Mason Jarrett L, Harb Hassan, Huizenga Caleb D, Ewigleben Joshua C, Topolski Josey E, Hratchian Hrant P, Jarrold Caroline Chick
Department of Chemistry , Indiana University , 800 East Kirkwood Avenue , Bloomington , Indiana 47405 , United States.
Department of Chemistry and Chemical Biology , University of California, Merced , 5200 North Lake Road , Merced , California 95343 , United States.
J Phys Chem A. 2019 Mar 14;123(10):2040-2048. doi: 10.1021/acs.jpca.8b12399. Epub 2019 Mar 1.
The electronic and molecular structure of the CeB molecular unit has been probed by anion PE spectroscopy and DFT calculations to gain insight into structural and electronic relaxation on edge and corner sites of this ionic material. While boron in bulk lanthanide hexaboride materials assumes octahedral B units, the monomer assumes a less compact structure to delocalize the charge. Two competitive molecular structures were identified for the anion and neutral species, which include a boat-like structure and a planar or near-planar teardrop structure. Ce adopts different orbital occupancies in the two isomers; the boat-like structure has a 4f superconfiguration while the teardrop favors a 4f 6s occupancy. The B ligand in these structures carries a charge of -4 and -3, respectively. The teardrop structure, which was calculated to be isoenergetic with the boat structure, was most consistent with the experimental spectrum. B-local orbitals crowd the energy window between the Ce 4f and 6s (HOMO) orbitals. A low-lying transition from the B-based orbitals is observed slightly less than 1 eV above the ground state. The results suggest that edge and corner conductivity involves stabilized, highly diffuse 6s orbitals or bands rather than the bulk-favored 5d band. High-spin and open-shell low-spin states were calculated to be very close in energy for both the anion and neutral, a characteristic that reflects how decoupled the 4f electron is from the B 2p- and Ce 6s-based molecular orbitals.
通过阴离子光电子能谱和密度泛函理论计算对CeB分子单元的电子和分子结构进行了探究，以深入了解这种离子材料边缘和角落位置的结构和电子弛豫。虽然块状镧系六硼化物材料中的硼呈现八面体B单元，但单体呈现出较松散的结构以使电荷离域。已确定了阴离子和中性物种的两种竞争分子结构，包括船状结构和平面或近平面泪滴状结构。Ce在两种异构体中采用不同的轨道占据情况；船状结构具有4f超构型，而泪滴状结构倾向于4f 6s占据。这些结构中的B配体分别带有-4和-3的电荷。计算得出泪滴状结构与船状结构能量相同，这与实验光谱最为一致。B局部轨道聚集在Ce 4f和6s（最高占据分子轨道）之间的能量窗口内。在基态上方略低于1 eV处观察到从基于B的轨道的低能跃迁。结果表明，边缘和角落导电性涉及稳定的、高度弥散的6s轨道或能带，而不是块状材料中占主导的5d能带。计算得出阴离子和中性物种的高自旋态和开壳层低自旋态在能量上非常接近，这一特征反映了4f电子与基于B 2p和Ce 6s的分子轨道的解耦程度。
