Formation of the Sub-oxide Sc 4 Au 2 O 1- x and the Drastically Negative 27 Al NMR Shift in Sc 2 Al.

During attempts to synthesize Sc 4 AuAl in the cubic Gd 4 RhIn-type structure, the solid solution Sc 2 Au 0.5 Al 0.5 in the PbCl 2 -type structure formed instead. Subsequently, the solid solution Sc 2 Au 1- x Al x was investigated with respect to its existence range along with the structure types formed for different compositions with x = 0, 0.25, 0.5, 0.75, and 1. According to X-ray powder diffraction studies, Sc 2 Al and nominal Sc 2 Au 0.25 Al 0.75 crystallized in the hexagonal Ni 2 In-type structure ( P 6 3 / mmc ), while Sc 2 Au 0.5 Al 0.5 , Sc 2 Au 0.75 Al 0.25 , and Sc 2 Au were found to crystallize in the orthorhombic PbCl 2 -type structure ( Pnma ). The crystal structures of Sc 2 Au and Sc 2 Au 0.59(1) Al 0.41(1) were refined from single-crystal data (Sc 2 Au: a = 648.0(1), b = 467.2(1), c = 835.2(2) pm, wR 2 = 0.0382, 535 F 2 values, 25 variables; Sc 2 Au 0.59(1) Al 0.41(1) : a = 632.48(5), b = 472.16(3), c = 848.67(6) pm, wR 2 = 0.0484, 540 F 2 values, 21 variables). Contamination with air during the synthesis of Sc 2 Au led to the discovery of a compound adopting the cubic W 4 Co 2 C-type structure (stuffed cubic Ti 2 Ni type). Using Sc 2 O 3 as a defined oxygen source led to samples with high amounts of Sc 4 Au 2 O 1- x . All intermetallic compounds exhibited Pauli paramagnetic behavior in the investigated temperature range of 2.1 to 300 K, and no superconductivity was observed at low temperatures and low fields. Sc 2 Au and Sc 2 Al were investigated by 27 Al and 45 Sc solid-state NMR investigations. For Sc 2 Al, one signal was found in the 27 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 Sc 2 Au in air is limited. This was investigated via thermal analysis and (temperature-dependent) powder X-ray diffraction. DFT calculations helped in assessing charge analysis, electronic properties, and chemical bonding.