Synthesis and Structural Properties of Three New Iron Phosphates Rb3M3Fe5(PO4)8 (M = Mn, Co, Ni)

Abstract

The preparation and structural characterization of three new iron phosphates with general formula Rb3M3Fe5(PO4)8 (M = Mn, Co, Ni) labeled: I, II and III respectively, are reported. Single crystals X-ray diffraction reveals that these compounds crystallize in an original structure, which adopts the monoclinic system with space group C2/c. The unit cell parameters are: a = 19.945(1) A; b = 14.935(7); c = 9.995(1) A; β = 119.10(3)° for I, a = 19.826(1) A; b = 14.948(1); c = 9.927(1) A; β = 117.14(1) ° for II and for III a = 19.792(2) A; b = 14.833(2); c = 9.908(2) A; β = 119.28(2)°. The structures consist of MO6 and (M,Fe)O6 octahedra, linked through common edges to form [M2(M,Fe)2O16]∞ crossing chains running along the [1 1 2] and [1 − 1 2] directions. These chains are interconnected by the FeO6 octahedra and PO4 tetrahedra, generating a 3D framework with intersecting tunnels where the Rb+ cations are located. This paper report the synthesis and the structural study of three new alkali iron phosphates Rb3M3Fe5(PO4)8 (M = Mn, Co, Ni). A projection of the Rb3M3Fe5(PO4)8 (M = Mn, Co, Ni) structure along the [112] direction.