Stepwise synthesis and structural characterization of two-dimensional (2-D) coordination polymer frameworks with positive charged or neutral cavities are reported. First, reactions of bis(4-pyridylmethyl)sulfide (L) with silver salts (1: nitrate and 2: perchlorate) afforded the respective double-stranded one-dimensional (1-D) chains [Ag(L)NO 3 ] n (1) and {[Ag 2 (L) 2 ](ClO 4 ) 2 } n (2), both of which are stabilized by face-to-face π-π interactions. In this case, the silver(I) center in the nitrato complex 1 shows four-coordinated distorted tetrahedral geometry, whereas that of the perchlorato complex 2 exhibits a distorted trigonal planar geometry. The difference of these structures indicates that the coordination ability of the anions has important effects on the silver(I) coordination environments. Interestingly, the perchlorato 1-D complex 2 allows further reactions with bridging ligands such as 4,4 0 -bipyridine (bpy) and terephthalate (tp 2-) to give a 2-D positive-charged network {[Ag 2 (L) 2 (bpy)] 3 (ClO 4 ) 2 3 C 6 H 6 } n (3) and a 2-D neutral network {[Ag 2 (L) 2 (tp)] 3 2DMSO 3 6H 2 O} n (4), respectively. The nitrato 1-D complex 1, however, showed no reactivity with the bridging ligands in the same condition. The results show that the replacement of anion by the bridging ligand in the coordination sphere of the 1-D precursor plays crucial roles in determining the reactivity for the synthesis of higher dimensional open frameworks.

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Helical structures have received much attention in supramolecular chemistry and materials science because of their fascinating similarities in biological systems to nucleic acids and proteins as well as their potential applications as functional materials in asymmetric catalysis and nonlinear optical materials. [1][2][3][4][5][6] Although many single-, double-, and multiple-stranded helical coordination polymers have been reported, 2-6 the rational and desirable construction of supramolecular helical structure is still constrained by the limited understanding of the structural constraints. In the preparation of helical coordination polymers, much effort should be devoted to the careful design of organic ligands and reasonable selection of metal ions with rational geometries.One of useful strategies in constructing supramolecular architectures with helical structures is the employment of the flexible ditopic ligands and metal ions with linear geometry. 7 In particular, the unsymmetrical dipyridyl ligand L is a good candidate for construction of helices because it is a nonlinear and flexible ligand and has two terminal pyridines with different substituted positions. Through self-assembly of the unsymmetrical ditopic ligand L with silver salts, we and the Gao group have already reported single-stranded helical coordination polymers. 2a,b In this report, we describe the crystal structure of a fascinating, infinite double-helical silver coordination polymer (1) derived from the unsymmetrical and flexible dipyridyl ligand L, and its physical properties including thermogravimetry analysis (TGA) and solid-state photoluminescence. To the best of our knowledge, infinite double-helical structure is less common, 4 whereas numerous discrete double helicates have been reported. 3 The dipyridyl ligand L was synthesized by the reaction of 3-aminopyridine and pyridine-4-carboxaldehyde according to literature methods. 8Colorless crystalline product of formula {[Ag(L)]Á CF 3 SO 3 } n (1) was obtained by the vapor diffusion of diethyl ether into the DMSO solution of the white precipitate afforded by the reaction of silver(I) trifluoromethanesulfonate with L in the molar ratio 1:1 in methanol. Single-crystal X-ray analysis revealed that 1 crystallized in the orthorhombic space group Pbcn and Z = 8. Crystallographic data including experimental details and refinement results, and selected geometric parameters relevant to the coordination geometry for 1 are listed in Tables 1 and S2, Supporting Information, respectively. The crystal structure of 1 is depicted in Figure 1.The asymmetric unit of 1 contains one Ag(I) atom, one L ligand, and one trifluoromethanesulfonate anion. As shown in Figure 1, two pyridine nitrogen atoms from two symmetry-related ligands coordinate strongly to the Ag center (Ag1-N1 = 2.148(6) Å, Ag1-N2 i = 2.154(5) Å), forming an infinite single-stranded helical chain. Thus, the Ag(I) atom is two-coordinate in a slightly distorted linear coordination geometry (N1-Ag1-N2 i = 167.7 (3) The striking feature is that...

The title compound, C20H22N6 2+·2PF6 −, was prepared by the reaction of 5,5′-bis­(bromo­meth­yl)-2,2′-bipyridine with 1-methyl­imidazole. The main mol­ecule lies on an inversion center located at the mid-point of the C—C bond joining the two pyridine rings. The asymmetric unit therefore contains one half-mol­ecule and one hexa­fluoro­phosphate anion. The dihedral angle between the pyridine and imidazole rings is 76.93 (7)°. In the crystal, weak inter­molecular C—H⋯F hydrogen bonds contribute to the stabilization of the packing.

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