Crystal structure of tris(2,2′-bipyridine)cobalt(II) bis(1,1,3,3-tetracyano-2-ethoxypropenide)

Polynitrile anions are known for their ability to combine with transition metals and co-ligands to form ternary systems. Here we report on the crystal structure of tris(2–2′-bipyridine)cobalt(II) bis(1,1,3,3-tetracyano-2-ethoxypropenide).


Chemical context
Ternary complexes of transition metals are mixed complexes where the transition-metal center is coordinated by more than one type of ligand (Gaamoune et al., 2010;Setifi et al., 2016;Yuste et al., 2009). Organic polynitrile anions are among the compounds able to form this type of complex. In addition to their ability to create original structures and different coordination modes, these organic anions exhibit interesting behaviour thanks to their high electronic delocalization (Thé tiot et al., 2003;Setifi et al., 2016) and magnetic properties (Benmansour et al., 2008(Benmansour et al., , 2010. Several studies of polynitrile ternary complexes with different transition metals and different co-ligands have been realized (Benmansour et al., 2008;Gaamoune et al., 2010;Setifi et al., 2013Setifi et al., , 2014bSetifi et al., , 2017Addala et al., 2015). To synthesize such types of complexes we chose 2,2 0 -bipyridine as co-ligand and cobalt(II) as the transition metal, in view of its promising applications in therapy and imaging, as well as in dye-sensitized solar cells (Renfrew et al., 2017;Yum et al., 2012). The synthesis and structural study of the title compound (I) is reported here.

Structural commentary
The asymmetric unit of the title compound (I) is illustrated in Fig. 1, and selected bond distances and angles are given in Table 1. The complex salt consists of half a tris(2,2 0 -bipyridine)cobalt(II) cation, the Co II ion being located on a twofold rotation axis, and a 1,1,3,3-tetracyano-2-ethoxypropenide (tcnoet À ), anion. The cobalt ion is ligated by the N atoms of the 2,2 0 -bipyridine ligands forming a slightly distorted octahedral coordination sphere; the Co1-N bond lengths vary from 2.122 (3) to 2.148 (3) Å . In the bpy (2,2 0bipyridine; N1/N2/C1-C10) unit, the pyridine rings are inclined to each other by 10.40 (16) , while in the other bpy unit (involving atom N3) bisected by a twofold rotation axis the pyridine rings are coplanar. The observed distortion of the Co II coordination sphere is probably the consequence of the hydrogen bonding between the [Co(C 10 H 8 N 2 ) 3 ] 2+ cation and the flexible tcnoet À anion (see Supramolecular features).

Supramolecular features
The crystal packing of (I) is illustrated in Fig. 2. It can be described as an infinite three-dimensional association of the structural units linked by C-HÁ Á ÁN hydrogen bonds and C-HÁ Á Á and C NÁ Á Á interactions; details of these intermolecular interactions are given in Table 2.
The cations are surrounded by six tcnoet À anions linked by eight C-HÁ Á ÁN hydrogen bonds as shown in Fig. 3; the various symmetry codes are give in the figure caption. In the equatorial plane of the cobalt octahedron, two of the six tcnoet À anions are doubly connected to the cationic units (N6, N7 and symmetry equivalents) via C8-H8Á Á ÁN7 iii ; C11 i -H11 i Á Á ÁN6 iii and their symmetric C8 i -H8 i Á Á ÁN7 iv ; C11-H11Á Á ÁN6 iv . Four tcnoet À anions are linked to atoms N4 and N5 (and symmetry equivalents) via C7-H7Á Á ÁN4 iv , C2-H2Á Á ÁN5 v , C7 i -H7 i Á Á ÁN4 ii and C2 i -H2 iÁ Á Á N5 vii . One of the anions plays the role of a donor in the structural linkage. Indeed, one tcnoet À anion is linked by an NÁ Á ÁH-C interaction to the same [Co(C 10 H 8 N 2 ) 3 ] 2+ unit (via N6Á Á ÁH11 iii -C11 iii and N7Á Á ÁC8 ii -H8 ii ) and to two other cationic units by N4Á Á ÁH7 i -C7 i and N5Á Á ÁH2 iv -C2 iv interactions. This environment where the negative charge is delocalized over the central propenide unit as well as into the cyano groups is

Figure 2
A view along the b axis of the crystal packing of compound (I). Table 2 Hydrogen-bond geometry (Å , ).

Figure 1
The independent components of compound (I), showing the atomnumbering scheme [symmetry code: (i) Àx + 1, y, Àz + 1 2 ]. Displacement ellipsoids are drawn at the 50% probability level. The hydrogen atoms have been omitted for clarity. illustrated in Fig. 4. The various symmetry codes are give in the figure caption.
The crystal structure of (I) is reinforced by the presence of a C-HÁ Á Á interaction involving the methyl group of the propenide unit of the anion and the centroid of pyridine ring (N1/C1-C5) of the cation (C24-H24BÁ Á ÁCg1 vi ; see Table 2), and an anionÁ Á Á interaction between the centroid of pyridine ring (N2/C6-C10) of the cation and the nitrogen atom N4 of the anion (C18-N4Á Á ÁCg2; see Table 2).

Database survey
A search in the Cambridge Structural Database (CSD, version 5.39, last update August 2018; Groom et al., 2016) using the query 1,1,3,3-tetracyano-2-ethoxypropenide gave 29 hits. 17 of these have the tcnoet À anion associated with an organic cation to form a salt-like compound (Setifi et al., , 2014a. The others have the anion associated to the metal ion acting as a coordinating ligand (Setifi et al., , 2013(Setifi et al., , 2017Addala et al., 2015;Gaamoune et al., 2010). The closest structure to (I) found in this investigation is tris(2,2 0 -bipyridine)iron(II) bis(1,1,3,3-tetracyano-2-ethoxypropenide) dihydrate (II) (CDS refcode CODZUS; Setifi et al., 2014b). The structural representation of (I) and (II) along the b axis points out some similarities in the cationic positions. However, in compound (II) the water molecule links the tcnoet À anion and the iron aggregate via O-HÁ Á ÁN hydrogen bonds, forming chains, whereas in (I) the cation is directly linked to the anion via C-HÁ Á ÁN hydrogen bonds forming a three-dimensional structure. There are nostacking interactions in either compound, but in contrast to compound (I), compound (II) does not display any anionÁ Á Á interactions. In the anion of (II), the mean planes of the N C-C-C N moieties are inclined to each other by ca 28.1 compared to 31.7 (3) in (I).

Tris(2,2′-bipyridine)cobalt(II) bis(1,1,3,3-tetracyano-2-ethoxypropenide)
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.