Crystal structure and vibrational properties of KMg4(PO4)3

Single crystals of potassium magnesium phosphate KMg4(PO4)3 have been obtained from flux and characterized by means of single-crystal X-ray diffraction method and IR and Raman spectroscopy. This compound crystallizes in the Pnnm space group with a=16.361(3), b=9.562(19), c=6.171(12)Å and Z=4. The structure is built up of PO4 tetrahedra, MgO6 octahedra and MgO5 polyhedra connected via POMg bridges to form a three-dimensional framework enclosing tunnels along b-axis occupied by K+ ions. IR and Raman spectra are consistent with the crystal structure. The internal and external modes are observed in the 350-1210 cm−1 range and below 330 cm−1, respectively.