Real Structure, Magnetism and Chemical Bonding of SmSi3‐x

New metastable SmSi 3−x ( x =0–0.05) is obtained by high‐pressure high‐temperature synthesis (9.5 GPa, 870–1270 K). Powder diffraction data refinements reveal that the crystal structure of SmSi 3 is isotypic to that of YbSi 3 (space group I 4/ mmm , a =7.23634(5) Å, c =11.0854(1) Å). In the crystal structure, two types of Si 2 dumbbells agglomerate into layers, which embed the samarium atoms. At ambient pressure, SmSi 3 decomposes exothermally upon heating into Si and SmSi 2−x . Single‐crystal structure refinements of a specimen SmSi 3−x ( x =0.05) reveal considerable electron density, which is not accounted for by the YbSi 3 ‐type model. The additional maxima can be assigned to disorder which affects the samarium positions and induces silicon vacancies. Scanning transmission electron microscopy experiments evidence that the disorder can be attributed to extended defects. Magnetic measurements on SmSi 3−x reveal van Vleck paramagnetic behavior and antiferromagnetic ordering at low temperatures. Computations within the local spin density approximation (LSDA and LSDA+ U ) on the crystal structure of SmSi 3 reproduce the antiferromagnetic coupling as the favored long‐range order. Quantum chemical analysis of the chemical bonding in SmSi 3 reveals two‐center two‐electron bonds within the Si 2 dumbbells plus a total of a little less than four electrons in lone pairs at each silicon atom.