Phosphorus Oligomerization in Zintl Phases: Synthesis, Crystal Structure, and Bonding Analysis of Mixed Alkali and Alkaline‐Earth Metal Phosphides

Abstract

Abstract Pnictides α‐Ba 5 P 4 and KBa 4 P 5 were prepared by melting the elements. The α‐Ba 5 P 4 compound crystallizes in the orthorhombic system (Sm 5 Ge 4 ‐type), space group Pnma, Z = 4, a = 8.330(3), b = 16.503(3), c = 8.405(2)Å, it contains two anionic species : P 2 4— dumbbells and P 3— . The KBa 4 P 5 compound crystallizes in the tetragonal system, space group P4 3 2 1 2, Z = 4, a = 8.559(1), c = 16.102(2)Å, it contains trimers P 3 5— and dumbbells P 2 4— . The crystal structures were solved from single crystal X‐ray data and refined by full‐matrix least‐squares to agreement factors R1 = 0.047 and 0.038, respectively. Using ionic charges, α‐Ba 5 P 4 is formulated as [5Ba 2+ , 2P 3— , P 2 4— ] and KBa 4 P 5 as [K + , 4Ba 2+ , P 2 4— , P 3 5— ]. The level of oligomerisation in these structures depends upon the overall valence electron content, bonding within the anionic oligomers has been analyzed on the basis of EHMO calculations and compared to classical or hypervalent bonding in other phosphide compounds.