| Abstract: | The crystal structures of four hydrothermally synthesized alkaline earth-copper-selenites were determined: BaCu(SeO3)2-I [a = 5.247(1), B = 13.353(2), C = 8.981(1) Å, space group Pnm21, Z = 4, Rw = 0.024 for 1270 reflections], BaCu(SeO3)2-II [a = 5.256(1), B = 13.231(2), C = 8.933(1) Å, β = 90.19(1)°, space group P21/c, Z = 4, Rw = 0.046 for 2238 reflections], BaCu(SeO3)2-III [a = 8.031(1), B = 5.185(1), C = 15.823(2) Å, β = 90.83(1)°, space group C2/c, Z = 4, Rw = 0.038 for 1866 reflections], and SrCu(SeO3)2 [a = 7.929(1), B = 5.132(1), C = 14.997(2) Å, β = 90.53(1)°, space group C2/c, Z = 4, Rw = 0.028 for 1414 reflections; isotypic with BaCu(SeO3)2-III].BaCu(SeO3)2-I and -II contain Cu(SeO3)2 sheets lying parallel to (100) formed by CuO4 “squares” and selenite groups. These sheets are topologically different: in BaCu(SeO3)2-I they are formed by the connection of Cu2(SeO3) and Cu6(SeO3)4 rings while in BaCu(SeO3)2-II they are formed by Cu2(SeO3)2 and Cu6(SeO3)6 rings. The Cu(SeO3)2 sheets are rugged in BaCu(SeO3)2-I and they are slightly waved in BaCu(SeO3)2-II. In both compounds they are connected to each other by a fifth Cu---O bond and by the Ba atoms. In BaCu(SeO3)2-III and in its isotypic Sr analog the CuO4 “squares” and the selenite groups form parallel chains [010], which are connected by the alkaline earth atoms. |
