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Papers by Chandana Sen

Research paper thumbnail of Lead(II) complexes of 1-alkyl-2-(arylazo)imidazole: synthesis, structure, photochromism and metallomesogenic properties

Polyhedron, 2016

Abstract The reaction between PbI2 and 1-alkyl-2-(arylazo)imidazole (Raai-CnH2n+1, R = H, Me and ... more Abstract The reaction between PbI2 and 1-alkyl-2-(arylazo)imidazole (Raai-CnH2n+1, R = H, Me and n = 10, 12, 14, 16, 18, 20, 22) has synthesized the iodo bridging complexes [Pb(Raai-CnH2n+1)(μ-I)4]n. These complexes were characterized by spectroscopic data and the structure has been confirmed in the case of [Pb(Meaai-C16H33)(μ-I)4]n by single crystal X-ray diffraction measurements. The complexes show E-to-Z (trans-to-cis) isomerisation of the coordinated Raai-CnH2n+1 ligand in DMF solution upon UV light irradiation. The reverse transformation, Z-to-E (cis-to-trans), is very slow with visible light irradiation and has been carried out by increasing the temperature. The quantum yield (ϕE→Z) and rate of E-to-Z isomerisation of [Pb(Raai-CnH2n+1)(μ-I)4]n are lower than those of the free ligand. The activation energy (Ea) of the Z-to-E isomerisation increases and the activation entropy (ΔS∗) decreases with the chain length, –CnH2n+1, in the coordinated ligand. [Pb(Meaai-C16H33)(μ-I)4]n (4b) shows metallomesogenic properties on cooling and undergoes phase transitions I (80.7 °C)–SmC (69.8 °C)– Cr (58.5 °C).

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

Polyhedron, 2015

ABSTRACT [Pd(Raai-CnH2n+1)2I)]2[Pd2I6] (Raai-CnH2n+1, 1-alkyl-2-(arylazo)imidazole) has been char... more ABSTRACT [Pd(Raai-CnH2n+1)2I)]2[Pd2I6] (Raai-CnH2n+1, 1-alkyl-2-(arylazo)imidazole) has been characterized by the spectral data (UV-Vis, FTIR, Mass, 1H-NMR). The single crystal X-ray structure of [Pd(Meaai-C2H5)2I)]2[Pd2I6] shows that one Meaai-C2H5 acts as monodentate N(imidazolyl) donor, while the other one is bidentate N(imidazolyl), N(azo) chelator; the charge is neutralized with [Pd2I6]2- anion. UV light irradiation in DMF solution of the complexes show trans-to-cis isomerisation of Raai-CnH2n+1 about –N=N– bond. Quantum yields (ϕt→c) of trans-to-cis isomerisation of the complexes are lower than that of the free ligand data. This observation is consistent with femtosecond transient absorption results of [Pd(Haai-C10H21)2][Pd2I6], which suggest that the trans→cis isomerization occurs in the monodentate azo-imidazole group and the bidentate azo-imidazole, because of chelation with Pd(II), does not exhibit photochromism.

Research paper thumbnail of Doubly end-on azido bridged mixed-valence cobalt trinuclear complex: Spectral study, VTM, inhibitory effect and antimycobacterial activity on human carcinoma and tuberculosis cells

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2015

Research paper thumbnail of Lead(II) complexes of 1-alkyl-2-(arylazo)imidazole: synthesis, structure, photochromism and metallomesogenic properties

Polyhedron, 2016

Abstract The reaction between PbI2 and 1-alkyl-2-(arylazo)imidazole (Raai-CnH2n+1, R = H, Me and ... more Abstract The reaction between PbI2 and 1-alkyl-2-(arylazo)imidazole (Raai-CnH2n+1, R = H, Me and n = 10, 12, 14, 16, 18, 20, 22) has synthesized the iodo bridging complexes [Pb(Raai-CnH2n+1)(μ-I)4]n. These complexes were characterized by spectroscopic data and the structure has been confirmed in the case of [Pb(Meaai-C16H33)(μ-I)4]n by single crystal X-ray diffraction measurements. The complexes show E-to-Z (trans-to-cis) isomerisation of the coordinated Raai-CnH2n+1 ligand in DMF solution upon UV light irradiation. The reverse transformation, Z-to-E (cis-to-trans), is very slow with visible light irradiation and has been carried out by increasing the temperature. The quantum yield (ϕE→Z) and rate of E-to-Z isomerisation of [Pb(Raai-CnH2n+1)(μ-I)4]n are lower than those of the free ligand. The activation energy (Ea) of the Z-to-E isomerisation increases and the activation entropy (ΔS∗) decreases with the chain length, –CnH2n+1, in the coordinated ligand. [Pb(Meaai-C16H33)(μ-I)4]n (4b) shows metallomesogenic properties on cooling and undergoes phase transitions I (80.7 °C)–SmC (69.8 °C)– Cr (58.5 °C).

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

Polyhedron, 2015

ABSTRACT [Pd(Raai-CnH2n+1)2I)]2[Pd2I6] (Raai-CnH2n+1, 1-alkyl-2-(arylazo)imidazole) has been char... more ABSTRACT [Pd(Raai-CnH2n+1)2I)]2[Pd2I6] (Raai-CnH2n+1, 1-alkyl-2-(arylazo)imidazole) has been characterized by the spectral data (UV-Vis, FTIR, Mass, 1H-NMR). The single crystal X-ray structure of [Pd(Meaai-C2H5)2I)]2[Pd2I6] shows that one Meaai-C2H5 acts as monodentate N(imidazolyl) donor, while the other one is bidentate N(imidazolyl), N(azo) chelator; the charge is neutralized with [Pd2I6]2- anion. UV light irradiation in DMF solution of the complexes show trans-to-cis isomerisation of Raai-CnH2n+1 about –N=N– bond. Quantum yields (ϕt→c) of trans-to-cis isomerisation of the complexes are lower than that of the free ligand data. This observation is consistent with femtosecond transient absorption results of [Pd(Haai-C10H21)2][Pd2I6], which suggest that the trans→cis isomerization occurs in the monodentate azo-imidazole group and the bidentate azo-imidazole, because of chelation with Pd(II), does not exhibit photochromism.

Research paper thumbnail of Doubly end-on azido bridged mixed-valence cobalt trinuclear complex: Spectral study, VTM, inhibitory effect and antimycobacterial activity on human carcinoma and tuberculosis cells

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2015

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