Nature of the metal–ligand bond in some [(CO)4M ← BIIM(R)] {M = Cr, Mo, W; R = H, F, Cl, Br} complexes: A theoretical study

Abstract

A theoretical study on the structure and nature of the M←N bond in some potential pharmacologically active complexes; [(CO)4M←BIIM(R)] {M=Cr, Mo and W, R=H, F, Cl and Br} with R(3,3 substitution), R(4,4 substitution), R(5,5 substitution) and R(3,3 4,4, 5,5 substitutions) was carried through density functional BP86 and ab initio MP2 methods using the def2-TZVPP basis set. The M←N bond was analyzed using NBO, AIM, EDA and ETS-NOCV to obtain the electrical charge and energy decomposition analysis (EDA). The results showed that [(CO)4W←BIIM(H)] and [(CO)4Cr←BIIM(F)] are related to the D form complex with the biggest and the smallest ΔEint, respectively. Additionally, the M←N bond interaction energies (ΔEint) increase in the group from top to bottom, from the lighter to the heavier elements (Cr<Mo<W). The EDA suggests that the [(CO)4M←BIIM(R)] attractive interactions come mainly from ΔEelstat, which provides ∼60% of ΔEint, while ∼40% comes from ΔEorb. The applicability of the ETS-NOCV scheme is demonstrated for the complexes and it is shown that the ΔEorb term arises mainly through [(CO)4M←BIIM(R)] σ-donation (in the range 54–61%) while a smaller part (∼27%) comes from [(CO)4M→BIIM(R)] π-back donation. The nature of the M←N bond in the complexes was also studied by AIM and NBO analyses. The data has confirmed that the M←N bond is partly covalent.