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Modulation of fluorescence emission of 1-(2-pyridyl) pyrazole derived Schiff base ligands by exploiting their metal ion sensitive binding modes

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Title: Modulation of fluorescence emission of 1-(2-pyridyl) pyrazole derived Schiff base ligands by exploiting their metal ion sensitive binding modes
Authors: Gupta, Samik1, Paul, Bijan Kumar1, Barik, Anil Kumar2, Mandal, Tarak Nath1, Roy, Somnath1, Guchhait, Nikhil1 nguchhait@yahoo.com, Butcher, Ray J.3, Kar, Susanta Kumar1 skkar_cu@yahoo.co.in
Source: Polyhedron. Nov2009, Vol. 28 Issue 16, p3577-3585. 9p.
Subjects: Schiff bases, Ligands (Chemistry), Fluorescence, Metal ions, Pyrazoles, Metal complexes, Molybdenum compounds, X-ray crystallography
Abstract: Abstract: Dioxomolybdenum(VI) complexes [MoO2(B1)H2O] (1), [MoO2(B2)EtOH] (2), [MoO2(B3)EtOH] (3) and [MoO2(B4)EtOH] (4) were synthesized using the Schiff base ligands H2B1(previously reported), H2B2, H2B3 and H2B4, respectively. These ligands were prepared by condensation of 1-(2-pyridyl) 5-methyl 3-pyrazole carbohydrazide with salicylaldehyde, o-hydroxy acetophenone, 5-bromo salicylaldehyde and 5-nitro salicylaldehyde respectively. Due to the presence of a substituted 1-(2-pyridyl) pyrazole unit, ligands H2B1, H2B2 and H2B3 exhibit fluorescent emissions, and the most intense emission was obtained for H2B3. H2B4 is incapable of showing fluorescence emission. As the ligands are capable of using different binding modes, according to the demands of the guest metal ions, their emission properties also change accordingly. The dioxomolybdenum(VI) complex of the ligand H2B1, i.e. complex 1, shows quenched emission compared to H2B1. Again when Cu2+, Co2+ or Ni2+ ions are added to a solution of 1, in each case a new complex of Cu2+ Co2+ or Ni2+ is formed in solution and further quenching was observed. However, with Zn2+ input to a solution of 1, fluorescence recovery was observed up to the level of the free ligand. The copper(II) complex of H2B1 (complex 5), produced by adding equivalent amount of Cu2+ salt to a solution of 1, was isolated and characterized. One of the dioxomolybdenum(VI) complexes, 3, when subjected to an oxo-transfer reaction with PPh3 produces complex [MoO(B3)CH3CN] (6). Complex 6 shows reduced fluorescence emissions compared to 3 in the solid phase. These observations open up the possibilities for these ligands to work as fluorescent signaling system with different metal ion inputs. All the complexes are characterized by elemental analyses, electronic spectra, IR, 1H NMR, magnetic measurements, EPR and by cyclic voltammetry. Complexes 1 and 5, as well as the ligands H2B2 and H2B3, have been crystallographically characterized. [Copyright &y& Elsevier]
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Abstract:Abstract: Dioxomolybdenum(VI) complexes [MoO2(B1)H2O] (1), [MoO2(B2)EtOH] (2), [MoO2(B3)EtOH] (3) and [MoO2(B4)EtOH] (4) were synthesized using the Schiff base ligands H2B1(previously reported), H2B2, H2B3 and H2B4, respectively. These ligands were prepared by condensation of 1-(2-pyridyl) 5-methyl 3-pyrazole carbohydrazide with salicylaldehyde, o-hydroxy acetophenone, 5-bromo salicylaldehyde and 5-nitro salicylaldehyde respectively. Due to the presence of a substituted 1-(2-pyridyl) pyrazole unit, ligands H2B1, H2B2 and H2B3 exhibit fluorescent emissions, and the most intense emission was obtained for H2B3. H2B4 is incapable of showing fluorescence emission. As the ligands are capable of using different binding modes, according to the demands of the guest metal ions, their emission properties also change accordingly. The dioxomolybdenum(VI) complex of the ligand H2B1, i.e. complex 1, shows quenched emission compared to H2B1. Again when Cu2+, Co2+ or Ni2+ ions are added to a solution of 1, in each case a new complex of Cu2+ Co2+ or Ni2+ is formed in solution and further quenching was observed. However, with Zn2+ input to a solution of 1, fluorescence recovery was observed up to the level of the free ligand. The copper(II) complex of H2B1 (complex 5), produced by adding equivalent amount of Cu2+ salt to a solution of 1, was isolated and characterized. One of the dioxomolybdenum(VI) complexes, 3, when subjected to an oxo-transfer reaction with PPh3 produces complex [MoO(B3)CH3CN] (6). Complex 6 shows reduced fluorescence emissions compared to 3 in the solid phase. These observations open up the possibilities for these ligands to work as fluorescent signaling system with different metal ion inputs. All the complexes are characterized by elemental analyses, electronic spectra, IR, 1H NMR, magnetic measurements, EPR and by cyclic voltammetry. Complexes 1 and 5, as well as the ligands H2B2 and H2B3, have been crystallographically characterized. [Copyright &y& Elsevier]
ISSN:02775387
DOI:10.1016/j.poly.2009.07.053