Ba5Tr2(Ge,Sn)2P8 and Ba5Tr5(Ga,Tt)2P12 (Tr = Al, Ga; Tt = Ge, Sn): Phosphides with Triel and Tetrel Mixing.

A series of new multinary phosphide Zintl compounds, Ba₅Ga₂GeSnP₈, Ba₅Al₂GeSnP₈, Ba₅Ga₆GeP₁₂, and Ba₅Ga₆SnP₁₂, have been synthesized through high-temperature Pb or Sn flux reactions. The structures of the compounds, which have been determined by single-crystal X-ray diffraction, feature two different new structural types bearing various polyanion chain fragments. Ba₅ Tr₂GeSnP₈ ( Tr = Al, Ga) crystallize in the monoclinic C2/ m (No. 12) space group with cell parameters: a = 16.8211(10)/16.7586(21) Å, b = 6.0115(4)/6.0867(8) Å, c = 9.5873(6)/9.5983(12) Å, β = 111.9270(10)/112.1880(10)° for the Al- and Ga-containing compounds, respectively. For Ba₅Ga₆ TtP₁₂ ( Tt = Ge, Sn), the compounds belong to a different orthorhombic system [space group: Cmcm (No. 63)] with the cell dimensions: a = 10.5222(6)/10.5802(9) Å, b = 16.2717(10)/16.3529(14) Å, c = 13.9093(8)/13.9643(12) Å for Ba₅Ga₆GeP₁₂ and Ba₅Ga₆SnP₁₂. Despite the clear differences in the crystallographic parameters, these two types of structures are closely related through the [ Tr₂P₄] and [ Tr₅P₁₂] polyanion chains ( Tr = triels) as well as the significant mixing between the triel and tetrel atoms. The close relationships between these phases and some previously reported analogues are also discussed in detail. Theoretical calculations based on DFT methods confirm the precise electron nature of these compounds, which are also consistent with results from crystallographic data and the optical absorption measurements. [ABSTRACT FROM AUTHOR]