Branson Jacob A, Smith Patrick W, Sergentu Dumitru-Claudiu, Russo Dominic R, Gupta Himanshu, Booth Corwin H, Arnold John, Schelter Eric J, Autschbach Jochen, Minasian Stefan G
Department of Chemistry, University of California, Berkeley, Berkeley, California 94720, United States.
Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.
J Am Chem Soc. 2024 Sep 18;146(37):25640-25655. doi: 10.1021/jacs.4c07459. Epub 2024 Sep 6.
The 4f orbitals of Ce(IV) have shown appreciably enhanced covalent mixing with ligand orbitals relative to those of Ce(III). Here, X-ray spectroscopy, magnetic susceptibility measurements, and theoretical methods are used to investigate 4f covalency in CeF and CeCl. These techniques show covalent mixing between Ce 4f and F 2p orbitals to be about 25% less than mixing between Ce 4f and Cl 3p orbitals, placing CeF among the most ionic Ce(IV) compounds to-date. However, ligand field analysis using the experimental data shows significantly higher 4f orbital overlap with the F 2p orbitals compared to the Cl 3p. This result is counterintuitive since the Ce-F bonds display less 4f covalency despite their higher orbital overlap, and greater overlap is traditionally associated with enhanced bond covalency. The weaker covalency is attributed to the large energy gap between Ce 4f and F 2p orbitals strongly counteracting the higher orbital overlap. These results highlight that only a concerted consideration of both atomic orbital overlap and energy matching in f-element systems leads to an accurate picture of their bonding.
相对于Ce(III)的4f轨道，Ce(IV)的4f轨道与配体轨道的共价混合明显增强。在此，利用X射线光谱、磁化率测量和理论方法研究了CeF和CeCl中的4f共价性。这些技术表明，Ce 4f与F 2p轨道之间的共价混合比Ce 4f与Cl 3p轨道之间的混合少约25%，这使得CeF成为迄今为止离子性最强的Ce(IV)化合物之一。然而，使用实验数据进行的配体场分析表明，与Cl 3p相比，Ce 4f与F 2p轨道的重叠明显更高。这一结果与直觉相反，因为尽管Ce-F键的轨道重叠更高，但它们的4f共价性却更低，而传统上更大的重叠与增强的键共价性相关。较弱的共价性归因于Ce 4f与F 2p轨道之间的大能量间隙强烈抵消了较高的轨道重叠。这些结果突出表明，只有同时考虑f元素体系中的原子轨道重叠和能量匹配，才能准确了解它们的键合情况。
