Theoretical investigation of perfect fullerene-like borospherene -B protected by alkaline earth metal: multi-layered spherical electride molecules as electric field manipulated second-order nonlinear optical switches.

For the challenge of stabilizing a fullerene-like borospherene, a perfect fullerene-like borospherene B20 with Ih symmetry is stabilized theoretically for the first time by selected 12 η5 (pentahapto)-Mg atoms capped on the 12 B5 pentagons, forming an exohedral metalloborospherene Ih Mg12&B20 molecule. Owing to the pull-push electron transfer relay, the molecule is converted to a spherical electride molecule (Mg2+)12&B2018- + 6e- with multiexcess electrons and high-valent B2018- polyanion with a full-shell electronic configuration, performing the stabilization of the fullerene-like B20 cage. Furthermore, we embed the metal M atom in the B20 cage, forming new endohedral electride molecules (Mg2+)12&(Mn+@B2018-) + (6 + n)e- (M = Li, n = 1 and Mg, n = 2). The embedded atom M increases the excess electron number. Notably, these electride molecules possess two different types of superatomic characteristics, exhibiting the behavior of an electron reservoir. Moreover, a compound (Mg12&B20)2O is designed and obtained, so Mg12&B20 might serve as a nano-building block. In addition, the Mg12&B20 and Mg12&(Mg@B20) electride molecules are efficient external electric field-manipulated nonlinear optical (NLO) switches with high sensitivity and reversibility. The embedding metal atom in the B20 cage can also serve as a new strategy to manipulate NLO switching.