Intercalated iodobismuthate in the layers of azoimidazoles. Structure, photochromism and DFT computation
摘要:
[RaaiR', RaaiR'H+](3) [Bi3I12](3-) are obtained by refluxing BiI3 and RaaiR' (1-alkyl-2-(arylazo)imidazoles) in a 2-methoxyethanol-methanol mixture. The X-ray structure determination of [MeaaiMe, MeaaiMeH(+)](3) [Bi3I12](3-) (MeaaiMe = 1-methyl-2-(p-tolylazo)imidazole) has shown that the iodide bridged bismuthate(III) ([Bi3I12](3-)) is intercalated in the channels formed by MeaaiMe-MeaaiMeH(+). UV light irradiation in DMF solution of the compounds shows E-to-Z (trans-to-cis) isomerisation of the arylazoimidazole about the -N=N- group. The reverse transformation, Z-to-E, is very slow with light irradiation, while it is induced by a thermal process. The quantum yield (phi(E -> Z)) of the E-to-Z isomerisation is dependent on the molar mass and rotor volume of the compounds. The activation energy (E-a) of the Z-to-E isomerisation is calculated by a controlled temperature experiment. DFT computations were performed to explain the spectra and the photochromism. (c) 2013 Elsevier Ltd. All rights reserved.
Structure and photochromism of zinc(II) complexes with 1-alkyl-2-(arylazo)imidazole, and the effect of number of coordinated ligands and halide type on the photochromism
摘要:
Zinc(II) complexes of 1-alkyl-2-(arylazo)imidazoles (RaaiR(/)) such as, [Zn(RaaiR(/))(DMF)X-2], [Zn(RaaiR(/))(2)X-2] (X = Cl, Br, I) and [Zn(RaaiR(/))(4)](ClO4)(2) are characterized by spectroscopic data. The structures have been confirmed by single crystal X-ray diffraction measurements of [Zn(MeaaiCH(2)Ph)(DMF)Cl-2] and [Zn(MeaaiCH(2)Ph)(2)I-2.] (MeaaiCH(2)Ph = 1-benzyl-2-(p-tolylazo)imidazole). These complexes are sensitive to irradiation of light and undergoes trans(t)-to-cis(c) isomerisation of coordinated azoimidazole upon UV light irradiation in DMF solution. Quantum yields (phi(t -> c)) are calculated and it is shown that free ligand shows higher phi(t -> c) than that of Zn(II) complexes. The reverse, cis-to-trans, transformation has been performed slowly with visible light irradiation and becomes fast with increasing temperature. The activation energy (E-a) is calculated by controlled temperature experiment. Effect of anions (Cl-, Br- and I-) and number of coordinated azoimidazoles (RaaiR(/)) [Zn(RaaiR(/))-; Zn(RaaiR(/))(2)-; Zn(RaaiR(/))(4)] on the rate and quantum yields of photochromism are examined. The rate of isomerisation follows the sequence [Zn(RaaiR(/))(n)Cl-2] < [Zn(RaaiR(/))(n)Br-2] < [Zn(RaaiR(/))(n)I-2] (n = 1 or 2) and [Zn(RaaiR(/))(DMF)X-2] > [Zn(RaaiR(/))(2)X-2] > [Zn(RaaiR(/))(4)](ClO4)(2). The effect of halide on the rate and quantum yields have been correlated with electronegativity in the order of I < Br < Cl. Gaussian 03 calculations of representative complexes are used to explain the difference in the rates and quantum yields of photoisomerisation. (C) 2014 Elsevier Ltd. All rights reserved.