Slow Relaxation of the Magnetization in Dysprosium–Aluminum Metallacrowns

High Resolution Image Download MS PowerPoint Slide A series of Dy III –Al III metallacrowns (MC) with the ligand salicylhydroxamic acid (H 3 shi) were investigated for magneto-structural interactions. The four MCs demonstrate that slight variations in reaction conditions and molecular components can lead to different classes of MCs. The Dy III –Al III MCs include an archetype Dy III Al III 4 [12-MC-4], the dimer Dy III 2 Al III 8 [12-MC-4] 2, a [3.3.1] metallacryptand (MCr) Dy III Al III 6 [3.3.1], and Dy III 2 Al III 6 [18-MC-6], representing a new type of MC. Dy III 2 Al III 6 [18-MC-6] consists of a MC ring with six ring Al III ions that have an octahedral propeller configuration with a stereoisomer pattern ΔΛΛΛΔΔ about the MC ring. The 18-MC-6 captures a [Dy III 2 (μ 3 -OH) 2 ] 4+ core, where each Dy III ion is nine-coordinate with muffin geometry ( C s ). Both the static and dynamic magnetic properties of the complexes were investigated. Models of the static magnetic data reveal that Dy III Al III 4 [12-MC-4] and Dy III 2 Al III 8 [12-MC-4] 2 do not have a significant axial ligand field, as the Dy III ions have a square antiprism geometry ( D 4d ). However, a similar analysis demonstrates that Dy III Al III 6 [3.3.1] and Dy III 2 Al III 6 [18-MC-6] do have a significant axial component to the ligand field, as the Dy III ions in these complexes have spherical capped square antiprism ( C 4v ) or muffin geometry, respectively. The Dy III geometry differences lead to differing dynamic magnetic susceptibility behavior. Dy III Al III 4 [12-MC-4] and Dy III 2 Al III 8 [12-MC-4] 2 do not display a frequency-dependent out-of-phase magnetic susceptibility signal in the absence of a static magnetic field. A frequency-dependent signal is observed only with the application of an 800 Oe magnetic field. However, Dy III Al III 6 [3.3.1] and Dy III 2 Al III 6 [18-MC-6] do exhibit SMM behavior in the absence and presence of a static magnetic field. For Dy III Al III 6 [3.3.1] and Dy III 2 Al III 6 [18-MC-6], the effective energy barrier to magnetization relaxation ( U eff ) with an 800 Oe magnetic field is 59 ± 2 and 35 ± 2 cm –1 with τ 0 = 2.5 ± 0.7 × 10 –8 and 3.5 ± 1.1 × 10 –8 s, respectively.