Synthesis, structure and properties of a tetranuclear europium(III) complex based on 9,9-dimethylfluorene-2,7-diphosphonic acid

One tetranuclear europium(III) phosphonate complex [Eu₂(H ₄MFDP)(H₃MFDP)₄(H₂MFDP)(H ₂O)₄]·13.5H₂O (EuMFDP), has been prepared by reactions of the new ligand 9,9-dimethylfluorene-2,7-diphosphonic acid (H₄MFDP) with europium(III) nitrates. The crystal structure of complex EuMFDP has been determined using single-crystal X-ray diffraction. It features a strip-like tetranuclear structure, in which four ligands and four Eu(III) ions constitute the core. Interestingly, the four ligands in the core possess paddle-like arrangement. Although the free ligand H₄MFDP exhibits the emission centered at 333 nm and 438 nm upon excitation at 310 nm, complex EuMFDP shows only very weak characteristic emission of Eu(III) ions, probably due to the strong quenching effect of OH vibration. The thermal property of EuMFDP has also been studied.