FIGURE 4 (a) Calculated geometries of 2a and2b . (b) Potential energy curves of Xe(MF)2 (M =
Au, Ag, Cu). (c) Potential energy curves of Xe(AuX)2 (X
= F, Cl, Br). (d) Potential energy curves of Ng(AuF)2(Ng = Xe, Kr, Ar). All geometries used in potential energy curve
illustration were obtained by full optimization at each bending angle
under the level of LC-ωPBE-D3/def2TZVPP.
3.4 | Competition between Ng-Nm bonds and
metallophilic
interactions
A fact should be addressed is that aurophilic interaction can be
generalized to a wider range of metals. The concept of metallophilic
interaction typically denotes a weak electrostatic attractive force and
is encountered mainly between adjacent low-valent closed shell
[(n-1)d10s0] or pseudo-closed
shell [(n-1)d8ns0] metal centers
like Cu(I), Ag(I), Hg(II) and so on.[60] The
competition between Ng-Nm bonds and metallophilic interactions is
undoubtedly an interesting issue that induce the bond-bending isomerism.
A good way to dig into the competition mechanism is to observe how the
molecular structure will respond once any one of the atoms in
Xe(AuF)n varies. For this purpose, the potential energy
curves of Ng(NmX)2 (Ng = Ar, Kr, Xe; Nm = Cu, Ag, Au; X
= F, Cl, Br) were calculated and illustrated in Figure 4 , by
flexibly scanning the potential energy surface via stepwise changing the
Nm-Ng-Nm angle. In contrast to Xe(AuF)2 and
Xe(AuCl)2 that have two minimums on the potential energy
curve representing the coexistence of 2a and 2bstructures, the rest species exhibit only one minimum at a Ng-Nm-Ng
angle of approximately 60°, indicative of the sole 2b isomer.
This may be because only Xe(AuF)2 and
Xe(AuCl)2 have Xe-Au bonds that are strong enough to
compete with metallophilic interactions, thereby allowing two types of
bond-bending isomers to coexist.
The optimized structures and the key geometrical parameters of
Ng(AuF)2 (Ng = Ar and Kr), Xe(NmF)2 (Nm
= Ag and Cu) and Xe(AuX)2 (X = Cl and Br) are calculated
as well and given in Figure S5 . RDG analysis of these molecules
shows a salient decrease of the Ng-Nm spike value from
~0.08 to ~0.06 (Figure 3 and
S6 ) once one arbitrary atom of Ng(AuF)2 is substituted.
It is noteworthy that weaker Ng-Nm bonds will lead to an increased
instability of the traditional structures while have negligible effects
on metallophilic structures, highlighting the significant role of Ng-Nm
bonding strength in bond-bending isomerism.
3.5 | Comparison among multi-coordinated Xe
complexes
As mentioned hereinbefore, in inorganic complexes
XeFn (n =2, 4, 6)[2,
14] or organic complexes Xe(CCH)n (n =
4, 6)[12], Xe tends to bind with an
electronegative group via electron donation from both parts. The Xe-F
bond in XeFn exhibits traditional σ -covalent
character with Xe in sp3dnhybridization, forming symmetrical geometries, e.g. , linearD 2h configuration for
XeF2[2], square planarD 4h structure for
XeF4[2], and square bipyramidalO h structure for XeF6[14]. Similar phenomena were observed for the
Xe-CCH bond in Xe(CCH)n (n = 4, 6), but
with slight difference in that this interplay is partially ionic and
partially covalent.[12] However, the strong
covalent Xe-Au bonding in this work was formed via the electron
donation-feedback mechanism for the whole family of
Xe(AuF)n (n = 2-4) with Xe insp3 hybridization. The comparison clearly shows
the differences regarding the formation mechanism of two types of Ng
complexes referred to in the introduction context and gives further
evidence to this work serving as an essential complement to the research
field of Ng chemistry.
4 | CONCLUSION
In summary, the geometrical and electronic structures of a novel family
of
multi-coordinated
Ng complexes, Xe(AuF)n (n = 2-4), were
theoretically predicted by using LC-ωPBE-D3/def2TZVPP method. Two types
of bond-bending isomers were located with different Au-Xe-Au bond angles
as a result of the competition between
intramolecular aurophilic
interactions and Xe-Au covalent bonds. Thorough potential energy surface
scanning of Ng(NmX)2 (Ng = Ar, Kr, Xe; Nm = Cu, Ag, Au;
X = F, Cl ad Br) shows the unique bond-bending isomerism merely exists
in Xe(AuF)n and Xe(AuCl)n ,
since their Xe-Au bonds are strong enough to compete against aurophilic
interactions. Systematic chemical bonding analysis, e.g. ,
ETS-NOCV, EFL, RDG, and QTAIM, between these two types of bond-bending
isomers confirms aurophilic interactions indeed exist and pronouncedly
affect the intensity of the covalent Xe-Au bonds in these
multi-coordinated Ng complexes. This work stands as an essential
complement to the research field of Ng chemistry and pave the way for
experimental progress in discovering multi-coordinated Ng complexes.
SUPPORTING INFORMATION
Comparison of the length and dissociation energy of Xe-Au bond in Xe-AuF
at different theoretical levels (Table S1); geometric parameters of
Xe(AuF)n (n = 1-4) (Table S2); QTAIM topological
analysis of linear NgMX (Ng = He, Ne, Ar, Kr, Xe; M = Cu, Ag, Au; X = F,
Cl, Br, I) molecule (Table S3); chemical bonding analysis of isomers3a , 4a and 4c , including ETS-NOCV, ELF and
RDG methods (Figure S1-S3); surface electrostatic potential map of AuF
molecule (Figure S4); the lowest-energy structures of
Ng(MX)2 (Ng = Xe, Kr, Ar; M = Cu, Ag, Au, X = F, Cl, Br)
with geometric and energic parameters; RDG analysis of
Xe(AgF)2 and Xe(CuF)2 (Figure S6).
ACKNOWLEDGEMENTS
This work was financed by the National Natural Science Foundation of
China (21873001), and by the Foundation of Distinguished Young
Scientists of Anhui Province. Q. Y. acknowledges support from the
start-up grants from Anhui University under No. S020318008/024. The
theoretical calculations were carried out at the High-Performance
Computing Center of Anhui University.
CONFLICT OF INTEREST
The authors declare no competing financial interest.
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GRAPHICAL ABSTRACT
This work predicts multi-coordinated Ng complexes
Xe(AuF)n (n = 2-4) and demonstrates
intramolecular bond-bending isomerism that exhibiting two types of
isomers due to the competition between Xe-Au covalent bonding and Au-Au
aurophilic interactions, with the aid of high-precision theoretical
calculations and electron and chemical bonding analysis. The present
study serve as an essential complement to the research field of Ng
chemistry and pave the way for experimental progress in discovering
multi-coordinated Ng-metal complexes.