Luminescent nine-coordinate lanthanide complexes derived from fluorinated β-diketone and 2,4,6-tris(2-pyridyl)-1,3,5-triazine

Abstract

The synthesis, photoluminescence, 4f–4f absorptions, and NMR studies of nine-coordinate lanthanide(III) complexes, [Ln(tfaa)₃(tptz)] (Ln = La, Nd, Sm, and Eu; tfaa is the anion of 1,1,1-trifluoro-2,4-pantanedione; and tptz = 2,4,6-tris(2-pyridyl)-1,3,5-triazine), are reported. These complexes are synthesized in a single pot by in situ method and thoroughly characterized. The β-diketone and tptz chemical shifts, in the cases of paramagnetic complexes, are in the opposite directions. The lanthanide-induced shifts are dipolar in nature. The luminescence and 4f–4f absorptions are analyzed and discussed. The samarium and europium complexes emit strong pink and red luminescences due to ⁴G_5/2 → ⁶H_j (j = 5/2, 7/2, 9/2) and ⁵D₀ → ⁷F_j (j = 0–4) transitions, respectively. The ⁴G_5/2→⁶H_7/2 (607 nm) emission transition of Sm(III) has no Stark components and indicates a higher local symmetry around Sm(III). The very strong hypersensitive ⁵D₀ → ⁷F₂ transition of Eu reflects a highly polarizable chemical environment around Eu(III). The absorption spectra of the neodymium complex are investigated and analyzed.

Keywords:

• Lanthanide
• 2,4,6-Tris(2-pyridyl)-1,3,5-triazine
• 1,1,1-Trifluoro-2,4-pentanedione
• 4f–4f Absorption
• Hypersensitivity
• Luminescence

Acknowledgments

Part of the work was supported by the UGC Special Assistance Programme of the Department of Chemistry, Jamia Millia Islamia (No. F.540/17/DRS/2007/SAP-1). R. Ilmi thanks the University Grants Commission for the award of a BSR fellowship.