Synthesis and characterization of tetra-substituted palladium phthalocyanine complexes

Tetra-substituted palladium phthalocyanine complexes with different electron withdrawing and electron donating substituents (–H, –NO2, –NH2, –Cl, –COOH, aryl thio) have been synthesized with a good yield. The synthesized complexes were characterized using XPS, UV–Vis, IR, Raman, XRD, TGA and electrochemistry. The XPS spectra show that the central metal ion is in the +2 state, while the UV–Vis spectra demonstrate split absorption peaks in the Q-band region 600–700 nm due to the presence of dimeric and oligomeric molecules in addition to the monomeric species. The UV–Vis and Raman spectra demonstrate a shift in the peaks/bands which is a result of the electron withdrawing and electron donating substituents at the periphery of the benzene ring compared to the parent palladium phthalocyanine. The thermogravimetic stability studies show that these complexes undergo two separate decomposition processes. The thermal stability for different complexes are in the order: PdPc < PdTPSPc < PdTClPc < PdTAPc < PdTCAPc = PdTNPc, indicating that the substituents at the periphery have an effect on the thermal stability. The cyclic voltammetric data in DMSO show that the central metal ion Pd does not undergo a redox process and the redox behaviour observed is mainly due to the macrocyclic ring reduction process.

► Different palladium phthalocyanine complexes have been synthesized for the first time.
► Palladium is in +2 state in the complex.
► UV–Vis and Raman spectra due to the variation in the electro charge density.
► The substituted complexes are highly thermally stable.
► The redox peaks observed are due to the phthalocyanine macrocycle.