A series of tris(pyrazolyl)borate mono-, di- and trinuclear Tb3+ and Dy3+ complexes, (Tp2Ln)nX (Ln = Tb, Dy, Tp– = tris(pyrazolyl)borate, Xn– = various mono- and oligo(β-diketonates)) were synthesized. These compounds behave as luminescent single molecular magnets (SMM) with quantum yields up to 73% and 4.4% for the Tb3+ and Dy3+ compounds, respectively. The complexes possess SMM behavior in non-zero dc field at low temperatures, while the polynuclear Dy3+ complexes show slow magnetic relaxation even in a zero dc field up to 8 K. Ueff-values determined from dynamic magnetic measurements are up to 31 for the Dy3+ and 6 cm–1 for the Tb3+ complexes. It was found that within a series of Dy3+ or Tb3+ compounds, Ueff and luminescence quantum yields decreased with increasing nuclearity of the compounds and a shortening of the intramolecular Ln-Ln distance. ΔOrbach-values estimated from low-temperature luminescence spectra were significantly higher than those obtained from ac magnetic data, which may be due to involvement of additional processes in the relaxation mechanism (quantum tunneling, Raman, direct) reducing the energy barrier.

Tb3+ and Dy3+ complexes with tris(pyrazolyl)borate and oligo(β-diketonate) ligands: New series of luminescent single-molecule magnets

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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