Various local minimum structures of an aniline complex with carbon monoxide; DFT and MP2 calculations

Role of the substituent effect over the squarate oxocarbonic ring: spectroscopy, crystal structure, and density functional theory calculations of 1,2-dianilinosquairane

This work presents the crystal structure and the investigation under a supramolecular perspective of a squaric acid derivative obtained from the replacement of the hydroxyl groups by anilines. The squaraine obtained (1,2-dianilinesquaraine) crystallizes in the Pbcn space group, in a unit cell with a = 26.5911(8) Å, b = 6.1445(10) Å, and c = 7.5515(5) Å. The bond lengths in the oxocarbon ring, squarate-N and C−O bonds present the character of double bonds. Also the difference between the longer and shorter C-C bond in the four-membered ring (ΔCC) is 0.0667 Å, showing a good degree of equalization of these bond lengths. The phenyl rings are slightly distorted in relation to the squarate ring, and the angle measured between the best plane fitted in each ring is 37.2(9)°. Each molecule is connected to the other through a hydrogen bond involving the N-H···O moieties, where the donor···acceptor distance is 2.826(1) Å, forming ribbons in a unidimensional arrangement C(5)R22(10) along the b axis. These structures are mutually connected by π-stacking interactions extending the supramolecular structure in a two-dimensional fashion. Besides, an interesting crossed structure can be easily identified in the formed sheets that are built through the C-H/π interactions. DFT calculations at the B3LYP/6-311++G(d,p) level of theory show an approximately planar molecular structure for the isolated molecule. However, when a dimer model built from hydrogen bonds is considered, the optimized structure presents considerable torsion between the phenyl and squarate rings, as observed in the experimental data. The electronic spectrum shows a strong absorption band at 341 nm that is red-shifted compared to the squarate maximum absorption (290 nm), indicating a more effective electronic delocalization. The most characteristic vibrational modes of the oxocarbon species were used as spectroscopic probe to understand how the substituent groups affect the oxocarbon moiety and, consequently, the vibrational spectra. The analysis shows that the modes associated with the C-Cox bonds are the most affected. Also the character of the double bond of squarate-N and the single bond for the phenyl-N are easily identified. In a general form, the calculated vibrational modes of the dimer model were in better accordance with the experimental data, mainly when the mode has a contribution from the acceptor molecule in the intermolecular interaction.

Fourier transform infrared and FT-Raman spectra, assignment, ab initio, DFT and normal co-ordinate analysis of 2-chloro-4-methylaniline and 2-chloro-6-methylaniline

The Fourier transform infrared (FTIR) and FT-Raman spectra of 2-chloro-4-methylaniline and 2-chloro-6-methylaniline have been measured in the range 4000-400 and 4000-100cm(-1), respectively. Utilising the observed FTIR and FT-Raman data, a complete vibrational assignment and analysis of the fundamental modes of the compounds were carried out. The vibrational frequency which were determined experimentally are compared with those obtained theoretically from ab initio HF and DFT gradient calculations employing the HF/6-31G(d,p) and B3LYP/6-31G(d,p) methods for optimised geometries. The geometries and normal modes of vibration obtained from the HF and DFT methods are in good agreement with the experimental data. The normal co-ordinate analysis was also carried out on the basis of ab initio force fields utilising Wilson's FG matrix method. The manifestations of NH-pi interactions and the influence of bulky chlorine and methyl group on the vibrational modes of the amino group are investigated.