Structural Studies and Photochromism of Mercury(II)−Iodo Complexes of (Arylazo)imidazoles

• Published in: Inorganic chemistry 2007-02, Vol.46 (3), p.670-680
• Main Authors: Sarker, K. K, Chand, B. G, Suwa, K, Cheng, J, Lu, T.-H, Otsuki, J, Sinha, C
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic061221u

Neat reaction between HgI2 and 1-methyl-2-(phenylazo)imidazole (Pai-Me) under microwave irradiation has isolated a novel compound whose structure shows intercalated HgI2 in the layers of Pai-Me. They exist independently in interpenetrated arrays. In a solution phase study, the same reaction has synthesized an iodo-bridged azoimidazole−Hg(II) complex, [Hg(RaaiR‘)(μ-I)(I)]2 (RaaiR‘ = 1-alkyl-2-(arylazo)imidazole). The structures have been characterized by X-ray diffraction studies. Chloro-bridged Hg(II) complexes of azoimidazoles, [Hg(RaaiR‘)(μ-Cl)(Cl)]2, are also known. These complexes upon irradiation with UV light show trans-to-cis isomerization. The reverse transformation, cis-to-trans isomerization, 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 than their Hg(II) complexes. The cis-to-trans isomerization is a thermally induced process. The activation energy (E a) of cis-to-trans isomerization is calculated by controlled temperature reaction. The E a's of free ligands are much higher than that of halo-bridged Hg(II)−azoimidazole complexes. Chloro-bridged Hg(II) complexes show lower E a's than those of iodo-bridged complexes. DFT calculation has been adopted to rationalize the experimental results.