Self-Assembly of {Ag2N4}-Core-Containing Coordination Polymers

Four new coordination polymers (1−4) were synthesized from solution reactions of L3−L4 with corresponding inorganic Ag(I) salts, respectively. Com...
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Self-Assembly of {Ag2N4}-Core-Containing Coordination Polymers from AgX (X ) NO3-, ClO4-, and PF6-) and Oxadiazole-Bridged 4,4′- and 3,3′- Biphenylamine Ligands

CRYSTAL GROWTH & DESIGN 2005 VOL. 5, NO. 2 585-591

Yu-Bin Dong,* Jun-Yan Cheng, Jian-Ping Ma, and Ru-Qi Huang College of Chemistry, Chemical Engineering and Materials Science and Shandong Key Lab of Functional Chemical Materials, Shandong Normal University, Jinan 250014, People’s Republic of China

Mark D. Smith Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208 Received June 16, 2004;

Revised Manuscript Received September 5, 2004

ABSTRACT: The coordination chemistry of the oxadiazole-bridged 4,4′- and 3,3′-biphenylamine ligands, namely, 2,5-bis(4-aminophenyl)-1,3,4-oxadiazole (L3) and 2,5-bis(3-aminophenyl)-1,3,4-oxadiazole (L4), with inorganic Ag(I) salts has been investigated. Four new coordination polymers (1-4) were synthesized from solution reactions of L3L4 with corresponding inorganic Ag(I) salts, respectively. Compound [Ag4(L3)4(NO3)2](NO3)2‚CH2Cl2 (1) (triclinic, P1 h , a ) 7.5566(5) Å, b ) 13.2903(8) Å, c ) 17.7449(11) Å, R ) 70.1790(10)°, β ) 81.7940(10)°, γ ) 83.4780(10)°, Z ) 4) was obtained from L3 and AgNO3 in a CH2Cl2/CH3OH mixed solvent system. In 1, cationic [Ag4(L3)4(NO3)2]2+ units are connected to each other by a long Ag-O bond into one-dimensional chains, which are further linked together by eight N-H‚‚‚O hydrogen-bonding systems into a three-dimensional H-bonded porous network with channels along the crystallographic a axis. [Ag(L3)]ClO4 (2) (monoclinic, I2/m, a ) 8.035(2) Å, b ) 17.395(5) Å, c ) 11.531(4) Å, β ) 103.807(4)°, Z ) 4) was generated from L3 and AgClO4 in a MeOH/H2O mixed solvent system. It adopts a novel three-dimensional structural motif in the solid state with big rhombic channels (ca. 14 × 8 Å). [Ag(L4)](NO3)‚ 0.5H2O (3) (orthorhombic, Ccca, a ) 11.8508(6) Å, b ) 15.8958(9) Å, c ) 15.9963(9) Å, Z ) 8) and Ag(L4)PF6 (4) (orthorhombic, Ccca, a ) 13.225(2) Å, b ) 15.998(3) Å, c ) 16.049(3) Å, Z ) 8) are isostructural and feature a novel two-dimensional zeolite-like net. All four new polymeric complexes contain the {Ag2N4} cluster moiety, and Ag‚‚‚Ag separations are in the range of 3.36-3.83 Å. Introduction The construction of new polymeric networks through the rational combination of organic ligands and metal ions is an area of intense current interest.1-4 In principle, some control over network topology can be gained by judicious selection of such reaction-influencing factors as the chemical structure of the organic spacers (ligands), the coordination geometry preference of the metal, the inorganic counterions, and the metal-toligand ratio.5-7 So far, of diverse elegant efforts to find key factors in the development of extended structures, the dominant synthetic strategy has been the use of various organic ligands. During the past decade, many one-, two-, and three-dimensional coordination polymers have been generated from transition-metal templates with rigid pyridyl-containing bidentate or multidentate organic spacers. A series of excellent reviews summarize some of these.1 In contrast to the well-developed coordination chemistry based on bipyridine-type ligands, efforts on biphenylamine-type ligands are quite unusual.8 Compared to bipyridine-type ligands, biphenylamine-type ligands have a relatively poor donor ability and an instability in solution and/or in air, which might be the reason for the limit of coordination chemistry * To whom correspondence [email protected].

should

be

addressed.

E-mail:

Chart 1. Rigid Organic Oxadiazole-Bridged Ligands Used in the Construction of Coordination Polymer Frameworks

based on biphenylamine-type ligands. A continuing project in our laboratory has been the development of coordination polymers generated from bent oxadiazolecontaining organic ligands9 and inorganic salts. So far, a variety of products resulting from the assembly of metal salts with bent oxadiazole-bridged 4,4′-bipy and 3,3′-bipy organic ligands (L1 and L2, Chart 1) have been synthesized by us and other research groups.10 Meanwhile, the coordination polymers or supramolecular complexes based on oxadiazole-bridged 4,4′-biphenylamine and 3,3′-biphenylamine organic ligands, such as 2,5-bis(4-aminophenyl)-1,3,4-oxadiazole (L3) and 2,5bis(3-aminophenyl)-1,3,4-oxadiazole (L4), are in general less numerous. Up to now, only two Ag(I)-containing

10.1021/cg049806r CCC: $30.25 © 2005 American Chemical Society Published on Web 10/26/2004

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Table 1. Crystallographic Data for 1-4 empirical formula fw cryst syst a (Å) b (Å) c (Å) R (deg) β (deg) γ (deg) V (Å3) space group Z F(calcd) (g/cm3) µ (Mo KR) (mm-1) temp (K) no. of observations (I > 3σ) final R indices [I > 2σ(I)]: R, Rw a

1

2

3

4

C56H48Ag4N20O16 1688.62 triclinic 7.5566(5) 13.2903(8) 17.7449(11) 70.1790(10) 81.7940(10) 83.4780(10) 1655.30(18) P1 h 1 1.694 1.246 150 6757 0.0297, 0.0728

C14H12AgClN4O5 459.60 monoclinic 8.035(2) 17.395(5) 11.531(4) 90 103.807(4) 90 1565.1(8) I2/m 4 1.951 1.494 293 4818 0.0456, 0.0870

C14H13AgN5O4.50 431.16 orthorhombic 11.8508(6) 15.8958(9) 15.9963(9) 90 90 90 3013.3(3) Ccca 8 1.901 1.373 150 1334 0.0268, 0.0627

C14H12AgF6N4OP 505.12 orthorhombic 13.225(2) 15.998(3) 16.049(3) 90 90 90 3395.6(10) Ccca 8 1.976 1.357 293 1872 0.0634, 0.1645

R ) ∑||Fo| - |Fc||/∑|Fo|. Rw ) {∑[w(Fo2 - Fc2)2]/∑[w(Fo2)2]}1/2.

polymeric compounds generated from L3 and L4 (Chart 1) have been reported by us.10b,g This encouraged us to undertake further studies on oxadiazole-bridged ligands of this type and explore their interesting coordination chemistry. Following this approach, we now expand this chemistry with L3 and L4. Four new Ag(I) coordination polymers, namely, [Ag4(L3)4(NO3)2](NO3)2‚CH2Cl2 (1), [Ag(L3)]ClO4 (2), [Ag(L4)](NO3)‚0.5H2O (3), and Ag(L4)PF6 (4), were successfully isolated. In addition, luminescent properties of L3 and L4 and 2 and 3 were investigated in the solid state. Experimental Section Materials and Methods. Ligands L3 (2,5-bis(4-aminobenzoyl)-1,3,4-oxadiazole) and L4 (2,5-bis(3-aminobenzoyl)-1,3,4oxadiazole) were prepared according to literature methods.11 All other solvents and reagents were used as received from commercial sources. Infrared (IR) samples were prepared as KBr pellets, and spectra were obtained in the 400-4000 cm-1 range using a Perkin-Elmer 1600 FTIR spectrometer. Elemental analyses were performed on a Perkin-Elmer model 2400 analyzer. All fluorescence measurements were carried out on a Cary Eclipse spectrofluorimeter (Varian, Australia) equipped with a xenon lamp and quartz carrier at room temperature. Safety note: Perchlorate salts of metal complexes with organic ligands are potentially explosive and should be handled with care. Preparation of [Ag4(L3)4(NO3)2](NO3)2‚CH2Cl2 (1). A solution of AgNO3 (17 mg, 0.10 mmol) in MeOH (8 mL) was layered onto a solution of L3 (25.2 mg, 0.10 mmol) in methylene chloride (8 mL). The solutions were left for about one week at room temperature, and yellow crystals were obtained. Yield: 90% (based on AgNO3). Anal. Calcd for Ag4C56H48N20O16‚CH2Cl2 (1): C, 38.56; H, 2.82; N, 15.79. Found: C, 37.93; H, 2.64; N, 16.02. IR (KBr, cm-1): 3540(s), 3400(s), 3290(s), 1610(vs), 1560(m), 1495(vs), 1445(m), 1390(vs), 1305(s), 1180(s), 1080(w), 1010(w), 980(w), 830(m), 740(m), 700(w). Preparation of [Ag(L3)]ClO4 (2). A solution of L3 (25.2 mg, 0.10 mmol) in MeOH (8 mL) was layered onto a solution of AgClO4 (20.8 mg, 0.10 mmol) in H2O (8 mL). The solutions were left for about three days at room temperature, and colorless crystals were obtained. Yield: 87% (based on AgClO4). Anal. Calcd for AgC14H12ClN4O5 (2): C, 36.55; H, 2.61; N, 12.18. Found: C, 36.11; H, 2.24; N, 11.70. IR (KBr, cm-1): 3350(vs), 1615(vs), 1565(m), 1500(vs), 1440(m), 1310(m), 1290(s), 1179(s), 1100(vs), 1070(vs), 1015(w), 870(w), 830(w), 740(w), 700(w). Preparation of [Ag(L4)](NO3)‚0.5H2O (3). A solution of L4 (25.2 mg, 0.10 mmol) in MeOH (8 mL) was layered onto a

solution of AgNO3 (17 mg, 0.10 mmol) in H2O (8 mL). The solutions were left for about one week at room temperature, and colorless crystals were obtained. Yield: 85% (based on AgNO3). Anal. Calcd for AgC14H13N5O4.50 (3): C, 38.96; H, 3.02; N, 16.24. Found: C, 38.49; H, 3.11; N, 15.98. IR (KBr, cm-1): 3500(w), 3350(s), 3200(s), 1615(s), 1595(s), 1560(vs), 1540(s), 1500(s), 1480(m), 1450(m), 1350(vs), 1245(m), 1220(w), 1080(m), 980(m), 855(s), 790(m), 728(m), 670(m). Preparation of Ag(L4)PF6 (4). A solution of AgPF6 (25.3 mg, 0.10 mmol) in MeOH (10 mL) was layered onto a solution of L4 (25.2 mg, 0.10 mmol) in THF (8 mL). The solutions were left for about three days at room temperature, and colorless crystals were obtained. Yield: 90% (based on AgPF6). Anal. Calcd for AgC14H12F6N4OP (4): C, 33.26; H, 2.38; N, 11.09. Found: C, 33.09; H, 2.33; N, 10.97. IR (KBr, cm-1): 3500(m), 3400(s), 3300(s), 1645(s), 1610(s), 1598(s), 1555(s), 1480(vs), 1320(s), 1240(m), 1148(m), 1080(m), 995(m), 840(vs), 728(m), 674(m). Single-Crystal Structure Determination. Suitable single crystals of 1-4 were selected and mounted onto the end of a thin glass fiber using inert oil. X-ray intensity data were measured at 150 K for compounds 1 and 3 and 293 K for 2 and 4 on a Bruker SMART APEX CCD-based diffractometer (Mo KR radiation, λ ) 0.71073 Å). The raw frame data for 1-4 were integrated into SHELX-format reflection files and corrected for Lorentz and polarization effects using SAINT.12 Corrections for incident and diffracted beam absorption effects were applied using SADABS.12 None of the crystals showed evidence of crystal decay during data collection. Compound 1 crystallized in the space group P1 ?, compound 2 crystallized in the space group I2/m, and compounds 3 and 4 crystallized in the unusual space group Ccca as determined by the systematic absences in the intensity data, intensity statistics, and the successful solution and refinement of the structures. All structures were solved by a combination of direct methods and difference Fourier syntheses and refined against F2 by the full-matrix least-squares technique. Crystal data, data collection parameters, and refinement statistics for 1-4 are listed in Table 1. Relevant interatomic bond distances and bond angles for 1-4 are given in Tables 2-5.

Results and Discussion Synthesis of Compounds 1-4. Compounds 1-4 were obtained as polymeric compounds by combination of L3 and L4 with different inorganic Ag(I) salts. In these specific reactions, the products do not depend on the ligand-to-metal ratio. However, increasing the metalto-ligand ratio resulted in somewhat higher yield and higher crystal quality. It is worthwhile to point out that the coordination chemistry of oxadiazole-containing

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Table 2. Interatomic Distances (Å) and Bond Angles (deg) with Esd’s in Parentheses for 1a Ag(1)-N(2) Ag(1)-N(7) Ag(2)-N(3) Ag(2)-O(11)

2.260(2) 2.300(2) 2.215(2) 2.4676(18)

Ag(1)-N(1)#1 Ag(1)-O(11)#2 Ag(2)-N(6) Ag(2)-O(12)

N(2)-Ag(1)-N(1)#1 128.45(8) N(1)#1-Ag(1)-N(7) 111.14(8)

2.292(2) 2.6351(17) 2.240(2) 2.5811(18)

N(2)-Ag(1)-N(7) 116.72(7) N(3)-Ag(2)-N(6) 127.79(7)

a Symmetry transformations used to generate equivalent atoms: #1, -x, -y + 2, -z + 1; #2, -x, -y + 1, -z + 1; #3, -x + 1, -y + 1, -z + 1.

Table 3. Interatomic Distances (Å) and Bond Angles (deg) with Esd’s in Parentheses for 2a Ag(1)-N(1)#1

2.314(3)

Ag(1)-N(2)#1

2.404(4)

N(1)#1-Ag(1)-N(1) 130.06(16) N(1)#1-Ag(1)-N(2)#1 97.93(12) N(1)-Ag(1)-N(2)#1 98.20(12) N(2)#1-Ag(1)-N(2) 141.18(18) a Symmetry transformations used to generate equivalent atoms: #1, -x, y, -z; #2, -x, -y, -z; #3, x, -y, z; #4, -x + 1/2, -y + 1/2, -z + 1/2; #5, x, -y + 1, z.

Table 4. Interatomic Distances (Å) and Bond Angles (deg) with Esd’s in Parentheses for 3a Ag(1)-N(1)

2.320(3)

Ag(1)-N(2)#2

2.417(2)

N(1)-Ag(1)-N(1)#1 N(2)#2-Ag(1)-N(2)#3

146.1(2) 116.39(11)

N(1)-Ag(1)-N(2)#2

90.35(10)

a

Symmetry transformations used to generate equivalent atoms: #1, x + 0, -y + 1/2, -z + 3/2; #2, -x + 1/2, -y + 1/2, -z + 1; #3, -x + 1/2, y, z + 1/2; #4, -x + 1, -y + 1/2, z; #5, -x + 1, y, -z + 3/2. Table 5. Interatomic Distances (Å) and Bond Angles (deg) with Esd’s in Parentheses for 4a Ag(1)-N(2)

2.348(5)

Ag(1)-N(1)#1

2.381(4)

N(2)#1-Ag(1)-N(2) N(2)-Ag(1)-N(1)#1

124.7(3) 118.20(15)

N(2)#1-Ag(1)-N(1)#1 N(1)#1-Ag(1)-N(1)

92.31(15) 112.9(2)

a Symmetry transformations used to generate equivalent atoms: #1, x + 0, -y + 3/2, -z + 3/2; #2, -x + 1/2, -y + 3/2, -z + 2; #3, -x + 0, -y + 3/2, z; #4, -x + 1, y, -z + 3/2.

ligands L1-L4 with Ag(I) appears to be quite versatile. Recently, a series of novel Ag(I) polymeric structures based on L1-L4 have been synthesized in our laboratory.10a-g In these polymeric Ag(I) compounds, the different coordination styles of oxadiazole-containingtype ligands were observed, which result in the network patterns of these polymeric compounds not achievable by other rigid linear bidentate organic spacers. Structural Analysis of [Ag4(L3)4(NO3)2](NO3)2‚ CH2Cl2 (1). Crystallization of L3 with AgNO3 in a methanol/methylene chloride mixed solvent system at room temperature afforded the infinite two-dimensional polymeric compound 1 in 90% yield. The metal-to-ligand ratio is 1:1. Crystals of 1 are not stable in air and turn opaque within minutes under ambient atmosphere. The compound crystallizes in the triclinic space group P1 ?. The crystallographically identifiable contents of the asymmetric unit consist of half of the [Ag4(L3)4(NO3)2]2+ complex situated on an inversion center, and another NO3- counterion. A region of disordered solvent is present parallel to the crystallographic [100] direction. Multiple electron density peaks were found in this region, for which no satisfactory disorder model could be achieved. The disorder species are probably a mixture of CH3OH, CH2Cl2, and H2O. The program SQUEEZE was used to account for the disorder: in the absence of

Figure 1. ORTEP figure of 1 with 50% probability ellipsoids (top). Side view of the cationic complex (bottom).

the solvent peaks, a solvent-accessible volume of 251.8 Å3, corresponding to 61e-, is present in the unit cell. The contribution of these species was removed from the final structure factor calculations. In the 1H NMR (in DMSO) spectrum of 1, proton resonance was observed at 5.60 ppm as a singlet, which was attributed to the CH2Cl2 guest molecule. Single-crystal analysis revealed that, as shown in Figure 1, there are two different Ag(I) centers in 1. The coordination sphere around the first silver atom is distorted triangular {AgN3}, being made of one Namino donor (Ag(1)-N(1)#1 ) 2.292(2) Å) and two Noxadiazole donors (Ag(1)-N(2) ) 2.260(2) Å and Ag(1)N(7) ) 2.300(2) Å) from three L3 ligands. The Ag-Namino bond length is considerably shorter than that of the compound Ag(L3)SO3CF310g (Ag-Namino ) 2.470(4) Å), but is almost identical with the Ag-Namino bond length found in Ag(L4)SO3CF310b (Ag-Namino ) 2.270(4)-2.312(4) Å). The second Ag(I) center adopts a distorted tetrahedral coordination environment which consists of two Noxadiazole donors (Ag(2)-N(3) ) 2.215(2) Å and Ag(2)-N(6) ) 2.240(2) Å) from two L3 ligands and two O donors from one bidentate NO3- counterion (Ag(2)O(11) ) 2.4676(18) Å and Ag(2)-O(12) ) 2.5811(18) Å). All Ag-N bond distances found in 1 are within the normal range observed in N-containing heterocyclic Ag(I) complexes.13 Each L3 acts as a tridentate ligand (one terminal -NH2 group is free) to bind four Ag(I) centers, including two Ag(1) and two Ag(2) centers. Ag(1) and Ag(2) atoms are bridged by four Noxadiazole atoms into a dinuclear core {Ag2N4} with a short Ag‚‚ ‚Ag distance of 3.50(4) Å, which is slightly longer than the sum of the van der Waals radii of two silver atoms, 3.44 Å.14 In addition, the ligand itself is not planar. The corresponding dihedral angles between three rings for each of two crystallographic L3 ligands are {C(1)‚‚‚C(6)}-{O(1)‚‚‚C(7)} ) 19.6°, {C(9)‚‚‚C(14)}{C(1)‚‚‚C(6)} ) 18.2°, and {O(1)‚‚‚C(7)}-{C(9)‚‚‚C(14)} ) 4.8° and {C(15)‚‚‚C(20)}-{O(2)‚‚‚C(22)} ) 7.9°, {C(15)‚‚‚C(20)}-{C(23)‚‚‚C(28)} ) 13.4°, and {O(2)‚‚‚C(22)}-{C(23)‚‚‚C(28)} ) 7.4°. It is noteworthy that only two of four NO3- counterions in the repeating

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Figure 2. One-dimensional chain in 1.

Figure 3. [100] view of the H-bonded three-dimensional network. Disordered CH2Cl2 solvent molecules in channels are shown as large red spheres.

unit are coordinated to Ag(I) centers; meanwhile the other two are free. So the [Ag4(L3)4(NO3)2]2+ repeating unit is a cationic complex. In the solid state, discrete [Ag4(L3)4(NO3)2]2+ cationic complexes are strung together by a long Ag-O (2.635(4) Å) bond into onedimensional chains along [010] (Figure 2). Eight extensive N-H‚‚‚O hydrogen-bonding systems (H‚‚‚Oanion ) 2.18-2.58 Å; N‚‚‚Oanion ) 2.941(3)-3.256(3) Å) consisting of uncoordinated -NH2 groups and four NO3counterions are present and link these one-dimensional chains into a three-dimensional H-bonded porous network with channels along the crystallographic a axis (effective cross section of ca. 11 × 17 Å15), in which distorted solvent molecules are located (Figure 3).

Figure 4. ORTEP figure of 2 with 50% probability ellipsoids.

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Structural Analysis of [Ag(L3)]ClO4 (2). Complex 2 consists of a polymeric cationic three-dimensional network and ClO4- anions, for which the asymmetric unit is shown in Figure 4. Compound 2 is air stable and crystallizes in the monoclinic space group I2/m. As shown in Figure 4, the Ag(I) center is located in a distorted tetrahedral coordination sphere which consists of two Noxadiazole donors (Ag-N(1) ) 2.314(3) Å and N(1)-Ag-N(1) ) 130.06(16)°) and two Namino donors (Ag-N(2) ) 2.404(4) Å and N(2)-Ag-N(2) ) 141.18(18)°). Two Ag(I) centers are bridged by four Noxadiazole atoms into a dinuclear core with a short Ag‚‚‚Ag contact ()3.3601(13) Å), which is slightly shorter than the sum of the van der Waals radii of two silver atoms, 3.44 Å.14 The ClO4- counterions are not involved in the Ag(I) coordination sphere. In 2, all four N donors (two Namino and two Noxadiazole donors) in L3 are fully utilized to bind Ag(I) metal ions into a polymeric structure, which is different from its coordination behavior in 1 and [Ag(L3)]SO3CF3, wherein L3 serves as a tridentate ligand. This may result from different templating effects caused by different counterions and solvent molecules. In the solid state, compound 2 exhibits a novel noninterpenetrating three-dimensional network with big rhombic channels along the crystallographic [001] direction (effective cross-section of ca. 14 × 8 Å), in which the uncoordinated ClO4- counterions are located. It is wellknown that the combination of tetrahedral Ag(I) or Cu(I) centers with rigid linear bidentate ligands generally results in the adamantoid structure.1b In 2, however, the specific geometry of the ligand L3 and also the coordination of the Noxadiazole donors result in the formation of this unique three-dimensional network (Figure 5) instead of the adamantoid framework. Structural Analysis of [Ag(L4)](NO3)‚0.5H2O (3) and Ag(L4)PF6 (4). The idea behind the use of ligand L4 is to control supramolecular motifs through 3,3′biphenylamine-type ligands. It is well-known that the relative orientations of the nitrogen donors on the pyridyl rings and also the different bridging spacings might result in unusual building blocks, which can lead to the construction of supramolecular motifs that have not been achieved using normal rigid linear organic ligands.1 We earlier reported on a series of novel coordination polymers generated from rigid bidentate 4,4′-bipyridine- and 3,3′-bipyridine-type Schiff-base

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Figure 5. Three-dimensional network of 2. ClO4- anions in channels are shown as large spheres.

Figure 7. Single two-dimensional net of 3 (top). Layer stacking of 3 (bottom).

Figure 6. Coordination environment of Ag(I) in 3.

ligands.16 Indeed, our previous studies demonstrated that the relative orientations of the coordinating sites are one of the most important factors to control the polymeric motifs. On the other hand, our previous studies also demonstrated that five-membered 1,3,4oxadiazole-bridged 3,3′-bipyridine ligand could bind metal ions by cis- or trans-conformation and result in the framework topology being versatile, sometimes even in affecting the formation of polymer vs molecule.10 When a solution of L4 in MeOH was treated with AgNO3 in H2O in a molar ratio of 1:1 (metal-to-ligand), compound 3 was obtained as colorless crystals in 85% yield. Compound 3 is air stable and forms with a high symmetry in the orthorhombic space group Ccca. All components of the crystal (Ag(I), L4, distorted NO3-, and distorted H2O) are situated on 2-fold axes. As shown in Figure 6, the Ag(I) center lies in a flattened tetrahedral coordination environment, which consists of two Namino donors (Ag-N(1) ) 2.320(3) Å and N(1)-Ag-N(1) ) 146.1(2)°) and two Noxadiazole donors (Ag-N(2) ) 2.417(2) Å and N(1)-Ag-N(1) ) 116.39(11)°). A similar {Ag2N4} cluster core is present with a Ag‚‚‚Ag distance of 3.70 Å, which is slightly longer than that in compounds 1 and 2. In the solid state, Ag(I) centers are connected to each other by cis-L4 ligands into a two-

dimensional porous network which is parallel to the crystallographic ac plane (Figure 7). The dimension of rhombic cavity is ca. 8.15 × 7.80 Å. There are two sets of equivalent two-dimensional nets in 1, which stack together in an “‚‚‚ABAB‚‚‚” fashion down the crystallographic b axis, such that the {Ag2N4} cluster core in one net occupies the center of the channels formed by the other (Figure 7). The closest interlayer Ag‚‚‚Ag separation is 8.27(3) Å. This stacking arrangement effectively reduces the void volume present in the structure; the distorted H2O guest molecules and NO3counterions are stuffed between the Ag(I)-L4 layers (Figure 8). Compound 4 was obtained by reaction of L4 and AgPF6 in a MeOH/THF mixed solvent system as colorless crystals at 90% yield. Single-crystal X-ray analysis revealed that compound 3 and 4 are isostructural. For compounds 3 and 4, there is an interesting change in the unit cell parameters upon increasing the counterion size from NO3- to PF6-. The cell volume increases as expected, and does so in an anisotropic way. The Ag‚‚‚Ag separation in dinuclear cluster core {Ag2N4} is 3.83 Å, which is longer than that in 3. The closest interlayer Ag‚‚‚Ag separation is 8.47(3) Å. It is interesting that no guest solvent molecules have been found in 4. Luminescent Properties. Mixed inorganic-organic hybrid coordination polymers and supramolecular com-

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Conclusions

Figure 8. Crystal packing of 3. NO3- anions between layers are shown as large spheres.

This study demonstrates that the oxadiazole-bridged 4,4′- and 3,3′- biphenylamine ligands 2,5-bis(4-aminophenyl)-1,3,4-oxadiazole (L3) and 2,5-bis(3-aminophenyl)-1,3,4-oxadiazole (L4) are capable of coordinating a Ag(I) metal center through both terminal phenylamine and bridged oxadiazole nitrogen donors, and of generating novel coordination polymers. Varying the orientation of terminal N donors is a decisive factor in determining the coordination environments of the metal centers and, moreover, the topologies of the polymeric products. We are currently extending this result by preparing new biphenylamine ligands of this type with different orientations of the nitrogen donors on the phenyl rings. We anticipate this approach to be useful for the construction of a variety of new transition-metal complexes and luminescent coordination polymers with novel structures that have the potential of leading to new fluorescent materials. Acknowledgment. We are grateful for financial support from the National Natural Science Foundation of China (Grant Nos. 20371030 and 20174023) and from the Open Fountain of State Key Lab of Crystal Materials. Supporting Information Available: Crystallographic data for the coordination compounds 1-4 in CIF format. This material is available free of charge via the Internet at http:// pubs.acs.org.

Figure 9. Photoinduced emission spectra of L3 and L4 and 2 and 3 in the solid state.

plexes have been investigated for fluorescence properties and for potential applications as light-emitting diodes (LEDs).17 Owing to the ability of affecting the emission wavelength of organic materials, syntheses of inorganicorganic coordination polymers by the judicious choice of organic spacers and transition-metal centers can be an efficient method for obtaining new types of electroluminescent materials, especially for d10 or d10-d10 systems18 and oxadiazole-containing complexes.19 The luminescent properties of L3 and L4 and compounds 2 and 3 were investigated in the solid state. The fluorescence spectra of L3 and L4 and compounds 2 and 3 are shown in Figure 9. L3 and L4 exhibit their emission maxima at 422 and 424 nm upon photoexcitation at 253 nm. The emission spectra of 2 and 3 exhibit their emission maxima at 458 and 475 nm (excitation wavelength 270 nm), respectively. Compared to the emission spectrum of L3 and L4, the maximum emission bands of 2 and 3 are red-shifted. However, no obvious enhancement of the fluorescence intensities are realized. The fluorescence properties of the free L3 and L4 were significantly affected by their incorporation into the Agcontaining polymeric compounds 2 and 3, as evidenced by the large red shift. In general, Ag(I) complexes might emit weak photoluminescence at low temperature, and consequently, compounds 2 and 3 reported herein represent the unusual examples of room-temperature luminescent Ag-containing polymeric compounds.20

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