Fluoride crystal structures. Part 29. Tetraethylammonium tetrafluoro(2-methylpyridine N-oxide)peroxotantalate(V): an example of pentagonal bipyramidal seven-co-ordination

Abstract

The structure of the title compound has been determined by the heavy-atom method from 1 676 reflections, measured with a diffractometer, and refined by full-matrix least-squares methods to R 0.061. Crystals are monoclinic, space group Cc, a= 10.04 (2), b= 13.76(2), c= 28.49(3)Å, β= 102.4(3)°, Z= 8. In the two crystallographically independent anions of the structure, which have the [Metal(bidentate)(unidentate)₅]^x± stoicheiometry, a seven-co-ordinate tantalum atom is at the centre of a pentagonal bipyramid; the pentagonal plane comprises two fluorine atoms (mean Ta–F 1.95 Å), the peroxo-group (mean Ta–O 1.92 Å), and the ligand oxygen atom (mean Ta–O 2.20 Å). The two capping positions are occupied by fluorine atoms (mean Ta–F 1.94 Å). The two independent cations were refined as rigid-groups and are not disordered.