Synthesis, Crystal Structure, and Characterization of the First Nb₃ Triangular Cluster Compound Bonded to Fluorine Ligands: Association of Nb₃IⁱFⁱ₃F^a₈L^a Units and Nb^IVL₆ Octahedra with L = O and F

The synthesis and the crystal structure of the first compound containing Nb3 triangular clusters bonded to fluorine ligands are presented in this work. The structure of Nb3IF7L(NbL2)0.25 with L = O and F, determined by single-crystal X-ray diffraction, is based on a Nb3IiFi3Fa8La unit and a NbL6 octahedron (tetragonal, space group I4/m, a = 13.8638(3) Å, c = 8.9183(2) Å, V = 1714.14(7) Å3, Z = 8). Two crystallographic positions (noted L5 and L6) are randomly occupied by fluorine and oxygen with two different F:O occupancies. These L ligands build an octahedral site for a single niobium atom, located between the units. The four L5 ligands of the NbL6 octahedron are shared with four Nb3 cluster units, while the two other L6 ligands are terminal. The Nb3 cluster is face-capped by one iodine and edge-bridged by three fluorine ligands. Two of the three niobium atoms constituting the cluster are bonded to three additional apical fluorine ligands, while the third one is bonded to two fluorines and one L5 ligand. The Nb3 cluster is linked to six adjacent ones via all the apical fluorine ligands. The developed formula of the unit is therefore Nb3IiFi3Fa-a8/2La according to the Schäfer and Schnering notation. The oxidation state of the single niobium and the random distribution of fluorine and oxygen on the two L sites will be discussed on the basis of structural analysis, the bond valence method, and IR and EPR measurements. The structural results will be compared to those of previously reported niobium compounds containing NbF6 or Nb(F,O)6 octahedra.