Structural, Physical, Theoretical and Spectroscopic Investigations of Mixed‐Valent Eu2Ni8Si3 and Its Structural Anti‐Type Sr2Pt3Al8

Abstract Eu 2 Ni 8 Si 3 and its anti ‐type representative Sr 2 Pt 3 Al 8 were synthesized from the elements. They crystallize in the tetragonal crystal system with space group P 4 2 / nmc and with lattice parameters of a =997.9(1) and c =747.6(1) pm (Eu 2 Ni 8 Si 3 ) as well as a =1082.9(2) and c =823.3(2) pm (Sr 2 Pt 3 Al 8 ). Both compounds were investigated via single crystal X‐ray diffraction, indicating slight Si/Ni mixing for the silicide. Sr 2 Pt 3 Al 8 exhibits a temperature independent magnetic susceptibility, suggesting superimposed dia‐ and Pauli ‐paramagnetic contributions. The independent Al and Pt sites of the platinide were further characterized by 27 Al and 195 Pt solid‐state NMR spectroscopy, which were assigned with the help of electronic structure calculations. ICOHP calculations and Bader charges were used to analyze the bonding situation. Eu 2 Ni 8 Si 3 in contrast is paramagnetic with a ferromagnetic transition at T C =46.9(2) K and exhibits an effective magnetic moment of μ eff =6.61(1) μ B per Eu atom. The latter is in line with an intermediate valence that was further proven by 151 Eu Mößbauer spectroscopic investigations. At 300 K, the refined Eu 2+ /Eu 3+ ratios are 60 %/40 %, at 78 K 62 % and 38 % (Eu 2+ /Eu 3+ ) are observed, being in line with the ratio deduced from the magnetic susceptibility. Finally, at 6 K a ratio of 68 % Eu 2+ and 32 % Eu 3+ was observed. Below the Curie temperature, the Eu 2+ signal shows a full magnetic hyperfine splitting, with an internal magnetic field value of B 0 =28.4 T.