Single Crystal X-Ray Structural Investigation of Alluaudite Related Monophosphate Na2FeMn2(PO4)3
<p>The compound Na<sub>2</sub>FeMn<sub>2</sub>(PO<sub>4</sub>)<sub>3</sub> 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<sub>1</sub> 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, b = 114.528(3)(°), unit cell volume = 911.8(3) Å<sup>3</sup>, Z = 8 and d<sub>cal.</sub>=3.618 g.cm<sup>-3</sup>. Three-dimensional network is formed by the [MnO<sub>6</sub>] octahedra linked in pairs to form Mn-based octahedral dimers: ([Mn<sub>2</sub>O<sub>10</sub>]). Each dimer shares six vertices with six tetrahedra [P(2)O<sub>4</sub>] to form sheets within the plane (100). The latter are connected by tetrahedra [P(1)O<sub>4</sub>] delimiting cages and tunnels which house either Fe<sup>3+</sup> or Na<sup>+</sup> cations. Each [FeO<sub>6</sub>] octahedron is linked to two [Mn<sub>2</sub>O<sub>10</sub>] dimers belonging to two adjacent sheets to form mixed Fe-Mn chains of the type: - Fe<sup>3+</sup> - Mn<sup>2+</sup> - Mn<sup>2+</sup> - Fe<sup>3+</sup> - Mn<sup>2+</sup> - Mn<sup>2+</sup> - Fe<sup>3+</sup> - ..., running along the direction [101].<strong></strong></p>