Publication Date:
2016-06-28
Description:
Superalkali cations, known to possess low vertical electron affinities (VEAs), high vertical detachment energies, and large highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) energy gaps, are intriguing chemical species. Thermodynamically, such species need to be the global minima in order to serve as the promising targets for experimental realization. In this work, we propose the strategies of polyhalogenation and polyalkalination for designing the superalkali cations. By applying these strategies, the local-minimum planar pentacoordinate carbon (ppC) cluster CBe 5 can be modified to form a series of star-like superalkali ppC or quasi-ppC CBe 5 X 5 + (X = F, Cl, Br, Li, Na, K) cations containing a CBe 5 moiety. Polyhalogenation and polyalkalination on the CBe 5 unit may help eliminate the high reactivity of bare CBe 5 molecule by covering the reactive Be atoms with noble halogen anions and alkali cations. Computational exploration of the potential energy surfaces reveals that the star-like ppC or quasi-ppC CBe 5 X 5 + (X = F, Cl, Br, Li, Na, K) clusters are the true global minima of the systems. The predicted VEAs for CBe 5 X 5 + range from 3.01 to 3.71 eV for X = F, Cl, Br and 2.12–2.51 eV for X = Li, Na, K, being below the lower bound of the atomic ionization potential of 3.89 eV in the periodic table. Large HOMO-LUMO energy gaps are also revealed for the species: 10.76–11.07 eV for X = F, Cl, Br and 4.99–6.91 eV for X = Li, Na, K. These designer clusters represent the first series of superalkali cations with a ppC center. Bonding analyses show five Be–X–Be three-center two-electron (3c-2e) σ bonds for the peripheral bonding, whereas the central C atom is associated with one 6c-2e π bond and three 6c-2e σ bonds, rendering (π and σ) double aromaticity. Born-Oppenheimer molecular dynamics simulations indicate that the CBe 5 motif is robust in the clusters. As planar hypercoordination carbon species are often thermodynamically unstable and highly reactive, the superalkali cation characters of these ppC species should be highlighted, which may be suitable for experimental realization.
Print ISSN:
0021-9606
Electronic ISSN:
1089-7690
Topics:
Chemistry and Pharmacology
,
Physics
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