X<sub>2</sub>Y<sub>2</sub> Isomers: Tuning Structure and Relative Stability through
Electronegativity Differences (X = H, Li, Na, F, Cl, Br, I; Y = O,
S, Se, Te)
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Abstract
We have studied the
XYYX and X<sub>2</sub>YY isomers of the X<sub>2</sub>Y<sub>2</sub> species (X = H, Li, Na, F, Cl, Br, I; Y = O, S, Se, Te) using density
functional theory at the ZORA-BP86/QZ4P level. Our computations show
that, over the entire range of our model systems, the XYYX isomers
are more stable than the X<sub>2</sub>YY forms except for X = F and
Y = S and Te, for which the F<sub>2</sub>SS and F<sub>2</sub>TeTe
isomers are slightly more stable. Our results also point out that
the Y–Y bond length can be tuned quite generally through the
X–Y electronegativity difference. The mechanism behind this
electronic tuning is the population or depopulation of the π*
in the YY fragment