A novel class of compounds—superalkalides: M+(en)3M3′O− (M, M′ = Li, Na, and K; en = ethylenediamine)—with excellent nonlinear optical properties and high stabilities

Abstract

With the aid of ab initio calculations at the MP2 level of theory, we designed a novel class of inorganic salts, M⁺(en)₃M₃′O⁻ (M, M′ = Li, Na, and K), by using the M₃′O superalkalis. These compounds are the first examples of inorganic salts wherein the superalkali occupies the anionic site, and termed superalkalides. The electronic structural features of the M⁺(en)₃M₃′O⁻ superalkalides are very similar to those of the corresponding M⁺(en)₃M′⁻ alkalides which have been reported by Zurek (J. Am. Chem. Soc., 2011, 133, 4829). In this study, the calculated NLO properties of M⁺(en)₃M₃′O⁻ and M⁺(en)₃M′⁻ (M, M′ = Li, Na, and K) show that both superalkalides and alkalides have significantly large first hyperpolarizabilities (β₀) with the values in the range of 7.80 × 10³ to 9.16 × 10⁴ a.u. and 7.95 × 10³ to 1.84 × 10⁵ a.u., respectively. Computations on the stabilities of M⁺(en)₃M₃′O⁻ and M⁺(en)₃M′⁻ demonstrate that the M⁺(en)₃M₃′O⁻ superalkalides are preferably stable than the corresponding M⁺(en)₃M′⁻ alkalides because of the presence of hydrogen bonds in M⁺(en)₃M₃′O⁻. Therefore, the designed superalkalides, M⁺(en)₃M₃′O⁻ (M, M′ = Li, Na, and K), with excellent nonlinear optical properties and high stabilities are greatly promising candidates for NLO materials. We hope that this article could attract more research interest in superatom chemistry and for further experimental research.