Abstract

La(III), Ce(III), Pr(III), Nd(III), Gd(III), Dy(III), Ho(III) and Er(III) complexes of Schiff bases derived from sulphamethoxazole and salicylaldehyde ( I), and thiophene-2-aldehyde ( II) have been characterized on the basis of IR, NMR, UV-Vis spectroscopy, elemental analysis, conductance measurements and molecular weight determinations. The Schiff bases act as monobasic bidentate ligands, rendering the metal eight-coordinated. The equilibrium constants have been studied in solution at 25, 30 and 35 °C. The nephelauxetic effect (1 - β), bonding parameter (β), b 1/2 and Sinha covalency parameter (δ) have been calculated. The positive values indicate the covalent nature of the metal-ligand bond. The covalent nature of the complexes is also supported by molar conductance measurements. The toxicities of the Schiff bases and their complexes were evaluated against insects. The LD 50 value for cockroaches and percent growth inhibition of the fungi show greater efficacy for the complexes than the Schiff bases.

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