Ein neues Selten‐Erd‐Metall(III)‐Fluorid‐Oxoselenat(IV): YF[SeO3

Abstract

AbstractA New Rare‐Earth Metal(III) Fluoride Oxoselenate(IV): YF[SeO3]Just two representatives of the rare‐earth metal(III) fluoride oxoselenates(IV) with the formula type MF[SeO3] (M = La and Lu) exist so far, whereas for the intermediate lanthanoids only M3F[SeO3]4‐type compounds (M = Gd and Dy) were accessible. Because of the similar radius of Y3+ to the radii of the heavier lanthanoid cations, a missing link within the MF[SeO3] series could be synthesized now with the example of yttrium(III) fluoride oxoselenate(IV). Contrary to LuF[SeO3] with its triclinic structure, YF[SeO3] crystallizes monoclinically in space group P21/c (no. 14, a = 657.65(7), b = 689.71(7), c = 717.28(7) pm, β = 99.036(5)° and Z = 4). A single Y3+ cation occupying the general site 4e is surrounded by six oxide and two fluoride anions forming [YO6F2]11− polyhedra (d(Y–O) = 228–243 plus 263 pm, d(Y–F) = 219–220 pm). These are linked via common O···O edges to $^{1}_{\infty}\rm \{[YO^{e}_{4/2}O^{t}_{2/1}F^{t}_{2/1}]^{7-}\}$ chains running along [010] and adjacent chains get tied to each other by sharing common O3···O3 and O3···F edges which results in $^{2}_{\infty}\rm \{[Y(O3)_{3/3}(O2)_{2/2}(O1)_{1/1}F_{2/2}]^{4-}\}$ sheets parallel to (100). The Se4+ cations connect these $^{2}_{\infty}\rm \{[YO_{3}F]^{4-}\}$ sheets as ψ1‐tetrahedral [SeO3]2− anions (d(Se–O) = 168–174 pm) for charge balance via all oxygen atoms. Despite the different coordination numbers of seven and eight for the rare‐earth metal(III) cations the structures of LuF[SeO3] and YF[SeO3] appear quite similar. The $^{1}_{\infty}\rm \{[LUO^{e}_{4/2}O^{t}_{1/1}F^{t}_{2/1}]^{5-}\}$ chains containing pentagonal bipyramids [LuO5F2]9− are connected to $^{2}_{\infty}\rm \{[LUO^{e}_{4/2}O^{t}_{1/1}F^{e}_{2/2}]^{4-}\}$ layers running parallel to the (100) plane again. In fact it is only necessary to shorten the partial structure of the straight $^{1}_{\infty}\rm \{[LUF_{2/2}]^{2+}\}$ chains along [001] to achieve the angular $^{1}_{\infty}\rm \{[YF_{2/2}]^{2+}\}$ chains in YF[SeO3]. As a result of this shortening one oxide anion at a time moves into the coordination sphere of a neighboring Y3+ cation and therefore adds up the coordination number for Y3+ to eight. For the synthesis of YF[SeO3] yttrium sesquioxide (Y2O3), yttrium trifluoride (YF3) and selenium dioxide (SeO2) in a molar ratio of 1 : 1 : 3 with CsBr as fluxing agent were reacted within five days at 750 °C in evacuated graphitized silica ampoules.