Th₄(PO₄)₄P₂O₇, a New Thorium Phosphate:  Synthesis, Characterization, and Structure Determination

Abstract

The chemistry of thorium phosphate reported in the literature has been found to be erroneous. It was reconsidered in terms of careful chemical preparations and specific analytical methods. Special attention has been paid to the atom ratio value referred to r = thorium/phosphorus, which was experimentally fixed in order to obtain the correct composition of the final compound. A new compound with the chemical formula Th4(PO4)4P2O7, derived from the crystal structure determination, has been obtained. The unit cell parameters were obtained from powder and single-crystal X-ray diffraction data. It is orthorhombic (space group Pcam, Z = 2) with the cell dimensions a = 12.8646(9) Å, b = 10.4374(8) Å, c = 7.0676(5) Å, and V = 949.00(9) Å3. The atomic positions were derived from Patterson and Fourier methods and the structure was refined to an R value of 0.039. The structure consists of layers parallel to (010) containing both PO4 and P2O7 groups. These layers alternate with planes of Th atoms. The coordination sphere of the two independent heavy atoms is formed by eight O atoms from five PO4 and one P2O7 groups. The formula of thorium phosphate Th4(PO4)4P2O7 is in good agreement with the elementary composition derived from electron microprobe analysis, which gave a ratio r = 2/3. Any other value of r (1/2 < r < 3/4) induces the formation of polyphase systems: Th4P6O23 and ThO2 for r > 2/3; Th4P6O23 and ThP2O7 for r < 2/3. The characterization of thorium phosphate diphosphate by means of infrared spectroscopy confirmed the presence of diphosphate groups in the compound.

Sorption of Eu(III) on Th4(PO4)4P2O7: effects of pH, complexing anions and fulvic acid

“…The signature of P 2 O 7 groups is not generally so intense and two bands at 950 and 750 cm -1 can be assigned to the P-O-P bridge. The obtained IR spectrum was identical to that in the literature [1].…”

“…Monazites are rich in rare earth elements, actinides and phosphates. The phosphate matrices show potential for use in radwaste storage because of their resistance to radiation effects and low solubility compared with glass matrices [1][2][3]. The chemical behavior of uranium and thorium in monazite and the use of uranium and thorium phosphates as storage materials have been investigated [4][5][6][7][8].…”

Structural Environment of Uranium (VI) and Europium (III) Species Sorbed onto Phosphate Surfaces: XPS and Optical Spectroscopy Studies

“…The protocol for synthesizing the three phosphate compounds has been previously described in the literature (42)(43) 3 or NaClO 4 (0.5 M) adjusted at the desired pH.…”

Hydrothermal Synthesis and Characterization of the Thorium Phosphate Hydrogenphosphate, Thorium Hydroxide Phosphate, and Dithorium Oxide Phosphate

“…The indexation of the peaks observed, as well as the XRD data of the DTOP, are reported in Table 5. The unit cell of the DTOP can be de"ned as orthorhombic by comparison with the DUOP (symmetry group Cmca), with the following calculated parameters: a"7.177 (4), b"9.225 (5), and …”