JOURNAL OF RARE EARTHS, Vol. 27, No. 1, Feb. 2009, p. 1 Foundation item: Project supported by the Ministry of Higher Education, Scientific Research and Technology of Tunisia Corresponding author: K. Horchani-Naifer (E-mail: karima_horchani@yahoo.com; Tel.: +216-71430470) DOI: 10.1016/S1002-0721(08)60179-9 Synthesis and crystal structure of sodium praseodymium polyphosphate, NaPr(PO 3 ) 4 K. Horchani-Naifer, J. Amami, M. Férid (Research Unit of Rare Earth Materials, National Research Center in Sciences of Materials, B. P. 95 Hammam-Lif, 2050, Tunisia) Received 27 January 2008; revised 4 September 2008 Abstract: Reaction of Na 2 CO 3 , Pr 6 O 11 and H 3 PO 4 gave the sodium praseodymium polyphosphate NaPr(PO 3 ) 4 . The title compound crystal- lized in the monoclinic P2 1 /n space group with a=0.9965(4) nm, b=1.31437(4) nm, c=0.72271(3) nm, β=90.429(3)°, V=0.9465(4) nm 3 , Z=4, R=0.0493 and wR=0.1266 for 1855 independent reflections. The structure of NaPr(PO 3 ) 4 consisted of PrO 8 polyhedra sharing oxygen atoms with phosphoric group PO 4 to form a three-dimensional framework, delimiting intersecting tunnels in which the sodium ion was located. Each Na + ion was bonded to seven oxygen atoms. Keywords: polyphosphate; praseodymium; crystal structure; infrared spectroscopy; rare earths Recently, widespread attention has been given to double condensed phosphates of rare earths and alkali metals, which are promising materials for quantum electronics and magnetic properties related to their chain structure. Good laser properties are also observed in the case of the trivalent praseodymium (Pr 3+ ) materials, which showed that the phosphates are excellent fluorescent hosts [1–5] and good fast scintillating materials [6,7] . The common chemical features of these polyphosphates indicate that they are relatively stable under normal conditions of temperature and humidity. Many polyphosphates of rare earth and sodium have been reported in the literature i.e. NaLn(PO 3 ) 4 (Ln=Pr [8] , Nd [9] , Ce [10] ). These phosphates are obtained by flux method or by study of the phase-equilibrium diagrams of the M I PO 3 -Ln(PO 3 ) 3 systems (M I =alkali metal; Ln=rare earth element). The bi- nary system NaPO 3 -Pr(PO 3 ) 3 are studied [8] but crystallo- graphic data have not been given. This work enters within the framework of a systematic investigation of the crystal structures and luminescent prop- erties of the double polyphosphate of the type M I Ln(PO 3 ) 4 . This paper deals with the synthesis and single crystal struc- ture of NaPr(PO 3 ) 4 by X-ray diffraction. The titled com- pound has been characterized by IR spectroscopy. 1 Experimental, results and discussion 1.1 Synthesis At room temperature, 5 g of Na 2 CO 3 and 0.4 g of Pr 6 O 11 were slowly added to 12 ml of phosphoric acid H 3 PO 4 (85%). The mixture was then slowly heated to 573 K and kept at this temperature for 7 d. Green crystals of title NaPr(PO 3 ) 4 were separated from the excess phosphoric acid by washing the product in boiling water. This title com- pound is stable in air. 1.2 Structure determination Diffraction data were collected at room temperature (293(2) K) on a Enraf Nonius CAD4 four-circle diffracto- meter with graphite monochromatized Mo Kα (0.071073 nm) radiation. 3668 reflections were measured for 2162 in- dependent reflections and 164 parameters. The structure resolution was performed with the WinGX program [11] . The positions of the praseodymium atoms were obtained using the Patterson heavy atom method [12] and successive Fourier analysis [13] allowed the other atoms to be located. The final R=0.0493, wR=0.1266 and S=1.092. 1.3 Structure of NaPr(PO 3 ) 4 As shown in Fig.1, neighboring PO 4 tetrahedra are con- nected by bridging oxygen atom to form a chain along the c axis. These chains are joined to each other by PrO 8 dodeca- hedra, resulting in a three dimensional net structure (Figs.2, 3). The sodium ions are located at the holes of the 3D net structure along the b direction (Fig.2). Each Na + ion is coor- dinated by seven oxygen atoms. The main interatomic distances and bond angles in the four independent tetrahedral PO 4 are given in Table 1. In