temperature, [(ADC)SnP]2 reversibly binds with CO2 and forms [(ADC)2 {SnOC(O)P}SnP]. [(ADC)SnP]2 enables catalytic hydroboration of CO2 and reacts with elemental selenium and Fe2 (CO)9 to afford [(ADC)2 {Sn(Se)P2 }SnSe] and [(ADC)Sn{Fe(CO)4 }P]2 , respectively. All compounds are characterized by multinuclear NMR spectroscopy and their solid-state molecular structures are determined by single-crystal X-ray diffraction.

Mobile hydrogen-bonding donor in covalent organic framework for efficient iodine capture

Covalent organic frameworks (COFs) show promise for applications in molecule capture such as radioactive iodine (I2) capture, which is important in the development for nuclear energy and radiation medicine. However, fast and efficient I2 capture and release have remained insufficient for practical applications. Here, we demonstrated that mobile cationic hydrogen-bonding donor in nanochannel of anionic covalent organic framework (COFs) can promote the absorption and desorption of I2. The adsorption rate of COF Bmim-TpPaSO3 affording unfixed hydrogen-bonding donor 1-butyl-3-methylimidazolium ([Bmim]+) in the nanochannel reaches 2.86 g h−1, which is higher those of COF TpPa-SO3H (0.57 g h−1) with fixed hydrogen-bonding donor and COF TpPa-SO3K without hydrogen-bonding donor. The adsorption capacity was also increased from 1.50 g g−1 to 5.25 g g−1. Experiments and quantum chemistry calculations show that introducing the hydrogen bond donor enhances the interaction of Bmim-TpPaSO3 with iodine and induces sulfonate ion of Bmim-TpPaSO3 to convert iodine molecules into polyiodide via charge-transfer mechanism. In addition, Bmim-TpPaSO3 has good recyclability and storage performance. This strategy has unlimited potential to significantly improve the performance of covalent organic framework materials in the field of gas adsorption.

Ba4B14O25: A Deep Ultraviolet Transparent Nonlinear Optical Crystal with Strong Second Harmonic Generation Response Achieved by a Boron-Rich Closed-Loop Strategy.

Discovering new deep ultraviolet (DUV) nonlinear optical (NLO) materials is the current research hotspot. However, how to perfectly integrate several stringent performances into a crystal is a great challenge because of the natural incompatibility among them, particularly wide band gap and large NLO coefficient. To tackle the challenge, a boron-rich closed-loop strategy is supposed, based on which a new barium borate, Ba4B14O25, is designed and synthesized successfully via the high-temperature solid-state melting method. It features a highly polymeric 3D geometry with the closed-loop anionic framework [B14O25]8- constructed by the fundamental building blocks [B14O33]24-. The high-density π-conjugated [BO3]3- groups and the fully closed-loop B-O-B connections make Ba4B14O25 possess excellent NLO properties, including short UV cutoff edge (<200nm), large second harmonic generation response (3.0 × KDP) and phase-matching capability, being a promising DUV-transparent NLO candidate material. The work provides a creative design strategy for the exploration of DUV NLO crystals.

PH/ROS dual stimuli-responsive anionic flexible supramolecular organic frameworks for synergistic therapy

Supramolecular organic frameworks (SOFs) have emerged as a promising class of organic porous materials with vast potential as nanocarriers for combination therapy. Here, we successfully construct an anionic flexible supramolecular organic framework (TPP-SOF) by leveraging multiple host-guest interactions. TPP-SOF is fabricated by the hierarchical orthogonal assembly between anionic water-soluble dimacrocyclic host (P5CD), porphyrin photosensitizers (TPP), and ROS-sensitive thioketal linked adamantane dimer (Ada-S-Ada). TPP-SOF exhibits pH-dependent activation of 1O2 production, which further facilitates the cleavage of Ada-S-Ada linker and promotes the disintegration of the framework. Moreover, leveraging electrostatic and hydrophobic interactions, the anionic TPP-SOF serves as an effective platform for loading cationic photosensitizer IR780 and chemotherapeutic prodrug PhenPt(IV), leading to the formation of supramolecular nanoparticles (IR780/Pt@TPP-SOF) for synergistic therapy. The obtained nanoparticles exhibit good stability, efficient generation of 1O2, and photothermal performance. In vitro and in vivo studies indicate that IR780/Pt@TPP-SOF exhibits remarkable synergistic chemo/PDT/PTT effects under 808 and 660 nm light irradiation. This study showcases a deep insight for the development of SOFs and a new approach for delivering cationic drugs and constructing synergistic combination therapy systems. Statement of SignificanceIn this work, a pH/ROS-responsive anionic flexible supramolecular organic framework, TPP-SOF, was innovatively designed by the hierarchical orthogonal assembly, to co-deliver cationic photosensitizer IR780 and prodrug PhenPt(IV) for synergistic cancer therapy. The drug-loaded TPP-SOF is termed IR780/Pt@TPP-SOF, in which the photoactivity of porphyrin within TPP-SOF could be activated under acidic conditions, the 1O2 generated by the photosensitizers could break the thioketal bonds in Ada-S-Ada, leading to the disassembly of the framework and releasing the drugs. This supramolecular drug delivery system displays good biocompatibility and exhibits remarkable synergistic chemo/PDT/PTT effects.

An anionic In(III)-MOF for efficient adsorption of CO2 from CO2/N2 mixture and dye removal

Efficient adsorption of CO2 and dye molecules is crucial for reducing carbon emission and environmental pollution. Metal-Organic Frameworks (MOFs) are considered to be the ideal candidates for gas adsorption material because of their designability. In this work, a new In(III)-MOF (HBU-22) was synthesized by the reaction of a tetracarboxylic acid ligand (H4L, 9,9′-bicarbazole-3,3′,6,6′-tetracarboxylic acid) with In3+ ions, which shows a three-dimensional (3D) coordination network. The saturated adsorption capacity of CO2 and N2 are 21.11 cm3‧g−1 and 0.66 cm3‧g−1 at ambient condition (298 K, 100 kPa). And the higher IAST selectivity of CO2/N2 (v/v, 15:85) reaches 347.37, exceeding that of most MOFs. Furthermore, it can also capture C2H2 with the maximum uptake of 42.80 cm3 g−1. More interestingly, HBU-22 as an anionic framework, which can selectively adsorb Rhodamine B (RhB) within 250 s with the maximum adsorption capacity of 105.04 mg‧g−1. Further studies show that higher gas adsorption capacity is mainly related to the larger Qst of the gas, while its adsorption of Rhodamine B (RhB) is mainly due to ion exchange mechanism.

Syntheses, Crystal Structure, and Second Harmonic Generation Response of Four Novel Noncentrosymmetric Tellurites of Quaternary A/M/Te/O (A = Ba, Sr, Ca; M = V, Nb, Ta) System: BaTa4Te3O17, BaNb4Te3O17, SrTa4Te3O17, and CaV2TeO8.

Four new noncentrosymmetric tellurites of quaternary A/M/Te/O (A = Ba, Sr, Ca; M = V, Nb, Ta) system, namely, BaTa4Te3O17 (1), BaNb4Te3O17 (2), SrTa4Te3O17 (3), and CaV2TeO8 (4), were synthesized and characterized by single-crystal X-ray diffraction, thermal analysis, diffuse reflectance spectroscopy, and powder second harmonic generation (SHG) response measurements. The isostructural compounds 1-3 crystallize in the P212121 space group and have a three-dimensional (Ta4Te3O17)2-/(Nb4Te3O17)2- anionic framework, whereas the layered compound 4 crystallizes in the Ccc2 space group and has a [V2TeO8]2- anionic layer. The phase-matching compounds 1, 2, and 3 and the non-phase-matching compound 4 show powder SHG responses equivalent to ∼27, ∼13, ∼24, and ∼68% of that of LiNbO3, respectively.

ELECTRICAL PROPERTIES INVESTIGATION OF Ag8GeS6 SINGLE CRYSTAL

The compounds of the argyrodite structure have high conductivity values in the solid state due to the simultaneous coexistence of a "rigid" anionic framework and disordered cationic sublattice. In this regard, argyrodites are considered to be promising superionic materials for use as a working element of solid-state batteries. This work presents the results of the study of the electrophysical parameters of Ag8GeS6 single crystal grown by directional crystallization from the melt technique. It was found by the XRD method that the grown Ag8GeS6 single crystal crystallizes in a low-temperature orthorhombic modification with unit cell parameters: a = 15.147 Å, b = 7.469 Å, c = 10.584 Å. The frequency (10 Hz - 0.3 MHz) and temperature (20 - 110°C) dependence of the electrical conductivity was studied on a single crystal plate of Ag8GeS6 oriented in the (011) plane by impedance spectroscopy. The frequency dependence of the total electrical conductivity of Ag8GeS6 shows an increase in the total electrical conductivity with increasing frequency, which is typical for mixed ionic-electronic conductors. It was determined that the total conductivity of the Ag8GeS6 single crystal is 3.82 × 10-5 S/cm, and the activation energy is 0.728 eV.&#x0D; Keywords: argyrodites; single crystals; electrical conductivity; phase analysis.

QUASIBINARY SYSTEM Ag7PSe6– Ag2Se

Semiconductor binary and ternary argentum selenides are of considerable practical interest, particularly as promising thermoelectric materials. These include Ag2Se, a narrow-band semiconductor, and Ag7PSe6, with a disordered cationic sublattice and a rigid anionic framework that causes efficient phonon scattering. Doping of Ag7PSe6 with the narrow bandgap semiconductor Ag2Se should increase its conductivity and Ag2Se with a more disordered Ag7PSe6 argyrodite phase to a decrease in thermal conductivity. In both cases, this should increase the thermoelectric figure of merit of the respective phases. At the same time, establishing the conditions for obtaining doped phases requires studying the conditions of their existence in the Ag7PSe6-Ag2Se system. Present work studies phase equilibria in the Ag7PSe6-Ag2Se system in the entire concentration range. A corresponding phase diagram was constructed based on the X-ray phase and differential thermal analysis results. It was found that the Ag7PSe6-Ag2Se system is quasi-binary. It is characterized by four processes: two eutectoid processes at 405 K and 433 K, caused by the presence of two polymorphic modifications in Ag2Se and Ag7PSe6, respectively; eutectic process at 893 K (the coordinates of the eutectic point are 893 K and ~8 mol% Ag2Se) and monotectic process at 977 K. Above this temperature, in the concentration range of ~9 - ~87 mol%, a region of immiscibility in the liquid is observed. The homogeneity regions of the initial components are less than 5 mol%.&#x0D; Keywords: quasibinary system; selenides; phase equilibria; phase diagram.

Enhancing Electroreduction CO2 to Hydrocarbons via Tandem Electrocatalysis by Incorporation Cu NPs in Boron Imidazolate Frameworks.

Due to the higher value of deeply-reduced products, electrocatalytic CO2 reduction reaction (CO2 RR) to multi-electron-transfer products has received more attention. One attractive strategy is to decouple individual steps within the complicated pathway via multi-component catalysts design in the concept of tandem catalysts. Here, a composite of Cu@BIF-144(Zn) (BIF = boron imidazolate framework) is synthesized by using an anion framework BIF-144(Zn) as host to impregnate Cu2+ ions that are further reduced to Cu nanoparticles (NPs) via in situ electrochemical transformation. Due to the microenvironment modulation by functional BH(im)3 - on the pore surfaces, the Cu@BIF-144(Zn) catalyst exhibits a perfect synergetic effect between the BIF-144(Zn) host and the Cu NP guest during CO2 RR. Electrochemistry results show that Cu@BIF-144(Zn) catalysts can effectively enhance the selectivity and activity for the CO2 reduction to multi-electron-transfer products, with the maximum FECH4 value of 41.8% at -1.6V and FEC2H4 value of 12.9% at -1.5V versus RHE. The Cu@BIF-144(Zn) tandem catalyst with CO-rich microenvironment generated by the Zn catalytic center in the BIF-144(Zn) skeleton enhanced deep reduction on the incorporated Cu NPs for the CO2 RR to multi-electron-transfer products.

Structural analysis and ionic conduction mechanism of sulfide-based solid electrolytes doped with Br

Sulfide glasses can exhibit notable ionic conductivity because of annealing-associated crystallization. One well-known example is Li7P3S11. Our research showed that adding bromine (Br) to Li3PS4 sulfide glass results in a similar crystal structure and high ionic conductivity comparable to that of another compound Li10GeP2S12. This structure differs from the PS4 anion framework of Li3PS4. In addition, the ionic conductivity decreases owing to a structural transition to the β-phase. Herein, we present our findings on the local structure of Li3PS4 sulfide glass and its crystallized glass ceramic with the addition of Br. This analysis relies on the pair distribution function analysis obtained from high-energy X-ray diffraction. Moreover, using the bond valence sum method, we verified that incorporating Br promotes the formation of Li ionic conduction pathways. Our results indicate that precise control over the anion molecular structure by introducing halogens holds promise for achieving high Li-ion conductivity.

Bimetallic Anionic Organic Frameworks with Solid‐State Cation Conduction for Charge Storage Applications

AbstractA new phosphonate‐based anionic bimetallic organic framework, with the general formula of A4−Zn−DOBDP (wherein A is Li+ or Na+, and DOBDP6− is the 2,5‐dioxido‐1,4‐benzenediphosphate ligand) is prepared and characterized for energy storage applications. With four alkali cations per formula unit, the A4−Zn−DOBDP MOF is found to be the first example of non‐solvated cation conducting MOF with measured conductivities of 5.4×10−8 S cm−1 and 3.4×10−8 S cm−1 for Li4‐ and Na4‐ phases, indicating phase and composition effects of Li+ and Na+ shuttling through the channels. Three orders of magnitude increase in ionic conductivity is further attained upon solvation with propylene carbonate, placing this system among the best MOF ionic conductors at room temperature. As positive electrode material, Li4−Zn−DOBDP delivers a specific capacity of 140 mAh g−1 at a high average discharge potential of 3.2 V (vs. Li+/Li) with 90 % of capacity retention over 100 cycles. The significance of this research extends from the development of a new family of electroactive phosphonate‐based MOFs with inherent ionic conductivity and reversible cation storage, to providing elementary insights into the development of highly sought yet still evasive MOFs with mixed‐ion and electron conduction for energy storage applications.

Bimetallic Anionic Organic Frameworks with Solid-State Cation Conduction for Charge Storage Applications.

A new phosphonate-based anionic bimetallic organic framework, with the general formula of A4 -Zn-DOBDP (wherein A is Li+ or Na+ , and DOBDP6- is the 2,5-dioxido-1,4-benzenediphosphate ligand) is prepared and characterized for energy storage applications. With four alkali cations per formula unit, the A4 -Zn-DOBDP MOF is found to be the first example of non-solvated cation conducting MOF with measured conductivities of 5.4×10-8 S cm-1 and 3.4×10-8 S cm-1 for Li4 - and Na4 - phases, indicating phase and composition effects of Li+ and Na+ shuttling through the channels. Three orders of magnitude increase in ionic conductivity is further attained upon solvation with propylene carbonate, placing this system among the best MOF ionic conductors at room temperature. As positive electrode material, Li4 -Zn-DOBDP delivers a specific capacity of 140 mAh g-1 at a high average discharge potential of 3.2 V (vs. Li+ /Li) with 90 % of capacity retention over 100 cycles. The significance of this research extends from the development of a new family of electroactive phosphonate-based MOFs with inherent ionic conductivity and reversible cation storage, to providing elementary insights into the development of highly sought yet still evasive MOFs with mixed-ion and electron conduction for energy storage applications.

Nanotrap Grafted Anionic MOF for Superior Uranium Extraction from Seawater.

On-demand uranium extraction from seawater (UES) can mitigate growing sustainable energy needs, while high salinity and low concentration hinder its recovery. A novel anionic metal-organic framework (iMOF-1A) is demonstrated adorned with rare Lewis basic pyrazinic sites as uranyl-specific nanotrap serving as robust ion exchange material for selective uranium extraction, rendering its intrinsic ionic characteristics to minimize leaching. Ionic adsorbents sequestrate 99.8% of the uranium in 120 mins (from 20,000 ppb to 24 ppb) and adsorb large amounts of 1336.8mg g-1 and 625.6mg g-1 from uranium-spiked deionized water and artificial seawater, respectively, with high distribution coefficient, Kd U ≥ 0.97 × 106 mL g-1 . The material offers a very high enrichment index of ≈5754 and it achieves the UES standard of 6.0mg g-1 in 16 days, and harvests 9.42mg g-1 in 30 days from natural seawater. Isothermal titration calorimetry (ITC) studies quantify thermodynamic parameters, previously uncharted in uranium sorption experiments. Infrared nearfield nanospectroscopy (nano-FTIR) and tip-force microscopy (TFM) enable chemical and mechanical elucidation of host-guest interaction at atomic level in sub-micron crystals revealing extant capture events throughout the crystal rather than surface solely. Comprehensive experimentally guided computational studies reveal ultrahigh-selectivity for uranium from seawater, marking mechanistic insight.

Excellent Nonlinear Optical M[M4 Cl][Ga11 S20 ] (M = A/Ba, A = K, Rb) Achieved by Unusual Cationic Substitution Strategy.

The typical chalcopyrite AgGaQ2 (Q = S, Se) are commercial infrared (IR) second-order nonlinear optical (NLO) materials; however, they suffer from unexpected laser-induced damage thresholds (LIDTs) primairy due to their narrow band gaps. Herein, what sets this apart from previously reported chemical substitutions is the utilization of an unusual cationic substitution strategy, represented by [[SZn4 ]S12 + [S4 Zn13 ]S24 + 11ZnS4 ⇒ MS12 + [M4 Cl]S24 + 11GaS4 ], in which the covalent Sx Zny units in the diamond-like sphalerite ZnS are synergistically replaced by cationic Mx Cly units, resulting in two novel salt-inclusion sulfides, M[M4 Cl][Ga11 S20 ] (M = A/Ba, A = K, 1; Rb, 2). As expected, the introduction of mixed cations in the GaS4 anionic frameworks of 1 and 2 leads to wide band gaps (3.04 and 3.01 eV), which exceeds the value of AgGaS2 , facilitating the improvement of high LIDTs (9.4 and 10.3 × AgGaS2 @1.06 µm, respectively). Furthermore, compounds 1 and 2 exhibit moderate second-harmonic generation intensities (0.84 and 0.78 × AgGaS2 @2.9 µm, respectively), mainly originating from the orderly packing tetrahedral GaS4 units. Importantly, this study demonstrates the successful application of the cationic substitution strategy based on diamond-like structures to provide a feasible chemical design insight for constructing high-performance NLO materials.

A Tb3+ ion encapsulated anionic indium-organic framework as logical probe for distinguishing quenching Fe3+ and Cu2+ ions

We successfully synthesized a stable anionic microporous metal-organic framework (MOF) HDU-1 ([Me2NH2]2In2[(TATAB)4(DMF)4](DMF)4(H2O)4) and constructed a fluorescent probe Tb@HDU-1 by an exchange strategy. Because of its suspension distinct fluorescent response of Tb(III) characteristic transition and ligand emission, the Tb@HDU-1 can be used as fluorescent probe for sensing towards Fe3+ and Cu2+ ions. It is surprising that Tb@HDU-1 is used as a ratiometric fluorescent probe for Cu2+ ions while only single peak detection for Fe3+ ions, which describes a particular rare example of a sensor based on Ln-MOFs to distinguish quenching Fe3+ and Cu2+ ions. Hence we designed a molecular logic gate device for making the distinction of Fe3+ and Cu2+ ions more clearly and appropriately. In addition, the different quenching effect between Fe3+ and Cu2+ ions may be ascribed to the differences of competitive absorption and interaction between frameworks and metal ions.

Combined Experimental and Mechanoelastic Modeling Studies on the Low-Spin Stabilized Mixed Crystals of 3D Oxalate-Based Coordination Materials.

Structural studies involving single-crystal and powder X-ray diffraction analysis have been performed on dehydrated coordination networks of the [NixCo1-x(bpy)3][LiCr(ox)3] series, 0 ≤ x ≤ 1, (bpy = 2,2'-bipyridine). The high-symmetry cubic 3D structure of these materials is formed by oxalate anions bridging alternating Cr3+ and Li+ ions into an anionic framework, which contains large cavities that incorporate the [NixCo1-x(bpy)3]2+ cations. Irrespective of the Co/Ni ratio, all of the mixed samples are phase-pure and retain the high-symmetry cubic structure, with the lattice parameters gradually decreasing upon increasing Ni(II) concentration. The influence of the Ni(II) dilution on the magnetic behavior of these materials is substantial. For pure [Co(bpy)3][LiCr(ox)3], a gradual but incomplete thermal spin-crossover is evident due to the effect of the chemical pressure applied by the [LiCr(ox)3]2- framework, which stabilizes the low-spin (LS) 2E state relative to the high-spin (HS) 4T1 state of the Co(II) ion. Upon increasing the Ni(II) content, the spin-crossover becomes even more gradual and incomplete and eventually is not observed for pure [Ni(bpy)3][LiCr(ox)3]. The average spin-crossover temperature increases with the increasing Ni(II) content, suggesting a higher degree of chemical pressure applied by the oxalate framework manifested by changing the ΔE0HL toward positive values. The magnetic behavior of all these framework materials has been explained by the mechanoelastic model, considering different radii for Co and Ni molecules and different interactions between Co-Co sites and Co-Ni sites. The model reproduced the incomplete transition, with the HS residual fraction at 300 K decreasing with increasing Ni concentration, and provided microscopic snapshots of the systems, showing how the existence of impurities prevented the spreading of Co atoms in the HS state.

An anionic MOF as a multifunctional platform for selective adsorption of CO2, separation of organic dyes and ionic conductivity

It is a very effective strategy to capture and separate carbon dioxide by incorporation of alkali cations into MOFs. Presented here is an anionic metal-organic framework (MOF) (Me2NH2)2Co(tpta)·2H2O (1), in which the exchange of alkali ions (Li+ and Na+) took place with H2N(Me)2+ cations. As expected, CO2/N2 selectivity of the framework was improved significantly and reached 61.6 due to the inclusion of Li + using the ideal adsorbed solution theory (IAST) model. The enhancement of its CO2 uptake capability and selectivity has been mainly attributed to the charge-quadrupole interaction. For the CO2/N2 system, it is found that the inclusion of Li+ rather than Na+ favors higher selectivity. Additionally, it successfully separated cationic dye crystal violet (CV+) from anionic dye methyl orange (MO−) by the column-chromatography. Evidently, the enhancement of the electrostatic interaction greatly improves the separation performance of the framework.