Two sensitizers of Tb(III) constructed from alkaline earth metals and semi-rigid tripodal ligand

Three alkaline earth (AE) coordination polymers, namely, [Mg(H2BCPBA)2(H2O)4]n (1), [Sr(HBCPBA)(H2O)2]n (2), [Ba(H2BCPBA)2]n (3), (H3BCPBA = 3,5-bi(4-carboxy-phenolxy)-ben-zoic acid) have been synthesized in mixed solvents under hydrothermal conditions. The single crystal analysis show 1 is mononuclear compound, which forms 3D supramolecular framework through H-bonding and π–π interaction. In compound 2, dinuclear Sr(II) subunits were connected by the tripod linkers to afford the 3D metal–organic framework. Compound 3 displays 3D structure and each Ba(II) center in the framework acts as a 4,8-connected binode to give a unique network with a Schläfli symbol of {44.62}2{48.618.82}. The solid-state luminescent spectra of complexes 1–3 reveals that all of them have different degree of redshift compared with free ligand. The experiments of sensitization to Eu(III) and Tb(III) are performed on these three compounds. The results show that 2 and 3 can sensitize Tb(III) ion to exhibit its characteristic green emission.