Syntheses, characterization and crystal structures of Schiff base zinc(II) complexes with antimicrobial activity

Three new zinc(II) complexes, [ZnL1(CH3OH)] (1), [ZnBrL2] (2), and [ZnBr2(HL3)]·CH3OH (3·CH3OH), where L1 is the dianionic form of N,N'-bis(4-bromosalicylidene)cyclohexane-1,2-diamine (H2L1), L2 is the monoanionic form of 5-bromo-2-(((3-morpholinopropyl)imino)methyl)phenol (HL2), and HL3 is the zwitterionic form of 5-bromo-2-(((2-(pyrrolidin-1-yl)ethyl)imino)methyl)phenol (HL3), were facile prepared by reaction of 1:1 molar ratio of the Schiff bases with zinc bromide in methanol. The complexes were characterized by IR and UV-Vis spectroscopy. Detailed structures of the three complexes were confirmed by single crystal X-ray determination. The Zn(II) atom in complex 1 has a square pyramidal coordination, with the Schiff base ligand L1 coordinated to the Zn(II) atom through phenolate oxygen and imino nitrogen atoms. The Zn(II) atom in complex 2 has a tetrahedral coordination, with the Schiff base ligand L2 coordinated to the Zn(II) atom through phenolate oxygen, imino nitrogen and morpholine nitrogen atoms. The Zn(II) atom in complex 3·CH3OH has a tetrahedral coordination, with the Schiff base ligand L3H coordinated to the Zn(II) atom through phenolate oxygen and imino nitrogen atoms. The remaining sites are occupied by one methanol oxygen atom for 1, one Br ligand for 2, and two Br ligands for 3·CH3OH. The compounds show significant antimicrobial activities.