Ternary Indides LnRhIn2 (Ln = La, Ce, Pr, Nd, Sm) with MgCuAl2 Type Structure

The ternary indides LnRhIn2 (Ln = La, Ce, Pr, Nd, Sm) were synthesized by arc-melting of the elements under an argon atmosphere and subsequent annealing at 870 K. The samples have been investigated by X-ray diffraction on powders and single crystals: MgCuAl2 type, Cmcm, a = 448.2(1), b = 1025.7(1), c = 795.1(1) pm, wR2 = 0.0372, 228 F2 values, 16 variables for LaRhIn2, a = 446.0(1), b = 1017.3(2), c = 792.7(1) pm for CeRhIn2, a = 444.03(6), b = 1013.1(1), c = 792.5(1) pm for PrRhIn2, a = 442.49(5), b = 1012.7(1), c = 789.3(1) pm for NdRhIn2, and a = 438.1(1), b = 1009.3(1), c = 788.3(1) pm, wR2= 0.0414, 304 F2 values, 16 variables for SmRhIn2. Geometrical motifs of these structures are tricapped trigonal prisms around the rhodium atoms. The shortest interatomic distances were observed for the Rh-In contacts: 280-282 pm for LaRhIn2 and 276-279 pm for SmRhIn2. Together, the rhodium and indium atoms build a three-dimensional [RhIn2] polyanion in which the lanthanoid atoms fill distorted pentagonal channels. According to one short La-Rh (282 pm) and Sm-Rh (284 pm) distance one can assume strong bonding of the lanthanoid atoms to the polyanion.