Nziko Vincent de Paul N, Scheiner Steve
Department of Chemistry and Biochemistry Utah State University, Logan, Utah 84322-0300, United States.
J Phys Chem A. 2015 Jun 4;119(22):5889-97. doi: 10.1021/acs.jpca.5b03359. Epub 2015 May 22.
SF2 and SF4 were each paired with a series of unsaturated hydrocarbons including ethene, ethyne, 1,3-butadiene, and benzene, in each case forming a chalcogen bond between the S atom and the carbon π-system. MP2 ab initio calculations reveal that the S atom is situated directly above one specific C═C bond, even when more than one are present. The binding energies range between 3.3 and 6.6 kcal/mol. SF2 engages in a stronger, and shorter, noncovalent bond than does SF4 for all systems with the exception of benzene, to which SF4 is more tightly bound. cis-Butadiene complexes contain the shortest chalcogen bond, even if not necessarily the strongest. The internal S-F covalent bonds elongate upon formation of each chalcogen bond. The molecules are held together largely by charge transfer forces, particularly from the C═C π-bonds to the σ*(SF) antibonding orbitals. In the case of SF2, a sulfur lone pair can transfer charge into the π* MOs of the alkene, a back-transfer which is more difficult for SF4.
SF2和SF4分别与一系列不饱和烃配对，包括乙烯、乙炔、1,3 - 丁二烯和苯，在每种情况下，S原子与碳π - 体系之间形成硫属元素键。MP2从头算计算表明，即使存在多个C═C键，S原子也直接位于一个特定的C═C键上方。结合能在3.3至6.6千卡/摩尔之间。除了苯（SF4与苯结合更紧密）之外，对于所有体系，SF2形成的非共价键比SF4更强且更短。顺式丁二烯配合物含有最短的硫属元素键，即使不一定是最强的。形成每个硫属元素键时，内部S - F共价键会伸长。分子主要通过电荷转移力结合在一起，特别是从C═C π键转移到σ*(SF)反键轨道。就SF2而言，硫的孤对电子可以将电荷转移到烯烃的π*分子轨道中，这种反向转移对SF4来说更困难。
