Synthesis and Structural Study of a Novel Mixed Phosphate: Cd0.5Zn2.5(PO4)2.4H2O

Single crystals of the new phosphate Cd 0.5 Zn 2.5 (PO 4 ) 2 .4H 2 O were successfully grown hydrothermally and structurally determined by single crystal X-ray diffraction data. This new phase is isotypic with the Hopeite and crystallizes in the orthorhombic space group Pnma with the cell parameters a = 10.6592(9) Å, b = 18.408(2) Å and c = 5.0565(4) Å. This crystal structure contains seven independent fully occupied cationic sites. The first six, that is located in 4c (.m.) Wycokoff positions, accommodate Cd(1)/Zn(1), four sites are filled by Zn(2) and three hydrogen, while the remaining site is entirely occupied by one P atom. This crystal structure can be described in terms of a net framework built up from a slightly distorted (Cd(1)/Zn(1))O 2 (OH 2 ) 4 octahedra and regular Zn(2)O 4 /PO 4 tetrahe-dra units. In the structure, two Zn 2 (2)O 7 dimers are held together by means of PO 4 groups in such way to form zigzag chains of corner-sharing. Adjacent chains are connected with the apical corners resulting in a complex layer of three-and four-membered sequential rings extending along [001]. The stacked layers are bridged by (Cd(1)/Zn(1))O 2 (OH 2 ) 4 octahedra that stabilizes the structure