SYNTHESIS AND CRYSTAL-STRUCTURE OF CULN(2 )[B2O5](2) (LN=ER3- 2 COPPER LANTHANOID BORATES WITH 2-PROPORTIONAL-TO[B2O5](4-)-ANIONS(, LU3+) )

Single crystals of the new compounds CuLn(2)[B2O5](2) (Ln = Er3+(I), L u3+(II)) were obtained by a B2O3 flux-technique. They crystallize in t he space group C-2h(5)-P 2(1)/c with I: a = 453.14(6); b = 721.94(5); c = 929.5(4) pm; beta = 90.01(3)degrees; Z = 2 und II: a = 451.4(4); b = 718.3(1); c = 928.1(3) pm; beta = 90.00(6)degrees; Z = 2. The compo unds are isotypic to CuTm2[B2O5](2) as well as to the mineral Gadolini te (FeY2[BeSiO5](2)) and exhibit layer like (2)(infinity) [B2O5](4-)-a nions consisting of edge sharing BO4-tetrahedra, which form four- and eight-membered rings. The berate anions are separated by layers of elo ngated CuO6-octahedra and slightly distorted tetragonal LnO(8)-antipri sms.