The cerium(III) fluoride oxoselenate(IV) CeF[SeO ₃ ]

Abstract The new fluoride oxoselenate(IV) CeF[SeO 3 ] was synthesized from cerium dioxide (CeO 2 ), cerium metal (Ce), cerium trifluoride (CeF 3 ) and selenium dioxide (SeO 2 ) at 700 °C in appropriate stoichiometric ratios with a surplus of fluxing cesium bromide (CsBr) by utilizing corundum-embedded silica tubes. It crystallizes in the monoclinic space group P 2 1 / c with the lattice parameters a = 1805.14(9) pm, b = 707.83(4) pm, c = 838.26(5) pm and β = 97.049(3)° for Z = 12. Its crystal structure comprises three crystallographically independent Ce 3+ cations, which are surrounded by both oxide and fluoride anions in different ratios within polyhedra described as [(Ce1)O 6 F 4 ] 13− , [(Ce2)O 4 F 7 ] 12− and [(Ce3)O 10 ] 17− . The fluoride-bearing ones share common edges and faces to erect corrugated <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <m:mrow> <m:mmultiscripts> <m:mo>{</m:mo> <m:mprescripts/> <m:mi>∞</m:mi> <m:mn>2</m:mn> </m:mmultiscripts> </m:mrow> </m:math> ${}_{\infty }{}^{2}\left\{\right.$ [Ce 2 O 5 F 3 ] 7– } sheets and so do the fluoride-free ones according to <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <m:mrow> <m:mmultiscripts> <m:mo>{</m:mo> <m:mprescripts/> <m:mi>∞</m:mi> <m:mn>2</m:mn> </m:mmultiscripts> </m:mrow> </m:math> ${}_{\infty }{}^{2}\left\{\right.$ [(Ce3)O 5 ] 7– }. The alternating interconnection via common oxygen vertices leads to a three-dimensional <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <m:mrow> <m:mmultiscripts> <m:mo>{</m:mo> <m:mprescripts/> <m:mi>∞</m:mi> <m:mn>3</m:mn> </m:mmultiscripts> </m:mrow> </m:math> ${}_{\infty }{}^{3}\left\{\right.$ [Ce 3 O 9 F 3 ] 15− } framework, whose structural stability is further enhanced by charge-compensating Se 4+ cations through connectivity via three distinct types of oxoselenate(IV) groups [SeO 3 ] 2– , easily identified by Raman spectroscopy depicting the four expected modes of these discrete ψ 1 -tetrahedral [SeO 3 ] 2– anions. Another structure description for CeF[SeO 3 ] highlights cationic <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <m:mrow> <m:mmultiscripts> <m:mo>{</m:mo> <m:mprescripts/> <m:mi>∞</m:mi> <m:mn>2</m:mn> </m:mmultiscripts> </m:mrow> </m:math> ${}_{\infty }{}^{2}\left\{\right.$ [Ce 2 F 3 ] 3+ } compartments with (Ce1) 3+ and (Ce2) 3+ as well as anionic <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <m:mrow> <m:mmultiscripts> <m:mo>{</m:mo> <m:mprescripts/> <m:mi>∞</m:mi> <m:mn>2</m:mn> </m:mmultiscripts> </m:mrow> </m:math> ${}_{\infty }{}^{2}\left\{\right.$ (Ce[SeO 3 ] 3 ) 3– } compartments with (Ce3) 3+ in alternating stacking along [100], which resemble very much the pure CeF 3 - and Ce 2 [SeO 3 ] 3 -structure sections to explain the large number of formula units ( Z = 12) for this rather simple composition (CeF[SeO 3 ]).