Crystal structure of high-spin tetraaquabis(2-chloropyrazine-κN 4)iron(II) bis(4-methylbenzenesulfonate)

Between the tosylate anions and the octahedral complex cations consisting of FeII, four aqua and two N-bound 2-chloropyrazine ligands, weak O—H⋯O as well as π–π interactions play important roles in the molecular self-assembly, resulting in the formation of a three-dimensional structure.


Chemical context
Transition metal complexes containing pyrazine or substituted pyrazines as ligands are of current interest due to their supramolecular arrangements and the probability of being spin-crossover compounds. Spin crossover, sometimes referred to as a spin transition or a spin equilibrium behaviour, is a phenomenon that occurs in some metal complexes wherein the spin state of a compound changes via influence of external stimuli such as temperature, pressure, light irradiation, magnetic field or guest effects (Gü tlich & Goodwin, 2004). As a result of the appearance of such features as thermochromic effects, magnetic susceptibility changes, changes of cell volume, etc. that accompany the molecular switching between high-spin and low-spin states, they can be applied in the development of micro-thermometers and photonic devices (Gural'skiy et al., 2012). ISSN 2056-9890 Aromatic ligands bearing two or more N atoms are known for their ability to form different coordination polymers and molecular complexes. Thus, a number of mononuclear highspin Fe II complexes with substituted pyrazines have been reported recently (Shylin et al., 2015). These heterocyclic ligands are also known for their ability to create threedimensional metal-organic framework structures, so called analogues of Hofmann clathrates with general formula Mn, Fe, Co, Ni, and L = pyrazine) in which the small-sized thiocyanate anions are terminally N-bound and therefore not involved in any magnetic exchange interactions are also known (Wriedt & Nä ther, 2011). Although 2-chloropyrazine could possess a N,N 0 -manner of coordination, it is frequently found to act as a monodentate ligand due to the bulky chlorine atom being in direct proximity to one of the nitrogen atoms (Wö hlert & Nä ther, 2013).
In this paper, we report on the crystal structure of [Fe II (C 4 H 3 ClN 2 ) 2 (H 2 O) 4 ](C 7 H 7 O 3 S) 2 containing a cationic iron(II) complex with 2-chloropyrazine and aqua ligands, and tosylate as an anion.

Structural commentary
The structure of the title compound consists of a complex cation [Fe(2-chloropyrazine) 2 (H 2 O) 4 ] 2+ and two tosylate anions. The Fe II atom, located on a special position with site symmetry 2/m, is sixfold coordinated by two N atoms of two symmetry-related 2-chloropyrazine ligands occupying the axial positions and four O atoms of four H 2 O molecules forming the equatorial plane (Fig. 1) The structure of the cationic and anionic components in the title salt. Displacement ellipsoids are drawn at the 50% probability level. Hydrogen bonds are indicated by dashed lines. [Symmetry codes: (i) 1 À x, Ày, 1 À z; (ii) 1 À x, y, 1 À z; (iii) x, Ày, z; (iv) x, 1 À y, z; (v) 1 À x, À1 + y, 1 À z.]

Figure 2
The crystal structure of the title compound, showing hydrogen bonds as dashed cyan lines andcontacts as green lines. Colour key: orange Fe, yellow S, blue N, grey C, green Cl, red O and white H. Table 1 Hydrogen-bond geometry (Å , ). Symmetry code: (i) Àx þ 1; y; Àz þ 2.

Supramolecular features
In the title compound, the crystal packing is stabilized by O1-H1AÁ Á ÁO2 and O1-H1BÁ Á ÁO3 i hydrogen bonds (Table 1) between the complex cations and the counter-anions (Figs. 1 and 2). Only two O atoms of the tosylate anion are involved in hydrogen bonding. Additional -stacking interactions (for numerical details, see: Table 2) between the pyrazine and benzene rings of the tosylate anion contribute to the stabilization (Fritsky et al., 2004) of the three-dimensional network (Fig. 2).

Synthesis and crystallization
Crystals of the title compound were obtained by adding 2chloropyrazine (0.046 g, 0.4 mmol) to Fe(OTs) 2 Á6H 2 O (0.096 g, 0.2 mmol) (OTs = p-toluenesulfonate) and ascorbic acid (0.001 g) in water (5 ml). After seven days this yielded colourless blocks of the title compound that were collected, washed with water and dried in air. Yield 0.090 g (64%).

Refinement
Crystal data, data collection and structure refinement details are summarized in