期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2018
卷号：115
期号：30
页码：E6972-E6977
DOI：10.1073/pnas.1806476115
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：While boron forms a wide range of metal borides with important industrial applications, there has been relatively little attention devoted to lanthanide boride clusters. Here we report a joint photoelectron spectroscopy and quantum chemical study on two octa-boron di-lanthanide clusters, Ln2B8− (Ln = La, Pr). We found that these clusters form highly stable inverse sandwich structures, [Ln–B8–Ln]−, with strong Ln and B8 bonding via interactions between the Ln 5d orbitals and the delocalized σ and π orbitals on the B8 ring. A (d–p)δ bond, involving the 5dδ and the antibonding π orbital of the B8 ring, is observed to be important in the Ln–B8 interactions. The highly symmetric inverse sandwich structures are overwhelmingly more stable than any other isomers. Upon electron detachment, the (d–p)δ orbitals become half-filled, giving rise to a triplet ground state for neutral La2B8. In addition to the two unpaired electrons in the (d–p)δ orbitals upon electron detachment, the neutral Pr2B8 complex also contains two unpaired 4f electrons on each Pr center. The six unpaired spins in Pr2B8 are ferromagnetically coupled to give rise to a septuplet ground state. The current work suggests that highly magnetic Ln…B8…Ln inverse sandwiches or 1D Ln…B8…Ln nanowires may be designed with novel electronic and magnetic properties.
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