Synthesis, Crystal Structure, and Photoluminescence of Homodinuclear Lanthanide 4-(Dibenzylamino)benzoate Complexes

• Published in: Inorganic chemistry Vol. 49; no. 5; pp. 2407 - 2415
• Main Authors: Ramya, A. R, Reddy, M. L. P, Cowley, Alan H, Vasudevan, Kalyan V
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 01.03.2010
• Subjects: Benzoates - chemistry; Crystallography, X-Ray; Lanthanoid Series Elements - chemistry; Ligands; Luminescent Measurements; Models, Molecular; Molecular Conformation; Organometallic Compounds - chemical synthesis; Organometallic Compounds - chemistry; Spectrophotometry, Ultraviolet; Temperature
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic902257u

Three new binuclear lanthanide complexes of general formula [Ln2(L)6(H2O)4] (Ln = Tb (1), Eu (2), and Gd (3)) supported by the novel aromatic carboxylate ligand 4-(dibenzylamino)benzoic acid (HL) have been synthesized. Complexes 1 and 2 were structurally characterized by single-crystal X-ray diffraction. Both 1 and 2 crystallize in the triclinic space group P 1̅, and their molecular structures consist of homodinuclear species that are bridged by two oxygen atoms from two carboxylate ligands via different coordination modes. The discrete bridged dimer of 1 is centrosymmetric and features 8-coordinate terbium atoms, each of which adopts a distorted square-antiprismatic geometry. Both coordination spheres comprise two η2-chelating benzoates, two μ-η1:η1 -carboxylate interactions from the bridging benzoates, and two water molecules. By contrast, in complex 2, the Eu3+ ion coordination environment is best described as a distorted tricapped-trigonal prism, each europium ion being coordinated to three η2-chelating benzoate ligands and two water molecules. One of the η2-carboxylate ligands is involved in a further interaction with an adjacent metal, thus rendering the overall binding mode bridging tridentate, μ-η2:η1. Scrutiny of the packing diagrams for 1 and 2 revealed the existence of a one-dimensional molecular array that is held together by intermolecular hydrogen-bonding interactions. The Tb3+ complex 1 exhibits high green luminescence efficiency in the solid state with a quantum yield of 82%. On the other hand, poor luminescence efficiency has been noted for the Eu3+−4-(dibenzylamino)benzoate complex.