Crystal structure of di-μ-chlorido-bis{chlorido[(−)-5,6-pinenebipyridine]cobalt(II)} aquadichlorido[(−)-5,6-pinenebipyridine]cobalt(II)

The crystal structure of the title compound comprises two different CoII complexes, one mononuclear and the other dinuclear, with the enantiopure, bidentate (−)-5,6-pinenebipyridine ligand. All three coordination polyhedra around the CoII cations are distorted trigonal bipyramids.

The crystal structure of [Co 2 Cl 4 (C 17 H 18 N 2 ) 2 ][CoCl 2 (C 17 H 18 N 2 )(H 2 O)] or [Co(L)Cl(-Cl)] 2 [Co(L)(Cl) 2 (OH 2 )], where L is the enantiopure bidentate ligand (À)-5,6-pinenebipyridine (C 17 H 18 N 2 ), has been determined. Crystals suitable for X-ray structure analysis were obtained by slow evaporation of an ethanolic solution containing equimolar amounts of L and CoCl 2 Á6H 2 O. The Co II cations all have a coordination number of five, and in each case the coordination polyhedron is a trigonal bipyramid. The Co-N bonds lengths range from 2.037 (7) to 2.195 (7) Å , and Co-Cl bonds lengths range from 2.284 (2) to 2.509 (2) Å . The asymmetric unit contains two discrete complexes, one dinuclear and the other mononuclear. Between the two molecules, two types of intermolecular interactions have been evidenced:stackings involving the bipyridine units, and O-HÁ Á ÁCl hydrogen bonds between the hydrogen atoms of the aqua ligand coordinating to the mononuclear complex and the nonbridging chlorido ligand coordinating to the dinuclear molecule. These interactions lead to a two-dimensional supramolecular arrangement parallel to the ab plane.

Chemical context
Single-molecule magnets (SMMs) are metal-organic compounds that are superparamagnetic below a blocking temperature. It is important to note that this type of magnetism has a molecular origin, instead of the more traditional bulk-originated magnetism (Zhu et al., 2013). Below the blocking temperature, a SMM exhibits magnetic hysteresis. In order to obtain a coordination compound behaving as an SMM, a paramagnetic metal cation has to be used, for example Co II (Lang et al., 2019). Moreover, the use of chiral ligands for these paramagnetic metal cations can lead to predetermination of their chirality and thus to the synthesis of magnetochiral materials (Liu et al., 2018). The enantiomers of 5,6-pinene bipyridine (C 17 H 18 N 2; L) and their derivatives have the ability to predetermine the chirality of d and f metal cations (Lama et al., 2008;Mamula & von Zelewsky, 2003).
Within a current project we are investigating the metal complexes obtained with paramagnetic metal cations, i.e. Co II , and report here the crystal structure of [Co(L)Cl(-Cl)] 2 [Co(L)(Cl) 2 (OH 2 )] (1) .

Structural commentary
The asymmetric unit of (1) comprises two discrete complexes (Fig. 1). The dinuclear complex possess two bidentate terminal (À)-5,6-pinenebipyridine ligands coordinated by two distinct Co II cations (Co1, Co2) via their nitrogen atoms. The two Co II cations are linked by two bridging chlorido ligands (Cl2, Cl3). Each coordination sphere is completed by two additional terminal chlorido ligands (Cl1, Cl4), leading to a coordination number of 5 in each case. The mononuclear complex (Co3) also features a Co II cation with a coordination number of 5. In this case, one bidentate (À)-5,6-pinenebipyridine, two terminal chlorido ligands (Cl5; Cl6) and an aqua ligand bind to the Co II cation. The two types of complexes interact via an O-HÁ Á ÁCl hydrogen bond (indicated with a dashed line in Fig. 1; Table 1) between one hydrogen atom belonging to the aqua ligand of the mononuclear complex and a terminal chlorido ligand belonging to the dinuclear complex. The other hydrogen atom of the water molecule forms another hydrogen bond with a dinuclear complex belonging to a neighbouring molecule (vide infra).
The geometric parameters for the trigonal-bipyramidal coordination environments are similar for the three Co II cations. In order to compare their coordination polyhedra, the values for the parameter were calculated. For a perfect trigonal-bipyramidal arrangement is 1, and for a perfect square-pyramidal arrangement is 0 (Addison et al., 1984). The polyhedron around the cation in the mononuclear complex (Co3 in Fig. 2) is the closest to trigonal-bipyramidal ( = 0.78). However, those of the cations of the dinuclear complex are not so different ( = 0.69 for Co1, = 0.64 for Co2, see Fig. 2).

Supramolecular features
In the crystal, hydrogen-bonding interactions occur between the dinuclear and mononuclear complexes, leading to a supramolecular zigzag chain extending parallel to the b axis Symmetry code: (i) Àx þ 1; y þ 1 2 ; Àz þ 1 2 .

Figure 2
The trigonal-bipyramidal coordination spheres of the Co II cations in (a) the dinuclear complex and (b) the mononuclear complex. Noncoordinating atoms are omitted for clarity.

Figure 1
The molecular structures of the two complexes present in (1), with the O-HÁ Á ÁCl hydrogen bond shown as a dashed line. Displacement ellipsoids are set at the 30% probability level. Carbon-bound hydrogen atoms are omitted for clarity. (Fig. 3). The hydrogen atoms of the aqua ligand of the mononuclear complex form hydrogen bonds with the terminal chlorido ligands belonging to the dinuclear complex. The bond lengths and angles (Table 1), are in the expected ranges for this type of interaction (Steiner, 2002). This arrangement is stabilized bystacking interactions, which are responsible for the cohesion of the structure by forming layers of alternating dinuclear and mononuclear complexes extending parallel to the ab plane (Fig. 4). Neighbouring dinuclear complexes are connected viainteractions between the bipyridine units whereby two -interactions are established between the two pyridine rings annelated to the pinene moiety and the two 'free pyridines' (the pinene-free pyridine rings of the pinene-bipyridine ligands). The distances between the aromatic centroids are 3.793 (5) Å (slippage 0.987 Å ) and 3.940 (5) Å (slippage 1.278 Å ). The two pinene bipyridine ligands belonging to neighbouring dinuclear complexes are connected via their 'free' pyridine entity to the 'free' pyridine entities of the pinenebipyridine ligands of the mononuclear complexes. The distances [3.625 (5) Å with a slippage of 1.137 Å , and 3.718 (5) Å with a slippage of 1.503 Å ] are typical for these kinds of interactions (Robin & Fromm, 2006).
Considering all the intermolecular interactions (hydrogen bonds andstackings), the two-dimensional supramolecular arrangement can be drawn schematically as shown in Fig. 5.

Figure 5
Schematic representation of the two-dimensional arrangement in the crystal structure of (1). [Symmetry codes: (iv) Àx, 1 2 + y, 1 2 À z; (v) À1 + x, y, z.] (250 mg, 1 mmol) in ethanol (20 ml) and stirred for a few minutes. A fraction of the total volume of the resulting blue solution (about 3 ml) was transferred into a test tube and left to evaporate slowly under ambient conditions. Within a few days, violet single crystals were harvested.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The C-bound H atoms were placed in geometrically idealized positions (C-H = 0.95-1.00 Å ) while those attached to O were positioned from a difference-Fourier map, then refined for a few cycles to ensure that reasonable displacement parameters could be achieved. Their coordinates were adjusted to give O-H = 0.87 Å . All hydrogen atoms were refined using a riding model with isotropic displacement parameters 1.2-1.5 times those of the parent atoms.   program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL (Sheldrick, 2015b); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: PLATON (Spek, 2020) and 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.