The room-temperature V NMR spectra for the more highly V-substituted monoclinic sample, Bi 0.852 V 0.148 O 1.648 , shown in Figure (right), reveal three major distinct features with isotropic shifts at -487, -493 and -508 ppm, with broad spinning sideband manifolds arising from the corresponding satellite transitions or STs ( 51 V is a quadrupolar nucleus with I = 7/2). Roomtemperature V NMR spectra taken at higher spinning speed (10 kHz) more easily allow the three distinct environments to be observed (shown in the SI), but unfortunately we could not acquire VT-NMR spectra at very high temperatures at this relatively fast MAS rate. The relatively small difference in chemical shift of these V environments is most likely due to small differences in the Figure : Variable-temperature V NMR spectra of Bi 0.913 V 0.087 O With increasing temperature, the V spinning sideband manifolds of Bi 0.852 V 0.148 O 1.648 first broaden, before reappearing and narrowing up to 823 K. We assign these characteristic changes to increasing rates of ionic motion on the order of the MAS rate (i.e., ∼4 kHz), as seen in similar studies. In particular, the relevant time scale for this process is influenced by the strengths of anisotropic spin interactions that give rise to the sidebands, primarily quadrupolar coupling for V but to a lesser extent chemical shift anisotropy (CSA). The three features remain distinct, with a gradual change to higher frequencies of -456, -472 and -505 ppm, at 673 K. The large change in the shift of the first site in particular is consistent with an increase in coordination number consistent with the formation of VO 5 , while the latter two sites remain closer to 4-coordinate.