TERNARY INTERMETALLIC COMPOUNDS LNMN(2)AL(10) (LN = Y, LA-ND, SM, GD-DY) AND LNRE(2)AL(10) (LN = CE, PR, SM) WITH CACR2AL10-TYPE STRUCTURE

The twelve title compounds have been prepared for the first time. Thei r CaCr2Al10-type structure (P 4/nmm, Z = 4) was refined from single-cr ystal X-ray data for the three representatives TbMn2Al10 (a = 1274.3(2 ) pm, c = 511.4(2) pm, R = 0.025 for 680 structure factors F and 43 va riable parameters V), CeRe2Al10 (a = 1295.5(5) pm, c = 517.2(4)pm, R = 0.054 for 810 F and 46 V), and SmRe2Al10 (a = 1291.5(2) pm, c = 516.5 (l)pm, R = 0.021 for 622 F and 46 V). The atomic positions of the lant hanoid and transition metal atoms are fully occupied. Significant devi ations from the full occupancies were observed for two aluminum sites in TbMn2Al10 and for all five aluminum sites of the two rhenium-contai ning compounds, resulting in the compositions TbMn2Al9.63(2), CeRe2Al9 .52(8), and SInRe2Al9.16(9) The cell volume of CeRe2Al10 and to a smal ler extent also that of CeMn2Al10 indicate mixed or intermediate +III/ +IV valencies of the cerium atoms in these compounds. The structural r elationships between the three closely related body-centered tetragona l structures of ThMn12, CeMn4Al8, DyFe6Al6, and the primitive tetragon al structure of CaCr1Al10 are briefly discussed.