Cooperative influence of pseudohalides and ligand backbone of Schiff-bases on nuclearity and stereochemistry of cobalt(iii) complexes: experimental and theoretical investigation?

Dalton Transactions Pub Date: 2017-10-03 DOI: 10.1039/C7DT03040A

Abstract

Four cobalt(III) complexes, [Co(HL1)(NCS)2(EtOH)] (1), [Co2(L1)2(N3)2] (2) and [Co(HL2)(NCS)2(EtOH)] (3), [Co(HL2)(N3)2] (4) were synthesized from two Schiff-base ligands namely, (E)-2-((2-(2-hydroxyethylamino)ethylimino)methyl)phenol (H2L1) and (E)-2-((3-(2-hydroxyethylamino)propylimino)methyl)phenol (H2L2), respectively. All the four complexes have been thoroughly characterised by using various physicochemical studies such as UV-Vis, FT-IR, ESI-MS, EPR and single crystal X-ray diffraction. Depending on flexibility of the ligand backbone subtle structural differences are observed in the synthesized complexes. In complex 1 the two thiocyanate ligands are trans to each other whereas in complex 3 they are cis to each other with addition of one additional methylene (–CH2–) group to the ligand system. Complex 2 is dinuclear while complex 4 is mononuclear in the presence of the azide co-anionic ligand. Theoretical studies are carried out in order to rationalize the structural differences observed in the complexes. Catecholase like activity of all the four complexes were performed in N,N-dimethylformamide (DMF) using 3,5-di-tert-butylcatechol (3,5-DTBC) as a model substrate. Complex 2 was found to exhibit the highest activity. Mechanistic investigation of the catecholase like activity revealed the formation of the imine radical during catalytic reactions of complexes 2 and 4 which are further corroborated by the EPR study.

Graphical abstract: Cooperative influence of pseudohalides and ligand backbone of Schiff-bases on nuclearity and stereochemistry of cobalt(iii) complexes: experimental and theoretical investigation
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