Conformation of the hydrazo bond in new 2-methyl-3,5-dinitro-6-(2-phenylhydrazinyl)pyridine and its influence on the structural and optic properties - Quantum chemical DFT calculations

A new methyl-dinitro-phenylhydrazinyl-pyridine derivative [2-methyl-3,5-dinitro-6-(2-phenylhydrazinyl)pyridine] was synthesised and characterised by means of structural and spectroscopic measurements. The X-ray diffraction studies revealed that the compound crystallises in the centrosymmetric monoclinic space group P21/n, with two symmetry-independent molecules in the asymmetric unit with Z = 8. Hydrazo bridge C-NH-NH-C links two fragments composed of phenyl ring and pyridine unit substituted with methyl and nitro groups. Such a structure was confirmed by 1H and 13C NMR studies as well as IR, Raman, UV-Vis, and emission spectra. The results were analysed using the quantum-chemical DFT calculations. The paper reports the vibrational characteristics and discusses dynamical properties of this moiety. The full set of the normal modes typical of the hydrazo bridge was identified and assigned to respective IR and Raman bands. The results of structural and spectroscopic studies were used to find the dependence between the conformation of the θ-NH-NH-ϕ system and its optic properties. The experimental UV-Vis and emission spectra were discussed in terms of the calculated singlet and triplet states that allowed assigning the unique spectral pattern originating from the electrons of the hydrazo-bridge system.