Theoretical Study of Chemical Binding of Noble Gas Atom and Transition Metal Complexes: Ng–NiCO, Ng–NiN2, Ng–CoCO (Ng = He–Xe)
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Ab initio multireference and coupled cluster methods (MR-SDCI(+Q), CASPT2, CCSD(T)) and density functional theory methods (B3LYP, MPWPW91) have been applied to examine geometrical structures and vibrational frequencies of noble gas (Ng) – transition metal compounds, Ng–NiCO, Ng–NiN2, and Ng–CoCO (Ng = He, Ne, Ar, Kr, Xe). It is shown that the respective compounds can have a larger binding energy than a typical van der Waals interaction energy. The binding mechanism is explained by a partial electron transfer from a noble gas atom to the low-lying 4s and 3d vacant orbitals of the transition metal atom. Theoretical calculations show that the binding of noble gas atom results in a large shift of the bending frequency: 361.1 cm−1 (NiCO) to 403.5 cm−1 (Ar–NiCO); 308.5 cm−1 (NiN2) to 354.8 cm−1 (Ar–NiN2); 373.0 cm−1 (CoCO) to 422.6 cm−1 (Ar–CoCO). The corresponding experimental frequencies determined in solid argon are 409.1 cm−1 (NiCO), 357.0 cm−1 (NiN2), and 424.9 cm−1 (CoCO), which are much closer to the corresponding frequency of Ar–NiCO, Ar–NiN2, and Ar–CoCO, respectively.
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