Single crystal X-ray structural investigation of alluaudite related monophosphate Na2FeMn2(PO4)3

The compound Na 2FeMn 2(PO 4) 3 has been successfully isolated with the alluaudite structural type. Accurate single crystal x-ray diffraction has allowed solving the structure with reliability factors of R 1 and Rw equal to 0.0322 and 0.0790 respectively. It was found that the symmetry is monoclinic with a space group of C2/c and lattice parameters: a = 12.180(2) Å, b = 12.660(2) Å, c = 6.500(2) Å, ? = 114.528(3)(°), unit cell volume = 911.8(3) Å 3, Z = 8 and d cal. = 3.618 g.cm -3. Three-dimensional network is formed by the [MnO 6] octahedra linked in pairs to form Mn-based octahedral dimers: ([Mn 2O 10]). Each dimer shares six vertices with six tetrahedra [P(2)O 4] to form sheets within the plane (100). The latter are connected by tetrahedra [P(1)O 4] delimiting cages and tunnels which house either Fe 3+ or Na + cations. Each [FeO 6] octahedron is linked to two [Mn 2O 10] dimers belonging to two adjacent sheets to form mixed Fe-Mn chains of the type: - Fe 3+ - Mn 2+ - Mn 2+ - Fe 3+ - Mn 2+ - Mn 2+ - Fe 3+-..., running along the direction [101].