posted on 2024-01-10, 16:39authored byYang Yang, Guanjun Wang, Mingfei Zhou
Cationic complexes of heavy alkaline earth metal and
carbon dioxide
[M(CO2)n]+ (M =
Ca, Sr, and Ba) are produced by a laser vaporization-supersonic expansion
ion source in the gas phase and are studied by infrared photodissociation
spectroscopy in conjunction with quantum chemistry calculations. For
the n = 1 complexes, the metal–ligand binding
arises primarily from the electrostatic interaction with the CO2 ligand bound to the metal (+I) center in an end-on η1-O fashion. The more highly coordinated complexes [M(CO2)n]+ with n ≥ 2 are characterized to involve a [M2+(CO2–)] core ion with the CO2– ligand bound to the metal (+II) center in a bidentate
η2-O, O manner. The activation of CO2 in
forming a bent CO2– moiety occurs via
solvation-induced metal cation-ligand electron transfer reactions.
Bonding analyses reveal that the attractive forces between M2+ and CO2– in the core cation come mainly
from electrostatic attraction, but the contribution of covalent orbital
interactions should not be underestimated. The atomic orbitals of
metal dications that are engaged in the orbital interactions are ns
and (n – 1)d orbitals.