Eu4Al13Pt9 - a coloring variant of the Ho4Ir13Ge9 type structure

Investigations in the ternary system Eu-Al-Pt led to the discovery of Eu4Al13Pt9, a new representative exhibiting a coloring variant of the Ho4Ir13Ge9 type structure. The orthorhombic structure was refined based on single crystal X-ray diffraction data (Pmmn, Wyckoff sequence e (9) b (3) a (5), a = 415.38(1), b = 1149.73(2), c = 1994.73(5) pm, wR2 = 0.0622, 1901 F (2) values, 88 variables) and full atomic ordering was observed for all atoms. The structure features a complex [Al13Pt9]( delta-) network with the Eu atoms occupying hexagonal prismatic cavities. The bonding situation of this new platinide was investigated via quantum-chemical calculations. According to Density Functional Theory (DFT) the title compound has to be described as a polar intermetallic material with a covalently bonded [Al13Pt9]( delta-) polyanion showing strong Pt-Al alongside weak Al-Al and Pt-Pt bonding and Eu cations in the cavities.