Six novel heterodinuclear d-f coordination complexes [LnCd(C 8 H 7 O 3 ) 5 (phen)(H 2 O)] (Ln = Sm 1, Eu 2, Tb 3, Nd 4, Ho 5, Er 6; C 8 H 7 O 3 = 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 Ln III ions, which are mainly attributed to the ef-