Investigating polyoxometalate self-assembly: from structural building units towards novel molecules and framework materials

Mitchell, Scott George (2010) Investigating polyoxometalate self-assembly: from structural building units towards novel molecules and framework materials. PhD thesis, University of Glasgow.

Abstract

This thesis focuses on the reactivity of polyoxometalate (POM) building blocks; more specifically, those derived from the Keggin {M12} and Wells-Dawson {M18} structural motifs. Lacunary Keggin and Wells-Dawson cages, i.e. those containing metal-atom site vacancies, are highly reactive and versatile fragments that can be employed as structural building units (SBUs) towards the design of novel high nuclearity compounds as well as the assembly of infinite supramolecular framework materials.

The isolation of a selection of ‘intermediate’ species from simple one-pot procedures has been made possible though the use of the water soluble tertiary amine N,N’-bis(2-hydroxyethyl)piperazine (bhep) as a pH buffer. These ‘intermediate’ Keggin-based POM fragments represent monomeric units of previously-reported transition metal-substituted polyoxometalate (TMSP) motifs. This multifunctional amine can be used either as a pH buffer or as a protonated counter cation and consequently plays a key role in the polyanion self-assembly process, often leading to the synthesis of novel POM fragments.

The cyclic, tetrameric [H7P8W48O184]33- polyanion, {P8W48}, retains its structural integrity in solution and its diverse coordination chemistry has been utilized to obtain a series of infinite framework materials. This particular polyanion contains a 1 nm integrated ‘pore’ (essentially an ‘aperture synthon’ SBU), and a range of extended framework architectures have been self-assembled from this component part. The net effect shows forcefully the value and validity of this fragment in the design of robust electrochemically switchable open framework materials, reminiscent of Metal Organic Frameworks (MOFs).

A new family consisting of triple Wells-Dawson assemblies of general formula [(P2W16M2O60)3]24-/30- (where M = Co, Fe, and Ni) has been synthesized. Three lacunary alpha isomers of the {P2W18} Wells-Dawson motif arrange around a central coordination pocket trapping six transition metal centres ({P2W16M2}3) and encapsulating alkali metal cations in the centre of this cavity.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Due to copyright restrictions the full text of this thesis cannot be made available online. Access to the printed version is available once any embargo periods have expired.
• Keywords: Polyoxometalates, self-Assembly, framework materials, catalysis, structural building units
• Subjects: Q Science > QD Chemistry
• Colleges/Schools: College of Science and Engineering > School of Chemistry
• Supervisor's Name: Cronin, Prof. Leroy
• Date of Award: 2010
• Depositing User: Mr Scott G. Mitchell
• Unique ID: glathesis:2010-1834
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 21 May 2010
• Last Modified: 17 Apr 2014 08:56
• URI: https://theses.gla.ac.uk/id/eprint/1834