jp508391r_si_001.pdf (51.94 kB)
Generalized Valence Bond Description of Chalcogen–Nitrogen Compounds. I. NS, F(NS), and H(NS)
journal contribution
posted on 2015-03-05, 00:00 authored by Tyler
Y. Takeshita, Thom H. DunningThe electronic structures of the
ground states (X2Π)
of NS and those (X1A′) of F(NS) and H(NS), where
X(NS) collectively refers to the XNS and NSX isomers, were analyzed
within the framework of generalized valence bond theory. The ground
state of NS has a recoupled pair π bond, which has a profound
effect on its reactivity. For example, the lowest-energy isomer of
F(NS) is NSF, which has a recoupled pair bond dyad with N–SF
and NS–F bonds lengths and strengths similar to their covalent
counterparts in NS and SF. The ground state of NSH, on the other hand,
is only weakly bound with a NS–H bond energy 40.20 kcal/mol
smaller than that in SH and a N–SH bond energy 40.20 kcal/mol
less than that in NS. At its equilibrium geometry, the NSH molecule
is best viewed as derived from the N(2D) + SH(X2Π) separated fragments, with the weak NS–H bond resulting
from unfavorable interactions between the SH bond pair and the nitrogen
lone pair. Addition of F/H atoms to the nitrogen atom in NS disrupts
the NS recoupled pair bond, which weakens both the FN–S/HN–S
and F–NS/H–NS bonds. In contrast to the formation of
recoupled pair σ bonds, formation of the recoupled pair π
bond in NS is expressed as a change in the spin-coupling coefficients,
rather than an interchange of the orbitals.