Influence of N-alkyl substituents on the coordination modes and oxidation states of cobalt in Schiff base complexes: crystal structures, spectroscopic characterization and urease inhibition

Two Schiff bases, 4-bromo-2-[(cyclopentylimino)methyl]phenol (HL 1 ) and 4-bromo-2-[(cyclohexylimino)methyl]phenol (HL 2 ), derived from 4-bromosalicylaldehyde and cyclopentylamine or cyclohexylamine, have been used to prepare the cobalt complexes [Co(L 1 ) 3 ] ( 1 ) and [Co(L 2 ) 2 ] ( 2 ). The compounds were characterized by IR and UV spectroscopy and single crystal X-ray diffraction. Although both complexes were prepared under the same air atmosphere, the steric demand of the N -alkyl substituent controls both the coordination chemistry and the oxidation state of the metal: the less hindered cyclopentyl group allows tris-chelation and gives a mononuclear octahedral Co(III) complex with three bidentate O,N-donor ligands, whereas the bulkier cyclohexyl group favors bis-chelation and affords a mononuclear tetrahedral Co(II) complex with two bidentate O,N-donor ligands. Complex 1 inhibits jack bean urease by 73% with an IC 50 of 32 µmol L − 1 , while complex 2 exhibits 91% inhibition with an IC 50 of 8.2 µmol L − 1 .