Estimating the binding ability of onium ions with CO₂ and π systems: a computational investigation.

Density functional theory (DFT) calculations have been employed on 165 complexes of onium ions (NH4(+), PH4(+), OH3(+), SH3(+)) and methylated onium ions with CO2, aromatic (C6H6) and heteroaromatic (C5H5X, X = N, P; C4H5Y, Y = N, P; C4H4Z, Z = O, S) systems. The stability of CO2···onium, CO2···π and onium···π complexes was shown to be mediated through various noncovalent interactions such as hydrogen bonding, NH-π, PH-π, OH-π, SH-π, CH-π and π-π. We have discussed 17 complexes wherein the proton transfer occurs between the onium ion and the heteroaromatic system.

A theoretical study on structural, spectroscopic and energetic properties of acetamide clusters [CH3CONH2] (n=1-15).

Insights into the formation of hydrogen bonded clusters are of outstanding importance and quantum chemical calculations play a pivotal role in achieving this understanding. Structure and energetic comparison of linear, circular and standard forms of (acetamide)(n) clusters (n = 1-15) at the B3LYP/D95** level of theory including empirical dispersion correction reveals significant cooperativity of hydrogen bonding and size dependent structural preference. A substantial amount of impact of BSSE is observed in these calculations as the cluster size increases irrespective of the kind of arrangement.

A theoretical study on interaction of cyclopentadienyl ligand with alkali and alkaline earth metals.

Ab initio and density functional theory calculations are performed on half-sandwich (M-Cp) and sandwich (Cp-M-Cp) complexes of alkali and alkaline earth metals (M = Li, Na, K, Mg, and Ca) with cyclopentadienyl ligand (Cp). A comparison of dissociation energies demonstrates the ease of dissociation of the complex as ions in solvent phase and preference for dissociation as radicals in gas phase. Atoms in molecules analysis is used to characterize this cation-π interaction based on electron density values obtained at the cage critical point.

Hydrogen bonding in water clusters and their ionized counterparts.

Ab initio and DFT computations were carried out on four distinct hydrogen-bonded arrangements of water clusters (H(2)O)(n), n = 2-20, represented as W1D, W2D, W2DH, and W3D. The variation in the strength of hydrogen bond as a function of the chain length is studied. In all the four cases, there is a substantial cooperative interaction, albeit in different degrees.

Ab initio investigation of benzene clusters: molecular tailoring approach.

An exhaustive study on the clusters of benzene (Bz)(n), n = 2-8, at MP2/6-31++G(∗∗) level of theory is reported. The relative strengths of CH-π and π-π interactions in these aggregates are examined, which eventually govern the pattern of cluster formation. A linear scaling method, viz.