Synthesis, Crystal Structure, and Magnetic Properties of FeP3SiO11: First Example of Iron(III)Silicophosphate

FeP3SiO11 has been prepared by solid state reaction of Fe(PO3)3 and SiO2 at 900°C under vacuum. This compound is isotypic with RuP3SiO11 and the atomic coordinates have been refined by the Rietveld method. The unit cell is trigonal, space group R-3c, with a=8.2896(9) ?, c= 39.054(4) ?, and Z=12. The structure is characterized by isolated FeO6 octahedra connected by bent P2O7 groups (126°) while Si2O7 units only share corners with P2O7 units. Neutron diffraction study shows that FeP3SiO11 is antiferromagnetic with a Néel temperature TN=3.5 K. In this compound, the magnetic interactions arise only from Fe–O–P–O–Fe superexchange mechanism. The magnetic structure is characterized by a stacking of antiferromagnetic (001) layers of double FeO6 octahedra sheets, with the spin perpendicular to the c-axis. The room temperature M?ssbauer spectrum is characteristic of the Fe3+ valence state. The magnetic interactions are discussed.