* The two values in each box for the 3b structure correspond to the
Xe-Au1 and Xe-Au3 bonds, respectively.
3.3 | Covalent character
investigation of Xe-Au bonds in Xe(AuF)n (n =
2-4)
The bonding character of Ng-Nm interactions has been one of hot issues
of the related research field. To further explore the chemical bonding
nature of Xe-Au bonds in Xe(AuF)n (n =
2-4), quantum-theory-of-atoms-in-molecules (QTAIM) analysis is
performed, aimed at providing extra evidence for a bond path among all
bonding interactions with a bond critical point (BCP) and a significant
accumulation of electron density within the bond (see electron densityρ bcp in Table 1 ). Typically, at the BCP
of a certain chemical bond, high electron densityρ (r c) and negative Laplacian electron
density ▽2ρ (r c) values
define a covalent bond, but this criterion does not always work
especially when heavier atoms are involved. The energy densityH (r c), ratio of local kinetic energy
density G (rc ) and electron densityρ (r c), however, are more proper parameters
in
these cases. Covalent bonds are characterized by BCPs with negativeH (r c) andG (r c)/ρ (r c)
lower than 1, while those with positiveH (r c) andG (r c)/ρ (r c)
exceeding 1 usually denote closed-shell
interaction.[59] Based on this criterion, theH (r c) andG (r c)/ρ (r c)
values at all BCPs suggest explicit covalent nature of the Xe-Au bonds
for the whole series of predicted structures. Moreover, as mentioned in
the RDG analysis, the electron density between Xe and Au atoms are
slightly bigger in traditional structures (2b , 3c and4a ). Topological analysis was additionally performed for linear
NgNmX (Ng = He, Ne, Ar, Kr and Xe; Nm = Cu, Ag and Au; X = F, Cl, Br and
I) molecules and compared in Table S3 , revealing that the Ng-Nm
bonds are gradually transformed from dispersive to covalent as the Ng
atom grows heavier and that the metal and halogen atoms are capable of
affecting the Ng-Nm bonding strength without altering the bonding
character.