Aromaticity of planar P5− anion in the P5M (M=Li, Na, and K) clusters

Geometries, electronic structures and vibrational frequencies of alkali metal-P5− P5M (M=Li, Na, and K) clusters were investigated using density functional theory (DFT) method. Calculation results show that planar P5− anion can coordinate with metal atoms to form two kinds of the P5M complexes that maintain the planar cyclo-P5− anion structure. Among these, the pyramidal structures of P5M clusters are the most stable isomers. On the basis of the molecular orbital (MO) analysis and nucleus-independent chemical shifts (NICS), we revealed that planar P5− anion exhibits characteristic of π-aromaticity with six delocalized π electrons and maintains its structural and electronic integrity inside the two kinds of P5M (M=Li, Na, and K) clusters.