Andris Erik, Navrátil Rafael, Jašík Juraj, Sabenya Gerard, Costas Miquel, Srnec Martin, Roithová Jana
Department of Organic Chemistry, Faculty of Science, Charles University, Hlavova 2030/8, 128 43, Prague 2, Czech Republic.
Departament de Quimica and Institute of Computational Chemistry and Catalysis (IQCC), University of Girona, Campus Montilivi, Girona, 17071, Spain.
Chemistry. 2018 Apr 6;24(20):5078-5081. doi: 10.1002/chem.201705307. Epub 2018 Jan 16.
We report for the first time infrared spectra of three non-heme pseudo-octahedral iron(V) nitride complexes with assigned Fe-N stretching vibrations. The intensities of the Fe-N bands in two of the complexes are extremely weak. Their detection was enabled by the high resolution and sensitivity of the experiments performed at 3 K for isolated complexes in the gas phase. Multireference CASPT2 calculations revealed that the Fe-N bond in the ground doublet state is influenced by two low-lying excited doublet states. In particular, configuration interaction between the ground and the second excited state leads to avoided crossing of their potential energy surfaces along the Fe-N coordinate, which thus affects the ground-state Fe-N stretching frequency and intensity. Therefore, DFT calculated Fe-N stretching frequency strongly depends on the amount of Hartree-Fock exchange potential. As a result, by tuning the amount of Hartree-Fock exchange potential in the B3LYP functional, it was possible to obtain theoretical spectra perfectly consistent with the experimental data. The theory shows that the intensity of the Fe-N stretching vibration can almost vanish due to strong coupling with other stretching modes of the ligands.
我们首次报道了三种具有指定Fe-N伸缩振动的非血红素伪八面体铁（V）氮化物配合物的红外光谱。其中两种配合物中Fe-N带的强度极其微弱。在3K下对气相中的孤立配合物进行的高分辨率和高灵敏度实验使得它们得以被检测到。多参考CASPT2计算表明，基态双重态中的Fe-N键受到两个低激发双重态的影响。特别是，基态与第二激发态之间的组态相互作用导致它们的势能面沿Fe-N坐标避免交叉，从而影响基态Fe-N伸缩频率和强度。因此，密度泛函理论（DFT）计算的Fe-N伸缩频率强烈依赖于哈特里-福克交换势的量。结果，通过调整B3LYP泛函中哈特里-福克交换势的量，可以获得与实验数据完美一致的理论光谱。理论表明，由于与配体的其他伸缩模式强烈耦合，Fe-N伸缩振动的强度几乎可以消失。
