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 TlMTe33- anions (M = Sn, Pb), obtained by the reaction of Tl2M2Te3 and K2Te 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 119Sn, 205Tl, 207Pb, and 125Te NMR spectroscopy. The small magnitudes of the relativistically corrected reduced coupling constants, 1(KM-Ch)RC and 1(KTl-Ch)RC, observed for the previously reported M2Ch32- (Ch = Se, Te) and the TlMTe33- 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 (KM-M)RC and (KTl-M)RC couplings are unusually large compared to those of the butterfly-shaped Tl2Ch22- 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 TlPbTe33- anion has also been structurally characterized by X-ray crystallography in (2,2,2-crypt-K+)3TlPbTe33-·2en [monoclinic system, space group P21/c, Z = 4, a = 15.256(5) Å, b = 26.087(9) Å, c = 20.984(8) Å, and β = 93.03(3)°] along with Pb2Ch32- (Ch = S, Se) in (2,2,2-crypt-K+)2Pb2Ch32-·0.5en [Pb2S32-: triclinic system, space group P1̄, Z = 2, a = 10.189(2) Å, b = 11.329(2) Å, c = 23.194(4) Å, α = 95.439(14)°, β = 92.562(14)°, and γ = 90.549(14)°; Pb2Se32-: triclinic system, space group P1̄, Z = 2, a = 10.187(2) Å, b = 11.403(2) Å, c = 23.360(6) Å, α = 95.26(2)°, β = 92.17(2)°, and γ = 90.89(2)°]. Density functional theory calculations show that the experimental structures for the M2Ch32- and TlPbTe33- 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.

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