Syntheses, crystal-solution structures and magnetic properties of a series of decanuclear heterometallic [Ln III2Co II4Co III4] (Ln = Eu, Gd, Tb, Dy) clusters

Abstract

Four unprecedented decanuclear heterometallic [Ln₂Co^II₄Co^III₄] clusters based on a diethanolamine ligand (H₂dea), namely [Eu₂Co^II₄Co^III₄(dea)₈(HCOO)₄(OH)₂(Cl)₂(CH₃OH)₂]Cl₂·4CH₃OH·2H₂O (1), [Gd₂Co^II₄Co^III₄(dea)₈(HCOO)₄(OH)₂(Cl)₂(CH₃OH)₂]Cl₂·4CH₃OH·2H₂O (2), [Tb₂Co^II₄Co^III₄(dea)₈(HCOO)₄(OH)₂(Cl)₂(CH₃OH)₂]Cl₂·2CH₃OH·4H₂O (3) and [Dy₂Co^II₄Co^III₄(dea)₈(HCOO)₄(OH)₂(Cl)₂(CH₃OH)₂]Cl₂·2CH₃OH·4H₂O (4) were synthesized through a facile solution method. Single-crystal X-ray diffraction analyses reveal that complexes 1–4 consist of a [Ln₂Co^II₄Co^III₄] core, which is constructed by bridging a quasi-double cuboidal [Ln₂Co^II₂Co^III₂] core with two [Co^IICo^III] units. Electrospray ionization mass spectrometry (ESI-MS) using methanol solution reveals that complexes 1–4 are stable in the solution, and the clusters undergo three different substitution reactions (Cl⁻ replaced by OH⁻, OH⁻ replaced by CH₃O⁻ and HCOO⁻ replaced by OH⁻/CH₃O⁻) at the same time in the ionization state. Magnetic susceptibilities reveal ferromagnetic couplings within complexes 3 and 4, and the magnetocaloric effect (MCE) for 2 was also evaluated and the maximum entropy change (−ΔS_m) value reaches 16.3 J kg⁻¹ K⁻¹ at about 3 K and 5 T.