The title compounds have been prepared by reactions of the metal acetates of zink, cadmium, and mercury with ethanolic solutions of sodium polyselenides in the presence of 15-crown-5. They form dark red crystals, which were characterized by their IR specta as well as by X-ray crystal structure determinations. All complexes [Na-15-crown-5]2[M(Se 4)2] with M = Zn (1), Cd (2), Hg (3) crystallize isotypically in the space group C2/c with 4 formula units per unit cell. In the anions [M(Se4)2]2- the metal atoms are coordinated tetrahedrally by four selenium atoms of two Se4 2- units, thus forming a spiro-bicyclus. The complex cations [Na-15-crown-5]+ have a Na---Se contact of approximately 299 pm with two selenium atoms of a MSe4 group, allowing formulation of triple ion species.
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Adel et al. (1988) studied this question.