Search

The syntheses, structures, and magnetic properties of two series of Cr-Ln heterometallic clusters based on the 2,2'-bipyridine (bipy) ligand are reported; binuclear [LnCr(bipy)2-(µ2-OH)2(H2O)6](ClO4)4·2H2O {Ln = Gd (1Gd) or Dy (1Dy)} and trinuclear [LnCr2(bipy)4(µ2-OH)4(H2O)4](ClO4)5·H2O {Ln = Gd (2Gd), Dy (2Dy), or Tb (2Tb)}. Their syntheses could be controlled by the amount of lanthanide perchlorate used. The binuclear [CrLn] clusters could be formed with 24 equivalents of Ln(ClO4)3, whereas 12 equivalents of Ln(ClO4)3 gave the trinuclear [Cr2Ln] species with a CrLnCr core. The Cr3+ and Ln3+ ions are bridged by µ2-OH groups in the two systems, and the [Cr2Ln] cluster is further assembled into a 1D supramolecular architecture by weak intermolecular p-p interactions. Magnetic analyses reveal that the Cr···Gd interactions in 1Gd and 2Gd are both antiferromagnetic. [ABSTRACT FROM AUTHOR]

Reactions between Ln3+ (Ln = Dy, Tb), Cr3+, and glycine (HGly) in aqueous solution led to two pentanuclear compounds, Na3[Dy3Cr2(HGly)6(μ3-OH)6(H2O)9] ·(ClO4)8 ·Cl4 ·14H2O ( 1) and Na3[Tb3Cr2(HGly)6(μ3-OH)6(H2O)9] ·(ClO4)6 ·Cl6 ·6H2O ( 2). Structural analyses showed that both 1 and 2 have a {Ln3Cr2} compressed trigonal-bipyramidal skeleton in which an axial Cr3+ ion lies above and below the triangular equatorial plane defined by the three Ln3+ ions. Magnetic measurements indicated that 1 and 2 exhibit single-molecule magnetic behavior with Ea ≈ 14.1 K and τ0 = 4.2 × 10-8 s for 1 and Ea ≈ 13.0 K and τ0 = 6.4 × 10-7 s for 2. Interestingly, the clusters are soluble in aqueous solution. The two terminal water molecules of 1 can be substituted by two monocoordinated 4,4′-dipyridyl N, N′-dioxide (dpyo) molecules to afford [Dy3Cr2(HGly)6(dpyo)2(μ3-OH)6(H2O)7] ·(ClO4)9 ·15H2O ( 3) with a three-dimensional cds network formed through π-π interactions. Magnetic analysis indicated that 3 also displays slow relaxation of the magnetization with Ea ≈ 13.24 K and τ0 = 9.16 × 10-8 s. [ABSTRACT FROM AUTHOR]