Endohedral metallofullerene electrides of Ca12O12 with remarkable nonlinear optical response

Quantum Chemical Approach of Hexaammine (NH3)6 complexant with alkali and alkaline earth metals for their potential use as NLO materials

In this study, nine new electron rich compounds are presented, and their electronic, geometrical, and nonlinear optical (NLO) characteristics have been investigated by using the Density functional theory. The basic design principle of these compounds is placing alkaline earth metal (AEM) inside and alkali metal (AM) outside the hexaammine complexant. The properties of nine newly designed compounds are contrasted with the reference molecule (Hexaammine). The effect of this doping on Hexaamine complexant is explored by different analyses such as electron density distribution map (EDDM), frontier molecular orbitals (FMOs), density of states (DOS) absorption maximum (λ_max), hyperpolarizabilities, dipole moment, transition density matrix (TDM). Non-covalent interaction (NCI) study assisted with isosurfaces has been accomplished to explore the vibrational frequencies and types of synergy. The doping of hexaammine complexant with AM and AEM significantly improved its characteristics by reducing values of HOMO-LUMO energy gaps from 10.7eV to 3.15eV compared to 10.7 eV of hexaammine. The polarizability and hyperpolarizability (α_o and β_o) values inquisitively increase from 72 to 919 au and 4.31 × 10^-31 to 2.00 × 10^-27esu respectively. The higher values of hyperpolarizability in comparison to hexaammine (taken as a reference molecule) are credited to the presence of additional electrons. The absorption profile of the newly designed molecules clearly illustrates that they are highly accompanied by higher λ_max showing maximum absorbance in red and far-red regions ranging from 654.07 nm to 783.94 nm. These newly designed compounds have superior outcomes having effectiveness for using them as proficient NLO materials and have a gateway for advanced investigation of more stable and highly progressive NLO materials.

Rational Design, Stabilities and Nonlinear Optical Properties of Non-Conventional Transition Metalides; New Entry into Nonlinear Optical Materials

Electronic and nonlinear optical properties of endohedral metallofullerenes are presented. The endohedral metallofullerenes contain transition metal encapsulated in inorganic fullerenes X₁₂Y₁₂ (X = B, Al & Y = N, P). The endohedral metallofullerenes (endo-TM@X₁₂Y₁₂) possess quite interesting geometric and electronic properties, which are the function of the nature of the atom and the size of fullerene. NBO charge and frontier molecular orbital analyses reveal that the transition metal encapsulated Al₁₂N₁₂ fullerenes (endo-TM@Al₁₂N₁₂) are true metalides when the transition metals are Ni, Cu and Zn. Endo-Cr@Al₁₂N₁₂ and endo-Co@Al₁₂N₁₂ are at the borderline between metalides and electrides with predominantly electride characteristics. The other members of the series are excess electron systems, which offer interesting electronic and nonlinear optical properties. The diversity of nature possessed by endo-TM@Al₁₂N₁₂ is not prevalent for other fullerenes. Endo-TM@Al₁₂P₁₂ are true metalides when the transition metals are (Cr-Zn). HOMO-LUMO gaps (E_H-L) are reduced significantly for these endohedral metallofullerenes, with a maximum percent decrease in E_H-L of up to 70%. Many complexes show odd-even oscillating behavior for E_H-L and dipole moments. Odd electron species contain large dipole moments and small E_H-L, whereas even electron systems have the opposite behavior. Despite the decrease in E_H-L, these systems show high kinetic and thermodynamic stabilities. The encapsulation of transition metals is a highly exergonic process. These endo-TM@X₁₂Y₁₂ possess remarkable nonlinear optical response in which the first hyperpolarizability reaches up to 2.79 × 10⁵ au for endo-V@Al₁₂N₁₂. This study helps in the comparative analysis of the potential nonlinear optical responses of electrides, metalides and other excess electron systems. In general, the potential nonlinear optical response of electrides is higher than metalides but lower than those of simple excess electron compounds. The higher non-linear optical response and interesting electronic characteristics of endo-TM@Al₁₂N₁₂ complexes may be promising contenders for potential NLO applications.

Electron Presolvation in Tetrahydrofuran-Incorporated Supramolecular Sodium Entities

Alkali metal atoms can repopulate their valence electrons toward solvation due to impact from solvents or microsurroundings and provide the remaining alkali metal cations for coordinating with a variety of specific solvents, forming various electron-expanded complexes or solvated ionic pairs with special interactions. Such special solute-solvent interactions not only affect their electronic structures but also enable the formation of entirely new species. Taking Na(THF)_n (n = 1-6, THF = tetrahydrofuran) and Na₂@THF complexes as typical representatives, density functional theory calculations are carried out to explore the solvation of a sodium atom and its dimer in THF and characterize their complexes as solvent-incorporated supramolecular entities and particularly valence electron presolvation due to their interaction with solvent THF. Electron presolvation is caused by the Pauli repulsion between THF containing a coordinating O atom with a lone pair of electrons and the alkali metal Na or Na₂ containing valence electrons, and THF coordination to them forces their valence electrons to redistribute, which can be easily realized in such solvents. Compared with strongly bound valance electrons of alkali metal atoms, THF coordination enables Na or Na₂ electrons to exhibit much more active states (i.e., the presolvated states) featuring small vertical detachment energies of electrons and distorted diffuse distributions in the frames of the generally structured metal cation complexes, acting as the electron-expanded chemical entities. Furthermore, the degree of electron diffusion and the polarity of the Na-Na bond are proportional to the coordination number (n) and the coordination number difference (Δn) between two Na centers in Na₂@THF. The unique properties of such entities are also discussed. This work offers a theoretical support to the supramolecular entities formed by alkali-metal atoms or their dimers with ligands containing O or N and uncovers the unique electron presolvation phenomena and also enriches our understanding of the novel metal atom complexes.

Structural and electronic properties of H2, CO, CH4, NO, and NH3 adsorbed onto Al12Si12 nanocages using density functional theory

In this study, the adsorption of gases (CH₄, CO, H₂, NH₃, and NO) onto Al₁₂Si₁₂ nanocages was theoretically investigated using density functional theory. For each type of gas molecule, two different adsorption sites above the Al and Si atoms on the cluster surface were explored. We performed geometry optimization on both the pure nanocage and nanocages after gas adsorption and calculated their adsorption energies and electronic properties. The geometric structure of the complexes changed slightly following gas adsorption. We show that these adsorption processes were physical ones and observed that NO adsorbed onto Al₁₂Si₁₂ had the strongest adsorption stability. The E _g (energy band gap) value of the Al₁₂Si₁₂ nanocage was 1.38 eV, indicating that it possesses semiconductor properties. The E _g values of the complexes formed after gas adsorption were all lower than that of the pure nanocage, with the NH₃-Si complex showing the greatest decrease in E _g. Additionally, the highest occupied molecular orbital and the lowest unoccupied molecular orbital were analyzed according to Mulliken charge transfer theory. Interaction with various gases was found to remarkably decrease the E _g of the pure nanocage. The electronic properties of the nanocage were strongly affected by interaction with various gases. The E _g value of the complexes decreased due to the electron transfer between the gas molecule and the nanocage. The density of states of the gas adsorption complexes were also analyzed, and the results showed that the E _g of the complexes decreased due to changes in the 3p orbital of the Si atom. This study theoretically devised novel multifunctional nanostructures through the adsorption of various gases onto pure nanocages, and the findings indicate the promise of these structures for use in electronic devices.

Can a molecular switch exist in both superalkali electride and superalkalide forms?

To combine both electride and alkalide characteristics in one molecular switch, it is shown herein that the phenalenyl radical and the M₃ ring (M₃-PHY, M = Li, Na, and K) stacked with parallel and vertical geometries are good candidates. The former geometry is the superalkali electride e^-⋯M₃⁺-PHY while the latter geometry is the superalkalide M^δ--M₂^(1-δ)+-PHY^-. The superalkalide M^δ--M₂^(1-δ)+-PHY^- may isomerize to the superalkali electride e^-⋯M₃⁺-PHY (M = Li, Na, and K) using suitable long-wavelength irradiation, while the latter may isomerize to the former with suitable short-wavelength irradiation. Also, applying suitable oriented external electric fields can drive the superalkalide M^δ-M₂^(1-δ)+-PHY^- to change into the superalkali electride e^-⋯M₃⁺-PHY (M = Li, Na, and K). The differences in the static and dynamic first hyperpolarizability (β₀) values between them were also studied.

Demonstrating the Potential of Alkali Metal-Doped Cyclic C6O6Li6 Organometallics as Electrides and High-Performance NLO Materials

In this report, the geometric and electronic properties and static and dynamic hyperpolarizabilities of alkali metal-doped C6O6Li6 organometallics are analyzed via density functional theory methods. The thermal stability of the considered complexes is examined through interaction energy (E int) calculations. Doping of alkali metal derives diffuse excess electrons, which generate the electride characteristics in the respective systems (electrons@complexant, e-@M@C6O6Li6, M = Li, Na, and K). The electronic density shifting is also supported by natural bond orbital charge analysis. These electrides are further investigated for their nonlinear optical (NLO) responses through static and dynamic hyperpolarizability analyses. The potassium-doped C6O6Li6 (K@C6O6Li6) complex has high values of second- (βtot = 2.9 × 105 au) and third-order NLO responses (γtot = 1.6 × 108 au) along with a high refractive index at 1064 nm, indicating that the NLO response of the corresponding complex increases at a higher wavelength. UV-vis absorption analysis is used to confirm the electronic excitations, which occur from the metal toward C6O6Li6. We assume that these newly designed organometallic electrides can be used in optical and optoelectronic fields for achieving better second-harmonic-generation-based NLO materials.

Quantum chemical studies of mercaptan gas detection with calcium oxide nanocluster

The electronic sensitivity and adsorption behavior for mercaptan natural gas of a Ca₁₂O₁₂ nanocluster were studied via ab initio computations. To be more specific, to fully grasp the influence of mercaptan molecules on the chemical and electronic features of Ca₁₂O₁₂ nanocluster, some parameters, namely, charge transfer of natural bond orbital, molecular electrostatic potential, binding energies, and frontier molecular orbitals, are computed. The interaction between CH₄S molecule and calcium atoms of Ca₁₂O₁₂ nanocluster through the sulfur head is strong. This strong interaction leads to a considerable transfer of charge from CH₄S to the nanocluster. After mercaptan adsorption, the existing energy gap between two levels, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the nanostructure, dropped by 2.21 eV, illustrating that the dissociation process has extensively increased the electrical conductance of nanostructure. This electrical signal can help to detect CH₄S molecules. Moreover, it could be concluded that Ca₁₂O₁₂ nanocluster has a short recovery time. In addition, solvent considerably influences the geometry factors and electronic features of CH₄S/Ca₁₂O₁₂ complexes, and the interactions between species are significantly weaker in the aqueous medium compared with those in the vacuum.

Design a novel type of excess electron compounds with large nonlinear optical responses using group 12 elements (Zn, Cd and Hg)

Based on the interesting Janus-type all-cis1,2,3,4,5,6-hexafluorocyclohexane (1) molecule, a novel type of excess electron compounds MF-1-MH (MF = Li, Na and K, MH = Zn, Cd and Hg) were designed theoretically. The geometric structures, electronic structures and nonlinear optical properties of MF-1-MH compounds were studied by density functional theory. Our results show that in Li-1-MH, the obvious charge transfer between Li and MH can be observed while in Na/K-1-MH, the charge transfer between Na/K and MH is negligible. Particularly, the MF-1-MH exhibit remarkable nonlinear optical (NLO) response and the first hyperpolarizability of the K-1-Zn almost achieve 1.0 × 10⁶ au. We hope this work will further enrich the family of excess electron compounds, so that more experimental interests and efforts can be attracted to propose and synthesize new excellent NLO materials.