Nature of the Chemical Bond in Polypnictides: The Lone Pair Aromatic Anions P_4~(2-) and As_4~(2-)

摘要

The nature of the chemical bond in inorganic 6pi aromatic systems such as P_4~(2-),S_4~(2+),or S_2N_2 is a matter of particular interest because the phenomenon of aromaticity is not as well established in these compounds as it is in the classic aromatic hydrocarbons.Here we present the synthesis,NMR spectra,and crystal structures of bis-(potassium(18-crown-6))cyclotetraphosphide-ammonia(1/2) (K@18-crown-6)_2P_4 centre dot 2NH_3,bis(rubidium(18-crown-6))-cyclotetraphosphide-cyclotetraarsenide-ammonia(1/3) (Rb@18-crown-6)_2(P_4)_(0.85)(As_4)_(0.15) centre dot 3NH_3,both containing the 6pi aromatic cyclotetraphosphide anion,P_4~(2-),and the synthesis and crystal structure of bis(potassium(18-crown-6))cyclotetraarsenide (K@18-crown-6)_2As_4.As a common motive,all three compounds feature neutral molecules with a tripledecker-like coordination of the cyclotetrapnictide anion between two crown ether-coordinated alkali metal cations.With ab initio calculations on the HF level and by employing the concept of the electron localization function ELF,we established that the cyclotetraarsenide anion,As_4~(2-),shows electron delocalization primarily through the lone pairs,as does P_4~(2-),and may consequently also be described as lone pair aromatic.