Structural Modulation of Fluorescent Rhodamine-Based Dysprosium(III) Single-Molecule Magnets

Area of Science:

• Coordination Chemistry
• Materials Science
• Magnetism

Background:

• Dysprosium complexes are investigated for single-molecule magnet (SMM) properties.
• Tuning the coordination environment is crucial for optimizing magnetic behavior.
• Rhodamine 6G derivatives offer potential for novel SMMs with luminescence.

Purpose of the Study:

• To synthesize and characterize novel rhodamine 6G-based dysprosium complexes.
• To investigate the impact of coordination environment on SMM properties.
• To explore the relationship between magnetic behavior and luminescence.

Main Methods:

• Synthesis of two mononuclear dysprosium complexes: [Dy(L^R)(L^A)₂](ClO₄)₃·Et₂O·1.5MeOH·0.5H₂O (1) and [Dy(L^R)(H₂O)₄(MeCN)](ClO₄)₃·2H₂O·MeCN (2).
• Magnetic property measurements to determine SMM behavior and energy barriers.
• Ab initio calculations to understand magnetic anisotropy and quantum tunneling effects.
• Luminescence spectroscopy to analyze emission properties.

Main Results:

• Both complexes exhibit single-molecule magnet behavior at zero dc field with hysteresis at 1.9 K.
• Complex 1 shows an energy barrier (U_eff/k_B) of 90 K, while complex 2 shows a significantly higher barrier of 320 K.
• Ab initio calculations confirm the short Dy-O_phenoxy bond dictates magnetic anisotropy.
• Quantum tunneling of magnetization (QTM) is significant in complex 1 but negligible in complex 2.
• Both complexes display red light emission (645 nm for 1, 658 nm for 2) due to the xanthene moiety.

Conclusions:

• The coordination environment, particularly the Dy-O_phenoxy bond, critically influences SMM performance.
• Complex 2 demonstrates superior SMM behavior with a high energy barrier attributed to suppressed QTM.
• These rhodamine 6G-based dysprosium complexes represent promising candidates for both magnetic and luminescent applications.