Molybdenum Oxide Nitrides of the Mo₂(O,N,□)₅ Type: On the Way to Mo₂O₅

Blue-colored molybdenum oxide nitrides of the Mo₂(O,N,□)₅ type were synthesized by direct nitridation of commercially available molybdenum trioxide with a mixture of gaseous ammonia and oxygen. Chemical composition, crystal structure, and stability of the obtained and hitherto unknown compounds are studied extensively. The average oxidation state of +5 for molybdenum is proven by Mo K near-edge X-ray absorption spectroscopy; the magnetic behavior is in agreement with compounds exhibiting Mo^VO₆ units. The new materials are stable up to ∼773 K in an inert gas atmosphere. At higher temperatures, decomposition is observed. X-ray and neutron powder diffraction, electron diffraction, and high-resolution transmission electron microscopy reveal the structure to be related to VNb₉O_24.9-type phases, however, with severe disorder hampering full structure determination. Still, the results demonstrate the possibility of a future synthesis of the potential binary oxide Mo₂O₅. On the basis of these findings, a tentative suggestion on the crystal structure of the potential compound Mo₂O₅, backed by electronic-structure and phonon calculations from first principles, is given.