Homoconjugation/homoaromaticity in main group inorganic molecules.

Quantum chemical computations show that three groups of inorganic ions and neutral molecules, whose structures have long been known and characterized, are aromatic due to through-space homoconjugation: (i) I(4)(2+), S(6)N(4)(2+), and S(2)I(4)(2+) dications and the (O(2))(4) cluster with pericyclic transition-state-like (PTS-like) homoaromaticity; (ii) the bishomoaromatic Te(6)(2+) and 1,5-diphosphadithiatetrazocines; and (iii) the spherically homoaromatic Te(6)(4+). The S(2)I(4)(2+) dication has an unusually high S-S bond order (approximately 2.3) and dual PTS-like aromaticity arising from two separate sets of four-center, six-electron (4c-6e) in-plane through-space conjugation. The diamagnetic (O(2))(4) structural unit recently observed in epsilon-phase oxygen solid has quadruple PTS-like aromaticity, each arising from 4c-6e in-plane through-space conjugation within an O(2)-O(2) plane. Finally, we note that the lighter S(6)(4+) and Se(6)(4+) homologues of Te(6)(4+) also are spherically homoaromatic and might be observable in complexes.