Theoretical Study On Periodic Trends Of Oxidation States, Electronic Structures And Catalytic Mechanism Of 3d Transition Metal Complexes

This thesis is divided into four chapters,in which density functional theory?DFT?computational calculations were carried out to study the geometrical configurations and electronic structures of a series of bis-?2,6-diimino-pyridine?metal divalent cations([ML₂]²⁺) containing all the 3d transition metals?Sc to Zn?,to identify and reveal the oxidation state of every complex and chemical bonding.Besides,the primary discussion for the electrocatalytic reaction mechanism of CO2 reduction on[ML]²⁺was given.The first chapter mainly introduced the background and significance of this study for[ML₂]²⁺.In the second chapter,we described the theoretical calculation methods,basis sets and related software of them briefly in this dissertation.The third chapter,focused on the geometrical configurations,electronic structures and chemical bonding for[ML₂]²⁺complexes based on DFT method.The results showed that under different spin multiplicity,ground state of complexes are the singlet[FeL₂]²⁺and[ZnL₂]²⁺,the doublet[ScL₂]²⁺,[CoL₂]²⁺and[CuL₂]²⁺,the triplet[TiL₂]²⁺,[CrL₂]²⁺and[NiL₂]²⁺,the quartet[VL₂]²⁺and the sextet[MnL₂]²⁺,respectively.Besides,we drew the conclusion that the oxidation states of Sc,Ti,Cr are+III in[ScL₂]²⁺,[TiL₂]²⁺and[CrL₂]²⁺complexes,while the rest of central 3d metal atoms possess+II oxidation states.The early 3d transition metal complexes showed in this work have not been reported in previous work for the[ML₂]²⁺?M=Sc-Cr?.In order to study the character of chemical bonding deeply,we gave the radial distribution functions of each atomic orbital?AO?and energy decomposition analysis?EDA?.From these analysis,it can be found that the overlap will be less efficient for 3d orbitals with ligand,so that the centred metal oxidation decreased gradually and the metal-ligand?M-N?bonds have more covalent character in all the considered complexes.In fourth chapter,we mainly investigated the electrocatalytic reaction mechanism of CO₂ reduction on[ScL]²⁺complex.It showed that we got two channels which produced*CO and*HCOOH,and the reaction channel of generating*HCOOH is the dominant channels related in the Proton-Coupled Electron-Transfer?PECT?progress.Based on these,we mainly discussed the reaction mechanism of the dominant reaction channels.Furthermore,we drew the conclusion that the two pathways of generating the CH₄ and CH₃OH are competitive reaction channels in the process of CO₂ reduction,where the reaction channel that generates CH₃OH is preferred.