Structural and Magnetic Investigations of the Novel Pyrophosphate Na7Ni3Fe(P2O7)(4)

A novel pyrophosphate Na7Ni3Fe(P2O7)(4) was synthesized in two distinct forms, singlecrystal and powder. Single-crystal X-ray diffraction was used to determine the crystal structure, and powder X-ray diffraction and scanning electron microscopy were used to examine the purity and morphology of the elaborated powder. This phosphate crystallizes in the P1 space group of the triclinic system with a = 6.3677 (2) angstrom, b = 9.3316 (4) angstrom, c = 10.8478 (4) angstrom, alpha= 65.191 (1)degrees, beta = 80.533 (1)degrees and gamma = 73.042 (1)degrees. The crystal framework is assembled from the linkage of centrosymmetrical clusters Ni-2(Ni/Fe)(2)P4O28. Each cluster consists of two (Fe-1/Ni-1)O-6 octahedra, two Ni2O6 octahedra and two P2O7 units. The linkage of these clusters is provided by two other P2O7 units to generate a three-dimensional structure with distinct tunnels in the [100], [010] and [001] directions, housing the Na+ cations. The infrared and Raman analyses show the characteristic bands of the pyrophosphate anion P2O7 (4-). Remarkably, the magnetic investigations revealed the coexistence of two magnetic transitions at similar to 29 K and similar to 4.5 K with dominating antiferromagnetic interactions.