Hydrothermal synthesis and solid-state structures of polynuclear technetium iodide compounds

Two new technetium iodide compounds, Tc 2 (O 2 CCH 3 ) 4 I and K[Tc 8 (μ-I) 8 I 4 ]I, were synthesized in an autoclave from the reaction of KTcO 4 in glacial acetic acid with hydroiodic acid and/or alkali metal iodide salts at 210 °C under 60–70 atm hydrogen pressure. The structures of Tc 2 (O 2 CCH 3 ) 4 I and K[Tc 8 (μ-I) 8 I 4 ]I were solved by single-crystal X-ray diffraction. The compound Tc 2 (O 2 CCH 3 ) 4 I crystallizes in the monoclinic space group C2/m with a = 7.1194(6) A, b = 14.5851(13) A, c = 7.1586(6) A, and β = 110.9540(10)°. The structure of Tc 2 (O 2 CCH 3 ) 4 I consists of infinite chains of Tc 2 (O 2 CCH 3 ) 4 + units linked by bridging iodides, an arrangement similar to the one found in Tc 2 (O 2 CCH 3 ) 4 X (X = Cl, Br). The Tc Tc separation in Tc 2 (O 2 CCH 3 ) 4 I (i.e., 2.1146(4) A) is consistent with the presence of a Tc Tc bond of order 3.5. Magnetic susceptibility measurements reveal Tc 2 (O 2 CCH 3 ) 4 I to be paramagnetic ( μ eff = 1.84 B.M.) and support the electronic configuration σ 2 π 2 δ 2 δ ∗1 for the Tc 2 5+ unit in the compound. The compound K[Tc 8 (μ-I) 8 I 4 ]I crystallizes in the monoclinic space group P2 1 /n with a = 8.0018(5) A, b = 14.5125(10) A, c = 13.1948(9) A, and β = 102.3090(10)°, and is the first octanuclear technetium iodide cluster to be reported. The Tc Tc separations in the [Tc 8 (μ-I) 8 I 4 ] cluster (i.e., 2.164(3) A, 2.5308(8) A and 2.72(3) A) suggest the presence of Tc Tc triple bonds, Tc Tc double bonds and Tc Tc single bonds.