Study by XPS and UV-visible and DRIFT spectroscopies of electropolymerized films of substituted Ni(II)-p-phenylporphyrins and -phthalocyanines.

ABSTRACT

Films of nickel tetrasulfophthalocyanine and - p-phenylporphyrin (NiTSPc and NiTSPP, respectively) were obtained by repetitive cyclic voltammetry (RCV) of the 1 mM complex in aqueous solution, while films of the water-insoluble nickel tetraaminophthalocyanine and - p-phenylporphyrin (NiTAPc and NiTAPP, respectively) had to be obtained by RCV of the 1 mM complex in organic solvents. Glassy carbon (GC), ITO, or platinum electrodes were used as substrates. The modified electrodes were characterized by cyclic voltammetry (CV) and UV-visible, infrared, and X-ray photoelectron spectroscopies. The CVs of the sulfo films showed the characteristic peaks of the Ni(II)/Ni(III) process, whereas the CVs of the amino films did not, very small Ni(II)/Ni(III) peaks appearing only after activation by RCV. Upon oxidation to Ni(III) both sulfo films changed from transparent to dark violet. The IR spectra of the polyNiTSPP and the polyNiTSPc films showed bands at 3628 cm (-1) and 3500 cm (-1), respectively, which could be due to interstitial water molecules occluded during the polymerization. The Ni 2p XP spectra indicate that the magnetic character of the Ni(II) ions in NiTSPP is dramatically changed by the polymerization, from diamagnetic in the monomer to paramagnetic in the polymeric film, indicating the formation of Ni-O-Ni bridges or of clusters of Ni(OH) 2. On the contrary, the Ni 2p XP spectra of the unactivated NiTAPP film, in which the Ni(II)/Ni(III) process was absent, showed only diamagnetic Ni(II). Therefore, it is concluded that only paramagnetic Ni(II) ions can be electrooxidized to Ni(III).