The asymmetry unit of 1 consists of two independent Ag(I) cations, two L ligands, one integrated nitrate and two counteranion nitrate halves, as shown in Figure 2. The environment of every Ag center is the same tetrahedron geometry. Each Ag(1) center is coordinated by two L ligands via the N_py [Ag(1)-N(4) = 2.238(4) Å] and N_bta [Ag(1)-N(3A) = 2.217(4) Å] nitrogen donor atoms. For the balance of electric charge, each Ag(1) cation also displays very weak contact to two different nitrates (counteranion half) with O(1) and O(5) [Ag(1)-O(1) = 2.588(6) and Ag(1)-O(5) = 2.404(15) Å, respectively]. Each Ag(2) center adopts almost the same coordination mode as Ag(1), coordinated by two N from two L ligands and two O atoms form two different nitrates (counteranion integrated), with the Ag-N distances ranging from 2.221(4) to 2.241(4) Å, and Ag-O distances ranging from 2.404(15) to 2.588(6) Å.

In each L molecule, the sp³ configuration of C of -CH₂- spacer forces the L ligand to be non-linear, with the N(1)-C(7)-C(8) angle 110.2(4)° and the N(5)-C(19)-C(20) angle 111.3(5)°. Each L behaves as an exo-bidentate linker, bridging adjacent Ag(I) cations to give rise to an [-Ag(L)-]_n infinite 2¹ helix strand, and such that each strand is interwind compactly by another [-Ag(L)-]_n strand through the aurophilic d¹⁰-d¹⁰ interactions (Ag···Ag distance 3.2683 Å) to form a double helical species. Unlike the standard tubular double helixes that have been reported [17–19], the double helical chain of 1 wriggles with an “S” configuration, as shown in Figure 3. This result can be attributed to the 3- position of the pyridyl ring as the metal coordination site, which limits the stretched-out direction. Each chiral double helical chain links to its adjacent symmetric-related equivalents via the weak attraction of nitrate anion, to generate a quasi 3D supramolecular architecture. In each monocrystal, the balanced packing of left (P) and right (M) chains counteracts the chirality.

A drawing of the asymmetric unit of 2 is shown in Figure 4, with selected bond distances and angles listed in Table 1. The crystal structure reveals that the Ag(I) center is coordinated with two N atoms from two different L, with the Ag-N distances 2.135(3) and 2.113(3) Å, and the N(3)-Ag(1)-N(4) angle 169.97(10)°. The perchlorate group chelates to the Ag(I) center through very weak attraction, with Ag-O distances 2.905(7) and 3.022(6) Å, and the O(2B)-Ag(1)-O(1B) angle 44.99(14)°. For each L ligand in 2, the N(1)-C(7)-C(8) angle is 111.3(2)° around the -CH₂- spacer.

In 2, each L group also behaves as an exo-bidentate linker, bridging adjacent Ag(I) cations to form an infinite “Z” configuration alone the [100] direction (Figure 5). Furthermore, each zigzag chain links to its adjacent symmetric-related equivalents via the duple π-π interactions with centroid to centroid distances 3.586(1) Å to generate a dimer. Other parameters of the π-π interactions are listed in Table 1. It is necessary to point out that these dual π-π interactions were not frequently observed in previously reported architectures [20,21].

Metal-organic polymer compounds with a d¹⁰ configuration have been found to exhibit photoluminescent properties [22–24]. Here, we wanted to examine the photoluminescence of 1 and 2. The solid-state emission spectra of L and complexes 1 and 2 at room temperature are shown in Figure 6. It can be observed that the intense emissions occurr in the same range for the two complexes (λ_ex = 350 nm, λ_em = 417.5 nm for 1; λ_ex = 340 nm, λ_em = 419.5 nm for 2), which show a very light red-shift to that observed from L (λ_ex = 340 nm, λ_em = 402 nm). In d¹⁰-metal ions with one or two positive charges, the d-orbitals are contracted and therefore the electrons in these orbitals are much less accessible for back bonding to p-acceptor ligands. Moreover, silver cations have weak electro-accepting nature with respect to electrons from L, so these emissions can be assigned to ligand-to-metal charge transfer (LMCT) bands [25].

Benzotriazole was purchased from Acros Ltd. Company and used without further purification, the other reagents were commercially available and used as purchased. The IR spectra as KBr discs were recorded on a Magna 750 FT-IR spectrophotometer. C, H, and N analysis were determined on an Elementary Vario ELIII elemental analyzer. Fluorescent spectra were measured on an Edinburgh Instruments analyzer model FL920.

The desired L was prepared by condensation of 1H-benzotriazole with the 3-picolyl chloride in DMF at reflux 4 h in the presence of triethylamine as basic catalyst [26]. Separation of pure L was performed by chromatography on a silica gel column (eluent ethyl acetate-light petroleum 40:60).

A solution of L (0.021 g, 0.10 mmol) in MeOH (5 mL) was carefully layered on a solution of AgNO₃ (0.017 g, 0.10 mmol) in H₂O (5 mL). Diffusion between the two phases over a period of two weeks produced colorless block crystals. Yield: 0.012 g (32% based on L); Elementary analysis: calcd. for Ag₂C₂₄H₂₀N₁₀O₆(760.24): C, 37.92; H, 2.65; N, 18.42%; found: C, 38.20; H, 2.89; N, 18.43%. IR (KBr, cm⁻¹): 3700–3600 (w), 1605 (w), 1482 (w), 1496 (w), 1384 (s), 1227(s), 1194 (m), 1164 (m), 1099 (m), 950 (m), 821(m), 779 (m), 744 (s), 708 (m), 645 (m).

The procedure of 2 is similar to the synthesis of 1 except that AgClO₄ was used instead of AgNO₃. Yield: 0.015 g (48% based on L); Elementary analysis: calcd. for AgClC₁₂H₁₀N₄O₄ (417.55): C, 34.52; H, 2.41; N, 13.42%; found: C, 34.37; H, 2.59; N, 13.65%. IR (KBr, cm⁻¹): 3568(m), 1614(m), 1498 (w), 1459 (w), 1384 (s), 1312 (m), 1224 (m), 1166 (m), 1120 (w), 781 (w), 764 (w), 743 (m), 725(w), 626 (w), 563 (w), 483 (w), 433(w).

The single crystal X-ray diffraction measurements were carried out on a Siemens Smart CCD area detector. Intensities of reflections were measured using graphite monochromatized Mo-Kα radiation (λ = 0.71073 Å) with ω scan mode at 293(2) K in the range of 2.11° < θ < 27.48° for 1 and 2.42° < θ < 27.48° for 2. Unit cell dimensions were obtained with least-squares refinements, and semi-empirical absorption corrections were applied using SADABS program [27]. The structure was solved by direct method [28] and non-hydrogen atoms were obtained in successive difference Fourier syntheses. The final refinements were performed by full-matrix least-squares methods on F² by SHELXL-97 program package [29]. For both 1 and 2, hydrogen atoms were generated geometrically and treated as riding. The crystallographic data for 1–2 are summarized in Table 2, and the selected bond distances and angles are listed in Table 3.