Rational design of closed shell, dicyanoaurate-containing coordination polymers for materials applications

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Thesis type
(Thesis) Ph.D.
Date created
2009
Authors/Contributors
Abstract
This thesis focuses on incorporating Au(CN)2¯ with zinc(II) and lead(II) to form diamagnetic coordination polymers. These cations were chosen based on the materials properties of previous Au(CN)2¯ containing coordination polymers. Four polymorphic forms of Zn[Au(CN)2]2 were synthesized. A zinc(II) centre in a tetrahedral geometry was always observed with Au(CN)2¯ units at each tetrahedral vertex. 3-D networks based on corner-sharing tetrahedra with various degrees of interpenetration were formed. Gold-gold interactions of 3.11 -- 3.33 Å link the networks. Three polymorphs are luminescent, with emissions ranging from 390 -- 480 nm. Upon exposure to ammonia vapour, the polymers alter their structure and emission energies. The adsorption route is dependent on the polymorph used. Five lead(II)-coordination polymers, Pb(H2O)[Au(CN)2]2, Pb[Au(CN)2]2, Pb(phenanthroline)2[Au(CN)2]2, Pb(bipyridine)2[Au(CN)2]2, and Pb(ethylenediamine)[Au(CN)2]2 were synthesized in order to determine the type of polymers lead(II) and Au(CN)2¯ produced; the polymers were also investigated by solid-state NMR spectroscopy. The more basic the ligand, and/or the less π-accepting the ligand, the more stereochemically active the lead(II) lone pair is. The span and isotropic chemical shift parameters of the 207Pb NMR increase with lone pair activity. The birefringence of Pb(H2O)[Au(CN)2]2 is 0.070. Substituting the water molecules in Pb(H2O)[Au(CN)2]2 with terpyridine produced a polymer with a birefringence of 0.396. Substituting Au(CN)2¯ with Ag(CN)2¯, or lead(II) with manganese(II) elicits no significant change in the birefringence, which was thus attributed to the terpyridine ligand aligned face-to-face by the polymer framework. Substituting the terpyridine with other terpyridine-based ligands such as 2-(2-pyridyl)-1,10-phenanthroline or 4'-Bromo/Chloro-2,2':6',2''-terpyridine produces polymers with birefringences ranging from 0.26 to 0.59. A recipe for birefringent coordination polymers was thus developed: Highly anisotropically polarizable ligands with judiciously substituted halogen atoms arranged face-to-face on a M[Au(CN)2]2 polymer framework. Related bismuth(III) and thallium(I) compounds with Au(CN)2¯ were synthesized and structurally characterized as proof-of-principle. Most bismuth(III) polymers, such as [Bi(terpyridine)(H2O)(μ-OH)]2[Au(CN)2]4} formed hydroxide-bridged dimers. Acidic (HNO3) synthetic conditions generated a series of compounds, including Bi(phenanthroline)2[Au(CN)2](NO3)2.H2O, which contained a short bisumth(III)-gold(I) interaction. The thallium(I) polymer Tl(phenanthroline)[Au(CN)2] shows a parallel alignment of the phenanthroline and Au(CN)2¯ units. This thesis clearly demonstrates that rational design of coordination polymers is a powerful tool.
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Language
English
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