New rare earth-rich aluminides and indides with cubic Gd4RhIn-type structure

Abstract  

The series of rare earth metal (RE)-rich intermetallics RE ₄ TAl and RE ₄ TIn (T = Ru, Rh, Ir) were synthesized by induction melting of the elements in sealed tantalum tubes. These compounds crystallize with the cubic Gd₄RhIn-type structure, space group F[`4]3mF\bar{4}3m. The structures of eight crystals (including the isotypic compounds Ce₄RuMg and Ce₄RuCd) have been refined from X-ray single-crystal diffractometer data. The structures are composed of condensed RE ₆ T trigonal prisms which form a rigid network with adamantane-like topology. Large cavities within these networks are filled with empty RE ₆ octahedra and Al₄, In₄, Mg₄, or Cd₄ tetrahedra, respectively. Some of the RE ₄ TAl and RE ₄ TIn show small homogeneity ranges that result from small degrees of Al/T and In/T mixing on the 16e sites. All cerium compounds show small anomalies in the plots of the cell volumes. This is confirmed by temperature-dependent magnetic susceptibility measurements. Ce₄RuMg, Ce₄RuCd, Ce₄RuAl, and Ce₄RuIn show intermediate cerium valence and no magnetic ordering down to 3 K. Ce₄RhAl shows essentially trivalent cerium.     

On permutation characters of wreath products

It is known that the character rings of symmetric groups S_n and the character rings of hyperoctahedral groups S₂?S_n are generated by (transitive) permutation characters. These results of Young are generalized to wreath products G?H (G a finite group, H a permutation group acting on a finite set). It is shown that the character ring of G?H is generated by permutation characters if this holds for G, H and certain subgroups of H. This result can be sharpened for wreath products G?S_n;if the character ring of G has a basis of transitive permutation characters, then the same holds for the character ring of G?S_n.     

A further test of the shape and anisotropy of the F---H2 interaction potential

A recently proposed anisotropic potential model for the interaction of a fluorine atom with a hydrogen molecule treated as a rigid rotor analysed by carrying out exact quantum calculations of elastic and rotationally inelastic differential cross sections for comparison with previoully reported F---H₂ and newly measured F---D₂ state selected measurements. The sensitivity of the cross sections to changes of the potential anisotropy and to isotopic substitution is examined. The results provide specific indications on the features of the best potential energy surface in terms of its average ‘size’ and its most likely anisotropy responsible for inelastic rotational excitations occuring at collision energies of about 85 meV.     

Synthesis of a new class of chiral 1,5-diphosphanylferrocene ligands and their use in enantioselective hydrogenation

A new family of ferrocenylphosphane ligands has been prepared. Their flexible synthesis allows many structural modifications. The asymmetric induction of these ligands was examined in the hydrogenation of functionalized C=C, C=O, and C=N bonds. The enantioselectivity of the reaction was strongly dependent on the substituent R at the position alpha to the ferrocene moiety. In many cases, both enantiomeric beta-hydroxyesters of the reduction product can be obtained by simply replacing a dimethylamino group in the ligand with a methyl group.     

Segregation of Cd2 Pairs in CaCu9Cd2 and EuCu9Cd2

The copper‐rich intermetallics CaCu₉Cd₂ and EuCu₉Cd₂ were synthesized from the elements in sealed tantalum tubes in a high‐frequency furnace. Both compounds were characterized by X‐ray powder and single crystal diffraction: Ce(Mn_0.55Ni_0.45)₁₁ type, P4/mbm, a = 844.2(1), c = 504.72(8) pm, wR2 = 0.0216, 345 F² values, 23 variables for CaCu₉Cd₂ and a = 844.1(2), c = 505.5(1) pm, wR2 = 0.0200, 331 F² values, 24 variables for EuCu_9.14Cd_1.86. The europium‐based crystal showed a small mixed Cu/Cd occupancy on the 4g site. The calcium (europium) atoms have the high coordination number 20 (16Cu + 4Cd). These polyhedra are condensed via common Cu₄ squares along the c axis. Other striking structural motifs are segregated Cd₂ pairs (291 pm in CaCu₉Cd₂) in copper coordination and slightly distorted Cu2@Cu₈Cd₄ icosahedra. The latter are connected via common Cd₂ pairs along c and form the motif of tetragonal rod packing. EuCu₉Cd₂ shows paramagnetic behavior above 100 K with an experimental magnetic moment of 7.82(1) μ_B/Eu atom, indicating purely divalent europium.