Acta Scientiarum Naturalium Universitatis Pekinensis

Previous Articles     Next Articles

Density Functional Thery Study on Proton Ionization Reaction of HFe(CO)+5

DENG Yuqing, CHEN Zhida, WANG Xiuzhen, LI Lemin, XU Guangxian   

  1. Department of Chemistry; State key Laboratory of Rare Earth Materials Chemistry and Application, Peking University, Beijing, 100871
  • Received:1996-03-25 Online:1996-11-20 Published:1996-11-20



  1. 北京大学化学系,稀土材料化学及应用国家重点实验室,北京,100871

Abstract: The geometry configurations of HFe(CO)+5 and Mn(CO)-5 are optimized with density functional method at LDA and NL/LDA approximation levels. The proton affinity EPA of Fe(CO)5 is estimated as 751.6kJ/mol from the results of NL/LDA. The EPA of Fe(CO)5 is in between those of HCN and NH3, which gives an explanation to the experimental facts that, on the one hand, Fe(CO)5 snatches a proton from H2CN+ conveniently, onthe other hand, it is impossible to transfer proton from NH+4 to Fe(CO)5. There is symmetry transformation of geometry configuration involving in the proton ionization reaction of HFe(CO)+5 ,i.e. from C4v point group symmetry of Fe(CO)5 in HFe(CO)+5 to D3h of free Fe(CO)5, which is similar to the geometry relaxation in proton ionization of isoelectronic HMn(CO)5. The calculated relaxation energy for the molecular fragment Fe(CO)5 is -59.78kJ/mol. Our investigation also shows that the backdonated π bonding,Fe→CO,is strengthened after ionization of H+ from HFe(CO)+5 ,leading to the shortening of the Fe--C bond length and lengthening of the C--O bond length; synchronously, the electron charge distributed on the Fe atom decreases, while negative charges on the C and O atoms increase. The Mulliken population analysis gives the same tendency, i.e. the F--C bond orders increase and the C--Obond orders decrease after ionization of H+ from HFe(CO)+5 .

Key words: density functional theory, proton affinity, geometry optimization, HFe(CO)+5

摘要: 用密度泛函方法(DFT)的LDA和NL/LDA优化分子片试剂HFe(CO)+5和Mn(CO)-5的几何结构,并计算了Fe(CO)5的NL/LDA质子亲合能,其值为751.6kJ/mol,介于文献报道的HCN和NH3的质子亲合能之间,解释了Fe(CO)5容易从H2CN+中得到质子而难以由 NH+4夺得质子的实验事实。HFe(CO)+5电离H+后其几何结构由 C4v 对称性变为D3h对称性,与等电子体 HMn(CO)5电离H+后几何构型的弛豫相类似。NL/LDA计算的分子片 Fe(CO)5的弛豫能为 -59.78kJ/mol。计算结果还表明,HFe(CO)+5电离H+后Fe→CO反馈 π键得到加强,使得 Fe--C键缩短,C--O键增长;同时,Fe原子上的电子电荷减少,而C和O原子上的电子电荷增加。Mulliken布居分析同样表明,在HFe(CO)+5电离H+后, Fe和C之间的Mulliken键级增加,C和O原子之间的键级减少。

关键词: 密度泛函, 质子亲合能, 优化几何结构, HFe(CO)+5

CLC Number: