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–CH2CH2–NCHR, R = C6H5, C6F5, Ortho-, Meta- and Para-XC6H4 (X = F, Cl, Br,CH3)) 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 C2v 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 (De = 59.8–65.4 kcal/mol) < Cr (De = 62.3–67.8 kcal/mol) < W (De = 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 ∆Eint 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.

The nature of the bonding in group-6 complexes of Schiff bases has been investigated with charge- and energy decomposition analyses.Figure optionsDownload as PowerPoint slideHighlights
► The (CO)4M–SB bond dissociation energies vary little for different SB ligands.
► The M–SB interactions come mainly from electrostatic attraction ( ∼60% to ∆Eint).
► The transition metals, specially Cr atom, carry large negative partial charges.