Synthesis and structure of a new family of 3d-4f heterometallic compounds Rb ₇LnFe ₆O ₂(PO ₄) ₈ (Ln=Sm, Eu, Gd, Dy): Magnetic properties of the Sm-, Gd-, Dy-derivatives

A new family of mixed lanthanide(III) and iron(III) oxo-phosphate phases, Rb ₇LnFe ₆O ₂(PO ₄) ₈ (Ln=Sm 1, Eu 2, Gd 3, Dy 4), was isolated by using a high-temperature, solid-state method in molten-salt media. The X-ray single-crystal structure analysis shows that these isomorphic derivatives crystallize in a triclinic space group P-1 (no. 2); Z=1. The 3-D framework of these 3d-4f oxo-phosphates are comprised of LnO ₆ octahedral, FeO ₅ trigonal bipyramidal (tbp), and μ ₃-oxo [Fe ₄O ₁₈] tetrameric units interconnected through PO ₄ tetrahedra. The preliminary results of the temperature-dependent magnetic susceptibility measurements for selected compounds (1, 3, 4) reveal antiferromagnetic-like behavior. 1 shows a weak antiferromagnetric ordering at T _N=∼7 K while others show little evidence of long-range magnetic order down to 2 K. All three compounds have measured magnetic moments significantly smaller than the expected values.