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- ItemRaman and NMR spectroscopic and theoretical investigations of the cubic laves-phases REAl2 (RE = Sc, Y, La, Yb, Lu)(London : Soc., 2023) Gießelmann, Elias C. J.; Engel, Stefan; Kostusiak, Weronika; Zhang, Yuemei; Herbeck-Engel, Petra; Kickelbick, Guido; Janka, OliverThe cubic Laves-phase aluminides REAl2 with RE = Sc, Y, La, Yb and Lu were prepared from the elements by arc-melting or using refractory metal ampoules and induction heating. They all crystallize in the cubic crystal system with space group Fd3̄m and adopt the MgCu2 type structure. The title compounds were characterized by powder X-ray diffraction and spectroscopically investigated using Raman and 27Al and in the case of ScAl2 by 45Sc solid-state MAS NMR. In both, the Raman and NMR spectra, the aluminides exhibit only one signal due to the crystal structure. DFT calculations were used to calculate Bader charges illustrating the charge transfer in these compounds along with NMR parameters and densities of states. Finally, the bonding situation was assessed by means of ELF calculations rendering these compounds aluminides with positively charged REδ+ cations embedded in an [Al2]δ− polyanion.
- ItemEngineering Kitaev exchange in stacked iridate layers: Impact of inter-layer species on in-plane magnetism(Cambridge : Royal Society of Chemistry, 2019) Yadav, R.; Eldeeb, M.S.; Ray, R.; Aswartham, S.; Sturza, M.I.; Nishimoto, S.; Van Den Brink, J.; Hozoi, L.Novel functionalities may be achieved in oxide electronics by appropriate stacking of planar oxide layers of different metallic species, MOp and M′Oq. The simplest mechanism allowing the tailoring of the electronic states and physical properties of such heterostructures is of electrostatic nature - charge imbalance between the M and M′ cations. Here we clarify the effect of interlayer electrostatics on the anisotropic Kitaev exchange in H3LiIr2O6, a recently proposed realization of the Kitaev spin liquid. By quantum chemical calculations, we show that the precise position of H+ cations between magnetically active [LiIr2O6]3- honeycomb-like layers has a strong impact on the magnitude of Kitaev interactions. In particular, it is found that stacking with straight interlayer O-H-O links is detrimental to in-plane Kitaev exchange since coordination by a single H-ion of the O ligand implies an axial Coulomb potential at the O site and unfavorable polarization of the O 2p orbitals mediating the Ir-Ir interactions. Our results therefore provide valuable guidelines for the rational design of Kitaev quantum magnets, indicating unprecedented Kitaev interactions of ≈40 meV if the linear interlayer linkage is removed.
- ItemStabilizing a three-center single-electron metal–metal bond in a fullerene cage(Cambridge : RSC, 2021) Jin, Fei; Xin, Jinpeng; Guan, Runnan; Xie, Xiao-Ming; Chen, Muqing; Zhang, Qianyan; Popov, Alexey A.; Xie, Su-Yuan; Yang, ShangfengTrimetallic carbide clusterfullerenes (TCCFs) encapsulating a quinary M3C2 cluster represent a special family of endohedral fullerenes with an open-shell electronic configuration. Herein, a novel TCCF based on a medium-sized rare earth metal, dysprosium (Dy), is synthesized for the first time. The molecular structure of Dy3C2@Ih(7)-C80 determined by single crystal X-ray diffraction shows that the encapsulated Dy3C2 cluster adopts a bat ray configuration, in which the acetylide unit C2 is elevated above the Dy3 plane by ∼1.66 Å, while Dy–Dy distances are ∼3.4 Å. DFT computational analysis of the electronic structure reveals that the endohedral cluster has an unusual formal charge distribution of (Dy3)8+(C2)2−@C806− and features an unprecedented three-center single-electron Dy–Dy–Dy bond, which has never been reported for lanthanide compounds. Moreover, this electronic structure is different from that of the analogous Sc3C2@Ih(7)-C80 with a (Sc3)9+(C2)3−@C806− charge distribution and no metal–metal bonding.
- ItemExpansion of the (BB)Ru metallacycle with coinage metal cations: Formation of B-M-Ru-B (M = Cu, Ag, Au) dimetalacyclodiboryls(Cambridge : Royal Society of Chemistry, 2018) Eleazer, B.J.; Smith, M.D.; Popov, A.A.; Peryshkov, D.V.In this work, we introduce a novel approach for the selective assembly of heterometallic complexes by unprecedented coordination of coinage metal cations to strained single ruthenium-boron bonds on a surface of icosahedral boron clusters. M(i) cations (M = Cu, Ag, and Au) insert into B-Ru bonds of the (BB)-carboryne complex of ruthenium with the formation of four-membered B-M-Ru-B metalacycles. Results of theoretical calculations suggest that bonding within these metalacycles can be best described as unusual three-center-two-electron B-M⋯Ru interactions that are isolobal to B-H⋯Ru borane coordination for M = Cu and Ag, or the pairs of two-center-two electron B-Au and Au-Ru interactions for M = Au. These transformations comprise the first synthetic route to exohedral coinage metal boryl complexes of icosahedral closo-{C2B10} clusters, which feature short Cu-B (2.029(2) Å) and Ag-B (2.182(3) Å) bonds and the shortest Au-B bond (2.027(2) Å) reported to date. The reported heterometallic complexes contain Cu(i) and Au(i) centers in uncharacteristic square-planar coordination environments. These findings pave the way to rational construction of a broader class of multimetallic architectures featuring M-B bonds.
- ItemTiNb2O7 and VNB9O25 of ReO3 type in hybrid Mg−Li batteries: Electrochemical and interfacial insights(Washington, DC : American Chemical Society, 2020) Maletti, Sebastian; Herzog-Arbeitman, Abraham; Oswald, Steffen; Senyshyn, Anatoliy; Giebeler, Lars; Mikhailova, DariaAs one of the beyond-lithium battery concepts, hybrid metal-ion batteries have aroused growing interest. Here, TiNb2O7 (TNO) and VNb9O25 (VNO) materials were prepared using a high-temperature solid-state synthesis and, for the first time, comprehensively examined in hybrid Mg−Li batteries. Both materials adopt ReO3-related structures differing in the interconnection of oxygen polyhedra and the resulting guest ion diffusion paths. We show applicability of the compounds in hybrid cells providing capacities comparable to those reached in Li-ion batteries (LIBs) at room temperature (220 mAh g−1 for TNO and 150 mAh g−1 for VNO, both at 0.1 C), their operability in the temperature range between −10 and 60 °C, and even better capacity retention than in pure LIBs, rendering this hybrid technology superior for long-term application. Post mortem X-ray photoelectron spectroscopy reveals a cathode−electrolyte interface as a key ingredient for providing excellent electrochemical stability of the hybrid battery. A significant contribution of the intercalation pseudocapacitance to charge storage was observed for both materials in Li- and Mg−Li batteries. However, the pseudocapacitive part is higher for TNO than for VNO, which correlates with structural distinctions, providing better accessibility of diffusion pathways for guest cations in TNO and, as a consequence, a higher ionic transport within the crystal structure. © 2020 American Chemical Society
- ItemStabilization of the ζ-Cu10Sn3 Phase by Ni at Soldering-Relevant Temperatures(Heidelberg : Springer Verlag, 2020) Wieser, C.; Hügel, W.; Martin, S.; Freudenberger, J.; Leineweber, A.A current issue in electrical engineering is the enhancement of the quality of solder joints. This is mainly associated with the ongoing electrification of transportation as well as the miniaturization of (power) electronics. For the reliability of solder joints, intermetallic phases in the microstructure of the solder are of great importance. The formation of the intermetallic phases in the Cu-Sn solder system was investigated for different annealing temperatures between 472 K and 623 K using pure Cu as well as Cu-1at.%Ni and Cu-3at.%Ni substrate materials. These are relevant for lead frame materials in electronic components. The Cu and Cu-Ni alloys were in contact to galvanic plated Sn. This work is focused on the unexpected formation of the hexagonal ζ-(Cu,Ni)10Sn3 phase at annealing temperatures of 523–623 K, which is far below the eutectoid decomposition temperature of binary ζ-Cu10Sn3 of about 855 K. By using scanning electron microscopy, energy dispersive X-ray spectroscopy, electron backscatter diffraction and X-ray diffraction the presence of the ζ phase was confirmed and its structural properties were analyzed.
- ItemConstruction of cost-effective bimetallic nanoparticles on titanium carbides as a superb catalyst for promoting hydrolysis of ammonia borane(London : RSC Publishing, 2018) Guo, Zhangwei; Liu, Tong; Wang, Qingtao; Gao, GuanhuiBimetallic cost-effective CoNi nanoparticles (NPs) are conveniently supported on titanium carbides (MXene) by a simple one-step wet-chemical method. The synthesized CoNi/MXene catalysts are characterized by XPS, TEM, STEM-HAADF and ICP-AES. The as-prepared CoNi NPs with a size of 2.8 nm are well dispersed on the MXene surface. It is found that among the CoNi bimetallic system, Co0.7Ni0.3 shows the best performance toward catalyzing ammonia borane (AB) decomposition with a turnover frequency value of 87.6 molH2 molcat−1 min−1 at 50 °C. The remarkable catalytic performance is attributed to the mild affiliation of MXene to NPs, which not only stabilizes NPs to maintain a good dispersion but also leaves sufficient surface active sites to facilitate the catalytic reaction.