Please use this identifier to cite or link to this item:
|Title:||Isomers of cyclo-heptasulfur and their coordination to Li+: An ab initio molecular orbital study|
|Authors:||Wong, M.W. |
|Citation:||Wong, M.W., Steudel, Y., Steudel, R. (2005-11-28). Isomers of cyclo-heptasulfur and their coordination to Li+: An ab initio molecular orbital study. Inorganic Chemistry 44 (24) : 8908-8915. ScholarBank@NUS Repository. https://doi.org/10.1021/ic050332a|
|Abstract:||The potential energy hypersurfaces (PESs) of heptasulfur (S7) and of [LiS7]+ have been investigated by ab initio molecular orbital calculations at the G3X(MP2) level of theory. Besides the chairlike seven-membered ring (1a) as the global minimum structure, eight local minimum structures and one transition state have been located on the PES of S7. The barrier for pseudorotation of 1 a is only 5.6 kJ mol -1. The boatlike S7 ring (1b) is 12.1 kJ mol-1 less stable than 1a, followed by three isomers of connectivity S6=S and four open-chain isomers. On the basis of multireference calculations at the MRCI(4,4)+Q/6-311G(d) level, the most stable open-chain form of S7 is a triplet of relative energy 133.1 kJ mol-1. Thus, the reaction energy (ΔE0) for the ring opening of 1a is 133.1 kJ mol -1, halfway between those of the highly symmetrical rings S 6 and S8. Because of their strong multireference characters, the stabilities of the biradicalic singlet chains are significantly overestimated by the single-reference-based G3X-(MP2) method. The calculated vibrational spectrum of 1a is in good agreement with experimental data. The various isomers of S7 form stable complexes with Li+ with coordination numbers of 1-4 for the metal atom and binding energies in the range of -93.8 to -165.7 kJ mol-1. A total of 15 isomeric complexes have been located, with 13 of them containing cyclic ligands. The global minimum structure (2a) is composed of 1a, with the Li+ cation linked to the four negatively charged sulfur atoms (symmetry Cs). The corresponding complex 2c containing the ligand 1b is by 23.4 kJ mol-1 less stable than 2a, and a bicyclic crown-shaped LiS7 cation (2e) is by 34.9 kJ mol-1 less stable than 2a. Even less stable are four complexes with the branched S6=S ligand. SS bond activation by polarization of the valence electrons takes place on coordination of Li+ to cycto-S 7 (1a). © 2005 American Chemical Society.|
|Source Title:||Inorganic Chemistry|
|Appears in Collections:||Staff Publications|
Show full item record
Files in This Item:
There are no files associated with this item.
checked on Dec 12, 2018
WEB OF SCIENCETM
checked on Dec 12, 2018
checked on Nov 16, 2018
Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.