Synthesis and structural explanation of mixed ligand complexes of selenium(Iv) with caffeine and some nitrogen-based ligands

Abstract

Mixed-ligand complexes of selenium(IV) ion chelating with caffeine (caf) molecule as a primary ligand and N,O donors (L-valine (L-val); L-proline (L-pro); 2,4-diaminophenol (dap)), or nitrogen−base donors (2,2'-bipyridine (bpy) and bathophenanthroline (bphen)) as secondary ligand were prepared. These complexes were assigned based on different techniques like molar conductance, UV-Visible (UV-Vis), infrared (FT-IR),1H-NMR spectroscopy, thermal analysis (TGA-DTG), X-ray diffraction (XRD), scanning (SEM) and transmission electron microscopes (TEM). The FT-IR and1H-NMR spectra deduced that the caf chelate is acts as a monodentate with Se(IV) through the nitrogen atom N9, while secondary ligands (L-val, L-pro, dap, bpy and bphen) coordinated as bi-dentate ligand towards Se(IV) via NO or NN donating atoms. Dependent on the spectroscopic results, it can be confirmed that Se(IV) complexes have an octahedral geometry with general formulas [Se(caf)(L)(Cl)3] (where L = L-val, L-pro and dap) I-III and [Se(caf)(L')(Cl)3]Cl (where L' = bpy and bphen) IV and V. The conductance data of the synthesized complexes revealed that the [Se(caf)(L)(Cl)3] complexes have a non-electrolyte properties, while [Se(caf)(L')(Cl)3]Cl complex has a 1:1 electrolyte nature. TGA-DTG analysis shows that the degradation of complexes occurs between 30-800°C. SEM, TEM, and XRD analyses revealed the particle size of synthesized complexes. All the five complexes in this study were evaluated for their anticancer effect towards two colorectal adenocarcinoma (Caco-2) and breast cancer (Mcf-7) cell lines.