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: S-4(2+), Se-4(2+), S2N2, P-5(-) and As-5(-) with 6 pi electrons; S3N3-, S4N3+ and S4N42+ with 10 pi electrons; and S5N5+ with 14 pi 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 pi currents, reinforced by sigma circulations in P-5(-), As-5(-), S3N3-, S4N3+, S4N42+ and S5N5+, but opposed by them in S-4(2+), Se-4(2+) and S2N2. The op position of pi and sigma effects in the four-membered rings is compatible with height profiles of calculated NICS (nucleus-independent chemical shifts).