Double-bond character of phosphates in the solid and liquid phases was investigated using the P=O π* peaks in O K-edge XAS. The double-bond character of phosphates is enhanced as the negative charge increases in the solid phase, where NaH2PO4 shows weak P=O π* peaks and Na3PO4 shows prominent P=O π* peaks. The double-bond character of Na3PO4 aqueous solution is reduced owing to the interactions of Na+ ions and the formation of hydration structures. The double-bond character of phosphates is changed by chemical environments and is related to the reactivity of various biological phenomena.
