English

• 1. INTRODUCTION

  The past few decades have witnessed amazing progress in exploring the structure-property relationship of silver clusters. Because of their peculiar structures^[1-5] and potential applications in catalysis, luminescent material, biology, and other interesting fields^[6-11], silver clusters have received sustained attention. Among all kinds of silver clusters, silver ethynide clusters have benefited from argentophilic interactions and Ag(Ⅰ)-ethynide interactions^[12-14]. In this family of silver clusters, there are various silver acetylide cages with anions acting as templates, because [RC≡C]⁻ is an anionic group with potential σ and π bonding interactions with silver atoms^{[15, 16]}. In addition, silver acetylide clusters may contain phosphine, amine, and thiolate ligands^[17-21], in which phosphine ligands are generally used as bridging ligands. However, silver acetylide clusters are usually polymers, which have very poor solubility in common solvents. Up to now, most silver acetylides have been obtained by using a simple alkynyl ligand (RC≡C)⁻ or mixed alkynyl/phosphine ligands, but few of them use both modified alkynyl and phosphine groups in a ligand. Therefore, under mild experimental conditions, we try to synthesize silver acetylide complexes with the use of ligands bearing both phosphine and alkynyl groups. The solubility and nucleation number of silver acetylides can be improved by the introduction of phosphine ligands. On the other hand, we hope that some progress will be made in the luminescent properties of silver acetylide clusters.

  In our previous studies, a bifunctional ligand, Ph₂P-C₆H₄-4-C≡CH (L₁) bearing both phosphine and alkynyl groups and its ability to assemble high-nuclearity silver clusters were reported. Phosphine ligands can limit the uncontrolled growth and increase the solubility of silver clusters^{[3, 22, 23]}. The combination of two donor groups makes it possible for silver clusters to construct 2D and 3D frameworks, based on the high-nuclearity clusters as building blocks. The size and shape of silver clusters can also be adjusted under different reaction and crystallization conditions. These structures are attrac-tive^[24]. In order to further explore the possible emissive properties, we designed the ligand Ph₂P-C₆H₄-3-C≡CH (L), based on which we obtained three silver clusters withsupramolecular structures, (CH₃CH₂)₃NH[Ag₃₆L₂₄Cl₃(ClO₄)₆-(CH₃CN)₈](ClO₄)₄ (1), [Ag₃₆L₂₄Cl₃(CO₃)₂(OH) (Py)₄-(CH₃CN)₄](BF₄)₄ (2), and (CH₃CH₂)₃NH[Ag₃₆L₂₄Cl₃-(CH₃CN)₁₀](SbF₆)₁₀ (3). They can be prepared by systematic methods and characterized by single-crystal X-ray diffraction method. The cage structures of complexes 1~3 are templated with chloride anions, and are formed by Ag(Ⅰ)−Ag(Ⅰ) and Ag(Ⅰ)-ethynide interactions, which are further stabilized by weak molecular interactions (π-π, C−H···π, C−H···F, C−H··· O) to build the supramolecular structures.

  2. EXPERIMENTAL

  2.1 General methods and materials

  All reactions were operated under nitrogen atmosphere using standard Schlenk line techniques. All reagents were commercially purchased and used as received. All solvents were treated by distillation and degassing in advance. Ligand Ph₂P-C₆H₄-3-C≡CH was synthesized according to previously reported methods^{[25, 26]}. Elemental analyses of C and H were recorded on a Vario EL-Ⅲ elemental analyzer. UV-vis absorption spectra were obtained using a Shimadzu UV-3600 spectrometer. The emission and excitation spectra were measured on the Hitachi F-7000 fluorescence spectrophotometer. The emission lifetime in the solid state was measured on an Edinburgh FIS1000 transient state fluorescence spectrometer. The absolute emission quantum yield in the solid state was determined by the Hamamatsu C9920-02G quantum efficiency measurement systems.

  2.2 Synthesis of complex 1

  Ph₂P-C₆H₄-3-C≡CH (57.36 mg, 0.20 mmol) reacted with 1.1 equivalent of AgClO₄ (45.61 mg, 0.22 mmol) in acetonitrile (5 mL) and dichloromethane (1 mL) solvent. Then, 1 mL of triethylamine was added. The reaction mixture was stirred overnight at room temperature. The solvent was removed on a rotary evaporator under reduced pressure. Recrystallization from anhydrous ether gave the crude product as a bright yellow powder. The crude product was further washed with ether, dried, and was then redissolved in 6 mL of acetonitrile and filtered. After filtration, slow vapor diffusion of hexane into the filtrate afforded pink crystalline plates of complex 1 in about 86% yield. Anal. Calcd. for C₅₀₂H₃₇₆Ag₃₆Cl₁₃P₂₄N₉O₄₀: C, 49.17; H, 3.09%. Found: C, 49.07; H, 3.16%.

  2.3 Synthesis of complex 2

  Ph₂P-C₆H₄-3-C≡CH (80.17 mg, 0.28 mmol) and AgBF₄ (65.29 mg, 0.34 mmol) were added to a mixture of acetonitrile (5 mL) and dichloromethane (1 mL) under stirring. Then, 1 mL of triethylamine was added to the mixture. During addition, colorless solution immediately turned yellow. The solution was stirred overnight at room temperature. The solvent was removed on a rotary evaporator under reduced pressure. The crude product was further washed with ether, dried in vacuo, redissolved in 9 mL of acetonitrile and filtered. To the filtrate, a few drops of pyridine were added. After filtration, slow vapor diffusion from acetone/hexane (V/V = 1/1) afforded pink crystalline block of complexes (62 mg, 68% yield). Anal. Calcd. for C₅₁₀H₃₆₉Ag₃₆Cl₃P₂₄B₄F₁₆N₈O₇: C, 51.90; H, 3.15%. Found: C, 51.90; H, 3.35%.

  2.4 Synthesis of complex 3

  Ph₂P-C₆H₄-3-C≡CH (40 mg, 0.14 mmol) and triethylamine (1 mL) were dissolved in dichloromethane (1 mL). The mixture was added dropwise to the acetonitrile solution (8 mL) of AgSbF₆ (58 mg, 0.28 mmol). The reaction mixture was stirred for two days at ambient temperature. The solvent was removed on a rotary evaporator under reduced pressure. The crude product was further washed with ether, dried under vacuum, redissolved in 5 mL of acetonitrile and filtered. Slow evaporation of the solution afforded complex 3 as pink crystalline plates (65% yield). Anal. Calcd. for C₅₀₆H₃₈₂Ag₃₆Cl₃P₂₄N₁₁Sb₁₀F₆₀: C, 44.34; H, 2.81%. Found: C, 44.12; H, 2.89%.

  2.5 X-ray crystallography

  Data were collected on a Bruker D8 QUEST X-ray diffractometer. The crystals of complexes 1, 2, and 3 were immersed in Paratone-N oil, mounted in a small fiber loop, and placed in a cooled nitrogen gas stream. Diffraction intensities were measured with graphite-monochromated MoKα radiation (λ = 0.71073 Å) at 153 K by using a φ-ω scan mode. The APEX2 program package was used for data collection, indexing, data reduction, and final unit cell refinements. Absorption corrections were applied to all data using the program SADABS. All structures were solved by direct methods using SHELXS^[27] and refined against F² on all data by full-matrix least-squares with SHELXL, following the established refinement strategies^[28-30].

  In all structures, non-hydrogen atoms were refined anisotropically. All hydrogen atoms binding to carbon were included in the model at geometrically calculated positions and refined using a riding model. The isotropic displacement parameters of all hydrogen atoms were fixed to 1.2 times the U value of the atoms they are linked to (1.5 times for methyl groups). In the crystal of 2, one hydroxyl anion was refined with the occupancy of 0.5. A series of restraints were applied to the solvent molecule and also to some phenyl rings of the main molecule. Though there are some large unresolved q-peaks in all structures, they are all found close to Ag(Ⅰ) cores. Some of the solvents were highly disordered in the crystal lattice of complexes 1~3, so they are treated by a SQUEEZE routine of the PLATON^[31]. The contribution of the missing solvent was not taken into account in the unit cell content. Details of the data quality and a summary of the residual values of the refinements are listed in Table 1.

  Table 1

  

  Table 1.  Crystal Data for the X-ray Structure Analyses of Complexes 1~3

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  Complex	1	2	3
  	C496H360Ag36Cl13	C510H369Ag36B4Cl3	C500H366Ag36Cl3F60
  	N8O40P24	F16N8O7P24	N10P24Sb10
  Fw	12159.37	11801.32	13604.48
  Temperature/K	162(2)	153(2)	153(2)
  Crystal system	Triclinic	Triclinic	Triclinic
  Space group	P$ \overline 1 $	P$ \overline 1 $	P$ \overline 1 $
  a/Å	23.3165(9)	24.601(8)	25.195(6)
  b/Å	23.7671(9)	25.851(8)	25.654(6)
  c/Å	23.9931(9)	26.209(9)	25.783(6)
  α/°	102.4590(10)	72.691(11)	73.276(7)
  β/°	110.4480(10)	65.506(10)	75.208(7)
  γ/°	95.7040(10)	66.505(10)	67.960(8)
  Volume/Å3	11941(8)	13735(8)	14589(6)
  Z	1	1	1
  ρcalcd/g·m−3	1.691	1.427	1.548
  μ/mm−1	1.653	1.387	1.773
  F(000)	5985	5808	6589
  Crystal size/mm3	0.2 × 0.2 × 0.2	0.2 × 0.2 × 0.1	0.2 × 0.2 × 0.1
  θ range/°	2.13 to 25	2.13 to 25	2.10 to 25
  Reflections collected	165344	297520	286523
  Independent reflections	41994	48355	51183
  	(Rint = 0.0761)	(Rint = 0.0696)	(Rint = 0.0768)
  Completeness	99.8%	99.9%	99.7%
  GOOF	1.007	1.093	1.191
  Final R indices (I > 2σ(I))	Ra = 0.0669	Ra = 0.0733	Ra = 0.1194
  	wRb = 0.1385	wRb = 0.2107	wRb = 0.3689
  R indices (all data)	Ra = 0.0966	Ra = 0.0967	Ra = 0.1358
  	wRb = 0.1531	wRb = 0.2313	wRb = 0.3935
  Largest diff. peak and hole/Å–3	2.360 and −2.197	4.303 and −1.458	7.181 and −5.161
  aR = Σ||Fo| − |Fc||/|Fo|, bwR = {Σ[w(Fo2 − Fc2)2]/Σ[w(Fo2)2]}0.5

  3. RESULTS AND DISCUSSION

  3.1 Structural analysis of 1

  Single-crystal structural analysis reveals that complex 1 crystallizes in triclinic space group P$ \overline 1 $ with Z = 1, which contains 36 Ag atoms, 24 Ph₂P-C₆H₄-3-C≡C⁻ ligands, 6 aceto-nitrile molecules, and 6 ClO₄⁻ anions (Fig. 1a). The dumbbell-like Ag₂₈ cluster can be regarded as formed by two Ag₁₄ subcomponents linked by a $ \overline 1 $ rotoinversion left (Fig. 1b). In the dodecahedral Ag₁₄ cage, the Ag(Ⅰ)−Ag(Ⅰ) distances ranged from 2.8652(9) to 3.2745(9) Å with an average value of 3.0342(9) Å, much shorter than the sum of Van der Waals radii of two silver atoms (3.44 Å)^{[12, 32]}. This indicates that strong argentophilic interactions are present in the crystal structure of complex 1. Furthermore, such interactions make the Ag₁₄ cage tightly assembled. The Ag₁₄ cage is capped by twelve Ph₂P-C₆H₄-3-C≡C⁻ ligands, each binding three Ag atoms through both σ and π bonds of the alkynyl moiety. There are three Ph₂P-C₆H₄-3-C≡C⁻ ligands taking μ₃-η¹, η², η² coordination mode and nine Ph₂P-C₆H₄-3-C≡C⁻ ligands adopting μ₃-η¹, η¹, η² coordination mode (Fig. 1c). The Ag(Ⅰ)−C bond distances fall in the 2.048(9)~2.696(8) Å range averaged by 2.348(8) Å.

  Figure 1

  

  Figure 1.  (a) Molecular structure of the cationic cluster. (b) Dumbbell-like Ag₂₈ core structure. (c) Two coordination models of ligand L in 1. Yellow: μ₃-η¹, η¹, η² coordination mode; Bright blue: μ₃-η¹, η², η² coordination mode. Color code: pink, Ag; orange, P; blue, N; red, O; green, Cl; gray, C. Partial hydrogen atoms and Ph₂P^- moieties are omitted for clarity

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  Inside the Ag₁₄ cage, the Cl(4) atom is coordinated to Ag(1), Ag(8) and Ag(12) atoms, the Ag(Ⅰ)−Cl bond distances are 2.839(2), 2.848(2) and 2.818(2) Å, respectively. According to the previous reports, the Cl^– anion could come from the decomposition of dichloromethane without the designed addition of Cl^– anion. The Ag(3) atom is coordinated to an O(6) atom of ClO₄⁻ anion, with the Ag(3)−O(6) bond to be 2.592(11) Å. The O(3) and O(9) atoms in ClO₄⁻ anion are coordinated to Ag(16) and Ag(18) outside the Ag₁₄ cage. The Ag(16)−O(3) bond distance is 2.456(9) Å and the Ag(18)−O(9) bond distance is 2.559(9) Å. The N(1) and N(2) atoms of acetonitrile molecules are coordinated to Ag(15) and Ag(17). The Ag(15)−N(2) bond is 2.386(9) Å and Ag(17)−N(1) 2.426(9) Å. The Ag(Ⅰ)−P bond distances are in the range of 2.489(2)~2.533(3) Å with the average of 2.499(2) Å. Another two uncoordinated acetonitrile molecules and four ClO₄⁻ counter anions were found in the X-ray structure of complex 1. According to structural analysis, the formula of complex 1 is determined to be (CH₃CH₂)₃NH[Ag₃₆L₂₄Cl₃(ClO₄)₆(CH₃CN)₈]⁴⁺, and the posi-tive charges were balanced by four uncoordinated ClO₄⁻ anions (Fig. S1). (CH₃CH₂)₃NH⁺ might be formed by the addition of excessive triethylamine protonation in our previous synthesis.

  As shown in Fig. S2, the face-to-face π-π stacking interactions^[33-35] (centroid-to-centroid distances of 3.712 Å) and C−H···π interactions^{[36, 37]} (H···centroid 2.789 Å with a C(42)−H(42)···centroid angle of 159°, H···centroid 2.836 Å with a C(92)−H(92)···centroid angle of 154°, and H···centroid 2.983 Å with a C(96)−H(96)···centroid angle of131°, respectively) were found in complex 1. Crystallographic studies showed that the adjacent Ag28 cages are linked by ClO₄⁻ anions and acetonitrile molecules to form a two-dimensional coordination network in the solid state^{[38, 39]}, which is depicted in Fig. 2. A linear silver chain is linked by C(242)−H(24B)···O(5) and C(23)−H(23)···O(5) hydrogen bonds between the ClO₄⁻ anions and acetonitrile molecules viewed along the c axis (Fig. 3).

  Figure 2

  

  Figure 2.  2D coordination network structures are linked by the C−H···O interactions in complex 1. Partial hydrogen atoms and benzene rings are omitted for clarity. Bond lengths: C(244)–H(24E)···O(9) H(24E)–O(9) 2.577 Å, C(29)–H(29)···O(12) H(29)–O(12) 2.576 Å, C(66)–H(66)···O(9) H(66)–O(9) 2.509 Å, C(86)–H(86)···O(12) H(86)–O(12) 2.531 Å

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  Figure 3

  

  Figure 3.  Silver chains linked by C(242)−H(24B)···O(5) and C(23)−H(23)···O(5) interactions viewed along the c axis between the acetonitrile molecules and ClO₄⁻ anions in complex 1

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  3.2 Structural analysis of 2

  Complex 2 crystallized in the triclinic space group $ P\stackrel{-}{1} $ with Z = 1, which contains 36 Ag atoms that were surrounded by 24 Ph₂P-C₆H₄-3-C≡C⁻ ligands, four pyridines(Py), four acetonitrile molecules, three Cl⁻ anions, one hydroxyl anion, and two CO₃²⁻ anions that were generated from the fixation of carbon dioxide in the air (Fig. 4). In the Ag₁₄ cage, the Ag(Ⅰ)−Ag(Ⅰ) distances ranged from 2.8740(12) to 3.3490(12) Å with an average value of 3.0438(12) Å, indicating the interactions between Ag(Ⅰ)−Ag(Ⅰ) atoms. The Ag₁₄ cage is coordinated to twelve Ph₂P-C₆H₄-3-C≡C⁻ ligands. Eight of them are adopting μ₃-η¹, η¹, η² ligation modes while the rest four are adopting μ₃-η¹, η², η² ligation modes, the ligation mode is clearly presented in Fig. S3a. The Ag(Ⅰ)−C bond distances are between 2.051(7) and 2.703(8) Å with an average value of 2.288(2) Å.

  Figure 4

  

  Figure 4.  Crystal structure of complex 2. Color code: pink, Ag; orange, P; right green, Cl; red, O; blue, N; gray, C. Partial hydrogen atoms and benzene rings are omitted for clarity

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  Inside each Ag₁₄ cage, the Cl(1) atom is coordinated to Ag(1), Ag(12), and Ag(13) atoms. The Ag(Ⅰ)−Cl bond distances are 2.884(19), 2.862(2), and 2.863(2) Å, respec-tively, which lead to a slight distortion of the dodecahedral Ag₁₄ cage. The Cl atom might come from the decomposition of the dichloromethane solvent. The pyridyl N(1) and N(2) bind to Ag(6) and Ag(2) atoms. The Ag(Ⅰ)−N bond distances are 2.376(5) and 2.400(7) Å. The N(3) and N(4) atoms in the acetonitrile molecule are coordinated to Ag(16) and Ag(4) atoms, respectively. The Ag(Ⅰ)−N bond distances are 2.596(8) and 2.458(8) Å. Apart from the cationic Ag₁₄ cage, there are other four Ag atoms lying outside the cage. Among those four Ag atoms, Ag(16) and Ag(18) are bound to three P atoms of the Ph₂P-C₆H₄-3-C≡C⁻ ligand, while Ag(15) and Ag(17) are bound to three P atoms and one additional oxygen. The Ag(Ⅰ)−P bond distances are in the range of 2.468(2)−2.530(2) Å, with an average value of 2.501(3) Å. Interestingly, Ag(15) and Ag(17) have different coordination environment. The Ag(15) atom is coordinated by carbonate through the O atom. Different from Ag(15), the Ag(17) atom is coordinated to an O atom from a half occupied hydroxyl anion. The introduction of OH⁻ and CO₃²⁻ anions terminates the growing of the structure, preventing it from assembling into coordination polymers. Based on the detailed analysis, complex 2 is positively charged with a formula of [Ag₃₆L₂₄Cl₃(CO₃)₂(OH)(Py)₄(CH₃CN)₄]⁴⁺, the positive charges are balanced by four uncoordinated BF₄⁻ anions established in the crystal lattice (Fig. S4).

  As shown in Fig. S5, weak intramolecular interactions are found in complex 2. The distances of the centroid to centroid between two parallel benzene rings are 3.631 and 3.795 Å, respectively, indicating the presence of π-π stacking interactions. The distances of H···centroid in non-classical C−H···π interactions are 2.514, 2.657, and 2.897 Å (C−H···centroid angles of 154°, 135°, 150°, respectively), and the distances of H···centroid are shorter than the normal C−H···π interaction of 3.050 Å^{[37, 40]}. Weak molecular interactions play a key role in supramolecular chemistry, a variety of weak molecular interactions are beneficial for the construction of structures and control the crystal structure packing^{[36, 38]}. A silver chain is formed by coordinated acetonitrile molecules between the adjacent silver clusters through C(253)−H(25A)···π interaction (H(25A)···centroid 2.761 Å with a C(253)−H(25A)···centroid angle of 156°) on the bc plane, which was also reinforced by weak face to face π-π stacking interaction (centroid to centroid distance 4.078 Å) and C(117)−H(117)···π stacking interaction (H(117)···centroid 2.749 Å with a C(117)−H(117)···centroid angle of 146°) (Fig. 5).

  Figure 5

  

  Figure 5.  A silver chain linked by a weak face-to-face π-π interaction (centroid-to-centroid distance 4.078 Å), C(253)−H(25A)···π interaction and C(117)−H(117)···π interaction

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  As shown in Fig. 6 and Fig. S6, a two-dimensional layer structure is linked by two kinds of hydrogen bonds between the adjacent four silver clusters. The first is linked by free BF₄⁻ anions and coordinated acetonitrile molecules via C(255)−H(25E)···F(8S) and C(255)−H(25E)···F(7S) hydro-gen bonds)^{[41, 42]}. The second is linked by free BF₄⁻ anion and benzene ring of ligand L through the C(25)−H(25)···F(6S), C(24)−H(24)···F(8S), C(143)−H(143)···F(5S), and C(223)− H(223)···F(8S) hydrogen bonds along the a direction. The free BF₄⁻ anions linked another silver chain by C(69)− H(69)···F(1S) and C(205)−H(205)···F(1S) interactions (Fig. S7).

  Figure 6

  

  Figure 6.  2D coordination structure linked by C−H···F interactions in complex 2. Partial hydrogen atoms, acetonitrile molecules, and BF₄⁻ anions are omitted for clarity

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  3.3 Structural analysis of 3

  The basic structure and shape of complex 3 are similar to 1 and 2. As shown in Fig. 7, complex 3 crystallizes in triclinic space group P$ \overline 1 $ with Z = 1. Each asymmetric unit of complex 3 contains an Ag₁₄ cage surrounded by 12 Ph₂P-C₆H₄-3-C≡C⁻ ligands and 5 acetonitrile molecules. In complex 3, five Ph₂P-C₆H₄-3-C≡C⁻ ligands have μ₃-η¹, η², η² bridging mode and seven Ph₂P-C₆H₄-3-C≡C⁻ ligands have μ₃-η¹, η¹, η² bridging mode (Fig. S3b). The Ag(Ⅰ)−Ag(Ⅰ) bond distances are between 2.8750(14) and 3.3537(14) Å with an average value of 3.0260(9) Å, clearly showing the existence of Ag(Ⅰ)−Ag(Ⅰ) interactions.

  Figure 7

  

  Figure 7.  Crystal structures of complex 3. Color code: pink, Ag; orange, P; bright green, Cl; red, O; blue, N; gray, C. Hydrogen atoms and partial benzene rings are omitted for clarity

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  Inside the Ag₁₄ cage, the Ag(Ⅰ)−C bond distances ranged from 2.039(13) to 2.688(13) Å averaged by 2.342(12) Å. The Ag(3), Ag(5), and Ag(7) atoms are coordinated to N donors of acetonitrile molecules, with the Ag(Ⅰ)−N bond distances to be 2.493(19), 2.428(19), and 2.499(14) Å, respectively. Outside the Ag₁₄ cage, the bond length between Ag(15) and acetonitrile N(2) atom is 2.424(12) Å. The bond length between Ag(18) and acetonitrile N(4) atom is 2.444(14) Å. All solvent acetonitrile molecules are coordinated to Ag atoms. However, the SbF₆⁻ counter anions are uncoordinated, established in the crystal lattice and balanced the positive charge of the cationic host. The formula of complex 3 can be determined to be (CH₃CH₂)₃NH[Ag₃₆L₂₄Cl₃(CH₃CN)₁₀]-(SbF₆)₁₀. The thermal ellipsoid plot of the X-ray structure of 3 is shown in Fig. S8.

  Weak intramolecular forces are found in the structure of complex 3, forming the supramolecular structure and stabilizing the rigid structure. Fig. S9 shows the C−H···π interac-tions in each asymmetric unit of complex 3 (H···centroid 2.936 Å with a C(126)−H(126)···centroid angle of 147°, H···centroid 2.849 Å with a C(111)−H(111)···centroid angle of 151°, and H···centroid 2.551 Å with a C(222)− H(222)···centroid angle of149°, respectively). The short dis-tances between the free SbF₆⁻ anions and coordinated CH₃CN molecules indicate the existence of interaction. A silver chain is linked by C(164)−H(164)···F(21) and C(9)−H(9)···F(24) interactions along the b direction, which is further linked by offset face-to-face π-π interaction (centroid-to-centroid distance 3.797 Å), C(70)−H(70)···π interaction, and C(11)− H(11)···π interaction along the a direction (Fig. 8). Another silver chain is constructed by C(84)−H(84)···F(30) and C(246)−H(24I)···F(30) interactions between the free SbF₆⁻ anions and CH₃CN molecules in 3 (Fig. 9).

  Figure 8

  

  Figure 8.  (a) Silver chain linked by C(164)−H(164)···F(21) and C(9)−H(9)···F(24) interactions. (b) Silver chain is formed by offset face-to-face π-π interaction, C(70)−H(70)···π interaction, and C(11)−H(11)···π interaction in complex 3

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  Figure 9

  

  Figure 9.  Silver chain formed by C(84)−H(84)···F(30) and C(246)−H(24I)···F(30) interactions in complex 3

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  3.4 Photochromic properties

  Upon excitation at λ ≥ 365 nm, complexes 1~3 emit intense orange room-temperature luminescence in the solid state. The photophysical data of complexes 1~3 are summarized in Table S1, and the luminescence properties were measured in the solid state at room temperature. As shown in Fig. S10, the UV-vis absorption spectra of complexes 1~3 in the solid state are acquired by a broad high-energy band at 270~360 nm and a low-energy band at ca. 490 nm. The high-energy absorption is typical for metal-perturbed intraligand (alkynyl and phosphine ligands) transitions and the low energy absorption band lefted at 490 nm shall be attributed to the characteristic transition of ligand-to-metal charge transfer (LMCT), mixed with a metal-cluster lefted character modified by argentophilic interaction^[43-46].

  The solid-state excitation and emission spectra are shown in Fig. 10. Complexes 1 and 2 showed the maximum emission at about 550 nm with the absolute luminescence quantum yield is 15.6% and 14.2%, respectively. Complex 3 has a maximum emission at about 545 nm with an absolute luminescence quantum yield of 6.40%. The lifetime of complexes 1, 2 and 3 was determined to be 1.31, 1.82, and 1.73 μs, respectively (Fig. 11). The microsecond lifetime, in accordance with large Stokes shifts between the excitation and emission spectra, shows that the emission origin is triplet excited states^[47-50].

  Figure 10

  

  Figure 10.  Excitation (left) and emission (right) spectra of complexes 1~3 at 298 K.Complexes 1 (black), 2 (red) and 3 (blue)

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  Figure 11

  

  Figure 11.  Luminescence decay of complexes 1~3 (λ_ex = 380 nm, 298 K)

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  4. CONCLUSION

  In summary, we report a bi-functional ligand Ph₂P-C₆H₄-3-C≡CH and three silver cluster complexes. As a family of cage complexes, complexes 1~3 are synthesized by the direct reaction between silver salts with alkynyl ligands and isolated by crystallization. Alkynyl ligands can bind silver atoms through δ and π bond to stabilize the cationic cages. Phosphine ligands increase the solubility and stability of silver clusters, structurally limit the uncontrolled growth of the silver cluster, and can be seen as a capping reagent. In the crystal structures of 1~3, the anions such as BF₄⁻, ClO₄⁻ and SbF₆⁻ are more than counter anions, and together with solvent acetonitrile and benzene rings of the ligand L, they provide sites for intramolecular interactions which improve the rigidity and stability of the crystal structures 1~3.

  
  We are grateful for support from the "Thousand Talents Program" of China
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  Figure 1  (a) Molecular structure of the cationic cluster. (b) Dumbbell-like Ag₂₈ core structure. (c) Two coordination models of ligand L in 1. Yellow: μ₃-η¹, η¹, η² coordination mode; Bright blue: μ₃-η¹, η², η² coordination mode. Color code: pink, Ag; orange, P; blue, N; red, O; green, Cl; gray, C. Partial hydrogen atoms and Ph₂P^- moieties are omitted for clarity

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  Figure 2  2D coordination network structures are linked by the C−H···O interactions in complex 1. Partial hydrogen atoms and benzene rings are omitted for clarity. Bond lengths: C(244)–H(24E)···O(9) H(24E)–O(9) 2.577 Å, C(29)–H(29)···O(12) H(29)–O(12) 2.576 Å, C(66)–H(66)···O(9) H(66)–O(9) 2.509 Å, C(86)–H(86)···O(12) H(86)–O(12) 2.531 Å

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  Figure 3  Silver chains linked by C(242)−H(24B)···O(5) and C(23)−H(23)···O(5) interactions viewed along the c axis between the acetonitrile molecules and ClO₄⁻ anions in complex 1

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  Figure 4  Crystal structure of complex 2. Color code: pink, Ag; orange, P; right green, Cl; red, O; blue, N; gray, C. Partial hydrogen atoms and benzene rings are omitted for clarity

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  Figure 5  A silver chain linked by a weak face-to-face π-π interaction (centroid-to-centroid distance 4.078 Å), C(253)−H(25A)···π interaction and C(117)−H(117)···π interaction

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  Figure 6  2D coordination structure linked by C−H···F interactions in complex 2. Partial hydrogen atoms, acetonitrile molecules, and BF₄⁻ anions are omitted for clarity

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  Figure 7  Crystal structures of complex 3. Color code: pink, Ag; orange, P; bright green, Cl; red, O; blue, N; gray, C. Hydrogen atoms and partial benzene rings are omitted for clarity

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  Figure 8  (a) Silver chain linked by C(164)−H(164)···F(21) and C(9)−H(9)···F(24) interactions. (b) Silver chain is formed by offset face-to-face π-π interaction, C(70)−H(70)···π interaction, and C(11)−H(11)···π interaction in complex 3

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  Figure 9  Silver chain formed by C(84)−H(84)···F(30) and C(246)−H(24I)···F(30) interactions in complex 3

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  Figure 10  Excitation (left) and emission (right) spectra of complexes 1~3 at 298 K.Complexes 1 (black), 2 (red) and 3 (blue)

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  Figure 11  Luminescence decay of complexes 1~3 (λ_ex = 380 nm, 298 K)

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  Table 1.  Crystal Data for the X-ray Structure Analyses of Complexes 1~3

  Complex	1	2	3
  	C496H360Ag36Cl13	C510H369Ag36B4Cl3	C500H366Ag36Cl3F60
  	N8O40P24	F16N8O7P24	N10P24Sb10
  Fw	12159.37	11801.32	13604.48
  Temperature/K	162(2)	153(2)	153(2)
  Crystal system	Triclinic	Triclinic	Triclinic
  Space group	P$ \overline 1 $	P$ \overline 1 $	P$ \overline 1 $
  a/Å	23.3165(9)	24.601(8)	25.195(6)
  b/Å	23.7671(9)	25.851(8)	25.654(6)
  c/Å	23.9931(9)	26.209(9)	25.783(6)
  α/°	102.4590(10)	72.691(11)	73.276(7)
  β/°	110.4480(10)	65.506(10)	75.208(7)
  γ/°	95.7040(10)	66.505(10)	67.960(8)
  Volume/Å3	11941(8)	13735(8)	14589(6)
  Z	1	1	1
  ρcalcd/g·m−3	1.691	1.427	1.548
  μ/mm−1	1.653	1.387	1.773
  F(000)	5985	5808	6589
  Crystal size/mm3	0.2 × 0.2 × 0.2	0.2 × 0.2 × 0.1	0.2 × 0.2 × 0.1
  θ range/°	2.13 to 25	2.13 to 25	2.10 to 25
  Reflections collected	165344	297520	286523
  Independent reflections	41994	48355	51183
  	(Rint = 0.0761)	(Rint = 0.0696)	(Rint = 0.0768)
  Completeness	99.8%	99.9%	99.7%
  GOOF	1.007	1.093	1.191
  Final R indices (I > 2σ(I))	Ra = 0.0669	Ra = 0.0733	Ra = 0.1194
  	wRb = 0.1385	wRb = 0.2107	wRb = 0.3689
  R indices (all data)	Ra = 0.0966	Ra = 0.0967	Ra = 0.1358
  	wRb = 0.1531	wRb = 0.2313	wRb = 0.3935
  Largest diff. peak and hole/Å–3	2.360 and −2.197	4.303 and −1.458	7.181 and −5.161
  aR = Σ||Fo| − |Fc||/|Fo|, bwR = {Σ[w(Fo2 − Fc2)2]/Σ[w(Fo2)2]}0.5

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