Heterometallic 3d–4f {Co2Gd4} phosphonates: new members of the potential magnetic cooler family

Abstract

Three new heterometallic phosphonate complexes with a novel 3d–4f metal core {Co₂Gd₄} were isolated. The reactions between CoCl₂, GdCl₃, ligand sodium salts, and 2,2′-bipyridine in methanol solution lead to new unexpected 3d–4f heterometallic complexes, [Na₂Co^III₂Gd₄(L)₆(bpy)₂(OR)₂]·nSolv (L = SAA³⁻ (1), BSAA³⁻ (2), and NAA³⁻ (3); bpy = 2,2′-bipyridine; OR = OH and OMe; Solv = H₂O and MeOH), composed of a rare case of two magnetically independent oxygen bridged Gd₂O₂ dinuclear units, which are separated by O–P–O bridges. According to the BVS calculations and measured magnetic properties, only Co^III ions are present in the obtained complexes. The magnetic properties of the compounds 1–3 were studied and the entropy changes for the designation of the magnetocaloric effect were calculated. The largest value for the magnetic entropy change −ΔS_M of 20 J kg⁻¹ K⁻¹ for complex 1 has been found for T_av = 2.25 K and H_f = 5 T.