Crystal structure of catena-poly[[diiodidomercury(II)]-μ-2,2′-dithiobis(pyridine N-oxide)-κ2 O:O′]

In the title compound, HgI2 units are joined by 2,2′-dithiobis(pyridine N-oxide) spacer ligands in a μ-κ2 O:O′ coordination mode, resulting in a one-dimensional coordination polymer extending in the [010] direction.


Chemical context
Research into one-dimensional coordination polymers has been an active field of research, not only due to the usually easy and straightforward synthesis, but also due to interesting structural features and introduction of these compounds as new materials such as coordination polymeric gels, fibres and nanostructures (Leong & Vittal, 2011). In the context of our structural studies on coordination polymers and discrete metallosupramolecular assemblies containing disulfide-based bridging (spacer) ligands (Seidel et al., 2013), 2,2 0 -dithiobis-(pyridine N-oxide) has attracted our interest. Recently, we reported one-dimensional coordination polymers from 2,2 0dithiobis(pyridine N-oxide), and Zn II and Cd II halides (Seidel et al., 2017), which represented the first structurally characterised coordination polymers containing 2,2 0 -dithiobis-(pyridine N-oxide) as a spacer ligand (i.e. involving both pyridine N-oxide moieties as coordinating groups). As a continuation of this work, we herein report the crystal structure of a one-dimensional coordination polymer formed from 2,2 0 -dithiobis(pyridine N-oxide) and HgI 2 . ISSN 2056-9890

Structural commentary
The title compound, (I), is a one-dimensional coordination polymer consisting of HgI 2 units joined by 2,2 0 -dithiobis-(pyridine N-oxide) as bridging ligands in a -2 O:O 0 coordination mode. Fig. 1 depicts the repeat unit of the coordination polymer and the coordination sphere of the Hg II ion. The Hg II ion is tetracoordinated by two iodide ligands and two O atoms of the bridging ligands, with a coordination sphere that is best described as a severely distorted tetrahedron or a seesaw form (Yang et al., 2007). The C2-S1-S2-C7 torsion angle is 77.2 (2) , which corresponds to the P form of the axially chiral gauche conformation of the disulfide-based ligand in the chosen asymmetric unit. The dihedral angle between the planes of the aromatic N1/C2-C6 and N2/C7-C11 rings is 71.8 (2) .
The strand of the coordination polymer propagates along a 2 1 -screw axis parallel to the b axis (Fig. 2). Within a single strand, 2,2 0 -dithiobis(pyridine N-oxide) exhibits exclusively either the right-handed P or the left-handed M conformation, i.e. the bridging ligands in each coordination polymer chain are homochiral. The centrosymmetric crystal structure (space group P2 1 /n) features, however, both enantiomeric conformations in adjacent strands, as shown in Fig. 2.

Database survey
A search for structures containing 2,2 0 -dithiobis(pyridine N-oxide) in the Cambridge Structural Database (CSD; Groom et al., 2016) via the WebCSD interface (Thomas et al., 2010) in February 2018 revealed the aforementioned one-dimensional coordination polymers containing Zn II and Cd II halide units (Seidel et al., 2017). In addition, there is an Na I coordination Two adjacent coordination polymer strands of the title compound, viewed along the [101] direction. P and M denote the handedness of the 2,2 0dithiobis(pyridine N-oxide) ligand in the chains. H atoms have been omitted for clarity. Table 1 Hydrogen-bond geometry (Å , ).

Synthesis and crystallization
A solution of 20 mg (0.044 mmol) HgI 2 in 2 ml of methanol was mixed with a solution of 12 mg (0.048 mmol) 2,2 0 -dithiobis(pyridine N-oxide) (Acros Organics) in 8 ml of methanol. The reaction mixture was left at room temperature and the solvent was allowed to evaporate slowly. Colourless crystals of (I) suitable for single-crystal X-ray analysis were obtained after ca four weeks.
After prolonged standing, colourless crystals of a second product appeared in the crystallization vessel, which were identified as [Hg 2 I 2 (C 5 H 4 NOS) 2 ] (C 5 H 4 NOS À is pyrithionate) in a preliminary X-ray analysis.

catena-Poly[[diiodidomercury(II)]-µ-2,2′-dithiobis(pyridine N-oxide)-κ 2 O:O′]
Crystal data Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.