Synthesis and characterisation of new framework materials

Abstract

Inorganic framework materials, with structures based on arsenate and phosphate, AsO4
and PO4, tetrahedra and a variety of octahedral metal units, such as hafnium, niobium
and iron, have been synthesised and fully characterised. These materials have been
synthesised by solvothermal techniques and the principal analytical technique to
characterise the resulting single crystals has been Single Crystal X-ray Diffraction.
Supporting analysis was carried out, using techniques such as Powder and Neutron
Diffraction, Thermogravimetric Analysis, Electron Dispersive Spectroscopy and
Infrared Spectroscopy.

Of the hafnium arsenates and phosphates that have been synthesised, several are
fluorinated and one is templated, such as Hf2F2(H(PO4)2)(NH4)2 and
[Hf2F8(AsO4)][DABCO-H2](NH4) respectively. Similar layered frameworks have also
been characterised and reported for titanium, zirconium and niobium. These structures
all offer ion exchange potential, due to their ammonium cations and/or water molecules.

The hydrogen iron phosphates that are discussed include two novel frameworks and
one material which offers an improved model for the mineral lipscombite,
Fe1.34(PO4)OH0.96. One of the new frameworks presented, (NH4)3Fe3(HPO4)6, offers
particularly interesting potential applications as a high capacity battery material via
lithium exchange reactions.

The hydrothermal synthesis of two novel hydrated sodium tungstate structures is also
discussed. One of these materials was found to contain a very high H : Na ratio,
resulting in strong hydrogen bonding and a densely packed framework, which may be of
interest in the field of high density liquids.

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