Intermetallics of the types REPd${}_3$X${}_2$ and REPt${}_3$X${}_2$ (RE=La–Nd, Sm, Gd, Tb; X=In, Sn) with substructures featuring tin and In atoms in distorted square-planar coordination

The intermetallic compounds RET${}_3$X${}_2$ (RE = La–Nd, Sm, Gd, Tb; T = Pd, Pt; X = In, Sn) have been synthesized from the elements by arc-melting and subsequent annealing sequences in tube or induction furnaces. The samples were characterized through Guinier powder diffraction patterns, and several structures were refined from single crystal X-ray diffractometer data. These indium and tin intermetallics crystallize with the orthorhombic CePd${}_3$In${}_2$-type structure, space group Pnma. The palladium (platinum) and indium (tin) atoms in the RET${}_3$X${}_2$ structures build up complex three-dimensional [T${}_3$X${}_2$]${}^{\delta -}$ polyanionic networks in which the rare earth atoms fill cavities. The striking structural motifs concern the indium, respectively tin substructures, in which part of the indium and tin atoms have distorted square planar homoatomic coordination environments: In1In1${}_2$In2${}_2$ units in PrPd${}_3$In${}_2$ with interatomic distances 325 pm In1-In1 and 332 pm In1–In2 as well as Sn1Sn1${}_2$Sn2${}_2$ units in PrPt${}_3$Sn${}_2$ with the larger distances of 356 pm for Sn1–Sn1 and of 344 pm for Sn1-Sn2. Temperature dependent magnetic susceptibility measurements have indicated Pauli paramagnetism or diamagnetism for the lanthanum compounds, van-Vleck paramagnetism for SmPt${}_3$In${}_2$ and Curie-Weiss paramagnetism for the remaining compounds. Antiferromagnetic ordering was detected at T${}_N$ = 4.0(1) K for CePt${}_3$In${}_2$ and at T${}_N$ = 3.5(1) K for SmPt${}_3$In${}_2$. CePt${}_3$In${}_2$ shows a metamagnetic transition at an external magnetic field of 47(3) kOe.