Magnetic Properties and New Structural Classification of Molybdenum Phosphates Containing Mo(V)

A combined theoretical and experimental study of molybdenum phosphates containing Mo(V) either as purely Mo(V) or as mixed-valent Mo(V)/Mo(VI) and Mo(IV)/Mo(V) is performed. This investigation, based on a structural classification of molybdenum phosphates, derived from that proposed by Costentin et al., allows a detailed discussion of both the valence of the different Mo sites as well as the different coupling mechanisms for the unpaired electron of the Mo(V) octahedra. Either direct Mo−Mo or indirect interaction through the shared oxygen atoms can lead to magnetic moments per Mo(V) lower than expected. It is shown that although the PO 4 tetrahedra do not effectively couple the unpaired electrons of the different Mo(V)O 6 octahedra, they play an important role in determining the magnetic properties of these solids by influencing the internal geometry of the MoO 6 octahedra.