FT-IR and FT-Raman spectroscopic and DFT theoretical studies on 4-azabenzimidazole

Quantum chemical and spectroscopic (FT-IR and FT-Raman) investigations of 3-methyl-3h-imidazole-4-carbaldehyde

FT-IR and FT-Raman spectra of 3-methyl-3h-imidazole-4-carbaldehyde (3M3HI4C) were recorded in the region 4000-400cm(-1) and 3500-50cm(-1), respectively. Optimized geometric parameters, conformational equilibria, normal mode frequencies, and corresponding vibrational assignments of 3M3HI4C were theoretically examined by quantum chemical methods for the first time. All vibrational frequencies were assigned in detail with the help of total energy distribution (TEDs). The experimental wavenumbers were compared with the scaled vibrational frequencies determined by DFT/B3LYP method. The results showed that the B3LYP/6-311++G(d,p) method predicts vibrational frequencies and the structural parameters effectively. The most stable conformer of the title compound was determined. The total electron density and molecular electrostatic potential surfaces of the molecule were constructed by using B3LYP/6-311++G(d,p) method to display electrostatic potential (electron+nuclei) distribution. The electronic properties HOMO and LUMO energies were measured. The lower energy band was assigned to the HOMO→LUMO transition. Natural bond orbital analysis of title molecule has been performed to indicate the presence of intramolecular charge transfer. Energies, relative stabilities, and dipole moments of title molecule were also compared and analyzed in the gas phase and in solvents. Furthermore, solvent effects on the geometry and vibrational frequency of 3M3HI4C were studied theoretically at the DFT/B3LYP level in combination with the conductor polarizable continuum model (C-PCM).

From 7-azaindole to adenine: molecular recognition aspects on mixed-ligand Cu(II) complexes with deaza-adenine ligands

For a better understanding of the versatile behaviour of adenine as a ligand, a series of 10 ternary copper(II) complexes with deaza-adenine ligands [7-azaindole (1,6,7-trideaza-adenine, H7azain), 4-azabenzimidazole (1,6-dideaza-adenine, H4abim), 5-azabenzimidazole (3,6-dideaza-adenine, H5abim), and 7-deaza-adenine (H7deaA)] have been synthesised and characterised by X-ray diffraction. Likewise, all the compounds studied have been analysed by spectral and thermal methods. The proton tautomers and donor capabilities of the above-mentioned deaza-adenine ligands have been calculated by DFT. We conclude that the increasing presence of N-donors in deaza-adenine ligands favours the proton tautomerism and their versatility as co-ligands. Notably, H7azain consistently uses the same tautomer, H4abim uses two different tautomers but is not protonated by the pentadentate H(2)EDTA(2-) ligand, and H(N1)5abim displays the μ(2)-N7,N9 mode, whereas H(N9)7deaA binds Cu(II) by N3 in cooperation with an intra-molecular N9-H···O interaction or using the unprecedented bidentate μ(2)-N1,N3 bridging mode.