Formation of the Sub-oxide ScAuO and the Drastically Negative Al NMR Shift in ScAl.

During attempts to synthesize ScAuAl in the cubic GdRhIn-type structure, the solid solution ScAuAl in the PbCl-type structure formed instead. Subsequently, the solid solution ScAuAl was investigated with respect to its existence range along with the structure types formed for different compositions with = 0, 0.25, 0.5, 0.75, and 1. According to X-ray powder diffraction studies, ScAl and nominal ScAuAl crystallized in the hexagonal NiIn-type structure (6/), while ScAuAl, ScAuAl, and ScAu were found to crystallize in the orthorhombic PbCl-type structure (). The crystal structures of ScAu and ScAuAl were refined from single-crystal data (ScAu: = 648.0(1), = 467.2(1), = 835.2(2) pm, 2 = 0.0382, 535 values, 25 variables; ScAuAl: = 632.48(5), = 472.16(3), = 848.67(6) pm, 2 = 0.0484, 540 values, 21 variables). Contamination with air during the synthesis of ScAu led to the discovery of a compound adopting the cubic WCoC-type structure (stuffed cubic TiNi type). Using ScO as a defined oxygen source led to samples with high amounts of ScAuO. All intermetallic compounds exhibited paramagnetic behavior in the investigated temperature range of 2.1 to 300 K, and no superconductivity was observed at low temperatures and low fields. ScAu and ScAl were investigated by Al and Sc solid-state NMR investigations. For ScAl, one signal was found in the Al NMR spectra in line with the crystal structure; however, an extremely negative resonance shift of δ = -673 ppm was observed. In both compounds, two Sc resonances were observed, in line with the proposed crystal structure. Finally, it was observed that the stability of ScAu in air is limited. This was investigated thermal analysis and (temperature-dependent) powder X-ray diffraction. DFT calculations helped in assessing charge analysis, electronic properties, and chemical bonding.