الفهرس 
Chapter I : IntroductionOnly 14 pages are availabe for public view
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Abstract
Recently, impressive attention has been paid toward noncovalent interactions due to the wide range of their applications in considerable fields, including drug design, crystal engineering, and materials science. Among noncovalent interactions, there is a growing demand for performing a full characterization of the pnicogen based interactions. More recently, the external electric field (EEF) has been detected with a significant effect on the strength of noncovalent interactions. Therefore, the current thesis has been designed to thoroughly study the effect of external electric field on pnicogen-bearing complexes with the help of quantum mechanical calculations.
σ-holes and lp-holes obviously occurred in all the selected pnicogen-bearing molecules, with variable sizes depending on the atomic size of the examined pnicogen and the directionality and strength of the employed EEF. Remarkably, an unanticipated effect was found for the strong negatively directed EEF (i.e., large EEF value) on the lp-hole size, demonstrating the larger lp-hole sizes for nitrogen-bearing monomers than for phosphorus-bearing ones. Under the field-free conditions and the influence of a positively-directed EEF, the MP2 results disclosed the further favorability of the σ-hole interactions compared to their lp-hole analogs, with substantial negative interaction energies. The PF3∙∙∙LB complexes exhibited more impressive interaction energies than the nitrogen-bearing complexes, in particular, with increasing positively-directed EEF value for the lp-hole interactions. Unexpectedly, the NF3-bearing complexes were evidently observed to have the most significant interaction energies for the lp-hole interactions under field-free conditions and weak positively directed EEF strength (i.e., small EEF value). Point-of-charge (PoC) calculations confirmed the preferential versatility of the examined pnicogens to interact via σ-holes more than lp-holes, with considerable negative molecular stabilization energies. These outstanding findings confirm the eminent role of a directed EEF in tuning the strength of group V interactions.
The potentiality of the σ-hole and lone-pair (lp)-hole pnicogen-containing molecules to form pnicogen∙∙∙pnicogen homodimers (PCl3)2 within σ-hole∙∙∙σ-hole, σ-hole∙∙∙lp-hole, and lp hole∙∙∙lp-hole configurations, was herein well-established, for the first time, under field-free conditions and the influence of the external electric field (EEF). The studied PCl3 molecule was denoted with potent ability to form σ-hole and lp-hole with a higher tendency for the anterior one. The positively-directed EEF enlarged the sizes of the pnicogen σ-hole and lp-hole while the negatively-directed EEF exhibited reverse amplitude. As well, the opted pnicogen-containing molecule can engage in preferential electrostatic interactions with Lewis bases and acids under field-free conditions and the influence of EEF. The investigated molecule was observed to be able to form pnicogen∙∙∙pnicogen homodimer (PCl3)2 within σ-hole∙∙∙lp-hole configuration more preferentially compared to the other modeled configurations. The strength of the studied homodimers within the latter configuration was boosted by directed EEF along the positive direction and plunged along the negative one. The symmetrical nature of σ-hole∙∙∙σ-hole and lp hole∙∙∙lp-hole configurations conclusively decline the directionality effect of the applied EEF. The dispersion energy was announced as the most prevalent force that dominated the σ-hole and lp-hole interactions within the studied pnicogen∙∙∙pnicogen homodimers. These results would be informative for future research in the brain area of chemistry and materials science.
All calculations were executed using High-Performance Computer (HPC) located at CompChem Lab, Minia University, and supported by the Science and Technology Development Fund, STDF, Egypt, Grants No. 5480 & 7972.