Polytellurides of Mn, Fe, and Zn from Mild Solvothermal Reactions in Liquid Ammonia

The reaction of elemental Mn, Fe, and Zn with Te in liquid ammonia at 50 °C leads to the polytellurides [Mn(NH3)6]Te4 (1), [Fe(NH3)6]Te4·NH3 (2), and [Zn(NH3)4]2Te15 (3) in quantitative yield for 1 and 3, and in 30–50% yield for 2. The compounds form black crystals, which are air sensitive and easily lose ammonia without a protective atmosphere of NH3. Compound 3 is semiconducting with a thermal activation energy of 1.2 eV. In the crystal structures of 1 and 2, tetratelluride anions Te42- in gauche conformation with dihedral angles around 90° are present, which are linked to form infinite spiral chains. Compound 3 contains an unusual Te154- polyanion in the form of a bent chain Te7–Te–Te7. The connection between the Te4 groups in 1 and 2 and the two Te7 groups in 3 is achieved via linear Te3 entities, which are strongly asymmetric in 1, almost symmetric in 2, and symmetric in 3 (for 1, Te–Te···Te 174.0°, d1 = 2.87, d2 = 3.25 A; for 2, Te–Te–Te 178.8°, d1 = 3.01, d2 = 3.09 A; for 3, Te–Te–Te 180°, d1 = d2 ...