A new family of decanuclear Ln7Cr3 clusters exhibiting a magnetocaloric effect

Abstract

Two dimeric Ln–Cr clusters with formula {Ln(H₂O)₈[Ln₆Cr₃(L)₆(CH₃COO)₆(μ₃-OH)₁₂(H₂O)₁₂]}·(ClO₄)₆·xH₂O (Ln = Gd, x = 35 for 1 and Ln = Dy, x = 45 for 2, HL = 2-pyrazinecarboxylic acid) were obtained by a ligand-controlled hydrolytic method with a mixed ligand system (2-pyrazinecarboxylic acid and acetate). Single crystal structure analysis showed that two trigonal bipyramids of [Gd₃Cr₂(μ₃-OH)₆]⁹⁺ worked as building blocks in constructing the metal-oxo cluster core of [Gd₆Cr₃(μ₃-OH)₁₂]¹⁵⁺ by sharing a common top – a Cr³⁺ ion. Additionally, compound 1 forms a three-dimensional framework with a one-dimensional nanopore channel along the a-axis through a hydrogen-bond interaction between the cationic cluster core and the free mononuclear cation [Gd(H₂O)₈]³⁺ and the π-bond interactions of the pyrazine groups on the two cationic cluster cores. Magnetic calculations indicated a weak ferromagnetic coupling interaction for Gd⋯Gd and Gd⋯Cr in compound 1, with its magnetic entropy change (−ΔS_m) reaching 21.1 J kg⁻¹ K⁻¹ at 5 K, 7 T, while compound 2 displayed an obvious frequency-dependency at H_dc = 2000 Oe.