Ambrish Kumar Srivastava

Novel Li3X3 supersalts (X = F, Cl, Br & I) and their alkalide characteristics

We have theoretically predicted the formation of novel species by the interaction of LiX2 superhalogens with Li2X superalkalies for X = F, Cl, Br and I. The resulting Li3X3 supersalts are found to be more stable than the traditional LiX salts. The chemical reactivity of Li3X3 is discussed with the help of various electronic parameters and it is shown that they may possess alkalide characteristics. The present report will pave a way for experimentalists to design such novel species with pronounced properties.

Novel (Li2X)+(LiX2)− supersalts (X = F, Cl) with aromaticity: a journey towards the design of a new class of salts

LiF2 and Li2F can be considered as representatives of main group superhalogens and superalkali species, respectively. For the first time, we present a study on the interactions between LiX2 and Li2X, for X = F, Cl. Our findings show that this interaction leads to the formation of ring-shaped Li3X3 supersalts. The quantum theory of atoms in molecule (QTAIM) approach is used to discuss superatomic bonding in these novel species. The aromatic character of Li3X3 rings is established by QTAIM in addition to various chemical-reactivity-based measures. Thus, the present work opens up an avenue to further investigate these new classes of aromatic species, theoretically as well as to synthesise them, experimentally.

Superalkali-hydroxides as strong bases and superbases

Alkali metals have the lowest ionization potentials of all the elements in the periodic table, and their hydroxides are the strongest bases existing in the neutral form. So-called “superalkalies” have even lower ionization potentials than do alkalies, have potential-reducing capabilities, and can be used in the synthesis of a variety of charge-transfer salts. Like alkali hydroxides, superalkali-hydroxides are also expected to be strong basic compounds. To test this expectation, we have computationally investigated superalkali hydroxides (FLi2OH, OLi3OH and NLi4OH) for the first time and compared their basicity levels with that of LiOH, employing second-order Moller–Plesset perturbation theory. The proton affinity and gas-phase basicity values of these species were calculated to be comparable to or larger than those of LiOH, suggesting that they are stronger bases than LiOH, and even act as superbases. Various other parameters of superalkali hydroxides that are closely associated with their chemical reactivity and basicity are also described. This work is expected to provide new insights into hydroxide bases as well as motivate further exploration of such novel species with pronounced properties.

FT-IR spectroscopy, intra-molecular C−H⋯O interactions, HOMO, LUMO, MESP analysis and biological activity of two natural products, triclisine and rufescine: DFT and QTAIM approaches

The present study deals with two natural products, triclisine and rufescine which are extracted from the Amazonian wines but ubiquitous in nature. The quantum chemical density functional method at B3PW91/6-311+G(d,p) level is used to obtain the equilibrium geometries of these molecules. The quantum theory of atoms-in-molecule approach is employed to study various intra-molecular C-H⋯O interactions within these molecules. We have also performed vibrational analyses of triclisine and rufescine at their equilibrium geometries and presented the complete assignments of the significant vibrational modes. The calculated vibrational frequencies are shown to be in perfect agreement with the experimentally observed FTIR spectra of molecules under study. In addition, the electronic properties of these molecules are also discussed with the help of HOMO-LUMO and MESP surfaces and a number of electronic as well as thermodynamic parameters are calculated which are closely related to their chemical reactivity and reaction paths. The biological activities of both molecules have also been predicted which highlight their pharmacological importance.

Ab initio investigations on the gas phase basicity and nonlinear optical properties of FLinOH species (n = 2–5)

Superalkalies, due to lower ionization potentials than alkalies, possess potential reducing capability and can be used in the synthesis of a variety of charge transfer salts. In order to check whether superalkali hydroxides are as basic as a typical alkali hydroxide, we have performed a systematic investigation on the hydroxides of small FLin (n = 2–5) superalkali clusters. The equilibrium structures are identified and their stability is analyzed against the elimination of LiOH and LiF molecules. Our MP2 calculations show that the proton affinity and gas phase basicity of the FLinOH species are lower than that of LiOH by 50–100 kJ mol−1. The trend of basicity of FLinOH is in accordance with their HOMO–LUMO energy gap as well as the LiOH and LiF elimination energies. Considering the fact that charge transfer salts possess significant nonlinear optical (NLO) responses, we have also calculated NLO parameters such as the total static dipole moment, the mean polarizability and the first static mean hyperpolarizability of the FLinOH species. The dipole moment and the polarizability values increase successively from FLi2OH to FLi5OH. On the contrary, the hyperpolarizability only increases for FLi3OH (2.7 × 103 a.u) and FLi5OH (2.6 × 105 a.u.). The dramatically large hyperpolarizability of FLi5OH is due to anionic Li possessing an excess electron, thus resembling the feature of an “alkalide”. The present work should provide new insights into the design of strong inorganic bases for chemical synthesis as well as potential NLO species for electro-optical applications.

Unusual bonding and electron affinity of nickel group transition metal oxide clusters

We perform density functional calculations on the ground state geometries of MOn clusters (M = Ni, Pd, Pt; n = 1–5) in neutral as well as anionic forms. Our calculations reveal that Ni can bind up to three O atoms while Pd and Pt bind with four O atomically indicating the fact that the maximum oxidation state of Ni can take the value of +6 and can go as high as +8 in case of Pd or Pt. The electron affinities of MOn suggest that these species behave as superhalogens for n ≥ 2. The large electron affinities of MOn species along with stability of their anions further point towards the synthesis of new class of compounds having unusual oxidising capabilities.

Unusual properties of novel Li3F3 ring: (LiF2–Li2F) superatomic cluster or lithium fluoride trimer, (LiF)3?

LiF2 and Li2F are typical examples of molecular species showing superhalogen and superalkali behavior, respectively. HF, DFT (B3LYP, B3PW91), MP2, CCSD and CCSD(T) calculations are performed to study the interaction between LiF2 and Li2F which forms a ring shaped Li3F3 superatomic cluster. It is well known that Li3F3 can be formed by trimerization of LiF. However, these two isostructures can be distinguished by considering the effect of extra electrons on Li3F3. Our MP2 calculations have shown that extra electrons are delocalized on Lis of the Li2F moiety in the case of LiF2–Li2F but delocalized over all Lis in the case of (LiF)3. Finally, we have discussed the formation of one dimensional assemblies of Li3F3 superatomic rings which may mimic the bulk behavior and can be realized by inserting Li3F3 rings in one dimensional nano templates such as carbon nanotubes.

Superhalogen properties of ReOn (n = 1–5) species and their interactions with an alkali metal: an ab initio study

First principle density functional approach is employed to investigate the ground-state geometries and stabilities of ReOn species (n = 1–5) in neutral as well as anionic forms. It is revealed that Re can bind stably with five O atoms indicating the maximum oxidation state of Re as high as +10. The electron affinities of ReOn suggest that these species behave as superhalogens for n ≥ 3 which become as large as 7.25 eV for n = 5. The interaction of ReOn superhalogens with appropriate alkali metals is stronger than that of halogens leading to the synthesis of more stable complex compounds. This idea is illustrated by considering the interaction of ReOn superhalogens with K atom, forming KReOn complexes which are relatively more stable than KF molecule. In such complexes, ReOn unit closely mimics the behaviour of F atom when compared with KF.

The aromaticity and electronic properties of monosubstituted benzene, borazine and diazadiborine rings: an ab initio MP2 study

A comparative Møller–Plesset perturbation theory-based study to analyze the substituent’s effect on the aromaticity and electronic properties of benzene, borazine and diazadiborine has been performed considering electron-donating groups (EDGs) such as –NH2 and –CH3 as well as electron-withdrawing groups (EWGs) such as –NO2 and –CF3 at various positions. The lowest energy structures of all monosubstituted rings follow the same trend of NICS values such that there is slight change in the aromaticity due to EDGs and EWGs. However, N-substituted borazine rings are more aromatic but less stable than B-substitution. More interestingly, the aromaticity of substituted diazadiborine rings increases with the increase in the energy of the isomers due to change in the position of substituent. Therefore, the aromaticity does not account for the relative stability of these species. The electronic properties of lowest energy isomers of benzene, borazine and diazadiborine are affected by the substituent in accordance with the aromaticity. For instance, the substitution of EDGs decreases and that of EWGs increases the ionization potential for all ring systems. The electronic properties of –NO2 (strong EDG)-substituted rings are particularly noticeable due to their large electrophilic index values and larger ionization potentials. This comprehensive report is intended to provide new insights into the energetics, aromaticity and related properties of substituted six-membered homocyclic as well as heterocyclic rings.

Ab initio investigations on lithium–superhalogen (Li–X) complexes (X = LiF2, BeF3, BF4 and PF6): competition between s-block and p-block anions

In this work, we investigate the formation of Li–X complexes by interaction of Li cation and superhalogen (X) anions belonging to s block (X = LiF2, BeF3) and p block (X = BF4, PF6). We discuss their structures and stabilities using the quantum chemical method at MP2/aug-cc-pVDZ level of theory. Considering polarisable continuum model, solvent effects are taken into account in a polar organic solvent, namely diethyl ether. Our findings establish that electronic and chemical properties of Li–LiF2 and Li–BeF3 closely resemble Li–BF4 and Li–PF6. However, Li–LiF2 may dissociate preferably into LiF salt; Li–BeF3 appears as a close analogue of Li–BF4, which is significantly stabilised by the solvent. Thus, the superhalogen anions possess electronic integrity irrespective of the nature of central atom.