Nature of Beryllium, Magnesium, and Zinc Bonds in Carbene⋯MX2 (M = Be, Mg, Zn; X = H, Br) Dimers Revealed by the IQA, ETS-NOCV and LED Methods
2022
Filip Sagan | Mariusz Mitoraj | Mirosław Jabłoński
The nature of beryllium&ndash:, magnesium&ndash: and zinc&ndash:carbene bonds in the cyclopropenylidene⋯:MX2 (M = Be, Mg, Zn: X = H, Br) and imidazol-2-ylidene⋯:MBr2 dimers is investigated by the joint use of the topological QTAIM-based IQA decomposition scheme, the molecular orbital-based ETS-NOCV charge and energy decomposition method, and the LED energy decomposition approach based on the state-of-the-art DLPNO-CCSD(T) method. All these methods show that the C⋯:M bond strengthens according to the following order: Zn <: Mg <:<: Be. Electrostatics is proved to be the dominant bond component, whereas the orbital component is far less important. It is shown that QTAIM/IQA underestimates electrostatic contribution for zinc bonds with respect to both ETS-NOCV and LED schemes. The &sigma: carbene&rarr:MX2 donation appears to be much more important than the MX2&rarr: carbene back-donation of &pi: symmetry. The substitution of hydrogen atoms by bromine (X in MX2) strengthens the metal&ndash:carbene bond in all cases. The physical origin of rotational barriers has been unveiled by the ETS-NOCV approach.
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