Synthesis, crystal structure, and vibrational study of K2Cu(HPO4)2·6H2O: A new metal hydrogenphosphate compound

• X-ray diffraction and vibrational study of a new metal phosphate compound K2Cu(HPO4)2·6H2O.
• The X-ray analysis is completed by infrared and polarized Raman measurements.
• The K2Cu(HPO4)2·6H2O is the first compound of the A2M(H2O)6(XO4)2 family, where the group (XO4)2− = H(PO4)2−.

The study reports on the synthesis, single-crystal X-ray structure, and infrared and polarized Raman spectra of a new metal phosphate. The chemical formula of the compound K2Cu(HPO4)2·6H2O resembled that of Tutton salts. The compound crystallized in the monoclinic system, space group P21/c, with a = 6.166(9), b = 12.118(19), c = 9.077(14) Å, β = 104.33(2), and Z = 2. The compound consisted of transition metal cations octahedrally coordinated by six water molecules, [Cu(H2O)6]2+, HPO4 pseudo-tetrahedra, and KO8 polyhedra. The KO8 polyhedra shared two edges with two HPO4 groups, two corners with the two other HPO4 groups, and two corners with Cu(H2O)6. The connection between [Cu(H2O)6]2+ octahedral and (HPO4)2− pseudo-tetrahedra was reinforced by hydrogen bonds formed between the water molecules and other oxygen atoms linked to the P atom. These structural results were corroborated by infrared and polarized Raman spectroscopy.

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