Crystal structure of hexakis(dimethyl sulfoxide-κO)manganese(II) tetraiodide

The crystal structure of hexakis(dimethyl sulfoxide-κO)manganese(II) tetraiodide is isotypic with the Co, Ni, Cu and Zn analogues.

The title salt, [Mn(C 2 H 6 OS) 6 ]I 4 , is made up from discrete [Mn(DMSO) 6 ] 2+ (DMSO is dimethyl sulfoxide) units connected through non-classical hydrogen bonds to linear I 4 2À tetraiodide anions. The Mn II ion in the cation, situated on a position with site symmetry 3., is octahedrally coordinated by O atoms of the DMSO molecule with an Mn-O distance of 2.1808 (12) Å . The I 4 2À anion contains a neutral I 2 molecule weakly coordinated by two iodide ions, forming a linear centrosymmetric tetraiodide anion. The title compound is isotypic with the Co, Ni, Cu, and Zn analogues.

Chemical context
Inorganic-organic hybrid compounds have attracted significant attention owing to their fascinating structural, optical and electrical properties (Stranks & Snaith, 2015). In particular, CH 3 NH 3 PbX 3 hybrids obtained from PbX 2 and CH 3 NH 3 X (X = I, Br, Cl) are interesting due to their high absorption coefficient and applications in optoelectronics (Stoumpos & Kanatzidis, 2015). In general, this family of materials adopts the perovskite ABX 3 structure type, where A is an organic cation, which is surrounded by twelve nearest X halide anions, and B is a metal cation (Grä tzel, 2014). There are continuous efforts on replacing Pb in these hybrids due to its toxicity (Wang et al., 2015). In the present work, one such attempt was made to produce a hybrid between CH 3 NH 3 I and MnI 2 . However, we obtained instead the title salt [Mn(DMSO) 6 ]I 4 (DMSO is dimethyl sulfoxide), and report here its crystal structure.

Structural commentary
The title salt is the first compound with a [Mn(DMSO] 2+ cation and a linear tetraiodide anion. The Mn 2+ cation is ISSN 2056-9890 bound to the O atoms of six DMSO molecules arranged in an octahedral configuration (Fig. 1). Owing to the 3. site symmetry of the metal cation, the deviations of corresponding angles from ideal values are minute [range cis O-Mn-O angles 86.28 (4)-93.73 (4) ; all trans angles 180 ]. The Mn-O bond length is 2.1808 (12) Å . The four I atoms are arranged in a linear fashion. The bond length between the two central I atoms is 2.8460 (5) Å ; this inner I 2 moiety is rather weakly bonded to two terminal I À anions with a bond lengths of 3.3251 (6) Å . This confirms the existence of a linear, centrosymmetric polyiodide ion I 4 2À , consistent with previous reports (Long et al., 1999). Both inner and terminal bond lengths of the I 4 2À anion are comparable with values found in [Cu(NH 3 ) 4 ]I 4 (Dubler & Linowsky, 1975) or other [M(DMSO) 6 ]I 4 compounds (Long et al., 1999;Tkachev et al., 1994;Garzó n-Tovar et al., 2013a,b). . The tetraiodide counter-anions are located between the rows (Fig. 3). An extended threedimensional supramolecular network is accomplished through non-classical hydrogen bonding between H atoms of the DMSO molecules and the linear I 4 2À polyiodide anions. Table 1 collates numerical details of these C-HÁ Á ÁI interactions.

Database survey
A number of transition metals have been reported to form complexes with DMSO (Meek et al., 1960). However, reports on Mn complexes of DMSO with halide anions are scarce, as revealed by a search in the Cambridge Structural Database (Groom et al. 2016). Recently Glatz et al. (2016) reported the crystal structure of [Mn(DMSO) 6 ]I 2 . In particular, polyiodide salts are interesting compounds owing to their high conductivity and non-linear properties that are predominantly observed in sulfur-rich compounds (Long et al., 1999). The structure of the title compound is isotypic with the Co, Ni, Cu, The molecular components of the title compound, with displacement ellipsoids drawn at the 50% probability level. H atoms have been omitted for clarity. [Symmetry code: ( 0 ) 4 3 À x, 2 3 À y, 5 3 À z.]  Packing diagram of the title compound. Non-classical hydrogen bonds are shown as dashed lines. Table 1 Hydrogen-bond geometry (Å , ). Symmetry codes: (i) Àx þ 5 3 ; Ày þ 4 3 ; Àz þ 4 3 ; (ii) Àx þ 1; Ày þ 1; Àz þ 1.

Synthesis and crystallization
The title manganese salt was formed in the course of the targeted synthesis of a hybrid compound between CH 3 NH 3 I and MnI 2 . Anhydrous MnI 2 and dimethyl sulfoxide (DMSO) were purchased from Alfa-Aesar and Sigma-Aldrich, respectively. CH 3 NH 3 I was purchased from Dyesol. The precursors were used without further purification. The title manganese salt was synthesized by adding anhydrous MnI 2 (308.7 mg) and CH 3 NH 3 I (158.9 mg) in a glass vial. Then 2 ml DMSO was added to the vial (capped afterwards) and stirred at 353 K for 24 h inside a nitrogen glove box. A reddish-black solution was observed after 24 h which was cooled down to room temperature and left for 7 d undisturbed. Single crystals of the title compound were obtained as the only solid product after 7 d. The crystals were removed from the vial and dried under nitrogen flow.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The methyl H atoms were treated as riding and U iso (H) values set at 1.5U eq (C).  SHELXL2014 (Sheldrick, 2015b); molecular graphics: DIAMOND (Brandenburg, 2006); software used to prepare material for publication: publCIF (Westrip, 2010). 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.