ABSTRACT
The 2,2,2-crypt salts of the Tl4Se8(4-) and [Tl2Se4(2-)]infinity1 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 P2(1)/n, with Z = 2 and a = 14.768(3) angstroms, b = 16.635(3) angstroms, c = 21.254(4) angstroms, beta = 94.17(3) degrees at -123 degrees C, and the [2,2,2-crypt-Na]2[Tl2Se4]infinity1.en crystallizes in the monoclinic space group P2(1)/c, with Z = 4 and a = 14.246(2) angstroms, b = 14.360(3) angstroms, c = 26.673(8) angstroms, beta = 99.87(3) degrees at -123 degrees C. The TlIII anions, Tl2Se6(6-) and Tl3Se7(5-), and the mixed oxidation state TlI/TlIII anion, Tl3Se6(5-), 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 Tl2Se6(6-) 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 Tl4Se8(4-) anion is formally derived from the Tl2Se6(6-) anion by coordination of each pair of terminal Se atoms to the TlIII atom of a TlSe+ cation. The structure of the [Tl2Se4(2-)]infinity1 anion is comprised of edge-sharing distorted TlSe4 tetrahedra that form infinite, one-dimensional [Tl2Se42-]infinity1 chains. The structures of Tl3Se6(5-) and Tl3Se7(5-) 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 Tl2Se6(6-), Tl3Se6(5-), Tl3Se7(5-), and Tl4Se8(4-) 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 Tl2Se6(6-), Tl3Se6(5-), Tl3Se7(5-), and Tl4Se8(4-) anions are electron-precise rings and cages.
ABSTRACT
The series of group 14 metal trigonal bipyramidal anions has been extended to the mixed group 13/group 14 metal TlMTe(3)(3)(-) anions (M = Sn, Pb), obtained by the reaction of Tl(2)M(2)Te(3) and K(2)Te in en or in en/ethylamine mixtures and a stoichiometric excess of 2,2,2-crypt with respect to K(+). The thallium anions were characterized in solution by (119)Sn, (205)Tl, (207)Pb, and (125)Te NMR spectroscopy. The small magnitudes of the relativistically corrected reduced coupling constants, (1)(K(M)(-)(Ch))(RC) and (1)(K(Tl)(-)(Ch))(RC), observed for the previously reported M(2)Ch(3)(2)(-) (Ch = Se, Te) and the TlMTe(3)(3)(-) anions are consistent with predominantly p-bonded cages, and this observation is supported by local and nonlocal density functional theory (DFT) calculations. Theory indicates M-M and Tl-M interactions of high s character corresponding to Mayer bond orders of 0.13-0.32. The (K(M)(-)(M))(RC) and (K(Tl)(-)(M))(RC) couplings are unusually large compared to those of the butterfly-shaped Tl(2)Ch(2)(2)(-) anions and likely arise from higher M-M and Tl-M bond orders, a larger number of coupling pathways, and smaller M-Ch-M and M-Ch-Tl bond angles. The TlPbTe(3)(3)(-) anion has also been structurally characterized by X-ray crystallography in (2,2,2-crypt-K(+))(3)TlPbTe(3)(3)(-).2en [monoclinic system, space group P2(1)/c, Z = 4, a = 15.256(5) Å, b = 26.087(9) Å, c = 20.984(8) Å, and beta = 93.03(3) degrees ] along with Pb(2)Ch(3)(2)(-) (Ch = S, Se) in (2,2,2-crypt-K(+))(2)Pb(2)Ch(3)(2)(-).0.5en [Pb(2)S(3)(2)(-): triclinic system, space group P&onemacr;, Z = 2, a = 10.189(2) Å, b = 11.329(2) Å, c = 23.194(4) Å, alpha = 95.439(14) degrees, beta = 92.562(14) degrees, and gamma = 90.549(14) degrees; Pb(2)Se(3)(2)(-): triclinic system, space group P&onemacr;, Z = 2, a = 10.187(2) Å, b = 11.403(2) Å, c = 23.360(6) Å, alpha = 95.26(2) degrees, beta = 92.17(2) degrees, and gamma = 90.89(2) degrees ]. Density functional theory calculations show that the experimental structures for the M(2)Ch(3)(2)(-) and TlPbTe(3)(3)(-) anions are true minima and reproduce the experimental bond distances and angles. The vibrational frequencies determined by DFT calculations are in good agreement with those determined by Raman spectroscopy and have been used in their assignment.