Recent Progress on the Design, Characterization, and Application of Superalkalis

Abstract

Superalkalis are clusters or molecules featuring lower ionization energies (IEs) than that of cesium atoms, and thus exhibit excellent reducing properties. Such special species have great potential to be used in the synthesis of unusual charge‐transfer salts and cluster‐assembled nanomaterials with tailored properties, in the reduction of carbon dioxide, or as hydrogen storage materials and noble‐gas‐trapping agents, etc. In this regard, ongoing efforts have been devoted to designing and characterizing superalkalis of new types. The recent progress on the study of superalkalis in terms of theoretical design, characterization, and potential application is summarized in this minireview. We hope this review will not only provide a broad overview of this research field, but also highlight the prospect of further extending the experimental synthesis and practical application of superalkalis.

Small lithium‐chloride clusters: Superalkalis, superhalogens, supersalts and nanocrystals

“…According to the initial definition of superalkalis, 32 these species are characterized by their lower IE 1 than those of alkali metal atoms. Some authors 33 use a more rigorous definition that only the species with IEs below the threshold of the atomic IE 1 (Cs) = 3.89 eV can be classified as superalkalis. Nevertheless, in this paper, the species with IE 1 lower than constitutive alkali atom, that is, Li (5.39 eV) were considered as superalkalis.…”

Designing Special Nonmetallic Superalkalis Based on a Cage-like Adamanzane Complexant

“…In ML k +1 , one more alkali metal atom will bring an extra valence electron for the electronic shell of M according to the octet rule. Consequently, such an ML k +1 complex has a great tendency to lose the extra valence electron and thus possess strong reducibility ( Sun and Wu, 2019 ).…”

“…In view of the great importance of superalkalis in chemistry, various superalkalis have been theoretically ( Tong et al, 2009 ; Tong et al, 2011 , Tong et al, 2012a , Tong et al, 2012b ; Hou et al, 2013 ; Liu et al, 2014 ; Sun et al, 2013 ; Sun et al, 2016a ; Giri et al, 2016 ; Zhao et al, 2017 ; Sun et al, 2018b ; Sun et al, 2019 ; Park and Meloni, 2018 ; Sun and Wu, 2019 ; Tkachenko et al, 2019 ; Sikorska and Gaston, 2020 ) and experimentally ( Lievens et al, 1999 ; Yokoyama et al, 2000 , 2001 ; Hou and Wang, 2020 ) characterized in the past decades. To date, conventional mononuclear ML k +1 superalkalis have been expanded to dinuclear ( Tong et al, 2009 ; Tong et al, 2011 ) and polynuclear ( Tong et al, 2012a ; Tong et al, 2012b ; Liu et al, 2014 ) superalkalis, aromatic superalkalis ( Sun et al, 2013 ), Zintl-ion-based superalkalis ( Giri et al, 2016 ; Sun et al, 2018b ), hyperalkalis ( Sun et al, 2016a ), alkali-metal complexes ( Tkachenko et al, 2019 ), and so on.…”

„Superalkali” clusters, production, potential application like energy storage materials

“…The theoretical work of several research groups has shown that in addition to mononuclear, there are other types of "superalkalis" such as, binuclear (M is two different electronegative atom, for example, CNLi2 or Li2CN cluster), polynuclear (M is CO3, SO3, PO4, AsO4), bimetallic (L are "mixed" alkali atoms, for example, LiNaCl cluster), and non-metallic species [17]. These clusters, their chemical bonds, which are more complex than previously described, as well as their isomers, go beyond the scope and goal of this paper and therefore are not described in detail.…”