Silver(I) Coordination Polymers Incorporating Neutral γ-Carbon Bound

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Silver(I) Coordination Polymers Incorporating Neutral γ-Carbon Bound N,N0-Bis(acetylacetone)alkanediimine Units Qi-Long Zhang,† Bi-Xue Zhu,*,† Yun-Qiuan Zhang,† Zhu Tao,† Jack K. Clegg,‡ Leonard F. Lindoy,*,‡ and Gang Wei*,§ †

Key Laboratory of Macrocyclic and Supramolecular Chemistry of Guizhou Province, Guizhou University, Guiyang 550025, P. R. China School of Chemistry, The University of Sydney, Sydney, New South Wales 2006, Australia § CSIRO Materials Science and Engineering, P.O. Box 218, Lindfield, New South Wales, Australia ‡

bS Supporting Information ABSTRACT: Five new silver(I) coordination polymers of types [Ag2L1(NO3)2]n (1), [Ag2L2(NO3)2]n (2), [Ag2L3(NO3)2]n (3), [Ag2L4(NO3)2]n (4), and [AgL5(NO3)]n (5) have been synthesized, where L1L5 are the Schiff base ligands formed from 2:1 condensation of acetylacetone with the symmetrical diamines H2N(CH2)nNH2, with n = 2 and 6 to give L1 and L2, 1,2-bis(2-aminophenoxy)ethane to give L3, 1,4-bis(2-aminophenoxy)butane to give L4, and 1,6-bis(4-aminophenoxy)butane to give L5. The single crystal X-ray structures of the Ag(I) complexes 15 have been determined. Both 1 and 2 adopt three-dimensional polymeric network structures, while 35 adopt two-dimensional-layered framework structures. In 1 and 2, the terminal O and γ-C atoms of two acacH-imine domains of the same ligand bind to different silver ions, while in each of 35 a γ-C from one or both acacH-imine domains binds to a silver ion, with the remaining coordination sites occupied by bridging monodentate or bidentate nitrato groups and/or a Schiff base ligand oxygen donor.

’ INTRODUCTION A common motivation for synthesizing new metal coordination polymers has been the prospect of generating unusual molecular architectures, especially with the aim of employing the resulting products as functional new materials.1 A range of influences, including the preferred coordination mode(s) of the metal ion, the nature of the ligand (including its flexibility), and the reaction conditions employed, may all influence the structure of the resulting polymeric product. As a consequence, it is not surprising that the control of molecular/ionic assembly processes used to form such systems still often remains a challenge.1,2 Over recent years, ligand systems incorporating different spacer groups between separated donor site domains have been increasingly employed to produce metal coordination polymers displaying a rich variety of structural motifs.3 For example, bis(β-diketone)4 and bis(β-diketone-imine) ligands57 incorporating both rigid and semirigid bridging spacers have been demonstrated to form a range of interesting oligo- and polymetallic complex architectures involving conventional metal ionheteroatom (O, N) coordination bonds. Typically, the β-diketone and β-diketoneimine ligand domains in such complexes coordinate to metal ions as bidentate units with loss of a proton, resulting in the formation of six-membered chelate rings.8 In contrast, examples in which bis-acetylacetone-imine (bis-acacH-imine) ligand complexes include metal coordination via the π-cloud associated with the “central” γ-carbon of this linkage have hitherto received r 2011 American Chemical Society

considerably less attention,6,7 even though the presence of γ-carbon coordination in simple β-diketone complexes has been well documented.9 We now describe the synthesis and complexation behavior toward Ag(I) of of the flexibly bridged Schiff base ligands, L1L5 (Scheme 1) formed from 2:1 condensation of acetylacetone with the symmetrical diamines H2N(CH2)nNH2 (with n = 2 and 6) to give L1 and L2, 1,2-bis(2-aminophenoxy)ethane to give L3, 1, 4-bis(2-aminophenoxy)butane to give L4, and 1,6-bis(4-aminophenoxy)butane to give L5. The d10 configuration of silver(I) is free from crystal field steric constraints and thus allows maximum coordination shell flexibility in forming metal complex species, a strategy that has been widely employed in the past to incorporate “low strain” metal nodes into metal-containing arrays.10,11 In part based on the results of our previous studies involving the interaction of enantiopure β-diketone-imine derivatives with Ag(I),6 we anticipated that the interaction of L1L5 (Scheme 1), incorporating acacH-imine units at either end of a flexible chain, might also give rise to unusual complexation behavior when reacted with this metal ion. The results of this investigation are presented below.

Received: September 16, 2011 Published: October 11, 2011 5688

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’ EXPERIMENTAL SECTION

1.93 (s, 6H, NdC(CH3)), 1.84 ppm (s, 6H, CdC(CH3)); IR (KBr, cm1): 3441 (m), 2948 (w), 1611 (s), 1583 (s), 1519 (m), 1444 (w), 1374 (w), 1288 (s), 1084 (w), 1019 (w), 978 (w), 851 (w) 738 cm1 (w). Anal. Calcd. for C12H20O2N2 (%): C, 64.26; H, 8.99; N, 12.49. Found: C, 64.25; H, 8.98; N, 12.50.

General. All reagents employed for syntheses were obtained commercially and were used either as supplied or purified by standard methods prior to use. Elemental (C, H, N) analysis data were obtained with a Vario ELIII elemental analyzer. IR spectra were recorded on samples as KBr pellets using a Bio-Rad FTIR spectrometer (in the 4004000 cm1 range).

Synthesis of N,N0 -Bis(acetylacetone)hexanediimine L2.

The synthesis of N,N0 -bis(acetylacetone)hexanediimine (L2)13 was similar to that for L1. Yield: 60%. 1H NMR (CDCl3): δ = 10.848 (s, 2H, enolOH), 4.937 (s, 2H, CdCH), 3.2043.231 (t, 4H, J = 6.5 Hz, CH2N=), 1.977 (s, 6H, NdC(CH3)), 1.898 (s, 6H, CdC(CH3)), 1.578 (s, 4H, CH2), 1.3851.400 ppm (t, 4H, J = 3.7 Hz, CH2); IR (KBr, cm1): 3441 (m), 3127 (m), 2930 (w), 2861 (w), 1609 (m), 1566 (s), 1388 (s), 1287 (w), 1101 (w), 1022 (w), 758 (w). Anal. Calcd. for C16H28N2O2 (%): C 68.53, H 10.06, N 9.99. Found: C 68.50, H 10.05, N 9.98.

Synthesis of N,N0 -Bis(acetylacetone)ethylenediimine L1.

N,N0 -Bis(acetylacetone)ethylenediimine (L1) was synthesized according to the reported procedure.12 Yield: 58%. 1 H NMR (CDCl 3): δ = 10.82 (s, 2H, enolOH), 4.93 (s, 2H, CH), 3.35 (s, 4H, CH2),

Scheme 1. Structures of L1L5

Synthesis of 1,2-Bis[2-(4-imino-pentan-20 -one)phenoxy]ethane (L3), 1,4-Bis[2-(40 -imino-pentan-20 -one)phenoxy]butane (L4),14 and 1,2-Bis[4-(40 -imino-pentan-20 -one)phenoxy]ethane (L5). L3: Acetylacetone (2.1 g, 20.2 mmol) in ethanol (10 mL) was

slowly added with stirring to 1,2-bis(20 -aminophenoxy)ethane (2.16 g, 10 mmol) in ethanol (60 mL) and the mixture was heated at reflux for 5 h. The solution was then allowed to cool and the solvent was partly removed under reduced pressure. The concentrated mixture was left overnight at room temperature in air, whereupon the L3 separated as white needle-like crystals. The crystals were collected by filtration and dried in air. Yield: 2.16 g (53%). 1H NMR (500 MHz, CDCl3): δ = 12.31 (s, 2H, enolOH), 6.917.27 (m, 8H, ArH), 5.16 (s, 2H, CdCH), 4.32 (s, 4H, OCH2), 2.096 (s, 6H, NC(CH3)), 1.916 ppm (s, 6H, C(CH3)); IR (KBr, cm1): 3432 (m), 3134 (s), 1611 (s), 1563 (s), 1508 (s), 1402 (s), 1305 (m), 1278 (m), 1217 (s), 1112 (w), 1060 (w), 1021 (w), 920 (m), 847 (w), 806 (w), 754 (m), 661 (w), 540 (w), 511(w). Anal. Calcd. for C24H28O4N2 (%): C, 70.57; H, 6.91; N 6.86. Found: C, 70.53; H, 6.89; N, 6.87.

Table 1. Crystallographic Data for Compounds 15 compound

1

2

3

4

5

empirical formula

C6H12AgN2O4

C8H14AgN2O4

C12H14AgN2O5

C13H16AgN2O5

C24H28AgO7

formula wt

282.03

310.08

374.12

388.15

578.36

space group

P21/c

P21/n

P21/c

P21/n

P21/c

a/Å

5.9790(5)

8.5611(4)

15.552(4)

16.456(2)

9.0801(5)

b/Å c/Å

18.5907(14) 8.1134(6)

9.6326(5) 14.2471(7)

5.1737(13) 18.305(5)

5.2236(7) 18.018(2)

8.1551(5) 33.2742(18)

α (deg)

90.00

90.00

90.00

90.00

90.00

β (deg)

90.217(3)

98.892(2)

114.020(9)

113.186(3)

95.781(2)

γ (deg)

90.00

90.00

90.00

90.00

90.00

V (Å3)

901.83(12)

2079.38(19)

1345.4(6)

1423.7(3)

2451.4(2)

Z

4

4

4

4

4

T (K)

293(2)

293(2)

293(2)

293(2)

293(2)

Fcalcd (g cm3) μ (mm1)

2.077 2.220

1.774 1.733

1.847 1.519

1.811 1.439

1.567 0.871 1184

F(000)

556

620

748

780

unique reflns

1747

2263

2571

2716

4716

obsd reflns

1569

2029

2279

2329

3736

parameters

119

120

183

191

317

Rint

0.0377

0.0261

0.0319

0.0561

0.0467

R1 (wR2) [I > 2σ(I)]

0.0749

0.0475

0.0283

0.0316

0.0356

GOF on F2

(0.1847) 1.146

(0.1343) 1.077

(0.0748) 1.048

(0.0937) 1.050

(0.0882) 1.065

largest diff. peak and hole (e Å3)

1.568

1.555

0.356

0.482

0.551

2.769

1.661

0.436

0.482

0.517

5689

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Table 2. Selected Bond Lengths (Å) and Angles (deg) for 15a 1 C(3)Ag(1)#1

2.387(13)

O(2)Ag(1)

2.347(10)

Ag(1)C(3)#2

2.387(13)

O(2)Ag(1)#3

2.524(10)

2.384(9)

Ag(1)O(2)#4

O(1)Ag(1) O(2)Ag(1)O(2)

#4

O(1)Ag(1)C(3)#2

127.28(17)

2.524(10) 115.5(5)

2 C(6)Ag(1)#5 O(1)Ag(1)

2.415(4) 2.370(3)

O(4)Ag(1) Ag(1)O(2)#7

O(2)Ag(1)#6

2.510(1)

Ag(1)O(3)#7

O1—Ag1—O4

92.09(14)

C(6)#5 Ag(1)O(2)#7

C(6)#5 Ag(1)O(3)#7

2.392(4) 2.510(5) 2.556(4) 149.48(13)

103.56(13) 3

C(3)Ag(1)

2.268(2)

O(4)Ag(1)

2.254(2)

O(4)Ag(1)#8

2.444(3)

Ag(1)O(4)#9

2.444(3)

O(4)Ag(1)C(3) C(3)Ag(1)O(4)#9

O(4)Ag(1)O(4)#9

163.20(9) 110.47(10)

85.87(6)

4 C(3)Ag(1)

2.287(3)

O(3)Ag(1)

2.243(2)

O(3)Ag(1)#10

2.497(2)

Ag(1)O(3)#11

2.497(2)

O(3)Ag(1)C(3)

161.04(11)

C(3)Ag(1)O(3)#11

108.00(10)

O(3)Ag(1)O(3)#11

86.01(6)

5 Ag(1)O(1)

2.272(3)

Ag(1)O(5)#12

2.539(3)

Ag(1)O(5) Ag(1)C(14)

2.368(3) 2.332(3)

O(5)Ag(1)#13

2.539(3)

O(1)Ag(1)C(14)

152.98(10)

O(1)Ag(1)O(5)#12

O(1)Ag(1)O(5)

92.16(11)

C(14)Ag(1)O(5)#12

92.09(10)

Ag(1)O(5)Ag(1)#13

143.24(11)

O(5)Ag(1)O(5)#12

123.68(4)

83.50(10)

Symmetry transformations used to generate equivalent atoms: #1, x + 1, y, z. #2, x  1, y, z. #3, x, y + 1/2, z  1/2. #4, x, y + 1/2, z + 1/2. #5, x + 2, y + 1, z + 2. #6, x + 3/2, y + 1/2, z + 3/2. #7, x + 3/2, y  1/2, z + 3/2. #8, x, y + 1/2, z + 1/2. #9, x, y  1/2, z + 1/2. #10, x + 3/2, y + 1/2, z + 1/2. #11, x + 3/2, y  1/2, z + 1/2. #12, x + 2, y  1/2, z + 3/2. #13, x + 2, y + 1/2, z + 3/2. a

L4 and L5 were synthesized by reaction of acetylacetone with 1, 4-bis(20 -aminophenoxy)butane and 1,2-bis(40 -aminophenoxy)ethane, respectively, using a procedure similar to that described for L3. L4: Yield: 2.83 g (65%). 1H NMR (500 MHz, CDCl3): δ = 12.26 (s, 2H, enolOH), 6.897.26 (m, 8H, ArH), 5.18 (s, 2H, CdCH), 4.07 (s, 4H, OCH2), 2.08 (s, 6H, NC(CH3)), 2.04 (s, 4H, CH2), 1.98 ppm (s, 6H, C(CH3)); IR (KBr, cm1): 3130 (s), 2938 (w), 2884 (w), 1614 (s), 1569 (m), 1518 (w), 1478 (w), 1448 (w), 1399 (m), 1354 (m), 1313 (w), 1272 (s), 1241 (m), 1189 (w), 1117 (w), 1053 (w), 972 (m), 917 (m), 849 (w), 754 (m), 679 (w). Anal. Calcd. for C26H32O4N2 (%): C 71.53; H, 7.39; N, 6.42. Found: C, 71.48; H, 7.38; N, 6.43. L5: Yield: 2.08 g (51%). 1H NMR (500 MHz, CDCl3): δ = 12.29 (s, 2H, enolOH), 6.947.27 (m, 8H, ArH), 5.16 (s, 2H, CdCH), 4.41 (s, 4H, OCH2), 2.07 (s, 6H, NC(CH3)), 1.95 ppm (s, 6H, C(CH3)); IR (KBr, cm1): 3432 (m), 3132 (s), 2992 (w), 2957 (w), 1618 (s), 1571 (m), 1515 (w), 1477 (m), 1450 (m), 1400 (m), 1353 (s), 1312 (w), 1273 (s), 1245 (m), 1209 (w), 1185 (w), 1119 (m), 1033 (m), 925 (w), 873 (w), 753 (s), 683 (w), 600 (w), 506 (w). Anal. Calcd. for C24H28O4N2 (%): C, 70.57; H, 6.91; N, 6.86. Found: C, 70.55; H, 6.89; N, 6.89. Preparation of Coordination Polymers 15. [Ag2L1(NO3)2]n (1). AgNO3 (0.17 g, 1 mmol) in ethanol (20 mL) was added dropwise over a period of 2 h to a stirred solution of L1 (0.112 mg, 0.5 mmol) in ethanol (20 mL). Slow evaporation of the solvent over 57 days in the absence of light led to colorless crystals, which were collected by filtration and dried in

air. Yield: 0.282 g (50%). Anal. Calcd. for C12H20Ag2N4O8 (%): C, 25.55; H, 3.57; N, 9.93. Found: C, 25.53; H, 3.54; N, 9.90. IR (KBr, cm1): 3465 (w), 3137 (w), 2948 (w), 1611 (m), 1578 (m), 1519 (w), 1436 (w), 1382 (s), 1289 (m), 1086 (w), 1020 (w), 980 (w), 846 (w), 737 (w), 646 cm1 (w). Compounds 25 were prepared in a manner analogous to the method used for [Ag2L1(NO3)2]n (1). Reagent and characterization details are listed below. Ag2L2(NO3)2]n (2). Reaction precursors: N,N0 -Bis(acetylacetone)hexanediimine (L2) and silver(I) nitrate (1:2); colorless block-shaped crystals. Yield: 0.279 g, 45%. Anal. Calcd. for C16H28Ag2N4O8 (%): C, 30.99; H, 4.55; N, 9.03. Found: C, 30.95; H, 4.50; N, 8.99. IR (KBr, cm1): 3441 (m), 3127 (s), 2930 (w), 2861 (w), 1609 (m), 1566 (m), 1388 (s), 1287 (w), 1101 (w), 1022 (w), 758 (m), 543 (w). [Ag2L3(NO3)2]n (3). Reaction precursors: L3 and silver(I) nitrate (1:2); colorless powder. Yield: 0.359 g, 48%. Anal. Calcd. for C24H28Ag2N4O10 (%): C, 40.25; H, 3.94; N, 7.82. Found: C, 40.28; H, 3.92; N 7.78. IR (KBr, cm1): 3131 (vs), 2928 (w), 1610 (s), 1563 (s), 1508 (m), 1388 (s), 1305 (m), 1280 (m), 1218 (m), 1112 (w), 1063 (w), 1022 (w), 921 (w), 848 (w), 811 (w), 754 (w), 663 (w), 543 (w), 514 (w), 416 (w). [Ag2L4(NO3)2]n (4). Reaction precursors: L4 and silver(I) nitrate (1:2); colorless powder. Yield: 0.388 g, 50%. Anal. Calcd. for C26H32Ag2N4O10 (%): C, 40.23; H, 4.16; N, 7.22. Found: C 40.19, H 4.13, N 7.25. IR (KBr, cm1): 3132 (vs), 2937 (w), 2883 (w), 1615 (s), 1570 (s), 1518 (w), 1479 (w), 1449 (w), 1384 (s), 1355 (m), 1314 (w), 1273 (s), 1242 5690

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Figure 2. (a) ORTEP diagram showing the coordination environments of Ag(I) in [Ag2L2(NO3)2]n (2) (displacement ellipsoids drawn at the 20% probability level). Symmetry codes: C1C1ai, C6Ag1ii, O2Ag1iii, Ag1O3iv; (i) x + 1, y + 2, z + 2; (ii) x + 2, y + 1, z + 2; (iii) x + 3/2, y + 1/2, z + 3/2; (iv) x + 3/2, y  1/2, z + 3/2. (b) View of nitrate anions linking the twisted eight-membered [Ag2L22] ring. (c) The 3D network of 2 viewed slightly obliquely to the a-axis. Hydrogen atoms have been omitted for clarity.

Figure 1. (a) View of [Ag2L1(NO3)2]n (1) with atom labeling (ORTEP diagram showing thermal ellipsoids drawn at 20% probability). Symmetry codes: (a) x + 2, y + 1, z. (b) Representation of the alternating arrangement of 22-membered and 12-membered rings, as viewed slightly off the a-axis. (c) The 3D network of 1 projected in the bc-plane. (m), 1189 (m), 1117 (w), 1053 (w), 1025 (w), 972 (w), 919 (w), 845 (w), 755 (m), 680 (w), 600 (w), 523 (w), 461 (w). [AgL5(NO3)]n (5). Reaction precursors: L5 and silver(I) nitrate (1:1); colorless powder. Yield: 0.434 g, 58%. Anal. Calcd. for C24H28AgN3O7 (%): C 49.84, H 4.88, N 7.27; Found: C, 49.85; H, 4.87; N 7.23. IR (KBr, cm1): 3129 (vs), 1618 (m), 1571 (w), 1515 (w), 1449 (w), 1385 (s), 1313 (w), 1274 (m), 1245 (w), 1118 (w), 1033 (w), 925 (w), 872 (w), 752 (m), 682 (w), 506 (w). X-ray Data Collection and Structure Determinations. Single-crystal X-ray diffraction studies of 15 were performed on a Bruker Smart Apex2 CCD diffractometer with a graphite-monochromated Mo Kα (λ = 0.71073 Å, μ = 0.828 mm1) radiation source in the jω scan mode . The data were corrected for Lorentz and polarization effects (SAINT),15 and multiscan absorption corrections based on equivalent reflections were applied (SADABS).16 The structure was elucidated by direct methods and refined by the full-matrix least-squares method on F2 with the SHELXS-97 and SHELXL-97 program packages, respectively.17 Crystallographic data are summarized in Table 1, and selected bond lengths and angles are given in Table 2.

’ RESULTS AND DISCUSSION Synthesis of Ag(I) Derivatives of L1L5. [Ag2L1(NO3)2]n

(1), [Ag2L2(NO3)2]n (2), [Ag2L3(NO3)2]n (3), [Ag2L4(NO3)2]n

(4), and [AgL5(NO3)]n (5) were isolated as colorless air-stable crystals by reaction of L1L5, respectively, with AgNO3 in ethanol. Microanalysis confirmed that 14 each exhibits a 2:1 ratio of Ag(I) to L, while the ratio in 5 is 1:1. Crystal Structures of the Ag(I) Derivatives. X-ray structures of each of the above compounds were obtained, and details of the structures are given in Figures 15 and Tables 13. All five compounds show some common structural features; for example, the respective silver centers are each bound to at least one bridging nitrato group and one η1 aryl-like interaction with the γ-carbon of the respective acacH-imine domains present in each Schiff-base ligand. The oxygens of bound acacH-imine domains may be considered to be present in their essentially deprotonated forms (see below), and the nitrogen atoms, which do not coordinate in any of the present systems, are concomitantly essentially protonated reflecting proton transfer from the adjacent “enol” oxygen site, with an intramolecular ionic N+H 3 3 3 O hydrogen bond (Table 3) linking each nitrogen atom to this oxygen atom (to generate a coplanar six-membered ring).18 As might be expected from this arrangement, the oxygen donors do in fact show substantial keto character, with CO bond lengths of 1.2421.257 Å that lie between those of a typical CO double bond (1.22 Å) and single bond (1.43 Å). The bound γ-carbon donor site adopts sp2 hybridization (the CCC angles range from 122 to 124°), with the structure being in accord with the presence of an essentially η1 aryl-like interaction between the π-cloud of the ligand and the silver ion; some charge polarization from the β-C and δ-C atoms to the central atom is expected to assist this binding.11 X-ray analyses show that 1 and 2 form 3D polymeric network structures, while 35 generate 2D layer structures (see below). [Ag2L1(NO3)2]n (1). The structure of 1 (Figure 1) shows that each Ag(I) ion adopts a distorted tetrahedral geometry, being bound to two oxygen donors from two different monodentate 5691

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Figure 3. (a) ORTEP diagram showing the coordination environments of Ag(I) in [Ag2L3(NO3)2]n (3) (displacement ellipsoids drawn at the 20% probability level). Symmetry codes: C12C12ai, O4Ag1ii. (i) x + 1, y + 1, z + 1. (ii) x, y + 1/2, z + 1/2. (b) The 2D grid layer of 3 resulting from the bridging of the adjacent 1D AgO chains by parallel L3 ligands. (c) The wave-like lamellar framework of 3 as viewed slightly off the b-axis.

bridging nitrate anions, as well as to a γ-carbon atom and an enolic O atom from two adjacent molecules of L1; the AgO bond distances range from 2.346(10)2.525(10) Å and the γ-CAg distance is 2.385(13) Å, typical of that observed in other Ag(I)π complexes.6,7 The bond angles around Ag(I) range from 97.1(4) to 127.29(18)°. The two acacH-imine domains of individual ligands are equivalent, with each domain bridging two silver sites through its terminal oxygen and γ-carbon (η1) sites. Each molecule of L 1 adopts a bis-bidentate coordination arrangement that connects four silver atoms (Figure 1a). Two Ag(I) centers are bound by the two γ-carbon atoms and the two O atoms present in the pair of acacH-imine domains of individual L1 ligands. This arrangement generates a 22-membered Ag2L12 ring in which the Ag 3 3 3 Ag separation is 8.95 Å. Ag(I) atoms in this Ag2L12 ring are further bridged by monodentate nitrate anions, forming a 12-membered ring with an approximate chair configuration incorporating four Ag atoms. As a consequence, a 2D layer is formed by an alternating arrangement of 22-membered and 12-membered rings; this is viewed slightly off the a-axis

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Figure 4. (a) ORTEP diagram showing the coordination environments of Ag(I) in [Ag2L4(NO3)2]n (4) (displacement ellipsoids drawn at the 20% probability level). Symmetry codes: C13C13ai, O3Ag1ii. (i) x + 2, y + 1, z; (ii) x + 3/2, y + 1/2, z + 1/2. (b) The 2D grid layer of 4 resulting from the bridging of the double-stranded AgOOAg chains by pairs of parallel L4 ligands. (c) The wave-like lamellar framework of 4 as viewed slightly off the b-axis. (d) The packing arrangement as viewed slightly off the b-axis.

in Figure 1b. The 2D layered framework is extended via a nitrate anion linking the adjacent Ag(I) centers to give a 3D network structure that projects in the bc-plane (Figure 1c). [Ag2L2(NO3)2(2). Unlike the structure of 1, the X-ray crystal structure of 2 [Ag2L2(NO3)2] shows that each Ag(I) ion is fivecoordinate being bound to three oxygen donors from two tribridging nitrate anions as well as to an oxygen from L2 and a η1-bound γ-carbon from another molecule of L2 (Figure 2a). As in 1, the two acacH-imine domains of individual ligands are equivalent in 2, with each domain connecting two silver sites via its terminal oxygen and its γ-carbon (η1) site. This connection of two equivalent Ag(I) ions by acacH-imine units from two L2 ligands results in a [Ag2L22] motif in the form of a twisted eightmembered ring (Figure 2b); the Ag 3 3 3 Ag separation in this ring is 5.16 Å. Pairs of tribridging nitrate anions are respectively 5692

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Figure 5. (a) ORTEP diagram showing the coordination environments of Ag(I) in [AgL5(NO3)]n (5) (20% probability ellipsoids). Symmetry codes: (i) x + 2, y  1/2, z + 3/2; (ii) x  1, y + 1/2, z + 1/2; (iii) x + 1, y + 1/2, z  1/2; (iv) x + 2, y + 1/2, z + 3/2. (b) The lamellar framework of 5 resulting from the bridging of the same two 1D linear zigzag chains by pairs of antiparallel L5 ligands. (c) The packing of the lamellar framework of 5 as viewed slightly off the b-axis.

positioned above and below the mean plane of this ring and connect the two Ag(I) of each [Ag2L22] motif to four adjacent Ag(I) centers located in different [Ag2L22] motifs (Figure 2b). This arrangement is repeated throughout the lattice to yield the 3D network (Figure 2c). [Ag2L3(NO3)2]n (3). The asymmetric unit of 3 comprises two Ag(I) ions, one L3 ligand, and two nitrate anions. As shown in Figure 3a, each Ag atom is trigonally coordinated by two oxygen atoms from two monodentate bridging nitrate anions, and a η1-bound γ-carbon from a L3 molecule. Unlike the arrangements

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in 1 and 2, each L3 adopts a bis-monodentate coordination mode in which each acacH-imine domain of a single L3 molecule binds a silver site only through its γ-carbon (η1) atom. Each nitrate anion acts as a bridging ligand to connect adjacent Ag(I) centers to form an AgO helical chain oriented along the crystallographic b-axis (Figure 3b) with an Ag 3 3 3 Ag distance of 4.24 Å. These AgO chains are cross-linked by parallel bis-monodentate L3 ligands to form a 2D grid layer, which shows a wave-like lamellar structure when viewed down the b-axis (Figure 3c). Pairs of adjacent L3 ligands connect the AgO helical chains to form a series of nonplanar 38-membered rings, with the Ag 3 3 3 Ag separation between “diagonally opposite” centers across each ring being 12.08 and 17.88 Å; the separation between Ag centers linked by L3 is 13.00 Å. These 2D layers are further extended in the crystallographic bc-plane to give the packing arrangement shown in Figure 3d. The shortest Ag 3 3 3 Ag distance between adjacent layers is 6.90 Å. [Ag2L4(NO3)2]n (4). The asymmetric unit of 4 comprises two Ag(I) cations, one bis-monodentate L 4 molecule, and two bridging bidentate nitrate anions (Figure 4a). Each Ag(I) ion is four-coordinated by three oxygen atoms from three different bridging bidentate nitrate anions, plus a η1-bound γ-carbon from a L4 ligand and shows a distorted tetrahedral geometry. The coordination of L4 is similar to that of L3 in 3, with each acac H-imine domain in a given L4 molecule binding to a silver site only through its γ-carbon (η1) atom. Each Ag(I) shows a distorted tetrahedral geometry, with AgO bond distances ranging from 2.246(3) to 2.701(3) Å and an AgC (γ-carbon) distance of 2.284(3) Å. The coordination bond angles around Ag(I) range from 76.61(6)° to 160.98(12)°. Unlike in 3, each nitrate ligand in 4 acts as a bidentate bridging group that connects adjacent Ag(I) centers to generate a doublestranded AgOOAg chain oriented along the crystallographic b-axis (Figure 4b)  with the Ag 3 3 3 Ag separation being 5.22 Å. Any two adjacent Ag(I) centers lying in the doublestranded chains and two bridging nitrate anions form a sixmembered ring with a Ag 3 3 3 Ag separation of 4.22 Å. These sixmembered rings are linked to form a ladder-shaped framework in which the double-stranded AgOOAg chain is cross-linked through parallel bis-monodentate L4 ligands to the AgO OAg chain of an adjacent ladder-shaped framework to yield a 2D grid layer (Figure 5b). This gives rise to a wave-like lamellar structure when viewed down the b-axis (Figure 5c). Two adjacent L4 ligands between AgOOAg chains form a noncoplanar 42-membered ring, with “diagonally opposite” Ag 3 3 3 Ag separations across this ring of 12.69 and 15.76 Å; the separation between Ag centers linked by L4 is 13.32 Å. The 2D layers are further extended in the crystallographic ac-plane to give the layered packing arrangement shown in Figure 4d. The shortest Ag 3 3 3 Ag distance between adjacent layers is 7.00 Å. [AgL5NO3]n (5). The structure of 5 (Figure 5a) shows that each Ag(I) ion is bound to two oxygen donors from two bridging nitrate anions as well as to a η1-bound γ-carbon from one L5 and an oxygen donor from a second (adjacent) L5 ligand. Each Ag(I) shows a distorted tetrahedral geometry, with the AgO bond distances ranging from 2.272(3) to 2.370(3) Å and a AgC (γ-carbon) distance of 2.331(3) Å. The coordination bond angles around silver range from 83.49(11)° to 123.65(4)°. In contrast to the structures discussed so far, the two acac H-imine domains in individual L5 ligands are nonequivalent. That is, one domain binds a silver site via its terminal oxygen, 5693

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Table 3. Intramolecular Ionic N+H 3 3 3 O Hydrogen-Bonding Geometries for 15 complex

donor

acceptor

DH (Å)

HA (Å)

DA (Å)

DHA angle (deg)

1

N(1)H(1) 3 3 3 (1) N(1)H(1) 3 3 3 O1) N(1)H(1) 3 3 3 O(1)

O(1)

0.8602

1.9624

2.639(15)

134.72

O(1)

0.8597

1.9379

2.635(4)

137.28

O(1)

0.8601

1.9721

2.695(3)

140.98

N(1)H(1) 3 3 3 O(1) N(1)H(1) 3 3 3 O(1)

O(1)

0.8601

2.0108

2.720(4)

139.12

O(1)

0.8601

1.9371

2.622(3)

135.66

2 3 4 5

while the other binds a different silver site through its γ-carbon (η1) atom. Neighboring Ag centers are connected by bridging monodentate NO3 groups to form a 1D zigzag chain that extends along the b-axis with an Ag 3 3 3 Ag separation of 4.66 Å (Figure 5b). Two adjacent pairs of antiparallel L5 ligands linked by doubly bridging AgOAg chains define a nonplanar 48membered macrocycle, with “opposite” Ag 3 3 3 Ag separations across this ring of 18.42 and 22.07 Å; the separation between Ag centers linked by L4 is 19.79 Å. In this case, the two 1D zigzag AgOAg chains cross-linked by pairs of antiparallel L5 ligands form thicker lamella than what occurs in 3 and 4 when viewed along the b-axis. The layers are further extended to give the layered packing arrangement shown in Figure 5c. The shortest Ag 3 3 3 Ag distance between adjacent layers in this wavelike structure is 8.53 Å.

’ CONCLUSION In this study, we have employed a series of five ligands incorporating two neutral acac-imine domains bridged by flexible linking groups to synthesize the new Ag(I) coordination networks 15. Apart from their considerable intrinsic interest, the respective polymer products are noteworthy on at least three counts. First, reflecting the presence of different spacer groups, the results serve to exemplify the remarkable structural diversity possible from using related ligands of type L1L5. Second, while numerous examples of metal complexes of deprotonated β-diketoneiminato-containing Schiff base ligands have been reported, examples of such motifs coordinating in their neutral (nondeprotonated) form are very rare. Third, all five complex species represent new examples of the exceedingly uncommon category of metal complexes incorporating η1-coordination of γ-carbon atoms incorporated in neutral acacHimine ligand units. ’ ASSOCIATED CONTENT Supporting Information. CIF files for structures 15. This material is available free of charge via the Internet at http:// pubs.acs.org.

bS

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected] (B.-X.Z.); [email protected]. edu.au (L.F.L.); [email protected] (G.W.).

’ ACKNOWLEDGMENT This work was supported by the National Natural Science Foundation of China (Grant No. 21061003), the International Collaborative Project of Guizhou Province (No. [2009]700104),

and the “Chun-Hui” Funds of Chinese Ministry of Education (No. Z092008).

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