Structure Refinement and Magnetic Properties of C–Fe(PO3)3 Studied by Neutron Diffraction and M?ssbauer Techniques

C–Fe(PO3)3 has been synthesized using H3PO4 and Fe(NO3)3·9H2O as starting compounds. Single crystals were grown under vacuum with a trace of FeCl2. Fe(PO3)3 crystallizes in the monoclinic space group Cc, with a=13.148(4) ?, b=19.076 (2) ?, c=9.410(3) ?, beta=127.00(2)°, and Z=12. Its structure has been determined through direct methods and difference Fourier synthesis and has been refined to R=0.0405 (RW=0.047). Fe(PO3)3 belongs to a series of isotypic M(PO3)3 trimetaphosphates (M=Al, V, Sc, In, Ti, Mo, Rh, Cr) which are characterized by a tridimensional network of isolated MO6 octahedra connected through PO4 tetrahedra. Fe(PO3)3 is antiferromagnetic below TN=10 K. The magnetic structure has been determinated by means of powder neutron diffraction: each iron atom is linked to six iron nearest neighbors of opposite spin, through six single Fe–O–P–O–Fe superexchange pathways. The moment direction lies in the (010) plane, making an angle of ~32° with the a axis (mu ~4.4 mu B). M?ssbauer spectra are fitted with two doublets and three sextuplets in the paramagnetic and the antiferromagnetic states, respectively. Their rather high isomer shifts are explained by the inductive effect.