RESUMEN
In order to prepare the first lanthanide coordination polymers (CPs) based on ditopic sulfide ligands, benzo[1,2-d:4,5-d']bisthiazole-2,6(3H,7H)-dithione (H2L) was used as a linker. The reactions of lanthanide silylamides Ln[N(SiMe3)2]3 (Ln = Nd, Gd, Er, and Yb) with H2L result in the formation of soluble dimethyl sulfoxide (DMSO) ionic salts [Ln(DMSO)8][L]1.5 [Ln = Nd (1), Gd (2), Er (3), and Yb (4)]. Due to the lack of coordination of anionic ligands, compounds 1, 3, and 4 do not show sensitized metal-centered photoluminescence (PL), while Gd compound 2 shows weak phosphorescence at 77 K. It was found that the heating of 1 in a 1:9 DMSO/1,4-dioxane mixture leads to the formation of large crystals of 2D CP [Nd(DMSO)3L1.5·0.5diox]n (5), where deprotonated dithione H2L plays the role of a ditopic linker. This linker acts as an "antenna" in compound 5, providing an intense near-infrared (NIR) PL of Nd3+ ion upon near-UV and blue-light excitation. The application of a synthetic protocol similar to that of compounds 2-4 led to the formation of amorphous compounds [Ln(DMSO)3L1.5·0.5diox]n [Ln = Gd (6), Er (7), and Yb (8)], whose PL properties significantly differ from those of the parental ionic salts. In the case of Yb polymer 8, the PL excitation spectra are shifted to the red region due to a low-energy ligand-to-metal charge-transfer state. The synthesized compounds 5-8 are the first examples of lanthanide CPs using soft-base ditopic linkers in their structures.
RESUMEN
A new mixed Eu(II)-Cu(I) iodide [Eu(DME)4][Cu2I4] (1) was synthesized by the reaction of an organosulphide salt of Eu(II) and CuI in DME media. X-ray analysis revealed that 1 is an ate-complex consisting of Eu(DME)4 dications and tetraiododicuprate dianions. Upon UV light excitation (λ = 365 nm), the compound exhibits intense double-peaked photoluminescence (PL) at 445 and 500 nm. The relative intensity of these peaks changes dramatically when the temperature changes in the range of 180-250 K. To understand the nature of the found PL thermochromism, the structure and time-resolved PL of 1 were studied at various temperatures. The time-resolved PL studies of 1 at various temperatures revealed the presence of two luminescent centers which are excited by the capture of an electron from the conduction band. The ratio of intensities at 445 and 500 nm (R = I445/I500) in the PL spectra of 1 changes by almost two orders of magnitude and the relative sensitivity S (S = (∂R/∂T)/R) exceeds 5% per K in the range of 190-245 K that makes this compound a promising luminescent thermometer for the range where ammonia exists in a liquid state.
