Test

Introduction

The whole attained complexes (2–7) are stable in air and have comparable colors, the test of solubility showed that the complexes are water insoluble and soluble in the polar aprotic solvents. Ligand (1) Ethyl 6‐ethyl‐2‐(2‐hydroxy‐benzylideneamino)‐4,5,6,7‐tetra‐hydrothieno[2,3‐c]‐pyridi‐ne‐3‐carboxylate (HL) was prepared by reaction of salicylaldehyde with 3 Ethyl 2‐amino‐6‐ethyl‐4,5,6,7‐tetrahydrothieno[2,3‐c]pyridine‐3‐carboxylate in refluxed ethyl alcohol with glacial acetic acid as a catalyst for four hours to give 79% as a yellow solid crystal (Figure 1). The prepared metal compounds had a molar conductivity located within 7.5–35.6 Ω⁻¹cm²mol⁻¹ range indicating their non‐electrolytes nature.[40] The whole spectroscopic analysis and thermal gravimetric data are presented in the experimental part and Tables 1–3. The data displayed that all complexes were formed in a molar ratio (1 L:1 M) (Figure 2).

The ¹H NMR for the Schiff base, Ethyl −6‐ethyl‐2‐(2‐hydroxybenzylideneamino)‐4,5,6,7‐tetrahydrothieno[2,3-c]pyridine-3-carboxylate (HL) was measured in DMSO‐d₆. ¹H‐NMR spectrum for the ligand (1) (Figure 3) displayed a peak of hydroxyl proton at δ = 12.56 ppm. This hydrogen chemical shift observed at high values of δ characteristic to their bonding to the oxygen atom that is lean to electronegativity in nature. This consequence was confirmed by the signal chart of the prepared ligand which showed that the notable decrease of the strength of the signals (Figure 4). While the azomethine proton H‐¹⁸C=N appeared as the singlet at δ = 8.76 ppm. The aromatic protons H‐C^21&24 can be observed as a doublet at δ = 7.65 and 7.40 ppm with JHH equal to 7.6 and 8 & 8.05 consecutively while the aromatic protons H‐C^22&23 appeared as multiple at 6.94.

Complexes of VO²⁺, Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺ ethyl‐6‐ethyl‐2‐((2‐hydroxybenzylidene)amino)‐4,5,6,7‐tetrahydrothieno[2,3‐c]pyridine‐3‐carboxylate were synthesized and characterized via different spectroscopic techniques. The whole results declared that the complexes assembled in 1:1 mole ratio furthermore, the spectroscopic data analysis proved the present ligand adhered to the different metal ions in neutral or monobasic tridentate ligand via azomethine nitrogen, carbonyl oxygen atoms and protonated/deprotonated phenolic hydroxyl group. The UV–Vis. and ESR spectroscopic data analysis proposed a distorted octahedral or octahedral structure for all complexes. The ESR spectra for Cu²⁺ complexes (5–6) revealed an axial symmetry with g‖ > g_┴ > g_e, denoting to distorted octahedral Cu²⁺ complex and the free electrons in the M shell exist in a d_(x2‐y2) orbital with a remarkable covalent bond aspect. The synthesized complexes showed moderate to superb fungicide activity. All complexes are more active than both standard drug and ligand against C. albicans where complexes (5–7) are more active against A. flavus and compounds (1), (4–5), (7) against S. cerevisiae whereas only complex (6) is more active against A niger.

Schiff bases resulted from the condensation of primary amines and carbonyl compounds which discovered by Hugo Schiff in 1894 are structurally recognized as imine or azomethine.^[1,2] These possess a vital role in organic, inorganic, medicinal chemistry and biological field owing to their structures; furthermore, these have an imperative role in the theme of coordination chemistry, particularly in the development of complexes owing to its facility to produce stable organo‐metal compounds with transition metal ions. Schiff bases and their complexes are versatile extensively used for industrial goals and expose a contrasting broad range of biological activities^[3–6] include, antifungal,^[7] antibacterial,^[7,8] Anti‐leishmanial,^[9] anti‐molluscicidal,^[8] antimalarial,^[10] anti‐proliferative,^[11] anti‐inflammatory, antitumor,^[12] anti‐amoebic,^[13] antiviral,^[14] antioxidant^[15] and antipyretic properties. The Schiff base ligands derived from o‐vanillin connected with Pd atom forming metal complexes showed a cytotoxic effect on three cancer cell lines: breast (MCF‐7), lung (A549) and ovarian (SKOV3).^[16] While Cu (II) complexes of Schiff bases of the pyrrolizine‐5‐carboxamides displayed cytotoxic effect on the breast (MCF‐7), ovary (A2780) and colon (HT29) human adenocarcinoma, in addition to MRC5 (normal human fetal lung fibroblast) cells.^[17] Niu.reported that the Zn²⁺ complexes of o‐vanillin Schiff Bases exhibited efficient DNA interaction and furthermore, showed in vitro cytotoxic effect against four different sets of human cancer cell lines (HL‐60, HeLa, K562 and A549,).^[18] Recently, Venkateswarlu et al. stated DNA binding, DNA cleavage, In addition to many other biological studies of Co²⁺ Ni²⁺ and Cu²⁺ complexes with “2‐((furan‐2‐yl) methylimino)methyl)‐6‐ethoxyphenol Schiff Base,^[19] were also carried out. Ghorai et al. reported the preparation and characterization of Cu²⁺ and Zn²⁺ complexes of “3‐methoxy propylimino) methyl)‐6‐methoxyphenol” and reported studies related to their capability to DNA binding, D cleavage.^[20] Numerous of Schiff base complexes show superb catalytic behavior in numerous dissimilar reactions particularly at elevated temperature and in dampness.^[21–24]