Photo luminescent Lanthanide-Organic Bilayer Networks with 2,3-Pyrazinedicarboxylate and Oxalate

The hydrothermal reaction between lanthanide nitrates and 2,3-pyrazinedicarboxylic acid led to a new series of two-dimensional (2D) lanthanide-organic frameworks: [Ln(2)(2,3-pzdc)(2)(ox)(H2O2](n)[where 2,3-pzdc2 = 2,3-pyrazinedicarboxylate, ox(2-) = oxalate, and Ln(III) = Ce, Nd, Sm, Eu, Gd, Tb, or Er]. The structural details of these materials were determined by single-crystal X-ray diffraction (for Ce3+ and Nd3+) that revealed the formation of a layered structure. Cationic monolayers of if {(2)(infinity)n(2,3-pzdc)(H2O](+)} are interconnected via the ox 2 ligand leading to the formation of neutral Ln2(2,3-pzdc)(2)(ox)(H2O2] bilayer networks; structural cohesion of the crystalline packing is reinforced by the presence of highly directional 0 H " " 0 hydrogen bonds between adjacent bilayers. Under the employed hydrothermal conditions 2,3-pyrazinedicarboxylic acid can be decomposed into ox(2) and 2-pyrazinecarboxylate (2-pzc), as unequivocally proved by the isolation of the discrete complex ITb2(2pzO(4)(ox)(H2O)(6) ]" (H2O)-H-10 Single-crystal X-ray diffraction of this latter complex revealed its co-crystallization with an unprecedented (H2O)(16) water cluster. Photoluminescence measurements were performed for the Nd3(+), Sm3+, Eu3+, and Tb3+ compounds which show, under UV excitation at room temperature, the Ln(3+) characteristic intra-4f(N) emission peaks. The energy level of the triplet states of 2,3-pyrazinedicarboxylic acid (18939 cm(-1)) and oxalic acid (24570 cm(-1)) was determined from the 12K emission spectrum of the Gd3+ compound. The D-5(0) and D-3(4) lifetime values (0.333 +/- 0.006 and 0.577 +/- 0.017 ms) and the absolute emission guantum yields (0.13 +/- 0.01 and 0.05 +/- 0.01) were determined for the Eu3+ and Tb3+ compounds, respectively. For the Eu3+ compound the energy transfer efficiency arising from the ligands' excited states was estimated (0.93 +/- 0.01).