Trigonal Bipyramidal M2Ch32- (M = Sn, Pb; Ch = S, Se, Te) and TlMTe33- Anions: Multinuclear Magnetic Resonance, Raman Spectroscopic, and Theoretical Studies, and the X-ray Crystal Structures of (2,2,2-crypt-K+)3TlPbTe33-·2en and (2,2,2-crypt-K+)2Pb2Ch32-·0.5en (Ch = S, Se)
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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.
