Assembly of heterobimetallic NiII–LnIII (LnIII = DyIII, TbIII, GdIII, HoIII, ErIII, YIII) complexes using a ferrocene ligand: slow relaxation of the magnetization in DyIII, TbIII and HoIII analogues

Abstract

A family of dinuclear 3d–4f heterobimetallic complexes [LNi(H₂O)(μ-OAc)Ln(NO₃)₂]·CH₃CN; {Ln = Dy^III (1), Tb^III (2), Ho^III (3), Gd^III (4), Er^III (5), Y^III (6)} have been synthesized by utilizing a ferrocene-based, dual compartmental ligand H₂L. 1–6 are isostructural and crystallize in the triclinic (P) space group. In these complexes Ni^II is present in the inner coordination sphere of the dianionic [L]²⁻ ligand; Ln^III is encapsulated in the outer coordination pocket. Ni^II shows a 2N, 4O coordination environment in a distorted octahedral geometry, while the Ln^III ion possesses a 9O coordination environment in a distorted tricapped trigonal prismatic geometry. ESI-MS studies suggest that the structural integrity of 1–6 is retained in solution. Electrochemical studies reveal that these complexes show a reversible one-electron response typical of the ferrocene motif along with an irreversible one-electron oxidation involving the Ni^II/Ni^III couple. Magnetic studies revealed the presence of ferromagnetic exchange coupling between Ni^II and Ln^III centers as shown by the increase of χ_MT value upon cooling below 50 K for compounds 1, 2, 4 and 5. Further, dynamic magnetic susceptibility measurements (1–3) confirm the absence of an out-of-phase (χ′′) signal at zero dc fields. However, when these measurements were carried out at 1000 Oe dc field the χ′′ signal was observed, although maxima could not be detected up to 2 K.