Details

Autor(en) / Beteiligte

• Marinho, Maria Vanda
• Reis, Daniella O
• Oliveira, Willian X. C
• Marques, Lippy F
• Stumpf, Humberto O
• Déniz, Mariadel
• Pasán, Jorge
• Ruiz-Pérez, Catalina
• Cano, Joan
• Lloret, Francesc
• Julve, Miguel

Titel

Photoluminescent and Slow Magnetic Relaxation Studies on Lanthanide(III)-2,5-pyrazinedicarboxylate Frameworks

Ist Teil von

• Inorganic chemistry, 2017-02, Vol.56 (4), p.2108-2123

Ort / Verlag

United States: American Chemical Society

Erscheinungsjahr

2017

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• In the series described in this work, the hydrothermal synthesis led to oxidation of the 5-methyl-pyrazinecarboxylate anion to the 2,5-pyrazinedicarboxylate dianion (2,5-pzdc) allowing the preparation of three-dimensional (3D) lanthanide­(III) organic frameworks of formula {[Ln2(2,5-pzdc)3(H2O)4]·6H2O} n [Ln = Ce (1), Pr (2), Nd (3), and Eu (4)] and {[Er2(2,5-pzdc)3(H2O)4]·5H2O} n (5). Single-crystal X-ray diffraction on 1–5 reveals that they crystallize in the triclinic system, P1̅ space group with the series 1–4 being isostructural. The crystal structure of the five compounds are 3D with the lanthanide­(III) ions linked through 2,5-pzdc2– dianions acting as two- and fourfold connectors, building a binodal 4,4-connected (4·648)­(426282)-mog network. The photophysical properties of the Nd­(III) (3) and Eu­(III) (4) complexes exhibit sensitized photoluminescence in the near-infrared and visible regions, respectively. The photoluminescence intensity and lifetime of 4 were very sensitive due to the luminescence quenching of the 5D0 level by O–H oscillators of four water molecules in the first coordination sphere leading to a quantum efficiency of 11%. Variable-temperature magnetic susceptibility measurements for 1–5 reveal behaviors as expected for the ground terms of the magnetically isolated rare-earth ions [2F5/2, 2H4, 4I9/2, 7F0, and 4I15/2 for Ce­(III), Pr­(III), Nd­(III), Eu­(III), and Er­(III), respectively] with M J = 0 (2 and 4) and ±1/2 (1, 3, and 5). Q-band electron paramagnetic resonance measurements at low temperature corroborate these facts. Frequency-dependent alternating-current magnetic susceptibility signals under external direct-current fields in the range of 100–2500 G were observed for the Kramers ions of 1, 3, and 5, indicating slow magnetic relaxation (single-ion magnet) behavior. In these compounds, τ–1 decreases with decreasing temperature at any magnetic field, but no Arrhenius law can simulate such a dependence in all the temperature range. This dependence can be reproduced by the contributions of direct and Raman processes, the Raman exponent (n) reaching the expected value (n = 9) for a Kramers system.