Synthesis, crystal structure and antibacterial activity of zinc(II) complexes with Schiff bases derived from 5-fluorosalicylaldehyde

By a condensation of aliphatic amine containing adamantyl groups (amantadine, memantine, or 3-amino-1-adamantanol) and 5-fluorosalicylaldehyde, three new Schiff base ligands, HL1–3, were synthesized. One Schiff base, zinc(II) chloride, and NaOH were stirred in anhydrous methanol generating three new zinc(II) complexes, C34H38F2N2O2Zn (1), C38H46F2N2O2Zn (2), and C34H38F2N2O4Zn (3), respectively. These complexes were characterized by melting point, elemental analysis, infrared spectrum, ultraviolet–visible spectrum, 1H NMR analysis, thermal analysis, and single-crystal X-ray diffraction analysis. Single-crystal X-ray diffraction analysis shows that 1 and 3 crystallize in the monoclinic system with space group P21/c, but 2 crystallizes in the orthorhombic system with space group Pbca. Each asymmetric unit in 1 is composed of one zinc(II) and two deprotonated ligands; each asymmetric unit in 2 is constituted of one zinc(II), two deprotonated ligands as well as one dichloromethane. Each asymmetric unit in 3 is made up of one zinc(II), two deprotonated ligands, one methanol, and one lattice water. The central zinc(II) in 1–3 is four-coordinate via two nitrogen atoms and two oxygen atoms from the corresponding Schiff base ligands, forming a distorted tetrahedral geometry. The antibacterial activities of the three Schiff base ligands and the corresponding complexes against two gram positive bacteria, Staphylococcus aureus and Bacillus subtilis, and a gram negative bacteria, Escherichia coli, were tested.