Merging the AuCu3- and BaAl4-based structure motifs: flux-assisted synthesis, crystal, and electronic structure of Ca2Pt7XP4- δ phosphide platinides (X = Al, Ti, and Zn)

Abstract

Three quaternary phosphide platinides, Ca₂Pt₇AlP_3.00(4), Ca₂Pt₇TiP_3.24(4), and Ca₂Pt₇ZnP_2.78(2), were synthesized by a high-temperature technique using lead as a flux. According to the single-crystal diffraction data, they are isotypic and crystallize in the tetragonal space group I4/mmm with Z = 2 (Ca₂Pt₇AlP_3.00(4): a = 3.9893(6) Å, c = 26.832(5) Å; Ca₂Pt₇TiP_3.24(4): a = 3.99610(10) Å, c = 26.9074(17) Å; Ca₂Pt₇ZnP_2.78(2): a = 4.0020(2) Å, c = 26.5549(17) Å) and thus represent first europium-free compounds of the Eu₂Pt₇AlP_2.95 structure type. Their structures can be described as an intergrowth of the AuCu₃- and CaBe₂Ge₂-type blocks. DFT calculations predict metallic conductivity and non-magnetic state for all three compounds. Bonding analysis based on the Bader charge distribution and ELF topology reveals a combination of localized covalent and ionic interactions in the CaBe₂Ge₂-type fragments and complex pattern of pairwise, multi-center, and ionic interactions in the AuCu₃-type fragments that closely reproduces bonding in the parent Pt₃X (X = Al, Ti, Zn) binary intermetallics.