Gas-phase electronic absorption spectroscopy of substituted bis(η6-benzene)chromium derivatives: Rydberg transitions in bis(η6-anisole)chromium and bis(η6-2,6-dimethylpyridine)chromium
作者:S. Yu. Ketkov、G. A. Domrachev、A. M. Ob’edkov、A. Yu. Vasil’kov、L. P. Yur’eva、C. P. Mehnert
DOI:10.1007/s11172-005-0051-8
日期:2004.9
Gas-phase electronic absorption spectra of chromium bisarene complexes with oxygen- and nitrogen-containing ligands, (η6-PhOMe)2Cr (1) and (η6-2,6-Me2C5H3N)2Cr (2), were first measured. Rydberg bands disappearing on going to the condensed-phase spectra were revealed. The first ionization potentials of complexes 1 and 2 (5.30 and 5.40 eV, respectively) were determined from the Rydberg frequencies. The Rydberg transitions were assigned and the corresponding Rydberg term values and quantum defects were determined. The effect of heteroatoms on the Rydberg structure parameters was revealed by comparing the spectra of complexes 1 and 2 with those of unsubstituted analogs. The appearance, in the ligand side chain, of an oxygen atom capable of being involved in conjugation with the π-electron system of the aromatic ring results in substantial broadening of the observed Rydberg bands. This can be associated with an increased ligand contribution to the HOMO of the sandwich compound. The influence of the oxygen atom on the ionization energy of the molecule is insignificant. In contrast to this, introduction of a nitrogen atom into the carbocycle leads to a noticeable increase in the ionization potential of the molecule, while the ligand contribution to the HOMO of the complex remains practically unchanged.
首先测量了含氧和含氮配体的二茂铬配合物(η6-PhOMe)2Cr(1)和(η6-2,6-Me2C5H3N)2Cr(2)的气相电子吸收光谱。发现瑞德堡带在进入凝聚态光谱时消失。根据瑞德堡频率确定了配合物1和2的首次电离电位(分别为5.30和5.40 eV)。确定了瑞德堡跃迁,并确定了相应的瑞德堡项值和量子缺陷。通过比较配合物1和2与未取代类似物的光谱,揭示了杂原子对瑞德堡结构参数的影响。配体侧链中氧原子的出现能够与芳香环的π电子系统共轭,导致观察到的瑞德堡带大幅变宽。这可能与配体对三明治化合物HOMO的贡献增加有关。氧原子对分子电离能的影响微不足道。与此相反,在碳环中引入氮原子会导致分子的电离电位明显增加,而配体对配合物HOMO的贡献几乎保持不变。