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

Novel mixed-metal coordination polymers (CPs) based on Pb1-xEux-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 [Eu-2(BDC)(3)(H2O)(4)], as shown by powder (including Rietveld analysis) and single-crystal X-ray diffraction. The unique Pb0.75Eu0.25-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.