Insights into the new cadmium(II) metalloporphyrin: Synthesis, X-ray crystal structure, Hirshfeld surface analysis, photophysical and cyclic voltammetry characterization of the (morpholine){(meso-tetra(para-chloro-phenyl)porphyrinato}cadmium(II)

Abstract

In this work we report the synthesis of the cadmium(II)-meso-tetra(para-chloro-phenyl)porphyrin with the morpholine O-donor axial ligand with formula [Cd(TClPP)(morph)] (I). This coordination compound adopts a distorted five-coordinate square pyramidal geometry indicated by a major doming, a moderate ruffling and saddle distortions of the porphyrinato core. The supramolecular architecture is dominated by intermolecular N–H⋯Cl and C–H⋯Cl interactions formed between the morpholine and the chlorine atom of the adjacent meso-phenylporphyrin of complex (I). Hirshfeld surface analysis was carried out to understand the nature of intermolecular contacts, where the fingerprint plot provides the information about the percentage contribution. UV–Vis spectroscopy study highlighted the red-shift of the absorption bands after the insertion of Cd(II) metal ion into TClPP moiety and after coordination of the morpholine axial ligand. Fluorescence emission spectroscopy study showed a remarkable blue-shift effect of the Q bands followed by a dramatical diminution of the fluorescence intensity, quantum yield (φf) and lifetime (τf) as consequence of the high quenching effect of the cadmium heavy metal and the distortion of the porphyrin core, which promotes the loss of the “motion energy” by other non-radiative energy dissipation processes than light emission. An increase of the singlet oxygen quantum yield (ΦΔ) is also observed due to the heavy atom effect of cadmium(II) cation. The cyclic voltammetry investigation of the free base H2TClPP, the starting material [Cd(TClPP)] and the Cd(II)-morpholine porphyrin species (I) is also reported.