Crystal structure of bis[tris(1,10-phenanthroline-κ2 N,N′)cobalt(II)] tetranitrate N,N′-(1,4-phenylenedicarbonyl)diglycine solvate octahydrate

The complex cation of the title compound includes one CoII atom with a distorted octahedral coordination environment defined by six N atoms from three bidentate phenanthroline ligands. The non-coordinating N,N′-(1,4-phenylenedicarbonyl)diglycine ligand links the cationic building blocks via C—H⋯O contacts and through lone-pair⋯π interactions. Further observed non-covalent interactions contribute to the consolidation of the supramolecular network.


Chemical context
In the past decades, the focus on metal-organic complexes which form coordination polymers of different dimensions has drawn much attention due to their interesting structures and physical and chemical properties. Application fields for these materials are in catalysis, in gas storage (Kitagawa et al., 2004), luminescence (Allendorf et al., 2015) and very recently as scintillation materials Doty et al., 2009;Perry et al., 2012). The structures of coordination polymers (Leong & Vittal, 2011;Yamada et al., 2013) often show various non-covalent intermolecular interactions and forces, and therefore are intimately connected with the field of supramolecular chemistry (Schneider, 2009) and self-assembly (Cook et al., 2013). Such non-covalent interactions are also of utmost importance in biological macromolecules like DNA, RNA and proteins (Salonen et al., 2011). They are typically observed in biochemical reactions as protein-ligand recognitions and are partly utilized in drug design (Meyer et al., 2003). Apart from classical and non-classical hydrogen bonding of the types O-HÁ Á ÁO, N-HÁ Á ÁO and C-HÁ Á ÁO, respectively, different -interactions of aromatic rings such asstacking, C-HÁ Á Á, ionÁ Á Á and lone-pairÁ Á Á play a crucial role in the assembly of metal-organic polymers. Nitrogen-containing heterocycles like bipyridine and phenanthroline are metalcoordinating, electron-deficient aromatic systems and predestined forstacking as -acceptors (Janiak, 2000). In addition, -donorÁ Á Áacceptor functions in different parts of an ISSN 2056-9890 aromatic molecule can lead to remarkable properties (Albrecht et al., 2010).
In previously synthesized transition metal complexes with N,N 0 -(1,4-phenylenedicarbonyl)diglycine as metal-linking ligand, zigzag chains are formed, constructing interpenetrating networks (see Database survey). In our synthetic approach, we offer such systems another electron-deficient bidentate aromatic ring system like phenanthroline or bipyridine in order to block parts of the coordination sphere of the metal atoms so that these zigzag chains are truncated or not formed at all. Thus, an alternative route for the resultant system lies in the use of the offered -interaction possibilities as well as in stacking interactions as a new linking mode. Recently, we have described the interactions of a cobalt(III) bipyridine complex with supramolecular synthons (Pook et al., 2014) as well as a precursor material (Pook et al., 2013) that both contain N,N 0 -(1,4-phenylenedicarbonyl)diglycine. The chosen ligand N,N 0 -(1,4-phenylenedicarbonyl)diglycine is a relatively rigid molecule with one sp 3 -hybridized methylene carbon atom that allows the acid moiety to rotate. Moreover, this ligand simultaneously possesses several coordination sites through the carboxylic group and the oxygen atom of the amide group. These functional groups can also be involved in hydrogen bonding and D-HÁ Á Á interactions.
In the present contribution we have determined the structure of a novel cobalt(II) coordination polymer with a noncoordinating N,N 0 -(1,4-phenylenedicarbonyl)diglycine solvent molecule linking two tris(phenanthroline)cobalt(II) cationic building blocks via the mentioned non-classical interactions.

Structural commentary
The molecular entities (Fig. 1) of the title compound include one Co II complex cation in which three bidentate phenanthroline ligands define a distorted octahedral coordination sphere. Distances and angles of this rather common cationic species, [Co(C 12 H 8 N 2 ) 3 ] 2+ , are well within expected ranges and are comparable to those found in the literature (Li et al., 2011;Geraghty et al., 1999). A crystallographic center of inversion is located at the centroid of the protonated and non-coordinating N,N 0 -(1,4-phenylenedicarbonyl)diglycine molecule. The asymmetric unit is completed by two non-coordinating nitrate counter-anions and four solvent water molecules. The N,N 0 -(1,4-phenylenedicarbonyl)diglycine molecule links two complex tris(phenanthroline-2 N,N 0 )cobalt(II) cations via lone-pairÁ Á Á interactions involving the carboxylic acid function and the phenanthroline aromatic system as well as C-HÁ Á ÁO contacts between the oxygen atom of the amide group and one phenanthroline ligand. Moreover,stacking interactions between different aromatic ring systems and C-HÁ Á Á as well as O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonding are observed and consolidate an extensive three-dimensional supramolecular network.

Figure 2
The crystal packing of the title structure in a view along the a axis. Selectedstacking and C-HÁ Á Á interactions are shown as dashed lines.

Figure 4
View of the anionÁ Á Á interaction and the extended network of O-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds with the embedded noncoordinating nitrate anion (N9/O4-O6) as well asstacking. O-HÁ Á ÁO contacts are indicated by red-white, C-HÁ Á ÁO by black andinteractions by dark-yellow dashed lines. Distances are given in Å .