Synthesis and Crystal Structure of CuLn2[B20 5]2 (Ln = Er3+, Lu3+): Two Copper Lanthanoid Borates with 2.[B20 5]4~-Anions

Single crystals of the new compounds CuLn2[B20 5]2 (Ln = Er3+(I), Lu3+(II)) were ob­ tained by a B9O 3 flux-technique. They crystallize in the space group C ih-P 2 \lc with I: a = 453.14(6); b = 721.94(5); c = 929.5(4) pm; ß = 90.01(3)°; Z = 2 und II: a = 451.4(4); b = 718.3(1); c = 928.1(3) pm; ß = 90.00(6)°; Z = 2. The compounds are isotypic to CuTm2[B20 5 ] 2 as well as to the mineral Gadolinite (FeY 2[BeSi0 5]2) and exhibit layer like 2.[B20 5]4 --anions consisting of edge sharing B 0 4-tetrahedra, which form fourand eight-membered rings. The borate anions are separated by layers of elongated C u 0 6-octahedra and slightly distorted tetragonal L n 0 8-antiprisms.