Theoretical Predictive Study On The Structures And Properties Of Tri-s-triazines

In this work, the geometries, electronic structures, harmonic vibrational frequencies, and high energy density material properties of tri-s-triazine (long time less studied) and its twenty-eight derivatives are investigated. The UV/vis absorption spectra and nonlinear optical (NLO) properties of some tri-substituted tris-s-triazines have also been studied. Moreover, the intermolecular interactions between several anions (F-, Cl-, N3-, N4-, and N5-) and tri-s-triazine molecule have been discussed. Our work focuses on the theoretical predictive study. Density functional theory has been used to study the geometries, electronic structures, vibrational frequencies of tri-s-triazine and its twenty-five derivatives (2,5,8-triR-tri-s-triazine, 2-R-tri-s-triazine, and 2-azido-5, 8-diR-tri-s-triazine R= NH2, OH, N3, NO2, F, Cl, Br, -C=N, -CH=CH2) at the B3LYP/aug-cc-pVDZ level of theory. From vibrational analysis, the tri-s-triazine molecule has a characteristic frequency at 869.8cm"1, which could be used to distinguish tri-s-triazine from s-triazine. The electronic distribution in tri-s-triazine is very similar to that in s-triazine. When an electron-donating group or a substituent containing jt bond is attached to the parent ring, the bond lengths of C-N bonds adjacent to the substituents increase, while an electron-withdrawing group or a halogen is attached, these bond lengths decrease. However, in all these cases, the parent ring always holds its rigid plane. The molecular electrostatic potential (MESP) study shows that introduction of electron-donating groups and substituents containing it bond except -C=N to the parent ring will extend the negative spatial domains mildly, whereas introduction of electron-withdrawing groups or halogens will shrink, split and even vanish the negative spatial domains. A special case is that when the -C=N group is attached to the ring; the negative spatial domains emerge near the cyanophoric nitrogen. To all substituted compounds, calculation results indicate that the large conjugation system still exists and the characteristic frequency of parent ring is around 830-870 cm"1, which shifts to a lower wave number compared with that in tri-s-triazine. Molecular orbital study shows that the LUMO of all the derivatives is shared all the atoms while the HOMO is only localized on the peripheral nitrogen atoms of the ring. All the HOMO and LUMO are component of 2Pz atomic orbitals. The introduction of a group containing n bond to the parent ring will result in the decrease of HOMO and LUMO energy gap. After successive replacement of C-H groups by nitrogen atoms in tri-s-triazine, three isoelectronic equivalents could be obtained. The geometric structures, electronic topologies, heats of formation of these nitrogen isoelectronic equivalents and decomposition of the C3N10 have been studied at MP2/6-31G(d) level of theory. The results reveal that all these species have a rigid planar structure and a conjugation system over the tricyclic ring, which is beneficial to their stabilities. The MESP analysis for all the species shows that the central region of the ring has a very strong positive electrostatic potential, which suggests that these heterocyclic rings should be applicable as anion recognition module in cyclophane chemistry. Along with the replacement of C-H group by nitrogen atom in tri-s-triazine molecule, the heats of formation for the substituted products increase substantially. The decomposition of the C3N10 starting from the rupture of one hexagon results in the release of a N2 molecule. Density functional theory has been used to predict the geometry, electronic structure, harmonic vibrational frequency, and azido-tetrazole isomerism of triazido-tri-s-triazine at the B3LYP/aug-cc-pVDZ level of theory. Calculation results show that triazido-tri-s-triazine molecule keeps a planar structure and there exists considerable conjugation over the molecule, which is advantage to the stability ofthis compound. The azido-tetrazole isomerism of triazido-tri-s-triazine is investigated in details. The reaction proceeds initially through loss of the linearity of the azido group, approaching the terminal nitrogen N8 atom of the azide group to the nitrogen atom Nl (or N3) of the ring, and this step is then followed by the attack of the lone pair on Nl (or N3) to the azido group, leading to formation of the bond between Nl (or N3) and N8. The bending of the N-N-N angle in the azide and the redistribution of electron density associated to these events give rise to a large free energy barrier. We have calculated the relative specific impulse using the method introduced by Peter Politzer to evaluate HEDMs (High Energy Density Materials) performance of tri-s-triazine and its twenty-eight derivatives. Our calculated results point out quite clearly that A3 and B3 with azide group, A10 and Bio with ethynyl group, A4, B4 and C2 with nitro group, A5 with cyano group and C3N10 are potential candidates for HEDMs. We have systematically described the results of quantum chemical calculations (MP2 (B3LYP)/6-31+G (d) level) on the intermolecular interactions of tri-s-triazine molecule with several anions. The geometries, energies, and electron density properties of these hydrogen bonding, electrostatic interaction and reactant complexes have been studied. The calculations have shown that all the complexes studied are local minima of the potential energy surface. The binding energies for these interactions range from -9 kcal/mol to -80 kcal/mol. Our calculation results predict that the tri-s-triazine ring should be applicable as a new anion recognition module in cyclophane chemistry and as a depot forming adjuvant for nitrogen cluster, such as N3~, N4~, and Ns~. The first-, second-, and third-order static and frequency-dependent polarizabilities of a series of octupolar tri-s-triazines have been investigated by using the ab initio coupled perturbed Hartree-Fock (CPHF) method. Effects of substitution have also been considered. The results show that a, p\ and y values for octupolar tri-s-triazines are much larger than those for s-triazine both in static and frequency-dependent cases. Attaching groups containing 71 system such as azide and ethenyl to the tri-s-triazine molecule results in a significant increase of first-, second-,and third-order polarizabilities. Our calculations predicted that the octupolar tri-s-triazines may be prospective candidates for nonlinear optical materials. We have investigated the vertical electronic excitations of tri-s-triazines by using the TDDFT method. The solvation effects have been taken into account through the PCM. Thirty singlet and triplet excited states are examined for each species in gas phase and in solution. Our calculations show that excitation energies calculated using PBEO are slightly higher than those calculated using B3LYP, but the energy order obtained by these two functionals is similar. Compared with the available experimental data, our computational results show a good agreement. Only the excited states with strongest oscillator strength of tri-s-triazine and triethynyl-tri-s-triazine correspond to π—>π* excitation and have a relative higher transition energies, compared with those of other tri-s-triazines. All the energy bands in solution show a small variation with those in gas phase although the corresponding oscillator strengths are increased.