Refined Crystal Structure and Idealized Structure of Mixed-Valent Eu4F5(CN2)2: Transition Possible

The new europium fluoride carbodiimide Eu4F5(CN2)2 was synthesized by solid state reaction from mixtures of EuF3 and Li2(CN2) at 700 °C. The crystal structure as refined by single crystal X-ray diffraction (P4̅21c, no. 114, a = 16.053(1) Å, c = 6.5150(6) Å, Z = 8) reveals three crystallographically distinct [NCN]2– ions in the structure of mixed-valent Eu4F5(CN2)2. The presence of one Eu3+ and three Eu2+ per formula unit Eu4F5(CN2)2 is confirmed by magnetic measurements and 151Eu–Mössbauer spectroscopy. The arrangement of Eu ions and gravity centers of [NCN]2– ions in the structure of Eu4F5(CN2)2 follow the motif formed by atoms in the CuAl2-type structure. A possible high-symmetry structure of Eu4F5(CN2)2 is discussed on the basis of a group-subgroup scheme.