Syntheses, structures and photophysical properties of new heterodinuclear Cd-Ln coordination complexes (Ln = Sm, Eu, Tb, Nd, Ho, Er)

Abstract

Six novel heterodinuclear d-f coordination complexes [LnCd(C 8H7O3)5(phen)(H2O)] (Ln = Sm 1, Eu 2, Tb 3, Nd 4, Ho 5, Er 6; C8H7O3 = 4-methoxybenzoato; phen = 1,10-phenanthroline) were synthesized by the hydrothermal method, and their structures were studied by single-crystal X-ray diffraction. The IR and UV/Vis/NIR absorption spectra and the luminescence spectra of the six complexes were determined at room temperature. They have the same molecular structure, and two neighboring molecules are connected by hydrogen bonds or by a Ln⋯O weak interaction to form dimer crystals. In the visible region, the emission spectra of complexes 1-3 show the intense characteristic bands of the corresponding LnIII ions, which are mainly attributed to the efficient energy transfer from the d block to the f block, that is, to the good sensitization of the d block. Moreover, in the Cd-Ln coordination complexes, the Cd⋯Ln separation is very small, and the 4d orbitals of the CdII ion may influence the 4f orbitals of the Ln III ion, which probably causes some of the f levels of the Ln III ion to be adjusted, and this effect can be observed in the shifts or splittings of the absorption bands in the UV/Vis/NIR spectra of the complexes. Especially in complexes 4-6, some energy levels of the Ln III ions have shifts or splittings, hence the corresponding emission bands exhibit shifts or splittings in the NIR region. © Wiley-VCH Verlag GmbH & Co. KGaA, 2008.