Tetranuclear [Cu3Ln] complexes derived from a tetraketone-type ligand

Abstract

A series of tetranuclear [Cu₃Ln] complexes, [Cu₃Gd(L)₃(NO₃)₂(H₂O)₃](NO₃)·H₂O (1), [Cu₃Tb(L)₃(NO₃)₂(H₂O)₃](NO₃) (2) and [Cu₃Dy(L)₃(NO₃)₃(H₂O)₂]·1.5(H₂O) (3), were synthesized by a one-pot reaction using a simple tetraketone-type ligand (H₂L = (3Z,5Z)-4,5-dihydroxy-3,5-octadiene-2,7-dione). X-ray structural analyses revealed that each complex has a planar tetranuclear core of [Cu₃Ln] (Ln = Gd, Tb, and Dy), in which the Ln ion is accommodated in the centre of a Cu₃O₆ metallocycle. A cryomagnetic study revealed that all complexes show intramolecular ferromagnetic interactions between Cu(II) and Ln(III) ions. The [Cu₃Gd] complex (1) has an S_T = 5 spin ground state and shows a magneto-caloric effect with a maximum magnetic entropy change (–ΔS_m) of 16.4 J kg⁻¹ K⁻¹ (5 T, 2.4 K). On the other hand, the [Cu₃Tb] complex (2) shows a slow magnetic relaxation behavior under a zero magnetic field. The analysis of an Arrhenius plot reveals that the effective energy barrier of spin reversal is 13.1 K. The [Cu₃Dy] complex (3) also shows a slow magnetic relaxation under 1300 Oe dc magnetic field with an effective energy barrier of 6.82 K.