Zur Elektronenstruktur hochsymmetrischer Verbindungen der f‐Elemente. 38 [1] Kristall‐, Molekül‐ und Elektronenstruktur von Tris(hydrotris(1‐pyrazolyl)borato)‐samarium(III)

Electronic Structures of Highly Symmetrical Compounds of f Elements. 38 [1] Crystal, Molecular and Electronic Structure of Tris(hydrotris(1‐pyrazolyl)borato)samarium(III) Tris(hydrotris(1‐pyrazolyl)borato)samarium(III) (SmTp₃) crystallizes in the space group P6₃/m (No. 176) with two molecules in the unit cell. The Sm³⁺ central ion is coordinated by nine N atoms in the shape of a tricapped trigonal prism, leading to an effective crystal field (CF) of D_3h symmetry. The underlying CF splitting pattern was extracted from the absorption and luminescence spectra run at room and low temperatures, and simulated by fitting the free parameters of a phenomenological Hamiltonian achieving an r.m.s. deviation of 9.4 cm^?1 for 58 assignments. The parameters used allow the estimation of the global ligand field strength experienced by the Sm³⁺ central ion, the insertion of SmTp₃ into empirical nephelauxetic and relativistic nephelauxetic series, and the set‐up of experimentally based nonrelativistic and relativistic molecular orbital schemes in the f range.     

Local structure and charge distribution in the UO(2)-U(4)O(9) system

Analysis of X-ray absorption fine structure spectra of UO(2+x) for x = 0-0.20 (UO(2)--U(4)O(9)) reveals that the adventitious O atoms are incorporated as oxo groups with U--O distances of 1.74 A, most likely associated with U(VI), that occur in clusters so that the UO(2) fraction of the material largely remains intact. In addition to the formation of some additional longer U--O bonds, the U sublattice consists of an ordered portion that displays the original U--U distance and a spectroscopically silent, glassy part. This is very different from previous models derived from neutron diffraction that maintained long U--O distances and high U--O coordination numbers. UO(2+x) also differs from PuO(2+x) in its substantially shorter An-oxo distances and no sign of stable coordination with H(2)O and its hydrolysis products.     

237Np Mössbauer Investigations of (U1−x Np x )2Rh2Sn

Surprisingly, Np₂Rh₂Sn does not order magnetically whereas the uranium counterpart U₂Rh₂Sn orders antiferromagnetically at 24 K with a 5f moment μ _U ≈0.38μ _B . We have investigated the magnetic and electronic properties of (U_1−x Np _x )₂Rh₂Sn solid solutions. For x=0.25 and 0.5, the ordering temperature decreases to 11 K whereas the Np-rich compound (x=0.75) shows the onset of magnetic order around T≈6 K. The average Np magnetic moment amounts to 0.84 μ _B ,0.83μ _B and 0.25 μ _B respectively. The isomer shift slightly decreases, from −9.6 mm/s to −10.4 mm/s (versus NpAl₂) as x increases. The values of the quadrupole interaction parameter in the ordered and paramagnetic state suggest that Np moments are parallel to c for x=0.25 and then rotate to the basal plane for higher x. This revised version was published online in September 2006 with corrections to the Cover Date.     

Morphological changes in ABC triblock copolymers by chemical modification

Various SBT triblock copolymers with S being polystyrene, B being polybutadiene, and T being poly(tert-butyl methacrylate) and their saponified analogues, SBA with A being poly(methacrylic acid) are characterized in terms of their morphology. The chemical modification of the third block leads to a change of the overall morphology observed in solution cast films, which is interpreted as a consequence of the change of the incompatibility between the different components and the solvent.