Energy decomposition analysis of the metal-imine bond in [(CO) ₄M-SB] (M = Cr, Mo, W; SB: RHCN-CH₂CH₂-NCHR)

The electronic and molecular structures of the metal-Schiff base complexes [(CO)₄M-SB] (M: Cr, Mo, W; SB: RHCN-CH₂CH ₂-NCHR, R = C₆H₅, C₆F₅, Ortho-, Meta- and Para-XC₆H₄ (X = F, Cl, Br,CH ₃)) have been investigated at the DFT level using the exchange correlation functional BP86. The nature of the TM-Schiff base interactions was analyzed with charge and energy decomposition methods. The octahedral equilibrium geometries have C_2v symmetry. The (CO)₄M-SB bond dissociation energies vary little for different substituents R. The calculated values indicate rather strong bonds which exhibit the trend for the different metals M = Mo (D_e = 59.8-65.4 kcal/mol) < Cr (D _e = 62.3-67.8 kcal/mol) < W (D_e = 69.9-75.8 kcal/mol). The energy decomposition analysis suggests that the (CO)₄M-SB attractive interactions come mainly from electrostatic attraction which provide ∼60% to E_int while ∼40% come from orbital interactions. The latter term arises mainly (∼70%) through (CO)₄M ← SB σ donation from the nitrogen lone-pair orbitals while a much smaller part (∼20%) comes from (CO)₄M→SB π backdonation. The transition metals carry large negative partial charges between -2.3 e for M = Cr and -1.1e for M = W.