CS[ER10(C2)2]I18 AND [ER10(C2)2]BR18 - 2 NEW EXAMPLES FOR REDUCED HALIDES OF THE LANTHANIDES WITH ISOLATED [M10(C2)2] CLUSTERS

Cs[Er10(C2)2]I18 is obtained from the reaction of ErI3 with caesium an d carbon in sealed tantalum containers at 700-degrees-C and [Er10(C2)2 ]Br18 through the metallothermic reduction of ErBr3 with rubidium in t he presence of carbon at 750-degrees-C in sealed niobium containers. T he crystal structures {Cs[Er10(C2)2]I18: triclinic, P1BAR; a = 1105.2( 8) pm, b = 1112.0(7) pm; c = 1122.9(8) pm; alpha = 66.91(3)-degrees, b eta = 87.14(3)-degrees; gamma = 60.80(3)-degrees; Z = 1; R = 0.049, R( w) = 0.043; [Er10(C2)2]Br18: monoclinic, P2(1)/n, a = 971.8(6) pm, b = 1623.4(9) pm, c = 1163.8(6) pm, beta = 104.00(6)-degrees; Z = 2; R = 0.077, R(w) = 0.057} contain isolated dimeric [Er10(C2)2] clusters. Du e to the inclusion of C2 units, the octahedra are elongated in the dir ection of the pseudo C4 axis. The connecting edges of the two octahedr a are exceptionally short (316.7 pm and 314.8 pm respectively). The di meric units are connected via X(i-a) and X(a-i) (X = Br, I) bridges ac cording to [Er10(C2)2X10(i)X8/2(i-a)]X8/2(a-i). Cs+ is surrounded by a cuboctahedron of iodide ions in Cs[Er10(C2)2]I18.