Lanthanide Coordination Polymers with Soft-Base Ditopic Bisthiazolate Ligands.

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(3 H ,7 H )-dithione (H 2 L) was used as a linker. The reactions of lanthanide silylamides Ln[N(SiMe 3 ) 2 ] 3 (Ln = Nd, Gd, Er, and Yb) with H 2 L 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) 3 L 1.5 ·0.5diox] n ( 5 ), where deprotonated dithione H 2 L plays the role of a ditopic linker. This linker acts as an "antenna" in compound 5 , providing an intense near-infrared (NIR) PL of Nd 3+ 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) 3 L 1.5 ·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.