A new family of decanuclear Ln7Cr3 clusters exhibiting a magnetocaloric effect

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 (−ΔSm) reaching 21.1 J kg−1 K−1 at 5 K, 7 T, while compound 2 displayed an obvious frequency-dependency at Hdc = 2000 Oe.