Anion-directed assemblies of europium(III) coordination polymers based on 1H-benzimidazole-5,6-dicarboxylate: structures and luminescence properties.

Abstract

Two europium(III) coordination polymers (CPs), namely, poly[[diaquabis(μ4-1H-benzimidazole-5,6-dicarboxylato-κ6N3:O5,O5':O5,O6:O6')(μ2-oxalato-κ4O1,O2:O1',O2')dieuropium(III)] dihydrate], {[Eu2(C9H4N2O4)2(C2O4)(H2O)2]·2H2O}n (1), and poly[(μ3-1H-benzimidazol-3-ium-5,6-dicarboxylato-κ5O5:O5',O6:O6,O6')(μ3-sulfato-κ3O:O':O'')europium(III)], [Eu(C9H5N2O4)(SO4)]n (2), have been synthesized via the hydrothermal method and structurally characterized. CP 1 shows a three-dimensional network, in which the oxalate ligand acts as a pillar, while CP 2 has a two-dimensional network based on a europium(III)-sulfate skeleton, further extended into a three-dimensional framework by hydrogen-bonding interactions. The structural diversity in the two compounds can be attributed to the different acidification abilities and geometries of the anionic ligands. The luminescence properties of 1 display the characteristic europium red emission with CIE chromaticity coordinates (2/3, 0.34). Interestingly, CP 2 shows the characteristic red emission with CIE chromaticity coordinates (0.60, 0.34) when excited at 280 nm and a near-white emission with CIE chromaticity coordinates (0.38, 0.29) when excited at 340 nm.