Crystal structure and Hirshfeld surface analysis of trans-2,5-dimethylpiperazine-1,4-diium tetrachloridocobaltate(II)

In the title molecular salt, (C6H16N2)[CoCl4], the complete dication is generated by crystallographic inversion symmetry and the piperazine ring adopts a chair conformation with the pendant methyl groups in equatorial orientations. The complete dianion is generated by crystallographic twofold symmetry. In the crystal, the (C6H16N2)2+ and [CoCl4]2− ions are linked by N—H⋯Cl and C—H⋯Cl hydrogen bonds, thereby forming a two-dimensional supramolecular network.


Chemical context
Tetrachlorocobalt/copper (II) salts with organic cations, such as (C 6 H 10 N 3 ) 2 [CoCl 4 ] (Titi et al. 2020), [(CH 3 ) 2 NH 2 ] 2 [CoCl 4 ] (Pietraszko et al. 2006) and (C 7 H 7 N 2 S) 2 [CuCl 4 ] (Vishwakarma et al. 2017) have received attention due to their potential applications in the electronic, magnetic, optical and antimicrobial fields. In these materials, the negative charge on the inorganic complex ion is balanced by the organic groups, which usually act as structure-directing agents by the formation of N-HÁ Á ÁCl hydrogen bonds and significantly affect the structure and dimensionality of the supramolecular network.
As an extension of these studies, we now describe the synthesis, structure and Hirshfeld surface analysis of the title molecular salt, (I).

Figure 2
(a) Crystal packing in the structure of (I) along the crystallographic a axis. (b) View of a supramolecular layer along the b-axis direction.

Figure 3
Hydrogen-bonding interactions between cations and anions showing the ring patterns of weak interactions formed by N-HÁ Á ÁCl/C-HÁ Á ÁCl links.

Hirshfeld surface analysis
To further understand the different interactions and contacts in the crystal of (I), its Hirshfeld surface (HS) (McKinnon et al., 2004) was calculated. The d norm surface (Fig. 4) and the associated two-dimensional fingerprint plots (see supporting information) were calculated using CrystalExplorer 3.1 (Wolff et al., 2013;Spackman & Jayatilaka, 2009). This figure shows the areas mapped in the range from À0.480 to 1.048 of the asymmetric ion-pair surrounded by neighboring ions where we can see some of the closest intermolecular contacts. The large dark-red spots on the HS indicate close contact interactions, which are primarily responsible for significant hydrogen-bond contacts.

Synthesis and crystallization
A 1:1 mixture of trans-2,5-dimethylpiperazine and cobalt(II) chloride hexahydrate was dissolved in a solution of concentrated hydrochloric acid and the resulting solution was magnetically stirred for 1 h. After two weeks of evaporation, dark-blue prismatic crystals of (I) had formed, which were recovered by filtration and dried in air.

Figure 4
Hirshfeld surface of (I) mapped over d norm and the two-dimensional fingerprint plot for all interactions.

trans-2,5-Dimethylpiperazine-1,4-diium tetrachloridocobaltate(II)
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.