catena-Poly[bis(μ-2,2′-bipyridin-6-olato)-κ3N,N′:O;O:N,N′-dicopper(I,II) [[tetrafluoridoniobium(V)]-μ-oxido]]

A novel copper-niobium oxyfluoride, {[Cu-2(C10H7N2O)(2)]-[NbOF4]}(n), has been synthesized by a hydrothermal method and characterized by elemental analysis, EDS, IR, XPS and single-crystal X-ray diffraction. The structural unit consists of one C-2-symmetric [NbOF4](-) anion and one centrosymmetric coordinated [Cu-2(obpy)(2)](+) cation (obpy is 2,2'-bipyridin-6-olate). In the [NbOF4](-) anion, each Nb-V metal centre is five-coordinated by four F atoms and one O atom in the first coordination shell, forming a square-pyramidal coordination geometry. These square pyramids are then further connected to each other via trans O atoms [Nb-O = 2.187 (3) angstrom], forming an infinite linear {[NbOF4](-)} n polyanion. In the coordinated [Cu-2(obpy)(2)](+) cation, the oxidation state of each Cu site is disordered, which is confirmed by the XPS results. The disordered Cu sites are coordinated by two N atoms and one O atom from two different obpy ligands. The [NbOF4](-) and [Cu-2(obpy)(2)](+) units are assembled via weak C-H center dot center dot center dot F hydrogen bonds, resulting in the formation of a three-dimensional supramolecular structure. pi-pi stacking interactions between the pyridine rings [centroid-centroid distance = 3.610 (2) angstrom] may further stabilize the crystal structure.