Energy decomposition analysis of the metal-imine bond in [(CO) 4M–SB] (M = Cr, Mo, W; SB: RHC [dbnd]N–CH 2CH 2–N [dbnd]CHR)

Abstract

The electronic and molecular structures of the metal-Schiff base complexes [(CO) 4M–SB] (M: Cr, Mo, W; SB: RHC N–CH 2CH 2–N CHR, R = C 6H 5, C 6F 5, Ortho-, Meta- and Para-XC 6H 4 (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.