Polyanions of the Heavy Group 13, 14 and 16 Elements in Basic Media

Abstract

<p>This thesis describes the preparation and characterization of some classical cluster main-group polyanions in solution by multinuclear magnetic resonance spectroscopy (multi-NMR) and in the solid state by X-ray crystallography.</p> <p>A novel series of classical anions, Pb2Ch3^2 (Ch = Se, Te) and M2Se3^2 (M = Sn, Pb), have been characterized in solution and the detailed geometry of Pb2Se3^2 and Pb2Te3^2 obtained from the crystal structures of (2, 2,2-crypt-K+)2 Pb2Ch3^2 (Ch = Se or Te) as determined by X-ray crystallography. The anions were found to have a trigonal bipyramidal structure with the Pb and/or Sn atoms in the axial positions and the chalcogen atoms in the equatorial plane.</p> <p>The Sen^2 and Ten^2 (n = 1-4) anions and the new chain-like heteropolychalcogenide anions, TekSe2-k^2 and TepSe4-p^2 and (k = 1, 2 and p = 2, 3) have been characterized in solution and their chemical exchange behaviour directly observed by the NMR spectroscopy. The structures of these anions can be rationalized on the principle that the more electronegative atom is positioned at the sites of highest electron density. Furthermore, the large one-bond coupling constants observed for Cht-Chb bonds indicate that the nature of these bonds are significantly different from those of Chb-Chb bonds. The detailed geometry of the V-shaped TeSe2^2- (C2v) and the pyramidal TeSe3^2- (C3v) anions have been determined from the X-ray crystal structures of (2, 2, 2-crypt-K+) 2TeSen^2-.en (n = 2, 3). In addition, the TeSmSe3-m^2- anions (m = 0-3), have been characterized in soltuion. A significant involvement of π(d-p) bonds is evident in these species.</p> <p>A new series of three-coordinated Sn(IV) telluride anions have been identified in solution by multi-NMR. The NMR data indicated the presence of polyanions consisting of linked trigonal planar SnTe3-units in which each SnTe3-unit is undergoing fast intramolecular "spinning" on the NMR time scale.</p> <p>The extraction of K/Sn/Tl and K/Pb/Tl alloys in ethylenediamine and/or liquid ammonia gave rise to new polyatomic Tl-Sn and Tl-Pb cluster anions. The formation of the anions were found to be strongly dependent on the solvent used for the extraction and the presence of 2, 2, 2-crypt, as well as the alloy preparation method. The multi-NMR study indicated that the new Tl-Sn cluster anions were nonfluxional. The structure of two of the anions have been proposed, i.e., a bicapped square antiprism for Tl2Sn8^4- and a coupled TlSn3-tetrahedra for (Sn3TlTlSn3)^4-.</p>