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Arylazoimidazole complexes of lead(II)-halide and their photochromism<br />

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Title Statement Arylazoimidazole complexes of lead(II)-halide and their photochromism<br />
 
Added Entry - Uncontrolled Name SINHA, CHITTARANJAN ; Professor
Financial support under minor research programme (PSW-158/13-14) from the UGC, New Delhi and the Council of Scientific and Industrial Research (CSIR, Sanction No. 01(2894)/17/EMR-II) New Delhi, India are gratefully acknowledged.
 
Uncontrolled Index Term Synthetic and structural inorganic chemistry; spectroscopy, theoretical & quantum chemistry;
Photochromism, Density functional calculations, Arylazoimidazoles, Lead halide complexes
 
Summary, etc. <p>Lead(II) complexes of 1-alkyl-2-(arylazo)imidazole (Raai-C<sub>n</sub>H<sub>2n+1</sub>), [Pb(Raai-C<sub>n</sub>H<sub>2n+1</sub>)X<sub>2</sub>] (X = Cl, Br, I; and Raai-C<sub>n</sub>H<sub>2n+1</sub>, R = H, Me and <em>n</em> = 4, 6, 8) have been characterized by UV-vis, IR and <sup>1</sup>H-NMR spectroscopy. The coordinated Raai-C<sub>n</sub>H<sub>2n+1 </sub>in the complexes undergoes E-to-Z (<em>trans</em>-to-<em>cis</em>) isomerisation about the –N=N– group upon being irradiated with UV light in DMF solution. The rate and quantum yields of E-to-Z photoisomerisation (f<sub>E®Z</sub>) of the complexes are poorer than the respective free ligand response and are also affected by the nature of halide present (Cl<sup>-</sup>, Br<sup>-</sup> and I<sup>-</sup>). Variation in physicochemical parameters may be correlated with the effective mass of the photochrome. The rate of isomerisation follows the sequence: [Pb(Raai-C<sub>n</sub>H<sub>2n+1</sub>)Cl<sub>2</sub>] &lt; [Pb(Raai-C<sub>n</sub>H<sub>2n+1</sub>)Br<sub>2</sub>] &lt; [Pb(Raai-C<sub>n</sub>H<sub>2n+1</sub>)I<sub>2</sub>]. The Z-to-E isomerisation has been carried out at varying temperatures (298–308 K) to determine the activation energy of Z-to-E (<em>cis</em>-to-<em>trans</em>) isomerisation <br /> (<em>E</em><sub>a</sub>: 47.09–63.42 kJ mol<sup>-1</sup>) and the entropy of activation (DS<em><sup> </sup></em>: 166.52 to –109.0 J mol<sup>-1</sup> K<sup>-1</sup>) which is a large negative in the complexes. Theoretical calculation supports cleavage of Pb(II)-N(azo) bond followed by the –N=N– rotation in a three-coordinated symmetry rather than the four-coordinated symmetry.</p>
 
Publication, Distribution, Etc. Indian Journal of Chemistry -Section A (IJCA)
2020-10-19 12:41:14
 
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http://op.niscair.res.in/index.php/IJCA/article/view/19708
 
Data Source Entry Indian Journal of Chemistry -Section A (IJCA); ##issue.vol## 57, ##issue.no## 3 (2018): INDIAN JOURNAL OF CHEMISTRY- SECTION A
 
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