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Summer Project (2022)

Synthesis and Characterization of Halide Ligands on Mononuclear Ni(II) Complexes with a Phenolic Tridentate Ligands.

Abstarct

The mononuclear Ni(II) complex [Ni(Sal-PPZ)(OH₂)₃]Cl₂ has been synthesized and structurally characterized. There has been seen that It formed [Ni(Sal-PPZ)(OH₂)₃]²⁺ complex cations, 2Cl^- counter-anions and 3H₂O molecules. For the electrically neutral system of complex, N atom of piperazine is Protonated.

The complex was characterized through the electronic spectra which were obtained by using UV-Spectrometer with MeOH as a solvent, and doing IR. Cyclic Voltammograms were recorded in DMF solution. It has been seen that [Ni(Sal-PPZ)(OH₂)₃]Cl₂ Complex do not show any catecholase activity upon addition of 3,5 -DTBC. Surprisingly seen that it is totally inactive complex. The co-ordination environment around the Ni(II) Complex is nearly Octahedral.

Experimental section

Synthesis of [Ni(Sal-PPZ)(OH₂)₃]Cl₂ Complex Diagram

In this experiment, 94.03 mg of Salicylaldehyde was taken in RB and it was dissolved with 5 ml of MeOH. It was kept in stirring on Oil bath through heating condition at 62-64^oC. The mixture was colourless. After that 100 mg of N-(2-aminoethyl) piperazine was taken into another vial and it was dissolved with 2.5 ml of MeOH. Then It was added slowly to the main reaction mixture in RB in continuation of stirring (Heating condition). The Colour of mixture changed from colourless to yellow and it was refluxed for 30 minutes (63^oC initial temperature, in 10 minutes it cooled down to 60^oC, after 30 minutes it was noted down to 62^oC). Reflux was stopped after 0.5 hrs. Then the MeOH solution (2.5 ml) of NiCl₂ .6H₂O (183.02 mg) was taken in another vial and was added slowly to the main reaction mixture during stirring at room temperature. The resulting solution was stirred for 3.5 hr at 1020 rpm. The colour of the mixture changed from yellow to green during stirring. Then it was transferred into another vial, and kept for slow evaporation. The light green coloured compound (200 mg) was collected after some days and it was kept in desiccator. After that, it has been used for characterization.

Yield: 74.6 %.

Results and Discussions

(i) IR and UV-Vis Spectra Of Complex

This Ni(II) complex were characterized by physiochemical techniques. Electronic spectra were recorded in MeOH. This Complex showed two highly intense band at 307 nm and 375 nm due to LMCT. Weak absorption band found at the range of 646 nm,765 nm, 973 nm. IR band showed C=N stretching at 1640-1656 cm^-1 , Skeleton vibration showed at the range of 1595-1611 cm^-1, C-N showed stretching at 1387-1411 cm^-1 , a broad signal is there due to presence of H bonded O-H group at the range of 3300-3500 cm^-1 .

(ii)Crystal structure Of Complex

Here structure of the complex consists of [Ni(C₁₃H₁₉N_3O)(OH₂)₃]²⁺ ion, 2Cl^- counter-anions, and Water molecule. The Ni(II) metal centre joined by three donor atoms (N1, N2, O1) of the (Sal-PPZ) Ligand, and three Diagram

OH₂ ligands in a distorted octahedral co-ordination environment with Meridional conformation. The bonds distance and the bond angles are shown in below -

	Bond length(Å)
Nil-N1	1.998
Nil-N2	2.218
Nil-O1	2.049
Nil-O2	2.063
Nil-O3	2.083
Nil-O4	2.099

Three OH₂ ligands and water molecules form H bond like O−H···Cl and O−H···O to generate supramolecular structure.

	Bond Angle(deg)
N1-Nil-O1	89.12
N1-Nil-O2	175.04
O1-Nil-O2	95.81
N1−Ni1−O3	89.96
O1−Ni1−O3	88.71
O2−Ni1−O3	89.54
N1−Ni1−O4	96.64
O1−Ni1−O4	88.13
O2−Ni1−O4	84.16
O3−Ni1−O4	172.64
N1−Ni1−N2	82.45
O1−Ni1−N2	171.57

(iii) Cyclic Voltammograms of complex

Complex	E^o or E_peakvalues
[Ni(Sal-PPZ)(OH₂)₃]	0.97, 1.25, 1.6, -1.10, -1.53

Conclusions

Here in this report, there has been described the structural and functional relationship in small coordination complexes of the Nickel(II) Schiff-base system. Ni(II) halide complex of tridentate Schiff-base ligand (Sal-PPZ) in the solid state have a beautiful octahedral co-ordination structure with 2Cl^- ions in the outer coordination sphere act as a counter-anion. These particular features have been authenticated by classical experimental verification because of a change in position of the Cl^- ions from counter-anions to coordinating ligands, effective charge neutralization of the central metal ion takes place to such an extent that enzyme substrate adduct formation. For this experimental data there has been given some supporting information such as X ray crystallographic data, IR spectral data, UV-Vis spectra, and CV.