Take five: the isotypic structures of Y₂WO₆ and Ho₂WO₆ comprising <i>non</i>-condensed [WO₅]⁴⁻ units

Abstract Solvochemical syntheses attempts to obtain fluoride oxidotungstates of yttrium and holmium yielded coarse single crystals of Y 2 WO 6 and Ho 2 WO 6 . Both compounds crystallize isotypically in the monoclinic space group C 2/ c ( a ≈ 1621, b ≈ 1100, c ≈ 535 pm; β ≈ 107.5°) with eight formula units per unit cell. The crystal structure contains three crystallographically distinguishable rare earth metal cations, which all exhibit a coordination number of eight in shapes between twisted tetragonal prisms and trigonal dodecahedra. The hexavalent tungsten cations are surrounded by five of the six crystallographically different oxide anions forming isolated, i.e. non -condensed, trigonal bipyramids that show a very strong distortion. The sixth oxygen atom is tetrahedrally coordinated by rare earth metal ( RE ) cations with the resulting [O RE 4 ] tetrahedra building up <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"> <m:mrow> <m:msup> <m:mi>∞</m:mi> <m:mn>1</m:mn> </m:msup> <m:mo>{</m:mo> <m:mrow> <m:mo>[</m:mo> <m:mi mathvariant="normal">O</m:mi> <m:msub> <m:mrow> <m:mfenced open="(" close=")" separators="|"> <m:mrow> <m:mrow> <m:mi>R</m:mi> <m:mi>E</m:mi> </m:mrow> <m:mn>2</m:mn> </m:mrow> </m:mfenced> </m:mrow> <m:mrow> <m:mn>2</m:mn> <m:mo>/</m:mo> <m:mn>4</m:mn> </m:mrow> </m:msub> <m:mrow> <m:mrow> <m:msup> <m:mrow> <m:mrow> <m:msub> <m:mrow> <m:mfenced open="(" close=")" separators="|"> <m:mrow> <m:mrow> <m:mi>R</m:mi> <m:mi>E</m:mi> </m:mrow> <m:mn>3</m:mn> </m:mrow> </m:mfenced> </m:mrow> <m:mrow> <m:mn>2</m:mn> <m:mo>/</m:mo> <m:mn>2</m:mn> </m:mrow> </m:msub> </m:mrow> <m:mo>]</m:mo> </m:mrow> <m:mrow> <m:mn>2.5</m:mn> <m:mo>+</m:mo> </m:mrow> </m:msup> <m:mo>}</m:mo> </m:mrow> </m:mrow> </m:mrow> </m:mrow> </m:math> ${\infty }^{1}\left\{[\mathrm{O}{\left(RE2\right)}_{2/4}{{\left(RE3\right)}_{2/2}]}^{2.5+}\right\}$ bands along [001]. These bands are arranged according to a hexagonal rod packing with the ( RE 1) 3+ cations and the [WO 5 ] 4− anions being situated between them.