Ring currents as probes of the aromaticity of inorganic monocycles: P5-, As5-, S2N2, S3N3-, S4N3+, S4N42+, S5N5+, S42+ and Se42+

Current-density maps were calculated by the ipsocentric CTOCD-DZ/6-311G** (CTOCD-DZ=continuous transformation of origin of current density-diamagnetic zero) approach for three sets of inorganic monocycles: S42+, Se42+, S2N2, P5− and As5− with 6 π electrons; S3N3−, S4N3+ and S4N42+ with 10 π electrons; and S5N5+ with 14 π electrons. Ipsocentric orbital analysis was used to partition the currents into contributions from small groups of active electrons and to interpret the contributions in terms of symmetry- and energy-based selection rules. All nine systems were found to support diatropic π currents, reinforced by σ circulations in P5−, As5−, S3N3−, S4N3+, S4N42+ and S5N5+, but opposed by them in S42+, Se42+ and S2N2. The opposition of π and σ effects in the four-membered rings is compatible with height profiles of calculated NICS (nucleus-independent chemical shifts).