Flux Growth of Vanadyl Pyrophosphate, (VO)2P2O7, and Spin Dimer Analysis of the Spin Exchange Interactions of (VO)2P2O7 and Vanadyl Hydrogen Phosphate, VO(HPO4)·0.5H2O

Large transparent blue crystals of vanadyl pyrophosphate, (VO)2P2O7, were grown from a phosphorus pentoxide flux, and the single-crystal X-ray structure of (VO)2P2O7 was determined with high precision. On the basis of spin dimer analysis, we examined the spin exchange interactions of (VO)2P2O7 and its precursor VO(HPO4)·0.5H2O. Our analysis of (VO)2P2O7 using two high-precision crystal structures shows unambiguously that the V3−V4 chain has a larger spin gap than does the V1−V2 chain and that the super-superexchange (V−O···O−V) interaction is stronger than the superexchange (V−O−V) interaction in the V3−V4 chain while the opposite is true in the V1−V2 chain. Our analysis of VO(HPO4)·0.5H2O reveals that the superexchange interaction must dominate over the super-superexchange interaction, in disagreement with the conclusion from a powder neutron scattering study of VO(DPO4)·0.5D2O.