Anion-Dependent Assembly of 3d-4f Heterometallic Clusters Ln5Cr2 and Ln8Cr4.

A series of heterometallic Ln-Cr clusters with the formulas [Ln5Cr2(H2L)2(OAc)6(μ3-OH)6(H2O)15](ClO4)7·xH2O (Ln = Gd and x = 33 for 1 and Ln = Dy and x = 21 for 2) and [Ln8Cr4(H2L)4(OAc)8(μ3-OH)16(μ4-O)1(H2O)8](Cl)(ClO4)5·10H2O (Ln = Gd for 3 and Ln = Dy for 4) was obtained through the reaction of the acetate ligands 2,2-dimethylolpropionic acid (H3L) and Ln(ClO4)3 in the presence of chromium salts with different anions under the same high pH conditions. X-ray analysis revealed that compound 1 contained a metal unit [Gd3Cr2] displaying the pentagonal bipyramid configuration and that compound 3 was templated by Cl- and ClO4- as a mixed anion template featuring a quadrangular structure. In compound 3, the 12 metal atoms were arranged in a wheel-shaped metal skeleton [Gd8Cr4], which was produced by 4 tetrahedral metal units [Gd3Cr] sharing vertices. The introduction of the mixed anion template increased the number of metal atoms in the Ln-Cr clusters. Magnetic calculations indicated that there was weak antiferromagnetic Gd···Cr coupling and weak ferromagnetic Gd···Gd coupling in 1, whereas both Gd···Cr and Gd···Gd in 3 exhibited weak antiferromagnetic interactions. Magnetothermal studies showed that compounds 1 and 3 displayed magnetic entropy changes of 25.2 J kg-1 K-1 at 5 K and 7 T and 33.8 J kg-1 K-1 at 2 K and 7 T, respectively.