Jerelle A. Joseph

The effect of atomic ions on model σ-hole bonded complexes of AH3Y (A = C, Si, Ge; Y = F, Cl, Br)

A computational study of ionic X···AH3-Y complexes (X = F(-), Cl(-), Br(-), Li(+), Be(2+); A = C, Si, Ge; Y = F, Cl, Br) predicted optimized structures which are held together by a combination of attractive forces, including ion-dipole and ion-σ-hole electrostatic interactions, and polarization forces. The trends (with variation in the halogen Y) for selected properties were rationalized by considering the electron density shifts due to the ions electric field. Although it has been found previously that the trends for binding energies in neutral complexes follow the sigma-hole strength, the present study found that the dependence on the dipole polarizability of the A-Y bond can explain the trends for binding energies in these more strongly bound ionic complexes.

Cooperative effects in novel LiF/HF⋯LiF⋯XF (X = F, Cl, Br) clusters

Highly stable trimeric clusters of general formula LiF∕HF⋯LiF⋯XF (X = F, Cl, Br) are predicted computationally. These clusters involve a LiF⋯XF dyad, with both the positively charged Li and negatively charged F atom of LiF non-covalently bonded to the X atom of XF. A third molecule (LiF or HF) is complexed to this dyad via ionic-type F⋯Li and Li(H)⋯F interactions to form a substantially stronger cluster.

Comparative computational study of model halogen-bonded complexes of FKrCl.

Quantum chemical calculations for the FKrCl molecule at various levels of theory were performed and suggest that this molecule is metastable and may be amenable to experimental synthesis under cryogenic conditions. The FKrCl molecule forms weak halogen-bonded complexes FKrCl···Y with small molecules like FH and H2O and its computed properties were compared with those for analogous complexes of its precursor, FCl, and its rare gas hydride counterpart, FKrH. The cooperative effect of additional noncovalent interactions introduced at the F atom in the FKrCl···Y dimer (to give Z···FKrCl···Y trimers) showed a general strengthening of the intermolecular interactions in the order halogen bond < hydrogen bond < beryllium bond < lithium bond.

Cooperative effects of noncovalent bonds to the Br atom of halogen-bonded H3N…BrZ and HCN…BrZ (Z = F, Br) complexes

A series of complexes formed between halogen-bonded H(3)N/HCN...BrZ (Z = Br, F) dimers and H(3)N/HCN...BrZ...XY (XY = HF, ClF, BeH(2), LiF) trimers were investigated at the MP2 and B3LYP levels of theory using a 6-31++G(d,p) basis set. Optimized structures, interaction energies, and other properties of interest were obtained. The addition of XY to the H(3)N/HCN...BrZ dyad leads to enhanced intermolecular binding with respect to the isolated monomers. This enhanced binding receives contributions from the electrostatic and inductive forces between the constituent pairs, with, in some instances, substantial three-body non-additive contributions to the binding energy. It was found that the XY = LiF interaction causes the greatest distortion of the H(3)N/HCN...BrZ halogen bond from the preferred linear orientation and also provides the strongest binding energy via the nonadditive energy.

A comparative study of model halogen-bonded, π-hole-bonded and cationic complexes involving NCX AND H2O (X = F, Cl, Br)

A MP2/6-311+ +G(d,p) study of NCX (X = F, Cl, Br) has shown that it is possible to attach an electrophile (H+, Be2+) to the positive halogen X surface of NCX. The stability and properties of model halogen-bonded and π-hole carbon-bonded NCX/H2O complexes were found to be significantly affected by H+ or Be2+ cationic attachment at the N atom. The halogen-bonded complexes are destabilised by binding at the N, while an attached proton enhances the binding in the π-hole bonded dimers. For the attached Be2+, an unusual complex was obtained with the NCF subunit, whereas the complexes containing Cl and Br were destabilised by the interaction.

Communication: An unusual halogen-bonding motif: The LiBr···BrF dimer as a model system

A stable complex, LiBr···BrF, is predicted in which the negative Br atom of LiBr is anchored to the Br atom of BrF by a halogen bond, while the positively charged Li atom interacts with the lone pair electron density on the Br atom of BrF in a direction roughly perpendicular to the halogen bond. As far as we are aware, this is the first reported instance of an atom of one diatomic molecule (Br of BrF) being bonded to two different, oppositely charged atoms (Li and Br) of another diatomic molecule (LiBr). Other less stable dimers of LiBr and BrF were predicted and compared with this novel complex.

Interplay of Hydrogen, Halogen, Lithium and Beryllium Bonds in Complexes of Thiirane

Hydrogen, halogen, lithium and beryllium bonding are briefly surveyed as a prelude to a report of a computational study of the interplay between these various non-covalent interactions. Our study used model dimers and trimers involving the thiirane molecule, (CH2)2S, complexed with small molecules like HF, ClF, BrF, LiF and BeH2 to assess and investigate the interplay between the different non-covalent interactions. The model trimer systems show positive cooperative effects when thiirane is one of the terminal molecules, whereas a negative cooperative effect is evident when it is at the center of the trimer. The changes in selected molecular properties, including the redistribution of charge densities obtained by the natural population analysis (NPA), implemented in the natural bond orbital (NBO) procedure, and an Atoms in Molecules (AIM) topological analysis, were useful in understanding these cooperative effects.