A series of Schiff base ligand, SALMPD, and its mono- and trinuclear Zn(II) metal complexes were synthesised from m-phenylenediamine and salicylaldehyde in alcoholic solution. The synthesis of ligand and mononuclear complex were synthesised using conventional condensation method, while the trinuclear complex was done using microwave-assisted synthesis method. The structure of each compound was elucidated by elemental analysis, infrared and ¹H NMR spectroscopy. The infrared spectrum of SALMPD shows a strong azomethine (C=N) band at 1621.62c m⁻¹, indicates the formation of the ligand. Upon complexation of the mononuclear complex, the C=N infrared band shifted and the disappearing of the phenolic hydrogen signal in ¹H NMR suggesting the chelation between Zinc(II) metal ion and ligand took place when azomethine and phenolic hydrogen deprotonated. The trinuclear complex, Zn3(SALMPD) obtained was consist of two moieties of mononuclear Zn₃(SALMPD), which act as ligands that chelating to the third Zn(II) metal ion through oxygen atom due to the shifting of M-O infrared band from 575.12-540.53cm⁻¹, which serves as a coordination site for the metal ion.
The coordination complexes of Co(II) and Zn(II) with Schiff bases derived from ophenylenediamine and substituted 2-hydroxybenzaldehyde were prepared. All compounds were characterized by Fourier transform infrared (FTIR) spectroscopy and Nuclear magnetic resonance (NMR) spectroscopy elemental analyzers. They were analyzed using impedance spectroscopy in the frequency range of 100Hz - 1MHz. L1 and L2 showed higher conductivity compared to their metal
complexes, which had values of 1.37 x 10-7 and 6.13 x 10-8S/cm respectively.
In this study, the new compound of thiourea derivatives were successfully synthesized, namely N-((3chlorophenyl) carbamothioyl) benzamide (T1) and N-((4-chlorophenyl) carbamothioyl) benzamide (T2). These series of thiourea compounds were prepared from the reaction of benzoyl chloride with ammonium thiocyanate to produce benzoyl isothiocyanate, then direct reaction with amines by using condensation method. Their structures were characterized on the basis elemental analysis and spectroscopic techniques namely infrared and nuclear magnetic resonance. The Infrared spectra showed the significant results of stretching vibrations of the compounds are ν(C=O), ν(C=S) and ν(C-N) at 1533.39-1671.00 cm-1, 1256.64-1261.73 cm-1 and 1144.22-1144.81 cm-1, respectively. These compounds were investigated as corrosion inhibitors on mild steel in 1M H2SO4 using linear polarization techniques. Results show the highest inhibition efficiency of T1 is 55% while for T2 is 73%. The percentage inhibition efficiency of T2 is higher than T1 due to the difference position of substituent at meta and para.
Two Schiff bases, 3-(4-hydroxyphenylimino)-1,3-dihydroindol-2-one (OPI) and 3-(4-Chlorophenylimino)-1,3-dihydroindol-2-one
(CPI) were successfully synthesized through condensation
reactions giving yields of 82% and 63%, respectively. The compounds were characterized via
physical and spectroscopic techniques, namely elemental analysis (C, H, N), 1H and 13C Nuclear
Magnetic Resonance (NMR) spectroscopy, Fourier Transform Infrared (FTIR) spectroscopy and
melting point. The corrosion inhibiting property of the Schiff bases on mild steel in 1 M HCl solution
was investigated by the weight loss (WL) measurements, electrochemical impedance spectroscopy
(EIS) and linear polarization resistance (LPR). The concentrations of the Schiff bases were varied
from 1 x 10-3 M to 1 x 10-5 M. The inhibition efficiencies obtained from all the methods employed were
in good agreement where the percentage of inhibition efficiencies increased with concentration. OPI
showed better inhibition efficiency than CPI with 91 % highest inhibition efficiency at 1 x 10-3 M
additive concentration. This is likely to be caused by the resonance donating effect due to the
presence of the hydroxyl group. The adsorption behaviour obeyed Langmuir isotherm for monolayer
formation.
Two imines of different molecular sizes namely 3-(phenylimino) indolin-2-one (PII) and 3,3- (1,4-phenylenebis (azan-1-yl-1-ylidene) diindolin-2-one (PDI) were investigated for their corrosion inhibition on mild steel in 1 M HCl solution using electrochemical impedance spectroscopy (EIS). The bigger molecule PDI containing double the amount of isatin moiety exhibited higher inhibition efficiency of 87.3% while PII that contained monoisatin moiety showed a lower inhibition efficiency of 74.8%. Both compounds had an increase in inhibition efficiencies percentage as concentrations increased. Density functional theory (DFT) was used to determine the correlation between the corrosion inhibition efficiency and electronic parameters. The DFT calculations indicated that the corrosion inhibition efficiency was mainly dependant on the frontier orbital energy gap and the chemical softness/hardness of the imines.