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Synthesis and characterisation of Mn\(^3\)\(^+\) condensed phosphate phases and Fe\(^3\)\(^+\) substituted analogues

Begum, Yasmin (2013)
Ph.D. thesis, University of Birmingham.

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This thesis describes the synthesis, properties and structural characterisation of a series of Mn\(_3\)\(_+\) condensed phosphate phases and Fe\(_3\)\(_+\) substituted analogues. To date, the synthesis of such mixed cation compositions has been unexplored, but this work has highlighted that they present an interesting array of properties.

α-NH\(_4\)MnP\(_2\)O\(_7\) was successfully synthesised and structurally characterised. A second polymorph β-NH\(_4\)MnP\(_2\)O\(_7\) was also identified, with both found to be key components of a commerical manganese violet pigment. The α-NH\(_4\)Mn\(_x\)Fe\(_1\)\(_-\)\(_x\)P\(_2\)O\(_7\) solid solution was also characterised, with the introduction of Fe\(_3\)\(_+\) resulting in a distinct colour change, an improvement in thermal stability and a change in the magnetic properties of these materials. Similar changes were seen in the RbMn\(_x\)Fe\(_1\)\(_-\)\(_x\)P\(_2\)O\(_7\) system but a marked improvement in thermal stability, with an unusual decomposition mechanism involving manganese expulsion observed for the intermediate members. Analogous studies were performed on compounds of composition RbMn\(_x\)Fe\(_1\)\(_-\)\(_x\)HP\(_3\)O\(_1\)\(_0\), Mn\(_x\)Fe\(_1\)\(_-\)\(_x\)H\(_2\)P\(_3\)O\(_1\)\(_0\) (x ≤ 0.5), Mn\(_x\)Fe\(_1\)\(_-\)\(_x\)P\(_3\)O\(9\) (0 ≤ x ≤ 0.4 and 0.75 ≤ x ≤ 1) and β-HMnP\(_2\)O\(_7\).

All phases showed interesting colourations which has been
attributed to the Jahn-Teller active Mn\(_3\)\(_+\) being able to exhibit a “plastic” coordination sphere. The magnetic structures of a number of compounds have also been solved in order to supplement the existing literature on condensed phosphate systems.

The layered compound MnH\(_2\)P\(_3\)O\(_1\)\(_0\)·2H\(_2\)O was also investigated and found to readily undergo monoamine intercalation. Attempts to incorporate additional transition metal ions into the interlayer region of this compound proved inconclusive.

Type of Work:Ph.D. thesis.
Supervisor(s):Wright, Adrian
School/Faculty:Colleges (2008 onwards) > College of Engineering & Physical Sciences
Department:School of Chemistry
Subjects:QD Chemistry
Institution:University of Birmingham
ID Code:4302
This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder.
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