Density Functional Theory Study On Binary Binuclear Iron Carbonyl Complexes

For decades,the metal–metal bonding is of fundamental interest in chemistry.The transition metal carbonyl complexes are generally considered as prototypical models for the metal–metal bonding,which can be significantly affected by the?-acidic carbonyl ligand by extensive mixing between metal and ligand orbitals of?symmetry.Scientists have used a variety of spectroscopic techniques to systematically carry out spectroscopic studies of neutral transition metal carbonyl compounds as well as their anionic and cationic counterparts in the gas phase and condensed phase,with significant motivation and promotion on the theoretical research their structures and bonding.In this thesis,the density functional theory calculations have been carried out to systematically study both homo-and hetero-dinuclear carbonyl neutral complexes containing iron,as well as their anionic and cationic counterparts,with the focus on the metal–metal bonding interaction.First,the density functional theory calculations have been performed to obtain the geometric structures of the three binuclear homoleptic iron carbonyl complex systems,namely,the cationic Fe₂(CO)_m⁺(m=4–8)system,the anionic Fe₂(CO)_n^–(n=4–8)system and the neutral Fe₂(CO)_p(p=4–8)system.It is found that,for the most stable complexes in all three systems,the carbonyl ligands are terminally coordinated to the iron centers and the metal–metal bond lengths increase with the increase of the number of carbonyl ligands.The carbonyl ligands in the ionic species prefer to be asymmetrically adsorbed to the iron dimer,while the CO ligands in the neutral species symmetrically attach to the iron dimer.For the cationic and anionic complexes,the CO ligands preferentially attach to one of two iron centers until this iron atom is saturate-coordinated to satisfy the 18-electron rule,and then the additional CO ligands successively attach to the other iron center.Furthermore,the ground-state electronic structures of these three systems have been investigated by natural charge population analysis,molecular orbital analysis and energy decomposition analysis in conjunction with natural orbital for chemical valence analysis,concentrating on the Fe–Fe bonding interaction.It is demonstrated that the total stability interactions in the three systems are mainly dominated by the orbital interactions.Moreover,different metal–metal chemical bonding interactions are found for the different charge state complex systems.It is found that the Fe–Fe bonds in both anionic Fe₂(CO)_n^–(n=4–8)system and neutral Fe₂(CO)_p(p=4–8)system are better to be described as electron-sharing interaction,while the cationic Fe₂(CO)_m⁺(m=4–8)system can be regarded as donor–acceptor complexes,in which the Fe–Fe bond comes from dative interaction.Further research is extended to one hetero-dinuclear carbonyl complexe containing iron.A joint photoelectron imaging and theoretical study is performed on Ag Fe(CO)₄^–anion,which is established to be a trigonal bipyramid with all of carbonyl ligands bonded to the iron center.The energy decomposition analysis in conjunction with natural orbital for chemical valence analysis reveals that the Ag–Fe bond in Ag Fe(CO)₄^–is better to be described as electron-sharing interaction.The charge-dependent and component-dependent trends in structures and bonding interactions revealed in this thesis will be benefit for the qualitative understanding of the CO adsorption on the metallic surface and the metal–metal bonding interactions.