Tetravalent Metal Research Articles

Interpenetration Control in Thorium Metal-Organic Frameworks: Structural Complexity toward Iodine Adsorption.

The rational design and synthesis of metal-organic frameworks with well-controlled interpenetration have been active research areas of inquiry, particularly for porosity-related applications. Herein, we extend the use of the ligand steric modulation strategy to initiate the first study of the interpenetration control of thorium-based MOFs. The approximate "hardness" of the Th4+ cation, which was conjugated with aromatic substitutions and delicately modified synthetic conditions, allows for the crystallization of single crystals of seven new Th-MOFs with five distinct topologies. Solvothermal reactions of Th(NO3)4 with the triphenyl H2TPDC ligand under variable conditions exclusively gave rise to an interpenetrated Th-MOF with a hex topology, namely Th-SINAP-16. Modifications of the ligand sterics with two pendant methyl groups to 2',5'-Me2TPDC2- and 2,2″-Me2TPDC2- afforded two noninterpenetrated UiO-68-type Th-MOFs (Th-SINAP-17 and Th-SINAP-20, respectively) with record-high pore volumes (74.8% and 75.3%, respectively) among all the thorium MOFs. Moreover, another four Th-MOFs Th-SINAP-n (n = 18, 19, 21, and 22) with three different topologies were obtained by a simple synthetic modulation. Notably, Th-SINAP-16 and Th-SINAP-21 represent the second rare examples of interpenetrated Th-MOFs reported to date. These findings revealed the unprecedented structural complexity and synthetic accessibility of Th-MOFs among all tetravalent metal containing MOFs. Such features make Th-MOFs as an ideal platform to elucidate the structure-property relationship for various applications, e.g. iodine adsorption.

Nonbonded Zr4+ and Hf4+ Models for Simulations of Condensed Phase Metal–Organic Frameworks

Recently, the practical applications of tetravalent metal-based metal–organic frameworks (MOFs) have been drawing increasing attention due to their excellent stability and varied functionality. Understanding the behavior of MOFs at the atomic level is important for their rational design and postsynthetic optimization. In classical simulations, the cationic dummy atom model, where the charge of the metal ion is distributed to surrounding dummy particles, has shown robustness in providing the appropriate coordination geometry while retaining the flexibility in the metal ligand interaction. Here, we present a set of eight-coordinated tetravalent metal (Zr4+, Hf4+) dummy model force fields with 12-6-4 type Lennard–Jones potential for describing ion-induced dipole interactions. This model can reproduce both the experimental solvation free energy of the bare ion and good metal–ligand distances and has been validated as useful and transferable among MOFs with the same metal-core topology. The model is inherently modular since nodes and linkers are independently parametrized. It was tested with three different solvents which all led to stable structures. It also was been further validated with different metal node structures and different linkers, Zr/Hf mixed MOFs, and defects containing MOFs. Since the model is nonbonded, the process of metal–ligand substitutions could be studied. The flexibility of the model makes its applicability to chemical problems broad.

Nano lamellar zirconium phosphate and screw speed changing properties of melt extrusion polypropylene nanocomposites

Tetravalent metal phosphates find application mainly as a catalyst and ionic exchangers besides structural and some other properties. In this study, pristine zirconium phosphate (ZrP) and chemically modified with Jeffamine™ (variable amine:phosphate ratio) were used as fillers to yield polypropylene nanocomposites by melt extrusion. Additionally, two different screw speeds (60 and 120 rpm) were carried out. Structural, crystallographic, thermal, dynamic-mechanical, and relaxometry properties were assessed. The morphology was also noticed. Wide-angle X-ray diffraction revealed that high speed and chemical modified ZrP led to the mixing of intercalated and exfoliated microstructures. Screw speed (60 rpm) and zirconium phosphate promoted a slight increase of thermal stability. Crystallization temperature and crystallinity degree were strongly influenced by screw speed and zirconium phosphate. Hydrogen nuclear magnetic resonance in the time domain endorsed the existence of polymer/filler interaction. Both screw speed and zirconium phosphate induced changes in glass transition temperature and moduli (storage and loss). Scanning electron microscopy images corroborated the polymer/filler interaction due to the low level of micro void and filler detachment. Crystallographic, thermal, calorimetric, relaxometry and morphologic evaluations endorsed the better effect of high screw speed and good interaction between polypropylene and phosphate.

Lanthanoid Complexes as Molecular Materials: The Redox Approach.

The development of molecular materials with novel functionality offers promise for technological innovation. Switchable molecules that incorporate redox-active components are enticing candidate compounds due to their potential for electronic manipulation. Lanthanoid metals are most prevalent in their trivalent state and usually redox-activity in lanthanoid complexes is restricted to the ligand. The unique electronic and physical properties of lanthanoid ions have been exploited for various applications, including in magnetic and luminescent materials as well as in catalysis. Lanthanoid complexes are also promising for applications reliant on switchability, where the physical properties can be modulated by varying the oxidation state of a coordinated ligand. Lanthanoid-based redox activity is also possible, encompassing both divalent and tetravalent metal oxidation states. Thus, utilization of redox-active lanthanoid metals offers an attractive opportunity to further expand the capabilities of molecular materials. This review surveys both ligand and lanthanoid centered redox-activity in pre-existing molecular systems, including tuning of lanthanoid magnetic and photophysical properties by modulating the redox states of coordinated ligands. Ultimately the combination of redox-activity at both ligands and metal centers in the same molecule can afford novel electronic structures and physical properties, including multiconfigurational electronic states and valence tautomerism. Further targeted exploration of these features is clearly warranted, both to enhance understanding of the underlying fundamental chemistry, and for the generation of a potentially important new class of molecular material.

A cationic thorium-organic framework with triple single-crystal-to-single-crystal transformation peculiarities for ultrasensitive anion recognition.

Single-crystal-to-single-crystal transformation of metal–organic frameworks has been met with great interest, as it allows for the creation of new materials in a stepwise manner and direct visualization of structural transitions when subjected to external stimuli. However, it remains a peculiarity among numerous metal–organic frameworks, particularly for the ones constructed from tetravalent metal cations. Herein, we present a cationic thorium–organic framework displaying unprecedented triple single-crystal-to-single-crystal transformations in organic solvents, water, and NaIO3 solution. Notably, both the interpenetration conversion and topological change driven by the SC–SC transformation have remained elusive for thorium–organic frameworks. Moreover, the single-crystal-to-single-crystal transition in NaIO3 solution can efficiently and selectively turn the ligand-based emission off, leading to the lowest limit of detection (0.107 μg kg−1) of iodate, one of the primary species of long-lived fission product 129I in aqueous medium, among all luminescent sensors.

Ti-ATMP catalyzed esterification of levulinic acid to synthesize butyl ester

In the present work, a hybrid catalytic material of the class of tetravalent metal acid (TMA) salts has been synthesized by the sol–gel method, wherein solution of titanium tetrachloride is allowed to react with claw-type organic phosphonic acid, amino tris methylenephosphonic acid (ATMP) under appropriate reaction conditions of pH, temperature, time and ageing period. The resultant hybrid material (Ti-ATMP) was found to possess proton donating behaviour, and hence it was thought of interest to use it as solid acid catalyst to perform catalysed esterification reaction of biomass-derived levulinic acid with n-butanol to synthesize n-butyl levulinate. Various process parameters such as catalyst concentration % (X1), LA:n–butanol molar ratio (X2) and reaction time (min) (X3) were optimized by response surface methodology (RSM), using the Box–Behnken Design (BBD). Analysis of variance was performed in order to check the suitability of the quadratic model. The catalytic reusability study has been performed in order to have an idea about feasibility of its reuse. Ti- ATMP catalyst was found efficient and promising with satisfactory yields and excellent reusability. The results clearly indicate its potentiality as solid acid catalyst to catalyse other organic transformations.

Decisive Role of 5f-Orbital Covalence in the Structure and Stability of Pentavalent Transuranic Oxo [M6O8] Clusters.

Actinide metal oxo clusters are of vital importance in actinide chemistry, as well as in environmental and materials sciences. They are ubiquitous in both aqueous and nonaqueous phases and play key roles in nuclear materials (e.g., nuclear fuel) and nuclear waste management. Despite their importance, our structural understanding of the actinide metal oxo clusters, particularly the transuranic ones, is very limited because of experimental challenges such as high radioactivity. Herein we report a systematic theoretical study on the structures and stabilities of seven actinide metal oxo-hydroxo clusters [AnIV6O4(OH)4L12] (1-An; An = Th-Cm; L = O2CH-) along with their group 4 (Ti, Zr, Hf, Rf) and lanthanide (Ce) counterparts [MIV6O4(OH)4L12] (1-M). The work shows the Td-symmetric structures of all of the 1-An/M clusters and suggests the positions of the -OH functional groups, which are experimentally challenging to determine. Furthermore, by removing six electrons from 1-An, we found that oxidation could happen on the AnIV metal ions, producing [AnV6O4(OH)4L12]6+ (2-An; An = Pa, U, Np), or on the O2- and OH- ligands, producing [AnIV6(O•-)4(OH•)2(OH)2L12]6+ (3-An; An = Pu, Am, Cm). On the basis of 2-An, we constructed a series of tetravalent and pentavalent actinide metal oxo clusters [AnIV6O14]4- (4-An) and [AnV6O14]2+ (5-An), which proves the feasibility of the highly important pentavalent actinyl clusters, demonstrates the f orbital's structure-directing role in the formation of linear [O≡AnV═O]+ actinyl ions, and expands the concept of actinyl-actinyl interaction into pentavalent transuranic actinyl clusters.

Hydroxypyridinone-based stabilization of Np(IV) enabling efficient U/Np/Pu separations in the Adapted PUREX process

The classical process to recover uranium (U) and plutonium (Pu) from used nuclear fuel using tributyl phosphate (TBP), namely the Plutonium Uranium Redox EXtraction (PUREX) process, is complicated by the persistent presence of neptunium (Np) and thus requires extra purification steps. The concept of Adapted PUREX seeks to achieve Np recovery by adjusting the valence of the metal more effectively, thereby controlling its behavior more precisely. This study introduces the use of an aqueous hydroxypyridinone chelator, 3,4,3-LI(1,2-HOPO) (abbreviated as HOPO), to dictate the behavior of Np for recovery and meanwhile simplify cumbersome reprocessing steps. The interactions between Np and HOPO were probed mechanistically by way of absorption spectrophotometry, in conjunction with cyclic voltammetry. UV–Vis-NIR spectra illustrated the reduction of NpO22+ to Np4+, with a fast reaction rate. Cyclic voltammetry revealed quasi-reversible processes between the oxidized and reduced forms of the ligand and its Np complexes. The corresponding heterogeneous rate constants (k0) were estimated from the peak-to-peak separation potentials (ΔEp), at ~ 4 – 35 μm/s for both HOPO and NpHOPO, with scan rates of 0.01 – 0.4 V/s. Meanwhile, the electromotive force (EMF) as well as the change of Gibbs free energy (ΔG) were assessed from the half-wave potential (E1/2), demonstrating the completeness of NpO22+ reduction to Np4+ by HOPO. The cumulative formation constant of the resulting NpHOPO complex (logβ101) was determined by metal competition titration to be 42.0 ± 0.6, corroborating the extraordinarily high affinity of HOPO to tetravalent metal ions. The prowess of valence control by HOPO and the high stability of the formed complex resulted in enhanced separations of Np from U and of Pu from U, with a maximum separation factor of ~7000 for both, nearly 90- and 10300-fold higher, respectively, than the values obtained using conventional PUREX formulae.

Rational design of Lithium-Sulfur battery cathodes based on differential Atom Electronegativity

Lithium-sulfur (Li-S) batteries show advantages for next-generation energy storage due to their high theoretical energy density and cost effectiveness. Despite tremendous efforts, rational cathode design for mitigating the shuttling of soluble lithium polysulfides (LiPSs) between electrodes and improving reversible capacity remains a challenge because effective characteristic descriptor for sulfur cathodes is not established. In this work, the surface electron affinity (defined as electron-acceptance ability of solid-state surface) is firstly established as a quantitative screening principle forcathode materials. We find that those materials with the -2.66 ~ -7.96 eV surface electron affinities do not only prevent LiPSs from dissolving but also exhibit good electronic conductivity. The design principle is verified by our comparative electrochemical characterizations that TiO (ΔVSEA = -4.42 eV) performs a lower capacity-decay rate than TiS2 (-1.12 eV) TiC (-10.86 eV) and TiN (-14.55 eV).The design principle is verified by available experimental data reported in the previous literatures and our comparative experimental studies. The optimum binding strength of LiPSs on cathodes is identified in the range of 1.65 ~ 2.90 eV. Furthermore, differential atom electronegativity is defined as a more universal descriptor for experimentally and theoretically screening high-performance cathodes of Li-S battery. We find that divalent metal oxides (MO) with M:O = 1:1 and tetravalent transition metal sulfides, selenides and carbides (M:X = 1:2) could promote battery performance in maintaining high reversible capacity. These findings provide important insight towards the understanding of interfacial adsorption mechanism in electrochemical systems and establishing design principles for future discovery of improved cathodes for Li-S batteries.

Advances and Challenges in the Creation of Porous Metal Phosphonates.

In the expansive world of porous hybrid materials, a category of materials that has been rather less explored than others and is gaining attention in development is the porous metal phosphonates. They offer promising features towards applications which demand control over the inorganic–organic network and interface, which is critical for adsorption, catalysis and functional devices and technology. The need to establish a rationale for new synthesis approaches to make these materials in a controlled manner is by itself an important motivation for material chemists. In this review, we highlight the various synthetic strategies exploited, discussing various metal phosphonate systems and how they influence the properties of porous metal phosphonates. We discuss porous metal phosphonate systems based on transition metals with an emphasis on addressing challenges with tetravalent metals. Finally, this review provides a brief description of some key areas of application that are ideally suited for porous metal phosphonates.

In-silico identification of adsorbent for separation of ethane/ethylene mixture.

We present here a high-throughput computational screening of 4,821 real metal-organic framework (MOF) structures that do not contain any open metal sites to isolate the best performing candidate for separation of ethane/ethylene mixture at ambient conditions. The MOF structures were assessed on the basis of several adsorption-based separation performance metrics. Some of these metrics were found to correlate strongly among themselves. We have presented various structures-property correlations which unfold useful insights. MOF ATAGEJ is found to be the top performing MOF with highest adsorbent performance score 12.38mol/kg and regenerability 93.88%. Several other MOFs OTOLIU (MIL-167), UMUMOG (UBMOF-8), and TOVGES (PCN-230) containing tetravalent metal cations such as Zr4+ and Ti4+ are found to be potential structures that are thermally, mechanically, and chemically stable and performs better than zeolites. Adsorption selectivity shows exponential correlation with difference of heat of adsorption of ethane and ethene at 0.1bar and 298K. We have also presented how various performance metrics correlate among themselves. These correlations unfold useful insights. Graphical abstract.

Bridging the Transuranics with Uranium(IV) Sulfate Aqueous Species and Solid Phases.

Isolating isomorphic compounds of tetravalent actinides (i.e., ThIV, UIV, NpIV, and PuIV) improve our understanding of the bonding behavior across the series, in addition to their relationship with tetravalent transition metals (Zr and Hf) and lanthanides (Ce). Similarities between these tetravalent metals are particularly illuminated in their hydrolysis and condensation behavior in aqueous systems, leading to polynuclear clusters typified by the hexamer [MIV6O4(OH)4]12+ building block. Prior studies have shown the predominance and coexistence of smaller species for ThIV (monomers, dimers, and hexamers) and larger species for UIV, NpIV, and PuIV (including 38-mers and 70-mers). We show here that aqueous uranium(IV) sulfate also displays behavior similar to that of ThIV (and ZrIV) in its isolated solid-phase and solution speciation. Two single-crystal X-ray structures are described: a dihydroxide-bridged dimer (U2) formulated as U2(OH)2(SO4)3(H2O)4 and a monomer-linked hexamer framework (U-U6) as (U(H2O)3.5)2U6O4(OH)4(SO4)10(H2O)9. These structures are similar to those previously described for ThIV. Moreover, cocrystallization of monomer and dimer and of dimer and monomer-hexamer phases for both ThIV (prior) and UIV (current) indicates the coexistence of these species in solution. Because it was not possible to effectively study the sulfate-rich solutions via X-ray scattering from which U2 and U-U6 crystallized, we provide a parallel solution speciation study in low sulfate conditions, as a function of the pH. Raman spectroscopy, UV-vis spectroscopy, and small-angle X-ray scattering of these show decreasing sulfate binding, increased hydrolysis, increased species size, and increased complexity, with increasing pH. This study describes a bridge across the first half the actinide series, highlighting UIV similarities to ThIV, in addition to the previously known similarities to the transuranic elements.

A Gold Nanocluster Constructed Mixed-Metal Metal-Organic Network Film for Combating Implant-Associated Infections.

The development of modular strategies for programming self-assembled supramolecular architectures with distinct structural and functional features is of immense scientific interest. We reported on the intrinsic antibacterial capability of anionic amphiphilic gold nanoclusters (GNCs) capped by para-mercaptobenzoic acid, which was closely related to the protonation level of terminal carboxylate groups. By using of the metal-ligand coordination-driven and solvent evaporation-induced self-assembly, we constructed GNCs-based mixed-metal metal-organic network (MM-MON) films on titanium disks as antibacterial nanocoatings. Taking the reasonable utilization of tetravalent metal ions M4+ (Ti, Zr, Hf; hard Lewis acid) and bactericidal divalent metal ions M2+ (Cu, Zn; borderline acid) co-incorporated metal-carboxylate coordination bonds, the MM-MON films exhibited superior stability due to the robust M4+-O bonds and M2+ releasing behavior resulting from the labile M2+-O coordinating. Together, the MM-MON films integrated the bacteria-responsive character of GNCs, exceptional chemical stability, and greatly enhanced antibacterial activity, ultimately killing adherent bacteria and initiating a self-defensive function. In a rat model for subcutaneous implant-associated infection, the MM-MON nanocoating showed an approximately 2 and 1 log lower multidrug-resistant Staphylococcus aureus implant and tissue colonization, respectively. The generalizable modular strategy of the GNC-metal networks is amenable to facilitate the functionalization of metal surfaces for combating implant-associated infections.

Molecular Design of Double-headed 2-Pyrrolidone Derivatives for Separation/Co-precipitation of UO22+ from/with Tetravalent Actinides towards Nuclear Fuel Recycling

Two kinds of novel double-headed 2-pyrrolidone derivatives (DHNRPs) were designed for efficient recovery of UO22+ from HNO3 (aq) and its separation from tetravalent metal ions (M4+). The DHNRPs bea...

Density functional study on electronic properties of transition metal-based vacancy-ordered halide perovskites

Replacing toxic Pb of halide perovskites is a serious challenge in the current investigation of perovskite solar cells. Vacancy-ordered double halide perovskites have attracted considerable research interest due to their excellent stability and optoelectronic properties. A series of vacancy-ordered double perovskites based on transition metal cations are comprehensively investigated in this work through first-principles calculations. Various electronic configurations of tetravalent transition metals are considered in spin-polarized calculation. Our calculations reveal electronic properties of vacancy-ordered double halide perovskites and provide a theoretical basis for the exploration of novel lead-free perovskites.

Computational screening of metal–organic framework structures for separation of propane/propene mixture

ABSTRACT In this article, we present a high-throughput computational screening of real metal–organic framework (MOF) structures to identify the best candidate material for the separation of propane/propene mixture. We assessed the performances of the MOFs by calculating various metrics such as adsorption selectivity, working capacity, regenerability and adsorbent performance score (APS). All most all of these MOFs are selective to propane over propene. We looked at various structures–property correlations that revealed some useful insights and ways of tuning the structural properties of the MOFs to yield high performance. The MOFs were ranked on the basis of APS. MOF RUFPUF was found to be the best performing MOF with a highest APS value of mol/kg and . We also screened out few potential stable MOFs containing tetravalent metal cations such as Zr4+, HF4+ and Ti4+. MOF BOLZIN (NU-1100) was found to be the best performing stable MOF with APS mol/kg and .

Reactivity of O,N-heterocyclic germylene and stannylene towards μ-dithio-bis(tricarbonyliron)

Synthesis and single-crystal X-ray diffraction study (SC-XRD) of the O,N-heterocyclic germylene Ge(PhAp) (1) containing chelate 4,6-di-tert-butyl-N-phenyl-o-amidophenolate ligand (PhApH2, where Ap – o-amidophenolate) are reported. Germylene 1 demonstrates a monomeric structure in contrast to earlier known related stannylene Sn(PhAp) (2) existing as a dimer. Diverse weak intermolecular interactions (Ge…Ge, CH…π(chelate) and Ge…π(arene)) were detected in the crystal packing of germylene 1. Hirshfeld surface analysis has been performed to evaluate such interactions. Reactivity of compounds 1 and 2 towards dithiodiiron hexacarbonyl has been examined. Low-valent germanium(II) and tin(II) centers are readily inserted into S-S bond of dithiodiiron hexacarbonyl with the formation of Fe4(µ4-ES4)(CO)12 (E: Ge(3); Sn(4)) and bis-ligand complexes of tetravalent metals E(PhAp)2. The resulting germanium(IV) and tin(IV) bis-o-amidophenolates were isolated as six-coordinated pyridine adducts E(PhAp)2(Py)2 (E: Ge(5); Sn(6)). All complexes were characterized by SC-XRD.

Properties in Reactive Structure Materials: ZrW2 and HfW2 – High Melting Temperatures, Densities, Hardness, and Exothermic Ignition Energies

ZrW2 and HfW2 were prepared by melting the constituent elements in an arc‐furnace. By cooling through perictectic phase lines above approximately 2000 °C, samples of the nominal 1:2 composition were obtained as products consisting of two phases, of which approximately 95 % adopts the MgCu2 type structure and 5 % the W structure. In ZrW2 and in HfW2, the MgCu2 type structure enables efficient topological compact spacefilling of the smaller W atoms into the cavities of the three‐dimensional net constructed by the larger tetravalent metals Zr and Hf. Correspondingly, very dense and hard alloys are obtained which burn at a crash in air in a strong exothermic ignition reaction. These materials are non‐toxic.

Density functional study of the effect of cation exchanged Sn-Beta zeolite for the diels-alder reaction between furan and methyl acrylate

We investigated the Diels-Alder (DA) reaction between furan and methyl acrylate over Lewis acidic Sn-Beta zeolite exchanged with Li, Na, K, Be, Mg and Ca cations by using density functional calculations. Sn-Beta requires lower barrier compared to uncatalyzed system due to its higher charge transfer from the furan to the adsorbed methyl acrylate, at the transition state. The catalytic activity for the CC bond formation in DA reaction can be altered by the exchange of cations in Sn-Beta. The catalytic activity of different tetravalent metal centers (Zr and Hf) substituted into Li-Sn-Beta is finally compared and found to be similar.

Effect of Transition Metal Ion Doping on the Microstructure, Defect Evolution, and Magnetic and Magnetocaloric Properties of CuFeO2 Ceramics

The polycrystalline CuFeO2 (CFO) and CuFe1-xMxO2 (M = Ti, Hf, Zr, M-CFO) samples are synthesized by solid-state reaction method. The doping effect of tetravalent nonmagnetic transition metal M4+ ions on the microstructure, defect evolution, and magnetic and magnetocaloric properties of the CFO system are comparatively investigated. The substitution of M4+ for Fe3+ increases lattice parameters, changes the bond length of Fe/Cu-O and bond angle of Fe-O-Fe, and improves the microstructure to some extent. Positron annihilation spectroscopy results indicate that M4+ doping induces the agglomeration of small-sized vacancy defects manifested as the increase in vacancy-type defect size and the suppression of inherent defect concentration. Magnetic measurements show that the antiferromagnetic stability of CFO system is clearly affected by M4+ doping, and Ti4+ doping has a more noticeable impact than Hf4+ and Zr4+ doping. Meanwhile, the coexistence of weak ferromagnetism and antiferromagnetism is detected in all doped samples, while Ti-doped system exhibits extraordinary magnetic properties. Especially for Ti-CFO2 (x = 0.03) sample, the maximum magnetization reaches as high as 11.81 emu/g at 0.5 T, which enhanced one order of magnitude than that of undoped CFO. Isothermal M-H data at different temperatures show that entropy change (ΔSM) and refrigerant capacity (RC) for CFO and M-CFO2 samples are significantly weakening with M4+ substitution in bulk CFO. The maximum ΔSM = 4.79 J·kg−1 K−1 and RC = 12.79 J·kg−1 for undoped CFO are obtained near the transition temperature TN2 = 12 K, with the applied fields up to 6 T. The possible reasons for the above observations are discussed in detail.