Alkali-Metal-Free Coinage Metalides: Specific Pairing and Location of Doping Atoms Bring Forth High Stability and Considerable Nonlinear Optical Response

Abstract

The possibility to design alkali-metal-free coinage metalides as alternative species to the unstable alkalides has been explored by constructing a series of M-1-M’ (M; M’ = Cu, Ag, and Au) based on the facially polarized all-cis 1,2,3,4,5,6-hexafluorocyclohexane (1) in this work. Under the joint action of inherent polarization of 1 and the electronegativity difference between M’ and M, the s electron of Cu/Ag atom can be ejected to the Au atom, forming the diffuse excess electron around the Au– anions in the Cu+-1-Au– and Ag+-1-Au– complexes. Hence, they can be regarded as the first examples of alkali-metal-free coinage metalides. These two compounds not only have higher stability (larger VIE and Ec values) than previously reported alkalides but also exhibit remarkably larger β0 values than the reported coinage metalides M+-1-Au– (M = Li, Na, and K), demonstrating their great potential to serve as new molecular materials with considerable NLO responses. Taking Cu+-1-Cu– and Cu+-1-Ag– as examples, it is proved that the rest of the M-1-M’ compounds can also be converted into coinage metalides under oriented external electric fields (OEEFs), which provides an approach to obtain novel NLO molecular switches. This work will pave the way to design stable NLO materials by using coinage metal atoms instead of alkali metals, which are more likely to be synthesized in the laboratory.