Malaysian Journal of Analytical Sciences Vol 25 No 1 (2021): 138 - 152

 

 

 

 

SYNTHESIS, CHARACTERIZATION AND ELECTROCHEMICAL STUDIES OF TRANSITION METAL COMPLEXES CONTAINING 3,6-BIS(3,5-DIMETHYLPYRAZOLYL) PYRIDAZINE LIGAND

 

(Sintesis, Pencirian dan Kajian Elektrokimia bagi Kompleks Logam Peralihan Mengandungi Ligan 3,6-Bis(3,5-Dimetilpirazolil) Piridazina)

 

Shankary Selvanathan and Woi Pei Meng*

 

Department of Chemistry, Faculty of Science,

Universiti Malaya, 50603 Kuala Lumpur, Malaysia

 

*Corresponding author:  pmwoi@um.edu.my

 

 

Received: 2 November 2020; Accepted: 21 January 2021; Published:  20 February 2021

 

 

Abstract

Four novel coordination complexes were synthesized based on 3,6-bis (3,5-dimethylpyrazolyl) pyridazine ligand with Cu(II), Fe(II), Ni(II) and Co(II) metals. The synthesized complexes were characterized using several analyses. The infrared (IR) spectra for all the complexes showed a significant shift at the ligand methyl group (C-H), pyrazole ring (C=N), pyridazine ring (C-N) and (N-N) at 2926 cm^-1, 1137 cm^-1, 1162 cm^-1 and 970 cm^-1, respectively. The elemental analyses of the complexes confined to the stoichiometry of 1:2 ratio between the ligand and the metal cation. The presence of the metal in the complexes was confirmed using the FESEM-EDX analysis. The complexation of the metals to the ligand was evidenced when all the complexes exhibit a significant shift in the position of the characteristic ligand band at around 260 nm due to the HOMO → LUMO π → π* transitions of the pyridazine and pyrazoles groups in the UV-Vis spectrum. Cyclic voltammetry (CV) method was used to explore the redox characteristics of the complexes. The Cu(II), Fe(II) and Ni(II) complexes exhibited quasi-reversible single electron transfer process while no peak was observed in Co(II) complex upon scanning from -1.5 to 1.5 V vs. Ag/AgCl. This observation is speculated to be the effect of poor complexation in between the metal and the ligand. The potential recorded for Cu(II) complex at 0.03 V vs. Ag/AgCl was corresponded to the reduction of Cu(II) to Cu(I) while the potential at  0.75 V was due to the oxidation of Cu(I) to Cu(II). For the Fe(II) complex, the redox couple Fe(II)/Fe(III) was recorded at -0.47 V and -0.67 V during its oxidation and reduction process respectively. Finally, the peak at 0.71 V in the CV of Ni(II) complex is attributed to its oxidation process of Ni(I) to Ni(II) while the peak at 0.12 V is due to its reduction from Ni(II) to Ni(I).

 

Keywords:  pyridazine, transition metal, coordination complex, electrochemical behavior

 

Abstrak

Empat kompleks koordinatan novel telah disintesis berdasarkan ligan 3,6-bis(3,5-dimetilpirazolil) piridazina dengan logam Cu(II), Fe(II), Ni(II) dan Co(II). Kompleks yang disintesis dicirikan dengan beberapa kaedah analisis. Spektrum IR bagi kesemua kompleks menunjukkan perubahan yang ketara pada kumpulan metil ligan (C-H), lingkaran pirazol (C=N), lingkaran piridazina (C-N) and (N-N) masing-masing pada 2926 cm^-1, 1137 cm^-1, 1162 cm^-1 and 970 cm^-1. Analisis unsur kompleks membataskan nisbah stoikiometri ligan: logam kepada 1: 2. Kehadiran logam dalam kompleks juga telah disahkan menerusi analisis FESEM-EDX. Pembentukan kompleks bersama logam dan ligan disahkan lebih lanjut kerana semua kompleks mempamerkan perubahan yang sangat ketara dalam pencirian pada 260 nm kerana peralihan HOMO → LUMO π → π* dalam lingkaran pirazol and piridazina menerusi spektrum UV-Vis. Sifat redoks kompleks telah disiasat dengan kaedah elektrokimia voltammetri kitaran (CV). Kompleks Cu(II), Fe(II) dan Ni(II) mempamerkan proses pemindahan elektron tunggal yang seakan-balik manakala tiada puncak diperhatikan bagi kompleks Co(II) apabila kesemua kompleks ini diimbas pada potensi -1.5 ke 1.5 V vs. Ag/AgCl. Potensi untuk kompleks Cu(II) pada 0.03 V vs. Ag/AgCl sepadan dengan penurunan Cu(II) kepada Cu(I) manakala potensi pada 0.75 V adalah disebabkan oleh pengoksidaan Cu(I) kepada Cu(II). Bagi kompleks Fe(II), pasangan redoks Fe(II)/Fe(III) mencatatkan potensi masing-masing pada -0.47 V dan -0.67 V semasa proses pengoksidaan dan penurunan. Akhirnya, potensi pada 0.71 V dalam voltammogram kitaran kompleks Ni(II) adalah disebabkan oleh proses pengoksidaan Ni(II) kepada Ni(I) manakala potensi pada 0.12 V adalah disebabkan oleh penurunan dari Ni(II) ke Ni(I).

 

Kata kunci:  piridazina, logam peralihan, kompleks koordinatan, tindakan elektrokimia

 

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