Two polymorphic forms of a mixed zinc/copper biquinoline dihydrogenphosphate

Two polymorphic forms of a mixed zinc/copper biquinoline dihydrogenphosphate are presented, showing almost identical monomeric units, viz. (2,2′‐biquinoline‐κ²N,N′)bis(dihydrogenphosphato‐κO)copper(II)/zinc(II), formulated as Zn_xCu_1−x(H₂PO₄)₂(C₁₈H₁₂N₂)], with x = 0.88 (1) and 0.90 (2). The cation is tetrahedrally coordinated to a chelating biquinoline system and two diprotonated phosphate anions. The structures differ mainly in their intermolecular hydrogen‐bonding interactions, leading to different packing schemes. No significant evidence of stress due to the Zn/Cu solid solution formation was detected.