Mixed crystal of bis(ammonium/oxonium) tetraaqua-μ3-fluorido-dodecakis(μ2-trifluoroacetato)octahedro-hexaytterbiate(III) tetrahydrate, [(NH4)1–x (H3O) x ]2[Yb6F8(O2CCF3)12(H2O)4]·4H2O (x = 1/4), containing a hexanuclear ytterbium(III) carboxylate complex with face-capping fluoride ligands and comprising an unusual kind of substitutional disorder

Abstract

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, [(NH4)1–x (H3O) x ]2[Yb6F8(O2CCF3)12(H2O)4]·4H2O (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 μ3-face-capping fluorido ligands. The main structural features of its [Yb6F8] 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.