  At room-temperature NaV2O5 was found to have the centrosymmetric space group
Pmmn. This space group implies the presence of only one kind of V site in
contrast with previous reports of the non-centrosymmetric counterpart P21mn.
This indicates a non-integer valence state of vanadium.
  Furthermore, this symmetry has consequences for the interpretation of the
transition at 34 K, which was ascribed to a spin-Peierls transition of one
dimensional chains of V4+.
