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Synthesis and structural characterization of the two new lanthanum-magnesium-stannides La 3 Mg 4x Sn 2+x (0.12x0.40) and LaMg 3-x Sn 2 (0.33x0.78) are reported. The crystal structures of these intermetallics were determined by single crystal X-ray diffraction analysis and confirmed by Rietveld refinement of powder X-ray diffraction patterns of the corresponding samples. The La 3 Mg 4-x Sn 2+x phase crystallizes in the hexagonal Zr 3 Cu 4 Si 2 structure type (P 62m, hP9, Z=3, x = 0.12(1), a = 7.7974(7), c = 4.8384(4) Å), which represents an ordered derivative of the hP9-ZrNiAl prototype, ubiquitous among equiatomic intermetallics. The LaMg 3-x Sn 2 phase is the second representative of the trigonal LaMg 3-x Ge 2 type, which is a superstructure of the LaLi 3 Sb 2 structure type (P 31c, hP34-0.12, Z=6, x = 0.35(1), a = 8.3222(9), c = 14.9546(16) Å). The scheme describing the symmetry reduction/colouring with respect to the parent type is reported here with the purpose to discuss the LaMg 3-x Sn 2 off-stoichiometry from the geometrical point of view. Structural relationships between the La-Mg-Sn ternary phases, including the already known equiatomic LaMgSn compound (oP12-TiNiSi), are presented in the framework of the AlB 2-related compounds family and discussed with the aid of group-subgroup relations in the Bärnighausen formalism.

The novel isostructural series of phases RMgSn2 (R = Y, La–Nd, Sm, Gd–Tm, Lu) is presented. They were prepared by direct synthesis in an induction furnace and subsequently annealed at 500 °C. Their crystal structures were determined through single‐crystal X‐ray diffraction analysis of the Ce representative [I42m, tI32‐LaMgSn2, Z = 8, a = 0.82863(3) nm, c = 1.23129(5) nm] and confirmed by powder X‐ray diffraction analysis of the other members of the series. Rietveld refinements were also performed on the homologues with R = Pr, Tm, and Y. The title phases show a unique space distribution of atoms, characterized by the presence of a Sn–Sn dumbbell distanced at around 0.29 nm. Their structures are related to those of a few binary AeTt3 (Ae = alkaline earth; Tt = Si, Ge; I4/mmm, tI32‐YbSi3) compounds that are stable at high pressure, characterized by a more complex 3D covalently bonded Tt network. Compounds CeMgSn2 and TbMgSn2 were magnetically characterized; they show paramagnetic behavior with the presence of ferromagnetic interactions, more pronounced in the case of TbMgSn2, as suggested by the Curie–Weiss temperatures, determined in the high‐temperature range, of 0.96 and 27.6 K for CeMgSn2 and TbMgSn2, respectively.