Departamento de Fisica y Quimica Teorica, DEPg. Facultad de Quimica, Universidad Nacional Autonoma de Mexico, Mexico D.F., C.P. 04510, Mexico.
J Phys Chem A. 2010 Jan 14;114(1):21-8. doi: 10.1021/jp906131g.
The adsorption of benzene on the magnetic Fe(6) cluster was studied by means of first principles all-electron calculations done with gradient corrected density functional theory. In the M = 2S + 1 = 13 (S is the total spin) ground state (GS) of Fe(6)-(C(6)H(6))(3) each benzene is bonded with one Fe atom, forming eta(6) coordinations with C-Fe contacts of 2.12-2.17 A; though the Fe(6) cluster structure is preserved, it presents more distortion than in bare Fe(6). The M = 13 GS of Fe(6)-(C(6)H(6))(4) shows a more distorted geometry with three eta(6) and one eta(2) coordinations, as the bonding with the fourth benzene was reduced to two C-Fe bonds. Thus, Fe(6)-(C(6)H(6))(4) may be viewed as a Fe(6) core covered by a layer of benzene molecules. The d-pi bonding interactions are clearly reflected by the estimated adiabatic ionization energies (4.60 and 4.42 eV for m = 3 and 4, respectively), because they are significantly smaller than that of bare Fe(6), 6.15 eV. The adiabatic electron affinities also are diminished clearly, 1.02 and 1.13 eV, for m = 3 and 4, respectively, as compared to that of Fe(6), 1.61 eV. The magnetic moments of the Fe(6)-(C(6)H(6))(3,4) complexes are strongly quenched, by 8.0 magneton bohrs (mu(B)), with respect to the value, 20.0 mu(B), of the isolated Fe(6) cluster. Lastly, the vibrational spectra show IR bands placed near those of free benzene and several forbidden IR modes of benzene turn IR active in the reduced symmetry of the complexes.
采用基于梯度修正密度泛函理论的第一性原理全电子计算方法研究了苯在磁性 Fe(6)团簇上的吸附。在 M = 2S + 1 = 13（S 是总自旋）基态（GS）中，每个苯与一个 Fe 原子键合，形成 C-Fe 接触距离为 2.12-2.17 A 的 eta(6)配位；尽管 Fe(6)团簇结构得以保留，但它比裸 Fe(6)表现出更多的扭曲。Fe(6)-(C(6)H(6))(4) 的 M = 13 GS 显示出更扭曲的几何形状，具有三个 eta(6)和一个 eta(2)配位，因为与第四个苯的键合减少到两个 C-Fe 键。因此，Fe(6)-(C(6)H(6))(4)可以看作是被苯分子层覆盖的 Fe(6)核。通过估算的绝热电离能（m = 3 和 4 时分别为 4.60 和 4.42 eV）清楚地反映了 d-pi 键合相互作用，因为它们明显小于裸 Fe(6)的 6.15 eV。绝热电子亲合能也明显降低，m = 3 和 4 时分别为 1.02 和 1.13 eV，而 Fe(6)的电子亲合能为 1.61 eV。与孤立的 Fe(6)团簇相比，Fe(6)-(C(6)H(6))(3,4)复合物的磁矩被强烈猝灭，为 8.0 磁子玻尔（mu(B)），而孤立的 Fe(6)团簇的磁矩为 20.0 mu(B)。最后，振动光谱显示 IR 带位于游离苯的附近，几个苯的禁阻 IR 模式在复合物的简并对称性下变成 IR 活性。
