Synthesis and Theoretical Investigations of the Solid Solution CeRu_1–<i>x</i>Ni_<i>x</i>Al (<i>x</i> = 0.1–0.95) Showing Cerium Valence Fluctuations

Members of the solid solution series of Ce­Ru_1–<i>x</i>Ni_<i>x</i>Al can be obtained directly by arc melting of the elements. The presented compounds with 0.1 ≤ <i>x</i> ≤ 0.85 crystallize in the orthorhombic space group <i>Pnma</i> (No. 62) in the LaNiAl structure type, while for 0.9 ≤ <i>x</i> ≤ 1, the hexagonal ZrNiAl-type structure is found. The orthorhombic members exhibit an anomaly in the trend of the lattice parameters as well as an interesting behavior of the magnetic susceptibility, suggesting that the cerium cations exhibit no local moment. Besides the mixed-valent nature of the cerium cations, valence fluctuations along with a change in the cerium oxidation state depending on the nickel content have been found. The oxidation state has been determined from the magnetic data and additionally by XANES. Density functional theory calculations have identified the shortest Ce–Ru interaction as decisive for the stability of the orthorhombic solid solution

Ba₃Pt₄Al₄Structure, Properties, and Theoretical and NMR Spectroscopic Investigations of a Complex Platinide Featuring Heterocubane [Pt₄Al₄] Units

Ba₃Pt₄Al₄ was prepared from the elements in niobium ampules and crystallizes in an orthorhombic structure, space group <i>Cmcm</i> (<i>oP</i>44, <i>a</i> = 1073.07(3), <i>b</i> = 812.30(3), <i>c</i> = 1182.69(3) pm) isopointal to the Zintl phase A₂Zn₅As₄ (A = K, Rb). The structure features strands of distorted [Pt₄Al₄] heterocubane-like units connected by condensation over Pt/Al edges. These are arranged in a hexagonal rod packing by further condensation over Pt and Al atoms with the barium atoms located inside cavities of the [Pt₄Al₄]^δ− framework. Structural relaxation confirmed the electronic stability of the new phase, while band structure calculations indicate metallic behavior. Crystal orbital Hamilton bonding analysis coupled with Bader effective charge analysis suggest a polar intermetallic phase in which strong Al–Pt covalent bonds are present, while a significant electron transfer from Ba to the [Pt₄Al₄]^δ− network is found. By X-ray photoelectron spectroscopy measurements the Pt 4f_5/2 and 4f_7/2 energies for Ba₃Pt₄Al₄ were found in the range of those of elemental Pt due to the electron transfer of Ba, while PtAl and PtAl₂ show a pronounced shift toward a more cationic platinum state. ²⁷Al magic-angle spinning NMR investigations verified the two independent crystallographic Al sites with differently distorted tetrahedrally coordinated [AlPt₄] units. Peak assignments could be made based on both geometrical considerations and in relation to electric field gradient calculations