Three Crystal Structures, One Chemical Formula – Barium Dihydrogen‐hypodiphosphate(IV)‐dihydrate, BaH 2 P 2 O 6 ·2H 2 O

Three polymorphs of barium dihydrogen‐hypodiphosphate(IV)‐dihydrate, BaH 2 P 2 O 6 · 2H 2 O ( A , B and C ), were obtained and structurally characterized by single‐crystal X‐ray diffraction. A crystallizes in the monoclinic space group P 2 1 / n (no. 14) with a = 7.459(1) Å, b = 8.066(1) Å, c = 12.460(2) Å, β = 91.27(1) ° and Z = 4. B crystallizes in the monoclinic space group C 2/ c (no. 15) with a = 11.049(8) Å, b = 6.486(3) Å, c = 10.956(6) Å, β = 106.89(5) ° and Z = 4. C crystallizes in the orthorhombic space group C 222 1 (no. 20) with a = 9.193(3) Å, b = 6.199(2) Å, c = 12.888(4) Å and Z = 4. Discrete [H 2 P 2 O 6 ] 2– units, barium cations and water molecules, held together by intermolecular hydrogen bonds of the type O–H ··· O, build up the structures of the three polymorphs. The phase purity of A and C was verified by powder diffraction measurements.