Two novel rare-earth metal complexes, namely, mononuclear Na4[EuIII(Dtpa)(H2O)]2 · 11.5H2O (I) and binuciear (NH4)4[EuIII(Dtpa)]2 · 10H2O (II) (H5Dtpa = diethylenetriamine-N,N,N′,N″,N″-pentaacetic acid), have successfully been synthesized and characterized by infrared spectrum, UV-Vis spectrum, fluorescence spectrum, thermal analysis, and single-crystal X-ray diffraction techniques. Since these two Eu(III) complexes have different counterions, causing different coordination environment, fluorescence spectrum analysis displays different fluorescence properties. X-ray diffraction reveals that the coordination polyhedra of both complexes adopt pseudo-D 3h tricapped trigonal prismatic conformation. However, I is a nine-coordinate mononuclear complex and crystallizes in the monoclinic crystal space group P21/n and II is a nine-coordinate binuciear complex and crystallizes in the triclinic crystal space group $$P\bar 1$$ . In addition, II has two independent binuciear structural units, [Eu(1)2(Dtpa)2] and [Eu(2)2(Dtpa)2]. Along the yz plane both [Eu(1)2(Dtpa)2] and [Eu(2)2(Dtpa)2] form a 1D chain structure, respectively. Further, along the y axis linking of each other forms a 2D planar structure.