Tetra-2,3-pyrazinoporphyrazines with externally appended pyridine rings. 16. A rare class of uncharged water soluble complexes: UV-vis spectral, redox, and photochemical properties

The synthesis and physicochemical characterization of a new class of water soluble homo/heteropentanuclear porphyrazine complexes are described. The investigated compounds, prepared from the previously reported mononuclear species [LM]⋅xH2O (L = tetrakis-2,3-[5,6-di(2-pyridyl) pyrazino]porphyrazinato dianion; M = MgII(H2O), ZnII, CuII, CoII, PdII, PtII; x = 3–8) in DMSO under mild experimental conditions, are represented as [{Pd(OAc)2}4LM]⋅xH2O (x = 11–22) and bear four Pd(OAc)2 units, each externally coordinated at the vicinal pyridine N atoms of a single dipyridinopyrazine fragment of the porphyrazine macrocycle (py–py coordination). The newly synthesized compounds were examined by IR and magnetic susceptibility measurements in the solid state. Solution UV-visible spectral studies on all of the species were conducted in the low-donor organic solvents pyridine, dimethyl sulfoxide and dimethylformamide and in the water medium, whereas electrochemical measurements were performed in these media in the presence of tetrabutylammonium perchlorate (organic solvents) and KCl or NaOAc (water). Data on the photosensitizing activity for the generation of singlet oxygen, 1O2, of interest in photodynamic therapy, were also obtained in dimethylformammide solution on the compounds [{Pd(OAc)2}4LM](M = MgII(H2O), ZnII, PdII, PtII) and the measured ΦΔ values are presented and discussed. NMR spectral data on the complex [{Pd(OAc)2}4LZn] are also included and discussed.