Synthesis, spectral characterisation, and electrochemistry of bis-(2,2′-bipyridine)(1-alkyl-2-(naphthylazo)imidazole)ruthenium(II) complexes: X-ray crystal structure of [bis-(2,2′-bipyridine)-{1-ethyl-2-(naphthyl-α-azo)imidazole}ruthenium(II) perchlorate

Conformation of azo-bridge in 3,3'-dinitro-2,2'-azobipyridine and its 4,4'(or 5,5' or 6,6')-dimethyl-derivatives: vibrational studies and DFT quantum chemical calculations

Syntheses of 3,3'-dinitro-2,2'-azobipyridine and 4,4' (or 5,5' or 6,6')-dimethyl-3,3'-dinitro-2,2'-azobipyridine have been described. Molecular structures of these compounds have been determined and compared, to the basic compound, azobipyridine, reported by us earlier. The conformation of the azo-bond and other structural data are discussed in terms of substitution place of methyl chromophore. Fourier transform IR and Raman spectra of these compounds have been measured and analysed. The 6-311G (2d,2p) basis set with the B3LYP functional have been used to discuss the space conformation and dynamics of the studied compounds.

Cadmium(II) complexes of (arylazo)imidazoles: synthesis, structure, photochromism, and density functional theory calculation

Reaction between CdX2 and 1-alkyl-2-(phenylazo)imidazole (RaaiR') has isolated complexes of composition Cd(RaaiR')2X2 in MeOH or MeCN. Crystallization of Cd(RaaiR')2I2 from N,N-dimethylformamide (DMF) has separated [Cd(RaaiR')I2.DMF], while Cd(RaaiR')2X2 (X = Cl and Br) remains unchanged in its composition upon crystallization under identical conditions. The structure has been established by spectral (UV-vis and 1H NMR) data and confirmation in the latter case by a single-crystal X-ray diffraction study of [Cd(TaiMe)I2.DMF] [where TaiMe = 1-methyl-2-(p-tolylazo)imidazole]. UV-light irradiation in a MeCN solution of Cd(RaaiR')2I2 and [Cd(RaaiR')I2.DMF] shows trans-to-cis isomerization of coordinated azoimidazole. The reverse transformation, cis-to-trans, is very slow with visible light irradiation. Quantum yields (phit-->c) of trans-to-cis isomerization are calculated, and the free ligand shows higher phi values than their cadmium(II) iodo complexes. The cis-to-trans isomerization is a thermally induced process. The activation energy (Ea) of cis-to-trans isomerization is calculated by a controlled-temperature experiment. The effects of the anions (Cl-, Br-, I-, and ClO4-) and the number of coordinated azoimidazoles (RaaiR') [Cd(RaaiR') or Cd(RaaiR')2] on the rate and quantum yields of photochromism are established in this work. A slow rate of photoisomerization of [Cd(RaaiR')4](ClO4)2 compared to Cd(RaaiR')I2 or Cd(RaaiR')2X2 may be associated with the increased mass and rotor volume of the complexes. The rate of isomerization is also dependent on the nature of X and follows the sequence Cd(RaaiR')2Cl2 < Cd(RaaiR')2Br2 < Cd(RaaiR')2I2. It may be related to the size and electronegativity of halide, which reduces the effective molar association in the order of I < Br < Cl and hence the rate. Gaussian 03 calculations of representative complexes and free ligands are used to explain the difference in the rates and quantum yields of photoisomerization.