Valencia Israel, Guevara-García Alfredo, Castro Miguel
Departamento de Física y Química Teórica, DEPg, Facultad de Química, Universidad Nacional Autónoma de México, México D. F., C. P. 04510, México.
J Phys Chem A. 2009 Jun 4;113(22):6222-38. doi: 10.1021/jp811065w.
The interactions of one and two benzene molecules with the superparamagnetic Fe(6) cluster were studied by means of gradient-corrected density functional theory. The ground state, GS, of bare Fe(6) presents a distorted octahedral structure with 2S = 20; S is the total spin. For the calculated 2S = 16 GS of the neutral Fe(6)-C(6)H(6) complex, as well as in the positive and negative ions both with 2S = 15, the benzene unit is adsorbed on one axial Fe(a) atom. The 2S = 14 GS for Fe(6)-(C(6)H(6))(2) resembles a sandwich structure, with the metal Fe(6) cluster separating the benzene rings that are bonded symmetrically on the two axial sites of Fe(6). The binding is accounted for by electrostatic interactions and by 3d-pi bonds, as revealed by the molecular orbitals. Though each C-Fe bond is weak, eta(6) coordinations were indicated by the topology of the electronic density. The 3d-pi bonding is reflected by the adiabatic ionization energies and electron affinities, which are smaller than those of bare Fe(6). The computed IR spectra show vibrational bands near those of bare benzene; some forbidden IR modes in benzene and in Fe(6) become IR active in Fe(6)-(C(6)H(6))(1,2). The results show a strong perturbation of the electronic structure of Fe(6). The decrease of its magnetic moment implies that the magnetic effects play an important role in the adsorption of benzene.
通过梯度校正密度泛函理论研究了一个和两个苯分子与超顺磁性Fe(6)团簇的相互作用。裸Fe(6)的基态（GS）呈现出扭曲的八面体结构，2S = 20；S为总自旋。对于计算得到的中性Fe(6)-C(6)H(6)配合物的2S = 16 GS，以及2S = 15的正离子和负离子，苯单元吸附在一个轴向Fe(a)原子上。Fe(6)-(C(6)H(6))(2)的2S = 14 GS类似于夹心结构，金属Fe(6)团簇将对称键合在Fe(6)两个轴向位置上的苯环隔开。如分子轨道所示，这种结合是由静电相互作用和3d-π键引起的。尽管每个C-Fe键都很弱，但电子密度拓扑结构表明存在η(6)配位。3d-π键合由绝热电离能和电子亲和能反映，它们比裸Fe(6)的绝热电离能和电子亲和能小。计算得到的红外光谱显示出靠近裸苯的振动带；苯和Fe(6)中一些禁阻的红外模式在Fe(6)-(C(6)H(6))(1,2)中变为红外活性。结果表明Fe(6)的电子结构受到强烈扰动。其磁矩的减小意味着磁效应在苯的吸附中起重要作用。
