Single-Ion Magnet and Photoluminescence Properties of Lanthanide(III) Coordination Polymers Based on Pyrimidine-4,6-Dicarboxylate

Abstract

Herein, we report the magnetic and photoluminescence characterization of coordination polymers (CP) built from the combination of lanthanide(III) ions, pyrimidine-4,6-dicarboxylate (pmdc) ligand and a co-ligand with formula {[Dy(μ-pmdc)(μ-ox)0.5(H2O)3]·2H2O}n (1-Dy), {[Dy(μ3-pmdc)(μ-ox)0.5(H2O)2] ~2.33H2O}n (2-Dy), {[Dy2(μ3-pmdc)(μ4-pmdc)(μ-ox)(H2O)3]·5H2O}n (3-Dy), {[Ln(μ3-pmdc)(μ-ox)0.5(H2O)2]·H2O}n (where Ln(III) = Nd (4-Nd), Sm (4-Sm), Eu (4-Eu) and Dy (4-Dy)) and {[Dy(μ4-pmdc)(NO3)(H2O)]·H2O}n (5-Dy). It must be noted the presence of oxalate anion acting as ditopic co-ligand in compounds 1-Dy, 2-Dy, 3-Dy and 4-Ln, whereas in 5-Dy the nitrate anion plays the role of terminal co-ligand. Direct current measurements carried out for the dysprosium-based CPs reveal almost negligible interactions between Dy3+ ions within the crystal structure, which is confirmed by computed values of the exchange parameters J. In addition, alternating current measurements show field-induced single-molecule magnet (SMM) behavior in compounds 1-Dy, 2-Dy, 4-Dy and 5-Dy, whereas slight-frequency dependence is also observed in 3-Dy. Solid state emission spectra performed at room temperature for those compounds emitting in visible region confirm the occurrence of significant ligand-to-lanthanide charge transfer in view of the strong characteristic emissions for all lanthanide ions. Emission decay curves were also recorded to estimate the emission lifetimes for the reported compounds, in addition to the absolute quantum yields. Among them, the high quantum yield of 25.0% measured for 4-Eu is to be highlighted as a representative example of the good emissive properties of the materials.

Lanthanide(III) Ions and 5-Methylisophthalate Ligand Based Coordination Polymers: An Insight into Their Photoluminescence Emission and Chemosensing for Nitroaromatic Molecules

“…The lifetimes were estimated by means of the weighted sum of the components, obtaining the values of 12.6(2) µs (for 1 Sm ), 289 (11) µs (for 2 Eu ) and 806(8) µs (for 4 Tb ). These results are in line with other previously reported CPs based on eight-coordinated Ln environments [53,61,63]. The cooling of the samples to 13 K does not affect the emission lifetimes (they are kept as 12.9(2) µs for 1 Sm and 816(8) µs for 4 Tb ) except for the Eu(III) counterpart, in which the lifetime increases to 543 (14) µs at low temperature.…”

“…In any case, the opposite situation is found in the excitation of this compound with regard to the intensity of the bands, which is characteristic of low sensitization of Sm(III) by the ligand. Surprisingly, when the temperature of the sample is cooled down to 10 K, the Sm-centered emission lines are comparatively less intense than the ligand-based pattern, which is an unexpected behavior because the antennae effect is usually enhanced with the decrease in the temperature [49,61]. However, in the present case, the cryoscopic decrease does not seem to affect the ligand-to-samarium energy transfer capacity while it substantially reduces the vibrational quenching in the ligand molecule, thus bringing an increase in the latter signal which, in turn, seems to mask the Sm-centered bands [62].…”

An experimental and theoretical study of the magnetic relaxation in heterometallic coordination polymers based on 6-methyl-2-oxonicotinate and lanthanide(iii) ions with square antriprismatic environment

“…To that end, and continuing with our relentless quest for multifunctional materials behaving as SIMs, 24,[42][43][44] in the present work we have resorted to the potential of the 6-methyl-2oxonicotinate ligand (6m2onic) to build SAPR-like environments owing to its carboxylate/ketone moiety that establishes chelating rings resembling those of previously reported β-diketonato ligands. [45][46][47][48] Moreover, with this arrangement the occurrence of additional links enabling superexchange bridges with neighbouring paramagnetic ions would be prevented.…”

Single-ion magnetism behaviors in lanthanide(iii) based coordination frameworks

“…83 Compounds 38–41 are proposed to be paramagnetic based on the rectilinear drop of the χ M −1 vs. T plot. 85 At low temperature (<4 K), a slight increase in the χ M T value for compound 49 indicates weak ferromagnetic interactions between Dy( iii ) ions. 86 An exchange of the coordinated and guest solvent molecules (acetone or DMF) was reported to result in different magnetic relaxation and ferroelectric properties of compound 50 .…”

“…Linkers such as carboxylictype ligands have been used to create compounds 23, 26, 29-33, 35-41, 46, 49-50 and 52. 35,42,[78][79][80][81][82][83][84][85][86][87][88] Compounds 31 and 32 have been reported to show ferromagnetic coupling in 3D frameworks, and such a magnetic interaction makes a positive contribution to the energy barrier of SMM/SIM properties. Magnetic studies of compound 33 reveal the existence of weak antiferromagnetic interactions among Dy(III) ions.…”