Synthesis and Spectrometric Study of New Iron Phthalocyanine Polymers: Influence of Peripheral COOH and CN Groups on Vibrational and Electronic Properties

We have prepared and isolated in solid form two types of polymers formed between iron (II) complexes ([FePc(COOH)₈] and [FePc(CN)₈]) and two bidentate ligands [trans-1,2-bis (4-pyridyl) ethylene (bpe); trans-1,2-bis (4-pyridyl) ethane (bpa)]. The electronic and vibrational absorption spectra of these complexes are discussed in comparison with those of previous work on [FePcL₂]n polymers with the same ligands. Infrared spectrometry shows a modulation in the intensities of certain characteristic bands of the complexes, reflecting a reorganization of the structure of these compounds through the formation of polymers and, above all, the emergence of new vibration bands attributable to the ligands. In electron absorption spectrometry, our results confirm those already available in the literature with the [FePcL₂]n series. The presence of the bpa ligand causes each macrocycle of the polymer to behave independently. In contrast, the bpe ligand induces a perfect linear connection between the macrocycles due to its alkene function, which allows electrons to move easily along the polymer chain. The presence of peripheral groups (COOH and CN) provides a novel result because they strongly influence not only the energy of the π→π* band, but especially that of the central metal-axial ligand charge transfer band (CT Fe→L). These charge transfers are responsible for the conductive properties of these compounds.