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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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## Abstract

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. Wright, Adrian Colleges (2008 onwards) > College of Engineering & Physical Sciences School of Chemistry QD Chemistry University of Birmingham 4302
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