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  1. Abstract

    The discovery of borospherenes unveiled the capacity of boron to form fullerene-like cage structures. While fullerenes are known to entrap metal atoms to form endohedral metallofullerenes, few metal atoms have been observed to be part of the fullerene cages. Here we report the observation of a class of remarkable metallo-borospherenes, where metal atoms are integral parts of the cage surface. We have produced La3B18and Tb3B18and probed their structures and bonding using photoelectron spectroscopy and theoretical calculations. Global minimum searches revealed that the most stable structures of Ln3B18are hollow cages withD3hsymmetry. The B18-framework in the Ln3B18cages can be viewed as consisting of two triangular B6motifs connected by three B2units, forming three shared B10rings which are coordinated to the three Ln atoms on the cage surface. These metallo-borospherenes represent a new class of unusual geometry that has not been observed in chemistry heretofore.

     
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  2. Abstract

    Multiple bonds between boron and transition metals are known in many borylene (:BR) complexes via metal dπ→BR back‐donation, despite the electron deficiency of boron. An electron‐precise metal–boron triple bond was first observed in BiB2O[Bi≡B−B≡O]in which both boron atoms can be viewed as sp‐hybridized and the [B−BO]fragment is isoelectronic to a carbyne (CR). To search for the first electron‐precise transition‐metal‐boron triple‐bond species, we have produced IrB2Oand ReB2Oand investigated them by photoelectron spectroscopy and quantum‐chemical calculations. The results allow to elucidate the structures and bonding in the two clusters. We find IrB2Ohas a closed‐shell bent structure (Cs,1A′) with BOcoordinated to an Ir≡B unit, (OB)Ir≡B, whereas ReB2Ois linear (C∞v,3Σ) with an electron‐precise Re≡B triple bond, [Re≡B−B≡O]. The results suggest the intriguing possibility of synthesizing compounds with electron‐precise M≡B triple bonds analogous to classical carbyne systems.

     
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  3. Abstract

    In a high‐resolution photoelectron imaging and theoretical study of the IrB3cluster, two isomers were observed experimentally with electron affinities (EAs) of 1.3147(8) and 1.937(4) eV. Quantum calculations revealed two nearly degenerate isomers competing for the global minimum, both with a B3ring coordinated with the Ir atom. The isomer with the higher EA consists of a B3ring with a bridge‐bonded Ir atom (Cs,2A′), and the second isomer features a tetrahedral structure (C3v,2A1). The neutral tetrahedral structure was predicted to be considerably more stable than all other isomers. Chemical bonding analysis showed that the neutralC3visomer involves significant covalent Ir−B bonding and weak ionic bonding with charge transfer from B3to Ir, and can be viewed as an Ir–(η3‐B3+) complex. This study provides the first example of a boron‐to‐metal charge‐transfer complex and evidence of a π‐aromatic B3+ring coordinated to a transition metal.

     
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  4. null (Ed.)
  5. null (Ed.)
    Size-selected negatively-charged boron clusters (B n − ) have been found to be planar or quasi-planar in a wide size range. Even though cage structures emerged as the global minimum at B 39 − , the global minimum of B 40 − was in fact planar. Only in the neutral form did the B 40 borospherene become the global minimum. How the structures of larger boron clusters evolve is of immense interest. Here we report the observation of a bilayer B 48 − cluster using photoelectron spectroscopy and first-principles calculations. The photoelectron spectra of B 48 − exhibit two well-resolved features at low binding energies, which are used as electronic signatures to compare with theoretical calculations. Global minimum searches and theoretical calculations indicate that both the B 48 − anion and the B 48 neutral possess a bilayer-type structure with D 2h symmetry. The simulated spectrum of the D 2h B 48 − agrees well with the experimental spectral features, confirming the bilayer global minimum structure. The bilayer B 48 −/0 clusters are found to be highly stable with strong interlayer covalent bonding, revealing a new structural type for size-selected boron clusters. The current study shows the structural diversity of boron nanoclusters and provides experimental evidence for the viability of bilayer borophenes. 
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  6. null (Ed.)
    While rare-earth borides represent a class of important materials in modern industries, there are few fundamental researches on their electronic structures and physicochemical properties. Recently we have performed combined experimental and theoretical studies on rare-earth boron clusters and their cluster-assembled complexes, revealing a series of rare-earth inverse sandwich clusters with fascinating electronic structures and chemical bonding patterns. In this overview article, we summarize recent progresses in this area and provide a perspective view on the future development of rare-earth boride clusters. Understanding the electronic structures of these clusters helps to design materials of f-element (lanthanide and actinide) borides with critical physiochemical properties. 
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