Prediction of magnetic properties in oxovanadium(IV) phosphates:: The role of the bridging PO4 anions

Oxovanadium phosphates constitute a crystallochemically very rich family that, in turn, results in a seemingly intricate magnetochemistry including from isolated dimers to 3-D systems. This magnetic diversity is due, in part, to the possible participation of phosphate groups in the spin transfer between VN centers. This way, P-31 solid-state NMR becomes a key tool in determining the exchange paths involving phosphorus orbitals. The magnetic behavior of several layered oxovanadium phosphates M(VOPO4)(2). 4H(2)0 (M = Na+, Ca2+, Ba2+, and Pb2+) has been investigated. Like it occurs in the case of other previously studied lamellar derivatives, the best fit of the temperature-dependent magnetic susceptibility data is obtained for a 2-D model. This is consistent with chairlike V(OPO)(2)V exchange pathways (i.e., through di-mu-(O,O')phosphate bridges). Both these results and those previously available for other oxovanadium phosphates can be nicely correlated with the structural data focusing the attention on the topological features concerning the environment of the phosphate bridging entities, a result that is consistently rationalized on the basis of extended Huckel calculations, The reliability of our approach is supported not only by its ability to interpret the diversity of experimental magnetic behavior but also by its predictive character concerning the approximate magnitude of the superexchange interactions in other related derivatives.