Characterization of Complexes Synthesized Using Schiff Base Ligands and Their Screening for Toxicity Two Fungal and One Bacterial Species on Rice Pathogens

Coordination complexes with metal ions Cu(II), Ni(II), Co(II), Fe(III), Mn(II), Cr(III), and VO(II) with six ligands formed by condensation products using azides and aldehydes or ketones are characterized. Both the ligands and the complexes synthesized are characterized by C, H, N, Cl and metal analyses, IR, UV-Vis, TGA, and magnetic susceptibility for tentative structure proposal. Several of them are screened for their toxicity (i.e., physiological activity) against fungal species Rhizoctonia solani and Acrocylindrium oryzae and a bacterium, Xanthomonas oryzae on rice pathogens. The study shows that the observed physiological activity is enhanced for the metal complexes as compared to the simple metal salts or ligands, except in the case of L3 or HAEP ligand, where the free –OH and –NH2 groups on the ligand seemed to have inhibited the activity. It is also observed that the order of activity has a dependence on the increased atomic weight of the metal ion in use. In some cases, especially the VO(II) complexes, they are found to be better than the standards in use, both for the fungicides and for the bactericide. 1. Introduction Ever since the Italian chemist, Hugo Schiff used imines to make several “metallo-imines”, numbers of variants of the condensation products of imines and aldehydes or ketones such as RCH=NR′—where R & R′ are alkyl and/or aryl substituent’s, are popularized. They are also known as Schiff bases (SBs), anils, imines or azomethines. They are also known as anils, imines, or azomethines. These have several applications in organic studies, such as for building new heterocyclic systems, for identification, detection, and determination of aldehydes and ketones, for purification of carbonyl or amino compounds, or for the protection of these groups during the complex formation or such sensitive reactions [1]. They have other side applications in various other fields, coordination chemistry [2–9], analytical chemistry [10–16], pigments and dyes [17], and polymer industries [18], in vitamins and enzymes [4] for model biomolecules. There is a special mention of these complexes in agriculture [4] as fungicides, pesticides, and bacteriocides. Survey of the literature for SB metal complexes and their applications showed excellent review articles [19, 20] for the detailed understanding of this class of compounds in all respects and one more especially dedicated to copper complexes [21]. They provide several details on number of metal complexes derived from SBs used widely for applications in food and dye industry, analytical chemistry, catalysis,