Novel supersalts formed by interaction of H 2 M 3 superalkalis (M = Li and Na) with AlF 4,BeF 3 and NO 3 superhalogens

Abstract

Supersalts are ionic compounds formed by pairing superalkali cations with superhalogen anions, resulting in systems with strong charge-transfer characteristics. This study investigates novel supersalts of the form H₂M₃–Y (M = Li or Na; Y = AlF₄, BeF₃, NO₃) using the MP2/aug-cc-pVTZ level of theory. Their stability was evaluated via binding energy (E_b) and dissociation energy (E_d), with H₂Li₃–AlF₄ showing the highest binding energy (11.35 eV), followed by H₂Li₃-BeF₃ (10.66 eV) and H₂Li₃-NO₃ (7.58 eV). Net charge analysis confirms significant charge separation (+0.93e / −0.92e in Li systems), supporting the ionic nature of these complexes, further validated by QTAIM analysis. The HOMO–LUMO gap is highest for H₂Li₃–BeF₃ (10.33 eV), indicating relatively higher electronic stability. The results indicate that Li-based supersalts are more stable than their Na-based counterparts, with stability following the trend AlF₄ > BeF₃ > NO₃. These findings provide a basis for understanding charge-transfer-driven molecular systems.

Keywords

superalkalis superhalogen supersalt binding energy QTAIM analysis

Introduction

Supersalts represent a distinct category of ionic compounds formed through the interaction of molecular species known as superatoms, which exhibit periodic element-like behavior. They are charge-transfer salts, comprising superalkali cations and superhalogen anions, similar to conventional ionic salts that contain alkali cations and halogen anions. However, they are distinct in their tendency to preferentially dissociate into ionic fragments, distinguishing them from traditional salts. Superalkalis,¹ characterized by ionization potentials lower than those of alkali metals, and superhalogens,² defined by their exceptionally high electron affinities, are prime candidates for forming such compounds. Khanna and Jena's³ pioneering work revealed that specific atomic clusters, known as superatoms, can replicate elemental properties. Recent studies showcase their potential for creating novel materials.⁴ This leads to a fascinating question: Can supersalts be crafted from the union of positively and negatively charged superatomic ions? Just as alkali metals and halogens combine to form conventional salts, the interaction of these two superatomic species leads to the development of supersalts. Several notable investigations have been conducted on supersalts. For instance, Li et al.⁵ studied the interactions of the BLi₆ superalkali with various superhalogens (LiF₂, BeF₃, and BeF₄), while Yang et al.,⁶ explored how the BF₄ superhalogen interacts with FLi₂, OLi₃, and NLi₄ superalkalis. More recently, a theoretical study on supersalts Na₂MgX₄ (X = F, Cl) was conducted by exploring their formation via association reactions involving superalkalis, superhalogens, dimers, and conventional salts in both ionic and neutral forms.⁷ Additionally, research has demonstrated that interactions between Li₂X-based superalkalis and LiX₂-based superhalogens lead to the formation of Li₃X₃ supersalts for X = F, Cl, Br, and I.^8,9 Similarly, potassium-iodide clusters K₂I and KI₂ generate a superalkali cation (K₂I⁺) and a superhalogen anion (KI₂⁻), which combine to form the stable supersalt K₃I_3.¹⁰ The series of supersalts, including (M₃O)⁺(Al₁₃)⁻ (M = Na, K),¹¹ and (Na₂X)⁺(Y)⁻ (X = SCN, OCN, CN; Y = MgCl₃, Cl, NO₂),¹² have been theoretically designed and identified as promising inorganic NLO molecules due to their significant nonlinear optical responses. The superacids and superbases can also be used as building blocks of the supersalts.¹³ Reportedly, classic superalkalis (FLi₂, OLi₃, NLi₄), when interacting with superhalogens (BeF₃, BF₄, and NO₃), can form salts while retaining the cationic and anionic nature of their components.¹⁴ Recent theoretical studies highlight that excess-electron-driven interactions play a key role in stabilizing unconventional ionic and supramolecular systems. In particular, superalkali-assisted metalide complexes and vdW-stabilized assemblies demonstrate how long-range electrostatics, charge transfer, and noncovalent interactions govern electronic structure and stability, providing a broader framework for understanding charge-separated molecular architectures.^15,16

In this work, we investigate supersalts derived from H₂M₃ (M = Li, Na)¹⁷ superalkalis through direct pairing with superhalogens (AlF₄, BeF₃, and NO₃). Unlike widely studied supersalt systems based on FLi₂, OLi₃, and NLi₄,¹⁴ this study focuses on supersalts formed from H₂M₃ units, which represent a comparatively less explored class. A systematic analysis of their stability, charge-transfer characteristics, and bonding nature is carried out, along with a comparison of Li- and Na-based systems to understand how the metal center influences interaction strength and overall stability. This also enables us to examine whether established supersalt formation trends remain valid for this class of systems.

Computational details

The equilibrium geometries were determined using second-order Møller-Plesset (MP2) perturbation theory,¹⁸ with the basis set aug-cc-pVTZ in the Gaussian 16 software package.¹⁹ For visualization purposes, we have used the GaussView package.²⁰ The MP2/aug-cc-pVTZ level was chosen for its reliable description of charge transfer and noncovalent interactions. Previous studies on superalkali-based and related charge-separated systems have successfully employed MP2-level calculations to describe interaction energies and structural properties.¹⁷ Therefore, the present level is considered appropriate for a comparative analysis of these systems. While higher-level methods such as CCSD(T) or multi-level approaches may provide more accurate absolute energies, MP2 offers a reasonable balance between accuracy and computational cost. Accordingly, the present results are interpreted within a comparative framework, and the observed energetic trends are expected to be qualitatively reliable. Frequency calculations were performed at the same level of theory to confirm that all optimized structures correspond to true minima on the potential energy surface, as no imaginary frequencies were observed. The calculated vibrational spectra for the optimized structures are provided in the Supporting Information (Figure S1 to Figure S11). Atomic charges were obtained using Natural Population Analysis (NPA) within the Natural Bond Orbital (NBO) framework, which provides a more reliable description of charge distribution in molecular systems.²¹ To gain deeper insight into the interactions, we performed Quantum Theory of Atoms in Molecules (QTAIM) analysis²² using the Multiwfn package.²³ The energy gap (E_gap), calculated as the difference between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), is a key parameter in understanding electronic properties and chemical reactivity. Their stability has been assessed based on binding and dissociation energy, which is determined using the following equations:

\begin{aligned} E_{b} = E [H_{2} M_{3}] + E [Y] - E [H_{2} M_{3} - Y] \\ E_{d} = E [H_{2} {M_{3}}^{+}] + E [Y^{-}] - E [H_{2} M_{3} - Y] \end{aligned}

where E [H₂M₃] represents the total electronic energy of the isolated superalkali clusters (H₂M₃), E [Y] denotes the total electronic energy of the isolated superhalogen cluster (AlF₄, BeF₃, and NO₃), and E [H₂M₃-Y] represents the total energy of the optimized complex (H₂M₃-Y), including zero-point correction. All energies include zero-point energy (ZPE) corrections obtained from vibrational frequency calculations at the same level of theory.

Results and discussion

In this section, we explore H₂M₃-Y (where M = Li and Na and Y = AlF₄, BeF₃, and NO₃) supersalts. Our analysis begins with the H₂M₃-AlF₄ (M = Li and Na) complexes. Figure 1 presents the optimized geometries of the ground-state and low-energy isomers of neutral H₂M₃-AlF₄ (M = Li and Na), along with their corresponding bond lengths and NPA charges. The relative energy (E_r) is listed in Table 1. The E_r of the H₂Li₃-AlF₄ (b) and H₂Li₃-AlF₄ (c) are 0.04 eV and 0.06 eV, respectively, whereas the E_r of H₂Na₃-AlF₄ (b) is 0.33 eV, indicating relative stability compared to the lowest energy isomer (a) in each case.

Figure 1.

Optimized geometries of isomers H₂M₃-AlF₄ (M = Li and Na) with selected bond lengths in Å and net charge at the MP2/aug-cc-pVTZ method.

Table 1.

Isomers, relative energy E_r (in eV), binding energies E_b (in eV), dissociation energy (in eV), HOMO-LUMO gap (in eV) for H₂M₃-Y (M = Li and Na and Y = AlF₄, BeF₃ and NO₃) clusters.

Systems	Isomers	E_r (eV)	E_b (eV)	E_d (eV)	E_gap (eV)
H₂Li₃-AlF₄	(a)	0	11.35	5.87	10.07
	(b)	0.04	11.32	5.84	8.82
	(c)	0.06	11.28	5.80	9.51
H₂Na₃-AlF₄	(a)	0	10.16	4.80	8.87
H₂Na₃-AlF₄	(b)	0.33	9.82	4.46	8.08
H₂Li₃-BeF₃	(a)	0	10.66	6.08	10.33
H₂Li₃-BeF₃	(b)	0.01	10.64	6.05	9.87
H₂Na₃-BeF₃	(a)	0	9.34	4.86	8.52
H₂Na₃-BeF₃	(b)	0.54	8.80	4.31	8.06
H₂Li₃-NO₃	-	-	7.58	6.20	9.99
H₂Na₃-NO₃	-	-	6.60	5.33	8.63

To investigate the electronic interactions within the H₂M₃-AlF₄ clusters, we computed NPA charges. The analysis reveals that all isomeric forms carry a net charge of approximately +0.93e at H₂Li₃ and +0.97e at H₂Na₃, while the AlF₄⁻ unit holds −0.95e, indicating significant charge transfer and confirming the ionic nature of bonding. This result aligns with experimental observations, where AlF₄ ⁻ was identified as a superhalogen due to its high electron affinity and stable tetrahedral geometry.²⁴ Furthermore, the Al–F bond lengths are in the range of 1.74 Å – 1.65 Å in H₂Li₃-AlF₄ and 1.73 Å – 1.66 Å in H₂Na₃-AlF₄ (Figure 1), consistent with experimental bond distances in ionic AlF₄⁻ salts (typically ∼1.66–1.72 Å) reported in crystal structures [3]. The strong ionic interaction stems from the donor–acceptor nature of the H₂M₃ and AlF₄ units. H₂Li₃ and H₂Na₃ act as superalkali donors, while AlF₄ acts as a superhalogen acceptor, reinforcing the charge-driven interaction. The ground state and low-lying optimized structures of H₂M₃-BeF₃ (M = Li, Na), along with the bond lengths and NPA charges, are shown in Figure 2. The energy difference between these isomers is minimal, such as the H₂Li₃-BeF₃(b) is 0.05 eV and H₂Na₃-BeF₃(b) is 0.54 eV, corresponding to the lowest energy isomers. The net charge transfer is about +0.96e and +0.99e on H₂Li₃ and H₂Na₃, respectively, while on the BeF₃ moiety, the charge is −0.96e. Previously, the reported charge on the BeF₃ unit was −0.90e in OLi₃-BeF₃,¹⁴ which agrees well with the calculated value.

Figure 2.

Optimized geometries of isomers H₂M₃-BeF₃ (M = Li and Na) with selected bond lengths in Å and net charges at the MP2/aug-cc-pVTZ method.

The Be-F bond length is 1.42 Å, whereas a slight stretch in the Be-F bond length (1.51 Å) is noticed when the F-atom interacts with the Li- atom of the H₂Li₃. Similarly, in H₂Na₃-BeF₃(b), the Be-F bond length is 1.52 Å, and the contraction in the bond Be-F is noticed in the interaction of BeF₃ with the H₂Na₃. This behavior occurs because Li, being smaller and more polarizing than Na, pulls more electron density toward F, causing greater Be–F bond elongation. In contrast, larger Na interacts more loosely, leading to less Be–F bond distortion or slight contraction.

We further examined the superhalogen anions BeF₃ and NO₃, both of which have received extensive experimental validation in gas-phase and condensed-phase studies. In particular, high-resolution photoelectron spectroscopy (PES) of NO₃ reveals distinct vertical detachment features around 4.66 eV, confirming its strong electron-accepting nature.²⁵

Additionally, vibrational spectroscopic investigations identify the antisymmetric stretching mode (ν₃) of NO₃ near 1349 cm⁻¹, supporting its structural rigidity.²⁶ While direct PES data for BeF₃ are limited, gas-phase thermochemical studies on related clusters such as Be₂F₅ report significant clustering enthalpies (∼290 ± 10 kJ/mol), providing indirect yet compelling evidence of its robust ionic bonding behavior.²⁷ These experimental insights align well with our computed binding energies and electronic properties of the corresponding supersalts.

To identify the most stable structures, a wide range of initial geometries (including different orientations and coordination modes between the superalkali and superhalogen units) was constructed and optimized using the same computational scheme. During the optimization process, several trial structures converged to higher-energy configurations, showed significant structural rearrangements, or exhibited imaginary frequencies, and were therefore discarded. Only structures that converged without imaginary frequencies were considered true minima and are reported here. The optimized structures of H₂M₃-NO₃ (M = Li and Na) are positioned in Figure 3. The oxygen center of the NO₃ moiety establishes interactions with two Li atoms in H₂Li₃ and two Na atoms in H₂Na₃, respectively.

Figure 3.

Optimized geometries of isomers H₂M₃-NO₃ (M = Li and Na) with selected bond lengths in Å and net charges at the MP2/aug-cc-pVTZ method.

The net charge on the H₂Li₃ and NO₃ is +0.93e and −0.92e, respectively. Thus, the calculated charges are comparable to the charges of H₂M₃-AlF₄ and H₂M₃-BeF₃ (M = Li and Na). The unequal O–Li bond lengths in H₂Li₃-NO₃ arise due to differences in charge distribution, influencing Li–O interactions. Also, the estimated net charge on the H₂Na₃ and NO₃ is +0.86e and −0.85e, respectively. The N-O bond length ranges from 1.30 Å to 1.21 Å in H₂Li₃-NO_3, and in H₂Na₃-NO₃, it ranges from 1.27 Å to 1.24 Å. Thus, no appreciable changes were noticed in the bond length on changing the superalkalis.

Stability and electronic properties

The stability and electronic properties of the resulting supersalts are analyzed using binding energy, dissociation energy, and the HOMO-LUMO gap, respectively, to highlight their distinct characteristics. A higher binding energy (E_b) indicates a stronger interaction and greater stability of the complex. Among all systems, H₂Li₃-AlF₄ (E_b = 11.35 eV, E_d = 5.87 eV) possesses the highest binding and dissociation energies, indicating a strong interaction within the complex. The systems H₂Li₃-BeF₃ and H₂Na₃-BeF₃ exhibit intermediate stability between AlF₄ and NO₃ complexes. The observed stability trend (AlF₄ > BeF₃ > NO₃) arises from differences in coordination environment, ligand electronegativity, and the extent of charge delocalization in the superhalogen units. The AlF₄ anion possesses a highly symmetric tetrahedral geometry with four strongly electronegative fluorine atoms surrounding the central Al atom, thereby facilitating effective charge delocalization and strong electrostatic interactions with the superalkali fragment. In contrast, BeF₃ contains only three fluorine atoms, resulting in slightly reduced charge delocalization and weaker electrostatic stabilization compared to AlF₄. On the other hand, the planar NO₃ distributes negative charge over the less electronegative oxygen atoms, which interact less strongly with the Li/Na centers, leading to comparatively weaker binding.

The H₂Li₃-BeF₃ system has higher binding energy (E_b = 10.66 eV) and dissociation energy (E_d = 6.08 eV) than H₂Na₃-BeF₃ (E_b = 9.34 eV, E_d = 4.86 eV), reflecting stronger Li interactions. The energy gap (E_gap) is highest in H₂Li₃-BeF₃ (10.33 eV), while Na-based systems exhibit lower E_gap, indicating relatively higher electronic softness. Overall, BeF₃ complexes are more stable than NO₃ but less stable than AlF₄, with Li-based systems consistently stronger than Na-based ones. For NO₃-based systems, H₂Li₃-NO₃ (E_b = 7.58 eV, E_d = 6.20 eV) is more stable than H₂Na₃-NO₃ (E_b = 6.60 eV, E_d = 5.33 eV). This trend is consistent across all three ligand types, indicating that Li⁺ forms stronger electrostatic interactions than Na⁺, in line with its smaller ionic radius and higher charge density.

The HOMO–LUMO gap (E_gap) is an important parameter related to the electronic stability and chemical hardness of a system. A larger E_gap generally indicates lower chemical reactivity and higher resistance to electronic excitation. To gain further insight into the electronic structure of the supersalt complexes, the frontier molecular orbitals were analyzed and are shown in Figure 4. Although both HOMO and LUMO were computed for evaluating the HOMO–LUMO energy gaps, only the HOMO orbitals are presented here, as they primarily reflect the electron-donating nature of the superalkali fragment. The LUMOs are largely delocalized over the superhalogen units and do not provide additional qualitative insight. The HOMO distribution for all investigated systems is predominantly localized on the superalkali fragment (H₂Li₃), reflecting the diffuse electron density associated with the superalkali unit. Meanwhile, the superhalogen moieties contribute mainly to deeper lying molecular orbitals. This orbital localization further supports the charge-separated nature of the supersalt complexes.

Figure 4.

Frontier molecular orbitals (HOMO) of the optimized H₂M₃–Y supersalt complexes (M = Li, Na; Y = AlF₄, BeF₃, NO₃) calculated at the MP2/aug-cc-pVTZ level. LUMOs are not shown as they exhibit similar delocalized features and do not provide additional insight.

Among the studied complexes, H₂Li₃-BeF₃ exhibits the highest E_gap (10.33 eV), suggesting improved electronic stability. Similarly, H₂Li₃-AlF₄ (10.07 eV) and H₂Li₃-NO₃ (9.99 eV) also possess relatively high energy gaps, highlighting the enhanced stability of Li-based systems. In comparison, the Na-based counterparts demonstrate slightly lower E_gap values, with H₂Na₃-AlF₄ (8.87 eV), H₂Na₃-NO₃ (8.63 eV), and H₂Na₃-BeF₃ (8.52 eV), indicating relatively lower stability. This trend indicates that replacing Li with Na results in a reduction in the electronic stability of the complexes. Additionally, the variation in E_gap among different superhalogen clusters (AlF₄, BeF₃, NO₃) highlights the influence of ligand electronegativity and structural effects on the electronic properties of these systems.

These trends indicate that Li-based systems not only exhibit stronger electrostatic and covalent interactions but also show larger HOMO–LUMO gaps. These observations are based on isolated molecular clusters and therefore reflect relative electronic stability at the molecular level. The nature of the superhalogen ligand significantly affects the complex stability, in the order AlF₄ > BeF₃ > NO₃, which can be attributed to their inherent electron affinities and structural rigidity.

QTAIM analysis

The bonding characteristics of the supersalt complexes formed by superalkalis (H₂Li₃, H₂Na₃) and superhalogens (AlF₄, BeF₃, NO₃) can be understood through various topological parameters, including electron density (ρ), Laplacian of electron density (∇²ρ), kinetic energy density (G), potential energy density (V), the energy ratio -G/V, and total energy density (H). In addition, the electron localization function (ELF) was computed to visualize the distribution of localized electrons within the complexes. The corresponding ELF maps are provided in the Supporting Information (Figure S12). Table 2 presents the analysis of several systems involving different interactions, where key quantities such as electron density (ρ), Laplacian of the electron density (∇²ρ), Lagrangian kinetic energy (G), potential energy density (V), and their corresponding ratios (-G/V) are reported for each interaction in H₂M₃-Y (M = Li and Na and Y = AlF₄, BeF₃ and NO₃).

Table 2.

QTAIM parameters of neutral and cationic H₂M₃-Y (M = Li and Na and Y = AlF₄, BeF₃ and NO₃) at MP2/aug-cc-pVTZ level. All values are given in a.u.

System	Interaction	ρ	∇²ρ	G	V	-G/V	H
H₂Li₃-AlF₄	Li-F	0.0407	3.917	0.0810	−0.0640	1.27	0.0170
H₂Na₃-AlF₄	Na-F	0.0155	1.200	0.0235	−0.0171	1.38	0.0065
H₂Li₃-BeF₃	Li-F	0.0249	2.194	0.0435	−0.0322	1.35	0.0113
H₂Na₃-BeF₃	Na-F	0.0149	1.159	0.0226	−0.0162	1.39	0.0064
H₂Li₃-NO₃	Li-O	0.0248	2.026	0.0410	−0.0313	1.31	0.0097
H₂Na₃-NO₃	Na-O	0.0152	1.113	0.0217	−0.0156	1.39	0.0060

The electron density (ρ) at the bond critical point (BCP) is an important indicator of interaction strength, where higher values generally correspond to stronger bonding interactions. From Table 2, it is evident that Li-based systems exhibit higher electron density values compared to their Na-based counterparts. For example, H₂Li₃-AlF₄ shows the highest ρ value (0.0407 a.u.), indicating relatively stronger interaction, whereas H₂Na₃-AlF₄ shows the lowest value (0.0155 a.u.), suggesting comparatively weaker interaction. Similarly, H₂Li₃-BeF₃ (0.0249 a.u.) and H₂Li₃-NO₃ (Li–O interaction, 0.0248 a.u.) also display higher electron densities than the corresponding Na-based systems, such as H₂Na₃–BeF₃ (0.0149 a.u.). This trend indicates that Li-containing supersalts possess stronger electron localization at the interaction region, leading to relatively stronger bonding interactions compared to the Na-based analogs.

The Laplacian of electron density (∇²ρ) provides important insight into the nature of bonding and the distribution of electron density within a system. In general, positive values of ∇²ρ correspond to closed-shell interactions such as ionic or van der Waals interactions, whereas negative values indicate covalent character. In all studied supersalt complexes, the Laplacian values are positive, confirming the predominance of ionic interactions between the superalkali and superhalogen units. A clear trend is observed: Li-based systems exhibit relatively higher ∇²ρ values than their Na-based counterparts, suggesting enhanced concentration of electron density in the interaction region. For instance, H₂Li₃-AlF₄ and H₂Li₃-BeF₃ show higher Laplacian values of 3.917 and 2.194 a.u., respectively, compared with H₂Na₃-AlF₄ (1.200 a.u.) and H₂Na₃-BeF₃ (1.159 a.u.). Among all systems, H₂Li₃-AlF₄ exhibits the highest ∇²ρ value, further supporting strong electrostatic interactions in this complex.

The kinetic energy density (G) and potential energy density (V) provide important insights into the nature and stability of the bonding interactions. The ratio −G/V, which is greater than 1 for all complexes, indicates closed-shell interactions and confirms the predominantly ionic character of the supersalt systems. The −G/V ratio is highest for H₂Na₃-BeF₃ (1.39) and H₂Na₃-NO₃ (1.39), suggesting a relatively stronger ionic interaction character, whereas H₂Li₃-AlF₄ (1.27) shows a slightly lower value, implying stronger electrostatic interactions. In general, Li-based systems exhibit higher kinetic energy density and more negative potential energy density values, indicating relatively stronger interactions. Although Na-based systems display slightly larger −G/V ratios, their overall electron densities and binding energies remain lower than those of the corresponding Li-based systems. Consequently, Li-based supersalts are energetically more stable despite the somewhat higher ionic character observed in Na-containing complexes.

The total energy density (H), defined as H = G + V, determines the overall stability of interactions. Positive values of H, as seen in all complexes, indicate weakly bound interactions, reinforcing the ionic nature of bonding. Similar closed-shell interaction features and electron density characteristics have also been reported for supramolecular systems stabilized through excess-electron interactions, supporting the general relevance of such bonding behavior in charge-separated molecular assemblies.¹⁵

The interaction between the H₂M₃ superalkali unit and the superhalogen moiety primarily occurs through Li/Na–F contacts in fluorine-containing superhalogens (AlF₄ and BeF₃), whereas Li/Na–O interactions dominate in nitrate-based systems. This difference arises because, in NO₃⁻, the negative charge is primarily localized over oxygen atoms, making them the preferred interaction sites. The QTAIM analysis further confirms that the bond critical points are located between Li/Na and F atoms for AlF₄ and BeF₃ systems, and between Li/Na and O atoms for NO₃ systems, consistent with the structural description of oxygen-mediated interactions observed in nitrate-based complexes. Overall, the H₂Li₃ complexes exhibit stronger interactions than their H₂Na₃ counterparts due to higher electron density and lower −G/V ratios, thereby rendering lithium-based supersalts more stable. Among all, H₂Li₃-AlF₄ shows the strongest interaction, making it the most stable supersalt, while H₂Na₃-AlF₄ has the weakest bonding. These findings confirm that superalkali-superhalogen interactions lead to highly ionic supersalt formations, with bond strength following the trend AlF₄ > BeF₃ > NO₃, and lithium-based complexes being more stable than sodium-based ones.

Conclusions

In this study, a series of typical supersalts with the general formula H₂M₃–Y (where M = Li or Na, and Y = AlF₄, BeF₃, or NO₃) was investigated. These systems represent novel compounds formed by combining superalkalis with superhalogens. All calculations were performed at the MP2/aug-cc-pVTZ level of theory. The structural properties, particularly bond lengths, were calculated for each possible configuration of these supersalts. Their stability was evaluated using two key energetic parameters: binding energy (E_b) and dissociation energy (E_d). The results indicate that these supersalts experience significant stabilization due to charge transfer from the superalkali unit to the superhalogen fragment.

To probe the electronic properties, the HOMO–LUMO energy gap (E_gap) was calculated. Among the studied complexes, H₂Li₃–BeF₃ exhibits the highest E_gap value of 10.33 eV, suggesting strong electronic stability. Analysis of net atomic charges revealed effective charge separation between H₂M₃ and the superhalogen moieties, supporting their ionic character. This ionic nature of bonding was further validated through QTAIM analysis, which confirmed significant electron localization between interacting centers.

Comparative results demonstrate that Li-based supersalts consistently show greater stability, stronger intermolecular interactions, and wider HOMO–LUMO gaps than their Na-based analogs. Additionally, among the superhalogens examined, AlF₄ exhibits the highest binding energy, followed by BeF₃ and NO₃, indicating that the choice of superhalogen significantly influences both the structural integrity and electronic behavior of the resulting complexes. Overall, these findings highlight the critical role of the central metal atom (Li vs. Na) and the nature of the superhalogen in determining the stability, bonding, and electronic properties of supersalts. This work provides theoretical insight into charge-transfer-driven molecular systems.

Supplemental Material

sj-docx-1-mgc-10.1177_10241221261456942 - Supplemental material for Novel supersalts formed by interaction of H₂M₃ superalkalis (M = Li and Na) with AlF₄, BeF₃ and NO₃ superhalogens

Supplemental material, sj-docx-1-mgc-10.1177_10241221261456942 for Novel supersalts formed by interaction of H₂M₃ superalkalis (M = Li and Na) with AlF₄, BeF₃ and NO₃ superhalogens by Harshita Srivastava and Ambrish Kumar Srivastava in Main Group Chemistry

Footnotes

ORCID iDs

Harshita Srivastava

Ambrish Kumar Srivastava

Ethical considerations and informed consent

Not applicable

Author contributions

HS: literature survey, calculations, data collection, and writing draft. AKS: conceptualization, supervision, editing, and finalizing the draft.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: Dr Ambrish Kumar Srivastava acknowledges the funding received from the Science & Engineering Research Board (SERB), New Delhi, through the State University Research Excellence (SURE) scheme (SUR/2022/002035).

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Data availability statement

Data associated with this article will be available upon reasonable request.

Supplemental material

Supplemental material for this article is available online.

References

Gutsev

Boldyrev

. DVM-Xα calculations on the electronic structure of “superalkali” cations. Chem Phys Lett 1982; 92: 262–266.

Gutsev

Boldyrev

. DVM-Xα calculations on the ionization potentials of MX _k ₊₁⁻ complex anions and the electron affinities of MX _k ₊₁ “superhalogens”. Chem Phys 1981; 56: 277–283.

Khanna

Jena

. Atomic clusters: building blocks for a class of solids. Phys Rev B 1995; 51: 13705–13716.

Jena

Sun

. Super atomic clusters: design rules and potential for building blocks of materials. Chem Rev 2018; 118: 5755–5870.

Z-R

. Compounds of superatom clusters: preferred structures and significant nonlinear optical properties of the BLi₆-X (X = F, LiF₂, BeF₃, BF₄) motifs. Inorg Chem 2008; 47: 9773–9778.

Yang

, et al. Structural properties and nonlinear optical responses of superatom compounds BF₄-M (M = Li, FLi₂, OLi₃, NLi₄). Int J Quantum Chem 2012; 112: 770–778.

Ulime

Pogrebnoi

Pogrebnaya

. Supersalts Na₂MgX₄ (X = F, cl): quantum chemical study of the structure, vibration spectra and thermodynamic properties. Br J Appl Sci Technol 2016; 12: 1–15.

Srivastava

Misra

. Unusual properties of novel Li₃F₃ ring: (LiF₂–Li₂F) superatomic cluster or lithium fluoride trimer, (LiF)₃? RSC Adv 2014; 4: 41260–41265.

Srivastava

Misra

. Novel Li₃X₃ supersalts (X = F, Cl, Br & I) and their alkalide characteristics. New J Chem 2014; 38: 2890–2893.

10.

Hou

G-L

Wang

X-B

. Potassium iodide cluster-based superhalogens and superalkalis: theoretical calculations and experimental confirmation. Chem Phys Lett 2020; 741: 137094.

11.

Omidvar

. Design of a novel series of donor–acceptor frameworks via superalkali–superhalogen assemblage to improve the nonlinear optical responses. Inorg Chem 2018; 57: 9335–9347.

12.

Anusiewicz

. The Na₂X superalkali Species (X = SH, SCH₃, OCH₃,CN, N₃) as building blocks in the Na₂XY salts (Y = MgCl₃, Cl, NO₂). An Ab initio study of the electric properties of the Na₂XY salts. Aust J Chem 2010; 63: 1573–1581.

13.

Srivastava

Misra

. Superbases and superacids form supersalts. Chem Phys Lett 2016; 644: –4.

14.

Giri

Behera

Jena

. Superalkalis and superhalogens as building blocks of supersalts. J Phys Chem A 2014; 118: 638–645.

15.

Ahsin

Qamar

Kaviani

, et al. Stacking interactions in stabilizing supramolecular assembly of M[9C] 2 M complexes: dynamic stability with remarkable nonlinear optical features. Phys Chem Chem Phys 2025; 27: 240–253.

16.

Ahsin

Qamar

Kaviani

, et al. Improving excited-state dynamic properties with the help of metalide character and excess electrons: earlier transition-metal pairing with superalkali clusters. New J Chem 2025; 49: 15434–15447.

17.

Srivastava

. Hydrogen-based binuclear superalkalis H₂M₃ (M = Li and Na) and their catalytic applications: a theoretical study. Chem Papers 2025; 79: 3921–3934.

18.

Møller

Plesset

. Note on an approximation treatment for many-electron systems. Phys Rev 1934; 46: 618–622.

19.

Frisch

Trucks

Schlegel

, et al. Gaussian 16, Revision C.01.

20.

Dennington

Keith

Millam

. GaussView 5.0.

21.

Reed

Weinstock

Weinhold

. Natural population analysis. J Chem Phys 1985; 83: 735–746.

22.

Bader

RFW

. Atoms in molecules: A quantum theory. 2nd ed. Oxford: Oxford University Press, 1994.

23.

Chen

. Multiwfn: a multifunctional wavefunction analyzer. J Comput Chem 2012; 33: 580–592.

24.

Srivastava

Misra

. Superhalogens as building blocks of complex hydrides for hydrogen storage. Electrochem Commun 2016; 68: 99–103.

25.

Lau

DeWitt

Franke

, et al. High-Resolution photoelectron spectroscopy of NO₃^– vibrationally excited along its ν₃Mode. J Phys Chem A 2025; 129: 1634–1647.

26.

Goebbert

Garand

Wende

, et al. Infrared spectroscopy of the microhydrated nitrate ions NO₃−(H₂O)₁₋₆. J Phys Chem A 2009; 113: 7584–7592.

27.

Linstrom

Mallard

. NIST chemistry WebBook. Gaithersburg, MD, USA: National Institute of Standards and Technology, 2011.

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Novel supersalts formed by interaction of H 2 M 3 superalkalis (M = Li and Na) with AlF 4,BeF 3 and NO 3 superhalogens

Abstract

Keywords

Introduction

Computational details

Results and discussion

Stability and electronic properties

QTAIM analysis

Conclusions

Supplemental Material

sj-docx-1-mgc-10.1177_10241221261456942 - Supplemental material for Novel supersalts formed by interaction of H2M3 superalkalis (M = Li and Na) with AlF4, BeF3 and NO3 superhalogens

Footnotes

ORCID iDs

Ethical considerations and informed consent

Author contributions

Funding

Declaration of conflicting interests

Data availability statement

Supplemental material

References

Supplementary Material

sj-docx-1-mgc-10.1177_10241221261456942 - Supplemental material for Novel supersalts formed by interaction of H₂M₃ superalkalis (M = Li and Na) with AlF₄, BeF₃ and NO₃ superhalogens