Mixed crystal of bis­(ammonium/oxonium) tetra­aqua-μ(3)-fluorido-dodeca­kis­(μ(2)-tri­fluoro­acetato)octa­hedro-hexa­ytterbiate(III) tetra­hydrate, [(NH(4))(1–x )(H(3)O)( x )](2)[Yb(6)F(8)(O(2)CCF(3))(12)(H(2)O)(4)]·4H(2)O (x = 1/4), containing a hexa­nuclear ytterbium(III) carboxyl­ate complex with face-capping fluoride ligands and comprising an unusual kind of substitutional disorder

The reaction of ytterbium metal with ammonium tri­fluoro­acetate in liquid ammonia resulted in a green substance comprising a substantial amount of ytterbium(II) tri­fluoro­acetate that is a useful precursor for the oxidative synthesis of the new ytterbium(III) compound, [(NH(4))(1–x )(H(3)O)( x )](2)[Yb(6)F(8)(O(2)CCF(3))(12)(H(2)O)(4)]·4H(2)O (x = 1/4), in aqueous tri­fluoro­acetic acid. This mixed ammonium/oxonium crystalline solid is the first example of a substance containing an octa­hedro-hexa­nuclear ytterbium(III) complex with μ(3)-face-capping fluorido ligands. The main structural features of its [Yb(6)F(8)] core are non-bonding Yb⋯Yb distances and Yb—F bond lengths of 3.7576 (3)–3.9413 (5) and 2.2375 (17)–2.3509 (17) Å, respectively. Yb—O bond lengths involving the O atoms of O,O′-bridging carboxyl­ato ligands and vertex-substituting aqua ligands are in the ranges 2.23 (4)–2.329 (2) and 2.448 (2)–2.544 (3) Å, respectively. These bond lengths are in accordance with expectations, taking into account lanthanoid contraction. Inter­estingly, there is a significant ammonium versus oxonium ion site dependence, not only of the hydrate water mol­ecule positions within the solid’s hydrogen-bonding framework, but also of the coordination sites of one carboxyl­ato and one aqua ligand in the hexa­nuclear complex.