New Dihydrogenhypodiphosphates of Alkaline‐Earth Metals: Preparation, Crystal Structure, Vibrational Spectrum and Thermal Behavior of AE[H 2 P 2 O 6 ] ⋅ n H 2 O (AE=Ca, Sr and n=1.5, 2)

Abstract Two new alkaline‐earth metal dihydrogenhypodiphosphates, AE[H 2 P 2 O 6 ] ⋅ n H 2 O (AE=Ca, Sr and n=1.5, 2) have been prepared and structurally characterized by single crystal X‐ray diffraction. Calciumdihydrogenhypodiphosphate sesquihydrate, Ca[H 2 P 2 O 6 ] ⋅ 1.5 H 2 O ( 1 ) (lattice parameters: a =6.619(1) Å, b =10.201(1) Å, c =20.922(2) Å, β =107.95(1)°, V EZ =1343.9(2) Å 3 , Z =4), crystallizes in the monoclinic space group P 2 1 /c and strontiumdihydrogenhypodiphosphate dihydrate, Sr[H 2 P 2 O 6 ] ⋅ 2 H 2 O ( 2 ) (lattice parameters: a =7.548(1) Å, b =11.906(1) Å, c =7.880(1) Å, V EZ =708.2(2) Å 3 , Z =4), in the orthorhombic space group Pbcn . The crystal structure of compound 1 consists of chains of edge‐ and face‐sharing of [CaO 6 ] and [CaO 8 ] polyhedra linked by dihydrogenhypodiphosphate(IV) anions to form a three‐dimensional network. The structure of 2 consists of alternating layers of chains of edge ‐ sharing [SrO 8 ] polyhedra and respective anionic units. The different water‐content compositions result from the corresponding alkaline‐earth metal coordination polyedra and by the preferred number of water molecules in their coordination sphere, respectively. The IR/Raman spectra of the title compounds have been recorded and interpreted, especially with respect to the [H 2 P 2 O 6 ] 2− group. The phase purity of 2 was verified by powder diffraction measurements.