Joe David Thompson

The crystal structures and the magnetic properties of three new binary rare-earth intermetallic phases are reported. α-Sm3Ge5 and β-Sm3Ge5 and Gd3Ge5 have been prepared from the corresponding elements through high-temperature reactions using the flux-growth method. The structures of the three compounds have been established using single-crystal X-ray diffraction:  α-Sm3Ge5 crystallizes with its own type in the hexagonal space group P6̄2c (No. 190) with cell parameters a = 6.9238(11) Å, c = 8.491(3) Å, and Z = 2, whereas β-Sm3Ge5 adopts the face-centered orthorhombic Y3Ge5 type with space group Fdd2 (No. 43) and with cell parameters a = 5.8281(6) Å, b = 17.476(2) Å, c = 13.785(2) Å, and Z = 8. The orthorhombic Gd3Ge5 with cell parameters a = 5.784(2) Å, b = 17.355(6) Å, and c = 13.785(5) Å is isostructural with β-Sm3Ge5. The structures of the title compounds can be described as AlB2 and α-ThSi2 derivatives with long-range ordering of the germanium vacancies. Temperature-dependent DC magnetization (5−300 K) measurements show evidence of antiferromagnetic ordering below ca. 30 and 10 K for α-Sm3Ge5 and β-Sm3Ge5, respectively. Gd3Ge5 undergoes two successive magnetic transitions below ca. 15 and 11 K. The temperature dependence of the resistivity and heat capacity of Gd3Ge5 are discussed as well.

Reaction of (C5Me5)2U(N-2,4,6-tBu3-C6H2) or (C5Me5)2U(N-2,6-iPr2-C6H3)(THF) with 5 equiv of CuXn (n = 1, X = Cl, Br, I; n = 2, X = F) affords the corresponding uranium(V)−imido halide complexes, (C5Me5)2U(N-Ar)(X) (where Ar = 2,4,6-tBu3-C6H2 and X = F (3), Cl (4), Br (5), I (6); Ar = 2,6-iPr2-C6H3 and X = F (7), Cl (8), Br (9), I (10)), in good isolated yields of 75–89%. These compounds have been characterized by a combination of single-crystal X-ray diffraction, 1H NMR spectroscopy, elemental analysis, mass spectrometry, cyclic voltammetry, UV–visible−NIR absorption spectroscopy, and variable-temperature magnetic susceptibility. The uranium LIII-edge X-ray absorption spectrum of (C5Me5)2U(N-2,4,6-tBu3-C6H2)(Cl) (4) was analyzed to obtain structural information, and the UNimido (1.97(1) Å), U−Cl (2.60(2) Å), and U−C5Me5 (2.84(1) Å) distances were consistent with those observed for compounds 3, 5, 6, 8–10, which were all characterized by single-crystal X-ray diffraction studies. All (C5Me5)2U(N-Ar)(X) complexes exhibit UV/UIV and UVI/UV redox couples by voltammetry, with the potential separation between these metal-based couples remaining essentially constant at ∼1.50 V. The electronic spectra are comprised of π→π* and π→nb5f transitions involving electrons in the metal−imido bond, and metal-centered f−f bands illustrative of spin–orbit and crystal-field influences on the 5f1 valence electron configuration. Two distinct sets of bands are attributed to transitions derived from this 5f1 configuration, and the intensities in these bands increase dramatically over those found in spectra of classical 5f1 actinide coordination complexes. Temperature-dependent magnetic susceptibilities are reported for all complexes with μeff values ranging from 2.22 to 2.53 μB. The onset of quenching of orbital angular momentum by ligand fields is observed to occur at ∼40 K in all cases. Density functional theory results for the model complexes (C5Me5)2U(N-C6H5)(F) (11) and (C5Me5)2U(N-C6H5)(I) (12) show good agreement with experimental structural and electrochemical data and provide a basis for assignment of spectroscopic bands. The bonding analysis describes multiple bonding between the uranium metal center and imido nitrogen which is comprised of one σ and two π interactions with variable participation of 5f and 6d orbitals from the uranium center.