Intermetallic Compound Re2Ga9Ge with Re- and Ge-Embedded Gallium Clusters: Synthesis, Crystal Structure, Chemical Bonding, and Physical Properties

Crystal structure, Chemical Bonding, and Magnetism of α-Fe6Ga5: How Local Interactions Shape the Structure and Properties of Intermetallic Compounds

α-Fe6Ga5 was synthesized from the elements as a polycrystalline powder. Its crystal structure was redetermined by high-resolution powder X-ray diffraction, which showed a complex monoclinic structure of the Fe6Ge5 type. The determined lattice parameters (a = 10.08380(6) Å, b = 7.97071(5) Å, c = 7.70489(5) Å, and β = 108.3062(2)°) differ notably from the previous reports. Despite possessing the same structure type as Fe6Ge5, α-Fe6Ga5 displays several distinctive features, such as short Ga-Ga bonds and distorted Fe layers. According to magnetization measurements, α-Fe6Ga5 is a soft ferromagnet with a high Curie temperature of 760 K, which is in stark contrast to the antiferromagnetic behavior of Fe6Ge5 reported in the literature. The electronic structure of α-Fe6Ga5 was studied theoretically using density functional theory-calculations, which showed the pronouncedly covalent character of the short Fe-Ga and Ga-Ga bonds. Similar calculations were performed for Fe6Ge5, which revealed stronger Fe-Ge interactions, which preclude the formation of short Ge-Ge bonds. In both cases, the theoretical calculations showed ferromagnetic instability, which leads to ferromagnetic ordering only in the case of α-Fe6Ga5, likely due to the different nature of Fe-Ga-Fe and Fe-Ge-Fe superexchange interactions.

Intermetallic Compound with CuNi Sites for Enhancing the Selectivity of Electrochemical CO2 Conversion

Although single-metal-site (SMS) catalysts have long been explored for the electrochemical CO2 reduction reaction (EC-CO2RR), the reactivity and selectivity of SMS catalysts remain rather low due to the competing hydrogen evolution reaction (HER). To improve the selectivity, in this work, a novel intermetallic particle of CuNi is decorated on the N-doped carbon substrate, which was first precisely fabricated by scarifying the bimetal-doped metal-organic framework (MOF). Thanks to the neighboring synergistic functions of Cu and Ni sites, CuNi/NC prominently boosts the electroreduction of CO2, far more than the SMS catalysts of Cu/NC and Ni/NC. Further, CuNi/NC presents superior selectivity toward CO with faradaic efficiency over a wide range of potentials (surpassing 90% at 0.6-1.0 V vs RHE, up to 98% at 0.6 V vs RHE) and excellent durability. The experimental results and theoretical calculations reveal that the Ni species can be highly activated due to the neighboring Cu species, which considerably facilitates the formation of an intermediate of COOH* and consequently enhances the selectivity of the reduction of CO2 to CO. This work paves a general way to precisely fabricate catalysts with multiple metal species and also demonstrates the significant synergetic efficiency between the neighboring sites to improve the catalytic performance.

From Laves Phases to Quasicrystal Approximants in the Na-Au-Cd System

The exploratory synthesis of gold-based polar intermetallic phases has revealed many new compounds with unprecedented crystal structures, unique bonding arrangements, and interesting electronic features. Here, we further understand the complexity of gold's crystal chemistry by studying the Na-Au-Cd ternary composition space. A nearly continuous structure transformation is observed between the seemingly simple binary NaAu₂-NaCd₂ phases, yielding three new intermetallic compounds with the compositions Na(Au_0.89(5)Cd_0.11(5))₂, Na(Au_0.51(4)Cd_0.49(4))₂, and Na₈Au_3.53(1)Cd_13.47(1). Two compounds adopt different Laves phases, while the third crystallizes in a complex decagonal quasicrystal approximant. All three compounds are related through Friauf-Laves polyhedral building units with the gold/cadmium ratio found to control the transition among the unique crystal structures. Electronic structure calculations subsequently revealed the metallic nature of all three compounds with a combination of polar covalent Na-(Au/Cd) interactions and covalent (Au/Cd)-(Au/Cd) bonding interactions stabilizing each structure. These results highlight the crystal and electronic structure relationship among Laves phases and quasicrystal approximants enabled by the unique chemistry of gold.