Synthesis, Spectroscopy and Electrochemistry of Cobalt(III) Schiff Base Complexes

Abstract

Three Co(III) complexes of the type [Co(chel)(PBu3)]ClO4.H2O, (chel = 5-BrSalen, 5-MeOSalen and 4-MeOSalen), were synthesised and characterised by elemental analysis, IR, UV-Vis and 1H NMR spectroscopy. In their electronic spectra, the absorptions between 550 and 750 nm of these complexes are attributable to the lowest d–d transition. The axial ligands affect this transition through a σ-intraction with the dz2 orbital and the equatorial ligands affect it by π-interaction with populated d-orbitals. On the basis of an electronic structural model, in which the dz2 orbital is populated in forming cobalt(II), it is suggested that equatorial ligand substitution affects the reduction potentials less than axial ligand substitution.

Spectroscopy and Electrochemistry of Cobalt(Iii) Salophen Complexes

“…The transition with the lowest energy (550-700 nm) is attributable to d → d transition. In the same way that we discussed in the last work, 17 electron-withdrawing groups decrease the energy of d orbitals via π-interactions and increase the energy of the d → d excitations, while electron donating groups operate it in the reverse trend. The axial ligand also affects this transition through σ-intraction with the dz 2 orbital (Table 1).…”

“…Via this property, in the Co(III) salophen complexes the d → d transition has a blue shift relative to Co(III)salen complexes (see ref. 17 and Table 1).…”

“…16 The effect of equatorial salophen Schiff base ligands on the reduction potentials is more than the salen complexes. While the maximum range of Co(III/II) potentials in Co(III)salen complexes is only 130mV 17 (for same axial ligand), the range of the corresponding Co(III/II) couples of salophen complexes is about 225mV (Table 2). This is because of the greater πacceptor property of salophen Schiff base complexes.…”

“…9 The catalytic activity of Co(III) with salen [10][11][12][13][14][15] and BAE 16 complexes has been investigated. In continuation of our studies on spectroscopy and electrochemical behaviour of cobalt(III) complexes containing Schiff base ligands, 17 the Co(III) salophen (salophen = bis(salicylaldehyde) phenylenediimine) complexes, were selected and the effect of the extention of π-system on these properties was investigated. We report the novel complex [Co(chel)(PBu 3 )]ClO 4 .H 2 O, where chel = 5-Brsalophen, 5-NO 2 salophen 5-MeOsalophen and 4-MeOsalophen.…”

Thermodynamic Study of Cobalt(III) Schiff Base Complexes in Mixed EtOH/H2O

“…For studying these effects and comparing the behaviour of these complexes with biological Co(III) complexes like vitamin B 12 several series of Co(III) Schiff base complexes with bonded carbon and phosphines as axial ligand have been proposed as model molecules. [1][2][3][4] In continuation of our studies on the synthesis, electronic spectra, electrochemical properties and the thermodynamics of cobalt (III) complexes containing Schiff base ligands, [5][6][7][8] we report the synthesis and spectroscopic characterisation of [Co(mdsp) ) and at various temperatures T = (288 to 308)K, with the goal of evaluating the effect of equatorial substitution(R) on electronic properties (Fig. 1).…”