On the structure of solid Ca(ND3)x; with x≈6

A nonlinear optical switch induced by an external electric field: inorganic alkaline–earth alkalide

Exploring a new type of nonlinear optical switch molecule with excess electron character is extremely important for promoting the application of excess electron compounds in the nonlinear optical (NLO) field. Here, we report external electric field (EEF) induced second-order NLO switch molecules of inorganic alkaline–earth alkalides, M(NH₃)₆Na₂ (M = Mg or Ca). The centrosymmetric structure of M(NH₃)₆Na₂ is destroyed in the presence of an EEF, and then a long-range charge transfer process occurs. It has been found that excess electrons are gradually transferred from one Na atom to the other Na atom through the inorganic metal cluster M(NH₃)₆. Finally, the excess electrons are completely located on one of the two Na atoms. In particular, the electronic contribution of the static first hyperpolarizability (β^e₀) for M(NH₃)₆Na₂ exhibits a large significant difference when the EEF is switched on. The β^e₀ value of M(NH₃)₆Na₂ is 0 when EEF = 0, while the peak β^e₀ values are 5.95 × 10⁶ (a.u.) for Mg(NH₃)₆Na₂ (EEF = 58 × 10⁻⁴ (a.u.)) and 1.83 × 10⁷ (a.u.) for Ca(NH₃)₆Na₂ (EEF = 53 × 10⁻⁴ (a.u.)). This work demonstrates that the compounds M(NH₃)₆Na₂ can serve as potential candidates for NLO switches.

The inorganic alkaline–earth alkalide M(NH₃)₆Na₂ (M = Mg or Ca) can serve as a potential candidate for a nonlinear optical switch.

A theoretical study on novel alkaline earth-based excess electron compounds: unique alkalides with considerable nonlinear optical responses

On the basis of stable alkaline earth metal ammines, a series of M(NH3)6NaCl and M(NH3)6Na2 (M = Mg and Ca) excess electron compounds were theoretically constructed and studied by using the density functional theory. The electride or alkalide characteristics of these compounds are verified by their electronic structures, HOMOs, and small VIE values. It is worth noting that the M(NH3)6Na2 alkalides have novel electronic structures that contain double alkali metal anions. As expected, all the noncentrosymmetric M(NH3)6NaCl and M(NH3)6Na2 compounds possess considerable first hyperpolarizabilities (β0) up to 123 050 au, which can be attributed to low excitation energies (ΔEs) and large oscillator strength (f0) of their crucial excited states. In addition, results reveal that the Ca(NH3)6-based species with lower ΔEs and larger transition moments (Δμ) show larger β0 values compared with the corresponding Mg(NH3)6-based ones with similar geometries. This study may be significant in terms of designing excess electron compounds of new-type, especially alkalides with multiple alkali metal anions.

The structure of calcium–ammonia solutions by neutron diffraction

The microscopic structures of calcium-ammonia solutions have been established by using neutron diffraction. Total structure factors measured at 230 K reveal immediately the evolution of an uncommonly intense diffraction prepeak in the metallic solutions. As concentration is increased from 4 mole percent metal to 10 mole percent metal (i.e., saturation), this feature intensifies and shifts from 0.6 to 0.9 A(-1). It is therefore evidence of well developed intermediate-range ordering among the solvated cations, and is a microstructural signature of the observed strong phase separation of metallic (concentrated) and nonmetallic (dilute) solutions. The technique of isotopic labelling of *N by 15N was then used in conjunction with difference analysis to focus on the solvent structure in metallic solutions at 4 and 10 mole percent metal. These nitrogen-centered functions are analyzed in conjunction with classical Monte Carlo computer simulation techniques, to provide us with detailed insight into the calcium solvation and the extent of hydrogen bonding. We find that calcium is solvated by approximately 6-7 ammonia molecules, with a Ca-N distance of around 2.45 A. There is evidence of hydrogen bonding among the solvent molecules, even in the saturated 10 mole percent metal solution.