Anion dependent formation of Ag(I) complexes of multidentate azine ligands: Synthesis and structural study

Polyhedron 27 (2008) 2681–2687

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Anion dependent formation of Ag(I) complexes of multidentate azine ligands: Synthesis and structural study Chih-Yu Wu, Chen-Shiang Lee, Sachindranath Pal, Wen-Shu Hwang * Department of Chemistry, National Dong Hwa University, 1, Sec. 2, Da-Hsueh Road, Shoufeng, Hualien 974, Taiwan, ROC

a r t i c l e

i n f o

Article history: Received 1 November 2007 Accepted 12 May 2008 Available online 28 June 2008 Keywords: Azine Ag(I) complexes Anion influence Supramolecular chemistry

a b s t r a c t The extended structures of Ag-complexes of the azine based ligands phenyl-2-pyridyl ketone azine (L1) and di-2-pyridyl ketone azine (L2) are reported, and focus is made on the investigation of the influence of the anion and supramolecular interactions on the self-assembly. Using AgNO3, AgClO4 and CF3COOAg salts as starting materials for both ligands in acetonitrile, we observed the formation of the dinuclear complexes [Ag2(L1)2](NO3)2 (1a), [Ag2(L1)2](ClO4)2 (1b), from L1, the tetranuclear complexes [Ag4(L2)2 (NO3)(CH3CN)2](NO3)3 (2a), [Ag4(L2)2(CF3COO)3CH3CN](CF3COO) (2b) and the linear chain polynuclear complex {[Ag3(L2)2] (ClO4)3}n (3) from L2. The X-ray structures show that the molecular geometry depends on the choice of anion. The silver centers have distorted tetrahedral coordination geometry in all the complexes. Weak hydrogen bonding and other interactions result in 2-D and 3-D networks in these complexes. Ó 2008 Elsevier Ltd. All rights reserved.

1. Introduction Azine and its derivatives are well known and are a useful class of organic compounds [1]. These compounds display important biological properties, are of importance for drug development [2], and are also used to develop supramolecular chemistry [1,3]. Supramolecular materials are found in a variety of applications including separation and host–guest interactions [4], catalytic properties [5], gas storage [6], non-linear optics [7] and magnetism [8]. So the design of metal–organic coordination polymers of supramolecular architecture, using non-covalent interactions such as electrostatic, hydrogen bonding and p-stacking, is an important area for supramolecular chemists and crystal engineers [9]. The formation of supramolecules is largely affected by the organic ligands, the nature of the metal ions, counter anions and other factors [10]. The role of anions in supramolecular chemistry is of enormous interest because of its application in ion pair recognition and anion exchange [11]. Recently, metallosupramolecular systems have been described for various types of ligands in which the anion and solvent play an important role in the design of the molecular architecture [9,11a,12]. As a soft acid the Ag(I) ion plays a central role in the formulation of such supramolecular assemblies, it favors stable coordination to soft bases like unsaturated nitrogen and sulfur [13]. There has only been a limited structural study of azine ligand based Ag-complexes [1b,3a,14]. Here we re-

* Corresponding author. Tel.: +886 3 8632001; fax: +886 3 8632000. E-mail address: [email protected] (W.-S. Hwang). 0277-5387/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2008.05.025

port the anion dependent formation of new Ag(I) complexes with pyridyl ketone azines. 2. Experimental 2.1. General The solvents and reagents were purchased from general sources and were used without further purification. L1 and L2 were prepared according to the literature [1b,14a]. NMR spectra were recorded on a Bruker DX-300 NMR spectrometer (1H, 300 MHz). Chemical shifts were referenced to TMS and deuterated acetonitrile (Acros) was used as the solvent. IR spectra were recorded using a Jasco FTIR 410 instrument. Mass spectra were measured on a Micromass Platform II spectrometer. Elemental analyses were carried out using a Perkin–Elmer 2400, 2400II elemental analyzer. 2.2. Synthesis of the complexes[(L1)2Ag2](NO3)2 (1a) and [(L1)2Ag2](ClO4)2 (1b) L1 (0.362 g, 1 mmol) was dissolved in 10 ml acetonitrile. To this solution AgNO3/AgClO4 salt (1 mmol) was added with stirring. After 6 h a light yellow precipitate was collected by filtration. After washing with ether and drying under vacuum 1a (81% yield)/1b (88% yield) was obtained. Complex 1a: 1H NMR (CD3CN) d (ppm): 7.11 (d, 2H, J = 7.2 Hz), 7.25 (t, 2H, J = 8.1 Hz), 7.33 (d, 1H, J = 8.1 Hz), 7.52 (tt, 1H, J = 7.5 Hz), 7.67 (ddd, 1H, J = 7.8 Hz), 7.97 (td, 1H, J = 7.8 Hz), 8.38 (dt, 1H, J = 4.8 Hz); IR (KBr film, cm1) mC@N: 1578, 1559,

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Table 1 Crystal data and structure refinement parameters for complexes 1a, 1b, 2b and 3 Compound

1a

1b

2b

3

Formula Formula weight Crystal size (mm) T (K) Crystal system Space group a (Å) b (Å) c (Å) a (°) b (°) c (°) V (Å3) Z DCalc (g cm3) l (mm1) h Range (°) Number of data unique/collected R1/wR2 [I > 2r(I)] Goodness-of-fit

C48H36Ag2N10O6 1064.61 0.07  0.07  0.06 273 (2) monoclinic P2(1)/c 12.6475(3) 33.8450(9) 12.2745(3)

C48H36Ag2Cl2N8O8 1139.49 0.08  0.08  0.07 273 (2) monoclinic P2(1)/c 17.3461(6) 15.1473(6) 19.4393(7)

C44H32Ag3Cl3N12O12 1350.78 0.09  0.09  0.08 273 (2) monoclinic Pc 20.7930(13) 9.4019(6) 25.0609(16)

109.0160(10)

112.1050(10)

4967.4(2) 4 1.445 0.85 2.3–19.4 9258/52 346 0.129/0.373 1.19

4732.2(3) 4 1.599 1.00 2.4–23.5 12 286/55 168 0.046/0.147 1.01

C54H41Ag4F12N13O11 1707.48 0.1  0.1  0.08 293 (2) triclinic  P1 14.4930(2) 15.2040(2) 15.3180(3) 67.5800(10) 79.7690(10) 84.7340(10) 3069.53(8) 2 1.847 1.36 2.0–25.0 10 732/25 969 0.049/0.173 1.048

mNO3 : 1384; MS (FAB): m/z 1065, 1061 [M]+. Anal. Calc. for C48H36Ag2N10O6: C, 54.14; H, 3.38; N, 13.16. Found: C, 53.98; H, 3.42; N, 13.08%. Complex 1b: 1H NMR (CD3CN) d (ppm): 7.10 (d, 2H, J = 7.2 Hz), 7.27 (t, 2H, J = 7.5 Hz), 7.35 (d, 1H, J = 7.8 Hz), 7.52 (tt, 1H, J = 7.5 Hz), 7.68 (ddd, 1H, J = 6.6 Hz), 7.97 (td, 1H, J = 7.8 Hz), 8.33 (dt, 1H, J = 5.1 Hz); IR (KBr film, cm1) mC@N: 1578, 1559, mClO4 : 1084; MS (FAB): m/z 1041, 1035 [MClO4]+. Anal. Calc. for C48H36Ag2Cl2N8O8: C, 50.59; H, 3.18; N, 9.83. Found: C, 50.73; H, 3.24; N, 9.90%. 2.3. Synthesis of complexes [(L2)2Ag4(NO3)(CH3CN)2](NO3)3 (2a) and {[(L2)2Ag3](ClO4)3}n (3) Ligand L2 (0.364 g, 1 mmol) was dissolved in 10 ml of acetonitrile. To this solution AgNO3/AgClO4 salt (2 mmol) was added with stirring. After 4 h the reaction mixture was concentrated and a yellow precipitate appeared immediately. The precipitate was collected by filtration, washed with ether and dried under vacuum to give complex 2a (yield 78%)/3 (yield 72%).

143.208(2) 2934.2(3) 2 1.529 1.19 2.2–19.8 22 298/13 237 0.055/0.127 1.036

Complex 2a: 1H NMR (CD3CN) d (ppm): 7.29 (d, 1H, J = 8.1 Hz), 7.45 (ddd, 1H, J = 7.8 Hz), 7.60 (m, 2H), 7.88 (m, 2H), 8.34 (d, 1H, J = 4.5 Hz), 8.41 (d, 1H, J = 5.1 Hz); IR (KBr film, cm1): m C@N: 1583, 1564, mNO3 : 1384. MS (FAB): m/z 1350, 1342 [M2(CH3CN)NO3]+, 1288, 1280 [M2(CH3CN)2(NO3)]+, 1224, 1216 [M2(CH3CN)3(NO3)]+. Anal. Calc. for C48H38Ag4N18O12: C, 38.66; H, 2.55; N, 16.91. Found: C, 38.59; H, 2.63; N, 16.80%. Complex 3: 1H NMR (CD3CN) d (ppm): 7.27 (d, 1H, J = 8.1 Hz), 7.52 (ddd, 1H, J = 7.8 Hz), 7.59 (m, 2H), 7.88 (m, 2H), 8.34 (d, 1H, J = 4.5 Hz), 8.40 (d, 1H, J = 5.1 Hz); IR (KBr film, cm1): m C@N: 1591, 1564, mClO4 : 1090; MS (FAB): m/z 1467, 1453 [M +Ag]+; 1358, 1349, 1346 [M]+. Anal. Calc. for C44H34Ag3Cl3N12O13 (3  H2O): C, 38.57; H, 2.48; N, 12.27. Found: C, 38.46; H, 2.54; N, 12.18%. 2.4. Synthesis of complex [(L2)2Ag4(CF3COO)3](CF3COO) (2b) Ligand L2 (0.364 g, 1 mmol) was dissolved in 10 ml of acetonitrile. To this solution AgOOCCF3 salt (2 mmol) was added with

Scheme 1.

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stirring. After 4 h the yellow solution was concentrated and stirred with a large volume of ether. The precipitate that formed was collected by filtration and dried under vacuum to give complex 2b (76% yield). 1H NMR (CD3CN) d (ppm): 7.25 (dt, 1H, J = 7.8 Hz), 7.61 (m, 2H), 7.71 (d, 1H, J = 7.8 Hz), 7.93 (ddd, 2H, J = 9.3 Hz), 8.38 (dt, 1H, J = 7.8 Hz), 8.43 (d, 1H, J = 5.1 Hz); IR (KBr film, cm1) mC=N: 1581, 1562; mCF3 COO : 1684. MS (FAB): m/z 1502, 1494 [M(CF3COO)]+. Anal. Calc. for C52H38Ag4F12N12O11 (2b  3H2O): C, 37.45; H, 2.28; N, 10.08. Found: C, 37.44; H, 2.24; N, 9.98%. 2.5. X-ray diffraction studies X-ray quality crystals of all the complexes were grown by the slow diffusion of ether into an acetonitrile solution of the complexes. Single crystals were mounted on a glass fiber and the X-ray diffraction intensity data were measured on a Bruker Smart APEXII CCD XRD. The intensity data were collected at 273 K. All data were collected with the x scan technique using graphite monochromatic Mo Ka radiation (k = 0.71073 Å). All non-hydrogen atoms were refined with anisotropic displacement parameters and hydrogen atoms were included at calculated positions. The structures were solved by direct methods using the SHELXS-97 computer program and refined by full-matrix least-squares methods on F2 using SHELXL-97 [15]. The crystal data and structure refinement parameters for complexes 1a, 1b, 2b, and 3 are tabulated in Table 1. Although the main complex cation of the structure of 1a is correct, there exists an unknown high electron density which could not be resolved with proper chemical meaning. In the structure of complex 2b, there are some unreasonable displacement parameters for some C atoms and short C–C distances on the F3CCOO anion groups due to the unsolved disorder problem.

N-atoms from each of the two ligands. Two Ag(I) ions are also doubly bridged by azine (N–N) groups. In this way each Ag(I) center is tetra-coordinated, but their geometry is far from tetrahedral (ptype geometry) due to twisting of the ligands. The Ag–Naz distances are much longer than the Ag–Npy distances in both complexes (Table 2). The Ag–Npy distances are comparable with those reported for similar complexes [14,16] whereas the Ag–Naz distances are longer than similar bonds reported in other Ag–azine bridge complexes [14b]. This is due to the steric crowding of the substituted phenyl rings. The two ligands lie above and below the line made between the two Ag(I) centers. The ligands undergo a twist due to the coordination to the metal centers and form a double helical structure [17]. The twist conformation of the ligands as well as the rings also prevents the formation of an intramolecular p–p interaction. The Ag–Ag separation in both complexes (average 4.829 Å) indicates that there is no argentophilic interaction. In the perchlorate complex 1b, C–H  p interactions also generate a two-dimensional network (Fig. 3b, H  p distance range 2.74– 2.83 Å, H  centroid distance 3.50 Å). Moreover, the perchlorate

X

N

N

X

N

N Ag

Ag N

N

N

X=C (L1) X=N (L2) N

3. Result and discussion

X To investigate Ag(I) chemistry in the presence of different anions, complexes 1a, 1b, 2a, 2b and 3 were prepared. The formation of complexes is given in Scheme 1. X-ray quality crystals of 1a, 1b, 2a, 2b, and 3 were grown by diffusing ether into an acetonitrile solution of the complexes. In all the complexes, L1 acts as a tetradentate ligand and L2 acts as a hexadentate one, using their all possible N-donor sites. A similar structure of nitrate complex 2a had been reported [14a] where it crystallized in the space group P21/c. Except for the coordination of anions or solvents, the coordination environments of the Ag(I) centers of the complexes of ligand L1 are almost same, in the presence of different anions, but the packing of the crystals are different for different anions. For the complexes of L2, both the coordination environment and the packing of the crystals are different with different anions. Nitrate and trifluoroacetate complexes are tetranuclear with different coordination environments of the Ag(I) centers whereas the perchlorate complex has a polynuclear chain structure. It is important to note that the main chromophore contains Ag2(Naz)4(Npy)4 units for the perchlorate and nitrate complexes of both ligands. The structural motif of the main chromophore is given in Fig. 1. In this chromophore two Ag centers and two azine (N–N) bridges form a six member distorted ring.

X

Fig. 1. The structural motif of the main chromophore in complexes 1a, 1b, 2a and 3.

3.1. Crystal structures of complexes 3.1.1. Molecular structures of 1a and 1b X-ray crystal structure determination of 1a and 1b lead to the formulation [Ag2(L1)2](NO3)2 and [Ag2(L1)2](ClO4)2, respectively. The structures indicated that both complexes are dimeric (Figs. 2 and 3a), with each Ag(I) center coordinated by two pyridine

Fig. 2. ORTEP view of 1a showing 30% probability ellipsoids. Anions and hydrogen atoms are omitted for clarity.

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a C21 C22 C5 ' C23

C11'

C15 C19 C8'

C4'

C6'

C17

C9'

C20

C12'

C14

C3'

C18 N4

C7' N3'

b

C16

C10'

C1'

C24

N2

N1' Ag1

N1 C24'

C13'

C2

Ag2

N2' C2'

C1

N4'

C13

N3 C7

C18'

C23' C22'

C3

C19'

C4 C20'

C6

C8

C14' C15'

C17'

C9 C10

C5

C12 C11

C16'

C21'

c

Fig. 3. (a) ORTEP view of 1b showing 30% probability ellipsoids. Anions and hydrogen atoms are omitted for clarity. (b) C–H  p interactions between molecules to form the 2-D network in complex 1b. (c) View of the 3-D network of C–H  O and C–H  p interactions in complex 1b.

groups also make a number of short O  H–C interactions [9a] in the range 2.38–2.66 Å (Fig. 3c). The perchlorate ions contact the pyridine ring protons and benzene ring protons, which may be involved in the stabilization of the solid state structure. Weak C– H  p interactions also help to make a three-dimensional (3-D) network structure. 3.1.2. Molecular structure of 2b The X-ray analysis of 2b reveals that the asymmetric unit of the complex contains a discrete polynuclear Ag4(L2)2 moiety formed by the assembly of four Ag atoms and two ligand molecules. The unit cell contains two of the above complete units with six coordinated trifluoroacetate (F3CCOO), two coordinated acetonitrile (CH3CN), two free F3CCOO ions and six water molecules. Unlike the nitrate complex, the complex crystallizes in the triclinic system with space  An ORTEP plot of the discrete unit is shown in Fig. 4. group P1. The coordination environment of each Ag(I) center is completely different from the nitrate complex 2a [14a]. Among the four Ag(I) centers in the nitrate complex, two Ag(I) ions are coordinated

by two azine N-atoms from two ligands and two pyridine N-atoms also from two ligands. Each of the other two Ag(I) ions is coordinated by two pyridine N-atoms from two ligands and a nitrate ion or acetonitrile solvent molecule. Whereas, in the trifluoroacetate complex each of the three Ag(I) centers Ag1, Ag2 and Ag4 completes its three coordination position with the same donor atoms – one azine N-atom and two pyridine N-atoms, and the fourth coordination position is satisfied by either F3CCOO or CH3CN. One azine N-donor and one pyridine N-donor of a ligand form a five member chelate ring with each Ag center. The remaining Ag3 center is coordinated by two pyridine nitrogen atoms and a F3CCOO ion. The Ag–Npy distances around all the Ag centers are in the range 2.250–2.323 Å (Table 2), similar to those found in other pyridine Ndonor Ag(I) complexes [12a,14b,16,18] and longer than other reported complexes [3,13b]. The Ag–Naz distances are quite a lot longer than the Ag–Npy distances, but are similar to those found in the reported azine bridged Ag complex 2a [14a] and also longer than another reported Ag complex [14b]. The N–Ag–N angles around the Ag centers are quite dissimilar from one Ag center to

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C.-Y. Wu et al. / Polyhedron 27 (2008) 2681–2687 Table 2 Selected bond lengths and angles Atom

1a

1b

2b

Bond distances (Å) Ag–Naz

Ag1

2.192(10) (N3) 2.222(10) (N8)

2.409(9) (N4) 2.525(9) (N1)

Ag2

2.253(9) 2.219(9) 2.198(3) 2.245(3)

2.460(10) (N2) 2.662(6) (N5) 2.435(3) (N1) 2.659 (N10 )

Ag1

(N7) (N6) (N30 ) (N3)

Ag2

2.206(3) (N4) 2.228(3) (N40 )

2.446(3) (N20 ) 2.583(3) (N2)

Ag1

2.250(5) (N8) 2.267(5) (N1)

Ag2

2.276(5) (N5) 2.323(5) (N4)

Ag3

2.231(5) 2.270(5) 2.259(5) 2.313(5)

2.539(5) (N2) 2.353(7) (N13) (CH3CN) 2.604(4) (N6) 2.414(5) (O1) (F3CCOO) 2.447(5) (O3) (F3CCOO) 2.586(4) (N7) 2.333(5) (O5) (F3CCOO) 2.516(6) (N2) 2.537(5) (N20 )

Ag4

3

Bond angles (°)

Ag–Npy

(N10) (N12) (N9) (N11)

Ag1

2.229(7) (N6) 2.240(6) (N60 )

Ag2

2.226(6) 2.265(6) 2.307(6) 2.339(6) 2.344(6) 2.330(6)

Ag3

(N5) (N50 ) (N3) (N40 i) (N4) (N30 i)

2.475(5) (N1) 2.561(6) (N10 )

N3–Ag1–N8 = 161.1(4), N3–Ag1–N4 = 128.1(3) N8–Ag1–N4 = 70.7(3), N3–Ag1–N1 = 70.1(3) N8–Ag1–N1 = 115.8(3), N4–Ag1–N1 = 88.8(3) N6–Ag2–N7 = 158.9(3), N6–Ag2–N2 = 130.5(3) N6–Ag2–N5 = 68.67(2), N7–Ag2–N2 = 69.0(3) N30 –Ag1–N3 = 152.35(11), N30 –Ag1–N1 = 136.18(11) N3–Ag1–N1 = 69.39(10), N10 –Ag1–N1 = 83.54(9) N10 –Ag1–N3 = 113.65(11), N30 –Ag1–N10 = 68.19(11) N4–Ag2–N40 = 164.85(12), N4–Ag2–N20 = 124.74(10) N40 –Ag2–N20 = 70.24(11), N4–Ag2–N2 = 69.29(10) N40 –Ag2–N2 = 113.60(11), N20 –Ag2–N2 = 84.13(10) N8–Ag1–N1 = 131.27(18), N8–Ag1–N13 = 99.6(2) N1–Ag1–N13 = 99.6(2), N8–Ag1–N2 = 119.34(16) N1–Ag1–N2 = 69.15(15), N13–Ag1–N2 = 136.9(2) N5–Ag2–N4 = 135.72(18), N5–Ag2–O1 = 112.2(2) N4–Ag2–O1 = 86.34(19), N5–Ag2–N6 = 66.78(15) N4–Ag2–N6 = 112.85(15), O1–Ag2–N6 = 154.04(17) N10–Ag3–N12 = 142.57(16), N10–Ag3–O3 = 115.93(18) N12–Ag3–O3 = 89.30(18) N9–Ag4–N11 = 130.92(16), N9–Ag4–O5 = 125.80(18) N11–Ag4–O5 = 89.25(17), N9–Ag4–N7 = 117.53(15) N11–Ag4–N7 = 67.54(14), O5–Ag4–N7 = 110.50(16) N6–Ag1–N6 = 171.4(2), N6–Ag1–N2 69.5(2) N60 –Ag1–N2 = 118.9(2), N6–Ag1–N20 = 117.2(2) N60 –Ag1–N20 = 68.2(2), N2–Ag1–N20 = 78.17(18) N5–Ag2–N50 = 169.4(2), N5–Ag2–N1 = 69.4(2) N50 –Ag2–N1 = 121.1(2), N50 –Ag2–N10 = 69.1(2) N50 –Ag2–N1 = 121.1(2), N5–Ag2–N10 = 114.5(2) N3–Ag3–N40 i = 101.2(2), N3–Ag3–N4 = 121.3(2) N40 i–Ag3–N4 = 106.8(2), N3–Ag3–N30 i = 117.0(2) N40 i–Ag3–N30 i = 118.2(2), N4–Ag3–N30 i = 93.1(2)

Symmetry codes for 3 (i) x, y  1, z.

Fig. 4. ORTEP view of 2b showing 30% probability ellipsoids. Anions and hydrogen atoms are omitted for clarity.

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C.-Y. Wu et al. / Polyhedron 27 (2008) 2681–2687

b

a C21' C20' C21

C22

C22'

C11' C10'

C11

C10 Ag2

C18

C9 C20 C19

C12 N3'

C18'

C8' Ag3

N1

C1 C13

C3 N5

N4'

C4'

C17'

C4

N2'

C1' N1' C14' C3' C15'

C17 C5

Ag1 C7

C2'

C13'

N4

C14

Ag2

C9'

N3

C2 C8

N2

C19'

C12'

N6

N6'

C15 C6

C16' C16

C5'

N5'

Ag1

C7' C6'

c

d

Fig. 5. (a) ORTEP view of 3 showing 30% probability ellipsoids. Anions and hydrogen atoms are omitted for clarity. (b) View of hydrogen bonding by perchlorate between two linear chains in complex 3. (c) Space-filling 2-D structure showing hydrogen bonding in complex 3. (d) 3-D packing diagram of complex 3.

the next (Table 2). The Ag2 and Ag4 centers are bridged by two azine N-atoms of one ligand, but the Ag1 and Ag3 centers are not bridged by the two azine N-atoms of another ligand. Only the Ag1 center is coordinated to one azine nitrogen whereas the large Ag3–Naz3 distance (2.778 Å) indicates that there is no bonding due to the strained conformation of the ligand. The large Ag–Ag distances also indicate that there is no argentophilic interaction. 3.1.3. Molecular structure of 3 The structure of the cation of 3 is a polymer of stoichiometry [Ag3(L2)2]3+, in which each tetrapyridyl azine ligand coordinates three Ag(I) centers (Fig. 5a). All the Ag centers are tetra-coordinated but they are also far from a tetrahedral geometry. Each ligand is bidentate to each Ag center. Each of the Ag1 and Ag2 centers in [Ag3(L2)2]3+ has a four coordinate pseudo-tetrahedral or p-type geometry with a coordination sphere consisting of two pyridine N-donors from two ligands and two azine N-donors from two ligands. The Ag3 center in [Ag3(L2)2]3+ also has a four coordinate distorted tetrahedral geometry with a coordination sphere consisting of two pyridine N-donors from the same ligand and two other pyridine N-donors from another ligand of another [Ag3(L2)2]3+ unit. The two pyridine rings of the same or different ligands are not co-planar. The dihedral angle (79.63°) of the two pyridine rings which coordinate to Ag1 and Ag2 means that they are almost per-

pendicular to each other. The dihedral angle of the other two pyridine rings which coordinate to Ag3 is 54.87°. The repetition of the [Ag3(L2)2]3+ unit form the linear polynuclear chain. In a closer look, the Ag3 centers helped to form the extended linear chain in the molecule and the linear chains are linked into a two-dimensional (2-D) (Fig. 5b and c) and three-dimensional (3-D) (Fig. 5d) network through C–H  O hydrogen bonding interactions involving pyridine ring protons with perchlorate ions (H  O distance range 2.5– 2.68 Å). 4. Conclusions Four coordination complexes constructed by self assembly of azine based ligands and Ag ions have been structurally characterized. This structural analysis revealed a great difference in the crystal packing due to the influence of the anion symmetry. Such variation in the environment of a complex molecule is termed as ‘Chemical Frustration’ [9a]. In these complexes, various weak interactions and hydrogen bonding generate 2-D or 3-D networks. Appendix A. Supplementary data CCDC 663164, 663165, 663166 and 663167 contain the supplementary crystallographic data for 3, 1b, 2b and 1a. These data can

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