Results and Discussion
Figure 1 shows the optimized geometries of the radical anions. The
T1 diagnostic values of the
CCSD(T)/def2-TZVP//M06-2X/def2-TZVP calculations are all lower than 0.02
suggesting single determinant character of the wave functions. For the
Be containing compounds, high lying isomers are also located in the
potential energy surface which feature no Be-Be interaction. These no
Be-Be bond isomers are very high in energy and represents bond stretch
isomers which were theoretically explained in 1972 by Hoffmann and
co-workers for the polytopal rearrangement of
(CH)5+, (CH)5 and
(CH)4CO.21 However, for Zn containing
compounds, such high lying isomers (or bond stretch isomers) were not
located on the potential energy surface. It is to be noted that all
these molecules shown in Figure 1 are local minima in the potential
energy surface with real values of Hessian matrix. The Be-Be distance in
these compounds ranges from 2.586 to 2.450 Å with the shortest been
found with –CN as the substituent attached to Be atoms. The computed
Wiberg bond indices (WBIs) are in the range of 0.146 to 0.195.
Similarly, for Zn containing compounds, the Zn-Zn bond distance ranges
from 2.909 to 3.023 Å. The computed WBIs are in the range of 0.258 to
0.268. Thus, these radical anions feature a strong Be-Be and Zn-Zn
bonds.