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

Abstract

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')(mu-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')(mu-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 (phi t-->c) of trans-to-cis isomerization are calculated, and the free ligand shows higher phi than their Hg(II) complexes. The cis-to-trans isomerization is a thermally induced process. The activation energy (Ea) of cis-to-trans isomerization is calculated by controlled temperature reaction. The Ea's of free ligands are much higher than that of halo-bridged Hg(II)-azoimidazole complexes. Chloro-bridged Hg(II) complexes show lower Ea's than those of iodo-bridged complexes. DFT calculation has been adopted to rationalize the experimental results.

Palladium(II)-iodo-{1-alkyl-2-(arylazo)imidazole} complexes: Synthesis, structure, dynamics of photochromism and DFT computation

“…1). The chelate ring may be stable to light irradiation and does not cleave unlike the complexes of Zn(II), Cd(II), Hg(II) and Pb(II) [25][26][27][29][30][31]. Thus, dangling Ar-N@N-may be responsible to isomerisation upon excitation to light irradiation (Scheme 2).…”

“…In our studies, 1-alkyl-2-(arylazo)imidazole (Raai-C n H 2n+1 ) both free ligand and coordinated one exhibit photochromic activity. We have examined the effect of metal ion coordination, H + addition, other external parameters (like innocent molecules, micelles, and reverse micelle) [24][25][26][27][28][29][30][31][32][33][34][35][36][37] on the photochromic activity.…”

1‐Alkyl‐2‐{(O‐Thioalkyl)Phenylazo}Imidazole Complexes of PbII and Their Photochromic Property

“…The φ EǞZ values are significantly dependent on the nature of the substituents, halide type and molecular weight. [19,20,[22][23][24][25] In presence of -Me and -Et groups, the quantum yields are reduced compared to those of the free ligands.…”

“…Our group has recently started to investigate the coordination chemistry of Pb II with 1-alkyl-2-(arylazo)-imidazole. [19,20] One of the interesting properties of arylazoimidazoles and their complexes is photoisomerization, [21][22][23][24][25] which is a reversible transformation between trans and cis erization of the coordinated azoimidazole. The rate of isomerization follows the sequence: [Pb(SRaaiNR') 2 Cl 2 ] Ͻ [Pb(SRaaiNR') 2 Br 2 ] Ͻ [Pb(SRaaiNR') 2 I 2 ].…”

Ru(II)–CO complexes of thioarylazoimidazoles: Syntheses, structures, spectroscopy and DFT calculation

“…The electronic spectra of 2 show intense band at 495-500 nm and the complexes 3 exhibit transition at 590-595 nm along with weak band at 790-810 nm. Azoimidazoles are susceptible to light both at free and coordinated state in Hg(II), Cd(II) and Pd(II) complexes and undergo trans-to-cis photoisomerisation upon light irradiation [13]. Ruthenium(II) complexes are silent to photoisomerisation.…”