Ternary complexes of neodymium(III) and samarium(III) picrate triethylene glycol: Structural, spectroscopic, and photoluminescent properties

The ternary complexation of neodymium(III) and samarium(III) with triethylene glycol (EO3) and picrate anion (Pic) were characterized by elemental analyses, FTIR (Fourier-transform infrared) spectroscopy, single crystal X-ray diffraction, and photoluminescence (PL). Both the [Nd(Pic)(H ₂O) ₂(NO ₃)(EO3)](Pic) and [Sm(Pic)(H ₂O) ₂(NO ₃)(EO3)](Pic)·H ₂O complexes were isostructural with a ten-coordination number. In both complexes, the picrate and nitrate anions were coordinated to Ln(III) in a bidentate manner, and with the the EO3 ligand in a tetradentate manner, the addition of two water molecules maintained a ten-coordination number. The lighter lanthanide-picrate complexes formed a ten-coordination number due to the lanthanide contraction effect, acyclic polyether chain length, and number of donor oxygen atoms. The acyclic EO3 ligand affected photoluminescent intensity and its conformation on the structure of the [Ln(Pic)(NO ₃)(H ₂O) ₂(EO3)] ⁺ moiety. Photoluminescent measurement showed complex Nd(III) emissions at 403, 486, and 682 nm, with the strongest emission peak at 403 nm. Formation of these peaks occurred due to the intraligand π-π transitions of the Pic anion. The Sm(III) complex exhibited the emission characteristic of the Sm(III) ion in the red spectral region at 616.7 nm ( ⁴G _5/2 → ⁶H _9/2 transition), even though the ligand emissions were also observed in the PL spectrum. The emission intensity of the 4f-4f transitions in the Sm complex was significantly higher than that found in its salt. We noted that the [Sm(Pic)(H ₂O) ₂(NO ₃)(EO3)](Pic)·H ₂O complex was an excellent red-light-emitter and would be considered as a candidate material for organic light emitting diodes.