Synthesis, characterization and pulse radiolysis of cobalt(ii) complexes of 2-picolinate and polypyridyl ligands

Abstract

Complexes of the type [Co(pic)(2)(LL)], where pic = picolinate; LL = (H(2)O)(2) (1), 2,2'-bipyridine (bpy) (2), 1,10-phenanthroline (phen) (3) and dipyrido[3,2-a:2',3'-c]phenazine (dppz) (4) have been synthesized and characterized by elemental analysis, IR, UV-visible and (1)H-NMR spectroscopy. Complex 2 crystallized from a mixture of chloroform and methanol in orthorhombic crystal system, space group Iba2. Complex 3 crystallizes from chloroform in monoclinic crystal system, space group P12(1)/a1 and in a mixture of water and methanol in triclinic crystal system, space group P1. Co(II)/Co(III) oxidation potentials have been determined by cyclic voltammetry and the concomitant spectral changes measured by spectroelectrochemistry. The reactions of one electron reducing (e(-)(aq), (CH(3))(2)*COH and CO(2)(*-)) and one electron oxidizing ( OH) radicals with the above metal complexes have been studied by pulse radiolysis. The rate constants for the reaction of e(-)(aq) and *OH radicals with the complexes are of the order of 10(10) and 10(9) dm(3) mol(-1) s(-1), respectively. The reaction of hydrated electron (e(-)(aq)) with the complexes results in the formation of a ligand radical anion species which decays by either protonation of ligand or reduction of metal by intramolecular electron transfer resulting in cobalt(I) species. The reaction of *OH radical forms the OH-adducts of the ligand.

Mixed ligand cobalt(ii) picolinate complexes: synthesis, characterization, DNA binding and photocleavage

“…Similarly, irreversible anodic and cathodic peaks were observed in complexes 2, 3 and 5. 20 The positive ion detection mode ESI-MS spectra of complex 1 shows an intense peak of the [Co(pic) ∑ Co(pic) 2 ] + ion and complexes 2-5 show more intense ion peaks at the m/z value of the [Co(pic)(NN)] + ion.…”

“…The precursor [Co(pic) 2 (H 2 O) 2 ] complex was prepared by the reported method. 19, 20 The mixed ligand complexes of the type [Co(pic) 2 (NN)] were synthesized by refluxing complex 1 (1 mmol) and the polypyridyl ligand (NN) (1 mmol) in methanol and isopropanol (1 : 1 v/v) or methanol (Scheme 2) under a N 2 atmosphere for 5-6 h, during which time orange (complexes 2 and 3), yellow (complexes 4 and 5) or pink (complex 6) coloured products were isolated and characterized by elemental analyses, IR, UV-vis, ESI-MS and NMR spectroscopy and single-crystal X-ray diffraction. These complexes are racemic mixture and no separation of the enantiomers was attempted.…”

“…The spectra obtained on irradiation indicate the oxidation of cobalt(II) to cobalt(III) complexes, as evidenced by the peak positions and intensity. 20,37,38 Density functional theory. The DFT calculations were carried out with the Gaussian03 package.…”

“…19 The complexes [Co(pic) 2 bpy] (2), [Co(pic) 2 phen] (3) and [Co(pic) 2 dppz] (5) were synthesized according to reported methods. 20 Calf thymus DNA and plasmid pBR322 DNA were obtained from SRL (India) and Bangalore Genei (Bangalore, India), respectively. The enzyme SOD was purchased from Sigma Chemical Co., USA.…”

Synthesis, X-ray Crystallographic, Electrochemical, and Spectroscopic Studies of Bis-(1,10-phenanthroline)(2,2′-bipyridine)cobalt(III) Hexafluorophosphate

“…Such studies include electron transfer reactions with biological reductants such as Lascorbic acid [1,9], application as electron mediators for water splitting [10], reactions in photoelectrochemical cells [11], radiolytic studies [12][13][14][15][16], and dichroism studies [17]. For many years, our research group and collaborators have been interested in studying the electron transfer reactions between small biological molecules and transition metal complexes [18][19][20][21][22][23][24][25][26][27], homogeneous catalysts [28] as well as developing electro-and photo-catalysts for the hydrogen production [29].…”