Mechanochemical synthesis, luminescent and magnetic properties of lanthanide benzene-1,4-dicarboxylate coordination polymers (Ln0.5Gd0.5)2 (1,4-BDC)3(H2O)4; Ln = Sm, Eu, Tb

Mechanochemical reactions of benzene-1,4-dicarboxylate (BDC2-) and lanthanide carbonates, Ln(2)(CO3)(3)center dot xH(2)O (Ln = Sm, Eu, Gd, Tb) yield phase pure lanthanide coordination polymers, (Ln(0.5)Gd(0.5))(2)(1,4-BDC)(3)(H2O)(4) with Ln = Sm, Eu, Tb, which are isostructural with Tb-2(1,4-BDC)(3)(H2O)(4) as confirmed by powder X-ray diffraction and vibrational spectroscopy. Upon excitation with UV light all three compounds display strong emissions, characteristic for the respective optically active lanthanide ion, namely, red for Eu3+, green for Tb3+ and orange-red for Sm3+. In case of the Tb3+-containing compound, the energy difference between the triplet energy level of benzene-1,4-dicarboxylate ligand (BDC2-) allows for the most efficient BDC2--Tb3+ energy transfer. As a consequence, an intense green luminescence with rather long lifetime (0.81 ms) and high quantum yield (22%) is observed after allowed excitation of the BDC2- ligand. The compounds are paramagnetic with no onset of long range magnetic ordering down to liquid He temperatures.