New representatives of the Er-6[Si11N20]O structure type. High-temperaturesynthesis and single-crystal structure refinement of Ln((6+x/3))[Si(11-y)AlyN(20+x-y)]O(1-x+y) with Ln = Nd, Er, Yb, Dy and 0 <= x <= 3, 0 <= y <= 3

According to the general formula Ln((6+x/3))[Si(11-y)AlyN(20+x-y]O(1-x+y) ( 0 less than or equal to x less than or equal to 3, 0 less than or equal to y less than or equal to3) four nitridosilicates, namely Er-6[Si11N20]O, Yb- 6.081[Si11N20.234]O-0.757, Dy0.33Sm6[Si11N20]N, and Nd-7[Si8Al3N20]O were s ynthesized in a radiofrequency furnace at temperatures between 1300 and 165 0 degreesC. The homeotypic crystal structures of all four compounds were de termined by single-crystal X-ray diffraction. The nitridosilicates are trig onal with the following lattice constants: Er-6[Si11N20]O: a = 978.8(4) pm, c = 1058.8(3) pm; Yb-6.081[Si11N20.243]O-0.757: a = 974.9(1) pm, c = 1055. 7(2)pm; Dy0.33Sm6[Si11N20]N: a = 989.8(1)pm, c = 1078.7(1) pm; Nd-7[Si8Al3N 20]O: a = 1004.25(9) pm, c = 1095.03(12) pm. The crystal structures were so lved and refined in the space group P31c with Z = 2. The compounds contain three-dimensional networks built up by corner sharing SiN4 and AlN4 tetrahe dra, respectively. The Ln(3+) and the "isolated" O2- ions are situated in t he voids of the structures. According to Ln((6+x/3))[Si(11-y)AlyN(20+x-y)]O (1-x+y) an extension of the Er-6[Si11N20]O structure type has been found.