Synthesis, crystal and electronic structures of the pnictides ae3trpn3 (AE = Sr, Ba; Tr = Al, Ga; Pn = P, As)

Abstract

The new ternary arsenides AE3TrAs3 (AE = Sr, Ba; Tr = Al, Ga) and their phosphide analogs Sr 3 GaP 3 and Ba3AlP3 have been prepared by reactions of the respective elements at high temperatures. Single-crystal X-ray diffraction studies reveal that Sr 3 AlAs 3 and Ba 3 AlAs 3 adopt the Ba 3 AlSb 3 -type structure (Pearson symbol oC56, space group Cmce, Z = 8). This structure is also realized for Sr 3 GaP 3 and Ba3AlP3. The compounds Sr 3 GaAs3 and Ba3GaAs3 crystallize with the Ba3GaSb3-type structure (Pearson symbol oP56, space group Pnma, Z = 8). Both structures are made up of isolated pairs of edge-shared AlPn4 and GaPn4 tetrahedra (Pn = pnictogen, i.e., P or As), separated by the alkaline-earth Sr 2+ and Ba 2+ cations. In both cases, there are no homoatomic bonds, hence, regardless of the slightly different atomic arrangements, both structures can be rationalized as valence-precise [AE 2+ ]3[Tr 3+ ][Pn 3- ]3, or rather [AE 2+ ]6[Tr 2 Pn 6 ] 12-, i.e., as Zintl phases.