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Issue 15, 2013
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A series of tetrabromocatecholate chelated cobalt(iii) complexes with various N-donor ancillary ligands: syntheses, crystal structures, co-crystallization, thermally induced valence tautomerism and electrochemical studies

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Abstract

Nine new tetrabromocatechol chelated mononuclear cobalt(III) complexes with various nitrogen-donor ancillary ligands, [Co(en)2(Br4Cat)]ClO4·0·5H2O (1) [Br4CatH2 = tetrabromocatechol, en = ethylenediamine], [Co(pn)2(Br4Cat)]ClO4 (2) [pn = propylenediamine], [Co(dpd)2(Br4Cat)]NO3·CH3OH (3) [dpd = 2,2′-dimethyl-1,3-propanediamine], [Co(amp)2(Br4Cat)]ClO4 (4) [amp = 2-aminomethylpyridine], [Co(aqn)2(Br4Cat)]NO3·CH3OH (5) [aqn = 8-aminoquinoline], [Co(phen)2(Br4Cat)]ClO4·0·5CH3OH (6) [phen = phenanthroline], [Co(bpy)2(Br4Cat)]NO3·Br4CatH2·2CH3OH (7) [bpy = 2,2′-bipyridine], [Et3NH][Co(pym)2(Br4Cat)2]·H2O (8) [pym = pyrimidine] and [Co(tren)(Br4Cat)]NO3·CH3OH·H2O (9) [tren = tris(2-aminoethyl)amine], are reported. All the complexes were characterised by various spectroscopic techniques and electrochemical methods, and their structures have been elucidated by X-ray crystallography. Structural analyses reveal that a 1 : 1 cobalt-dioxolene adduct is the exclusive product with bi- or tetradentate ancillary ligands, while for the monodentate pyrimidine ligand 2 : 1 cobalt-dioxolene is the only outcome. Importantly, an unusual co-crystallization of complex 7 with one molecule of tetrabromocatechol was observed in the crystal lattice. The electrochemical studies of all the complexes disclose quasi-reversible redox processes due to the o-dioxolene ligands, in addition to reductive responses corresponding to the reduction of the cobalt(III) centres to cobalt(II). Although in the solid state all the complexes are diamagnetic, complexes 5 and 8 undergo thermally induced valence tautomerism in solution associated with the drastic change in the optical absorption properties of the complexes in the UV-vis spectroscopy.

Graphical abstract: A series of tetrabromocatecholate chelated cobalt(iii) complexes with various N-donor ancillary ligands: syntheses, crystal structures, co-crystallization, thermally induced valence tautomerism and electrochemical studies

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Publication details

The article was received on 14 Nov 2012, accepted on 27 Jan 2013 and first published on 07 Feb 2013


Article type: Paper
DOI: 10.1039/C3RA22897E
RSC Adv., 2013,3, 4954-4963

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    A series of tetrabromocatecholate chelated cobalt(III) complexes with various N-donor ancillary ligands: syntheses, crystal structures, co-crystallization, thermally induced valence tautomerism and electrochemical studies

    A. Panja, RSC Adv., 2013, 3, 4954
    DOI: 10.1039/C3RA22897E

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