Synthesis, magnetic and NMR spectroscopic properties of the MAl₅Pt₃ series (M = Ca, Y, La-Nd, Sm-Er)

Following recent investigation in the ternary system Sr-Al-Pt led to the discovery of SrAl₅Pt₃ which crystallizes in the orthorhombic YNi₅Si₃ type (Pnma) structure. Interestingly, only two more aluminum representatives, CeAl₅Pt₃ and EuAl₅Pt₃, have been reported to adopt this structure type. Therefore, we decided to investigate the existence range of compounds adopting the YNi₅Si₃ type structure. Besides the already known Sr, Ce and Eu members, the series could be extended to Ca, Y and La-Nd as well as Sm-Er. All compounds were synthesized from the elements and characterized by powder X-ray diffraction. While for CaAl₅Pt₃ and LaAl₅Pt₃ also the respective M₂Al₁₆Pt₉ members were observed, the other compounds could be obtained either as X-ray pure materials or with small amounts of Al₃Pt₂ as a side phase. The structure of ErAl₅Pt₃ could be refined from single crystal data, verifying that also the small rare-earth elements adopt the YNi₅Si₃ type structure. Selected members of the series were furthermore characterized by magnetization and susceptibility measurements. Since YAl₅Pt₃ could be obtained as a phase pure material and exhibits no paramagnetic behaviour it was investigated by ²⁷Al MAS NMR investigations. Also, XPS measurements were conducted on this compound to gain an insight into the charge distribution. Finally, quantum-chemical calculations supported the NMR measurements and gave an insight into the chemical bonding and the charge distribution.