Electrophilic Attack on Sulfur–Sulfur Bonds: Coordination of Lithium Cations to Sulfur‐Rich Molecules Studied by Ab Initio MO Methods

Abstract

Complex formation between gaseous Li+ ions and sulfur-containing neutral ligands, such as H2S, Me2Sn (n = 1-5; Me = CH3) and various isomers of hexasulfur (S6), has been studied by ab initio MO calculations at the G3X(MP2) level of theory. Generally, the formation of LiS(n) heterocycles and clusters is preferred in these reactions. The binding energies of the cation in the 29 complexes investigated range from -88 kJ mol(-1) for [H2SLi]+ to -189 kJ mol(-1) for the most stable isomer of [Me2S5Li]+ which contains three-coordinate Li+. Of the various S6 ligands (chair, boat, prism, branched ring, and triplet chain structures), two isomeric complexes containing the S5==S ligand have the highest binding energies (-163+/-1 kJ mol(-1)). However, the global minimum structure of [LiS6]+ is of C(3v) symmetry with the six-membered S(6) homocycle in the well-known chair conformation and three Li--S bonds with a length of 256 pm (binding energy: -134 kJ mol(-1)). Relatively unstable isomers of S6 are stabilized by complex formation with Li+. The interaction between the cation and the S6 ligands is mainly attributed to ion-dipole attraction with a little charge transfer, except in cations containing the six sulfur atoms in the form of separated neutral S2, S3, or S4 units, as in [Li(S3)2]+ and [Li(S2)(S4)]+. In the two most stable isomers of the [LiS6]+ complexes, the number of S--S bonds is at maximum and the coordination number of Li+ is either 3 or 4. A topological analysis of all investigated complexes revealed that the Li--S bonds of lengths below 280 pm are characterized by a maximum electron-density path and closed-shell interaction.

Interaction of Zinc Oxide Clusters with Molecules Related to the Sulfur Vulcanization of Polyolefins (“Rubber”)

“…However, in our previous work we have shown that the sulfur homocycles S 6 , [45] S 7 , [46] and S 8 [47] form chelate complexes of the type [MS n ] + with univalent metal cations such as Li + , Ca + , V + , and Cu + . The last three metal ions are even able to break down the S 8 molecule to form complexes with two S 4 ligands which are more stable than the isomeric S 8 complexes.…”

“…Previously, we have shown that the methyl derivatives Me 2 S n with n = 2-5 form chelate complexes with Li + ions. [45] In these cases the interaction energy ranges from À140 to À190 kJ mol À1 and the bonding has been explained by iondipole attraction after the metal cation induced or enhanced the dipole moment of the polysulfide ligand by polarization. A similar interaction can be expected with the positively charged zinc atoms at the surface of ZnO.…”

Coordination of Li+, Ca+, V+, and Cu+ to the Molecules S8 and S4 –A Computational Study

“…We did not intend to scan the total PES of this system. Instead, using existing knowledge of the various isomers of [LiS 6 ] + [11] we investigated mainly the coordination of Li + to the previously studied isomeric cyclic forms of S 8 and to only one of the eight- Figure 1. Various cyclic and chain-like isomers of the S 8 molecule with relative energies (kJ·mol -1 ) and symmetries (according to ref.…”

“…[11] In this work we have investigated theoretically the interaction of the sulfur homocycle S 8 with gaseous Li + which serves as a simple model ion to allow calculations at a high level of theory. Besides S 6 , [11] only the coordination of gaseous S 3 to Li + has been investigated previously by quantum-chemical calculations: [LiS 3 ] + is of C 2v symmetry. [12] In the case of [LiS 6 ] + , 15 isomeric structures have been identified on the potential energy hypersurface (PES).…”

“…The metal ion is linked to three equivalent sulfur atoms resulting in a binding energy of -134 kJ·mol -1 . [11] We define here the (adiabatic) binding energy as the energy difference between the complex and the sum of the energies of the two separated components in the same (or closest) conformation as found in the complex.…”