Assembly of one-, two-, and three-dimensional Ln(III) complexes constructed from a novel asymmetric tricarboxylic acid: synthesis, structure, photoluminescence and tunable white-light emission

By reacting an asymmetric semi-rigid V-shaped linker H(3)dpob (H(3)dpob = 3-(2'3'-dicarboxylphenoxy)benzoic acid) and Ln(NO3)(3)center dot 6H(2)O, nine novel Ln-based luminescent materials, from 1D to 3D, namely {[Eu.dpob).phen)]center dot H2O}(n) (1), {[Ln(Hdpob)(ox)(0.5)(H2O)(2)]}(n) (Ln = Eu(2), Sm(3), Gd(4), Tb(5)), {[Eu(dpob)(H2O)(2)]center dot 0.5H(2)O}(n) (6), and {[Ln(dpob)(H2O)(2)]center dot mH(2)O} n (Ln = Eu(7), Gd(8), Tb(9), m = 0.5 for 7 and 9; m = 1 for 8) (phen = 1,10-phenanthroline; H(2)ox = oxalic acid) have been hydrothermally synthesized and characterized by single-crystal X-ray diffraction, infrared (IR) spectroscopy, elemental analysis, and PXRD. The crystal structures of 1-9 indicate that the coordination modes and coordination configuration of the H(3)dpob ligand play critical roles in the formation of the lanthanide architectures. Complexes 1-5 display multiple structures from double-stranded 1D chains to 4-connected 2D layers, through [Eu-2(CO2)(4)] or [Eu-2(CO2)(2)] dinuclear units with different auxiliary ligands. Complexes 6 and 7 are genuine supramolecular isomers which are induced by the concentration effect. 6 possesses a 2D kgd network with a Schlafli symbol of (4(3))(2)(4(6).6(6).8(3)) built from 6-connected [Eu-2(CO2)(2)] units and 3-connected H(3)dpob, which further connects to a (3,8)-connected tfz-d topology through O-H center dot center dot center dot O hydrogen bonds. 7 displays a 3D (3,6)-connected rtl network with the Schlafli symbol (4.6(2))(2)(4(2).6(10).8(3)). Eu complexes 1, 2, 6, and 7 as well as Tb complexes 5 and 9 could provide intense and bright characteristic D-5(0) -> F-7(J)/D-5(4) -> F-7(J) red/green luminescence under UV excitation in the solid state at 298 K and 77 K. The calculated singlet and triplet energies of H(3)dpob as well as phen and H(2)ox ligands indicate that these ligands act as antenna chromophores that are able to efficiently absorb and transfer energy to Ln(III) ions. In complexes 1, 2 and 5, ligand-to-metal energy transfer processes could occur in mixed ligands. However, these processes occurred in a single H3dpob ligand in complexes 6 and 7. With careful adjustment of the relative concentration of the lanthanide ions and by varying the excitation wavelengths of {[Gd0.92Eu0.04Tb0.04(dpob)(H2O)(2)]center dot 0.5H(2)O} n (10), tunable yellow (CIE coordinate: 0.51, 0.40) to white-light (CIE coordinate: 0.33, 0.34) emission has been obtained.