Crystal structure of a CoII coordination polymer with a dipyridyl ligand: catena-poly[[bis(nitrato-κ2 O,O′)cobalt(II)]-μ-N-(pyridin-2-ylmethyl)pyridine-3-amine-κ3 N,N′:N′′]

The CoII atom in the title compound is seven-coordinate, being bound to two pyridine N atoms, one amine N atom and four O atoms to form a distorted pentagonal–bipyramidal environment. Each dipyridyl-type ligand links the CoII atoms into polymeric zigzag chains, which are connected via intermolecular π–π stacking interactions and N/C—H⋯O hydrogen bonds.

The asymmetric unit of the title compound, [Co(NO 3 ) 2 L] n , L = N-(pyridine-2ylmethyl)pyridine-3-amine (C 11 H 11 N 3 ), contains one Co II centre, two nitrate anions and one L ligand in which the C py -C-N-C py moiety adopts a trans conformation with a torsion angle of À173.1 (3) Å . The coordination geometry of the Co II atom is a distorted pentagonal bipyramid. One amine N atom from the L ligand and four O atoms from two 2 -nitrato ligands form the basal plane and two pyridyl N atoms from two symmetry-related L ligands occupy the apical positions  ]. The displacement of the central Co II atom from the basal plane (r.m.s. deviation = 0.085 Å ) is 0.1491 (12) Å . Each bidentate nitrate group is bonded asymmetrically to the cobalt atom in an chelating fashion. The Co II ions are linked by the L ligands to form a zigzag chain propagating along the c-axis direction. Within the zigzag chain, C-HÁ Á ÁO hydrogen bonds between the ligands and the nitrate anions are observed. Adjacent zigzag chains are connected via intermolecularstacking interactions [centroid-to-centroid distance = 3.844 (2) Å ] between the pyridine rings together with N/C-HÁ Á ÁO hydrogen bonds.

Chemical context
Over the past few decades, the continuous efforts have been devoted to the design and development of metal-organic frameworks (MOFs) obtained by linking transition metal centers with several organic bridging ligands. In particular, rigid or flexible dipyridyl-type ligands have been widely used to construct MOFs with attractive structures and potential applications in materials chemistry (Silva et al., 2015;Furukawa et al., 2014;Wang et al., 2012;Leong & Vittal, 2011). Our group has also tried to develop diverse dipyridyl-type MOFs with intriguing topologies including a cyclic dimer (Moon et al., 2011), zigzag chain (Moon et al., 2016), double helical chain (Lee et al., 2015), helical looped-chain (Ju et al., 2014) and twodimensional pseudo-polyrotaxane network (Im et al., 2017), and reported their crystal structures. As a part of our ongoing efforts to develop dipyridyl-type MOFs with different structural motifs, we prepared the title compound obtained by the reaction of cobalt(II) nitrate with a dipyridyl ligand, namely N-(pyridine-2-ylmethyl)pyridine-3-amine. Herein, we report its crystal structure, which is the first example of a Co II complex with an N-(pyridine-2-ylmethyl)pyridine-3-amine ligand. ISSN 2056-9890

Structural commentary
The asymmetric unit of the title compound comprises one Co II atom, one L ligand and two nitrate anions, which coordinate the cobalt ion in a bidentate chelating fashion. The coordination geometry of the Co II atom is distorted pentagonal bipyramidal with the five basal sites being occupied by one amine N atom from the L ligand and four O atoms from two 2 -nitrato ligands and the two apical positions occupied by two pyridyl N atoms from two symmetry-related L ligands [N1-Co1-N3 i = 171.86 (11) ; symmetry code: (i) x, Ày + 1 2 , z À 1 2 ] (  (9) ]. This distortion may reflect the narrow bite angles of the bidentate nitrate ions.

Figure 3
The three-dimensional structure formed through intermolecularstacking interactions (black dashed lines) and N/C-HÁ Á ÁO hydrogen bonds (green dashed lines). H atoms not involved in intermolecular interactions have been omitted for clarity. the structure of the Co II complex described above. Therefore, the title compound is the first example of a Co II complex with an L ligand.

Synthesis and crystallization
The L ligand was synthesized according to a literature method (Lee et al., 2013). X-ray-quality single crystals of the title compound were obtained by slow evaporation of an acetonitrile solution of the L ligand with Co(NO 3 ) 2 Á6H 2 O in the molar ratio 1:1.

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

catena-Poly[[bis(nitrato-κ 2 O,O′)cobalt(II)]-µ-N-(pyridin-2-ylmethyl)pyridine-3-amine-κ 3 N,N′:N′′]
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.