Pb6Co9(TeO6)5

Pb6Co9(TeO6)5, hexalead(II) nonacobalt(II) pentatellurate(VI), is isotypic with its nickel(II) analogue. The asymmetric unit contains two Pb atoms (site symmetries .2., ..2), four Co atoms (..2, ..2, 3.., 3.2) two Te atoms (..2, 3..) and six O atoms (all in general positions), with the Te and Co sites in octahedral coordination environments. The crystal structure can be subdivided into two types of layers parallel to (001). The first layer at z ≃ 0.25 is made up of edge-sharing [CoO6] and [TeO6] octahedra, with 1/6 of the octahedral holes not occupied. The second layer, situated at z ≃ 0, consist of an alternating arrangement of PbII atoms and of double octahedra that are made up from face-sharing [CoO6] and [TeO6] octahedra. The two types of layers are linked together through corner-sharing of [CoO6] and [TeO6] octahedra. The PbII atoms are situated in the cavities of the framework and are stereochemically active with one-sided [4]- and [6]-coordinations, respectively.


Christine Artner and Matthias Weil Comment
Single crystals of the title compound, Pb 6 Co 9 (TeO 6 ) 5 , were serendipitously obtained as a minority phase during phase formation studies in the system Pb II /Co II /Te VI /O intended on crystal growth of cubic Pb 2 CoTeO 6 .
The crystal structure of Pb 6 Co 9 (TeO 6 ) 5 is isotypic with its nickel analogue (Wedel et al., 1998) The crystal structure of Pb 6 Co 9 (TeO 6 ) 5 can be described in terms of (001) layers A at z ≈ 0.25 and B at z ≈ 0 that stack alternately along [100] ( Pb2 from 1.64 to 1.96 vu. The bond valence sum at O3 is also raised from 1.60 to 1.80 vu. Therefore the overall coordination of Pb1 might be described as [4 + 4] and that of Pb2 as [6 + 4] (Fig. 4).

Experimental
1.281 (5.7 mmol) PbO, 0.216 g (2.9 mmol) CoO and 0.914 g (5.7 mmol) TeO 2 were mixed and thoroughly ground and heated in an alumina crucible under atmospheric conditions during 6 h to 1023 K and held at that temperature for 48 h.
Then the furnace was shut-off. Several crystal phases could be identified from the cooled reaction mixture by singlecrystal diffraction: Dark blue isometric crystals of Pb 2 CoTeO 6 , dark-red (nearly black) block-like crystals of Pb 5 TeO 8 (Artner & Weil, 2012), colourless crystals of α-Al 2 O 3 and dark red crystals of Pb 6 Co 9 (TeO 6 ) 5 with a block-like shape.

Refinement
The highest remaining electron density was found 1.49 Å from atom Pb1 and the lowest remaining electron density 0.52 Å from atom Pb2. The refined Flack parameter indicates racemic twinning with an approximate ratio of 1:6 for the twin components.

Figure 1
The crystal structure of Pb 6 Co 9 (TeO 6 ) 5 in a projection along [010]. Displacement ellipsoids are drawn at the 90% probability level. Letters A and B indicate the two types of layers present in the structure.  Layer A (situated approximately at z ≈ 1/4) in the crystal structure of Pb 6 Co 9 (TeO 6 ) 5 . Colour code and probability of the displacement parameters as in Fig. 1.   The coordination spheres around the two lead atoms, considering bond lengths up to 3.5 Å; short Pb-O distances < 2.75 Å are given in black, emphasizing the one-sided [4]-coordination for Pb1 and [6]-coordination for Pb2. Longer bonds augmenting the coordination spheres are given in yellow. Probability of the displacement parameters as in Fig. 1.

hexalead(II) nonacobalt(II) pentatellurate(VI)
Crystal data   (10) Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq