and Two-Dimensional Ag(I) Networks Generated from Double Schiff

Novel One- and Two-Dimensional Ag(I) Networks Generated from Double Schiff Base Ligands with Disubstituted Quinoxaline Diazenes as the Terminal Binding Sites

CRYSTAL GROWTH & DESIGN 2005 VOL. 5, NO. 5 1857-1866

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

Cheng-Yong Su School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou 510275, People’s Republic of China Received April 14, 2005

ABSTRACT: The new double Schiff base ligand L7 (2,5-bis(2-benzodiazine)-3,4-diaza-2,4-hexadiene) with disubstituted quinoxaline diazenes was synthesized. Four new polymeric Ag(I) complexes based on L7, namely {Ag3(L7)3(BF4)3(CH2Cl2)3(H2O)}n (1), {Ag2.5(L7)1.5(ClO4)2.5(H2O)2}n (2), {Ag4(L7)3(PF6)4}n (3), and {Ag4(L7)3(SbF6)4}n (4), have been synthesized successfully. They were fully characterized by infrared spectroscopy, elemental analysis, and single-crystal X-ray diffraction. In compound 1, two Ag(I) atoms are held together by two L7 ligands through the inside middle chelating N donors to generate a binuclear “X-shaped” helical secondary building block. In compounds 2-4, three Ag(I) atoms are held together by three L7 ligands through the inside middle chelating N donors to afford a trinuclear crownlike secondary building block. These spontaneous self-organized supramolecular secondary building blocks were further linked together into the higher extended hierarchy through outside N-Ag(I) coordination interactions. Compound 1 features a two-dimensional net containing a molecular cage, and compounds 2-4 feature two- (2 and 3) and one-dimensional (4) molecular crown-containing polymeric complexes in the solid state, respectively. Introduction The use of organic spacers and metal ions to promote the self-assembly of organic-inorganic polymeric coordination frameworks has become a very active and important synthetic strategy recently.1 Generally, some control over the type and topology of the coordination polymers or supramolecular complexes generated from the self-assembly of inorganic metal species and organic spacers can be achieved by careful choice of organic ligand,2 inorganic counterion,3 solvent system,3 and metal salt to ligand ratio.4 Among these factors, the choice of the organic spacers is the single greatest influence in determining the type and topology of the product. As we know, the organic spacers serve to link metal sites and to propagate structural information expressed in the metal coordination preferences through the extended structure. Properties of organic spacers, such as coordination activity, length, geometry, and relative orientation of the donor groups, play a very important role in dictating polymer framework topology and even in affecting the formation of polymer vs oligomer vs molecule. This has been demonstrated well by many previous studies.5 Double Schiff base ligands, due to their specific geometry, including the different relative orientations of N donors and the zigzag conformation of the spacer moiety (-RCdNNdCR-) between the two terminal * To whom correspondence [email protected].

should

be

addressed.

E-mail:

coordination groups, may result in coordination polymers with novel network patterns not achievable by other rigid linking ligands, such as 4,4′-bipyridine, 1,2bis(4-pyridyl)ethene, and 1,2-bis(4-pyridyl)ethyne. Moreover, N donors on the bridging spacer could be the additional coordination sites and cause the double Schiff base molecules to behave as multidentate ligands. We have investigated the construction of polymeric metalorganic frameworks using double Schiff base ligands bridged by the zigzag -RCdNNdCR- spacer (Chart 1). We have demonstrated that the -RCdNNdCRbridging bipyridine bipyrazine ligands with different transition-metal ions did result in a series of coordination polymers with novel network patterns. Moreover, different attachments of side chains on the bridging -RCdNNdCR- spacer (from H to -CH3), different terminal coordination groups (from pyridyl to pyrazinyl), and different substituents on the terminal coordinating groups (from H to -CH3) gave rise to clear changes of coordination modes of the existing ligand system and, subsequently, the topologies of the final polymeric products.6 This encourages us to continue this project and expand the bipyridine and bipyrazine ligands L1L6 to the bibenzodiazine ligand L7. Herein, we report the four novel one- and two-dimensional polymeric complexes {Ag3(L7)3(BF4)3(CH2Cl2)3(H2O)}n (1), {Ag2.5(L7)1.5(ClO4)2.5(H2O)2}n (2), {Ag4(L7)3(PF6)4}n (3), and {Ag4(L7)3(SbF6)4}n (4), which are based on the new double Schiff base ligand L7 and AgBF4, AgClO4, AgPF6, and AgSbF6, respectively (Scheme 1).

10.1021/cg0501534 CCC: $30.25 © 2005 American Chemical Society Published on Web 07/13/2005

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Chart 1.

Dong et al.

Double Schiff Base Ligands Used in Construction of Polymeric Metal-Organic Complexes

Scheme 1. Synthesis of the New Ligand L7 and Its Ag(I) Coordination Polymers

Experimental Section Materials and Methods. AgClO4, AgPF6, AgSbF6, and AgBF4 (Acros) were used as obtained without further purification. 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. 1H NMR data were collected using an AM-300 spectrometer. Chemical shifts are reported in δ relative to TMS. All fluorescence measurements were carried out on a Cary Eclipse Spectrofluorimeter (Varian, Australia) equipped with a xenon lamp and quartz carrier at room temperature. Caution! One of the crystallization procedures involves AgClO4, which is a strong oxidizer. Synthesis of L7. 2-Acetyl-(1,4)-benzodiazine (1.29 g, 7.5 mmol) was dissolved in ethanol (30 mL), followed by dropwise addition of the hydrazine solution (85 wt % solution in water, 0.22 g, 3.75 mmol) to ethanol (8 mL). After 2 drops of formic acid were added, the mixture was stirred at room temperature for 48 h. After removal of the solvent under vacuum, the residue was extracted with methylene chloride and washed with water several times. The organic phase was dried over MgSO4 and filtered, and, upon removal of the solvent, an

analytically pure bright yellow crystalline solid was obtained in 85% yield. 1H NMR (CDCl3, ppm): 9.72 (s, 2 H, -C4N2H), 8.14-8.03 (q, 4 H, -C6H4), 7.81-7.70 (q, 4 H, -C6H4), 2.47 (s, 6 H, -CH3). IR (KBr, cm-1): 3112 (m), 3000 (m), 2940 (w), 1619 (s), 1489 (m), 1458 (m), 1400 (s), 1366 (s), 1202 (m), 1126 (m), 962 (s), 767 (s), 620 (s), 480 (s). Anal. Calcd for C20H16N6: C, 70.59; H, 4.71; N, 24.71. Found: C, 70.29; H, 4.82; N, 24.27. Synthesis of 1. A methanol solution (5 mL) of AgBF4 (9.75 mg, 0.050 mmol) was slowly diffused into a CH2Cl2 solution (5 mL) of L7 (8.6 mg, 0.025 mmol). Light yellow crystals formed in about one week in 86% yield. IR (cm-1, KBr pellet): 3461 (br), 2976 (s), 1607 (s), 1546 (s), 1491 (s), 1460 (s), 1367 (s), 1206 (s), 1081 (vs), 1028 (vs), 936 (s), 767 (s), 687 (s), 600 (s). 1H NMR (DMSO, ppm): 9.73 (s, 2 H, -C4N2H), 8.20-8.18 (q, 4 H, -C6H4), 7.96-7.92 (q, 4 H, -C6H4), 2.50 (s, 6 H, -CH3). Anal. Calcd for C63H56Ag3B3Cl6F12N18O: C, 40.26; H, 2.98; N, 13.42. Found: C, 40.41; H, 2.65; N, 13.14. Synthesis of 2. A methanol solution (5 mL) of AgClO4 (12.0 mg, 0.058 mmol) was slowly diffused into a CH2Cl2 solution (5 mL) of L7 (10.0 mg, 0.029 mmol). Light yellow crystals formed in about 5 days in 96% yield. IR (cm-1, KBr pellet): 3444 (br), 2976 (s), 2956 (w), 1601.73 (m), 1544.19 (m), 1490.83 (m), 1460.01 (m), 1366.82 (ms), 1204.60 (m), 1126.39 (m), 1098.63 (m), 1026.40 (w), 937.89 (s), 844.08 (vs), 766.55 (s), 561.13 (s). 1H NMR (DMSO, ppm): 9.73 (s, 2 H, -C4N2H), 8.21-8.18 (q, 4 H, -C6H4), 7.96-7.92 (q, 4 H, -C6H4), 2.50 (s, 6 H, -CH3). Anal. Calcd for C30H30Ag2.50Cl2.50N9O12: C, 33.74; H, 2.81; N, 11.81. Found: C, 33.54; H, 2.75; N, 11.54. Synthesis of 3. A methanol solution (5 mL) of AgPF6 (0.060 mmol) was slowly diffused into a CH2Cl2 solution (5 mL) of L7 (0.030 mmol). Light yellow crystals formed in about 1 week in 90% yield. IR (cm-1, KBr pellet): 3421 (br), 3200 (s), 1608 (s), 1544 (ms), 1495 (s), 1416 (w), 1368.8 (s), 1215 (ms), 1107 (s), 1081 (ms), 967 (w), 836 (vs), 765 (s), 558 (s). 1H NMR (DMSO, ppm): 9.71 (s, 2 H -C4N2H), 8.21-8.16 (q, 4 H, -C6H4), 7.94-7.91 (q, 4 H, -C6H4), 2.48 (s, 6 H, -CH3). Anal. Calcd for C60H48Ag4F24N18P4: C, 35.42; H, 2.36; N, 12.40. Found: C, 35.34; H, 2.28; N, 12.24. Synthesis of 4. A methanol solution (5 mL) of AgSbF6 (24 mg, 0.070 mmol) was slowly diffused into a CH2Cl2 solution (5 mL) of L7 (12.0 mg, 0.035 mmol). Light yellow crystals formed in about 1 week in 93% yield. IR (cm-1, KBr pellet):

One- and Two-Dimensional Ag(I) Networks

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Table 1. Crystallographic Data for 1-4 empirical formula fw cryst syst a (Å) b (Å) c (Å) β (deg) V (Å3) space group Z value F(calcd) (g/cm3) µ(Mo KR) (mm-1) temp (K) no. of observns (I > 3σ) final R indices (I > 2σ(I)): R1; wR2a a

1

2

3

4

C63H56Ag3B3Cl6F12N18O 1878.00 monoclinic 23.665(3) 34.893(5) 19.818(3) 111.076(2) 15270(4) C2/c 8 1.634 1.055 298(2) 12666 0.0843; 0.1968

C30H30Ag2.50Cl2.50N9O12 1066.93 monoclinic 24.059(3) 13.2261(16) 29.020(4) 99.581(2) 9105.5(19) C2/c 8 1.557 1.276 298(2) 7973 0.0843; 0.2076

C60H48Ag4F24N18P4 2032.52 monoclinic 23.589(12) 13.646(5) 25.115(11) 108.199(14) 7680(6) C2/c 4 1.758 1.197 298(2) 6665 0.0965; 0.1904

C60H48Ag4F24N18P4 2032.52 monoclinic 23.846(5) 13.773(3) 25.239(5) 108.33(3) 7868(3) C2/c 4 2.022 2.431 298(2) 6883 0.0751; 0.1512

R1 ) ∑||Fo| - |Fc||/∑|Fo|. wR2 ) {∑[w(Fo2 - Fc2)2]/∑[w(Fo2)2]}1/2. Table 2. Interatomic Distances (Å) and Bond Angles (deg) with Esd’s in Parentheses for 1a Ag(1)-N(7) Ag(1)-N(1) Ag(2)-N(18)#2 Ag(2)-N(13) Ag(3)-N(11) Ag(3)-N(14)#3 N(7)-Ag(1)-N(6)#1 N(6)#1-Ag(1)-N(1) N(6)#1-Ag(1)-N(3) N(18)#2-Ag(2)-N(2) N(2)-Ag(2)-N(13) N(2)-Ag(2)-N(15) N(11)-Ag(3)-N(8)#2 N(8)#2-Ag(3)-N(14)#3 N(8)#2-Ag(3)-N(9)#2

2.291(5) 2.371(4) 2.241(3) 2.331(5) 2.229(5) 2.298(5) 122.87(18) 122.80(16) 98.53(16) 123.42(14) 111.76(15) 117.43(13) 122.3(2) 109.40(18) 68.3(2)

Ag(1)-N(6)#1 Ag(1)-N(3) Ag(2)-N(2) Ag(2)-N(15) Ag(3)-N(8)#2 Ag(3)-N(9)#2 N(7)-Ag(1)-N(1) N(7)-Ag(1)-N(3) N(1)-Ag(1)-N(3) N(18)#2-Ag(2)-N(13) N(18)#2-Ag(2)-N(15) N(13)-Ag(2)-N(15) N(11)-Ag(3)-N(14)#3 N(11)-Ag(3)-N(9)#2 N(14)#3-Ag(3)-N(9)#2

2.296(4) 2.476(4) 2.287(4) 2.444(5) 2.292(6) 2.581(6) 111.35(16) 117.02(16) 69.56(14) 121.61(14) 98.23(14) 69.69(15) 124.7(2) 100.4(2) 116.65(18)

a Symmetry transformations used to generate equivalent atoms: (#1) -x, y, -z + 3/ ; (#2) -x + 1, y, -z + 3/ ; (#3) x + 1/ , y - 1/ , z; (#4) 2 2 2 2 x - 1/2, y + 1/2, z; (#5) -x + 1/2, -y + 1/2, -z + 2.

Table 3. Interatomic Distances (Å) and Bond Angles (deg) with Esds in Parentheses for 2a Ag(1)-N(1)#1 Ag(1)-N(3)#1 Ag(2)-N(7) Ag(2)-N(9) Ag(3)-N(6)#2 Ag(3)-O(12) N(1)#1-Ag(1)-N(1) N(1)-Ag(1)-N(3)#1 N(1)-Ag(1)-N(3) N(4)-Ag(2)-N(7) N(7)-Ag(2)-N(5) N(7)-Ag(2)-N(9) N(8)-Ag(3)-N(6)#2 N(6)#2-Ag(3)-O(12) N(6)#2-Ag(3)-N(2)#3

2.309(5) 2.348(5) 2.343(5) 2.402(4) 2.340(5) 2.403(7) 130.2(2) 126.74(14) 70.05(15) 137.22(17) 21.69(16) 70.68(15) 141.83(17) 100.0(2) 98.22(17)

Ag(1)-N(1) Ag(1)-N(3) Ag(2)-N(5) Ag(3)-N(8) Ag(3)-N(6)#2 Ag(3)-N(2)#3 N(1)#1-Ag(1)-N(3)#1 N(1)#1-Ag(1)-N(3) N(3)#1-Ag(1)-N(3) N(4)-Ag(2)-N(5) N(4)-Ag(2)-N(9) N(5)-Ag(2)-N(9) N(8)-Ag(3)-O(12) N(8)-Ag(3)-N(2)#3 O(12)-Ag(3)-N(2)#3

2.309(5) 2.348(5) 2.381(4) 2.300(5) 2.340(5) 2.462(5) 70.05(15) 126.74(14) 144.5(2) 70.58(15) 141.21(15) 123.32(15) 113.2(2) 103.08(18) 84.4(2)

a Symmetry transformations used to generate equivalent atoms: (#1) -x + 2, y, -z + 3/ ; (#2) x + 1/ , y + 1/ , z; (#3) x, y + 1, z; (#4) x, 2 2 2 y - 1, z; (#5) x - 1/2, y - 1/2, z.

3449 (br), 1620 (s), 1550 (s), 1490 (s), 1370 (s), 1205 (m), 1130 (m), 1110 (s), 1080 (s), 960 (m), 770 (s), 670 (vs), 600 (s). 1H NMR (DMSO, ppm): 9.73 (s, 2 H -C4N2H), 8.20-8.17 (q, 4 H, -C6H4), 7.96-7.92 (q, 4 H, -C6H4), 2.50 (s, 6 H, -CH3). Anal. Calcd for C60H48Ag4F24N18Sb4: C, 30.05; H, 2.00; N, 10.52. Found: C, 30.14; H, 2.05; N, 10.23. Single-Crystal Structure Determination. Suitable single crystals of 1-4 were selected and mounted in air onto thin glass fibers. X-ray intensity data were measured at 298(2) K on a Bruker SMART APEX CCD-based diffractometer (Mo KR radiation, λ ) 0.710 73 Å). The raw frame data for 1-4 were integrated into SHELX-format reflection files and corrected for Lorentz and polarization effects using SAINT.7 Corrections for incident and diffracted beam absorption effects were applied using SADABS.7 None of the crystals showed evidence of crystal decay during data collection. 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 Structural Analysis of 1. The reaction of AgBF4 with L7 in a 1:1 ratio in a CH2Cl2/MeOH mixed-solvent system afforded 1 as light yellow crystals in 86% yield (Scheme 1). Compound 1 crystallizes in the monoclinic space group C2/c. Compound 1 is not stable outside of the mother liquor and loses guest solvent molecules

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Table 4. Interatomic Distances (Å) and Bond Angles (deg) with Esds in Parentheses for 3a Ag(1)-N(5) Ag(1)-N(4) Ag(2)-N(1) Ag(2)-N(3)#1

2.281(10) 2.324(10) 2.300(9) 2.341(10)

N(5)-Ag(1)-N(7) N(7)-Ag(1)-N(4) N(7)-Ag(1)-N(9) N(1)-Ag(2)-N(1)#1 N(1)#1-Ag(2)-N(3)#1 N(1)#1-Ag(2)-N(3)

Ag(1)-N(7) Ag(1)-N(9) Ag(2)-N(1)#1 Ag(2)-N(3)

126.8(3) 129.4(4) 71.7(4) 125.7(5) 71.7(4) 129.9(4)

2.292(10) 2.328(8) 2.300(9) 2.341(10)

N(5)-Ag(1)-N(4) N(5)-Ag(1)-N(9) N(4)-Ag(1)-N(9) N(1)-Ag(2)-N(3)#1 N(1)-Ag(2)-N(3) N(3)#1-Ag(2)-N(3)

71.3(4) 129.6(4) 138.3(3) 129.9(4) 71.7(4) 137.9(5)

a Symmetry transformations used to generate equivalent atoms: (#1) -x + 1, y, -z + 1/2; (#2) -x + 1/2, -y + 1/2, -z; (#3) -x + 1/2, -y + 5/2, -z; (#4) -x + 1/2, -y + 3/2, -z + 1.

Table 5. Interatomic Distances (Å) and Bond Angles (deg) with Esds in Parentheses for 4a Ag(1)-N(1) Ag(1)-N(3) Ag(2)-N(5)#2 Ag(2)-N(4)#2 N(1)-Ag(1)-N(8) N(8)-Ag(1)-N(3) N(8)-Ag(1)-N(7) N(5)#2-Ag(2)-N(5) N(5)-Ag(2)-N(4)#2 N(5)-Ag(2)-N(4)

2.302(12) 2.337(12) 2.313(13) 2.377(11) 128.2(4) 129.5(5) 70.7(5) 127.1(6) 128.9(4) 72.8(5)

Ag(1)-N(8) Ag(1)-N(7) Ag(2)-N(5) Ag(2)-N(4)

2.329(13) 2.368(11) 2.313(12) 2.377(11)

N(1)-Ag(1)-N(3) N(1)-Ag(1)-N(7) N(3)-Ag(1)-N(7) N(5)#2-Ag(2)-N(4)#2 N(5)#2-Ag(2)-N(4) N(4)#2-Ag(2)-N(4)

70.0(5) 131.2(4) 138.3(4) 72.8(5) 128.9(4) 136.3(5)

a Symmetry transformations used to generate equivalent atoms: (#1) -x + 3/2, -y + 5/2, -z; (#2) -x + 2, y, -z + 1/2; (#3) -x + 3/2, -y + 3/2, -z + 1; (#4) -x + 3/2, -y + 1/2, -z.

quickly. The single-crystal X-ray structure of 1 revealed that the two-dimensional cationic network is composed of Ag(I) ions and double multidentate Schif base ligands L7 in a 1:1 ratio. As shown in Figure 1a, there are three

Dong et al.

crystallographically independent Ag(I) centers in 1, and each Ag(I) center lies in a distorted-tetrahedral coordination sphere which is defined by three pyrazinyl N donors from each of three L7 ligands and one Schiff base N donor from one of the three L7 ligands. The ligand is tetradentate and uses one pair of chelating donors in the middle and two exo-monodentate donors at the ends to coordinate to the Ag(I) atoms (Figure 1b). Two 2-fold symmetry-related Ag(I) centers are held together by two L7 ligands through the middle chelating N donors, affording a novel “X-shaped” binuclear helical secondary building block in which the Ag(I)‚‚‚Ag(I) distance is 8.0 Å (Figure 1c). In 1, the Ag-Npyrazinyl bond lengths range between 2.241 and 2.371 Å, while the Ag-NSchiff base bond distances lie in the range of 2.444-2.476 Å. All these bond lengths are very close to the corresponding bond lengths found in the reported Ag(I)-Schiff base molecular complexes.6 In compound 1, one Npyrazinyl and one NSchiff base atom in L7 are uncoordinated, probably due to the steric arrangement of the ligand. As shown in Figure 1b, the ligand in 1 is severely twisted. Two terminal benzodiazine groups do not lie in the same plane, and the dihedral angle between them is ca. 40°. In the solid state, binuclear helical secondary building blocks are connected to each other through exoNpyrazinyl-Ag(I) bonds to generate a novel two-dimensional network extended in the crystallographic ab plane (Figure 2a). In this two-dimensional net, a cagelike unit has been found. As shown in Figure 2b, six Ag(I) atoms are bound together by six L7 ligands into a {M6L6} molecular cage with crystallographic dimensions of ca. 11 × 16 Å, in which BF4- anions, CH2Cl2, and H2O guest

Figure 1. (a) Coordination environments of Ag(I) centers in 1. Key: Ag, sky blue; N, blue; C, white. (b) Ligand conformation and coordination mode of L7 in 1. Key: Ag, sky blue; N, blue; C, white. (c) Double helical secondary building block in 1. The two helical chains are shown in purple and green.



Figure 3. Crystal packing of 1 (viewed down the crystallographic c axis). Key: Ag, sky blue; N, blue; C, white; B, yellow; F, maroon; O, red; Cl, green-gray.

Figure 2. (a) Two-dimensional network of 1. (b) Molecular cage in 1. BF4- anions, CH2Cl2, and H2O guest solvent molecules are omitted for clarity. Key: Ag, sky blue; N, blue; C, white.

solvent molecules are located. In addition, these sheets are stacked together along the crystallographic c axis exactly to generate a noninterpenetrating porous framework that contains honeycomblike channels (Figure 3). The shortest interlayer Ag(I)‚‚‚Ag(I) distance is 10.02(3) Å. The assembly of honeycomblike channels is challenging, since the hexagon represents one of the most common motifs in nature;8 however, synthetic noninterpenetrating networks with honeycomblike cross sections are still unusual, because two-dimensional nets are always inclined to stack together in an -ABABor -ABCABC- stacking sequence, such as the stacking fashion observed in the compound [Ag(TCB)(CF3SO3)] (TCB ) 1,3,5-tricyanobenzene).8b Previously, in the bipyrazine ligand system L5-AgBF4, the compound [Ag(L5)](BF4)‚0.5CH3OH6c presents a noninterpenetrating zeolitelike three-dimensional network based on the 3 + 1 capped-trigonal-planar coordinated Ag(I) atoms, which is distinctly different from the L7-AgBF4 system herein, although L5 and L7 both act as tetradentate spacers. Varying the terminal coordination sites from pyrazinyl to benzodiazinyl groups is a decisive factor in determining the sub-building block and, moreover, the topologies of the polymeric products. Thermogravimetric analysis of 1 shows a weight loss of 4.1% from 35 to 175 °C corresponding to the loss of

the CH2Cl2 and H2O guest molecules (calculated 16.4%), which further confirms that compound 1 is unstable and loses guest solvent molecules quickly once it is removed from the mother liquor. A second weight loss of 36.5% from 225 to 400 °C corresponds to removal of two of the three L7 ligands (calculated 36.2%). The third weight loss, observed above 430 °C, corresponds to the release of the remaining ligand accompanied by the decomposition of AgBF4. Structural Analysis of 2-4. The reaction of AgClO4 with L7 in a 1:2 ratio in a CH2Cl2/MeOH mixed-solvent system afforded 2 as light yellow crystals in 96% yield (Scheme 1). Compound 2 crystallizes in the monoclinic space group C2/c. The X-ray crystal structure of 2 revealed that the two-dimensional cationic network is composed of Ag(I) ions and the double multidentate Schiff base ligand L7 in a 5:3 ratio. In 2, there are three types of crystallographically independent Ag(I) ions, each lying in a distorted-tetrahedral coordination environment. The tetrahedral coordination spheres of the first and second Ag(I) ions consist of two pyrazinyl N donors and two Schiff base N donors from two L7 ligands, respectively. The corresponding bond lengths vary within Ag(1)-N ) 2.309-2.348 Å and Ag(2)-N ) 2.309-2.348 Å. Thus, the L7 ligand herein is sixcoordinated and provides two pairs of chelating donors in the middle formed by one Npyrazine donor and one adjacent NSchiff base donor, which is different from the case in 1. As shown in Figure 4a, three L7 ligands use two pairs of chelating donors to crosswise link one Ag(1) and two Ag(2) ions into the novel trinuclear crownlike secondary building block M3L3,9 in which three Ag(I) atoms (one Ag(1) and two Ag(2) atoms) form an approximately equilateral triangle with Ag‚‚‚Ag distances of 4.676(3) and 4.693(3) Å. In the crownlike subunit, all three benzodiazine moieties are located on both sides of the trisilver plane, and the dihedral angle between two benzodiazine planes on the same side is ca. 110°. The dimensions of the crown (i.e. the distances between the exo-monodentate pyrazinyl N donors on the same side of the trisilver plane) are 8.82(3) and 9.72(3) Å, and the shortest distance between Ag(I) and the exomonodentate pyrazinyl N donor is 5.09(3) Å. In the solid state, these trisilver crownlike building blocks use six

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Figure 4. (a) Crown-like secondary building block in 2. Key: Ag, sky blue; N, blue; C, white. (b) Space-filling view of the crownlike secondary building block in 2. (c) Coordination mode of L7 in 2. Key: Ag, sky blue; N, blue; C, white.

exo-monodentate pyrazinyl N donors to bind the third tetrahedrally coordinated Ag(3) nodes into a novel noninterpenetrating two-dimensional crown-containing net extended in the crystallographic ab plane. Thus, the crown building block herein could be considered as a metal-containing six-coordinated ligand.10 As shown in Figure 5a, one Ag(3) ion shares three secondary crownlike building blocks through three external N-Ag(3) bonds (2.300-2.462 Å). In addition, one ClO4- anion coordinates to the Ag(3) center with a Ag-O bond length of 2.403(7) Å. These two-dimensional crown-containing nets arrange along the crystallographic c axis, and the coordinated ClO4- counterions are located between the layers (Figure 5c). The similar crown-like secondary building block generated from L6 and AgNO3 has been found in the compound Ag5(L6)3(NO3)3][Ag(NO3)3]‚CHCl3, which was reported by us previously.6c In this compound, three L6 ligands wrap around three Ag(I) atoms into a trinuclear {M3(L6)3} crownlike unit which is similar to the {M3(L7)3} moiety herein. The {M3(L6)3} unit is also six-

coordinated and is linked together through six external pyrazinyl N-Ag(I) bonds into a three-dimensional framework (Figure 6) instead of a two-dimensional net, as in 2. The difference between these two structures is obviously due to the coordination terminals, changing from a pyrazinyl group in L6 to a benzopyrazinyl group in L7. To confirm the universality of this novel self-assembly reaction, AgPF6 was used instead of AgClO4 to perform the reaction under the same conditions. The combination of AgPF6 with L7 afforded 3 as light yellow crystals in 90% yield (Scheme 1). Compound 3 crystallizes in the monoclinic space group C2/c. The single-crystal X-ray structure of 3 revealed that the two-dimensional cationic network is composed of Ag(I) ions and double multidentate Schiff base ligands L7 in a 1:1 ratio. As shown in Figure 7a, L7 herein acts as a five-coordinated ligand and uses two pairs of chelating donors to crosswise link three Ag(I) ions (one Ag(1) and two Ag(2)) into the trinuclear crownlike building block M3L3, as in 2 (Figure 7b). In the M3L3 subunit, three Ag(I) atoms form a


Figure 5. (a) Crownlike secondary building blocks connected by outside Ag-Npyrazine coordination interactions (viewed down the crystallographic c axis). Coordinated ClO4- counterions and hydrogen atoms are omitted for clarity. (b) Two sets of twodimensional nets stacking together along the crystallographic c axis. Coordinated ClO4- counterions are located between the layers. Key: Ag, sky blue; N, blue; C, gray; Cl, green; O, red.

exactly equilateral triangle with a Ag‚‚‚Ag distance of 4.75(3) Å (Figure 6b). The dimensions of the crown (i.e. the distances between the exo-monodentate N donors on the same side of the trisilver plane) are 8.89(3) and 8.88(3) Å, and the shortest distance between Ag(I) and the exo-monodentate N donor is 5.05(3) Å, which is almost identical with the corresponding data in 2. This trisilver crownlike building block uses four of six exomonodentate N donors to bind the third tetrahedrally


coordinated Ag(3) ions (Ag(3) is badly disordered and occupies a split position) into a novel noninterpenetrating two-dimensional crown-containing net (Figure 8). In comparison to compound 2, the inside crown Ag(I)-N bond lengths (2.281(10)-2.341(9) Å) are almost identical, whereas the four outside crown Ag(I)-N bond distances are remarkably elongated (2.576(14) Å). This difference is perhaps caused by the different templating effect of the PF6- counterion.3 Thus, the crown-like building block herein could be a tetradentate metalcontaining ligand instead of the six-coordinated ligand in 2. When 3 is viewed down the crystallographic [101] direction, elliptical cavities with an effective crosssection of ca. 14 × 8 Å have been found. These layers stack together to form tubular channels along the crystallographic c axis, in which uncoordinated PF6anions and distorted Ag(3) atoms are located (Figure 9). For exploring the templating role of counterions in the self-assembly process, AgSbF6 was used instead of AgPF6 to carry out the same reaction. The reaction of AgSbF6 with L7 in a 1:1 ratio in a CH2Cl2/MeOH mixedsolvent system afforded 4 as light yellow crystals in 93% yield (Scheme 1). Compound 4 crystallizes in the monoclinic space group C2/c. Single-crystal X-ray analysis showed that there are three crystallographically independent Ag(I) centers in 4. Two Ag(1) and one Ag(2) atoms incorporate the three L7 ligands into the same M3L3 crownlike secondary building block found in 2 and 3. The difference is that the M3L3 secondary building block in 4 acts as a bidentate spacer (Figure 10) to bind the third two-coordinated Ag(3) atoms with two long Ag-N bonds (2.52(2) Å) into a one-dimensional zigzag chain extended along the crystallographic c axis (Figure 11). Metal-assembled discrete molecular containers have attracted considerable attention recently. During the past few decades, numerous crownlike, bowllike, and conelike molecular containers have been designed and synthesized.11 To our knowledge, polymeric frameworks containing molecular containers as secondary building units and driven by M-L coordination interactions are still rare, especially for the molecular crown containing species.12 The present cases suggest a new approach to

Figure 6. View of the crown-containing three-dimensional framework of Ag5(L6)3(NO3)3][Ag(NO3)3]‚CHCl3.6c Hydrogen atoms and coordinated NO3- counterions are omitted for clarity. Key: Ag, sky blue; N, blue; C, white.

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Figure 9. Two-dimensional net stacking along the crystallographic c axis to generate tubular channels, in which uncoordinated PF6- counterions and distorted Ag(3) ions are located. Key: Ag, sky blue; N, blue; C, white; P, purple; F, green.

Figure 7. (a) Coordination mode of L7 in 3. (b) Crownlike secondary building block as a tetradentate spacer in 3. Key: Ag, sky blue; N, blue; C, white.

Figure 8. Two-dimensional net in 3. Key: Ag, sky blue; N, blue; C, white.

build up such types of polymolecular containers. That is, (1) spontaneous self-organization of a complicated secondary building unit with “inside” coordinating donors and (2) linkage of these secondary building units together into the higher extended hierarchy through “external” coordinating donor-metal interactions. Compounds 2-4 reported herein present additional good examples of crownlike secondary building block containing polymeric complexes based on this construction strategy, although some polycages driven by metalcounterions have been reported quite recently.13 Luminescent Properties of L7 and 2. Inorganicorganic hybrid coordination polymers have been investigated for fluorescence properties and for potential applications as luminescent materials, such as light-

Figure 10. Crownlike secondary unit as a bidentate spacer in 4. Key: Ag, sky blue; N, blue; C, white.

emitting diodes (LEDs).14 Owing to the ability of affecting the emission wavelength of organic materials, syntheses of inorganic-organic coordination polymers by the judicious choice of conjugated organic spacers and transition-metal centers can be an efficient method for obtaining new types of electroluminescent materials, especially for d10 or d10-d10 systems.15 We have been exploring the luminescent properties of L5-L6 and organic/inorganic coordination polymers and supramolecular complexes based on them in the solid state.6c,d The results indicate that emission colors of organic spacers were remarkably affected by their incorporation into metal-containing coordination compounds. The



Figure 11. One-dimensional zigzag crown-containing chain in 4. Key: Ag, sky blue; N, blue; C, white.

Figure 12. Photoinduced emission spectra of L7 (green) and 2 (blue) in the solid state.

luminescent properties of L7 and polymeric compounds 2 were investigated in the solid state and CH3CN solution. The solid-state fluorescence spectra of L7 and 2 are shown in Figure 12. As indicated in Figure 12, L7 exhibits one emission maximum at 375 nm (excitation wavelength 223 nm). For compound 2, the maximum emission bands are red shifted to 383 nm (excitation wavelength 218 nm). However, no enhancement of the fluorescence intensity is realized. The emission color of free L7 was significantly affected by its incorporation into the Ag(I)-containing polymeric compounds, as evidenced by the shift in emission. As shown in Figure 13, the emission maximum of L7 in CH3CN is at 460 nm, and that of complex 2 in the same solvent is almost identical (462 nm). This implies that the polymeric complexes disaggregate into oligomers or starting materials in solution, which is further confirmed by the 1H NMR spectra of complexes 1-4 being the same as that of the free ligand L7 in DMSO (Experimental Section). Conclusions One new double Schiff base ligand with a disubstituted quinoxaline diazenes (L7) and four new metalorganic polymeric compounds based on it and various Ag(I) salts were prepared. In comparison to L1-L6, the different benzodiazine terminal coordination group in L7 does result in different building blocks (a binuclear “X-shaped” helical core for 1 and a trinuclear crownlike core for 2-4) and, subsequently, topologies of the final products. Current efforts toward the preparation of new double Schiff base ligands by modification of

Figure 13. Photoinduced emission spectra of L7 (green) and 2 (blue) in CH3CN.

attachment of side chains and polar and nonpolar functional groups attached to 1,4-pyrazine and polymeric systems containing Ag(I) and other transitionmetal ions based on them are underway. Acknowledgment. We are grateful for financial support from the National Natural Science Foundation of China (No. 20371030), and we are also thankful for financial support from the Natural Science Foundation of Shandong province (No. Z2004B01). Supporting Information Available: Crystal structure data for compounds 1-4 as CIF files. This material is available free of charge via the Internet at http://pubs.acs.org.

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Dong et al. (10) (a) Dong, Y.-B.; Smith, M. D.; zur Loye, H.-C. Solid State Sciences 2000, 2, 335. (b) Dong, Y.-B.; Smith, M. D.; zur Loye, H.-C. Solid State Sciences 2000, 2, 861. (c) Dong, Y.B.; Smith, M. D.; zur Loye, H.-C. Angew. Chem., Int. Ed. 2000, 39, 4271. (d) Dong, Y.-B.; Smith, M. D.; zur Loye, H.C. Inorg. Chem. 2000, 39, 1943. (11) For reviews on metal-organic molecular containers, see: (a) Lehn, J.-M. Supramolecular Chemistry, Concepts and Perspectives; VCH: Weinheim, Germany, 1995. (b) Fujita, M. Chem. Soc. Rev. 1998, 27, 417. (c) Leininger, S.; Olenyuk, B.; Stang, P. J. Chem. Rev. 2000, 100, 853. (d) Jones, C. J. Chem. Soc. Rev. 1998, 27, 289. (e) Cotton, F. A.; Lin, C.; Murillo, C. A. Acc. Chem. Res. 2001, 34, 759. (12) The pyrazine-containing ligand L6-AgPF6 system was reported by Hannon and co-workers recently. Binuclear helical secondary building blocks are linked together into a two-dimensional net therein. See: Pascu, M.; Tuna, F.; Kolodziejczyk, E.; Pascu, G. I.; Clarkson, G.; Hannon, M. J. Dalton 2004, 1546. In this paper, the authors gave a wrong reference number in the figure captions of Figures 6 and 7. The corrected reference number should be ref 20 instead of ref 18. The L6-AgX (X ) SbF6-, NO3-) systems were reported earlier by us; see: Dong, Y.-B.; Zhao, X.; Tang, B.; Huang, R.-Q.; Wang, H.-Y.; Smith, M. D.; zur Loye, H.-C. Chem. Commun. 2004, 2, 220. In the compounds [Ag5(L6)3(NO3)3][Ag(NO3)3]‚3CHCl3 and [Ag2(L6)2](SbF6)2‚CH2Cl2, trinuclear crownlike and binuclear helical secondary building blocks are connected to each other by outside AgNpyrazine interactions into novel three-dimensional and onedimensional tubelike frameworks therein. (13) Su, C.-Y.; Cai, Y.-P.; Chen, C.-L.; Smith, M. D.; Kaim, W.; zur Loye, H.-C. J. Am. Chem. Soc. 2003, 125, 8595 and references therein. (14) (a) Altmann, M.; Bunz, U. H. F. Angew. Chem. 1995, 34, 569. (b) Bunz, U. H. F. Chem. Rev. 2000, 100, 1605. (15) (a) Ciurtin, D. M.; Pschirer, N. G.; Smith, M. D.; Bunz, U. H. F.; zur Loye, H.-C. Chem. Mater. 2001, 13, 2743. (b) Cariati, E.; Bu, X.; Ford, P. C. Chem. Mater. 2000, 12, 3385. (c) Wu¨rthner, F.; Sautter, A. Chem. Commun. 2000, 445. (d) Harvey, P. D.; Gray, H. B. J. Am. Chem. Soc. 1988, 110, 2145. (e) Catalano, V. J.; Kar, H. M.; Bennett, B. L. Inorg. Chem. 2000, 39, 121. (f) Tong, M.-L.; Chen, X.-M.; Ye, B.H.; Ji, L.-N. Angew. Chem., Int. Ed. 1999, 38, 2237. (g) Burini, A.; Bravi, R.; Fackler, J. P., Jr.; Galassi, R.; Grant, T. A.; Omary, M. A.; Pietroni, B. R.; Staples, R. J. Inorg. Chem. 2000, 39, 3158. (h) Seward, C.; Jia, W.-L.; Wang, R.Y.; Enright, G. D.; Wang, S.-N. Angew. Chem., Int. Ed. 2004, 43, 2933. (i) Yam, V. W.-W.; Lo, K. K.-W. Chem. Soc. Rev. 1999, 28, 323. (j) Wu, C.-D.; Ngo, H. L.; Lin, W. Chem. Commun. 2004, 1588.

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and Two-Dimensional Ag(I) Networks Generated from Double Schiff

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