To
deeply understand the characteristics and regulation of red/blue-shifting
hydrogen bonds (HBs), a theoretical investigation was conducted to
explore the cooperativity between regium bonds and HBs in the complexes
of Y···MCN···HCX3 (M = Cu,
Ag, Au; Y = H2O, HCN, NH3; X = F, Cl). When
MCN formed a hydrogen bonding dimer with CHF3 or CHCl3, the blue shift of C–H vibration frequency v(C–H) decreases as the following sequence Au >
Cu
> Ag, and the red shift decreases following the order Ag > Cu
> Au.
Upon the formation of ternary complexes, the presence of regium bonding
interactions exerts a positive synergistic effect, resulting in the
strengthening of the HBs. This, in turn, leads to noticeable changes
in the red and blue shifts of v(C–H). In CHF3 complexes, v(C–H) undergoes a decrease
in the blue shift, whereas that in CHCl3 exhibits an increase
in the red shift. Especially, a transition from blue to red shift
is observed within the AuCN···HCCl3 complex.
As the strength of the regium bond increases, the trend of shifting
from blue to red becomes more pronounced. For a given MCN, the changes
occur in the order of NH3 > HCN > H2O.
The interplay
between two interactions was revealed by the molecular electrostatic
potentials (MEP), the atoms in the molecule (AIM), and natural bond
orbitals (NBO) analysis. It is revealed that Δv(C–H) is linearly correlated with a series of configuration
and energy parameters. We explain the red- and blue-shifting HBs and
their changes from the perspective of hyperconjugation and rehybridization.
The presence of the positive synergistic effect enhances the hyperconjugation
effect, thereby leading to a reduction in the blue shift and an increase
in the red shift of v(C–H) within the complexes.
This study enriches previous mechanisms regarding red- and blue-shifting
HBs and introduces a novel idea to manipulate the characteristics
of HBs, with the potential to impact the functioning of intricate
systems.