Oxidation of europium with ammonium perfluorocarboxylates in liquid ammonia: pathways to europium(II) carboxylates and hexanuclear europium(III) fluoridocarboxylate complexes.

The novel coordination polymer [Eu(OCCF)(dmf)] (1) (dmf = ,-dimethylformamide) containing europium(II) and the two new compounds (NH)[EuF(OCCF)(CFCOOH)] (2) and (NH)[EuF(OCCF)(CFCOOH)]·8CFCOOH (3), both based on hexanuclear europiate(III) complexes, were synthesized from precursors with a Eu : Eu ratio >1, obtained by reaction of europium metal with ammonium perfluorocarboxylates in liquid ammonia. In the crystal structure of 1 the europium(II) ions are bridged by carboxylate groups and ,-dimethylformamide to form polymeric chains with Eu⋯Eu distances of 408.39(13)-410.49(13) pm. The compound crystallizes in the triclinic space group 1̄ ( = 2). To the best of our knowledge, this is the first example of a (solvated) perfluorocarboxylate containing a lanthanoid in a subvalent oxidation state. In the crystal structures of 2 and 3 the europium(III) ions are bridged by fluoride ions and carboxylate groups to form hexanuclear complex anions with an octahedral arrangement of the cations. The Eu⋯Eu distances are in the range of 398.27(15)-400.93(15) pm in 2 and 395.37(4)-399.78(5) pm in 3, respectively. Both compounds crystallize in the monoclinic space group type 2/ ( = 4) and are the first examples of -hexanuclear europium carboxylates for which fluoride is reported as a bridging ligand. In all compounds the oxidation state of europium was monitored Eu Mössbauer and photoluminescene spectroscopy.