Abstract. The potassium salt of the [(CeO)₃(PW₉O₃₄)₂]¹⁵-polyanion was investigated by FT-IR and UV-VIS spectroscopy. Both α-A-[PW₉O₃₄]⁹- trilacunary Keggin units function as bidentate ligands for one cerium(III) ion. The most affected Ff-IR bands of the Keggin units after the cerium coordination are that corresponding to the v_as(P-O_a), v_as(W-O_a) and v_as(W-O_c-W) vibrations, suggesting that the Ce(Ill) ions coordinate the vacant regions of the trilacunary Keggin units. The UV spectrum of the complex contains the p_π-d_π electronic transitions into the W=O bonds (≈ 200 nm) and the d_π-p_π-d_π electronic transitions between the energetic levels of the tricentric bonds W-O-W (≈ 250 nm).

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