A combined computational and experimental study of Fe(II) complexes with hemilabile phosphine-based P,O donor ligands

Abstract Iron(II) complexes of the type [FeCl2(P∩X)2] [P∩X = o-(diphenylphosphino)benzaldehyde{PPh2(o-C6H4CHO)}(1) and o-(diphenylphosphino)benzoic acid {PPh2(o-C6H4COOH)}(2)] have been synthesized by the reaction of FeCl2.4H2O with respective ligands in DMF solution under refluxing condition. The structure of the complexes was identified using elemental analysis, ESI-mass, Fourier Transform Infrared spectra (FTIR), UV-Vis, 1H, and 31P{1H} NMR spectroscopy. FTIR measurements predicted trans-isomers to be the most stable complex for both (1) and (2). To confirm the stable isomer from the experiment, theoretical calculations at the level of first-principles density functional theory (DFT) was performed to provide a detailed molecular-level comparison of the structure, molecular orbitals, electronic and optical properties. The gas-phase calculations confirm trans-isomers to be the minimum energy geometries, with the energy difference of 5.7-8.7 kcal/mol between its geometrical cis-isomers. The complexes were characterized as high-spin (S=5/2) octahedral complexes. The time-dependent DFT calculations on the optimized structure were performed to compare the electronic absorption spectra with the experiment. Our combined integrative approach provides a good agreement between experimental and theoretical data and suggests trans-isomers to be the most preferable structures for the two studied Fe(II) complexes.