The complexant shape effect on first (hyper)polarizability of alkalides Li+ (NH2 CH3 )4 M− (M = Li, Na, and K)

Abstract

In our previous work, new alkalides Li+(calix [4]pyrrole)M− with cup-like complexant have been reported for the large static first hyperpolarizabilities (β0) (Chen et al., J Am Chem Soc 2006, 128, 1072). In this work, new inorganic alkalides are found by using a more flexible complexant, methylamine (NH2CH3)4. The structures with all real frequencies and β0 values of the inorganic alkalides Li+(cage [4]methylamine)M− (M = Li, Na, and K) are obtained at MP2 level. The result shows that these inorganic alkalides have more considerable β0 values to be 18,825 (M = Li) < 27,942 (M = Na) < 81,094 au (M = K), which are more than two times larger than those (10,969 ∼ 35,934 au) of the reported alkalides Li+(calix [4]pyrrole)M−. To understand this structure–property relationship, two cup-like Li+(NH2CH3)4M− (M = Li, Na, and K) models are designed to compare their β0 values. By comparing the β0 values among the cup-like alkalides Li+(calix [4]pyrrole)M−, Li+(NH2CH3)4M−, and cage-like alkalides Li+(cage [4]methylamine)M− (M = Li, Na, and K), the complexant shape effect of alkalides has been revealed. It is found that the complexant shape is an important factor in large β0 values. Moreover, the monotonic dependences of β0 on the Li–M distance and the NBO charges of cation (Li+) and anions (M−) in inorganic alkalides Li+(cage [4]methylamine)M− have been shown. In this work, the frequency dependent first (hyper)polarizabilities are also determined. It is found that both the frequency dispersion and the effects of the electron correlation are strong. Moreover, the dependence of both the static and frequency dependent β on the atomic number of alkali metal anions is similar. This work provides a new way to understand the nature of high-performance nonlinear optical (NLO) materials, and it is helpful to design new NLO materials. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011.