Browsing by Author "Wontcheu, Joseph"

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    Crystal structure of digadolinium(III) oxide disulfide, Gd2OS2
    (2014) Wontcheu, Joseph; Schleid, Thomas
    Gd2OS2, monoclinic, P121/c1 (No. 14), a = 8.3365(6) Å, b = 6.9872(5) Å, c = 6.9231(5) Å, β = 99.463(6)°, V = 397.8Å3, Z = 4, Rgt(F) = 0.022, wRref(F2) = 0.047, T = 293 K.
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    Oxoselenates(IV) of the trivalent rare earth elements and some derivatives
    (2004) Wontcheu, Joseph; Schleid, Thomas (Prof. Dr.)
    This work was initially intended to investigate how far the existence range of the oxoselenates(IV) M2[SeO3]3 can be extended to small and heavy lanthanides, and to synthesise rare-earth oxoselenates(IV) containing O2- centered [M3+]4 tetrahedra units as well as to determine the influence of halide anions (Cl-, Br-) on the structure of lanthanides oxide oxoselenates(IV). The first part could be successfully done. It could be shown that under suitable reaction condition, oxoselenates(IV) of the type M2[SeO3]3, M = Sc, Y, La – Lu, could be obtained with all M3+ cations. While Sc2[SeO3]3 adopts a new structure type, Ce2[SeO3]3 is isostructural with La2[SeO3]3, Pr2[SeO3]3 with Nd2[SeO3]3 and the remaining Y, Sm until Lu with the published Er2[SeO3]3. Also, during attempts to synthesize Lu2[SeO3]3, a new Li3Lu5[SeO3]9 was obtained and its structure elucidated. The second class of compounds, (M2O[SeO3]2), shows an existence range limited to the elements M = Sm – Tm with the same reaction conditions, although experiments at other conditions (temperature, composition of the educt mixture, flux) are still to be done. For the rare-earth oxyhalide oxoselenates(IV), four new structure types of either smaller or heavier rare-earth elements were synthesized and characterized, namely M3O2Cl[SeO3]2 (M = Tb, Dy, Er), M4O3Cl2[SeO3]2 (M = Er, Yb), M5O4X3[SeO3]2 (M = Gd, Tb) and finally M9O8X3[SeO3]4 (M = La, Pr with X = Br and M = Pr, Nd, Sm, Gd with X = Cl). The first class crystallizes with the same formula in two different structure types depending only upon the cationic radius of the rare-earth element, whereas all compounds belonging to the same groups of the remaining three are isostructural. As we can see, their existence range is so limited that even by varying the conditions of preparation, very little could be found out about the four series of compounds. However many other measurements which could lead to analogues structures are still to be carried out. Two side products CsTmCl2[SeO3] and CsEu4O3Cl3[SeO3]2 were detected and structurally characterized during the course of this dissertation. Remarkably enough, our presumption at the beginning of this work that halide anions X- (X = Cl, Br) could given isotypical oxyhalide oxoselenates(IV) of the trivalent lanthanides seem to be fully confirmed and both are crystallographically identical in a given structure type. Nevertheless, experiments to try and synthesize similar compounds with the remaining halides still to be done. Those experiments and results are among the first in the chemistry of rare-earth oxide and oxyhalide oxoselenate(IV). The work on such structures were taken up later on and have not been so extensively explored.