Quantum Chemical Study On The Structures And Properties Of The Molecular Clusters Of Azides

The dissertation is about quantum chemical calculations on the molecular clusters of azides. There are two parts:In the first part, we present our systematical studies on intermolecular interactions for the simple azides clusters. The aim is to provide a pioneer model for the study of intermolecular weak interaction in the high energetic materials of the azides compounds. It not only provides important information for the design of mixed explosives, but also plays a promotive role in the development of energetic materials.DFT theory at B3LYP level with different basis sets is performed to calculate the supermolecular systems consisting of up to four hydrazoic acid molecules (HN3)n (n=2-4). The fully optimized geometries have been obtained for the first time. The dimers are found to exhibit cyclic and chain structures. The trimers and tetramers both possess cyclic structures. Both the structural changes of submolecules and charge transfers increase in the cluster processing. The Mulliken populations on intermolecular N...H increase in the sequence of dimer, trimer and tetramer for the same shape. The transition from the trimer to the tetramer involves larger stabilization than that from the dimer to the trimer. As for the trimer and tetramer, the contribution of cooperative effect to the interaction energy is mainly investigated. It is found that cooperative effect increases from the trimer to the tetramer. The basis set superposition error (BSSE) and zero point energies (ZPE) corrections are absolutely necessary for the interaction energies of the clusters. Compared to the monomer, the N-H stretching vibrational frequencies show a marked red shift, as the size of the cluster growths, the shifts increase, reaching more than 200 cm-1 in the tetramer. The changes of thermodynamic properties from the monomer to the (HN3)2-4 clusters at different temperature have been also discussed. The results with the 6-311G**, 6-311++G** and cc-pVTZ basis sets show it is suitable to choose the economic 6-311G** basis set to study the system of (HN3)1₄.Five optimized geometries of (CH3N3)2 dimers and three optimized geometries of (CH3CH2N3)2 and (CH2CHN3)2 supersystems are obtained respectively at the HF/6-311++G** level for the first time. Both the structural changes and charge transfers ofeach cluster are slight compared to the monomer, which implies that the influence of interaction on the geometry and charge is very weak. The corrected interaction energies of the most stable (CH3N3)2, (CH3CH2N3)2 and (CH2CHN3)2 dimers are predicted to be-10.78, -10.45 and -8.66 kJ mol-1 respectively at the MP2/6-311++G*V/HF/6-311++G** level, which shows that the intermolecular interaction of the organic azides molecules is weak. The similar corrected interaction energies of the most stable (CH3N3)2 and (CH3CH2N3)2 indicate that the methyl and ethyl group have little influence on the intermolecular interaction. The electron correlation energies and BSSE correction are absolutely necessary for the interaction energies of the dimers. The ZPE corrections are much less than the electron correlation energies and BSSE correction for the interaction energies. Natural bond orbital (NBO) analysis is performed to reveal the origin of the interaction. On the basis of vibrational analysis and statistical thermodynamic, thermodynamic properties for the monomer and the dimers at different temperature have been obtained.In the second part, we discuss the relationship between the structures and properties of the Group IIIA inorganometallic and organometallic azide clusters. The clusters have been applied widely. The basic studied results not only provide useful information for the design and synthesis of them, but also develop the bonding and structural theory.Firstly, the DFT/B3LYP method with different basis sets used to calculate the (H2AlN3)1-4 clusters predicts that the (H2AlN3)2-4 clusters all possess cyclic-like structures. (H2AlN3)2-4 clusters are formed by Al atoms bridged by the a-nitrogen of the azide groups (connectivity: H2A1-Na-NB-Nr)...