Chiral Separation of Copper Sulfide [S-Cu36] Nanocluster Using a Chiral Adaptive Counterion.

This work presents a new strategy to achieve the growth of copper sulfide nanoclusters with high nuclearity. Through a phosphine-assisted C-S reductive cleavage approach, an intrinsically chiral [Cu4] cluster passes through a [S-Cu9] cluster and transforms into a higher-nuclearity [S-Cu36] cluster, which features a core-shell structure with a [Cu4]4+ core encapsulated by a chiral [Cu20S12] shell. Interestingly, the spiral arrangement of the bidental ligands on the surface of the [S-Cu36] cluster leads to the L-/R-enantiomeric configurations. Moreover, by utilization of [Na(THF)6]+ as a chiral adaptive counterion, [S-Cu36] can be interlocked separately, thus enabling the isolation of homochiral clusters. Theoretical calculation suggests that the configuration transition between two enantiomeric [Na(THF)6]+ species is favorable at room temperature, thereby promoting the cocrystallization of resulting chiral products. This study introduces a novel perspective on the synthesis of chiral copper sulfide nanoclusters and presents an innovative approach to achieving the chiral separation of nanoclusters.

Trickier than It Looks: Isomerization between Five- and Six-Coordinated Zinc in Heterometallic Li2Zn2 Molecule.

This report describes the synthesis and characterization of two heterobimetallic Li-Zn coordination isomers [Li2Zn2(tbaoac)6] (tbaoac = tert-butyl acetoacetato) that have been isolated separately by the same stoichiometric reaction run in different organic solvents. The 6-coordinated zinc isomer (6-Zn) was synthesized in acetone with high yield, while the 5-coordinated one (5-Zn) was readily obtained from ethanol. The 5-Zn isomer has a low solubility in organic solvents such as alkanes and haloalkanes, while its 6-Zn counterpart exhibits a good solubility in almost all common solvents. Two isomeric molecules feature similar centrosymmetric tetranuclear cyclic assemblies, which are different in their arrangement of tbaoac ligands. While all ligands act as µ2-type in the structure of 5-Zn, the two tbaoac groups chelating Li appear as µ3-type in 6-Zn, thus providing an additional coordination for Zn ions. However, the real structural transformation between these isomers was shown to be more complex than simply making or breaking a couple of Zn-O bonds. X-ray single-crystal structure analysis, powder X-ray diffraction, multinuclear NMR, DART mass spectrometry, ICP-OES analysis, and TGA have been employed for the characterization of the isomers. The combination of powder X-ray diffraction and 1H NMR investigation revealed that 6-Zn isomer can be quantitatively transformed to 5-Zn in ethanol, while the reverse conversion instantly takes place in acetone.

Heterometallic Molecular and Ionic Isomers.

Numerous descriptions of structural isomerism in metal complexes do not list any molecular vs ionic isomers. At the same time, one of the most striking examples of structural isomerism in organic chemistry is molecular urea, which has the same atomic composition as the chemically distinct ionic ammonium cyanate. This iconic organic couple now meets its inorganic heterometallic counterpart. We introduce a new class of structural isomers, molecular vs ionic, that can be consummated in complex and coordinatively unsaturated polynuclear/heterometallic compounds. We report inorganic molecular and ionic isomers of the composition [NaCrFe (acac)3(hfac)3] (acac = acetylacetonate; hfac = hexafluoroacetylacetonate). Heterometallic molecular [CrIII(acac)3-Na-FeII(hfac)3] (1m) and ionic {[CrIII(acac)3-Na-CrIII(acac)3]+[FeII(hfac)3-Na-FeII(hfac)3]-} (1i) isomers have been isolated in pure form and characterized. While both ions are heterobimetallic trinuclear entities, the neutral counterpart is a heterotrimetallic trinuclear molecule. The two isomers exhibit distinctly different characteristics in terms of solubility, volatility, mass spectrometry ionization, and thermal behavior. Unambiguous assignment of the positions and oxidation/spin states of the Periodic Table neighbors, Fe and Cr, in both isomers have been made by a combination of characterization techniques that include synchrotron X-ray resonant diffraction, synchrotron X-ray fluorescence spectroscopy, Mössbauer spectroscopy, and DART mass spectrometry. The transformation between the two isomers that does take place in solutions of noncoordinating solvents has also been tested.

A High-Nuclearity Copper Sulfide Nanocluster [S-Cu50] Featuring a Double-Shell Structure Configuration with Cu(II)/Cu(I) Valences.

This work represents an important step in the quest for creating atomically precise binary semiconductor nanoclusters (BS-NCs). Compared with coinage metal NCs, the preparation of BS-NCs requires strict control of the reaction kinetics to guarantee the formation of an atomically precise single phase under mild conditions, which otherwise could lead to the generation of multiple phases. Herein, we developed an acid-assisted thiolate dissociation approach that employs suitable acid to induce cleavage of the S-C bonds in the Cu-S-R (R = alkyl) precursor, spontaneously fostering the formation of the [Cu-S-Cu] skeleton upon the addition of extra Cu sources. Through this method, a high-nuclearity copper sulfide nanocluster, Cu50S12(SC(CH3)3)20(CF3COO)12 (abbreviated as [S-Cu50] hereafter), has been successfully prepared in high yield, and its atomic structure was accurately modeled through single-crystal X-ray diffraction. It was revealed that [S-Cu50] exhibits a unique double-shell structural configuration of [Cu14S12]@[Cu36S20], and the innermost [Cu14] moiety displays a rhombic dodecahedron geometry, which has never been observed in previously synthesized Cu metal, hydride, or chalcogenide NCs. Importantly, [S-Cu50] represents the first example incorporating mixed Cu(II)/Cu(I) valences in reported atomically precise copper sulfide NCs, which was unambiguously confirmed by XPS, EPR, and XANES. In addition, the electronic structure of [S-Cu50] was established by a variety of optical investigations, including absorption, photoluminescence, and ultrafast transient absorption spectroscopies, as well as theoretical calculations. Moreover, [S-Cu50] is air-stable and demonstrates electrocatalytic activity in ORR with a four-electron pathway.

Multiscale hierarchical structures from a nanocluster mesophase.

Spontaneous hierarchical self-organization of nanometre-scale subunits into higher-level complex structures is ubiquitous in nature. The creation of synthetic nanomaterials that mimic the self-organization of complex superstructures commonly seen in biomolecules has proved challenging due to the lack of biomolecule-like building blocks that feature versatile, programmable interactions to render structural complexity. In this study, highly aligned structures are obtained from an organic-inorganic mesophase composed of monodisperse Cd37S18 magic-size cluster building blocks. Impressively, structural alignment spans over six orders of magnitude in length scale: nanoscale magic-size clusters arrange into a hexagonal geometry organized inside micrometre-sized filaments; self-assembly of these filaments leads to fibres that then organize into uniform arrays of centimetre-scale bands with well-defined surface periodicity. Enhanced patterning can be achieved by controlling processing conditions, resulting in bullseye and 'zigzag' stacking patterns with periodicity in two directions. Overall, we demonstrate that colloidal nanomaterials can exhibit a high level of self-organization behaviour at macroscopic-length scales.

Multi-functional Single-Source Molecular Precursors for Carbon-Coated Mixed-Metal Phosphates.

We introduce a new synthetic concept that can be broadly adopted for the low-temperature preparation of mixed-metal energy storage materials, such as phosphates, silicates, fluorides, fluorophosphates, and fluorosulfates that exhibit intrinsic low electronic conductivity and thus require a carbon modulation. The development of novel low-temperature approaches for assembling energy-related materials with a complex core-shell microstructure is of great importance for expanding their application scope. The traditional definition of single-source precursors refers to their ability to yield a phase-pure material upon thermal decomposition. We have developed a new way for the utilization of heterometallic molecular precursors in synthesis that goes beyond its common delineation as a single-phase maker. The utility of this approach has been demonstrated upon the low-temperature synthesis of lithium-iron phosphate@C, which represents a celebrated cathode material for Li-ion batteries. The first atomically precise carbonaceous molecular precursors featuring a desired Li:Fe:P ratio of 1:1:1, divalent iron, and sufficient oxygen content for the target LiFeIIPO4 phosphate were shown to enable a spontaneous formation of both the olivine core and conductive carbon shell, yielding a carbon-coated mixed-metal phosphate.

Chemical Bond Bridging across Two Domains: Generation of Fe(II) and In Situ Formation of FeSx on Zerovalent Iron.

Sulfidation of zerovalent iron (SZVI) can strengthen the decontamination ability by promoting the electron transfer from inner Fe0 to external pollutants by iron sulfide (FeSx). Although FeSx forms easily, the mechanism for the FeSx bonding on the ZVI surface through a liquid precipitation method is elusive. In this work, we demonstrate a key pathway for the sulfidation of ZVI, namely, the in situ formation of FeSx on ZVI surface, which leads to chemical bonding across two domains: the pristine ZVI and the newly formed FeSx phase. The two chemically bridged heterophases display superior activity in electron transportation compared to the physically coated SZVI, eventually bringing about the better performance in reducing Cr(VI) species. It is revealed that the formation of chemically bonded FeSx requires balancing the rates for the two processes of Fe(II) release and sulfidation, which can be achieved by tuning the pH and S(-II) concentration. This study elucidates a mechanism for surface generation of FeSx on ZVI, and it provides new perspectives to design high-quality SZVI for environmental applications.

Interplay between Chemical Transformations and Atomic Structure in Nanocrystals and Nanoclusters.

ConspectusChemically induced transformations are postsynthetic processing reactions applied to first generation (as-synthesized) nanomaterials to modify property-defining factors such as atomic structure, chemical composition, surface chemistry, and/or morphology. Compared with conditions for direct synthesis of colloidal nanocrystals, postsynthetic chemical transformations can be conducted in relatively mild conditions with a more controllable process, which makes them suitable for the precise manipulation of nanomaterials and for trapping metastable phases that are typically inaccessible from the conventional synthetic routes. Each of the chemically induced transformations methods can result in substantial restructuring of the atomic structure, but their transformation pathways can be very different. And the converse is also true: the atomic structure of the parent material plays a large role in the pathway toward and the resulting chemically transformed product. Additionally, the characteristic length of the parent material greatly affects the structure, which affects the outcome of the reaction.In this Account, we show how the atomic structure and nanoscale size directs the product formation into materials that are inaccessible from analogous chemically transformations in bulk materials. Through examples from the three chemical transformation processes (cation/anion exchange, redox reactions, and ligand exchange and ligand etching), the effect of the atomic structure on chemical transformations is made apparent, and vice versa. For cation exchange, an anisotropic atomic lattice results in a unidirectional exchange boundary. And because the interface can extend through the full crystal, a substantial strain field can form, influencing the phase of the material. In the redox reaction that leads to the nanoscale Kirkendall effect, the atomic structure is the key to inverting the diffusion rates in a diffusion couple to form the hollow cores. And for ligand etching, if one of the materials in a heterostructure has a defected and\or defect-tolerant atomic structure, it can be preferentially etched and its atomic structure can undergo phase transformations while the other composition remains intact. For length scales, we show how the chemically induced transformations greatly differ between bulk, nanocrystal, and nanocluster characteristic sizes. For instance, the structural transformation on relatively large nanocrystals (2-100 nm) can be a continuous process when the activation volume is smaller than the nanocrystal, while for smaller nanoclusters (<2 nm) the transformation kinetics could be swift resulting in only discrete thermodynamic states. Comparing the two nanosystems (nanocrystals to small nanoclusters), we address how their atomic structural differences can direct the divergent transformation phenomena and the corresponding mechanisms. Understanding the nanoscale mechanisms of chemically induced transformations and how they differ from bulk processes is key to unlocking new science and for implementing this processing for functional materials.

Tertiary Hierarchical Complexity in Assemblies of Sulfur-Bridged Metal Chiral Clusters.

Self-assembly of three-dimensional structures with order across multiple length scales-hierarchical assembly-is of great importance for biomolecules for the functions of life. Creation of similar complex architectures from inorganic building blocks has been pursued toward artificial biomaterials and advanced functional materials. Current research, however, primarily employs only large, nonreactive building blocks such as Au colloids. By contrast, sulfur-bridged transition metal clusters (<2 nm) are able to offer more functionality in catalytic and biochemical reactions. Hierarchical assembly of these systems has not been well researched because of the difficulty in obtaining single-phase clusters and the lack of suitable ligands to direct structure construction. To overcome these challenges, we employ a rigid planar ligand with an aromatic ring and bifunctional bond sites. We demonstrate the synthesis and assembly of 1.2 nm sulfur-bridged copper (SB-Cu) clusters with tertiary hierarchical complexity. The primary structure is clockwise/counterclockwise chiral cap and core molecules. They combine to form clusters, and due to the cap-core interaction (C-H···π), only two enantiomeric isomers are formed (secondary structure). A tertiary hierarchical architecture is achieved through the self-assembly of alternating enantiomers with hydrogen bonds as the intermolecular driving force. The SB-Cu clusters are air stable and have a distribution of oxidation states ranging from Cu(0) to Cu(I), making them interesting for redox and catalytic activities. This study shows that structural complexity at different length scales, mimicking biomolecules, can occur in active-metal clusters and provides a new platform for investigation of those systems and for the design of advanced functional materials.

Heterotrimetallic Precursor with 2:2:1 Metal Ratio Requiring at Least a Pentanuclear Molecular Assembly.

This work represents an important step in the quest to make heteromultimetallic molecules featuring specific metal types and complicated metal ratios. The rational design, synthesis, and characterization of a complex heterotrimetallic single-source molecular precursor for the next generation sodium-ion battery cathode material, Na2Mn2FeO6, is described. A unique pentametallic platform [MnII(ptac)3-Na-MnIII(acac)3-Na-MnII(ptac)3] (1) was derived from the known polymeric structure of [NaMnII(acac)3]∞, through a series of elaborate design procedures, such as mixed-ligand, unsymmetric ligand, and mixed-valent approaches. Importantly, the application of those techniques results in a molecule with distinctively different transition metal positions in terms of ligand environment and oxidation states. An isovalent substitution of FeIII for the central MnIII ion forms the target heterotrimetallic precursor [MnII(ptac)3-Na-FeIII(acac)3-Na-MnII(ptac)3] (3) with an appropriate metal ratio of Na:Mn:Fe = 2:2:1. The arrangement of metal ions and ligands in this pentametallic assembly was confirmed by single crystal X-ray investigation. The unambiguous assignment of the positions and oxidation states of the Periodic Table neighbors Fe and Mn in 3 has been achieved by a combination of investigative techniques that include synchrotron resonant diffraction, X-ray multiwavelength anomalous diffraction, X-ray fluorescence spectroscopy, Mössbauer spectroscopy, and gas-phase DART mass spectrometry. The heterotrimetallic single-source precursor 3 was shown to exhibit a clean decomposition pattern yielding the phase-pure P2-Na2Mn2FeO6 quaternary oxide with high uniformity of metal ion distribution as confirmed by electron microscopy.

Surface Modulation and Chromium Complexation: All-in-One Solution for the Cr(VI) Sequestration with Bifunctional Molecules.

The sulfidation of zero valent iron (ZVI) to an Fe@FeSx (S-ZVI) composite has been intensively explored in the ZVI field. Yet, further benefits from the FeSx coating layer are seldom realized, especially those effectively using its intrinsic physical and chemical properties for elaborate design. Here, we demonstrate that in a traditional Cr(VI) sequestration reaction, the FeSx layer displays a great utility in immobilizing molecules containing hydroxyl groups (-OH) and hence, attracting Cr(VI) complexes chelated with carboxyl organics (RCOOH). Such intermolecular attraction readily promotes the diffusion of the Cr(VI) complexes to the S-ZVI surface, affording a higher reaction rate for the Cr(VI) sequestration process. In addition, the above mechanism was used to guide a rational selection of molecules incorporating both hydroxyl and carboxyl functional groups with a proper ratio and thereby, a significantly improved reaction efficiency was achieved. Furthermore, the FeSx phase was revealed to be consumed in the reaction, acting as a supplementary reductant. This work is the first to unveil the relationship between molecules with specific functionalization and the FeSx phase, providing a general rule in choosing appropriate reaction media for Cr(VI) sequestration and related reactions.

Heterotrimetallic Mixed-Valent Molecular Precursors Containing Periodic Table Neighbors: Assignment of Metal Positions and Oxidation States.

A known trinuclear structure was used to design the heterobimetallic mixed-valent, mixed-ligand molecule [CoII (hfac)3 -Na-CoIII (acac)3 ] (1). This was used as a template structure to develop heterotrimetallic molecules [CoII (hfac)3 -Na-FeIII (acac)3 ] (2) and [NiII (hfac)3 -Na-CoIII (acac)3 ] (3) via isovalent site-specific substitution at either of the cobalt positions. Diffraction methods, synchrotron resonant diffraction, and multiple-wavelength anomalous diffraction were applied beyond simple structural investigation to provide an unambiguous assignment of the positions and oxidation states for the periodic table neighbors in the heterometallic assemblies. Molecules of 2 and 3 are true heterotrimetallic rather than a statistical mixture of two heterobimetallic counterparts. Trinuclear platform 1 exhibits flexibility in accommodating a variety of di- and trivalent metals, which can be further utilized in the design of molecular precursors for the NaMM'O4 functional oxide materials.

From cubane-assembled Mn-oxo clusters to monodispersed manganese oxide colloidal nanocrystals.

The assemblies of [M4O4] (M = metal) cubanes represent a fascinating class of materials for a variety of application fields. Although such a structural characteristic is relatively common in small molecules and in extended bulk solids, high nuclearity clusters composed of multiple [M4O4] units as their backbones are rare. In this work, we report two new Mn-oxo clusters, MnII 8MnIII 10O10(OOCMe)12(OMe)14(py)2 ([Mn18-Ac]) and MnII 4MnIII 14O14(OOCCMe3)8(OMe)14(MeOH)5(py) ([Mn18-Piv]), whose core structures are assemblies of either 6- or 7-cubanes in different packing patterns, which have been unambiguously revealed by single crystal X-ray diffraction technique. The cubane-assembled structural features can be deemed as the embryonic structures of the bulk manganese oxide. Herein, this report demonstrates the first case study of utilizing Mn-oxo clusters as precursors for the preparation of manganese oxide nanocrystals, which has never been explored before. Through a simple colloidal synthetic approach, high-quality, monodisperse Mn3O4 nanocrystals can be readily prepared by employing both precursors, while their morphologies were found to be quite different. This work confirms that the structural similarity between precursors and nanomaterials is instrumental in affording more kinetically efficient pathways for materials formation, and the structure of the precursor has a significant impact on the morphology of final nanocrystal products.

Stepwise deprotonation of truxene: structures, metal complexation, and charge-dependent optical properties.

As a planar subunit of C60-fullerene, truxene (C27H18) represents a highly symmetrical rigid hydrocarbon with strong blue emission. Herein, we used truxene as a model to investigate the chemical reactivity of a fullerene fragment with alkali metals. Monoanion, dianion, and trianion products with different alkali metal counterions were crystallized and fully characterized, revealing the core curvature dependence on charge and alkali metal coordination. Moreover, a 1proton nuclear magnetic resonance study coupled with computational analysis demonstrated that deprotonation of the aliphatic CH2 segments introduces aromaticity in the five-membered rings. Importantly, the UV-vis absorption and photoluminescence of truxenyl anions with different charges reveal intriguing charge-dependent optical properties, implying variation of the electronic structure based on the deprotonation process. An increase in aromaticity and π-conjugation yielded a red shift in the absorption and photoluminescent spectra; in particular, large Stokes shifts were observed in the truxenyl monoanion and dianion with high emission quantum yield and time of decay. Overall, stepwise deprotonation of truxene provides the first crystallographically characterized examples of truxenyl anions with three different charges and charge-dependent optical properties, pointing to their potential applications in carbon-based functional materials.

The gut microbial metabolite trimethylamine N-oxide and cardiovascular diseases.

Morbidity and mortality of cardiovascular diseases (CVDs) are exceedingly high worldwide. Researchers have found that the occurrence and development of CVDs are closely related to intestinal microecology. Imbalances in intestinal microecology caused by changes in the composition of the intestinal microbiota will eventually alter intestinal metabolites, thus transforming the host physiological state from healthy mode to pathological mode. Trimethylamine N-oxide (TMAO) is produced from the metabolism of dietary choline and L-carnitine by intestinal microbiota, and many studies have shown that this important product inhibits cholesterol metabolism, induces platelet aggregation and thrombosis, and promotes atherosclerosis. TMAO is directly or indirectly involved in the pathogenesis of CVDs and is an important risk factor affecting the occurrence and even prognosis of CVDs. This review presents the biological and chemical characteristics of TMAO, and the process of TMAO produced by gut microbiota. In particular, the review focuses on summarizing how the increase of gut microbial metabolite TMAO affects CVDs including atherosclerosis, heart failure, hypertension, arrhythmia, coronary artery disease, and other CVD-related diseases. Understanding the mechanism of how increases in TMAO promotes CVDs will potentially facilitate the identification and development of targeted therapy for CVDs.

Lanthanide-mediated tuning of electronic and magnetic properties in heterotrimetallic cyclooctatetraenyl multidecker self-assemblies.

The synthesis of a novel family of homoleptic COT-based heterotrimetallic self-assemblies bearing the formula [LnKCa(COT)3(THF)3] (Ln(iii) = Gd, Tb, Dy, Ho, Er, Tm, and Yb) is reported followed by their X-ray crystallographic and magnetic characterization. All crystals conform to the monoclinic P21/c space group with a slight compression of the unit cell from 3396.4(2) Å3 to 3373.2(4) Å3 along the series. All complexes exhibit a triple-decker structure having the Ln(iii) and K(i) ions sandwiched by three COT2- ligands with an end-bound {Ca2+(THF)3} moiety to form a non-linear (153.5°) arrangement of three different metals. The COT2- ligands act in a η8-mode with respect to all metal centers. A detailed structural comparison of this unique set of heterotrimetallic complexes has revealed consistent trends along the series. From Gd to Yb, the Ln to ring-centroid distance decreases from 1.961(3) Å to 1.827(2) Å. In contrast, the separation of K(i) and Ca(ii) ions from the COT-centroid (2.443(3) and 1.914(3) Å, respectively) is not affected by the change of Ln(iii) ions. The magnetic property investigation of the [LnKCa(COT)3(THF)3] series (Ln(iii) = Gd, Tb, Dy, Ho, Er, and Tm) reveals that the Dy, Er, and Tm complexes display slow relaxation of their magnetization, in other words, single-molecule magnet (SMM) properties. This behaviour is dominated by thermally activated (Orbach-like) and quantum tunneling processes for [DyKCa(COT)3(THF)3] in contrast to [ErKCa(COT)3(THF)3], in which the thermally activated and Raman processes appear to be relevant. Details of the electronic structures and magnetic properties of these complexes are further clarified with the help of DFT and ab initio theoretical calculations.

Phase evolution of the surface iron (hydr)oxides to the iron sulfide through anion exchange during sulfidation of zero valent iron.

The naturally-formed iron (hydr)oxides on the surface of zero valent iron (ZVI) have long been considered as passivation layer and inert phases which significantly reduce the reaction activities when they are employed in environmental remediation. Although it seems there are no direct benefits to keep these passivation layers, here, we show that such phases are necessary intermediates for the transformation to iron sulfides through an anion exchange pathway during sulfidation of ZVI. The pre-formed (hydr)oxides undergo a phase evolution upon aging and specific phases can be effectively trapped, which can be confirmed by a combination of different characterization techniques including scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRPD), and X-ray absorption near edge structure (XANES) spectroscopy. Interestingly, after sulfidation, the resultant samples originated from different (hydr)oxides demonstrate different activities in the Cr(VI) sequestration. The XANES investigation of Fe K edge and Fe L2,3 edge indicates Fe remains the same after sulfidation, suggesting a non-redox, anion exchange reaction pathway for the production of iron sulfides, where O2- anions are directly replaced with S2-. Consequently, the structural characteristics of the parent (hydr)oxides are inherited by the as-formed iron sulfides, which make them behave differently because of their different structural natures.

Protective Spinel Coating for Li1.17Ni0.17Mn0.50Co0.17O2 Cathode for Li-Ion Batteries through Single-Source Precursor Approach.

The Li1.17Ni0.17Mn0.50Co0.17O2 Li-rich NMC positive electrode (cathode) for lithium-ion batteries has been coated with nanocrystals of the LiMn1.5Co0.5O4 high-voltage spinel cathode material. The coating was applied through a single-source precursor approach by a deposition of the molecular precursor LiMn1.5Co0.5(thd)5 (thd = 2,2,6,6-tetramethyl-3,5-heptanedionate) dissolved in diethyl ether, followed by thermal decomposition at 400 °C inair resulting in a chemically homogeneous cubic spinel. The structure and chemical composition of the coatings, deposited on the model SiO2 spheres and Li-rich NMC crystallites, were analyzed using powder X-ray diffraction, electron diffraction, high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and energy-dispersive X-ray (EDX) mapping. The coated material containing 12 wt.% of spinel demonstrates a significantly improved first cycle Coulombic efficiency of 92% with a high first cycle discharge capacity of 290 mAhg-1. The coating also improves the capacity and voltage retention monitored over 25 galvanostatic charge-discharge cycles, although a complete suppression of the capacity and voltage fade is not achieved.

From lithium to sodium: design of heterometallic molecular precursors for the NaMO2 cathode materials.

Based on the well-established model structure of Li2M2(tbaoac)6, the first series of heterometallic molecular precursors Na2M2(tbaoac)6(THF)2 (M = Fe, Co, and Ni) have been designed and successfully utilized for the preparation of NaMO2 oxide cathode materials of sodium-ion batteries.

Three to tango requires a site-specific substitution: heterotrimetallic molecular precursors for high-voltage rechargeable batteries.

Design of heterotrimetallic molecules, especially those containing at least two different metals with close atomic numbers, radii, and the same coordination number/environment is a challenging task. This quest is greatly facilitated by having a heterobimetallic parent molecule that features multiple metal sites with only some of those displaying substitutional flexibility. Recently, a unique heterobimetallic complex LiMn2(thd)5 (thd = 2,2,6,6-tetramethyl-3,5-heptanedionate) has been introduced as a single-source precursor for the preparation of a popular spinel cathode material, LiMn2O4. Theoretical calculations convincingly predict that in the above trinuclear molecule only one of the Mn sites is sufficiently flexible to be substituted with another 3d transition metal. Following those predictions, two heterotrimetallic complexes, LiMn2-x Co x (thd)5 (x = 1 (1a) and 0.5 (1b)), that represent full and partial substitution, respectively, of Co for Mn in the parent molecule, have been synthesized. X-ray structural elucidation clearly showed that only one transition metal position in the trinuclear molecule contains Co, while the other site remains fully occupied by Mn. A number of techniques have been employed for deciphering the structure and composition of heterotrimetallic compounds. Synchrotron resonant diffraction experiments unambiguously assigned 3d transition metal positions as well as provided a precise "site-specific Mn/Co elemental analysis" in a single crystal, even in an extremely difficult case of severely disordered structure formed by the superposition of two enantiomers. DART mass spectrometry and magnetic measurements clearly confirmed the presence of heterotrimetallic species LiMnCo(thd)5 rather than a statistical mixture of two heterobimetallic LiMn2(thd)5 and LiCo2(thd)5 molecules. Heterometallic precursors 1a and 1b were found to exhibit a clean decomposition yielding phase-pure LiMnCoO4 and LiMn1.5Co0.5O4 spinels, respectively, at the relatively low temperature of 400 °C. The latter oxide represents an important "5V spinel" cathode material for the lithium ion batteries. Transmission electron microscopy confirmed a homogeneous distribution of transition metals in quaternary oxides obtained by pyrolysis of single-source precursors.