A new family of decanuclear Ln(7)Cr(3) clusters exhibiting a magnetocaloric effect

Two dimeric Ln–Cr clusters with formula {Ln(H(2)O)(8)[Ln(6)Cr(3)(L)(6)(CH(3)COO)(6)(μ(3)-OH)(12)(H(2)O)(12)]}·(ClO(4))(6)·xH(2)O (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 [Gd(3)Cr(2)(μ(3)-OH)(6)](9+) worked as building blocks in constructing the metal-oxo cluster core of [Gd(6)Cr(3)(μ(3)-OH)(12)](15+) by sharing a common top – a Cr(3+) 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(H(2)O)(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.