Pentanuclear {Cr2Ln3} (Ln = Dy, Tb) Heterometallic Clusters Based on an Amino Acid Ligand: Slow Relaxation of Magnetization and Substitution Reactions.

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]