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

Begum, Yasmin (2013). Synthesis and characterisation of Mn\(^3\)\(^+\) condensed phosphate phases and Fe\(^3\)\(^+\) substituted analogues. University of Birmingham. Ph.D.

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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: Thesis (Doctorates > Ph.D.)
Award Type: Doctorates > Ph.D.
College/Faculty: Colleges (2008 onwards) > College of Engineering & Physical Sciences
School or Department: School of Chemistry
Funders: None/not applicable
Subjects: Q Science > QD Chemistry


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