Syntheses; ⁷⁷Se, ²⁰³Tl, and ²⁰⁵Tl NMR; and Theoretical Studies of the Tl₂Se₆^6-, Tl₃Se₆^5-, and Tl₃Se₇^5- Anions and the X-ray Crystal Structures of [2,2,2-crypt-Na]₄[Tl₄Se₈]·en and [2,2,2-crypt-Na]₂[Tl₂Se₄]_∞¹·en

The 2,2,2-crypt salts of the Tl4Se84- and [Tl2Se42- anions have been obtained by extraction of the ternary alloy NaTl0.5Se in ethylenediamine (en) in the presence of 2,2,2-crypt and 18-crown-6 followed by vapor-phase diffusion of THF into the en extract. The [2,2,2-crypt-Na]4[Tl4Se8]·en crystallizes in the monoclinic space group P21/n, with Z = 2 and a = 14.768(3) Å, b = 16.635(3) Å, c = 21.254(4) Å, β = 94.17(3)° at −123 °C, and the [2,2,2-crypt-Na]2[Tl2Se4 ·en crystallizes in the monoclinic space group P21/c, with Z = 4 and a = 14.246(2) Å, b = 14.360(3) Å, c = 26.673(8) Å, β = 99.87(3)° at −123 °C. The TlIII anions, Tl2Se66- and Tl3Se75-, and the mixed oxidation state TlI/TlIII anion, Tl3Se65-, have been obtained by extraction of NaTl0.5Se and NaTlSe in en, in the presence of 2,2,2-crypt and/or in liquid NH3, and have been characterized in solution by low-temperature 77Se, 203Tl, and 205Tl NMR spectroscopy. The 1J(203,205Tl−77Se) and 2J(203,205Tl−203,205Tl) couplings of the three anions have been used to arrive at their solution structures by detailed analyses and simulations of all spin multiplets that comprise the 205,203Tl NMR subspectra arising from natural abundance 205,203Tl and 77Se isotopomer distributions. The structure of Tl2Se66- is based on a Tl2Se2 ring in which each thallium is bonded to two exo-selenium atoms so that these thalliums are four-coordinate and possess a formal oxidation state of +3. The Tl4Se84- anion is formally derived from the Tl2Se66- anion by coordination of each pair of terminal Se atoms to the TlIII atom of a TlSe+ cation. The structure of the [Tl2Se42- anion is comprised of edge-sharing distorted TlSe4 tetrahedra that form infinite, one-dimensional [Tl2Se42- chains. The structures of Tl3Se65- and Tl3Se75- are derived from Tl4Se4-cubes in which one thallium atom has been removed and two and three exo-selenium atoms are bonded to thallium atoms, respectively, so that each is four-coordinate and possesses a formal oxidation state of +3 with the remaining three-coordinate thallium atom in the +1 oxidation state. Quantum mechanical calculations at the MP2 level of theory show that the Tl2Se66-, Tl3Se65-, Tl3Se75-, and Tl4Se84- anions exhibit true minima and display geometries that are in agreement with their experimental structures. Natural bond orbital and electron localization function analyses were utilized in describing the bonding in the present and previously published Tl/Se anions, and showed that the Tl2Se66-, Tl3Se65-, Tl3Se75-, and Tl4Se84- anions are electron-precise rings and cages.