Tinuvin-P metal complexes as new photo-stabilizers for PVC: Synthesis, characterization and DFT studies

Abstract

In the present study, new metal complexes of Tinuvin-P (Tp), a well-known photostabilizer for vinyl polymers, [Co(Tp)2(H2O)2] 0.5EtOH (1), [Ni(Tp)2(H2O)2] 1.5H2O (2), [Cu(Tp)2(H2O)2] EtOH (3) and [Zn(Tp)2] H2O (4) have been synthesized, characterized (elemental analyses, FT-IR, 1H-NMR, UV-vis., MS, EPR, magnetic, TG and conductivity), and investigated as photo-stabilizers for PVC. Theoretical calculations involving geometry optimization have been performed at DFT/B3LYP level of theory. According to the spectral data, Tp behaved as mononegative bidentate ligand and coordinated to metal ions via deprotonated phenolic O and triazole N. According to Uv-vis, EPR, and magnetic moment measurements, the complexes 1-3 have octahedral geometry, while the complex 4 has square planar geometry. XRD study pointed out that complex 1 is amorphous while complexes 2-4 were semicrystalline. The photostabilization efficiency results, based on the determination of percent weight loss and the percent gelation, showed a rational stabilizing effect of the studied complexes comparing with the free ligand, and the stabilizing efficiency was found to be in the following order: 1 > 2 > Tp > 4 ~ 3. The optimized structures of the ligand and its investigated complexes as the lowest energy configurations was carried out at B3LYP/6-311G (d, p) level at the density functional theory (DFT) level. The Co (II)-complex (1), with the lower ionization potential, higher dipole moment and lowest Eg, was found to be highly effective as light stabilizer agent than the ligand and other complexes.