It is evident from Table 1 that accumulation of significant electron
density between the Be-Be and Zn-Zn bond critical points. The negative
values of laplacian of electron density, ∇2ρand total electronic energy density, H (r) suggests significant
covalency in the Be-Be bonds. However, the positive value of laplacian
of electron density, ∇2ρ and negative value of
total electronic energy density, H (r) for Zn-Zn bond suggests
polar covalent character. The calculated values of ELF populations,
V(M,M) are significantly higher for Be-Be bonds but somewhat smaller for
Zn-Zn bonds. The electron population of the Be-Be bond and Zn-Zn bonds
obtained through NBO analyses15 are very close to the
value of 1.0 suggesting 2-centre-1-electron interaction. The
hybridization of the Be-Be and Zn-Zn bonds have significant ns (2s for
Be and 4s for Zn) character supporting covalent nature of these bonds.
The contribution of s character decreases slightly for Zn-Zn bonds which
has also reflected in the ELF basin populations, V(Zn,Zn) (Table 1). The
V(Zn,Zn) values of Zn-Zn bonds are close to 0.7 while they are close to
0.9 for Be-Be bonds. Figure 4 shows the molecular graphs and 3D ELF
plots of the compounds.