Struktur- und Bindungsverhältnisse in cyclischen Schwefel-Stickstoff-Verbindungen - Molekülorbitalbetrachtungen

From eight-membered 10π electron sulfur-nitrogen cycles to bicycles and cages: a theoretical approach

A simple way of rationalizing the structures of cyclic, bicyclic, and tricyclic sulfur-nitrogen species and their congeners is presented. Starting from a planar tetrasulfur tetranitride with 12π electrons, we formally derived on paper a number of heterocyclic eight-membered 10π electron species by reacting the 3p orbitals of two opposite sulfur centers with one radical each, or by replacing these centers by other atoms with five (P) or four (Si, C) valence electrons. This led to planar aromatic 10π electron systems, nonplanar bicyclic structures with a transannular S-S bond, and tricyclic structures by bridging the planar rings with an acceptor or donor unit. The final structures depend on the number of π electrons in the bridges. Intermediate biradicals are stabilized by Jahn-Teller distortion, giving transannular S-S bonds between the NSN units. This procedure may be summarized by two rules, which provide a rationale for the structures of a large number of sulfur-nitrogen-based molecules. The long bonds between the NSN units show a p character of >95 %. The qualitative results have been compared with known molecular structures and the results of B3LYP/cc-pVTZ calculations as well as CASSCF and CASVB calculations. B3LYP/cc-pVTZ calculations have also provided the UV/Vis spectra and the NICS values of the planar 10π systems.

The new heteronuclear cluster cation [GeGa4]8+ in GeGa4S4: a summary of single crystal and mixed crystal studies

The yellow-transparent, air stable solid GeGa4S4 (a = 1142.50(9) pm, Z = 8, Pa[unk]) is a new isotypic member of the family of cubic MM′4X4 compounds (M: Sn, Ge, M′: Ga, In, X: S, Se) with S atoms in a ψ-tetrahedral coordination (one lone pair, three gallium atoms). Striking feature of the structure is a slightly distorted tetrahedral cationic cluster [GeGa4]8+ with hitherto unknown covalent Ge–Ga bonds (d Ge-Ga ≈ 244 pm). Ga is tetrahedrally coordinated by one Ge and three S atoms with the Ge atom common to four GaGeS3 tetrahedra resulting in the formation of GeGa4S12 groups (truncated tetrahedra). Detailed analyses of the geometrical conditions of the crystal structure in connection with systematic X-ray studies of selected mixed crystal systems show an anomalous short non-bonding S–S contact to be responsible for the low flexibility of the structure with respect to substitution of M, M′ and X by other elements. In particular the non-existence of tellurides of this structure type can be made reasonable.

A bonding quandary--or--a demonstration of the fact that scientists are not born with logic

We document here a spirited debate among three colleagues and friends who have strong opinions on a specific bonding problem, the presence or absence of a cross-ring sulfur-sulfur bond in a trinuclear Cu(3)S(2) cluster. The example may seem esoteric, but through their struggles with this specific bond (and with each other) the authors approach the more general problematic of chemistry, the chemical bond. The discussion focuses on bond lengths and the population of bonding and antibonding orbitals, and on oxidation states, electron counting, and associated geometries. It expands to encompass other bonding criteria, and introduces examples ranging far across organic and inorganic chemistry. The authors suggest molecules that might test their ideas. An Appendix to the paper discusses a matter rarely broached in the chemical literature--should one review for publication a paper which criticizes one of your own contributions.

Electronic Structure of Metallacyclophosphazene and Metallacyclothiazene Complexes

The electronic structure of metallacyclotriphosphazene complexes with several substituents at the phosphorus atoms and metallacyclothiazene complexes is explored for a variety of transition metal elements using density functional theory methods. Accordingly the metallacyclophosphazenes possess a large HOMO-LUMO energy separation while the metallacyclothiazenes bear stronger open-shell character. In addition our calculations predict the existence of experimentally so far unknown dimetallacyclophosphazenes. All structures show to be highly dynamical. The double bond character of the transition metal nitrogen bond is much less pronounced than in nitrido or imido complexes. For the ring compounds vibrational spectra are reported and compared with experimental data.