Several rare earth metal containing pseudo-ternary compounds in the RE2TAl3 series (RE=Sc, Y, La–Nd, Sm, Gd–Lu; T=Ru, Rh, Ir) have been synthesized from the elements by arc-melting or in tantalum capsules. Within the Rh series, the compounds with RE=La–Nd crystallize in the cubic MgCu2-type (Fd3̅m) structure. For Sm besides the cubic Laves phase also the hexagonal Laves phase (MgZn2 type, P63/mmc) is found. For the remaining compounds of both series, also the hexagonal MgZn2-type structure is observed. The structures of Ho2Ru0.96(1)Al3.04(1) (a=547.4(1), c=875.7(1) pm, wR=0.0397, 201 F2 values, 13 variables), Sc2Rh1.01(1)Al2.99(1) (a=528.0(1), c=852.8(1) pm, wR=0.0228, 184 F2 values, 13 variables), Ho2Rh1.00(1)Al3.00(1) (a=546.5(1), c=873.8(1) pm, wR=0.0590, 222 F2 values, 13 variables) and Tb2Ir1.06(1)Al2.94(1) (a=550.8(1), c=870.0(1) pm, wR=0.0743, 221 F2 values, 13 variables) have been refined from single-crystal data, indicating T/Al mixing on both crystallographic Zn sites of the aristotype. The Sc, Y, La and Lu containing compounds exhibit Pauli-paramagnetic behavior, while the other compounds show paramagnetism, in line with the rare earth atoms in the trivalent oxidation state. Ferro- and antiferromagnetic ordering up to TC=50.2(1) K for Gd2RhAl3 is observed, while Sm2RuAl3 shows van Vleck paramagnetism and Yb2RuAl3, finally, exhibits only partially trivalent Yb atoms, evident from a reduced magnetic moment and increased lattice parameters.

Abstract:The REPt 2 Al 3 compounds of the late rare-earth metals (RE = Y, Dy-Tm) were found to crystallize isostructural. Single-crystal X-ray investigations of YPt 2 Al 3 revealed an orthorhombic unit cell (a = 1080.73(6), b = 1871.96(9), c = 413.04(2) pm, wR2 = 0.0780, 942 F 2 values, 46 variables) with space group Cmmm (oC48; q 2 pji 2 hedb). A comparison with the Pearson database indicated that YPt 2 Al 3 forms a new structure type, in which the Pt and Al atoms form a [Pt 2 Al 3 ] δ− polyanion and the Y atoms reside in the cavities within the framework. Via a group-subgroup scheme, the relationship between the PrNi 2 Al 3 -type structure and the new YPt 2 Al 3 -type structure was illustrated. The compounds with RE = Dy-Tm were characterized by powder X-ray diffraction experiments. While YPt 2 Al 3 is a Pauli-paramagnet, the other REPt 2 Al 3 (RE = Dy-Tm) compounds exhibit paramagnetic behavior, which is in line with the rare-earth atoms being in the trivalent oxidation state. DyPt 2 Al 3 and TmPt 2 Al 3 exhibit ferromagnetic ordering at T C = 10.8(1) and 4.7(1) K and HoPt 2 Al 3 antiferromagnetic ordering at T N = 5.5(1) K, respectively. Attempts to synthesize the isostructural lutetium compound resulted in the formation of Lu 2 Pt 3 Al 4 (Ce 2 Ir 3 Sb 4 -type, Pnma, a = 1343.4(2), b = 416.41(8), c = 1141.1(2) pm), which could also be realized with thulium. The structure was refined from single-crystal data (wR2 = 0.0940, 1605 F 2 values, 56 variables). Again, a polyanion with bonding Pt-Al interactions was found, and the two distinct Lu atoms were residing in the cavities of the [Pt 3 Al 4 ] δ-framework. X-ray photoelectron spectroscopy (XPS) measurements were conducted to examine the electron transfer from the rare-earth atoms onto the polyanionic framework.