Date of Award

3-1989

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Supervisor

Professor G.J. Schrobilgen

Abstract

This Thesis describes the preparation and characterization of some classical and cluster main-group polyanions in solution by multinuclear magnetic resonance spectroscopy (multi-NMR) and in the solid state by X-ray crystallography.

A novel series of classical anions, Pb₂Ch₃²ˉ (Ch = Se, Te) and M₂Se₃²ˉ (M = Sn, Pb), have been characterized in solution and the detailed geometry of Pb₂Se₃²ˉ and Pb₂Te₃²ˉ obtained from the crystal structures of (2,2,2-crypt-K⁺)₂ Pb₂Ch₃²ˉ (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.

The Sen²ˉ and Ten²ˉ (n = 1 - 4) anions and the new chain-like heteropolychalcogenide anions, TekSe₂_k²ˉ and TepSe4-p²ˉ and (k = 1, 2 and p = 2, 3) have been characterized in solution and their chemical exchange behavior directly observed by 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 TeSe₂²ˉ (C₂ν) and the pyramidal TeSe₃²ˉ (C₃ν) anions have been determined from the X-ray crystal structures of (2,2,2-crypt-K⁺)₂TeSen²ˉ∙en (n = 2, 3). In addition, the TeSmSe₃_m²ˉ anions (m = 0 - 3), have been characterized in solution. A significant involvement of π(d-p) bonds is evident in these species.

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.

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 structures of two of the anions have been proposed, i.e., a bicapped square antiprism for Tl₂Sn₈⁴ˉ and a coupled TlSn₃-tetrahedra for (Sn₃TlTlSn₃)⁴ˉ.


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