Crystal structure of a twisted-ribbon type double-stranded AgI coordination polymer: catena-poly[[silver(I)-μ3-bis(pyridin-3-ylmethyl)sulfane-κ3 N:N′:S] nitrate]

The reaction of AgI with the tridentate ligand bis(pyridin-3-ylmethyl)sulfane afforded a one-dimensional double-stranded chain polymeric structure with the charge balanced by a nitrate anion that is disordered over two sites. The AgI cation adopts a highly distorted trigonal–planar geometry coordinated by two pyridine N atoms and one S atom from three individual ligands. Each ligand bridges the AgI atoms to form a zigzag chain. Two adjacent chains are connected by an Ag—S bond, resulting in the formation of a twisted-ribbon type double-stranded chain. These chains are linked by π–π interactions, generating a three-dimensional supramolecular network.

The asymmetric unit in the title compound, {[Ag(C 12 H 12 N 2 S)]ÁNO 3 } n or {[AgL]ÁNO 3 } n , L = bis(pyridin-3-ylmethyl)sulfane, consists of an Ag I cation bound to a pyridine N atom of an L ligand and an NO 3 À anion that is disordered over two orientations in an 0.570 (17):0.430 (17) occupancy ratio. Each Ag I cation is coordinated by two pyridine N atoms from adjacent L ligands to form an infinite zigzag chain along [110]. In addition, each Ag I ion binds to an S donor from a third L ligand in an adjacent parallel chain, resulting in the formation of a twisted-ribbon type of double-stranded chain propagating along the [110] or [110] directions. The Ag I atom is displaced out of the trigonal N 2 S coordination plane by 0.371 (3) Å because of interactions between the Ag I cation and O atoms of the disordered nitrate anions. Intermolecularstacking interactions [centroid-to-centroid distance = 3.824 (3) Å ] occur between one pair of corresponding pyridine rings in the double-stranded chain. In the crystal, the double-stranded chains are alternately stacked along the c axis with alternate stacks linked by intermolecularstacking interactions [centroid-to-centroid distance = 3.849 (3) Å ], generating a three-dimensional supramolecular architecture. Weak intermolecular C-HÁ Á ÁO hydrogen bonds between the polymer chains and the O atoms of the nitrate anions also occur.

Chemical context
Among the diverse key factors in the development of Ag I coordination polymers, the structures of the spacer ligands play important roles in determining the structural topology of the self-assembled polymer units (Zheng et al., 2009;Liu et al., 2011). For this reason, continuous efforts have focused on the design and development of such suitable ligands. In particular, dipyridyl-type molecules functioning as bridging ligands have been widely used to construct diverse Ag I coordination polymers with fascinating structures and attractive functional properties (Leong & Vittal, 2011;Moulton & Zaworotko, 2001;Wang et al., 2012). We have also reported several Ag I coordination polymers with interesting structures using dipyridyl-type ligands (Lee et al., 2012(Lee et al., , 2015Moon et al., 2015Moon et al., , 2016Park et al., 2010). The continuing interest in dipyridyltype-ligand-based Ag I coordination polymers prompted us to investigate the use of the ligand bis(pyridin-3-ylmethyl)sulfane (L), which can coordinate to three Ag I cations in a T-shape via the two pyridine nitrogen donors as a bridgehead and the sulfur donor atoms, binding to the Ag I cations at both ends of the dipyridyl bridge as well as at its centre. A reaction of silver(I) nitrate with L (synthesized using a literature procedure; Park et al., 2010;Lee et al., 2012) afforded the title compound. Herein, we report its one-dimensional twistedribbon type double-stranded chain structure in the crystal.

Structural commentary
As shown in Fig. 1, the asymmetric unit of the title compound comprises one Ag I cation, bound to the N1 pyridine atom of a bis(pyridin-3-ylmethyl)sulfane ligand, L, and an NO 3 À anion that is disordered over two orientations in an 0.570 (17):0.430 (17) occupancy ratio. Pyridine N atoms N1 and N2 from two symmetry-related L ligands bind to the Ag I cations to form an infinite zigzag chain. In addition, each Ag I ion binds to an S1 donor from a third L ligand in an adjacent parallel chain, resulting in the formation of a twisted-ribbon type of double-stranded chain propagating along the [110] or [110] directions (Figs. 2 and 3). The Ag I atom is therefore three-coordinated and the coordination geometry around the Ag I cation can be considered as a highly distorted trigonal plane. Selected bond lengths and angles around the Ag1 atom are given in Table 1. N-Ag-N and N-Ag-S angles fall in the range 106.03 (12)-133.18 (12) , deviating significantly from ideal trigonal-planar geometry. This may reflect the influence of additional AgÁ Á ÁO-NO 2 À interactions between the Ag I ion and O atoms of the disordered nitrate anion [Ag1Á Á ÁO1 = 2.730 (18), Ag1Á Á ÁO1 0 = 2.55 (2) Å ; indicated by a dashed line in Fig. 1]. The Ag I atom is displaced out of the trigonal N1, S1, N2 coordination plane by 0.372 (2) Å . The two pyridine rings coordinated to the Ag I centre are tilted by 53.20 (15) with respect to each other. In the double-stranded chain, intermolecularstacking interactions between the N1-pyridine rings [Cg1Á Á ÁCg1 i = 3.824 (3) Å ; yellow dashed lines in Fig. 2; Cg1 is the centroid of the N1/C1-C5 ring; symmetry code: (i) Àx + 1 2 , Ày + 1 2 , Àz + 1] contribute to the stabilization of the double-stranded chain.    (16) N1-Ag1-S1 ii 106.03 (12) N2 i -Ag1-S1 ii 133.18 (12) Symmetry codes: (i) x À 1 2 ; y þ 1 2 ; z; (ii) Àx þ 1 2 ; Ày þ 1 2 ; Àz þ 1.

Figure 1
View of the molecular structure of the title compound, showing the atomnumbering scheme. Displacement ellipsoids are drawn at the 50% probability level. Disordered O atoms of the NO 3 À anion have been omitted for clarity. The dashed line represents the AgÁ Á ÁO interaction. [Symmetry codes: Table 2 Hydrogen-bond geometry (Å , ).

Synthesis and crystallization
The L ligand was synthesized according to a literature method (Park et al., 2010;Lee et al., 2012). Colourless plate-like X-ray quality single crystals of the title compound were obtained by vapor diffusion of diethyl ether into a DMSO solution of the L ligand with AgNO 3 in a 1:1 molar ratio.

Figure 3
Three-dimensional supramolecular network via intermolecularstacking interactions (yellow dashed lines) between the N2-containing pyridine rings. NO 3 À anions and H atoms have been omitted for clarity.

catena-Poly[[silver(I)-µ 3 -bis(pyridin-3-ylmethyl)sulfane-κ 3 N:N′:S] nitrate]
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.