Synthesis and characterization of molybdenum and vanadium framework materials

Abstract

Molybdenum and vanadium inorganic framework materials, with structures based on phosphate and arsenate tetrahedra have been synthesised by hydrothermal techniques and characterised by single crystal X-ray diffraction; additional techniques including thermogravimetric analysis, electron dispersive spectroscopy and infrared spectroscopy were carried out to fully characterise these materials. Of the molybdenum phosphates that have been synthesised, a new layer structure type has been identified. This exhibits perpendicular channels through the molybdenophosphate sheets wherein multiple guest ions, ammonium cations and free orthophosphate (PO4)3- or halide (Cl-, Br-), are hosted. Anion exchange investigations were performed, showing the affinity of the Br- analogue to be completely exchange with Cl- anions. Hydrothermal syntheses with a variety of organic amines resulted in the formation of four compounds. These include three distinct cluster polyanions in addition to a ribbon structure type. The effect of fluoride ions into the synthesis of molybdenum phosphates has been investigated; this approach has led to the discovery of a new oxyfluorinated molybdenum phosphate compound templated by piperazine. Further studies were concentrated on the preparation of molybdenum phosphonate compounds. An amine template bipyridine. During investigations of the role of fluoride ions in the formation of vanadium phosphate and arsenate frameworks, four amine templated compounds have been synthesised and fully characterised. Three of these materials presented, exhibit similar but rather distinct framework topologies including two new layered structure types, which comprise flat or super-corrugated vanadoarsenate layers, and onedimensional tubular structure. Reactions were also performed using inorganic templates, and a number of new structure types were produced with ammonium, rubidium, barium and caesium. The series of materials includes two-dimensional layer structures, and two main structural topologies have been generally observed. During investigations into vanadium borate and phosphate compounds, a threedimensional vanadium phosphate was discovered. Further studies on previously reported vanadium polyborate compounds have led to the isolation of the series of the analogous alkali metal templated structures

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