A theoretical study of 18+δ complexes

The 19e organometallic complexes [Co(CO)2(PH3)(L2X)], [Fe(CO)3(L2X)]− and [MnBr(CO)3(L2X)]−, where L2X=2,3-bisphosphino maleic anhydride (X=O), 4,5-bisphosphino maleimide (X=NH), and 4,5-bisphosphino cyclopentene-1,3-dione (X=CH2) have been studied computationally at the B3LYP level. All the complexes have shown 18+δ character, in which the 19th electron is predominantly distributed over the chelating ligand L2X. The value of δ has been estimated computationally using IR-frequencies (IR method) and natural atomic charges (AC method). The δ values estimated using AC method were higher than those using IR method. Computed δ values in the presence of solvents were consistently lower than those in vacuo.