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(O 2 CCF 3 ) 2 (dmf) 2 ] ∞ (1) (dmf = N , N -dimethylformamide) containing europium(II) and the two new compounds (NH 4 ) 2 [Eu 6 F 8 (O 2 CCF 3 ) 12 (CF 3 COOH) 6 ] (2) and (NH 4 ) 2 [Eu 6 F 8 (O 2 CC 2 F 5 ) 12 (C 2 F 5 COOH) 6 ]·8C 2 F 5 COOH (3), both based on hexanuclear europiate(III) complexes, were synthesized from precursors with a Eu 2+  : Eu 3+ 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 N , N -dimethylformamide to form polymeric chains with Eu 2+ ⋯Eu 2+ distances of 408.39(13)-410.49(13) pm. The compound crystallizes in the triclinic space group P 1̄ ( Z = 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 3+ ⋯Eu 3+ 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 P 2 1 / n ( Z = 4) and are the first examples of octahedro -hexanuclear europium carboxylates for which fluoride is reported as a bridging ligand. In all compounds the oxidation state of europium was monitored via 151 Eu Mössbauer and photoluminescene spectroscopy.