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－１，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ＮＨ４＋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－１。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ＦｅＣ键缩短，ＣＯ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。Ｍｕｌｉｋｅｎ布居分析同样表明，在ＨＦｅ（ＣＯ）５＋电离Ｈ＋后，Ｆｅ和Ｃ之间的Ｍｕｌｉｋｅｎ键级增加。
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 E PA of Fe(CO) 5 is estimated as 751.6 kJ·mol -1 from the results of NL/LDA. The E PA of Fe(CO) 5 is in between those of HCN and NH 3, which gives an explanation to the experimental facts that, on the one hand, Fe(CO) 5 snatches a proton from H 2CN + conveniently, on the 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 C 4v point group symmetry of Fe(CO) 5 in HFe(CO) 5 + to D 3h 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 -1 .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 C Fe bond length and lengthening of the O C 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 C Fe bond orders increase and the O C bond orders decrease after ionization of H + from HFe(CO) 5 +.
出处
《北京大学学报（自然科学版）》
CAS
CSCD
北大核心
1996年第6期686-692,共7页
Acta Scientiarum Naturalium Universitatis Pekinensis
基金
国家自然科学基金
关键词
密度泛函
量子化学
金属羰基化合物
电离反应
density functional theory
proton affinity
geometry optimization
HFe(CO) 5 +
