Photooxidation of some nickel(II) macrocyclic complexes in non-aqueous solvents

Dhanasekaran Thirunavukkarasu, Parimal Paul, P. Natarajan

Research output: Contribution to journalArticle

9 Citations (Scopus)

Abstract

The complexes [Ni(tet-a)](ClO4)2, 1, [Ni(htcd)](ClO4)2, 2 and [Ni(AT)]ClO4, 3 (where tet-a=5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, htcd=5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene and AT=11,13-dimethyl-1,4,7,10-tetraazacyclotrideca-10,12-dienato) were photolysed in the charge transfer to solvent band in non-aqueous solvents using 254nm radiation. The complex [Ni(BG-opdn)], 4 (where BG-opdn=4,9-dihydroxy-3,4,9,10-tetraphenyl-6,7-benzo-1,2,5,8,11,12- hexaazacyclotetradeca-2,6,10,12,14-pentaene) was photolysed using sunlight in dichloromethane and the solid product was isolated and characterised. Flash photolysis of the complex 1 or 2 in pure acetonitrile produces transients which could be assigned to the nickel(III)-carbon bonded species whereas continuous photolysis in presence of oxygen produces stable five coordinated nickel(III) complexes. Formation of nickel(III) complex is seen as a growth in absorbance at 370nm in the case of complexes 1 and 2 on flash photolysis in oxygenated acetonitrile containing dichloromethane. Rate constants for the formation of nickel(III) by the reaction of alkylperoxyl radical with nickel(II) complex were determined as a function of the concentration of the complex. Formation of stable nickel(III)-complex was confirmed in the case of complexes 1 and 2 by absorption and ESR spectra on continuous photolysis of complexes in acetonitrile solutions containing 1M dichloromethane. In the case of complex 3 which contains a negatively charged macrocyclic ligand the oxidation of the metal centre is followed presumably by another intramolecular electron transfer to produce a nickel(II) radical centred on nitrogen which decays subsequently. In the case of complex 4 continuous photolysis using sunlight in air-equilibrated dichloromethane shows absorption spectral change and the photoproduct was isolated and characterised as nickel(II) stabilised ligand radical. Flash photolysis of 4 does not show any transient species in the microsecond time scale.

Original languageEnglish
Pages (from-to)75-83
Number of pages9
JournalJournal of Photochemistry and Photobiology A: Chemistry
Volume131
Issue number1-3
Publication statusPublished - 29 Feb 2000
Externally publishedYes

Fingerprint

Photooxidation
photooxidation
Nickel
Photolysis
nickel
photolysis
Methylene Chloride
Dichloromethane
Acetonitrile
acetonitrile
flash
sunlight
Ligands
absorption spectra
ligands
Alkenes
dienes
Paramagnetic resonance
Charge transfer
Rate constants

Keywords

  • Macrocycles
  • Nickel(II) complexes
  • Non-aqueous solvents
  • Photooxidation

ASJC Scopus subject areas

  • Bioengineering
  • Physical and Theoretical Chemistry

Cite this

Photooxidation of some nickel(II) macrocyclic complexes in non-aqueous solvents. / Thirunavukkarasu, Dhanasekaran; Paul, Parimal; Natarajan, P.

In: Journal of Photochemistry and Photobiology A: Chemistry, Vol. 131, No. 1-3, 29.02.2000, p. 75-83.

Research output: Contribution to journalArticle

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N2 - The complexes [Ni(tet-a)](ClO4)2, 1, [Ni(htcd)](ClO4)2, 2 and [Ni(AT)]ClO4, 3 (where tet-a=5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, htcd=5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene and AT=11,13-dimethyl-1,4,7,10-tetraazacyclotrideca-10,12-dienato) were photolysed in the charge transfer to solvent band in non-aqueous solvents using 254nm radiation. The complex [Ni(BG-opdn)], 4 (where BG-opdn=4,9-dihydroxy-3,4,9,10-tetraphenyl-6,7-benzo-1,2,5,8,11,12- hexaazacyclotetradeca-2,6,10,12,14-pentaene) was photolysed using sunlight in dichloromethane and the solid product was isolated and characterised. Flash photolysis of the complex 1 or 2 in pure acetonitrile produces transients which could be assigned to the nickel(III)-carbon bonded species whereas continuous photolysis in presence of oxygen produces stable five coordinated nickel(III) complexes. Formation of nickel(III) complex is seen as a growth in absorbance at 370nm in the case of complexes 1 and 2 on flash photolysis in oxygenated acetonitrile containing dichloromethane. Rate constants for the formation of nickel(III) by the reaction of alkylperoxyl radical with nickel(II) complex were determined as a function of the concentration of the complex. Formation of stable nickel(III)-complex was confirmed in the case of complexes 1 and 2 by absorption and ESR spectra on continuous photolysis of complexes in acetonitrile solutions containing 1M dichloromethane. In the case of complex 3 which contains a negatively charged macrocyclic ligand the oxidation of the metal centre is followed presumably by another intramolecular electron transfer to produce a nickel(II) radical centred on nitrogen which decays subsequently. In the case of complex 4 continuous photolysis using sunlight in air-equilibrated dichloromethane shows absorption spectral change and the photoproduct was isolated and characterised as nickel(II) stabilised ligand radical. Flash photolysis of 4 does not show any transient species in the microsecond time scale.

AB - The complexes [Ni(tet-a)](ClO4)2, 1, [Ni(htcd)](ClO4)2, 2 and [Ni(AT)]ClO4, 3 (where tet-a=5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, htcd=5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene and AT=11,13-dimethyl-1,4,7,10-tetraazacyclotrideca-10,12-dienato) were photolysed in the charge transfer to solvent band in non-aqueous solvents using 254nm radiation. The complex [Ni(BG-opdn)], 4 (where BG-opdn=4,9-dihydroxy-3,4,9,10-tetraphenyl-6,7-benzo-1,2,5,8,11,12- hexaazacyclotetradeca-2,6,10,12,14-pentaene) was photolysed using sunlight in dichloromethane and the solid product was isolated and characterised. Flash photolysis of the complex 1 or 2 in pure acetonitrile produces transients which could be assigned to the nickel(III)-carbon bonded species whereas continuous photolysis in presence of oxygen produces stable five coordinated nickel(III) complexes. Formation of nickel(III) complex is seen as a growth in absorbance at 370nm in the case of complexes 1 and 2 on flash photolysis in oxygenated acetonitrile containing dichloromethane. Rate constants for the formation of nickel(III) by the reaction of alkylperoxyl radical with nickel(II) complex were determined as a function of the concentration of the complex. Formation of stable nickel(III)-complex was confirmed in the case of complexes 1 and 2 by absorption and ESR spectra on continuous photolysis of complexes in acetonitrile solutions containing 1M dichloromethane. In the case of complex 3 which contains a negatively charged macrocyclic ligand the oxidation of the metal centre is followed presumably by another intramolecular electron transfer to produce a nickel(II) radical centred on nitrogen which decays subsequently. In the case of complex 4 continuous photolysis using sunlight in air-equilibrated dichloromethane shows absorption spectral change and the photoproduct was isolated and characterised as nickel(II) stabilised ligand radical. Flash photolysis of 4 does not show any transient species in the microsecond time scale.

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