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Crystal Engineering of Supramolecular Materials Built of Octahedral Niobium Cyano-chloride Clusters and Metal Complexes

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abstract
Great advances in Supramolecular Chemistry and Crystal Engineering have motivated materials scientists to use functional molecular building units to prepare materials with desired structures and properties. This dissertation focuses on using octahedral niobium cyano-chloride cluster [Nb6Cl12(CN)6]4- and Mn(III) Schiff-base complexes as building units to prepare hybrid inorganic-organic materials ranging from discrete supramolecular assemblies to 1D, 2D, and 3D coordination polymers, and correlating the structures with their observed chemical/physical properties. [Nb6Cl12(CN)6]4- consists of [Nb6Cl12]2+ core in which six Nb atoms are bonded to each other and arranged in an octahedral fashion with each of twelve inner ligands connecting two neighboring Nb atoms. Each Nb atom is axially coordinated by a ditopic ligand CN- through Nb–C bond to give anionic cluster. It has been chosen as building units because of its ease of preparation, large size, stability in air, electrochemical properties, and inexpensive starting materials. [Nb6Cl12(CN)6]4- represents an expanded analogue of hexacyanometallates. The number of electrons available for metal-metal bonding (VEC) is 16, the same as those precursors prepared from high-temperature solid-state reactions. A 3D framework [Me4N]2[MnNb6Cl12(CN)6] containing [Nb6Cl12(CN)6]4- as building unit was firstly obtained from the self-assembly reaction between [Me4N]4[Nb6Cl12(CN)6]•2MeOH and excess MnCl2•2H2O in aqueous solution. The reaction is fast, the structure of the resulting product is difficult to control, and the crystal is hard to grow. To make compounds with low-dimensionalities and desired structures in a more predictable way, I used the “directional-bonding” approach. The term “directional-bonding” was first cited by Stang and coworkers and systematized by coordination chemists to prepare 0D supramolecular assemblies. The fundamental principle is to use coordinatively unsaturated metal complexes with coordination sites available for incoming ligands at appropriate angles to “direct” the formation of desired supramolceular structures. Mn(III) Schiff-base complexes have been chosen as the second building units due to their two coordination , interesting sites available for further linkage at angles c.a 180 magnetic properties, and their potential cooperative catalytic properties. The methodology used in this dissertation to prepare hybrid materials is performed in a stepwise approach: i) the precursor Li2Nb6Cl16 featuring a 2D extended framework is prepared through C. ii) the reaction between Me4NCl and solid-state reaction at c.a. 700 the solution of Li2Nb6Cl16 in EtOH leads to the formation of [Nb6Cl18]3-; iii) the reaction between [Nb6Cl18]3- and KCN affords [Nb6Cl12(CN)6]4- in which all the six apical positions are taken up by CN- . Cation metathesis are carried out to prepare materials with different cations that have different solubility in organic solvents; iv) Reactions between [Nb6Cl12(CN)6]4- and Mn(III) Schiff-base complexes are performed in solutions at room temperature. Systematic investigation has shown a number of factors such as Schiff-base ligands, cations, solvents, and stoichiometries can affect the formation, structures, and chemical/physical properties of the resulting hybrid inorganic-organic supramolecular materials. From the structural point of view, non-covalent forces including coordination bonds, hydrogen bonding, electrostatic and charge-transfer attractions, and aromatic π-π stacking interactions are employed to build extended frameworks with different dimensionalities and topologies depending on the components used and experimental conditions. Most of the materials are robust and stable in air, and decompose only after being heated at temperatures above 200ºC. These results illustrate the use of the concept of “metal complex-directed assembly” to build supramolecular structures and help design and prepare more cluster-based materials with novel structures and properties.
subject
Coordination polymers
Metal cluster
Self-assembly
Supramolecular Chemistry
contributor
Zhou, Huajun (author)
Natalie A. W. Holzwarth (committee chair)
Abdessadek Lachgar (committee member)
Christa L. Colyer (committee member)
Ronald E. Noftle (committee member)
Mark E. Welker (committee member)
creator
Zhou, Huajun
date
2008-09-28T10:55:23Z (accessioned)
2010-06-18T18:59:31Z (accessioned)
null (available)
2008-09-28T10:55:23Z (available)
2010-06-18T18:59:31Z (available)
2006-11-27 (issued)
degree
null (defenseDate)
Chemistry (discipline)
Wake Forest University (grantor)
MD/PHD (level)
identifier
Andrew'sThesis.pdf
http://hdl.handle.net/10339/14861 (uri)
migration
etd-07252007-151905 (oldETDId)
rights
Release the entire work immediately for access worldwide. (accessRights)
I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to Wake Forest University or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. (license)
title
Crystal Engineering of Supramolecular Materials Built of Octahedral Niobium Cyano-chloride Clusters and Metal Complexes

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