Octanuclear [NiII4LnIII4] complexes. Synthesis, crystal structures and magnetocaloric properties

Abstract

Two original heterooctanuclear [Ni^II₄Ln^III₄] complexes (Ln^III = Sm^III, Gd^III) have been obtained starting from the [Ni^II(valpn)(H₂O)₂] mononuclear precursor [H₂valpn = 1,3-propanediylbis(2-iminomethylene-6-methoxy-phenol)] and the corresponding lanthanide nitrates, in the presence of azide anions, through slow capture of atmospheric CO₂. Three weak and competitive exchange interactions, J_GdGd, J_GdNi, J_NiNi, make the ground state of this magnetic system degenerate at cryogenic temperature and zero field. This, along with the high spin of Gd^III, lead to a significant magnetocaloric effect spread in the temperature range 1 to 20 K (ΔS_m[0–7 T, 3.5 K] = 19 J kg⁻¹ K⁻¹).