Mononuclear pyrazine-2-carbohydrazone metal complexes: Synthesis, structural assessment, thermal, biological, and electrical conductivity studies

Abstract

Mononuclear complexes of VO(IV), Cr(III), Fe(III), MoO2(VI), WO2(VI), and UO2(VI) with pyrazinecarbohydrazone ligand (N'-(1-(5-chloro-2-hydroxyphenyl)ethylidene)pyrazine-2-carbohydrazide) were synthesized and the prepared complexes were characterized by elemental analysis, magnetic susceptibility, powder X-ray analysis, various spectroscopic techniques (IR, 1H NMR, 13C NMR, and Mass spectra), SEM, and thermal analysis. VO(IV) complex was additionally characterized by ESR study. The ligand behaves as a dibasic tridentate, coordinating through the phenolate oxygen, azomethine nitrogen, and enolate oxygen atoms towards the central metal ion. The analytical data suggest 1:1 metal to ligand stoichiometry for all complexes. The physicochemical data suggested octahedral geometry to Cr(III), Fe(III), MoO2(VI), WO2(VI), and UO2(VI) complexes while square pyramidal to VO(IV) complex. The SEM analysis indicated the presence of well-defined crystals free from any shadow of the metal ion on their external surface with particle sizes of greater than 10 μm. Various kinetics and thermodynamic parameters are calculated using Coats-Redfern method and on the basis of half decomposition temperature the thermal stability order of complexes was found to be Cr(III) < WO2(VI) < Fe(III) < MoO2(VI) < VO(IV) < UO2(VI). The solid-state electrical conductivity of compounds was measured in their pellet form in the temperature range form 313-373 K. The conductivity data vary exponentially with the absolute temperature and obey Arrhenius equation indicating their semiconducting behavior. The antibacterial as well as antifungal activities of ligand and its metal complexes were evaluated in vitro against Gram positive bacteria (S. aureus and B. subtilis) and Gram-negative bacteria (E. coli and S. typhi.) and fungal strains (C. albicans and A. niger). The activity data revealed metal complexes are found to be more active than the ligand.

A heterocyclic N'-(4-(diethylamino)-2-hydroxybenzylidene)-4-oxopiperidine-1-carbohydrazide Schiff base ligand and its metal complexes: Synthesis, structural characterization, thermal behavior, fluorescence properties, and biological activities

“…The ligand field parameters such as the crystal field splitting energy (Dq), the Racah parameter (B), the nephelauxetic ratio (β), and the v2/v1 were evaluated by using the König equation [19] and values are found to be 1653 cm -1 , 676 cm -1 , 0.74 and 1. 16, respectively, which are also in agreement with the octahedral Cr(III) complexes. The value of interelectronic repulsion parameter B was found to be lower (676 cm -1 ) than that of the free ion, confirming the presence of covalency in the metalligand bond.…”

“…This is also further confirmed by the shifting of amide ν(C=O) to lowering frequency by 5-50 cm -1 from 1625-1665 cm -1 in these complexes, suggesting the coordination of carbonyl oxygen atom to metal ions as such without experiencing the enolization. However, these bands are completely absent in Cr(III), Fe(III), and Zn(II) complexes, which confirmed the enol formation act in accordance with the coordination linkages to the metal ion after deprotonation [16,17]. Furthermore, the existence of coordinated water molecules was confirmed by the presence of non-ligand bands 820-850 cm -1 , which was further supported by the thermal analysis.…”

Spectroscopic Characterization, Cyclic Voltammetry, Biological Investigations, MOE, and Gaussian Calculations of VO(II), Cu(II), and Cd(II) Heteroleptic Complexes

“… 8 Moreover, VO(II) complexes showed a very similar strength of activity to standard drugs such as ciprofloxacin (an antibacterial drug) and clotrimazole (an antifungal drug). 9 Further, Cd(II) complexes with some hydrazone derivatives, such as ethyl-2-[(pyridine-2-ylmethylene)hydrazino] acetate, showed very similar biological activity to ampicillin as an antibacterial drug. 10 …”

“…In particular, 2-acetylpyridine hydrazone derivatives of benzothiazole exhibit a potent toxic effect on lymphomas, leukemias, and breast tumors. , Also, Cu­(II) complexes are more potent against rheumatoid arthritis and ulcers due to their role as acidic anti-inflammatory supplementary agents in gastrointestinal damage . Moreover, VO­(II) complexes showed a very similar strength of activity to standard drugs such as ciprofloxacin (an antibacterial drug) and clotrimazole (an antifungal drug) . Further, Cd­(II) complexes with some hydrazone derivatives, such as ethyl-2-[(pyridine-2-ylmethylene)­hydrazino] acetate, showed very similar biological activity to ampicillin as an antibacterial drug …”