In this study, Raman, infrared, UV/vis, NMR, and single crystal X-ray diffraction spectroscopies are used to elucidate the tautomeric equilibrium of azo dyes derived from 1-phenyl-azo-2-naphthol (Sudan I). A new crystallographic structure is described for Sudan I, revealing the presence of intramolecular hydrogen bonds and supramolecular interactions, such as the unconventional C-H···O hydrogen bond type, π-stacking, and charge-dipole interactions. All of these weak intermolecular interactions play a role in the stability of the crystalline structure. Theoretical calculations are also reported for geometries, energy, and spectroscopic properties. The predicted spectra are in accordance with the experiments carried out in the solid state and in solution of dichloromethane, carbon tetrachloride, and chloroform, suggesting the hydrazo form as the preferable tautomer in gas and condensate phases for Sudan I and its derivatives.
In this work, four new transition metal complexes of general formula {[M(bipy)(H 2 O) 4 ](B) 2 }(H 2 O) 6 (where M]Co 2+ , Ni 2+ , Cu 2+ and Zn 2+ , B is barbiturate anion and bipy is 4,4 0 -bipyridine) were obtained and investigated by means of single crystal X-ray diffraction and vibrational (Raman and infrared) spectroscopic techniques. The CoB 2 bipy$10H 2 O, NiB 2 bipy$10H 2 O and CuB 2 bipy$10H 2 O basic units give rise to polymers, where Ni(II) and Cu(II) compounds are isomorphous, however all compounds present the same molecular structure. The metal sites appear in a distorted octahedral geometry coordinated by two pyridine nitrogen atoms and four oxygen atoms from coordinated water molecules. Each structure showing one covalent linear [M(bipy)(H 2 O) 4 ] 2+ chains one-dimensional, which interact by hydrogen-bonding with the barbiturate anion and crystallization water resulting in a 3D arrangement. The analysis of the Ni 2+ and Cu 2+ complexes' structures show flexible 2D hydrogen bonded networks being constructed by the barbiturate anions and the crystallization waters molecules, which may be deemed to be the host, while the robust 1D [M(bipy)(H 2 O) 4 ] 2+ chains may be deemed to be the guest, in a very intriguing and interesting structure. The vibrational spectra of the compounds are very similar, in agreement to the crystal data. In all infrared spectra a medium band at 1690 cm À1 has been observed, assigned to the CO stretch of the barbiturate anion. In the Raman spectra the most important bands referring to 4,4 0 -bipyridine are the ones at 1616, 1290 and 1020 cm À1 , assigned to d CC/ CN , d ring and d CH modes, respectively. The vibrational results strongly suggest the Zn 2+ compound presents the same molecular arrangement, based on the fact that the spectra of all complexes are similar.
Raman spectra of dilute solutions of acetonitrile in ionic liquids reveal the characteristic features of ionic liquids' polarity. This is accomplished by investigating the Raman bandshape of the ν (CN) band, corresponding to the CN stretching mode of CH 3 CN, which is a very sensitive probe of the local environment. The amphiphilic nature of the CH 3 CN molecule allows us to observe the effect of electron pair acceptor and electron pair donor characteristics on ionic liquids. It has been found that the overall polarity of nine different ionic liquids based on 1-alkyl-3-methylimidazolium cations is more dependent on the anion than cation. The observed wavenumber shift of the ν (CN) band of CH 3 CN in ionic liquids containing alkylsulfate anions agrees with the significant different values previously measured for the dielectric constant of these ionic liquids. The conclusions obtained from the analysis of the ν (CN) band were corroborated by the analysis of the symmetric ν 1 (CD 3 ) stretching mode of deuterated acetonitrile in different ionic liquids.
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