Ab initio and density functional calculations were used to analyze the interaction between a molecule of the isocyanic acid with 1 up to 4 molecules of ammonia at the B3LYP/6-311??G(d,p) and MP2/6-311??G(d,p) computational levels. The cooperative effect is increased with the increasing size of studied clusters. Red shifts of the H-N stretching frequency for complexes involving the isocyanic acid as an H-donor were predicted. Atom in molecules was used to analyze cooperative effects on topological parameters.
The interactions of arachno-B(5)H(11) with N(2) and O(2) were theoretically studied. In the B(5)H(11)···N(2) and B(5)H(11)···O(2) complexes, the terminal hydrogens of B(5)H(11) work as electron donors whereas the bridge ones as electron acceptors. The optimized structures and the corresponding harmonic vibration spectra were investigated through the MP2/aug-cc-pVDZ level of theory. In order to characterize the hydrogen bonds, the topological calculations inherent to the QTAIM protocol and MEP analysis were carried out. The NBO analyses were useful in the interpretation of the red-shifts and blue-shifts on the stretch frequencies of the proton donors, of course in agreement with the Bent rule for the chemical bonding as well as by the conceptions of hyperconjugation or hybridization.
The dihydrogen bond complexes (H 3 SiH•••HOX) and halogen bond complexes (H 3 SiH•••XOH) formed between SiH 4 and hypohalous acids HOX (X = F, Cl, and Br) have been studied at the MP2/6-311++G(2d,2p) computational level. The analyses of structure and infrared vibration frequencies have revealed tendencies in the red shifts and blue shifts of the stretch frequencies of the Si-H, H-O, and O-X bonds. Besides the computation of the interaction energies, punctual atomic charges and charge transference amounts were determined at light of the Natural Bond Orbital (NBO) approach, by which the quantifications of the s-and p-characters of hydrogen, oxygen, and silicon also were useful to unveil the frequency shifts aforementioned. With the purpose to elucidate the donor/acceptor interface along the charge transfer mechanism between the dihydrogen bonds and halogen bonds, the application of the hierarchical cluster analysis (HCA) and principal component analysis (PCA) chemometric techniques were useful in this regard. Moreover, the interaction strengths of the H 3 SiH•••HOX and H 3 SiH•••XOH complexes was computed through a model that embodies the frequency shifts and topological parameters derived from quantum theory of atoms in molecules (QTAIM).
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