Oxynitrides

Oxynitrides:

Oxynitrides offer a chance to explore the region between oxides and the more covalent nitrides, and we have been doing this in collaboration with Professor Matt Rosseinsky at the University of Liverpool. Tuning the oxide/nitride ratio allows one to tune the band-gap, bandwidth and hence electronic properties of materials. This has been achieved for the range of materials ZrTiOxNy(1 < x < 2; M3.8+) with fluorite-related structures [3], and has led to the investigation of new oxide/nitride/vacancy ordering schemes possible in fluorite-related oxynitrides such as Zr4O5N2 [4]. Recently, we have synthesised Ba2VO3N [5] - the first oxynitride to contain a MO3Nm- tetrahedral anion for the first row transition metals.



Nitrides:




Because nitrogen is less electronegative than oxygen, nitrides, containing the N3- ion, exhibit a range of structures and properties somewhat different from those of the more familiar oxides. For example, BaSiN2 prepared as single crystals in molten sodium at 900°C or by the low temperature oxidation of the intermetallic BaSi by ammonia [1] crystallises in a new structure type containing a network of edge-sharing SiN4 tetrahedra, which are not found in the analogous silicates. This motif exists in nitridosilicates and not in oxosilicates, because the more polarisable nitride ion can better screen the repulsion between the silicon atoms.



The reaction between intermetallic compounds and ammonia is a rich source of new nitrides. We have recently synthesised [2] the first ternary tin nitride NaSnN, which is also the first example of divalent tin in a nitride.




Oxford Univ Inorganic Chemistry Dept.
http://www.chem.ox.ac.uk/icl/sjclarke/research.html