Synthesis, characterisation and antimicrobial activity of new palladium and nickel complexes containing Schiff bases

• Four new Pd(II) and Ni(II) complexes, [M(L)2], of Schiff base ligands were synthesised.
• IR, NMR, UV–Vis., CHN and single crystal XRD were used as characterisation techniques.
• The analytical and single crystal XRD data showed LH binds to M(II) ions in (O−, N) mode.
• The crystals of [Pd/Ni(L1)2] contain CH⋯O intermolecular secondary interactions.
• New ligands and the complexes were screened for their antibacterial and antifungal activities.
• The antimicrobial activity of complexes was higher than the ligands and Pd ones showed higher than Ni.
• The L1H and 2 are among the best antifungal and antibacterial agents.

New Schiff base ligands were synthesized by condensation of 2-(3,4-dimethoxyphenyl)ethanamine with 2-hydroxy benzaldehyde (L1H) and 2′-hydroxy acetophenone (L2H) respectively. Reaction of L1H or L2H with Na2PdCl4 or NiCl2·6H2O in 2:1 ratio obtained four new coordination complexes [M(L1–2)2] (where M = Pd(II); 1 and 2 and M = Ni(II); 3 and 4). Both the ligands and four complexes were characterised by elemental analysis, FT-IR and UV–Vis, spectroscopy. L1H, L2H, 1 and 2 were also characterised by 1H and 13C{1H} NMR spectroscopy. The molecular structures of 1 and 3 were determined by single crystal X-ray diffraction. The spectroscopic and crystal structure data showed that the ligands coordinated to M(II) ion in a bidentate monoanionic (O−, N) fashion. The PdO and PdN bond lengths in 1 are 1.984(11) and 2.020(12) Å in 3 the NiO and NiN bond lengths are 1.8222(13) and 1.9262(15) Å respectively. The CN bond length in 3 found 1.290(2) Å which was shorter than 1.310(19) Å in 1. The bond angles provided square planar geometry around Pd(II) and Ni(II) in both 1 and 3. There exists CH⋯O type (2.50–2.52 Å) intermolecular hydrogen bonding in both 1 and 3 resulting in supramolecular structures. The antimicrobial activity of new Schiff base ligands and their Pd(II) and Ni(II) complexes against pathogenic microbial strains by agar well diffusion method was conducted. All the ligands and complexes showed significant antibacterial and antifungal activities. The bacterial and fungi growth inhibition activity of ligands has been increased on complexation as well as among complexes palladium complexes were found better antibacterial and antifungal agents than the nickel complexes of corresponding ligands. Ligand L1H and the complex 2 showed highest antibacterial activity against Pseudomonas desmolyticum and highest antifungal activity against Candida albicans.

Antibacterial activity of [Pd(L2)2] (2) by agar well diffusion method.Figure optionsDownload as PowerPoint slide