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trans-Dichloro-bis-(arylazoimidazole)palladium(II): Synthesis, Structure, Photoisomerization, and DFT Calculation

Pratihar, P and Mondal, TK and Patra, AK and Sinha, C (2009) trans-Dichloro-bis-(arylazoimidazole)palladium(II): Synthesis, Structure, Photoisomerization, and DFT Calculation. In: Inorganic Chemistry, 48 (7). 2760 -2769.

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Official URL: http://pubs.acs.org/doi/abs/10.1021/ic8012365

Abstract

Reaction between PdCl2 and 1-alkyl-2-(arylazo)imidazole (RaaiR') or 1-alkyl-2-(naphthyl-alpha/beta-azo)imidazole (alpha/beta-NaiR') under reflux in ethanol has isolated complexes of compositions Pd(RaaiR')(2)Cl-2 (5, 6) and Pd(alpha/beta-NaiR')(2)Cl-2 (7, 8). The X-ray structure determination of one of the molecules, Pd(alpha-NaiBz)(2)Cl-2 (7c), has reported a trans-PdCl2 configuration, and alpha-NaiBz acts as monodentate N(imidazole) donor ligand. The spectral (IR, UV-vis, H-1 NMR) data support the structure. UV light irradiation (light source: Perkin-Elmer LS 55 spectrofluorimeter, Xenon discharge lamp, lambda = 360-396 nm) in a MeCN solution of the complexes shows E-to-Z isomerization of the coordinated azoimidazole unit. The reverse transformation, Z-to-E, is very slow with visible light irradiation. Quantum yields (phi(E-Z)) of E-to-Z isomerization are calculated, and phi is lower than that of the free ligand but comparable with those of Cd(II) and Hg(II) complexes of the same ligand. The Z-to-E isomerization is a thermally induced process. The activation energy (E-a) of Z-to-E isomerization is calculated by controlled-temperature experimentation. cis-Pd(azoimidazole)Cl-2 complexes (azomidazole acts as N(imidazole) and N(azo) Chelating ligand) do not respond upon light irradiation, which supports the idea that the presence of noncoordinated azo-N to make free azo (-N=N-) function is important to reveal photochromic activity. DFT calculation of Pd(alpha-NaiBz)(2)Cl-2 (7c) has suggested that the HOMO of the molecule is constituted of Pd (32%) and Cl (66%), and hence photo excitation may use the energy of Pd and Cl instead of that of the photofunctional -N=N-Ar motif; thus, the rate of photoisomerization and quantum yield decrease versus the free ligand values.

Item Type: Journal Article
Additional Information: Copyrights of this article belongs to American Chemical Society.
Keywords: X-Ray-Structure; Effective Core Potentials; Molecular Calculations; Crystal-Structures; Metal-Complexes; Spectral Characterization; Electronic-Properties; Photochromism; Azobenzene; Haaime=1-Methyl-2-(Phenylazo)Imidazole
Department/Centre: Division of Chemical Sciences > Inorganic & Physical Chemistry
Date Deposited: 16 Nov 2009 12:27
Last Modified: 19 Sep 2010 05:30
URI: http://eprints.iisc.ernet.in/id/eprint/19952

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