Cao Rui, Thomas Kolle E, Ghosh Abhik, Sarangi Ritimukta
Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Stanford University Menlo Park California 94025 USA
Department of Chemistry, UiT - the Arctic University of Norway N-9037 Tromsø Norway
RSC Adv. 2020 May 29;10(35):20572-20578. doi: 10.1039/d0ra02335c. eCollection 2020 May 27.
A combination of Cr K-edge XAS and DFT calculations have been performed on archetypal chromium porphyrinoid complexes Cr[TMP]O (2) and Cr[TPC]O (3), and the results have been compared to the reference compound Cr[TPP]Cl (1), where TPP, TMP, and TPC are the anions of -tetraphenylporphyrin, -tetramesitylporphyrin, and -triphenylcorrole, respectively. The intensity-weighted average energy position in 1 (5990.9 eV), 2 (5992.0 eV) and 3 (5992.6 eV) are consistent with increasing the metal oxidation state along the series. EXAFS and theoretical analysis of 2 and 3 reveal that the Cr-O bond is longer and weaker in 3 relative to 2, despite the structural similarity and increase in oxidation state in 3. This is also reflected in a comparison of the Cr K-pre-edge transitions. The roughly twenty-fold increase in intensity in the two oxo complexes is unsurprising and well-precedented for other first-row transition metals. However, although 3 had greater overall intensity, the intensity of transitions along the Cr-O bond is greater. EXAFS, DFT and TDDFT analyses show that the more contracted N core of the corrole results in a greater out-of-plane displacement of the Cr in 3 relative to 2, which in turn accentuates the lower local symmetry of the Cr in 3 relative to 2. This difference helps us to appreciate the TDDFT result that whereas two 1s→ 3d transitions make up the majority of the intensity in the pre-edge of 2, the pre-edge of 3 also includes fairly intense transitions to molecular orbitals with 3d , 3d and 3d character, thus accounting for the somewhat higher overall intensity for 3.
已对典型的铬卟啉类配合物Cr[TMP]O（2）和Cr[TPC]O（3）进行了Cr K边X射线吸收光谱（XAS）和密度泛函理论（DFT）计算，并将结果与参考化合物Cr[TPP]Cl（1）进行了比较，其中TPP、TMP和TPC分别是 - 四苯基卟啉、 - 四甲基卟啉和 - 三苯基卟吩的阴离子。1（5990.9 eV）、2（5992.0 eV）和3（5992.6 eV）中强度加权平均能量位置与该系列中金属氧化态的增加一致。对2和3的扩展X射线吸收精细结构（EXAFS）和理论分析表明，尽管3的结构相似且氧化态增加，但相对于2，3中的Cr - O键更长且更弱。这也反映在Cr K边前边缘跃迁的比较中。两种含氧配合物中强度大约增加了二十倍并不奇怪，并且其他第一行过渡金属也有类似情况。然而，尽管3的整体强度更大，但沿Cr - O键的跃迁强度更大。EXAFS、DFT和含时密度泛函理论（TDDFT）分析表明，卟吩中更收缩的N核导致3中Cr相对于2有更大的面外位移，这反过来又加剧了3中Cr相对于2较低的局部对称性。这种差异有助于我们理解TDDFT结果，即虽然两个1s→3d跃迁构成了2的前边缘强度的大部分，但3的前边缘还包括到具有3d 、3d 和3d特征的分子轨道的相当强的跃迁，因此3的整体强度略高。
