Density functional theory studies on structure, spectra, and electronic properties of 3,7-dinitrodibenzobromolium cation and chloride

Abstract

The structural and electronic properties of the 3, 7-dinitrodibenzobromolium cation and chloride were studied using first-principle methods, based on the density functional theory (DFT). Different forms of exchange and correlation functions and basis sets were considered, and their suitability in studying such large molecules were assessed by comparing the calculated results with available X-ray diffraction data. The DFT results were also compared with those obtained previously using the Hartree - Fock (HF) method. The DFT methods improved on the calculated IR and Raman spectra, confirming the superiority of the DFT methods over the HF method in predicting harmonic frequencies, particularly for organic nitro compounds. The geometric parameters obtained using the hybrid DFT methods, such as B3LYP, B3P86, and B3PW91, are compatible with the results of the HF method. The structure of 3,7-dinitrodibenzobromolium chloride was optimized with and without symmetry constraints (such and C s and C 2v) separately. The C 1 structure obtained from optimization without any symmetry constraints and the C s structure were proven to be identical, using more-stringent convergence criteria in the structure optimization. Intrinsic reaction coordinate (IRC) calculation was performed, following the frequency calculation for the optimized C 2v structure. The results confirmed that the C 2v structure is the transition structure connecting the two energy minimum stuctures in C s symmetry. A strong ionic bond is formed between the chloride anion and the 3,7-dinitrodibenzobromolium cation, with a Br-Cl bond length of 2.606 Å. Further studies were conducted to obtain the electronic density, electrostatic potential, and charge distribution of the chloride and the cation in its planar form and with the rotation of the nitro group. The charge distribution of other halides are also investigated and discussed. Knowledge of the electron properties is useful for understanding the bonding and biological activities of this molecule.