Germanium-based superatom clusters as excess electron compounds with significant static and dynamic NLO response; a DFT study

Herein, the geometric, electronic, and nonlinear optical properties of excess electron zintl clusters Ge₅AM₃, Ge₉AM₅, and Ge₁₀AM₃ (AM = Li, Na, and K) are investigated. The clusters under consideration demonstrate considerable electronic stability as well as superalkali characteristics. The NBO charge is transferred from the alkali metal to the Ge-atoms. The FMO analysis shows fabulous conductive properties with a significant reduction in SOMO-LUMO gaps (0.79-4.04 eV) as compared with undoped systems. The designed clusters are completely transparent in the deep UV-region and show absorption in the visible and near-IR region. Being excess electron compounds these clusters exhibit remarkable hyperpolarizability response up to 8.99 × 10^-26 esu, where a static second hyperpolarizability (γ _o) value of up to 2.15 × 10^-30 esu was recorded for Ge₉Na₅ superatom clusters. The excitation energy is the main controlling factor for hyperpolarizability as revealed from the two-level model study. The electro-optical Pockel's effect and the second harmonic generation phenomenon (SHG) are used to investigate dynamic nonlinear optical features. At a lower applied frequency (=532 nm), the dynamic hyperpolarizability and second hyperpolarizability values are significantly higher for the studied clusters. Furthermore, for the Ge₉K₅ cluster, the hyper Rayleigh scattering (HRS) increases to 5.03 × 10^-26 esu.

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

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.

Computational investigation of LiF containing hypersalts

This study explores the design of possible hypersalts starting from the hyperhalogen Li₃F₄ plus a Li atom and the hyperalkali Li₄F₃ plus a F atom.

Ab initio analysis on potential superbases of several hyperlithiated species: Li3F2O and Li3F2OHn (n = 1, 2)

A systematic investigation on the potential basicity of the novel hyperlithiated species Li₃F₂O and Li₃F₂(OH)_n (n = 1, 2) based upon the superalkali cluster Li₃F₂ was conducted using high-level ab initio techniques.

Reduction of carbon dioxide with a superalkali

The ability of the superalkali Li₃F₂ to reduce CO₂ and N₂ is investigated using the CBS-QB3 composite method and intriguing results are presented.

Attaching an alkali metal atom to an alkaline earth metal oxide (BeO, MgO, or CaO) yields a triatomic metal oxide with reduced ionization potential and redirected polarity

The existence of a series of neutral triatomic metal oxides MON and their corresponding cations MON (+) (M = Be, Mg, Ca; N = Li, Na, K) was postulated and verified theoretically using ab initio methods at the CCSD(T)/6-311+G(3df)//MP2/6-311+G(3df) level of theory. The calculations revealed that the vertical ionization potentials (IPs) of the MON radicals (calculated using the outer-valence Green's function technique (OVGF) with the 6-311+G(3df) basis set) were ca. 2-3 eV smaller than the IPs of the corresponding MO and NO systems or that of the isolated M atom. Population analysis of the neutral triatomic MON molecules and their corresponding MO counterparts indicated that the attachment of an alkali metal atom to any oxide MO (BeO, MgO, CaO) reverses its polarity, which manifests itself as the redirection of the dipole moment vector.

Organo-Zintl Clusters [P7R4]: A New Class of Superalkalis

Zintl ions composed of Group 13, 14, and 15 elements are multiply charged cluster anions that form the building blocks of the Zintl phase. Superalkalis, on the other hand, are cationic clusters that mimic the chemistry of the alkali atoms. It is, therefore, counterintuitive to expect that Zintl anions can be used as a core to construct superalkalis. In this paper, using density functional theory, we show that this is indeed possible. The results are compared with calculations at the MP2 level of theory. A systematic study of a P7(3-) Zintl core decorated with organic ligands [R = Me, CH2Me, CH(Me)2 and C(Me)3] shows that the ionization energies of some of the P7R4 species are smaller than those of the alkali atoms and hence can be classified as superalkalis. This opens the door to the design and synthesis of a new class of superalkali moieties apart from the traditional ones composed of only inorganic elements.

Organic heterocyclic molecules become superalkalis

A new strategy has been developed to create superalkali molecules from aromatic heterocycles. C₃N₂(CH₃)₅ has the ionization energy close to 3.0 eV.