954374-08-4Relevant academic research and scientific papers
Cadmium(II) complexes of (Arylazo)imidazoles: Synthesis, structure, photochromism, and density functional theory calculation
Sarker,Sardar,Suwa,Otsuki,Sinha
, p. 8291 - 8301 (2007)
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)I 2·DMF] [where TaiMe = 1-methyl-2-(p-tolylazo)imidazole]. UV-light irradiation in a MeCN solution of Cd(RaaiR′)2I 2 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 (φt→c) of trans-to-cis isomerization are calculated, and the free ligand shows higher φ 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 2Br2 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.
