  The antimonides RE2Ir3Sb4 (RE = La, Ce, Pr, Nd) were synthesized by
arc-melting of the elements and subsequent annealing or via high-frequence
melting. The samples were characterized by X-ray powder diffraction and the
four structures were refined from sin-gle-crystal X-ray diffraction data:
Pr2Ir3Sb4-type, Pnma, Z = 4, a = 1621.9(2), b = 458.60(8), c = 1099.8(1) pm,
wR2 = 0.036, 1558 F2 values for La2Ir3Sb4, a = 1616.6(8), b = 456.5(2), c =
1094.8(5) pm, wR2 = 0.092, 1080 F2 values for Ce2Ir3Sb4, a = 1613.0(5), b =
454.9(2), c = 1094.1(5) pm, wR2 = 0.057, 1428 F2 values for Pr2Ir3Sb4, and a =
1609.8(6), b = 452.9(2), c = 1092.3(5) pm, wR2 = 0.052, 1472 F2 values for
Nd2Ir3Sb4, with 56 parameters per refinement. The Sb1 atoms show enhanced
displace-ment off the mirror planes at y = 1/4 and y = 3/4. A series of
temperature dependent structure refinements of Pr2Ir3Sb4 down to 90 K are
indicative of static disorder. The iridium and antimony atoms build up complex
covalently bonded three-dimensional [Ir3Sb4] networks with Ir-Sb distances
ranging from 256-269 pm (Nd2Ir3Sb4). The two crystallographically independent
rare earth sites fill cavities of coordination numbers 17 (8 Ir + 9 Sb) and 15
(6 Ir + 9 Sb) within the [Ir3Sb4] polyanions. Temperature dependent magnetic
susceptibility measurements indicate a stable trivalent ground state for the
ce-rium compound. No magnetic ordering was evident down to 3 K.
