Low-spin Electronic Configuration Research Articles

Effects of Temperature, Axial Ligand, and Photoexcitation on the Structure and Spin-State of Nickel(II) Complexes with Water-Soluble 5,10,15,20-Tetrakis(1-methylpyridinium-4-yl)porphyrin.

Water-soluble metalloporphyrins, depending on the metal center, possess special spectral, coordination, and photochemical features. In nickel(II) porphyrins, the Ni(II) center can occur with low-spin or high-spin electronic configuration. In aqueous solution, the cationic nickel(II) complex (Ni(II)TMPyP4+, where H2TMPyP4+ = 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin), exists in both forms in equilibrium. In this study, an equilibrium system involving the low-spin and high-spin forms of Ni(II)TMPyP4+ was investigated via application of irradiation, temperature change, and various potential axial ligands. Soret band excitation of this aqueous system, in the absence of additional axial ligands, resulted in a shift in the equilibrium toward the low-spin species due to the removal of axial solvent ligands. The kinetics and the thermodynamics of the processes were also studied via determination of the rate and equilibrium constants, as well as the ΔS, ΔH, and ΔG values. Temperature increase had a similar effect. The equilibrium of the spin isomers was also shifted by decreasing the solvent polarity (using n-propanol) as well as by the addition of a stronger coordinating axial ligand (such as ammonia). Since triethanolamine is an efficient electron donor in Ni(II)TMPyP4+-based photocatalytic systems, its interaction with this metalloporphyin was also studied. The results promote the development of efficient photocatalytic systems based on this complex.

Light-induced spin-state switching in Fe(II) spin-crossover complexes with thiazole-based chelating ligands.

Homoleptic complexes [Fe(4bt)3](ClO4)2 (1), [Fe(2bt)3](ClO4)2 (2), and [Fe(3tpH)3](ClO4)2 (3) were obtained by a reaction between the Fe(II) precursor salt and the corresponding thiazole-based bidentate ligand (L = 4bt = 4,4'-bithiazole, 2bt = 2,2'-bithiazole, 3tpH = 3-(thiazol-2-yl)pyrazole). X-ray crystal structure determination revealed crystallization of solvent-free complex 1, a solvate 2·MeOH, and a co-crystal 3·2(3tpH). The crystal packing of all these complexes is dominated by one-dimensional interactions between the [Fe(L)3]2+ cations. These interactions are stronger in 2·MeOH and 3·2(3tpH), leading to cooperative and slightly hysteretic transitions between the high-spin and low-spin electronic configurations at ∼235 K and 159 K, respectively. In contrast, weaker intermolecular interactions in 1 result in a gradual spin crossover above 300 K, with the maximum fraction of the HS state ∼25% achieved at 400 K. Complexes 2 and 3·2(3tpH) exhibit light-induced excited spin state trapping (LIESST) under irradiation with white light or a 532 nm laser at 5 K. After the photoexcitation, the trapped metastable HS state relaxes to the ground LS state with the average relaxation temperature of 81 K and 68 K, respectively. Examination of the relaxation dynamics by optical absorption spectroscopy on a single crystal of 3·2(3tpH) revealed the sigmoidal shape of the relaxation curves at lower temperatures, attributed to cooperative effects, as well as a plateau at ∼10% of the HS fraction at intermediate temperatures, hinting at a more complex mechanism for the relaxation of the LIESST phase in this material.

The Nephelauxetic Effect Becomes an Important Design Factor for Photoactive First-Row Transition Metal Complexes.

The expansion of d-orbitals as a result of metal-ligand bond covalence, the so-called nephelauxetic effect, is a well-established concept of coordination chemistry, yet its importance for the design of new photoactive complexes based on first-row transition metals is only beginning to be recognized. Until recently, much focus has been on optimizing the ligand field strength, coordination geometries, and molecular rigidity, but now it becomes evident that the nephelauxetic effect can be a game changer regarding the photophysical properties of 3d metal complexes in solution at room temperature. In CrIII and MnIV complexes with the d3 valence electron configuration, the nephelauxetic effect was exploited to shift the well-known ruby-like red luminescence to the near-infrared spectral region. In FeII and CoIII complexes with the low-spin d6 electron configuration, charge-transfer excited states were stabilized with respect to detrimental metal-centered excited states, to improve their properties and to enhance their application potential. In isoelectronic (3d6 ) isocyanide complexes of Cr0 and MnI , the nephelauxetic effect is likely at play as well, enabling luminescence and other favorable photoreactivity. This minireview illustrates the broad applicability of the nephelauxetic effect in tailoring the photophysical and photochemical properties of new coordination compounds made from abundant first-row transition metals.

Spin Manipulation in a Metal-Organic Layer through Mechanical Exfoliation for Highly Selective CO2 Photoreduction.

Spin manipulation of transition-metal catalysts has great potential in mimicking enzyme electronic structures to improve activity and/or selectivity. However, it remains a great challenge to manipulate room-temperature spin state of catalytic centers. Herein, we report a mechanical exfoliation strategy to in situ induce partial spin crossover from high-spin (s=5/2) to low-spin (s=1/2) of the ferric center. Due to spin transition of catalytic center, mixed-spin catalyst exhibits a high CO yield of 19.7 mmol g-1 with selectivity of 91.6 %, much superior to that of high-spin bulk counterpart (50 % selectivity). Density functional theory calculations reveal that low-spin 3d-orbital electronic configuration performs a key function in promoting CO2 adsorption and reducing activation barrier. Hence, the spin manipulation highlights a new insight into designing highly efficient biomimetic catalysts via optimizing spin state.

New iron(III) complexes with 2-formylpyridine thiosemicarbazones: Synthetic aspects, structural and spectral analyses and cytotoxicity screening against MCF-7 human cancer cells

2-Formylpyridine thiosemicarbazone - iron (III) chelates [FeL2] Cl•2H2O {L = L1 (C1) [HL1 = 4-(4-Nitrophenyl)-1-((pyridin-2-yl)methylene)thiosemicarbazide] and L = L2 (C2) [HL2 = 4-(2,5-Dimethoxyphenyl)-1-((pyridin-2-yl)methylene)thiosemicarbazide]} were prepared. The two ligand anions in each complex resulted in saturation of the iron coordination number and consequently the existence of these complexes as 1:1 electrolytes. As well, the iron in these complexes exhibits low-spin electronic configuration. X-ray crystallography of complex C1 indicated its triclinic crystal system and P 1‾ space group. In addition, it proved the ligation through a thiol sulfur atom and two nitrogen atoms of pyridine and azomethine groups. This is while the presence of two water molecules of crystallization in the complex structure was also indicated. The ligand HL1 was selected for cytotoxicity screening against human MCF-7, A-549, HEPG-2 and HCT-116 cancer cells and the most enhanced activities were detected against the breast cells. Against these cells, the compounds HL1, HL2, C1 and C2 induced cytotoxicity, respectively, with IC50 values of 52.4, 145.4, 34.3 and 62.0 μM. However, against the healthy BHK cells, HL1 and HL2 caused cytotoxicity, respectively, with IC50 values of 54.8 and 110.6 μM and cytotoxicity with percent viabilities of 56.7 and 55.4% of the BHK cells by the complexes (137.4 μM of C1 and 131.9 μM of C2) was determined. These activities against MCF-7 cells are less significant compared with the measured value for doxorubicin. But this standard is more toxic to normal cells than the thiosemicarbazones (IC50 (doxorubicin) = 9.66 μM against MCF-7 cells and 36.42 μM against BHK cells).

Multistep synthesis, reactivity and X-ray structure of the anisole-terminated iron(II) polyhalogenoclathrochelates and their monoribbed-functionalized macrobicyclic derivatives

Multistep synthetic pathway towards a series of the anisoleboron-capped ribbed-functionalized iron(II) cage complexes was developed. Their hexachloroclathrochelate precursor was obtained by the template condensation of three dichloroglyoximate chelating ligand synthons with two molecules of 4-methoxyphenylboronic acid as a Lewis-acidic cross-linking agent on the iron(II) ion as a matrix. It easily underwent a stepwise nucleophilic substitution with S2- and O2-dinucleophilic aliphatic (ethanedithiolate) or aromatic (pyrocatecholate) agents, forming the stable X2 (X = S or O)-six-membered ribbed substituent(s) at a quasiaromatic cage framework. Performing these reactions under the different reaction conditions (i.e., at various hexachloroclathrochelate-to-nucleophile molar ratios, a wide range of temperatures and a series of the solvents) allowed to control a predominant formation of its mono-, di- or triribbed-substituted macrobicyclic derivatives. Thus obtained iron(II) di- and tetrachloroclathrochelates can undergo their post-synthetic transformations with active nucleophilic agents. The latter complexes underwent a further nucleophilic substitution with the anionic derivative of n-butanthiol, thus giving the hexasulfide macrobicyclic compound with two functionalizing n-alkyl substituents in one of its three chelate α-dioximate fragments and two apical biorelevant anisole substituents. The obtained iron(II) clathrochelates, possessing a low-spin electronic d6 configuration, were characterized using elemental analysis, MALDI-TOF mass spectrometry, UV–Vis, 1H and 13C{1H} NMR spectroscopies, and by the single-crystal X-ray diffraction experiments for the hexachloroclathrochelate precursor, its dichlorotetrasulfide macrobicyclic derivative and the monoribbed-functionalized hexasulfide cage complex. In all their molecules, the encapsulated iron(II) ion is situated in the centre of its FeN6-coordination polyhedron, the geometry of which is intermediate between a trigonal prism and a trigonal antiprism with the distortion angles φ from 21.4 to 23.4°. Halogen bonding between the polyhalogenoclathrochelate molecules in their crystals is observed.Graphical abstract

Hydrogen Atom Abstraction from an OsII(NH3)2 Complex Generates an OsIV(NH2)2 Complex: Experimental and Computational Analysis of the N-H Bond Dissociation Free Energies and Reactivity.

Double hydrogen atom abstraction from (TMP)OsII(NH3)2 (TMP = tetramesitylporphyrin) with phenoxyl or nitroxyl radicals leads to (TMP)OsIV(NH2)2. This unusual bis(amide) complex is diamagnetic and displays an N-H resonance at 12.0 ppm in its 1H NMR spectrum. 1H-15N correlation experiments identified a 15N NMR spectroscopic resonance signal at -267 ppm. Experimental reactivity studies and density functional theory calculations support relatively weak N-H bonds of 73.3 kcal/mol for (TMP)OsII(NH3)2 and 74.2 kcal/mol for (TMP)OsIII(NH3)(NH2). Cyclic voltammetry experiments provide an estimate of the pKa of [(TMP)OsIII(NH3)2]+. In the presence of Barton's base, a current enhancement is observed at the Os(III/II) couple, consistent with an ECE event. Spectroscopic experiments confirmed (TMP)OsIV(NH2)2 as the product of bulk electrolysis. Double hydrogen atom abstraction is influenced by π donation from the amides of (TMP)OsIV(NH2)2 into the d orbitals of the Os center, favoring the formation of (TMP)OsIV(NH2)2 over N-N coupling. This π donation leads to a Jahn-Teller distortion that splits the energy levels of the dxz and dyz orbitals of Os, results in a low-spin electron configuration, and leads to minimal aminyl character on the N atoms, rendering (TMP)OsIV(NH2)2 unreactive toward amide-amide coupling.

Materials design of Kitaev spin liquids beyond the Jackeli–Khaliullin mechanism

The Kitaev spin liquid provides a rare example of well-established quantum spin liquids in more than one dimension. It is obtained as the exact ground state of the Kitaev spin model with bond-dependent anisotropic interactions. The peculiar interactions can be yielded by the synergy of spin-orbit coupling and electron correlations for specific electron configuration and lattice geometry, which is known as the Jackeli–Khaliullin mechanism. Based on this mechanism, there has been a fierce race for the materialization of the Kitaev spin liquid over the last decade, but the candidates have been still limited mostly to 4d- and 5d-electron compounds including cations with the low-spin d5 electron configuration, such as Ir4+ and Ru3+. Here we discuss recent efforts to extend the material perspective beyond the Jackeli–Khaliullin mechanism, by carefully reexamining the two requisites, formation of the jeff = 1/2 doublet and quantum interference between the exchange processes, for not only d- but also f-electron systems. We present three examples: the systems including Co2+ and Ni3+ with the high-spin d7 electron configuration, Pr4+ with the f1-electron configuration, and polar asymmetry in the lattice structure. In particular, the latter two are intriguing since they may realize the antiferromagnetic Kitaev interactions, in contrast to the ferromagnetic ones in the existing candidates. This partial overview would stimulate further material exploration of the Kitaev spin liquids and its topological properties due to fractional excitations.

Influence of Ring Contraction on the Electronic Structure of Nickel Tetrapyrrole Complexes: Corrole vs Porphyrin

The influence of the contracted corrole macrocycle, in comparison to the larger porphyrin macrocycle, on the electronic structure of nickel was studied with X-ray and ultraviolet photoelectron spectroscopy (XPS, UPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Synthesis and in situ characterization of the Ni complexes of octaethylporphyrin (NiOEP) and hexaethyldimethylcorrole (NiHEDMC) were performed in ultra-high vacuum. XPS and NEXAFS spectra reveal a +2 oxidation state and a low-spin d8 electron configuration of Ni in both complexes, despite the formal trianionic nature of the corrole ligand. UPS, in combination with density functional theory (DFT) calculations, support the electronic structure of a Ni(II) corrole with a π-radical character of the ligand. The NEXAFS spectra also reveal differences in the valence electronic structure, which are attributed to the size mismatch between the small Ni(II) center and the larger central cavity of NiOEP. Analysis of the gas-phase structures shows that the Ni−N bonds in NiOEP are 4%–6% longer than those in NiHEDMC, even when NiOEP adopts a ruffled conformation. The individual interactions that constitute the Ni−ligand bond are altogether stronger in the corrole complex, according to bonding analysis within the energy decomposition analysis and the natural orbitals for chemical valence theory (EDA-NOCV).

Planar three-coordinate iron sulfide in a synthetic [4Fe-3S] cluster with biomimetic reactivity.

Iron-sulfur clusters are emerging as reactive sites for the reduction of small-molecule substrates. However, the four-coordinate iron sites of typical iron-sulfur clusters rarely react with substrates, implicating three-coordinate iron. This idea is untested because fully sulfide-coordinated three-coordinate iron is unprecedented. Here we report a new type of [4Fe-3S] cluster featuring an iron center with three bonds to sulfides. Although a high-spin electronic configuration is characteristic of other iron-sulfur clusters, the planar geometry and short Fe–S bonds lead to a surprising low-spin electronic configuration at the three-coordinate Fe center as determined by spectroscopy and ab initio calculations. In a demonstration of biomimetic reactivity, the [4Fe-3S] cluster reduces hydrazine, a natural substrate of nitrogenase. The product is the first example of NH2 bound to an iron-sulfur cluster. Our results demonstrate that three-coordinate iron supported by sulfide donors is a plausible precursor to reactivity in iron-sulfur clusters like the FeMoco of nitrogenase.

Synthesis of Thin-Film Metal Pyrites by an Atomic Layer Deposition Approach.

Late 3d transition metal disulfides (MS2 , M=Fe, Co, Ni, Cu, Zn) can crystallize in an interesting cubic-pyrite structure, in which all the metal cations are in a low-spin electronic configuration with progressive increase of the eg electrons for M=Fe-Zn. These metal pyrite compounds exhibit very diverse and intriguing electrical and magnetic properties, which have stimulated considerable attention for various applications, especially in cutting-edge energy conversion and storage technologies. The synthesis of the metal pyrites is certainly very important, because highly controllable, reproducible, and reliable synthesis methods are virtually essential for both fundamental materials research and practical engineering. In this Concept, a new approach of (plasma-assisted) atomic layer deposition (ALD) to synthesize the thin-film metal pyrites (FeS2 , CoS2 , NiS2 ) is introduced. The ALD synthesis approach allows for atomic-precision control over film composition and thickness, excellent film uniformity and conformality, and superior process reproducibility, and therefore it is of high promise for uniformly conformal metal pyrite thin-film coatings on complex 3D structures in general. Details and implications of this ALD approach are discussed in this Concept, mainly from a conceptual perspective, and it is envisioned that, with this new ALD synthesis approach, a significant amount of new studies will be enabled on both the fundamentals, and novel applications of the metal pyrite materials.

Variations in the molecularity of bis(formylpyrrolyl)cobalt(II) complexes

Abstract This work aims to extend the coordination chemistry of Co(II) with bis(2-formylpyrrolyl) ligands to different donor molecules. Treatment of a mixture of anhydrous CoCl2 and excess of pyridine in THF with two equivalents of sodium 2-formylpyrrolyl gives rise to complex [Co{κ2N,O-NC4H3-C(H) O}2(Py)2] (1) in good yields, after standard work-up procedures. By contrast, the reaction of two equivalents of sodium 2-formylpyrrolyl with anhydrous CoCl2 in neat THF or MeCN solutions systematically led, after standard work-up, to the identification of the tetrameric complex [Co{κ2N,O-NC4H3-C(H) O}2]4 (2) and other unknown contaminations. Analytically pure samples of complex 2 were only prepared when the synthesis reaction was performed in toluene at 90 °C. Complexes 1 and 2 are paramagnetic and were characterized by elemental analysis, magnetic susceptibility measurements (Evans method) and X-ray diffraction. Complex 1 is a hexacoordinated octahedral complex with a low-spin (S = 1/2) electronic configuration. On the other hand, the tetrameric complex 2 results from the self-assembling of the elusive and highly unsaturated complex “[Co{κ2N,O-NC4H3-C(H) O}2]” giving rise to a tetranuclear distorted cubane structure, comprising two hexacoordinated octahedral and two pentacoordinated trigonal bipyramidal Co(II) centers. Complex 2 revealed an overall high-spin (S = 3/2 per Co center) nature, as suggested in solution by the Evans method and in the solid state by SQUID magnetometry.

Spin-Crossover Complexes

Spin-crossover (SCO) is a spin-state switching phenomenon between a high-spin (HS) and low-spin (LS) electronic configurations in a transition metal center.

Metallointercalators and Metalloinsertors: Structural Requirements for DNA Recognition and Anticancer Activity.

As the carrier of the inheritable information in cells, DNA has been the target of metal complexes for over 40 years. In this chapter, the focus will be on non-covalent recognition of the highly structured DNA surface by substitutionally inert metal complexes capable of either sliding in between the normal base pairs as metallointercalators or flipping out thermodynamically destabilized mispaired nucleobases as metalloinsertors. While most of the compounds discussed are based on ruthenium(II) and rhodium(III) due to their stable octahedral coordination environment and low-spin 4d6 electronic configuration, most recent developments of alternative metal complexes, based on both transition metals and main group elements, will also be highlighted. A particular focus of the coverage is on structural data from X-ray structure analysis, which now provides details of the interaction at unprecedented details and will enable development of novel DNA binding probes for fundamental studies as well as new anticancer drug candidates.

Selective, Tunable O2 Binding in Cobalt(II)-Triazolate/Pyrazolate Metal-Organic Frameworks.

The air-free reaction of CoCl2 with 1,3,5-tri(1H-1,2,3-triazol-5-yl)benzene (H3BTTri) in N,N-dimethylformamide (DMF) and methanol leads to the formation of Co-BTTri (Co3[(Co4Cl)3(BTTri)8]2·DMF), a sodalite-type metal–organic framework. Desolvation of this material generates coordinatively unsaturated low-spin cobalt(II) centers that exhibit a strong preference for binding O2 over N2, with isosteric heats of adsorption (Qst) of −34(1) and −12(1) kJ/mol, respectively. The low-spin (S = 1/2) electronic configuration of the metal centers in the desolvated framework is supported by structural, magnetic susceptibility, and computational studies. A single-crystal X-ray structure determination reveals that O2 binds end-on to each framework cobalt center in a 1:1 ratio with a Co–O2 bond distance of 1.973(6) Å. Replacement of one of the triazolate linkers with a more electron-donating pyrazolate group leads to the isostructural framework Co-BDTriP (Co3[(Co4Cl)3(BDTriP)8]2·DMF; H3BDTriP = 5,5′-(5-(1H-pyrazol-4-yl)-1,3-phenylene)bis(1H-1,2,3-triazole)), which demonstrates markedly higher yet still fully reversible O2 affinities (Qst = −47(1) kJ/mol at low loadings). Electronic structure calculations suggest that the O2 adducts in Co-BTTri are best described as cobalt(II)–dioxygen species with partial electron transfer, while the stronger binding sites in Co-BDTriP form cobalt(III)–superoxo moieties. The stability, selectivity, and high O2 adsorption capacity of these materials render them promising new adsorbents for air separation processes.

Infrared optical absorption in low-spin Fe2+-doped SrTiO3

Band gap engineering in SrTiO3 and related titanate perovskites has long been explored due to the intriguing properties of the materials for photocatalysis and photovoltaic applications. A popular approach in the materials chemistry community is to substitutionally dope aliovalent transition metal ions onto the B site in the lattice to alter the valence band. However, in such a scheme there is limited control over the dopant valence, and compensating defects often form. Here we demonstrate a novel technique to controllably synthesize Fe2+- and Fe3+-doped SrTiO3 thin films without formation of compensating defects by co-doping with La3+ ions on the A site. We stabilize Fe2+-doped films by doping with two La ions for every Fe dopant, and find that the Fe ions exhibit a low-spin electronic configuration, producing optical transitions in the near infrared regime and degenerate doping. The novel electronic states observed here offer a new avenue for band gap engineering in perovskites for photocatalytic and photovoltaic applications.

Flexibility is Key: Synthesis of a Tripyridylamine (TPA) Congener with a Phosphorus Apical Donor and Coordination to Cobalt(II).

Tripyridylamine (TPA), a tetradentate ligand that forms 5-membered chelate rings upon metal coordination, has demonstrated significant utility in synthetic inorganic chemistry. An analogue with a phosphorus apical donor is a desirable target for tuning electronic structure and enhancing reactivity. However, this congener has been synthetically elusive. Prior attempts have resulted in tridentate coordination to transition metal ions due to a lack of ligand flexibility. Herein, we report the successful synthesis of tris(2-pyridylmethyl)proazaphosphatrane (TPAP), a more accommodating tripyridyl ligand containing an apical phosphorus donor. The TPAP ligand forms 6-membered chelate rings upon coordination and binds in the desired tetradentate fashion to a Co(II) ion. Structural studies elucidate the importance of ligand flexibility in tripodal ligands featuring phosphorus donors. Cyclic voltammetry, UV-vis, and solution magnetic susceptibility experiments of [Co(TPAP)(CH3CN)](2+) are also reported and compared to [Co(TPA)(CH3CN)](2+). Notably, magnetic susceptibility measurements of [Co(TPAP)(CH3CN)](2+) indicate a low spin electronic configuration, in contrast to [Co(TPA)(CH3CN)](2+), which is high spin.

A five-coordinate heme dioxygen adduct isolated within a metal-organic framework.

The porphyrinic metal-organic framework (MOF) PCN-224 is metalated with Fe(II) to yield a 4-coordinate ferrous heme-containing compound. The heme center binds O2 at -78 °C to give a 5-coordinate heme-O2 complex. For the first time, this elusive species is structurally characterized, revealing an Fe(III) center coordinated to superoxide via an end-on, η(1) linkage. Mössbauer spectroscopy supports the structural observations and indicates the presence of a low-spin electronic configuration for Fe(III). Finally, variable-temperature O2 adsorption data enable quantification of the Fe-O2 interaction, providing a binding enthalpy of -34(4) kJ/mol. This value is nearly half of that observed for comparable 6-coordinate, imidazole-bound heme-O2 complexes, a difference that further illustrates the importance of axial ligands in biological heme-mediated O2 transport and storage. These results demonstrate the ability of a MOF, by virtue of its rigid solid-state structure, to enable isolation and thorough characterization of a species that can only be observed transiently in molecular form.

Low-Cost, Long-Cycle-Life Sodium-Ion Battery to Enable Grid Scale Energy Storage

Large-capacity, cost-effective energy storage is the transformational technology needed to enable large scale integration of renewable energy (e.g. wind, solar). The rechargeable battery offers efficient electrical energy storage (EES). The Li-ion battery has been the leading option based on its performance, but it is too expensive for large-scale EES. Unlike Li, Na is readily available worldwide and therefore much less costly than Li.Sodium-ion batteries (SIBs) based on a hexacyanometallate (HCM) cathode are good options for the purpose of a low cost battery for EES. These materials correspond to the general chemical formula, AxM1[M2(CN)6]y·zH2O, consisting of a cubic framework with cyanide (C≡N)- ligands bridging metal-ions, M1 and M2, thus forming large lattice interstitial spaces to facilitate efficient alkali-ion, “A”, intercalation. Electronic configurations of M1 and M2 are strongly affected by the cyanide ligands. In particular, ligand field splitting energy is higher for M2-ions associated with carbon than for M1-ions associated with nitrogen, which results in a low spin (LS) electron configuration for M2, but a high spin (HS) electron configuration for M1.We will present our study on HCM-based cathode materials, including their bulk and surface structures as well as their electrochemical performance. We will demonstrate that the HCM-based cathodes provide promising low-cost and long-cycle life SIBs of high specific energy density and efficient EES.

Structure and magnetism of epitaxial SrTi0.78Cu0.22O3−δ films with mixed-valence Cu ions

The structure and magnetic behavior of Cu-substituted Sr2+Ti4+O3-δ (STCu) thin films with ∼22% Cu on the Ti sites, grown on CeO2/yttria stabilized zirconia buffered (001) Si substrates were investigated. STCu films grew with (110) orientation or with a mixed (001)+(110) orientation and were under in-plane compressive strain. They showed weak room temperature ferromagnetism with a saturation magnetization of 0.3 ∼ 1.7 emu/cm3. Cu ions in STCu grown in an oxygen atmosphere existed mainly as Cu3+ with a small proportion of Cu2+, while in STCu grown in vacuum, Cu1+ ions were dominant with small amounts of Cu2+ and Cu3+. The saturation magnetization was attributed to the Cu2+ (3d9, S = 1/2) concentration, and the majority of Cu3+ (3d8, S = 0) ions were stabilized in the low-spin diamagnetic electron configuration similar to that found in mixed-valence layered perovskite superconductor compounds.