Site-selective Eu(iii) spectroscopy of highly efficient luminescent mixed-metal Pb(ii)/Eu(iii) coordination polymers

Abstract

Novel mixed-metal coordination polymers (CPs) based on Pb_1−xEu_x–BDC (x = 0.05, 0.10, 0.25, 0.50 and BDC = 1,4-benzenedicarboxylic acid) are reported. The materials display different coordination structures as the Pb : Eu metal ratio is modified. Whereas for x < 0.25 the Eu³⁺ ions essentially replace the Pb²⁺ ones in the [Pb(BDC)_n] structure, for x > 0.25 the samples are isotypical with [Eu₂(BDC)₃(H₂O)₄], as shown by powder (including Rietveld analysis) and single-crystal X-ray diffraction. The unique Pb_0.75Eu_0.25–BDC compound displays a mixture of both crystalline phases with the highest emission quantum yield value reported for luminescent CPs based on Pb(II), 69 ± 7%. Site-selective excitation using a common Xe lamp permits the detailed study of the two Eu³⁺ local sites, illustrating how powerful the Eu³⁺ luminescence is as a local probe spectroscopic tool.