Crystal structure of KNaCuP₂O₇, a new member of the diphosphate family

Potassium sodium copper(II) diphosphate(V), KNaCuP₂O₇, was synthesized by solid-state reactions. It crystallizes in the α-Na₂CuP₂O₇ structure type in space group P2₁/n. In the crystal, CuO₅ square-pyramids are linked to nearly eclipsed P₂O₇ groups by sharing corners to build up corrugated layers with composition [CuP₂O₇]^2- that extend parallel to (010). The K⁺ and Na⁺ cations reside in the inter-layer space and are connected to nine and seven O atoms, respectively. The structural model was validated by bond-valence-sum (BVS) and charge-distribution (CHARDI) analysis.