PNNL

Abstract

The salts [18-crown-6-K]4[Sn4Se10]?5en and [18-crown-6-K]4[Sn4Te10]?5en?2THF were isolated by extracting the alloys KSn0.90Se1.93 and K4Sn4Te10 in ethylenediamine (en) in the presence of 18-crown-6 (1,4,7,10,13,16-hexaoxacyclooctadecane). The Sn4Te104- anion has been structurally characterized for the first time by a single-crystal X-ray diffraction study of [18-crown-6-K]4[Sn4Te10]?5en?2THF: P21/n, a = 22.420(5) ?, b = 19.570(4) ?, c = 24.680(5) ?, ? = 96.90(3)o, V = 10750.2(37) ?3, Z = 4 and R1 = 0.0468 at -183 oC and, in addition to Si4Te104- and Ge4Te104-, represents the only other known group 14 adamantanoid telluride. The crystal structure determination of the related [18-crown-6-K]4[Sn4Se10]?5en salt has also been determined: P21/n, a = 22.003(2) ?, b = 18.966(2) ?, c = 24.393(2) ?, ? = 97.548(8)o, V = 10091.0(17) ?3, Z = 4 and R1 = 0.0843 at -123 oC. The anion geometries are of the adamantanoid type where the SnIV atoms occupy the bridgehead positions and the chalcogen atoms occupy the bridging and terminal sites. The energy minimized geometries of Sn4Ch104- have also been determined using density functional theory (DFT). Mayer bond order analyses, Mayer valencies and empirical bond valencies reveal that the terminal Sn-Ch bonds have significant multiple bond character, with the terminal Sn-Se bond having more multiple bond character than Sn-Te. The vibrational frequencies of the Sn4Se104- and Sn4Te104- anions have been calculated using DFT methods, allowing the Raman spectrum of Sn4Se104- to be fully assigned.