DOI: 10.1021/cg900443c
Influence of Different N-Donor Ligands on the Supramolecular Architectures and Abundant Weak Interactions of Silver 2-Sulfobenzoate Polymers
2009, Vol. 9 4407–4414
Xiao-Feng Zheng and Long-Guan Zhu* Department of Chemistry, Zhejiang University, Hangzhou 310027, People’s Republic of China Received April 21, 2009; Revised Manuscript Received July 11, 2009
ABSTRACT: Six topologically diverse complexes based on the Ag(I)/2-sulfobenzoate/N-donor ligands system [Ag2(sb)]n (1), [Ag4(sb)2(apy)4] (2), [Ag2(sb)2(apy)2] 3 2apyH (3), {[Ag2(sb)(bipy)2(H2O)] 3 (H2O)2}n (4), {[Ag4(sb)2(bpe)4] 3 (H2O)9}n (5), and {[Ag4(sb)2(hmt)2(H2O)] 3 (H2O)2}n (6) (sb=2-sulfobenzoate dianion, apy=2-aminopyridine, bipy=4,40 -bipyridine, bpe=1,2bis(4-pyridyl)ethylene, and hmt= hexamethylenetetramine) were synthesized and characterized. Complex 1, a water-soluble species, is a two-dimensional (2-D) structure constructed by [Ag2(sb)] binuclear units. Complexes 2 and 3 are tetrameric and dimeric species, respectively. For both complexes 2 and 3 hydrogen bonds generate one-dimensional (1-D) chains, and weak interactions such as Ag 3 3 3 π or C-H 3 3 3 π extend chains into three-dimensional (3-D) supramolecular structures. Complex 4 is a 1-D polymer with double ladder chains connected by Ag 3 3 3 Ag bonds. Complex 5 is a 2-D brick-wall-like layer framework. Complex 6 is a 2-D polymer. Moreover, complexes 4-6 are assembled into 3-D supramolecular frameworks by hydrogen bonds, π-π and C-H 3 3 3 π interactions. Additionally, Ag 3 3 3 Ag, Ag 3 3 3 π, and N-H 3 3 3 Ag interactions are found in these complexes. These interactions provide important roles in the assembly of the structures and function properties. And in particular the influences of Ag 3 3 3 Ag, Ag 3 3 3 π, and π-π interactions on the conducting properties are discussed. In all, thermal stability behaviors, fluorescent properties, and electric conductivities provide a way of understanding the relationship between these diverse structures and properties.
Introduction The core research areas involved in the crystal engineering of silver coordination polymers are its fascinating mechanisms of molecular self-assembly and abundant weak interactions and potential applications in many areas such as optical or electrical conductivity, magnetism, host-guest chemistry, and catalysis.1 Silver(I) ions give rise to an ever-interesting array of stereochemistry and geometric configurations with coordination numbers of two to six all occurring.2 Although the closed d10 configuration of silver(I) appears to cancel any intermetallic bonding in metal complexes, there are many examples of dimeric or polymeric silver(I) complexes with definite Ag 3 3 3 Ag, Ag 3 3 3 C, Ag 3 3 3 π interactions and various kinds of hydrogen bonds including X-H 3 3 3 X, X-H 3 3 3 π, C-H 3 3 3 X, X-H 3 3 3 Ag (X=O, N, halogen), and C-H 3 3 3 n (n: lone pair electrons) interactions.3 Ag 3 3 3 Ag interactions have possessed the common worldwide interest due to its special ability of controlling the conformation and topology of metallic clusters with d10, d8, s2 configurations of metal centers,4 which has been termed as argentophilicity and considered to be relatively weaker than Au 3 3 3 Au interactions.3a,5,6 To the best of our knowledge, only a few examples of X-H 3 3 3 Ag (X = C, N, O) close interactions have been identified by X-ray diffraction on the basis of the van der Waals radii, though its importance in supramolecular coordination architectures.7,8 Ag-π and π-π interactions are two other kinds of important transverse interactions except Ag-Ag binds, producing semimetallic Fermi surfaces in the conductive materials of single-component molecular metals. Moreover, in recent years C-H 3 3 3 π interactions have been *To whom correspondence should be addressed. r 2009 American Chemical Society
widely discussed in the field of crystal engineering,9,10 while the depictions in Ag complexes are sparse. On the basis of all mentioned above, silver(I) complexes are interesting. We selected 2-sulfobenzoate to synthesize new Ag complexes based on following 3-fold strategies: (a) the 2sulfobenzoate is a versatile ligand for coordination bonding; (b) it has five hydrogen bond donors or/and acceptors; (c) its aromatic ring may form multiple weak interactions. These characters combined with argentophilicity in silver complexes will generate interesting supramolecular assembly involved in abundant weak interactions. Herein, we report the systhesis, structures, supramolecular assemblies, and properties of six Ag(I) complexes, namely, [Ag2(sb)]n (1), [Ag4(sb)2(apy)4] (2), [Ag2(sb)2(apy)2] 3 2apyH (3), {[Ag2(sb)(bipy)2(H2O)] 3 (H2O)2}n (4), {[Ag4(sb)2(bpe)4] 3 (H2O)9}n (5), and {[Ag4(sb)2(hmt)2(H2O)] 3 (H2O)2}n (6) (sb= 2-sulfobenzoate, apy = 2-aminopyridine, bipy = 4,40 -bipyridine, bpe=1,2-bis(4-pyridyl)ethylene, and hmt=hexamethylenetetramine). Experimental Section Materials and Physical Measurements. All chemicals were obtained from commercial sources and were of reagent grade. The infrared spectra were taken on a Nicolet Nexus 470 infrared spectrophotometer as KBr pellets in the 400-4000 cm-1 region. Elemental analyses for C, H, and N were carried out on a PerkinElmer analyzer model 1110. The fluorescence study was carried out on powdered sample in the solid state at room temperature using SHIMADZU RF-540 spectrometer. Thermogravimetric analysis (TGA) was carried out on a Delta Series TA-SDT Q600 in nitrogen atmosphere in the temperature range room temperature to 800 °C (heating rate=10 °C/min). The measurements of electric conductivity were made by a conventional two-probe technique at room temperature with Published on Web 08/19/2009
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Table 1. Crystallographic Data and Refinement Parameters for Complexes 1-6 complex
1
2
3
4
5
6
empirical formula Mr crystal system space group size/mm3 a/A˚ b/A˚ c/A˚ R/° β/° γ/° V/A˚3 Z Dc/Mg 3 m-3 μ/mm-1 θ range unique reflections observed reflections parameters F(000) T/K R1, wR2[I > 2σ(I)] R1, wR2[all data] GOF largest peak and hole (e A˚-3)
C7H4Ag2O5S 415.91 monoclinic P21/a 0.21 0.09 0.07 9.8676(8) 8.3825(7) 11.0733(9) 90 103.987(1) 90 888.77(13) 4 3.108 4.634 3.1-25.5 1657 1593 136 784 295 0.025, 0.065 0.027, 0.066 1.047 0.832, -0.971
C34H24Ag4N8O10S2 1208.30 monoclinic P21/a 0.29 0.18 0.17 8.9094(8) 21.7393(18) 10.6538(9) 90 109.819(1) 90 1941.25(8) 2 2.067 2.163 2.6-27.5 4429 3514 274 1184 295 0.034, 0.071 0.047, 0.076 1.052 1.377, -1.043
C34H34Ag2N8O10S2 994.57 monoclinic P21/c 0.25 0.11 0.07 10.6470(4) 23.8670(9) 7.9880(3) 90 107.313(1) 90 1937.88(13) 2 1.704 1.185 1.7-25.05 3127 2241 253 1000 295 0.055, 0.170 0.083, 0.245 1.052 1.524, -0.946
C27H26Ag2N4O8S 782.32 monoclinic C2/c 0.17 0.12 0.10 18.0322(14) 11.3434(8) 28.0498(21) 90 107.972(1) 90 5457.6(7) 8 1.904 1.571 2.2-25.2 4905 4079 370 3120 295 0.113, 0.396 0.122, 0.399 1.147 3.735, -1.700
C62H66Ag4N8O19S2 1722.85 monoclinic P21/n 0.25 0.13 0.06 18.3498(15) 20.1355(17) 18.6306(16) 90 102.890(1) 90 6710.2(10) 4 1.705 1.290 1.4-25.05 11857 8064 859 3464 295 0.054, 0.117 0.087, 0.133 1.009 1.002, -0.620
C26H36Ag4N8O13S2 1164.23 monoclinic P21 0.30 0.07 0.03 13.5178(13) 10.4635(10) 13.5715(13) 90 117.869(1) 90 1697.0(3) 2 2.279 2.476 2.6-25.0 5303 5001 469 1144 295 0.033,0.078 0.036,0.080 1.066 0.733, -0.703
compacted pellets. A papery mold, which is 311 mm3, was filled with the powder sample of a complex and pressed with a tablet machine in about 500 Kgf/cm2. The two copper probes were adhered onto the sample to place the circuit, and the resistance of the compacted pellet for the complex was recorded until its value becomes constant. In order to avoid the reaction of Ag(I) with copper generating metal silver, the ends of the copper probes were covered with a layer of silver metal. X-ray Structure Determination. Crystals with suitable sizes of 1-6 were selected for data collection by a Bruker Smart CCD area detector with graphite-monochromatized Mo KR radiation (λ = 0.71073 A˚). The data were integrated by use of the SAINT program,11 and this program also did the intensities corrected for Lorentz effect. The absorption was done by the SADABS program.12 The structures were solved by the heavy-atom method and successive Fourier syntheses. Full-matrix least-squares refinements on F2 were carried out using the SHELXL-97 package.13 All non-H atoms were anisotropically refined. H atoms on C atoms were placed in idealized positions and refined as riding atoms, with C-H=0.93 A˚ and Uiso(H)=1.2Ueq(C). All H atoms bonded to O atoms were located in difference Fourier maps and refined with distance restraints of O-H = 0.85(1) A˚. The crystal quality of complex 4 is not high, and the largest peak is near Ag2 (1.59 A˚), but the structure and composition are true and fully characterized by several methods. The drawings of the molecules were realized with the help of ORTEP-3 for Windows and Diamond 2.1e. All of the programs used are included in the WinGX Suite with version 1.70.14 Information concerning the crystallographic data collection and structure refinements is summarized in Table 1. The selected bond distances and angles for all these complexes are provided in Table S1, Supporting Information.
Results and Discussion Synthesis. Our aim is to study the influence of different N-donor ligands on the supramolecular architectures of silver 2-sulfobenzoate complexes and the coordination modes of sb2ligands. It is very interesting that complex 1 with polymeric structure, [Ag2(sb)]n, is soluble in water. This solubility provided simple reaction conditions in which a series of new complexes containing [Agx(sb)y] motifs could be easily synthesized. It is common knowledge that Ag complexes are not stable in the light. So we placed the reaction mixtures in the dark to protect them from light. During the exploration, precipitates
were quickly formed when mixing the reactants even by slow diffusion. Therefore, our new strategy was to drop ammonia solution into the reaction mixture until it was mostly dissolved and then it was filtered to get clear liquor to evaporate in the air. Many factors can influence the final products in the formation of self-assembled frameworks with compositional and structural diversity.15 In the process of synthesis of 2, we found that heating can improve the quality of the crystals. Moreover, it should be pointed that the sb salts prepared by NaOH but not acids used in the syntheses of complexes 4 and 5 led to good quality crystals. All these complexes, except 1 (soluble in water), are insoluble in normal solvents such as water, ethanol, methanol, acetone, and DMF. Structure of 1. Single-crystal X-ray analysis revealed that complex 1 is a two-dimensional (2-D) structure constructed by [Ag2(sb)] binuclear units. There exist two kinds of crystallographically unique silver ions in 1 (Figure 1a and Table S1, Supporting Information). The Ag1 is a six-coordinated distorted octahedral geometry completed by one silver ion and five oxygen atoms from four different sb2- ligands. The Ag2 is four-coordinated by four oxygen atoms from three different sb2- ligands. In the Ag1 and Ag2 coordinated environments, there are two kinds of Ag 3 3 3 Ag interactions, one of which is between the symmetric Ag1 ions, being 2.8029(7) A˚, which is significantly shorter than the Ag-Ag separation in metallic state (2.889 A˚), and the other of which is between Ag1 and Ag2 ions (dashed lines in Figure 1a), being 3.566 and 3.630 A˚, respectively, which is slightly longer than the sum of the van der Waals radii (3.44 A˚),16 indicating the absence of the metallic interactions. There is no classic hydrogen bond in 1; only Ag 3 3 3 O and O 3 3 3 O weak interactions are found in the alveolate 2-D network constructed by Ag(I) and sb ligands (Figure S1, Supporting Information). Additionally, weak π-π interactions occur between the adjacent aromatic rings with the centroid-to-centroid distance of 3.715(3) A˚, which enhances the integration of the 2-D networks in the three-dimensional (3-D) framework (Figure 1b).
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Figure 1. (a) ORTEP view of the asymmetric unit of complex 1. The thermal ellipsoids are drawn at 30% probability. Symmetry codes: i, 2 - x, -y, 1 - z; ii, 2 - x, 1 - y, 1 - z; iii, -1/2 þ x, 1/2 - y, z; iv, 2/3 - x, y þ 1/2, 1 - z; v, 2/3 - x, -1/2 þ y, 1 - z; vi, 2/5 - x, y - 1/2, 1 - z; vii, 5/2 - x, 3/2 - y, 1 - z; viii, -1/2 þ x, 1/2 - y, z; ix, 1/2 þ x, 1/2 - y, z. (b) The 3-D framework connected by π-π stacking in complex 1.
Structures of 2 and 3. Determination of the structures of 2 and 3 by X-ray crystallography showed that these two complexes are tetrameric and dimeric species, respectively. The asymmetric unit of 2 contains two crystallographically unique silver ions, each of which is four-coordinated distorted tetrahedral geometry (Figure 2a). The Ag1 and Ag2 bind to each other with a distance of 3.2521(5) A˚. Moreover, it is worth noting that examination of the intramolecular distances further shows the presence of obvious N-H 3 3 3 Ag close intramolecular interactions (Table S3, Supporting Information) between the metal centers and the amido H11 and H13 atoms (dashed lines in Figure 2a).17a Such N-H 3 3 3 Ag close interactions can be well-described as weak intramolecular N-H 3 3 3 M hydrogen bonding (a special case of hydrogen bonding).17,18 As shown in Figure 3a, in 3 the Ag1 is also four-coordinated distorted tetrahedral geometry completed by one nitrogen donor from an apy ligand and three oxygen atoms from two sb2- ligands.
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Figure 2. (a) The coordination environments of silvers in complex 2 with 30% thermal ellipsoids. Symmetry code: i = -x, -y, -z. (b) The 1-D double chain linked by N-H 3 3 3 O hydrogen bonds and the C-H 3 3 3 π (arene) interactions (H atoms and the π-ring are expressed in plum) in 2. (c) The Ag 3 3 3 π interactions in the 2-D layer (the related Ag atoms and π rings are shown in purple and blue).
Different from 1, four-membered rings (Ag2O2) are formed in the structures of 2 and 3. In 2, these rings are parallel to each other with a centroid-to-centroid distance of 3.1086(13) A˚, constructing cage-geometry tetrameric species with argentophilic Ag-Ag bonds of 3.2521(5) A˚ and O1 3 3 3 O3 weak interactions of 2.974 A˚. These species in 2 and 3 are linked by strong N-H 3 3 3 O hydrogen bonds (Table S2, Supporting Information) to form one-dimensional (1-D) chains, in which intra/intermolecular C-H 3 3 3 π (2.75 A˚ in 2 and 2.910 A˚ in 3) interactions reinforce the structures (Figures 2b and 3b). And in 2 every two chains are further connected by C-H 3 3 3 O (2.707 A˚) and Ag 3 3 3 π (3.352 A˚ to the π center and the two shortest Ag-C distances being 3.193 to 3.363 A˚) interactions to form a stair-like 2-D layer (Figure 2c). Furthermore, every tetramer in the stairs of 2 and dimer in the chains of 3 are linked to the adjacent six ones by intermolecular C-H 3 3 3 π (2.773 A˚ in 2 and 2.650 A˚ in 3) and C-H 3 3 3 O (2.699 A˚ in 2 and 2.893 A˚ in 3) interactions to form 3-D supramolecular structures.
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Figure 3. (a) The coordination environments of silvers in complex 3 with 30% thermal ellipsoids. Symmetry code: i = 1 - x, -y - 2, -z. (b) The 1-D double chains linked by N-H 3 3 3 O hydrogen bonds and the C-H 3 3 3 π (arene) interactions (H atoms and the π-ring are shown in plum) in 3. The unrelated H atoms are omitted for clarity.
Additionally, π-π interactions are found between apy ligands with centroid-to-centroid distances of 3.683(3) A˚ and 3.863(5) A˚ in 2 and 3, respectively. Structures of 4 and 5. X-ray crystallography has established that 4 is a 1-D double ladder-like chain (Figure 4b and Table S1, Supporting Information). As shown in Figure 4a, the asymmetric unit of 4 contains two silver ions, one sb2- and two bipy ligands and three water molecules. Both of the silver ions exhibit slightly distorted T-shaped geometries. The Ag1 is coordinated by two nitrogen donors from two different bipy ligands and one silver ion, with a Ag-Ag bond distance of 3.338(4) A˚ longer than those in 1 and 2. The Ag2 is coordinated by one oxygen and two nitrogen atoms. Complex 5 is a 2-D brick-wall-like layer framework constructed by the 1-D [Ag4(bpe)4(sb)2]n double chains (Figure 5b) and lattice water molecules. There are four crystallographically unique silver ions in its asymmetric unit (Figure 5a). The coordinated modes of Ag1 and Ag3 are similar to three-coordinated T-shaped geometries completed by two nitrogen atoms from two different bpe ligands, and one oxygen atom (O5) of the sb2- ligand. The Ag4 is fourcoordinated geometry by two nitrogen atoms from two different bpe ligands and two oxygen atoms of another sb2- ligand. The Ag2 is two-coordinated near-linear structure linked to two nitrogen atoms with a 177.8(2)° angle. And in the structure of complex 5, there are only two kinds of
Figure 4. (a) ORTEP view of the asymmetric unit of complex 4. The thermal ellipsoids are drawn at 30% probability. Symmetry codes: i, x, y - 1, z; ii, -x, y, 2/3 - z. (b) The 1-D [Ag2(bipy)2(sb)(H2O)]n tetra-chains in 4. The hydrogen atoms and uncoordinated water molecules are omitted for clarity. (c) The 3-D brick-wall-like hydrogen-bond structure in 4.
weak argentophilic Ag 3 3 3 Ag interactions (3.4677(8) A˚ and 3.6197(8) A˚). Each bipy ligand in 4 bridges silver(I) centers directly to form a double 1-D chain (Figure 4b) where the distance of Ag1-Ag2 is 3.678(3) A˚. There are face-to-face π-π stacking interactions between the arene rings of bipy ligands with the centroid separations from 3.709(12) A˚ to 3.805(13) A˚, which combines C-H 3 3 3 π (arene) intermolecular interactions (2.66 A˚ and 2.61 A˚) and hydrogen bonds between sb2- and water molecules to result in a 3-D structure. Different from complex 4, each bpe ligand in 5 bridges silver(I) centers to form a 2-D layer constructed by the almost vertical double chains (Figures 5b1 and 5b2). The centroid separations of π-π stacking interactions between the arene rings are 3.558(7) to 3.798(7) A˚. The 2-D layers intersect each other through the hydrogen bonds (Table S2, Supporting Information) between sb2- ligands and lattice water molecules and the C-H 3 3 3 π (arene) (2.88 and 2.96 A˚)
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Figure 6. (a) ORTEP view of the asymmetric unit of complex 6. The thermal ellipsoids are drawn at 30% probability. Symmetry codes: i, x, 1 þ y, z; ii, 2 - x, 1/2 þ y, -z; iii, 2 - x, -1/2 þ y; 1 - z. (b) Perspective views showing the 2-D sheet by Ag(hmt), including the coordinated oxygen atoms. The uncoordinated atoms in sb2are omitted for clarity. All the hydrogen atoms in (a) and (b) are omitted for clarity.
Figure 5. (a) ORTEP view of the asymmetric unit of complex 5. The thermal ellipsoids are drawn at 30% probability. Symmetry codes: i, -x - 1/2, y - 1/2, 3/2 - z; ii 1 þ x, 1 þ y, z; iii, x - 1, y - 1/2, z; iv, x - 1, y - 1, z. (b1) The 2D [Ag2(bpe)2(sb)]n layer in 5. (b2) Side view of the brick-wall-like layer in 5.
interactions between the hydrogen atoms of bpe and the arene rings of sb2- ligands to expand a 3-D brick-wall-like structure (Figure S2, Supporting Information). Structure of 6. Complex 6 is a 2-D polymer generated from combination of Ag(I), sb, and hmt ligands. Four kinds of crystallographically unique silver ions are found in its asymmetry unit (Figure 6a and Table S1, Supporting Information). The Ag1 adopts a five-coordinated distorted square-pyramidal geometry completed by one nitrogen atom from one hmt ligand, and four oxygen atoms from two sb2ligands. Both Ag2 and Ag3 are four-coordinated by nitrogen and oxygen atoms: three nitrogen atoms from three hmt ligands, one carboxylate oxygen atom from sb2- ligand for Ag2 and two nitrogen atoms of another two hmt ligands, two oxygen atoms of another sb2- ligand for Ag3, respectively. The Ag4 has T-shaped geometry completed by one nitrogen atom of a hmt ligand, one carboxylate oxygen atom and one water molecule. The hmt ligands bridge the silver atoms into a new topological motif of 2-D Ag-hmt puckered (6,3) and (8,3)
sheets in which hmt moieties act as 3- or 4-connecting nodes, as shown in Figure 6b. This is a new structural motif seen in Ag-hmt structures.19-21 The sb2- anions act as interlayered bridges to generate a 3-D network from the 2-D layers through hydrogen bonds. It should be pointed out that no strong π-π stacking interactions exist in complex 6 because of the huge space effect of hmt ligands. However, intermolecular C-H 3 3 3 π (arene) interactions (2.41, 2.74, and 2.86 A˚) exist between the arene rings of sb ligands and hydrogen atoms of hmt and sb ligands. Coordination Modes of sb2- in Complexes 1-6. As shown in Figures 1a-6a, all sb ligands are fully deprotonated in the form of sb2-. In 1, each sb2- group adopts a new μ8coordination mode, in which sulfonate group binds to five silver ions with two κ2-O atoms (binding to two longconnected silver ions with 3.630 and 3.566 A˚, respectively, dash lines in (1a) and (1b) of Chart 1) and one κ1-O atom. And two oxygen atoms are bridged by a Ag-Ag metallic bond of 2.8029(7) A˚ as shown in (1a) of Chart 1. The carboxylate group binds to four silver ions, and three of them are connected by metallic (2.8029(7) A˚) and argentophilic Ag-Ag interactions (3.566 A˚). The sb2- ligands in 2 display a μ4-coordination mode, in which both carboxylate and sulfonate groups adopt a monodentating mode bridging two metal atoms, with two kinds of Ag-Ag distances being 3.2521 A˚ and 3.602 A˚, respectively. In 3, each sb2adopts a μ2- coordination mode. The coordination mode of
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Chart 1. New Kinds of Coordination Modes of 2-Sulfobenzoates in 1-6
sb2- ligand in 4 is the same as that in 3 except the distances of Ag-O bonds as shown in (4) of Chart 1, which is not found in the previous references. In 5, two crystallography sb2ligands adopt two kinds of coordination modes ((5a) and (5b) in Chart 1), and one of them is a new μ3-coordination mode for sb2-. Like in the complex 5, the two crystallographically unique sb2- ligands in 6 adopt μ3- and μ2geometry modes, respectively, while in one of them two carboxylate oxygen atoms bridge three silver ions and two metal ions bridge three oxygen atoms as shown in (6) of Chart 1. Characterizations. Thermal Stability Behavior. Complex 1 experiences a two-step departure of sb2- ligands without a clear platform in the range 228-384 °C (calculated 28.84%, observed 29.30%), with a plateau in the range 375-533 °C, and loses weight again from 533 to 750 °C, leaving residue Ag2O (calculated 44.23%, observed 45.96%). Complex 2 starts to lose apy ligands in the temperature range 114-261 °C (calculated 31.11%, observed 29.98%), with the second-step weight loss of sb2- ligands with (Ag2SO3) 3 (Ag2O) left (calculated 25.22%, observed 26.54%). Complex 3 starts to lose weight at 75 °C, and in the range 75-621 °C, the weight loss is 60.72%, corresponding to the release of apy, apyHþ, and sb2- ligands (calculated 60.20%). For 4, the first-step weight loss of 15.46% from 79 to 172 °C corresponds to the release of two guest water molecules and sb2- ligands (calculated 15.86%). After a platform from 172 to 224 °C, 4,40 -bipy ligands and the coordinated water molecule starts to release until 442 °C (calculated 42.18%, observed 43.24%). Complex 5 starts to lose weight at 40 °C, and in the temperature range 40-141 °C, the weight loss is 9.79%, which corresponds to the release of nine water molecules (calculated 9.40%), followed by a short plateau to 157 °C and a two-step departure of ligands in the temperature range 157-271 °C and 271-459 °C, corresponding to the release of bpe and sb2- ligands (calculated 52.53%, observed 52.12%). Complex 6 is stable up to 98 °C, and the first-step weight loss is 3.48% in the temperature range 98-208 °C for the release of guest water (calculated 3.09%). Then from 208 to 498 °C hmt, the coordinated water and sb2- ligands begin to release without a clear inflection with the residue of Ag2SO4 (calculated 43.50%, observed 43.59%). These TG curves are provided in Figure S3, Supporting Information. Upon comparison to complexes 1-6, we find that the temperature sequence of the ligands-release is the following:
guest molecules < N-donor ligands < coordinated sb2ligands, which indicates that the Ag-N bonds are easier to break than Ag-O bonds. Compared to 1 and 2, complexes 3-6 begin to lose weight at lower temperatures due to the existence of the guest molecules. Fluorescent Emission. An obvious feature is that complexes 1-6 display strong blue emissions at 426, 453, and 470 nm for 1, 416, 452, and 470 nm for 2, 403, 453, and 465 nm for 3, 454 and 470 nm for 4, 410, 440, 453, and 470 nm for 5, and 387, and 470 nm for 6 in solid state at room temperature (λex = 220 nm) (Figures S4-S9, Supporting Information). The maximum emissions occur at 470 nm for complexes 1, 2, and 4-6, which is the same as that of sb ligand. While in 3 it occurs at 403 nm, which is blue-shifted about 70 nm compared to those of the free sb and apy ligands (both are at 470 nm). Compared to the similar-structure complex 2, such large blue shifts may likely be caused by the existence of the protonated counterion apyHþ, which baffled the ligand-to-ligand or ligand-to-metal charge transfer. And the maximum emission of complex 4 is red-shifted about 50 nm to 4,4-bipy ligand while that of 5 is blue-shifted about 30 nm to bpe ligand notwithstanding their similar structures, which may be ascribed to the different coordination modes of sb2- ligands in 4 and 5. Conductivity Studies. The room-temperature conductivities for four complexes were measured, with 4.08 10-6 S 3 cm-1 for 1, 5.64 10-6 S 3 cm-1 for 2, 3.93 10-6 S 3 cm-1 for 4, and 2.34 10-6 S 3 cm-1 for 5, indicating the semiconducting properties of these complexes, which can be attributed to corresponding different interactions considering the discrepancies in structures. In 1, there are several kinds of Ag-Ag interactions with one strong metallic bonding of 2.8028(7) A˚, significantly shorter than the metallic Ag-Ag separation (2.889 A˚), which guarantees the electrons transfer by forming Ag(0) and Ag(II) within the Ag chain.22 In the structure of 2, there are Ag-Ag 3 3 3 Ag 3 3 3 π chains (Figure 7a), linked by strong hydrogen bonds to construct a sheet (Figure 2c), which combines the π-π interactions (3.683(3) A˚) and may contribute to the conductivity traits. However, because the shortest distance from C to Ag(I) ion (3.193(4) A˚ and 3.363(3) A˚) is at the upper limit of the 2.89-3.37 A˚ range of Ag-η6 arene π interactions,23 its conductivity value is much lower than the PAH complexes.24 In 4 and 5 the existing compacted columnar aromatic π-π stacking (3.709(12) to 3.805(13) A˚ in 4 and 3.588(7) to
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much research is needed to study the method of strengthening the crystal packing. And further studies directed toward the synthesis of other silver-sb complexes to establish the relationship between the supra-molecular interactions and the electrical properties are underway. Conclusion In summary, six new silver(I) complexes with unique topological structures have been prepared. The sb2- ligands are fully deprotonated, with different coordination modes in complexes 1-6. It is μ8-coordination mode in 1, μ4-coordination mode in 2, and μ2-coordination mode in 3. In 4, sb2ligand just exists as a counterion with long Ag-O bonds. Two crystallographically unique sb2- are individually found in 5 and 6 with one new coordination mode, respectively. In 5, one sulfonate oxygen atom bridges two long-connected metal ions and one of the metal ion coordinates to one carboxylate oxygen atom. In 6, sb2- ligands adopt another new μ3geometry mode. In all, five kinds of new sb2- coordination modes and one new sulfonate mode have been found in these complexes. Interestingly, these six complexes provide a way of understanding abundant weak interactions, such as Ag-Ag argentophilicity, π-π stacking effects, Ag 3 3 3 π, C-H 3 3 3 π, N-H 3 3 3 Ag, and C-H 3 3 3 O interactions, and these interactions in 1-6 further assemble the structures into supramolecular architectures, showing different topologies and different properties, such as fluorescence and conductivity properties. Particularly for conducting properties, different interactions in the researched complexes contribute to electron-transfer. In 1, strong metallic Ag-Ag bonds (2.8028(7) A˚) and in 2, 4, and 5 Ag 3 3 3 π and/or π-π interactions provide the electron transfer pathway. Acknowledgment. The authors thank the National Natural Science Foundation of China (Grant 50073019) and the Zhejiang Provincial Natural Science Foundation (Grant Z407036). Supporting Information Available: Preparation of complexes 1-6, CIFs, additional figures, and tables. This information is available free of charge via the Internet at http://pubs.acs.org.
References Figure 7. (a) Perspective views showing Ag-Ag 3 3 3 Ag 3 3 3 π chains in 2. (b) The compacted aromatic π-π stacking interactions in 4. (c) The compacted aromatic π-π stacking interactions in 5. The corresponding Ag 3 3 3 Ag and significant interactions are labeled.
3.798(7) A˚ in 5) with Ag 3 3 3 Ag argentophilic interactions (3.338(4) to 4.222(4) A˚ in 4 and 3.472(3) to 3.624(4) A˚ in 5) may be the reasons for the conductivity (Figure 7b,c), whose values are lower than that observed in Ag(TCNQ).25 Obviously, the requirements for designing single component,26 neutral molecular metals have partially been fulfilled in the four complexes above, though the conducting values are relatively low, it still illustrates that some moderate interactions can act as transverse interactions to decrease the HOMO-LUMO gaps. As far as we know, this is the first reported conductive ternary silver complex with a different donor-atom. The poly component trait obstructs the compact packing between metal and ligands, which restricts the conducting performances, so it is more difficult to obtain ternary neutral molecule metals. This is only a threshold in this area and
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