Designing aromatic heterocyclic superacids in terms of Brønsted and Lewis perspectives.

The unexplored area of organic superacids was investigated in terms of both Brønsted and Lewis concepts of acids and bases. The primary requirement of a superacid-high affinity for electron/fluoride ions was fulfilled using two strategies: (i) using the superhalogen-type heterocyclic framework and (ii) selecting systems that have an electron count one short of attaining (4n + 2) Hückel aromaticity. With these in mind, eleven systems were considered throughout the study, expected to cross the target of 100% H2SO4 acidity and/or the fluoride affinity of SbF5. To enhance the pKa and F- affinity values of the considered systems, electron-withdrawing ligands F and CN were employed. The superhalogen and aromaticity properties were verified by vertical detachment energy (VDE) and nucleus independent chemical shift (NICS) calculations, respectively. Finally, the collective effect of the potential super Lewis acids was looked into using a BL3 skeleton with them acting as ligands.

Unique reactivity of B in B[Ge9Y3]3 (Y = H, CH3, BO, CN): formation of a Lewis base.

Boron compounds usually exhibit Lewis acidity at the boron center due to the presence of vacant p-orbitals. We show that this chemistry can be altered by an appropriate choice of ligands to decorate the boron center. To elucidate this effect, we studied the interactions of boron with two classes of ligands, one based on penta-substituted phenyl species (C6X5, X = F, BO, CN) and the other based on Zintl-ion-based groups (Ge9Y3, Y = H, CH3, BO, CN). An in-depth analysis of the charges and Fukui function values at the local atomic sites of the substituted boron derivatives B(C6X5)3 and B[Ge9Y3]3 shows that the B-center in the former is electrophilic, while it is nucleophilic in the latter. The chemical stability of the B[Ge9Y3]3 species is shown to be due to the presence of strong 2c-2e bonds between the B and Ge centers. Thus, the general notion of the Lewis acid nature of a boron center depends upon the choice of the ligand.

Tailoring the properties of manganocene: formation of magnetic superalkali/superhalogen.

A new magnetic superalkali/superhalogen molecule based on the sandwich complex manganocene is reported. The hydrogen atoms of the cyclopentadienyl rings are periodically substituted with electron-donating and electron-withdrawing ligands (or both) to design substituted manganocene complexes. The substituted manganocene complexes exhibit the properties of superalkali and/or superhalogen depending on the nature of the substituents. The substituents, therefore, act as "switches" that can modify the properties of the parent manganocene moiety by keeping its magnetic nature intact. The substituted complexes also show marked nonlinear optical behavior.

Superhalogens as Building Blocks of Super Lewis Acids.

Lewis acids play an important role in synthetic chemistry. Using first-principle calculations on some newly designed molecules containing boron and organic heterocyclic superhalogen ligands, we show that the acid strength depends on the charge of the central atom as well as on the ligands attached to it. In particular, the strength of the Lewis acid increases with increasing electron withdrawing power of the ligand. With this insight, we highlight the importance of superhalogen-based ligands in the design of strong Lewis acids. Calculated fluoride ion affinity (FIA) values of B[C2 BNO(CN)3 ]3 and B[C2 BNS(CN)3 ]3 show that these are super Lewis acids.

A New Class of Superhalogen Based Anion Receptor in Li-Ion Battery Electrolytes.

In the search for new additives (anion receptors) in Li-ion battery electrolytes especially for LiPF6 and LiClO4, we have theoretically designed boron-based complexes by coupling with different heterocyclic ligands. The validation of the formation of modeled compounds involves reproduction of available experimentally reported absolute magnetic shielding and chemical shift values for different boron complexes. As compared to the commonly used tris(pentafluorophenyl) borane, our designed compounds suggest that the complexes like B[C2HBNO(CN)2]3, B[C2HBNS(CN)2]3, and B[C4H3BN(CN)2]3 are promising additives.

Zintl superalkalis as building blocks of supersalts.

Alkali metal cations and halogen anions are common components of ionic salts. Recently, a new class of salts termed supersalts was reported, each of which contains a superalkali and a superhalogen that mimic an alkali metal cation and a halogen anion, respectively. Using three different functionals, namely B3LYP, wB97X, and M06-2X, we theoretically investigated a new subset of supersalts composed of Zintl-based superalkalis and inorganic superhalogens via computational modeling. The calculated dipole moment and first-order hyperpolarizability values for these supersalts indicate that they present nonlinear optical (NLO) behavior. The supersalts of Zintl superalkalis (Ca2P7, Sr2P7, Ba2P7) and superhalogens (BF4, BeF3, NO3) studied here were found to be stable. Graphical Abstract Using the first-principles calculation, a new class of supersalts by using Zintl-based superalkalis and inorganic superhalogens has been designed.

Deltahedral Organo-Zintl Superhalogens.

Zintl ions constitute a special type of naked anionic clusters, mainly consisting of Group 13, 14, and 15 elements of the Periodic Table. Due to the presence of multiple negative ions, the chemistry of Zintl ions is unique. They not only form Zintl phases with alkali and alkaline-earth metal cations, but also form organo-Zintl clusters with distinct properties. By first-principles calculations based on density functional theory, we have designed a new deltahedral organo-Zintl cluster with Ge94- as the core and aromatic heterocyclic compounds as ligands. Calculations on such complexes show that they form a special class of system known as a superhalogen (SH), with a high vertical detachment energy of 4.9 eV. The density of states (DOS), partial DOS, and different molecular orbitals give additional information about the bonding features of the complexes.

On the making of aromatic organometallic superalkali complexes.

Superalkalis are complexes that have a lower ionization energy than that of the corresponding alkali and alkaline earth metals. Based on First Principles calculations, the plausible existence of a superalkali complex consisting of an all-metal aromatic trigonal Au3 core coupled with pyridine (Py) and imidazole (IMD) ligands is suggested. The calculated ionization energy (IE) values of the subsequent organometallic complexes, Au3(Py)3 and Au3(IMD)3, are low, thereby mimicking the usual behavior of a superalkali. First order hyperpolarizability calculations show the existence of non-linear optical properties in some of the complexes, which is also on par with the properties of a superalkali.

Functionalized deltahedral Zintl complexes Ge9R3 (R = CF3, CN, and NO2): a new class of superhalogens.

The assembly of atoms leads to the formation of clusters. These clusters have a tendency to gain their stability by forming either cations or anions. Among the anionic clusters, Zintl ions with multiple negative charges are a special type of inorganic complex generally formed from group 13, 14 and 15 elements in the periodic table. On the other hand, superhalogens are neutral molecules which have high electron affinity. Between the two different types of molecules, the former stabilized in the neutral state by forming a phase with alkali metal atoms, while the latter prefers the anionic state. Using first principle calculations, we show that it is also possible to design superhalogens having a Zintl core by functionalizing with suitable ligands like CF3, CN and NO2. The vertical detachment energies of these complexes indicate that they can be classified as superhalogens. The stability of these complexes is explained in terms of the jellium model. Density of states, partial density of states and natural localized molecular orbitals (NLMO) of these molecules lend additional information on the structure and bonding of these complexes.

Residue Specific Interaction of an Unfolded Protein with Solvents in Mixed Water-Ethanol Solutions: A Combined Molecular Dynamics and ONIOM Study.

The molecular mechanism of ethanol governed unfolding of an enzymatic protein, chymotrypsin inhibitor 2 (CI2), in water-ethanol mixed solutions has been studied by using combined molecular dynamics simulations and ONIOM study. The residue specific solvation of the unfolded protein and the interactions between the individual amino acid residues of the protein with ethanol as well as water have been investigated. The results are compared with that obtained from the folded state of the protein. Further, emphasis has been given to explore the residue's preferential site of attraction toward the nature of the solvents. The heterogeneous structuring of water and ethanol around the hydrophobic and hydrophilic surfaces of the protein is found to correlate well with their available surface areas to the solvents. Both hydrophobic and hydrophilic interactions are found to have important contributions in rupturing protein's secondary structural segments. Further, residue-water as well as residue-ethanol binding energies show significant involvement of the hydrogen bonding environment in the unfolding process; particularly, residue-water hydrogen bonds are found to play an indispensable role.

Organic heterocyclic molecules become superalkalis.

An organic molecule which behaves like a superalkali has been designed from an aromatic heterocyclic molecule, pyrrole. Using first-principles calculation and a systematic two-step approach, we can have superalkali molecules with a low ionization energy, even lower than that of Cs. Couple cluster (CCSD) calculation reveals that a new heterocycle, C3N2(CH3)5 derived from a well-known aromatic heterocycle, pyrrole (C4H5N) has an ionization energy close to 3.0 eV. A molecular dynamics calculation on C3N2(CH3)5 reveals that the structure is dynamically stable.