3D Framework Research Articles

Trailblazing 3D MOFs Featuring 1,2,4‐Dinitrimino Triazole: Redefining Energetic Materials and Iodine Encapsulation

AbstractThe quest for high‐performance energetic materials for defense and aerospace has intensified, focusing on balancing energy output and safety. This study presents the synthesis of 3D energetic metal‐organic frameworks (EMOFs) [Na3(DNT)(H2O)]n (Na‐MOF), [K2(DNT)2(H2O)]n (K‐MOF), and [Cs2(DNT)]n (Cs‐MOF) using 1,2,4‐dinitrimino triazole (DNT) through a hydrothermal process. The synthesized EMOFs are characterized using infrared spectroscopy, powder X‐ray diffraction, scanning electron microscopy (SEM), elemental analysis, and thermogravimetric analysis and differential scanning calorimetry, and structures confirmed via single‐crystal X‐ray diffraction, revealing 3D frameworks with crystal densities of 2.15, 2.16, and 2.86 g cm−3, respectively. Among them, Na‐MOF exhibits excellent detonation performance (VOD = 8900 m s−1, DP = 26.21 GPa), high thermal stability (Td = 369 °C), and insensitivity to impact and friction (IS = 40 J, FS = 360 N). K‐MOF displays balanced energetic and mechanical properties, while Cs‐MOF, though moderate in energetic performance, shows significant potential in pyrotechnic applications, producing a bright red flame. Intermolecular interactions are analyzed through Hirshfeld surface, 2D fingerprint, and SEM analyses, enhancing the understanding of particle size and morphology. Na‐MOF also demonstrates high iodine encapsulation capacity, positioning it as a potential replacement for traditional materials like RDX and heat‐resistant explosives such as HNS, with comparability to PYX.

Three Co-MOFs with various structures based on 4, 4’, 4’’-nitrilotrisbenzoic acid: Structure, magnetic properties and multifunctional luminescence sensing

In this work, we designed and presented three Co(II) metal-organic frameworks (MOFs), {[Co3(NTB)2(DIMB)]·H2O·DMA}n (NTB-1), {[Co3(NTB)2(DMIMB)]·DMA}n (NTB-2), and {Co(HNTB)(dpa)(H2O)2}n (NTB-3) (H3NTB = 4, 4′, 4′’-nitrilotrisbenzoic acid, DIMB = 1,4-di(1H-imidazol-1-yl) butane), DMIMB = 1,4-di(1H-2-methylimidazol-1-yl) butane), dpa = 9,10-di(4-pyridyl)anthracene) by mix-ligand strategy. X-ray diffraction analysis revealed that NTB-1 and NTB-2 exhibited three-dimensional (3D) architectures with 2, 3, 8-c net topology based on the trinuclear [Co3O12] units, while NTB-3 displayed 2D framework and further subsequently extended to 3D supramolecular structure via classical OH···O hydrogen bond. Thermogravimetric analysis (TGA) and Powder X-ray diffraction (PXRD) exhibited thermal and chemical stability of NTB-1–3. Investigation of magnetic susceptibilities indicated the antiferromagnetic coupling was existed in neighboring Co(II) ions for NTB-1–3. NTB-3 displayed single-molecule magnet characteristics with τ0 = 1.67×10−5 s and Ueff = 9.4 K. Luminescence sensing analyses demonstrated that NTB-1–3 can be regarded as promising luminescent sensors for Pb2+, Fe3+, CrO42− and Cr2O72−. Finally, the possible quenching mechanism for various ions were fully discussed.

On-Surface Synthesis of 2D Radical Frameworks

The design of atom thick two-dimensional (2D) frameworks by on-surface synthesis has recently contributed to the development of advanced materials with high control over their structural, electronic, optical and magnetic properties. Countless 2D frameworks, with a large variety of applications, can be synthesized made of purely organic molecules (covalent organic and supramolecular frameworks) or combining both metals and organic molecules (metalorganic frameworks). Here, we focus on the design and synthesis of radical 2D frameworks, composed of open-shell nanographenes equipped with azaindole units, on an Au(111) surface. Interestingly, the deposition of transition metal atoms on such frameworks allow the tuning of their magnetic properties, expanding their possible applications. The structural, electronic and magnetic characterization of the frameworks was performed by scanning tunneling microscopy/spectroscopy (STM/STS) and non-contact atomic force microscopy, and supported by density functional theory (DFT) calculations. Additionally, the magnetic characterization was complemented by nickelocene-functionalized tips investigations, which act as a magnetic sensor that unveils the magnetism of the frameworks at the single molecule level.

Unlocking the potential: strategic synthesis of a previously predicted pyrazolate-based stable MOF with unique clusters and high catalytic activity.

The metal-organic framework (MOF) constructed from [Co4Pz8] clusters (Pz = pyrazolate) and 1,3,5-tris(pyrazolate-4-yl) benzene (BTP3-) ligands was structurally predicted many years ago, and expected to be a promising candidate for various applications owing to its unique clusters and highly open 3D framework structure. However, this MOF has not been experimentally prepared yet, despite extensive efforts were made. In this work, we present the successful construction of this MOF, hereinafter referred to as BUT-124(Co), by adopting a two-step synthesis strategy, involving the initial construction of a template framework (BUT-124(Cd)) followed by a post-synthetic metal metathesis process. The effects of various cobalt sources and solvents were systematically investigated, and an innovative stepwise metathesis strategy was employed to optimize the exchange rates and the porosity of the material. BUT-124(Co) demonstrates high catalytic activity in the oxygen evolution reaction (OER), achieving a competitive performance with an overpotential of 393 mV at a current density of 10 mA cm-2, and also affords remarkable long-term stability during potentiostatic electrolysis in 1 M KOH solution, surpassing the durability of many benchmark catalysts. This work not only introduces a novel MOF material with promising properties but also exemplifies a strategic synthesis approach for pyrazolate-based MOFs, paving the way for advancements in diverse application fields.

Progress and Challenges of Monometallic Titanium Coordination Polymers.

The realm of titanium coordination polymer research is still in its nascent stages and presents a formidable challenge in the field of coordination chemistry. In recent decades, the focus has predominantly been on manipulating titanium reactions in solution, resulting in the synthesis of ≈60 targeted compounds. Despite the limited number of documented instances, these materials showcase a diverse array of structures, encompassing 1D chains, 2D layers, and 3D frameworks. This suggests potential for fine-tuning coordination modes and structural features in future investigations. Moreover, titanium coordination polymers not only exhibit photo-active and photo-responsive properties but also hold promise for various other significant applications. This article offers an exhaustive review tracing the evolution of titanium coordination polymer development while providing an update on recent advancements. The review encompasses a synopsis of reported synthetic strategies, methodologies, structural diversity, and associated applications. Additionally, it delves into critical issues that necessitate attention for future progressions and proposes potential avenues to effectively propel this research field forward at an accelerated pace.

Synergistic effect of Ni(OH)2 and MXene nanosheets in 3D framework on the improvement of dielectric, energy storage, mechanical and thermal characteristics of polyvinylidene fluoride(PVDF) polymeric composites

This work introduces a novel method for incorporating meticulously designed nanohybrids to improve the dielectric characteristics of polymer composites. Conventional ceramic fillers have problems with dispersion even if they are good at increasing permittivity. Here, we overcome this constraint by creating nanohybrids made of MXene, polyvinylidene fluoride (PVDF), and single-layered and three-dimensional Ni(OH)2. An essential coupling agent, polyethyleneimine (PEI), fosters a robust electrostatic connection between Ni(OH)2 and superior adhesion with MXene. Using only 9.5 wt percent filler loading, we are able to achieve a low loss tangent (tan δ=0.4) at 1 kHz with a considerable permittivity improvement (ε=1000) thanks to this creative design. The nanohybrid structure's ability to promote longer interfacial contact is crucial to this enhancement. Moreover, the integrated Ni(OH)2 layer functions as a semiconductor, obstructing the passage of current through the MXene flakes and lowering conductivity overall. At a low Ni(OH)2/MXene loading of 1.5 wt%, our three-phase composites also show higher dielectric strength (248.68 MV/m). Specifically, the synergistic coupling of MXene with Ni(OH)2 provides notable increases in mechanical and thermal properties. The tensile strength and Young's modulus of these films are much higher than those of virgin PVDF and Ni(OH)2-modified composites.

Topologically guided exfoliation of 3D metal-organic frameworks into nanosheets

Herein a general concept for screening 3D metal-organic frameworks (MOFs) for 2D nanosheets design is presented. Active coordination centers and terminal ligands of 3D-to-2D MOF nanosheets can result in self-assembly of multilayer structures. In comparison to 2D MOFs, 3D frameworks can provide nanosheets with better adhesion, strength, adsorptive capacity and catalytic activity. They are also promising in semiconductors, sensorics, and drug delivery systems. However, less than a dozen of 3D-to-2D MOF nanosheets have been produced to date. Therefore, we applied topological tools of ToposPro and Cambridge Structural Database for screening 3D MOFs as sources of new 2D nanosheets. Cluster representation uncovered the potential existence of 2D nanosheets as subnets of 3D networks in 3032 structures. Furthermore, parameters of building units, net topologies, and accessible channels were analyzed. The concept was proved by synthesis and successful exfoliation of new compound [Zn4(THIP)(HCO2)3(H2O)4]∙DMF (1), which was assembled from 4,5,6-trihydroxyisophtalic acid (H5THIP) as intralayer linker, formate anions as both intralayer linker and interlayer pillar, and Zn(II) as coordination center. In the compound, H5THIP shows complete deprotonation that is unique for hydroxyisophthalate ligands. The crystalline phase of the compound was studied by SCXRD, PXRD, FTIR, and TGA measurements. Nanosheets of height 0.1–90 nm and lateral sizes above 400 nm were produced by sonication of crystals in ethanol. The exfoliation was proved by SEM with EDS, PXRD, AFM, TEM, and BET surface measurements.

New cosolvent-dependent electrochemical sensing behavior of a pair of isostructural ionic nickel(II) coordination polymers

A pair of isostructural ionic nickel(II) chain coordination polymers, {[Ni(bbbm)(H2O)4]·ATBIP·2DMF·2H2O}n (CP 1) and {[Ni(bbbm)(H2O)4]·ATBIP·2DMA·2H2O}n (CP 2) with the multi-functional ATBIP2- anion and flexible bbbm linker was synthesized under ambient condition [H2ATBIP = 5-amino-2,4,6-tribromoisophthalic acid, bbbm = 1,4-bis(benzimidazole-1-methyl)benzene]. Furthermore, the composite of CP 1 with carbon nanotubes (CP 1@CNTs) was constructed by adopting “one pot” synthesis strategy. With the help of the hydrogen-bonded chain, CPs 1–2 extend into a 3D supramolecular framework with 1D channels occupied by the cosolvent molecules (DMF/DMA). Remarkably, CPs 1–2/GCE demonstrate cosolvent-dependent electrochemical sensing behavior to H2O2 and Fe3+. CP 1/GCE shows more sensitive oxidation sensing to H2O2 than CP 2/GCE in 0.1 M NaOH. Meanwhile, CP 1/GCE demonstrates sensitive reduction sensing to Fe3+ in 0.1 M H2SO4, while CP 2/GCE doesn't. Both CPs 1–2/GCE have similar oxidation sensing capabilities to ascorbic acid (AA) in 0.1 M H2SO4. Moreover, CP 1@CNTs/GCE shows superior electrochemical sensing performance to CP 1/GCE. The LOD of CP 1@CNTs/GCE for sensing of H2O2, AA and Fe3+ reaches 0.1 μM, 1.7 μM and 3.4 μM, respectively. Moreover, CP 1@CNTs/GCE was used in the sensitive detection of H2O2, AA and Fe3+ in the real-world samples.

Pose-Driven Compression for Dynamic 3D Human via Human Prior Models.

To cost-effectively transmit high-quality dynamic 3D human images in immersive multimedia applications, efficient data compression is crucial. Unlike existing methods that focus on reducing signal-level reconstruction errors, we propose the first dynamic 3D human compression framework based on human priors. The layered coding architecture significantly enhances the perceptual quality while also supporting a variety of downstream tasks, including visual analysis and content editing. Specifically, a high-fidelity pose-driven Avatar is generated from the original frames as the basic structure layer to implicitly represent the human shape. Then, human movements between frames are parameterized via a commonly-used human prior model, i.e., the Skinned Multi-Person Linear Model (SMPL), to form the motion layer and drive the Avatar. Furthermore, the normals are also introduced as an enhancement layer to preserve fine-grained geometric details. Finally, the Avatar, SMPL parameters, and normal maps are efficiently compressed into layered semantic bitstreams. Extensive qualitative and quantitative experiments show that the proposed framework remarkably outperforms other state-of-the-art 3D codecs in terms of subjective quality with only a few bits. More notably, as the size or frame number of the 3D human sequence increases, the superiority of our framework in perceptual quality becomes more significant while saving more bitrates.

Comparison and validation of stochastic microstructure characterization and reconstruction: Machine learning vs. deep learning methodologies

In the world of computational materials science, the knowledge of microstructure is vital in understanding the process-microstructure–property linkage across various length-scales. To circumvent costly experimental characterizations, typically, analyses on ensembles of 3D microstructures within a numerical framework are preferred. Utilizing a moment invariants-based physical descriptor, the current work quantifies the variations in the microstructural topology of 3D synthetic data of polycrystalline materials. For the first time, the validation of synthetic microstructures based on two unique AI-based reconstruction approaches was compared, providing valuable insights into the diverse characteristics of each methodology. Virtual 3D microstructure volumes of forged Ti-7Al and additively manufactured 316L stainless steel alloys were generated from 2D experimental data using two methods — Markov Random Field (MRF) and deep learning-based volumetric texture synthesis. Quantitative evaluation and validation of the reconstructed volumes were carried out with the aid of moment invariants by comparing local features associated with grain-level properties, such as grain size and shape. The normalized central moments previously employed to compare 2D grain topology were expanded to 3D. With the advent of various reconstruction algorithms, especially AI-based, the validation methodology outlined in this work can be adopted to evaluate the robustness of various 3D reconstruction frameworks as well as ensure spatial equivalency of the target microstructures.

Helical Ni‐Cluster Organic Framework Constructed from Enantiopure Lactate Derivative: Synthesis, Structure and Properties

AbstractUnder hydrothermal condition, lactate derivative (R)‐4‐(1‐ carboxyethoxy)‐2‐methylbenzoic acid ((R)‐H2cma) as chiral synthon assembled with 4,4′‐di(1H‐imidazol‐1‐yl)‐1,1′‐biphenyl (4,4’‐dib) and Ni(II) ions to obtain complex {[Ni2((R)‐cma)2(4,4’‐dib)2(H2O)] ⋅ 2H2O}n (HU20‐R). In complex HU20‐R, carboxyl group from lactate unit of (R)‐cma2− anion and coordinating H2O molecule adopt a μ2‐coordination mode to obtain dinuclear [Ni2(CO2)2(H2O)]2+ cluster. (R)‐cma2− anions and Ni(II) ions build single left‐handed (R)‐cma‐Ni‐chain, while 4,4’‐dib ligands are bridged by different Ni(II) centers to form double left‐handed 4,4’‐dib‐Ni‐chain. These helical secondary structures are further connected together to result in an 8‐connected 3D framework. PXRD tests indicated that complex HU20‐R has well hydro‐stability. UV‐vis absorption experiment confirmed that HU20‐R is a semi‐conducting material with strong absorption capacity for ultraviolet‐visible (UV‐vis) light. Additionally, electrochemical experiment revealed that HU20‐R has low impedance and high charge transport capacity. Further test results confirm that HU20‐R has noticeable photo‐catalytic effect in photodegradation of Rhodamine B (RhB) and antiferromagnetic property.

Versatility and stability of melamine foam-based biosensors (f-ELISA) using antibodies, nanobodies, and peptides as sensing probes

Macroporous three-dimensional (3D) framework structured melamine foam-based Enzyme-Linked Immunosorbent Assay (f-ELISA) biosensors were developed for rapid, reliable, sensitive, and on-site detection of trace amount of biomolecules and chemicals. Various ligands can be chemically immobilized onto the melamine foam, which brings in the possibility of working with antibodies, nanobodies, and peptides, respectively, as affinity probes for f-ELISA biosensors with improved stability. Different chemical reagents can be used to modify the foam materials, resulting in varied reactivities with antibodies, nanobodies, and peptides. As a result, the f-ELISA sensors produced from these modified foams exhibit varying levels of sensitivity and performance. This study demonstrated that the chemical reagents used for immobilizing antibodies, nanobodies, and peptides could affect the sensitivities of the f-ELISA sensors, and their storage stabilities under different temperatures varied depending on the sensing probes used, with f-ELISA sensors employing nanobodies as probes exhibiting the highest stability. This study not only showcases the versatility of the f-ELISA system but also opens new avenues for developing cost-effective, portable, and user-friendly diagnostic tools with optimized sensitivity and stability.

Development of a 2D Network of Zinc Organophosphate with an 8-Membered Ring Core Having Corrosion Resistance Properties.

A 2D framework, i.e., zinc organophosphate [Zn(tmbiph)(solv)]2 (tmbiphH4 = tetramethyl-[1,1'-biphenyl]-4,4'-diyl bis(dihydrogen phosphate); solv = 2H2O) with an eight-membered ring core has been developed. The hierarchical and rational design of the zinc organophosphate has been achieved by carefully designing an organic bisphosphate ligand with two phosphate monoester groups connected through extended aromatic rings with methyl groups at ortho positions. The development of the 2D network does not require any ancillary ligand due to participating two phosphate groups in the coordination. The molecular structure of the zinc phosphate material was determined using single-crystal X-ray diffraction technique. The corresponding Co and Cu organophosphate materials have also been obtained using the same synthetic method; however, these compounds could not be confirmed structurally due to nondiffractive crystal quality. The structure of zinc organophosphate obtained through single-crystal X-ray diffraction has also been supported by theoretical calculations using density function theory. Furthermore, the zinc organophosphate material has been employed as an corrosion inhibitor for mild steel. The effect of the zinc phosphate framework on mild steel in 1 M HCl was investigated using polarization and electrochemical impedance spectroscopy. This study suggests that such phosphate inhibitors can be employed in the form of a thin protective layer on the electrode surface.

A Rare-Earth-Based Borate Optical Crystal with Enlarged Dihedral Angles of Distinct [BO3] Groups Exhibiting a Wide UV Transparent Range.

Borates, as advanced optical materials, have garnered wide interest due to their diverse structural configurations and great potential for applications in the ultraviolet (UV) regions. Herein, we synthesized a new rare-earth borate crystal, namely, K2NaYB2O6, which is classified as one of the ABReB2O6 compounds, where A and B represent alkali metal and Re denotes rare-earth metal. K2NaYB2O6 adopts in the monoclinic space group P21/c (No. 14), showcasing a three-dimensional (3D) framework composed of a planar triangular configuration of [BO3] units and distortive [YO7] polyhedra. Notably, both dihedral angles between distinct [BO3] units reach 79.6°, which represents an unprecedented structural feature in monoclinic ABReB2O6-type crystals. Moreover, the compound has a short UV absorption edge at around 204 nm, corresponding to a wide band gap of approximately 5.67 eV. Additionally, it possesses a moderate birefringence of 0.028 at 1064 nm. Further analysis utilizing theoretical calculations suggests that the optical behaviors of K2NaYB2O6 are mainly governed by its basic structural unit [BO3] triangles and distorted [YO7] polyhedra. These findings enrich the structure chemistry of rare-earth borates and offer valuable insights for the design of optical crystals in the UV wavelength range.

Photocatalytic Hydrogen Peroxide Production by a Mixed Ligand-Functionalized Uranyl-Organic Framework.

Hydrogen peroxide (H2O2) production driven by solar energy has received enormous attention due to its high efficiency, low cost, and environmental friendliness characteristics. Searching for new photocatalytic materials for H2O2 production is one of the most important targets. In this work, a new three-dimensional (3D) uranyl-organic framework material was constructed with mixed ligands via a solvothermal reaction and used for photocatalytic H2O2 production. The mixed ligand strategy not only benefits the construction of a 3D uranyl-organic framework but also introduces strong photon absorption groups into the framework. The thiophene and pyridine rings in the framework enhance photon absorption and carrier transfer. In addition, with the assistance of the hydrogen abstraction reaction of uranyl centers, the H2O2 production rate reaches 345 μmol h-1 g-1. This study provides a new blueprint for exploring the artificial photosynthesis of H2O2 through uranium-based metal-organic frameworks.

Large-Scale Solar Potential Analysis in a 3D CAD Framework as a Use Case of Urban Digital Twins

Solar radiation impacts diverse aspects of city life, such as harvesting energy with PV panels, passive heating of buildings in winter, cooling the loads of air-conditioning systems in summer, and the urban microclimate. Urban digital twins and 3D city models can support solar studies in the process of urban planning and provide valuable insights for data-driven decision support. This study examines the calculation of solar incident radiation at the city scale in Sofia using remote sensing data for the large shading context in a mountainous region and 3D building data. It aims to explore the methods of geometry optimisation, limitations, and performance issues of a 3D computer-aided design (CAD) tool dedicated to small-scale solar analysis and employed at the city scale. Two cases were considered at the city and district scales, respectively. The total face count of meshes for the simulations constituted approximately 2,000,000 faces. A total of 64,379 roofs for the whole city and 4796 buildings for one district were selected. All calculations were performed in one batch and visualised in a 3D web platform. The use of a 3D CAD environment establishes a seamless process of updating 3D models and simulations, while preprocessing in Geographic Information System (GIS) ensures working with large-scale datasets. The proposed method showed a moderate computation time for both cases and could be extended to include reflected radiation and dense photogrammetric meshes in the future.

Rationalizing the stability and noncovalent interactions of N-(benzo[d][1,3]dioxol-5-ylmethyl)-2-(methylthio)thiazole-4-carboxamide: Insights from X‐ray structure and QTAIM analysis

A novel thiazole derivative, N-(benzo[d][1,3]dioxol-5-ylmethyl)-2-(methylthio)thiazole-4-carboxamide was synthesized and the structural interpretations were accomplished unambiguously by single crystal X-ray diffraction study. Structure investigation revealed that the crystal packing is stabilized by CH…N, and NH…O intermolecular interactions. Hirshfeld surface analysis used to explore the quantitative details of noncovalent interactions which are responsible for the crystal packing. The 3D energy framework, interaction energies and lattice energy of the compound were computed. Density functional theory (DFT) calculation was also employed to study various physicochemical properties of the compound. Quantum theory of atoms in molecules (QTAIM) analysis have been performed to study the intra and intermolecular interactions present in the thiazole derivative and also validate with the experimental results.

A Propeller-Like Ligand-Directed Construction of a Tetranuclear Cerium-Organic Framework for Single-Step Ethylene Purification from Ternary C2 Mixtures.

The efficient single-step purification of ethylene from ternary C2 mixtures containing ethane and acetylene is challenging and demanding. Herein, we introduce a novel cerium-based metal-organic framework (MOF) of Ce-NTB-rtk synthesized via a ligand-conformer strategy. The Ce-NTB-rtk features a rare tetranuclear cerium cluster and 2D kgd layers pillared by a 3D rtl framework concomitant with an extraordinary (3,3,12)-c network. The compound encompasses microporous cavities replete with a nonpolar microenvironment. Gas sorption and breakthrough experiments demonstrate its superior affinity for C2H6 and C2H2 over C2H4, enabling effective single-step ethylene purification. Computational simulations reveal that preferential adsorptions are facilitated by different interaction strengths of C-H···O hydrogen bonds. The performance of Ce-NTB-rtk in separation selectivity and regeneration capacity makes it a promising candidate for sustainable and cost-effective ethylene purification, showcasing the potential of MOFs in advanced gas separation applications.

Zn(II)/Cd(II) MOFs based on 2,5-thiophenedicarboxylic acid and bis(Imidazole) linkers for highly selective and sensitive detection of Fe3+ and Cr2O72-

Two new MOFs [(Zn2(bib)(tdc)2(H2O)2)]n1 and [Cd(bib)(tdc)(H2O)]n2 [bib = 1,4-bis(imidazole)butane, tdc = 2,5-thiophenedicarboxylic acid] were synthesized by solvothermal method. The synthesized MOFs were characterized by elemental analysis, FT-IR, PXRD, thermal analysis and X-ray single crystallography. Both 1 and 2 are 3D frameworks, in which 1 exhibits 8-fold interpenetrating ths network, whereas 2 shows uninodal 4-connected 3-fold interpenetrating network with lvt topology. Furthermore, 1 and 2 demonstrate selective and sensitive sensing capabilities towards Fe3+ and Cr2O72- ions in presence of various interfering metal ions and inorganic anions. The LOD for Fe3+ using 1 and 2 are 0.085 and 0.167 µM, and for Cr2O72- are 0.037 and 0.045 µM, respectively. The results demonstrate the potential applications of 1 and 2 as a multifunctional fluorescent material for sensing of Fe3+ and Cr2O72- ions.

Topochemical Modulations from 1D Iron Fluoride Precursor to 3D Frameworks.

Topochemical reactions are powerful pathways to modify inorganic extended structures, but the present approaches are limited by the degrees of freedom to tune the structural connectivity and dimensionality. In this work, we unveil a new topochemical bottom-up approach to tailor three-dimensional (3D) iron fluoride frameworks from the same one-dimensional (1D) FeF3.3H2O (IF) precursor upon reacting with iodide-based reagents (AI; A+ = Na+, K+, and NH4+). To elucidate their formation mechanism, a series of topochemical reactions are performed by varying the concentration of precursors, reaction temperatures, and durations, and their corresponding products are analyzed through X-ray diffraction, nuclear magnetic resonance, and Mössbauer spectroscopy techniques. Although the lower molar ratio of AI:IF (≈0.25:1.0) produces the same hexagonal tungsten bronze (HTB)-type AxFeF3, the topochemical reactions with higher AI:IF ratios yield weberite-Na1.95Fe2F7, tetragonal tungsten bronze (TTB)-K0.58FeF3, and pyrochlore-NH4Fe2F6 phases. Our density functional theory calculations attribute the formation of iron fluoride phases to their thermodynamic stability. Moreover, kinetics also play an important role in enabling weberite and HTB fluorides with high purity, while the pyrochlore-NH4Fe2F6 retains a minor HTB-(NH4)xFeF3 impurity. Overall, this work shows a new possibility of modulating the low-dimensional precursor to attain 3D frameworks with different structural arrangements via topochemical approaches.