Crystal structure of a one-dimensional helical-type silver(I) coordination polymer: catena-poly[[silver(I)-μ-N-(pyridin-4-ylmethyl)pyridine-3-amine-κ2 N:N′] nitrate dimethyl sulfoxide disolvate]

The reaction of AgI atom with the unsymmetrical ligand N-(pyridin-4-ylmethyl)pyridine-3-amine afforded a helical chain. The AgI atom adopts a slightly distorted linear coordination geometry. The symmetry-related right- and left-handed helical chains are alternately arranged via Ag⋯Ag interactions and π–π stacking interactions, resulting in the formation of a two-dimensional supramolecular network.


Chemical context
Self-assembled supramolecular architectures based on the reaction of the silver ion with dipyridyl-type ligands continue to attract attention not only because of the fascinating structures caused by a variety of coordination geometries for the Ag I cation, but also their potential applications as functional materials (Lee et al., 2012;Leong & Vittal, 2011;Park et al., 2010;Zhang et al., 2009Zhang et al., , 2013. However, although there has been rapid growth in Ag I coordination chemistry based on symmetrical dipyridyl ligands with nitrogen donor atoms in the same positions on two terminal pyridines, investigations based on unsymmetrical dipyridyl ligands with nitrogen donor atoms in different positions on two terminal pyridines are still rare Zhang et al., 2013). Therefore, the development of Ag I coordination polymers using unsymmetrical dipyridyl ligands is a challenging project and deserves exploration. Herein, we report the crystal structure of the title compound prepared by the reaction of silver nitrate with the unsymmetrical dipyridyl ligand, N-(pyridin-4-ylmethyl)pyridine-3-amine, which was been synthesized by the reaction of 3-aminopyridine and pyridine-4-carboxaldehyde according to literature methods (Foxon et al., 2002;Lee et al., 2013). The structure of the title compound is related to that of the monohydrated Ag I coordination polymer with the same ligand (Zhang et al., 2013).

Structural commentary
The molecular components of the title structure are shown in Fig. 1. The asymmetric unit consists of one Ag I atom, one N-(pyridin-4-ylmethyl)pyridine-3-amine ligand, one nitrate anion and two DMSO molecules. The S atom of one of the DMSO molecules is disordered over two sites [site-occupancy factors of 0.937 (3) for S2 and 0.063 (3) for S2 0 ]. The Ag atom links two pyridine N atoms from two symmetry-related ligands, forming a helical chain. Thus the Ag I atom is twocoordinate in a slightly distorted linear coordination geometry  ], with the Ag-N bond lengths of 2.158 (2) and 2.162 (2) Å . The helical chain propagates along the b-axis direction (Fig. 2) and its pitch length is 16.7871 (8) Å , much longer than that [10.135 (2) Å ] of the monohydrated Ag I coordination polymer reported by Zhang et al. (2013). The two pyridine rings coordinating to the Ag atom are tilted by 9.77 (16) with respect to each other. In the N-(pyridin-4-ylmethyl)pyridine-3-amine ligand, the two pyridine rings are almost perpendicular, the dihedral angle between their mean planes being 86.28 (7) .

Database survey
The structures of the silver(I) nitrate and perchlorate complexes of the same ligand have been reported as their monohydrated and non-solvated forms, respectively, by Zhang et al. (2013). These complexes have been also studied for their luminescent properties in the solid state.

Synthesis and crystallization
N-(Pyridin-4-ylmethyl)pyridine-3-amine was prepared according to the procedure described by Lee et al. (2013) and Foxon et al. (2002). Crystals of the title compound suitable for X-ray analysis were obtained by vapour diffusion of diethyl ether into a DMSO solution of the white precipitate afforded by the reaction of the ligand with silver(I) nitrate in the molar ratio 1:1 in methanol.

Refinement details
Crystal data, data collection and structure refinement details are summarized in Table 2. Atoms S2 and S2 0 of one DMSO molecule are disordered over two sites with site-occupation factors of 0.937 (3) and 0.063 (3), respectively. All H atoms were positioned geometrically and refined using a riding model, with C-H = 0.95 Å for Csp 2 -H, 0.88 Å for amine N-H and 0.99 Å for methylene C-H. For all H atoms, U iso (H) = 1.2U eq (C,N). Computer programs: SMART and SAINT-Plus (Bruker, 2000), SHELXS97, SHELXL97 and SHELXTL (Sheldrick, 2008) and DIAMOND (Brandenburg, 2005).