σ-Aromaticity and σ-antiaromaticity in saturated inorganic rings

The magnetic properties of a series of inorganic saturated rings, (SiH2)(n), (GeH2)(n), (NH)(n), (PH)(n), (AsH)(n), O-n, S-n, and Se-n (n = 3-6), exhibit zigzag behavior with ring size resembling that of aromatic and antiaromatic Huckel pi-systems and (CH2))(n) rings. Computed GIAO-SCF nucleus-independent chemical shifts (NICS) and localized (LMO) NICS analysis indicate that the sigma-ring electrons are chiefly responsible for this zigzag behavior. This evidence for sigma-aromaticity is further supported by theoretical strain energy (TSE). The Huckel 4n + 2/4n aromaticity/antiaromaticity rule for pi-electron systems applies well to the smaller saturated rings.