Synthesis, spectroscopic, biological activities and DFT calculations of nickel(II) mixed-ligand complexes of tridentate Schiff bases

Abstract

Ni(II) mixed-ligand complexes of [NiLNH3] (where L= N-salicylidene-o-aminophenol (L1), N-(5-methoxysalicylidene-o-aminophenol) (L2) and N-(2-hydroxy-1-naphthalidene)-o-aminophenol) (L3) containing ONO tridentate Schiff bases and ammonia were synthesized and characterized by elemental analysis, infrared, ultraviolet-visible, proton and carbon-13 spectroscopies. Theoretical calculations were also performed on the optimized structures of the Ni(II) mixed-ligand complexes. The Infrared and ultraviolet-visible spectra of the complexes were calculated, and the results compared with the corresponding experimental spectra to augment the experimental structural identification. The elemental analysis data confirmed the formation of 1:1:1 [metal: Schiff base: ammonia] molar ratio. The NMR spectra showed that the Schiff bases coordinated to the Ni(II) ion via the two deprotonated phenolic oxygen and azomethine nitrogen atoms. The biological studies showed that the complexes exhibited higher antibacterial and antioxidant activities than the free Schiff base ligands.

Preparation, spectroscopic study of Schiff base derived from dopamine and metal Ni(II), Pd(II), and Pt(IV) complexes, and activity determination as antioxidants

“…The bands at around 3,444, 3,185, 2,993, 2,833, 1,672, and 1,598 cm −1 are attributed to stretching vibration (OH) of the phenolic ring, C–H aromatic, C–H aliphatic, C–H aldehyde stretching vibration, CN of azomethine group, and CC aromatic, respectively. [ 16–23 ] The infrared spectra of Ni(L 2 ) 2 , Pd(L 2 ) 2 , and Pt(L 2 ) 2 Cl 2 complexes are shown in Figures 3–5 and Table 2. The band at around 3,450, 3,441, and 3,394 cm −1 is attributed to stretching vibration (OH) of the phenolic ring.…”

DFT Calculations and Total Antioxidant Capacity Studies of some Substituted Monodentate Salicylaldimines

“…The aromatic protons appeared as multiplets at δ 7.70-6.90 ppm [15,30,31,35]. A sharp singlet signal assigned to the protons of methoxy and methyl groups appeared at δ 3.81 and 2.20 ppm in the spectra of compounds I and III respectively [11,[35][36][37]. The 13 C NMR spectra of the compounds were consistent with the 1 H NMR.…”

“…All the salicylaldimines displayed a singlet signal at δ 8.91-8.85 ppm assigned to the azomethine (−HC=N) protons [15,27,30,31,[33][34][35][36] which further confirmed the formation of the salicylaldimines. The aromatic protons appeared as multiplets at δ 7.70-6.90 ppm [15,30,31,35]. A sharp singlet signal assigned to the protons of methoxy and methyl groups appeared at δ 3.81 and 2.20 ppm in the spectra of compounds I and III respectively [11,[35][36][37].…”

“…The TAC studies were performed three times and the mean was expressed as equivalents of ascorbic acid [22] 13 The 1 H NMR spectra of the salicylaldimines displayed a singlet signal at δ 13.90-12.70 ppm which was attributed to the phenolic -OH protons [18,27,[29][30][31][32][33]. All the salicylaldimines displayed a singlet signal at δ 8.91-8.85 ppm assigned to the azomethine (−HC=N) protons [15,27,30,31,[33][34][35][36] which further confirmed the formation of the salicylaldimines. The aromatic protons appeared as multiplets at δ 7.70-6.90 ppm [15,30,31,35].…”

“…The spectra displayed the azomethine carbon peaks in the range 163.25-161.75 ppm and the aromatic carbons around 160.12-112.80 ppm. The spectra of compounds I and III displayed the carbons of the methoxy and methyl groups at δ 56.31 and 17.73 ppm respectively [11,15,27,33,[35][36][37]. The UV spectra of the compounds displayed two absorption peaks around 286-262 and 351-360 nm which were attributed to n-π* of the azomethines and π-π*of the aromatic rings in the compounds.…”