Density Functional Theory Investigation On The Geometrical And Electronic Structures Of Group ?B Metal And Monooxide Carbonyl Complexes

Based on 18-electron rules,a series of stable and classical mononuclear metal carbonyl complexes Y?CO?₈⁺?Ti?CO?₇?Cr?CO?₆?Fe?CO?₅?Ni?CO?₄?Zn?CO?₃ have been verified by theoretical or experimental research.The Sc⁺,Y⁺and La⁺cations have similar electronic configurations.According to the 18-electron rules,the positive ions can adsorb eight CO ligands to form the 18-electrons d¹⁰s²p⁶rare gas stable electronic configuration.The author systematically studied M?CO?_m⁺,MO?CO?_n⁺?M=Sc,Y,La;m=1–9;n=1–8?series of carbonyl compounds using several different density functional methods.The geometric structures,electronic structures,vibration frequencies and thermochemical stability of these complexes were investigated,and their structural evolution was discussed.These results help us to understand the adsorption of CO molecules on the metal surface and the effect of CO adsorption on the electronic structure.Firstly,we systematically studied the structural evolution of the ground state configuration of the M?CO?_m⁺?M=Sc,Y,La;m=1–9?.The geometries of the complexes have been calculated and analyzed using three different density functional methods.We have analyzed bond distance,vibration frequencies and other information.At the same time,the rationality of our chosen methods has been comfirmed by the comparision between our calculations and the previously reported results.It's found that the ground state configurations of low coordination number metal cation carbonyl complexes are high-spin triplet states.The La⁺carbonyl complexes satisfy the 18-electron rules when it reaches the saturation coordination number.Then,we studied the MO?CO?_n⁺?M=Sc,Y,La;n=1–8?system,using the same methods as the pure metal carbonyl complexes,with the focus on their geometric configurations,bond length,vibration frequencies and thermochemical stability.The results show that the ground states of all configurations are low-spin singlet states.For this system,the MO⁺can chemisorb up to six CO ligands.In addition,through the infrared spectrum,we found that the carbonyl vibration frequencies of the two systems complexes of M?CO?_m⁺,MO?CO?_n⁺?M=Sc,Y,La;m=1–9;n=1–8?are obviously different.For M?CO?_m⁺?M=Sc,Y,La;m=1–9?,the carbonyl stretch vibrational frequencies show a significant red shift,while for MO?CO?_n⁺?M=Sc,Y,La;n=1–8?,the carbonyl stretch vibrational frequencies show a significant blue shift.Therefore,we performed an electronic structure analysis of the complexes about these two systems,including natural bond order?NBO?charge analysis and the energy decomposition analysis in conjunction with the natural orbital for chemical valence?EDA–NOCV?analysis,with the focus on the bond between metal and oxygen,metal and carbonyl.The results show that for the M?CO?_m⁺?M=Sc,Y,La;m=1–9?system,the bond between the metal cation and the carbonyl,the?back-donation accounts dominant part for the orbital bond interaction but for the interaction between the metal oxide and the carbonyl ligand,the?donation of the ligand to the metal oxide accounts dominant part.It clearly explains there are significant differences in the CO vibration frequencies of the two systems.Meanwhile,it's found that in the metal oxide carbonyl complexes,the oxygen atom serves as not two-electron donor but four-electron donor.Therefore,for MO?CO?_n⁺?M=Sc,Y,La;n=1–8?system,when the saturation chemisorption coordination number reaches 6,the metals satisfy the 18–electron rules.