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Anion-assisted silver(I) coordination complexes from flexible unsymmetrical bis(pyridyl) ligands: Syntheses, structures and luminescent properties
Polyhedron 59 (2013) 38–47
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Anion-assisted silver(I) coordination complexes from flexible unsymmetrical bis(pyridyl) ligands: Syntheses, structures and luminescent properties Zhu-Yan Zhang a,b, Zhao-Peng Deng a, Li-Hua Huo a,⇑, Hui Zhao a, Shan Gao a,⇑ a Key Laboratory of Functional Inorganic Material Chemistry, Ministry of Education, School of Chemistry and Materials Science, Heilongjiang University, Harbin 150080, People’s Republic of China b Laboratory Centre of Pharmacy, College of Pharmacy Harbin Medical University, Harbin 150081, People’s Republic of China
a r t i c l e
i n f o
Article history: Received 1 March 2013 Accepted 16 April 2013 Available online 30 April 2013 Keywords: Coordination polymer Unsymmetrical bis(pyridyl) ligand Structure diversity Luminescent property
a b s t r a c t The reaction of AgX (X = NO3 and ClO4 ) salts, triphenylphosphine (PPh3) and four flexible unsymmetrical bis(pyridyl) ligands, namely N-(pyridin-2-ylmethyl)pyridin-2-amine (L1), N-(pyridin-3-ylmethyl) pyridin-3-amine (L2), N-(pyridin-2-ylmethyl)pyridin-3-amine (L3) and N-(pyridin-4-ylmethyl)pyridin3-amine (L4), leads to the formation of six complexes, [Ag2(L1)2(ClO4)2]n (1), [Ag2(L2)2(ClO4)2]nn(CH3CN) (2), [Ag(L1)(NO3)]n (3), [Ag(L2)(NO3)]n (4), [Ag(L3)(NO3)(PPh3)]n (5) and [Ag(L4)(NO3)(PPh3)]n (6), which have been characterized by elemental analysis, IR, TG, PL, powder and single-crystal X-ray diffraction. In contrast to the chain structure of complexes 1 and 2, induced by the weakly coordinated perchlorate anion, the nitrate anion can coordinate to the Ag(I) cation in monodentate, chelating and even more intricate l2-j3 modes, thus defining dinuclear (complex 3), various chain motif (complexes 5 and 6) and layer structures (complex 4). The four ligands in the six complexes present diverse cis–cis, cis–trans and trans– trans conformations, which are responsible for the structural diversities and, together with the nature of the inorganic anions, the coordination spheres of the Ag(I) cations. Moreover, solid-state luminescent properties demonstrate that the emission intensities of the perchlorate-containing complexes are stronger than those of the nitrate-containing complexes. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction Silver(I) coordination complexes with bis(pyridyl) ligands have attracted intensive interest owing to their fascinating architectures, along with their potential applications such as adsorption, photoluminescence and catalysis [1–3]. To date, a variety of Ag(I) coordination complexes with beautiful topologies and properties have been obtained, in which the ligands used are mainly focused on rigid bis(pyridyl) ligands [4–7]. By contrast, flexible bis(pyridyl) ligands have many degrees of freedom and hence few conformational restraints, as well as the unpredictable nature of such a system [8]. When flexible bis(pyridyl) ligands adopting different conformations react with silver salts, interesting and unusual structures may facilitate the formation of novel supramolecular architectures. However, a close inspection reveals that most of the flexible bis(pyridyl) ligands in the reported Ag(I) coordination complexes are symmetrical [9–11], i.e. a symmetrical spacer attached to the same substituted position of the two terminal pyridines (Scheme 1). In comparison, Ag(I) coordination complexes construct from unsymmetrical bis(pyridyl) ligands (unsymmetrical ⇑ Corresponding authors. Tel.: +86 0451 86609148. E-mail addresses: [email protected] (L.-H. Huo), [email protected] (S. Gao). 0277-5387/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.poly.2013.04.041
spacer and/or different substituted position of the two terminal pyridines) are less common [12,13]. Hence, it is still a great challenge and an interesting issue to construct silver(I) complexes from flexible unsymmetrical bis(pyridyl) ligands. To expand our research on Ag(I)-bis(pyridyl) complexes [11], we selected four flexible bis(pyridyl) ligands with a non-coordinating amine group in the unsymmetrical –CH2–NH– spacer, N-(pyridin-2-ylmethyl)pyridin-2-amine (L1), N-(pyridin-3-ylmethyl) pyridin-3-amine (L2), N-(pyridin-2-ylmethyl)pyridin-3-amine (L3) and N-(pyridin-4-ylmethyl)pyridin-3-amine (L4) (Scheme 1). The two pyridyls can freely twist around the unsymmetrical – CH2–NH– group with different bond angles to meet the requirements of the Ag(I) centers, resulting in diverse structures. The amine group in the flexible spacer of the four ligands can potentially form hydrogen bonds with the acceptor groups to direct the self-assembly of interesting supramolecular systems. Meanwhile, the coordination direction and different positions of the pyridyl N atoms in the positional isomeric ligands may benefit the formation of different structures. Bearing this conception in mind, we further report here the syntheses, structures and properties of six silver(I) complexes based on the aforementioned four ligands, PPh3 and AgX (X = NO3 and ClO4 ) salts, namely [Ag2(L1)2 (ClO4)2]n (1), [Ag2(L2)2(ClO4)2]nn(CH3CN) (2), [Ag(L1)(NO3)]n (3), [Ag(L2)(NO3)]n (4), [Ag(L3)(NO3)(PPh3)]n (5) and [Ag(L4)(NO3)
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Scheme 1. Flexible symmetrical and unsymmetrical bis(pyridyl) ligands in the reported and present Ag(I) coordination polymers.
(PPh3)]n (6). In contrast to the chain motif of the perchlorate-containing complexes, the nitrate-containing complexes 3–6 present various dinuclear, chain motif (zig-zag and curving chain) and double layer structures. The structural diversities of the six complexes can be mainly attributed to the nature of the inorganic anions, the coordination spheres of the Ag(I) cations and the conformations of the four flexible unsymmetrical bis(pyridyl) ligands. Moreover, solid-state luminescent properties demonstrate that the emission intensities of the perchlorate-containing complexes are stronger than those of the nitrate-containing complexes. 2. Experimental 2.1. Materials and methods All chemicals and solvents were of A.R. grade and were used without further purification in the syntheses. L1–L4 were synthesized according to a previously reported method [14]. Elemental analyses were carried out with a Vario MICRO from Elementar Analysensysteme GmbH, and the infrared spectra (IR) were recorded on KBr pellets in the range 4000–400 cm 1 on a Bruker Equinox 55 FT-IR spectrometer. Powder X-ray diffraction (PXRD) patterns were measured at 293 K on a Bruker D8 diffractometer (Cu Ka, k = 1.54059 Å). The TG analyses were carried out on a Perkin Elmer TG/DTA 6300 thermal analyzer under a flowing N2 atmosphere, with a heating rate of 10 °C/min. Luminescence spectra were measured on a Perkin Elmer LS 55 luminance meter.
Complex 2: Yield: 65% (based on Ag). Anal. Calc. for C24H25N7O8Cl2Ag2: C, 34.89; H, 3.05; N, 11.87. Found: C, 34.85; H, 3.10; N, 11.91%. IR (m/cm 1): 3147m, 2254m, 1600s, 1579m, 1517m, 1097s. Complex 3: Yield: 68% (based on Ag). Anal. Calc. for C22H22N8O6Ag2: C, 37.21; H, 3.12; N, 15.78. Found: C, 37.25; H, 3.06; N, 15.73%. IR (m/cm 1): 3160m, 1603s, 1570m, 1514m, 1384s. Complex 4: Yield: 63% (based on Ag). Anal. Calc. for C11H11N4O3Ag: C, 37.21; H, 3.12; N, 15.78. Found: C, 37.24; H, 3.18; N, 15.75%. IR (m/cm 1): 3176m, 1597s, 1569m, 1518m, 1380s. Caution! Although not encountered in our experiments, metal perchlorates are potentially explosive. They should be handled carefully and in small quantities. 2.2.2. Synthesis of complexes 5–6 The procedure was similar to that for complexes 1–4, except an equimolar amount of PPh3 was added into the reactions and stirred for an additional 10 min. Colorless crystals of 5 and 6 were obtained from the solution after avoiding illumination for several days. Complex 5: Yield: 63% (based on Ag). Anal. Calc. for C29H26N4O3PAg: C, 56.42; H, 4.24; N, 9.07. Found: C, 56.46; H, 4.17; N, 9.12%. IR (m/cm 1): 3179m, 1599s, 1571m, 1516m, 1485s, 1386s, 746m, 696m. Complex 6: Yield: 69% (based on Ag). Anal. Calc. for C29H26N4O3PAg: C, 56.42; H, 4.24; N, 9.07. Found: C, 56.37; H, 4.29; N, 9.11%. IR (m/cm 1): 3159m, 1598s, 1567m, 1518m, 1483s, 1382s, 744m, 696m. 2.3. X-ray crystallographic measurements
2.2. Syntheses 2.2.1. Synthesis of complexes 1–4 2 mmol L1 or L2 were dissolved in 10 mL methanol solution and then added to a MeCN solution (10 mL) containing an equal amount of silver(I) nitrate or silver(I) perchlorate. The mixture was stirred at room temperature for 10 min, and then filtered. Colorless crystals of 1–4 were isolated from the filtrate after avoiding illumination for several days. Complex 1: Yield: 62% (based on Ag). Anal. Calc. for C22H22N6O8Cl2Ag2: C, 33.66; H, 2.82; N, 10.70. Found: C, 33.63; H, 2.77; N, 10.74%. IR (m/cm 1): 3141m, 1602s, 1576m, 1512m, 1095s.
Table 1 provides a summary of the crystal data, data collection and refinement parameters for complexes 1–6. All the diffraction data were collected at 295 K on a RIGAKU RAXIS-RAPID diffractometer with graphite monochromatized Mo Ka (k = 0.71073 Å) radiation in the x scan mode. All the structures were solved by the direct method and difference Fourier syntheses. All non-hydrogen atoms were refined by full-matrix least-squares techniques on F2 with anisotropic thermal parameters. The hydrogen atoms attached to carbon and nitrogen atoms were placed in calculated positions with C–H = 0.93 (pyridyl), 0.96 (methyl), 0.97 (methylene), N–H = 0.86 Å and U (H) = 1.2Ueq (C, N) in the riding model
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Table 1 Crystal data and structure refinement parameters of complexes 1–6. Complex
1
2
3
Empirical formula Mr Crystal system Space group a (Å) b (Å) c (Å0 a (°) b (°) c (°) V(Å3) Z Dcalc (g cm 3) l (mm 1) h range Reflections collected Unique reflections No. of parameter F (0 0 0) R1, wR2 [I > 2r(I)] Goodness-of-fit (GOF) on F2 Largest and hole (e A 3)
C22H22N6O8Cl2Ag2 785.10 monoclinic C 2/c 32.558(7) 9.4926(19) 18.757(4) 90.00 110.40(3) 90.00 5434(2) 8 1.919 1.696 3.05–27.47 24391 6165 361 3104 0.0637, 0.1684 1.044 1.404, 0.980
C24H25N7O8Cl2Ag2 826.15 triclinic P1
C22H22N8O6Ag2 710.22 triclinic P1
9.4683(19) 10.711(2) 14.742(3) 85.96(3) 82.43(3) 83.28(3) 1469.6(5) 2 1.867 1.574 3.06–27.48 14042 6701 389 820 0.0639, 0.1427 0.990 0.908, 0.918
8.3134(17) 8.9521(18) 9.2973(19) 96.52(3) 94.94(3) 114.60(3) 618.2(2) 1 1.908 1.640 3.09–27.48 6102 2812 172 352 0.0500, 0.1023 1.088 1.076, 1.129
4
5
6
C11H11N4O3Ag 355.11 tetragonal P 43212 8.6397(12) 8.6397(12) 32.425(7) 90.00 90.00 90.00 2420.4(7) 8 1.949 1.676 3.02–27.45 23852 2765 172 1408 0.0432, 0.0782 1.090 0.772, 0.887
C29H26N4O3PAg 617.38 orthorhombic P bca 17.2479(5) 14.5923(4) 21.1904(6) 90.00 90.00 90.00 5333.3(2) 8 1.538 0.854 3.18–26.00 26918 5225 343 2512 0.0336, 0.0745 1.041 0.317, 0.535
C29H26N4O3PAg 617.38 monoclinic Cc 15.8352(8) 10.7875(5) 16.6099(7) 90.00 108.007(5) 90.00 2698.4(2) 4 1.520 0.844 3.77–27.56 14868 6198 543 1256 0.0367, 0.0884 1.063 0.540, 0.615
Empirical formula Mr Crystal system Space group a (Å) b (Å) c (Å) a (°) b (°) c (°) V (Å3) Z Dcalc (g cm 3) l (mm–1) h Range Reflections collected Unique reflections No. of parameter F (0 0 0) R1, wR2 [I > 2r(I)] Goodness-of-fit (GOF) on F2 Largest and hole (e A 3)
approximation. All calculations were carried out with the SHELXTL97 program [15]. Selected bond lengths and hydrogen bond parameters for complexes 1–6 are listed in Tables S1 and S2, respectively.
3. Results and discussion
demonstrates the existence of the MeCN molecule. The characteristic vibrations of the perchlorate anion in complexes 1 and 2 are at 1095 and 1097 cm 1, whereas the characteristic vibrations of the nitrate anion in complexes 3–6 are at 1384, 1380, 1386 and 1382 cm 1, respectively. Moreover, the characteristic vibrations of PPh3 are at 696, 746 and 1485 cm 1 for complex 5 and 696, 744 and 1483 cm 1 for complex 6.
3.1. Syntheses and IR spectroscopy In order to investigate the influence of the anions and ligand conformations on the final structures of Ag(I)-bis(pyridyl) complexes, four complexes were synthesized by the self-assembly of the flexible unsymmetrical bis(pyridyl) ligands and different AgX (X = NO3 and ClO4 ) salts under similar experimental conditions, while complexes 5 and 6 were obtained with the addition of PPh3. Due to the stronger coordination ability of the nitrate anion, the nitrate-containing complexes exhibit diverse dinuclear, chain motif and layer structures. By contrast, the weakly coordinating perchlorate anions only afford the formation of chain structures. The N–H stretching vibrations for all the salts fall in the region 3179–3141 cm 1, in which the energy of the vibrations largely depends on the positional isomeric ligands and the extent of hydrogen bonding. The vibration at 2254 cm 1 in complex 2
3.2. Crystal structures 3.2.1. Structural description of [Ag2(L1)2(ClO4)2]n (1) and [Ag2(L2)2(ClO4)2]nn(CH3CN) (2) As shown in Fig. 1, complexes 1 and 2 possess a similar composition, with the molecular structure comprising of two Ag(I) cations, two ligands L and two perchlorate anions, together with one additional free MeCN molecule in the molecular structure of complex 2. Owing to the weak coordination ability of the perchlorate anion, the Ag(I) cations in the present two complexes exhibit linear coordination geometries, with one or two longer contacts (2.788(7)–2.922(1) Å) to oxygen atoms of perchlorate anions. Furthermore, the two unsymmetrical bis(pyridyl) ligands show different conformations, resulting in diverse architectures.
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Fig. 1. Perspective view of the asymmetric unit of complexes 1 and 2 showing the coordination environment around the Ag(I) cations.
In complex 1, two independent trans–trans conformations of the ligand L1 are present. The N1-containing one bridges adjacent Ag1 cations to form a curving chain along the c-axis (Fig. 2), in which the nearest Ag Ag distance is 7.554(2) Å. Meanwhile, the N4-containing one links two Ag2 cations, producing a 14-membered macrometallacyclic ring, in which the Ag Ag separation is 3.797(1) Å. Subsequently, the weakly coordinated Cl2-containing perchlorate anion connects the two types of motifs, leading to the formation of a layer structure (Fig. 2). Moreover, the terminal coordinated Cl1-containing perchlorate anions forms intermolecular hydrogen bonding interactions (Table S2) with the amine groups (N2–H2N), which result in a 3-D supramolecular network, as shown in Fig. S1. Differing from the ligand L1, the two L2 ligands in complex 2 exhibit different cis–trans and trans–trans conformations. The Ag1 and Ag2 cations are alternately connected by the two ligands to generate curving chains along the c-axis, which then link through the weak Ag Ag interactions (3.358(1) Å) and p p stacking interactions between the N3- and N6-containing pyridyl rings (the centroid-to-centroid distance being 3.663(1) Å) to a form double chain involving 38-membered macrometallacyclic rings (Fig. 3a). Adjacent double chains are further connected into a layer motif through C–H O interactions (C16–H16 O2 = 3.263(1) Å, \C–H p = 127.0°) (Fig. S2) [16]. The N–H O interactions between Cl2-containing perchlorate anions and the amine groups (N2–H2N) extend adjacent layers into a 3-D porous supramolecular network (Fig. S3, Table S2), with the 1-D channels filled by free MeCN molecules (Fig. 3b). Furthermore, p p stacking interactions
between the N1- and N4-containing pyridyl rings are detected, with the centroid-to-centroid distance being 3.567(9) Å, which strengthens the stability of the 3-D supramolecular network. 3.2.2. Structural description of [Ag(L)(NO3)]n [L = L1 (3) and L2 (4)] Single-crystal X-ray analyses indicate that complexes 3 and 4 possess a similar composition, with the molecular structure comprising of one Ag(I) cation, one ligand L (L indicating L1 or L2) and one nitrate anion (Fig. 4). The Ag(I) cations in the two complexes are all five-coordinated, except for the two longer contacts (2.828(8)–2.963(6) Å) to oxygen atoms of nitrate anions in complex 3. Despite of the similarity of the two complexes, they exhibit diverse architectures with the alteration of the two unsymmetrical bis(pyridyl) ligands and the different coordination modes of the nitrate anion. For complex 3, as shown in Fig. 5, two adjacent L1 ligands act in the cis–cis conformation and cooperatively coordinate to two Ag(I) cations, producing a 14-membered macrometallacyclic ring with the Ag Ag separation being 4.678(1) Å (Ag Agi), in which the aliphatic N2–H2N group forms a hydrogen bonding interaction with the atom O3 of the nitrate anion. The binuclear units are further linked together through two weakly coordinated nitrate anions, generating a chain structure along the a-axis (Fig. 5) with the shortest adjacent Ag Ag separation being 4.352(2) Å (Ag Agii). Meanwhile, C–H p interactions (C1–H1 p, 3.581(6) Å, \C–H p = 132.8°) between the p electron density of the N3-containing pyridyl ring and the adjacent pyridine CH are observed [16], which further strengthen the stability of the chain
Fig. 2. Layer structure of complex 1 formed by curving chains (grey) and the 14-membered macrometallacyclic rings (black).
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Fig. 3. (a) Double chain in complex 2 involving 38-membered macrometallacyclic rings. (b) Porous supramolecular network of complex 2 with 1-D channels filled by free MeCN molecules in the space-filling mode.
Fig. 4. Perspective view of the asymmetric unit of complexes 3 and 4 showing the coordination environment around the Ag(I) cations.
(Fig. 5). Moreover, another group of C–H p interactions (C10– H10 p, 3.801(8) Å, \C–H p = 143.9°) between the p electron density of the N1-containing pyridyl ring and the adjacent CH group [16] connect adjacent chains to generate a layer structure, as shown in Fig. S4.
The ligand L2 in complex 4 adopts the cis–trans conformation and bridges adjacent Ag(I) cations to form a linear chain along the diagonal ab plane (Fig. 6), in which the distance between subsequent Ag(I) cations is 12.218(1) Å. Meanwhile, the nitrate anions in the present complex connect adjacent Ag(I) cations in a l2
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Fig. 5. Infinite chain structure in complex 3 comprising of 14-membered macrometallacyclic rings.
(j1O1:j1O2:j1O3) bridging mode, thus generating a helical chain with the Ag Ag distance being 6.058(1) Å. Subsequently, the combination of the two types of chains results in the formation of a double layer structure along the bc plane (Fig. 6), in which C–H p interactions (C6–H6A p, 3.484(6) Å, \C–H p = 137.1°) between the p electron density of the N3-containing pyridyl ring and adjacent methylene group are observed [16]. Moreover, p p stacking interactions between the N1-containing pyridyl rings are also detected with the centroid-to-centroid distance being 3.657(3) Å, which extend the adjacent layers into a 3-D supramolecular network, as shown in Fig. S5. 3.2.3. Structural description of [Ag(L)(NO3)(PPh3)]n [L = L3 (5), L4 (6)] As the case of complexes 3 and 4, complexes 5 and 6 also possess a similar composition, with the molecular structure comprising of one Ag(I) cation, one ligand L (L indicating L3 or L4), one nitrate anion and one PPh3 molecule (Fig. 7). The Ag(I) cations in the two complexes exhibit diverse coordination spheres, with the coordination numbers being 4 and 5 owing to the different coordination modes of the nitrate anion. Moreover, these two complexes exhibit diverse architectures with the alteration of the two unsymmetrical bis(pyridyl) ligands. The ligands L3 and L4 of the two complexes present a similar cis–trans conformation and bridge adjacent Ag(I) cations to form different zig-zag chains along the b-axis (complex 5, Fig. 8a) and a curving chain along the c-axis (complex 6, Fig. 8b), in which the nearest Ag Ag distances are 10.112(4) and 9.222(5) Å, respectively. Furthermore, the terminal coordinated nitrate anions in the two complexes form intermolecular hydrogen bonding interactions with the amine groups (Table S2), which results in a brick wall shaped layer in complex 5 and a (4,4) layer motif in complex 6, as shown in Fig. 9a and b. Therefore, the introduction of the PPh3 molecule gives rise to more architectures. 3.3. Influence of the anions on the architectures From the aforementioned descriptions, the nature of the inorganic anions plays an important role in the structural diversities of the six complexes, owing to their different coordination abilities. For the nitrate-containing complexes 3–6, the stronger coordinating nitrate anion is involved in the coordination environment of the Ag(I) cations and allows the Ag(I) cations in the four complexes to exhibit diverse coordination spheres with the coordination numbers varying from 3 to 5. The nitrate anion can coordinate to the Ag(I) cation in monodentate, chelating and even more intricate l2-j3 modes, thus defining the dinuclear unit in complex 3, zig-zag chain motif in complex 5, curving chain motif in complex 6 and double layer structure in complex 4. By comparison, the perchlorate anion exhibits a weak coordination ability, and all the Ag(I) cations in the perchlorate-containing complexes 1 and 2 exhibit
Fig. 6. Double layer structure in complex 4 constructing from linear –Ag–L2– and helical –Ag–NO3– chains.
a linear coordination geometry with two coordinated N atoms from L1 and L2. Thus, complexes 1 and 2 only present curving chain motifs.
3.4. Influence of the ligands on the crystal structures Except for the inorganic anions, the crystal structures of the six complexes are also influenced by the conformations and the different positions of the pyridyl N atoms in the four positional isomeric unsymmetrical bis(pyridyl) ligands. Table 2 lists the conformations of the four bis(pyridyl) ligands in the present six complexes. Owing to the flexibility of the four ligands, the two pyridyl rings can rotate freely around the unsymmetrical –CH2–NH– spacer with different angles to form cis- and trans-conformations (Scheme 2), which exhibit a special ability to coordinate to metal centers, leading to interestingly structural motifs. For complexes 1 and 3, the ligand L1 exhibits different cis-cis and trans–trans conformations, which then results in different architectures (curving chain and dinuclear unit in complex 1; dinuclear unit in complex 3), without considering the coordination of the inorganic anions. Similarly, the ligand L2 exhibits different cis–trans conformations in complex 4 and cis–trans and trans–trans conformations in complex 2. The conformational differences directly result in the formation of linear and curving chains in the two complexes. Differing from the above two ligands, the ligands L3 and L4 in complexes 5 and 6 act in the same cis–trans conformation with similar dihedral angles and axis angles (Table 2), which leads to the diverse zig-zag chain in
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Fig. 7. Perspective view of the asymmetric unit of complexes 5 and 6 showing the coordination environment around the Ag(I) cations.
Fig. 8. (a) Zig-zag chain in complex 5. (b) Curving chain in complex 6.
complex 5 and curving chain in complex 6. Furthermore, the coordination of the PPh3 molecule also limits the extension of the dimension. For the same ligand, the cis–cis conformation can only lead to a dinuclear unit, while the cis–trans and trans–trans conformations can lead to the formation of various chain motifs. Moreover, the different positions of the pyridyl N atoms in the four positional isomeric unsymmetrical bis(pyridyl) ligands can cause subtle differences in these complexes. As observed in Table 2, with the change of the positions of the pyridyl N atoms, the Ag Ag separations show a regular increase, with the sequence of L1, L3, L4 and L2. Meanwhile, for the same conformation of one ligand, a small axis angle results in a longer AgAg separation, such as the ligand L1 in complex 1, and the ligand L2 in complexes 2 and 4. Therefore, the conformations and the different positions of the pyridyl N atoms in the four positional isomeric unsymmetrical bis(pyridyl) ligands play crucial roles on the structural diversities of these complexes. 3.5. Luminescent properties The luminescent properties of complexes 1–6 and the four free ligands in the solid-state at room temperature were investigated, in which the emission spectrum of the ligand L2 has been reported
in our previous work [17]. As shown in Fig. 10, the four free ligands present an emission maximum at 463, 420, 428 and 402 nm upon excitation at 384, 352, 372 and 361 nm, respectively, which could probably be attributed to the p⁄–p transitions. Upon different excitation (exmax = 340 nm for 1, 341 nm for 2, 392 nm for 3, and 339 nm for 4), complexes 1–4 exhibit an emission maximum at 456, 402, 460 and 410 nm, respectively. In contrast to the emissions of their corresponding free ligands, the luminescent emission band for the above four complexes can probably be assigned to intraligand (IL) p–p⁄ transitions (Fig. 10) [18]. Moreover, it is interesting to note that the emission intensities for these four complexes present a regular increase with the sequence of free ligands, nitrate-containing complexes and perchlorate-containing complexes. The increasing intensity of the complexes is probably attributable to the coordination of the ligand to the Ag(I) cation, which effectively restricts the flexibility and increases the rigidity of the free ligands, thus reducing the loss of energy [19]. Especially, the sharp increase of emission intensity for the perchlorate-containing complexes could be ascribed to the p p interactions in these complexes, as well as the abundant electrons in the delocalized P58 of ClO4 (delocalized P46 in NO3 ), which makes it more preferable to increase the chance of intraligand charge transfer and the quantum efficiency [19].
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Fig. 9. (a) Brick wall shaped layer of complex 5 extended by N–H O interactions. The PPh3 molecules are omitted for clarity. (b) (4,4)-Layer of complex 6 extended by N–H O interactions. The PPh3 molecules are omitted for clarity.
Table 2 Conformations of the four flexible unsymmetrical bis(pyridyl) ligands. Ligands
Complexes
Conformationsa
Dihedral angles (°)
Axis anglesb (°)
M(II) M(II) distances (Å)
L1
1
L2
3 2
L3 L4
4 5 6
trans–trans trans–trans cis–cis cis–trans trans–trans cis–trans cis–trans cis–trans
48.95 63.38 71.04 89.71 83.69 79.22 74.11 70.18
40.52 83.41 15.97 67.70 74.83 23.89 72.80 84.33
7.554(2) 3.797(1) 4.678(1) 7.606(3) 10.696(3) 12.218(1) 10.112(4) 9.222(5)
(N1) (N4) (N1) (N1)
a The former are defined by the position of the pyridine ring: located on the opposite side of the –CH2–NH– line is trans while the same side is cis; the latter are defined by the orientation of the N atoms in the pyridine ring: pointed in the opposite direction is trans while the same direction is cis. b Axis angle refers to the angle between the two Ag–N bonds of the same ligand.
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Scheme 2. Diverse conformations of the four unsymmetrical bis(pyridyl) ligands in complexes 1–6.
Fig. 10. Normalized emission spectra of the free ligands L1–L4 and complexes 1–6 in the solid-state at room temperature.
As is the case in complexes 1–4, the emission maximum at 424 and 398 nm upon a different excitation of 374 and 363 nm for complexes 5 and 6 respectively can also probably be assigned to the intraligand (IL) p–p⁄ transitions because of their resemblance to the emission spectra (Fig. 10) [18]. Their stronger emission intensities may be attributed to coordination of the ligands to the Ag(I) cations and the influence of the introduced PPh3 molecule on the freedom of the flexible ligands. The bulky PPh3 molecules restrain the twisted degrees of the flexible ligands (L3 and L4) and reduce the loss of energy via radiationless decay of the intraligand emission excited state, which cause the enhancement of the fluorescence intensity.
salts leads to the formation of six Ag(I)-bis(pyridyl) complexes, which exhibit structural diversities of macrometallacycle, curving and zig-zag chain, as well as double layer. The four ligands in the six complexes present diverse cis–cis, cis–trans and trans–trans conformations. The stronger coordination ability of the nitrate anion can extend adjacent Ag(I) cations into more intricate architectures. Therefore, the variation of these structures can be mainly attributed to the nature of the inorganic anions and the conformations of the four flexible unsymmetrical bis(pyridyl) ligands. Moreover, solid-state luminescent properties demonstrate that the emission intensities of the perchlorate-containing complexes are stronger than those of the nitrate-containing complexes.
4. Conclusions
Acknowledgements
In conclusion, the self-assembly of four flexible unsymmetrical bis(pyridyl) ligands, PPh3 and different AgX (X = NO3 and ClO4 )
This work is financial supported by the Key Project of Natural Science Foundation of Heilongjiang Province (No. ZD200903), Key
Z.-Y. Zhang et al. / Polyhedron 59 (2013) 38–47
Project of the Education bureau of Heilongjiang Province (Nos. 12511z023, and 2011CJHB006), and the Innovation team of the Education bureau of Heilongjiang Province (No. 2010td03). We thank the University of Heilongjiang (Hdtd2010-04) for supporting this study. Appendix A. Supplementary data CCDC reference numbers 917106–917111 contains the supplementary crystallographic data for paper. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/ retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336 033; or e-mail: [email protected]. Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.poly.2013.04.041. References [1] (a) L. Applegarth, N. Clark, A.C. Richardson, A.D.M. Parker, I. RadosavljevicEvans, A.E. Goeta, J.A.K. Howard, J.W. Steed, Chem. Commun. (2005) 5423; (b) L.R. Hanton, A.G. Young, Cryst. Growth Des. 6 (2006) 833; (c) T.J. Burchell, D.J. Eisler, R.J. Puddephatt, Cryst. Growth Des. 6 (2006) 974. [2] (a) H.C. Chen, H.L. Hu, Z.K. Chan, C.W. Yeh, H.W. Jia, C.P. Wu, J.D. Chen, J.C. Wang, Cryst. Growth Des. 7 (2007) 698; (b) V.J. Catalano, A.L. Moore, Inorg. Chem. 44 (2005) 6558; (c) Y. Zheng, J.R. Li, M. Du, R.Q. Zou, X.H. Bu, Cryst. Growth Des. 5 (2005) 215. [3] (a) C. He, C.Y. Duan, C.J. Fang, J. Chem. Soc., Dalton Trans. (2000) 2419; (b) B. Schmaltz, A. Jouaiti, M.W. Hosseini, A.D. Cian, Chem. Commun. (2001) 1242; (c) R. Horikoshi, T. Mochida, N. Maki, S. Yamada, H. Moriyama, J. Chem. Soc., Dalton Trans. (2002) 28. [4] M. Maekawa, H. Konaka, Y. Suenaga, T. Kuroda-Sowa, M. Munakata, J. Chem. Soc., Dalton Trans. (2000) 4160. [5] (a) A.R. Kennedy, K.G. Brown, G. Duncan, J.B. Kirkhouse, M. Kittner, C. Major, C.J. McHugh, P. Murdoch, W.E. Smith, New J. Chem. 29 (2005) 826; (b) H.C. Wu, P. Thanasekaran, C.H. Tsai, J.Y. Wu, S.M. Huang, Y.S. Wen, K.L. Lu, Inorg. Chem. 45 (2006) 295; (c) Y.B. Dong, H.Y. Wang, J.P. Ma, R.Q. Huang, Cryst. Growth Des. 5 (2005) 789. [6] G.J. Halder, S.M. Neville, C.J. Kepert, CrystEngComm 7 (2005) 266. [7] A.N. Khlobystov, A.J. Blake, N.R. Champness, D.A. Lemenovskii, A.G. Majouga, N.V. Zyk, M. Schröder, Coord. Chem. Rev. 222 (2001) 155. [8] A.J. Blake, N.R. Brooks, N.R. Champness, M. Crew, A. Deveson, D. Fenske, D.H. Gregory, L.R. Hanton, P. Hubberstey, M. Schröder, Chem. Commun. (2001) 1432.
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Anion-assisted silver(I) coordination complexes from flexible unsymmetrical bis(pyridyl) ligands: Syntheses, structures and luminescent properties Zhu-Yan Zhang a,b, Zhao-Peng Deng a, Li-Hua Huo a,⇑, Hui Zhao a, Shan Gao a,⇑ a Key Laboratory of Functional Inorganic Material Chemistry, Ministry of Education, School of Chemistry and Materials Science, Heilongjiang University, Harbin 150080, People’s Republic of China b Laboratory Centre of Pharmacy, College of Pharmacy Harbin Medical University, Harbin 150081, People’s Republic of China
a r t i c l e
i n f o
Article history: Received 1 March 2013 Accepted 16 April 2013 Available online 30 April 2013 Keywords: Coordination polymer Unsymmetrical bis(pyridyl) ligand Structure diversity Luminescent property
a b s t r a c t The reaction of AgX (X = NO3 and ClO4 ) salts, triphenylphosphine (PPh3) and four flexible unsymmetrical bis(pyridyl) ligands, namely N-(pyridin-2-ylmethyl)pyridin-2-amine (L1), N-(pyridin-3-ylmethyl) pyridin-3-amine (L2), N-(pyridin-2-ylmethyl)pyridin-3-amine (L3) and N-(pyridin-4-ylmethyl)pyridin3-amine (L4), leads to the formation of six complexes, [Ag2(L1)2(ClO4)2]n (1), [Ag2(L2)2(ClO4)2]nn(CH3CN) (2), [Ag(L1)(NO3)]n (3), [Ag(L2)(NO3)]n (4), [Ag(L3)(NO3)(PPh3)]n (5) and [Ag(L4)(NO3)(PPh3)]n (6), which have been characterized by elemental analysis, IR, TG, PL, powder and single-crystal X-ray diffraction. In contrast to the chain structure of complexes 1 and 2, induced by the weakly coordinated perchlorate anion, the nitrate anion can coordinate to the Ag(I) cation in monodentate, chelating and even more intricate l2-j3 modes, thus defining dinuclear (complex 3), various chain motif (complexes 5 and 6) and layer structures (complex 4). The four ligands in the six complexes present diverse cis–cis, cis–trans and trans– trans conformations, which are responsible for the structural diversities and, together with the nature of the inorganic anions, the coordination spheres of the Ag(I) cations. Moreover, solid-state luminescent properties demonstrate that the emission intensities of the perchlorate-containing complexes are stronger than those of the nitrate-containing complexes. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction Silver(I) coordination complexes with bis(pyridyl) ligands have attracted intensive interest owing to their fascinating architectures, along with their potential applications such as adsorption, photoluminescence and catalysis [1–3]. To date, a variety of Ag(I) coordination complexes with beautiful topologies and properties have been obtained, in which the ligands used are mainly focused on rigid bis(pyridyl) ligands [4–7]. By contrast, flexible bis(pyridyl) ligands have many degrees of freedom and hence few conformational restraints, as well as the unpredictable nature of such a system [8]. When flexible bis(pyridyl) ligands adopting different conformations react with silver salts, interesting and unusual structures may facilitate the formation of novel supramolecular architectures. However, a close inspection reveals that most of the flexible bis(pyridyl) ligands in the reported Ag(I) coordination complexes are symmetrical [9–11], i.e. a symmetrical spacer attached to the same substituted position of the two terminal pyridines (Scheme 1). In comparison, Ag(I) coordination complexes construct from unsymmetrical bis(pyridyl) ligands (unsymmetrical ⇑ Corresponding authors. Tel.: +86 0451 86609148. E-mail addresses: [email protected] (L.-H. Huo), [email protected] (S. Gao). 0277-5387/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.poly.2013.04.041
spacer and/or different substituted position of the two terminal pyridines) are less common [12,13]. Hence, it is still a great challenge and an interesting issue to construct silver(I) complexes from flexible unsymmetrical bis(pyridyl) ligands. To expand our research on Ag(I)-bis(pyridyl) complexes [11], we selected four flexible bis(pyridyl) ligands with a non-coordinating amine group in the unsymmetrical –CH2–NH– spacer, N-(pyridin-2-ylmethyl)pyridin-2-amine (L1), N-(pyridin-3-ylmethyl) pyridin-3-amine (L2), N-(pyridin-2-ylmethyl)pyridin-3-amine (L3) and N-(pyridin-4-ylmethyl)pyridin-3-amine (L4) (Scheme 1). The two pyridyls can freely twist around the unsymmetrical – CH2–NH– group with different bond angles to meet the requirements of the Ag(I) centers, resulting in diverse structures. The amine group in the flexible spacer of the four ligands can potentially form hydrogen bonds with the acceptor groups to direct the self-assembly of interesting supramolecular systems. Meanwhile, the coordination direction and different positions of the pyridyl N atoms in the positional isomeric ligands may benefit the formation of different structures. Bearing this conception in mind, we further report here the syntheses, structures and properties of six silver(I) complexes based on the aforementioned four ligands, PPh3 and AgX (X = NO3 and ClO4 ) salts, namely [Ag2(L1)2 (ClO4)2]n (1), [Ag2(L2)2(ClO4)2]nn(CH3CN) (2), [Ag(L1)(NO3)]n (3), [Ag(L2)(NO3)]n (4), [Ag(L3)(NO3)(PPh3)]n (5) and [Ag(L4)(NO3)
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39
Scheme 1. Flexible symmetrical and unsymmetrical bis(pyridyl) ligands in the reported and present Ag(I) coordination polymers.
(PPh3)]n (6). In contrast to the chain motif of the perchlorate-containing complexes, the nitrate-containing complexes 3–6 present various dinuclear, chain motif (zig-zag and curving chain) and double layer structures. The structural diversities of the six complexes can be mainly attributed to the nature of the inorganic anions, the coordination spheres of the Ag(I) cations and the conformations of the four flexible unsymmetrical bis(pyridyl) ligands. Moreover, solid-state luminescent properties demonstrate that the emission intensities of the perchlorate-containing complexes are stronger than those of the nitrate-containing complexes. 2. Experimental 2.1. Materials and methods All chemicals and solvents were of A.R. grade and were used without further purification in the syntheses. L1–L4 were synthesized according to a previously reported method [14]. Elemental analyses were carried out with a Vario MICRO from Elementar Analysensysteme GmbH, and the infrared spectra (IR) were recorded on KBr pellets in the range 4000–400 cm 1 on a Bruker Equinox 55 FT-IR spectrometer. Powder X-ray diffraction (PXRD) patterns were measured at 293 K on a Bruker D8 diffractometer (Cu Ka, k = 1.54059 Å). The TG analyses were carried out on a Perkin Elmer TG/DTA 6300 thermal analyzer under a flowing N2 atmosphere, with a heating rate of 10 °C/min. Luminescence spectra were measured on a Perkin Elmer LS 55 luminance meter.
Complex 2: Yield: 65% (based on Ag). Anal. Calc. for C24H25N7O8Cl2Ag2: C, 34.89; H, 3.05; N, 11.87. Found: C, 34.85; H, 3.10; N, 11.91%. IR (m/cm 1): 3147m, 2254m, 1600s, 1579m, 1517m, 1097s. Complex 3: Yield: 68% (based on Ag). Anal. Calc. for C22H22N8O6Ag2: C, 37.21; H, 3.12; N, 15.78. Found: C, 37.25; H, 3.06; N, 15.73%. IR (m/cm 1): 3160m, 1603s, 1570m, 1514m, 1384s. Complex 4: Yield: 63% (based on Ag). Anal. Calc. for C11H11N4O3Ag: C, 37.21; H, 3.12; N, 15.78. Found: C, 37.24; H, 3.18; N, 15.75%. IR (m/cm 1): 3176m, 1597s, 1569m, 1518m, 1380s. Caution! Although not encountered in our experiments, metal perchlorates are potentially explosive. They should be handled carefully and in small quantities. 2.2.2. Synthesis of complexes 5–6 The procedure was similar to that for complexes 1–4, except an equimolar amount of PPh3 was added into the reactions and stirred for an additional 10 min. Colorless crystals of 5 and 6 were obtained from the solution after avoiding illumination for several days. Complex 5: Yield: 63% (based on Ag). Anal. Calc. for C29H26N4O3PAg: C, 56.42; H, 4.24; N, 9.07. Found: C, 56.46; H, 4.17; N, 9.12%. IR (m/cm 1): 3179m, 1599s, 1571m, 1516m, 1485s, 1386s, 746m, 696m. Complex 6: Yield: 69% (based on Ag). Anal. Calc. for C29H26N4O3PAg: C, 56.42; H, 4.24; N, 9.07. Found: C, 56.37; H, 4.29; N, 9.11%. IR (m/cm 1): 3159m, 1598s, 1567m, 1518m, 1483s, 1382s, 744m, 696m. 2.3. X-ray crystallographic measurements
2.2. Syntheses 2.2.1. Synthesis of complexes 1–4 2 mmol L1 or L2 were dissolved in 10 mL methanol solution and then added to a MeCN solution (10 mL) containing an equal amount of silver(I) nitrate or silver(I) perchlorate. The mixture was stirred at room temperature for 10 min, and then filtered. Colorless crystals of 1–4 were isolated from the filtrate after avoiding illumination for several days. Complex 1: Yield: 62% (based on Ag). Anal. Calc. for C22H22N6O8Cl2Ag2: C, 33.66; H, 2.82; N, 10.70. Found: C, 33.63; H, 2.77; N, 10.74%. IR (m/cm 1): 3141m, 1602s, 1576m, 1512m, 1095s.
Table 1 provides a summary of the crystal data, data collection and refinement parameters for complexes 1–6. All the diffraction data were collected at 295 K on a RIGAKU RAXIS-RAPID diffractometer with graphite monochromatized Mo Ka (k = 0.71073 Å) radiation in the x scan mode. All the structures were solved by the direct method and difference Fourier syntheses. All non-hydrogen atoms were refined by full-matrix least-squares techniques on F2 with anisotropic thermal parameters. The hydrogen atoms attached to carbon and nitrogen atoms were placed in calculated positions with C–H = 0.93 (pyridyl), 0.96 (methyl), 0.97 (methylene), N–H = 0.86 Å and U (H) = 1.2Ueq (C, N) in the riding model
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Table 1 Crystal data and structure refinement parameters of complexes 1–6. Complex
1
2
3
Empirical formula Mr Crystal system Space group a (Å) b (Å) c (Å0 a (°) b (°) c (°) V(Å3) Z Dcalc (g cm 3) l (mm 1) h range Reflections collected Unique reflections No. of parameter F (0 0 0) R1, wR2 [I > 2r(I)] Goodness-of-fit (GOF) on F2 Largest and hole (e A 3)
C22H22N6O8Cl2Ag2 785.10 monoclinic C 2/c 32.558(7) 9.4926(19) 18.757(4) 90.00 110.40(3) 90.00 5434(2) 8 1.919 1.696 3.05–27.47 24391 6165 361 3104 0.0637, 0.1684 1.044 1.404, 0.980
C24H25N7O8Cl2Ag2 826.15 triclinic P1
C22H22N8O6Ag2 710.22 triclinic P1
9.4683(19) 10.711(2) 14.742(3) 85.96(3) 82.43(3) 83.28(3) 1469.6(5) 2 1.867 1.574 3.06–27.48 14042 6701 389 820 0.0639, 0.1427 0.990 0.908, 0.918
8.3134(17) 8.9521(18) 9.2973(19) 96.52(3) 94.94(3) 114.60(3) 618.2(2) 1 1.908 1.640 3.09–27.48 6102 2812 172 352 0.0500, 0.1023 1.088 1.076, 1.129
4
5
6
C11H11N4O3Ag 355.11 tetragonal P 43212 8.6397(12) 8.6397(12) 32.425(7) 90.00 90.00 90.00 2420.4(7) 8 1.949 1.676 3.02–27.45 23852 2765 172 1408 0.0432, 0.0782 1.090 0.772, 0.887
C29H26N4O3PAg 617.38 orthorhombic P bca 17.2479(5) 14.5923(4) 21.1904(6) 90.00 90.00 90.00 5333.3(2) 8 1.538 0.854 3.18–26.00 26918 5225 343 2512 0.0336, 0.0745 1.041 0.317, 0.535
C29H26N4O3PAg 617.38 monoclinic Cc 15.8352(8) 10.7875(5) 16.6099(7) 90.00 108.007(5) 90.00 2698.4(2) 4 1.520 0.844 3.77–27.56 14868 6198 543 1256 0.0367, 0.0884 1.063 0.540, 0.615
Empirical formula Mr Crystal system Space group a (Å) b (Å) c (Å) a (°) b (°) c (°) V (Å3) Z Dcalc (g cm 3) l (mm–1) h Range Reflections collected Unique reflections No. of parameter F (0 0 0) R1, wR2 [I > 2r(I)] Goodness-of-fit (GOF) on F2 Largest and hole (e A 3)
approximation. All calculations were carried out with the SHELXTL97 program [15]. Selected bond lengths and hydrogen bond parameters for complexes 1–6 are listed in Tables S1 and S2, respectively.
3. Results and discussion
demonstrates the existence of the MeCN molecule. The characteristic vibrations of the perchlorate anion in complexes 1 and 2 are at 1095 and 1097 cm 1, whereas the characteristic vibrations of the nitrate anion in complexes 3–6 are at 1384, 1380, 1386 and 1382 cm 1, respectively. Moreover, the characteristic vibrations of PPh3 are at 696, 746 and 1485 cm 1 for complex 5 and 696, 744 and 1483 cm 1 for complex 6.
3.1. Syntheses and IR spectroscopy In order to investigate the influence of the anions and ligand conformations on the final structures of Ag(I)-bis(pyridyl) complexes, four complexes were synthesized by the self-assembly of the flexible unsymmetrical bis(pyridyl) ligands and different AgX (X = NO3 and ClO4 ) salts under similar experimental conditions, while complexes 5 and 6 were obtained with the addition of PPh3. Due to the stronger coordination ability of the nitrate anion, the nitrate-containing complexes exhibit diverse dinuclear, chain motif and layer structures. By contrast, the weakly coordinating perchlorate anions only afford the formation of chain structures. The N–H stretching vibrations for all the salts fall in the region 3179–3141 cm 1, in which the energy of the vibrations largely depends on the positional isomeric ligands and the extent of hydrogen bonding. The vibration at 2254 cm 1 in complex 2
3.2. Crystal structures 3.2.1. Structural description of [Ag2(L1)2(ClO4)2]n (1) and [Ag2(L2)2(ClO4)2]nn(CH3CN) (2) As shown in Fig. 1, complexes 1 and 2 possess a similar composition, with the molecular structure comprising of two Ag(I) cations, two ligands L and two perchlorate anions, together with one additional free MeCN molecule in the molecular structure of complex 2. Owing to the weak coordination ability of the perchlorate anion, the Ag(I) cations in the present two complexes exhibit linear coordination geometries, with one or two longer contacts (2.788(7)–2.922(1) Å) to oxygen atoms of perchlorate anions. Furthermore, the two unsymmetrical bis(pyridyl) ligands show different conformations, resulting in diverse architectures.
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Fig. 1. Perspective view of the asymmetric unit of complexes 1 and 2 showing the coordination environment around the Ag(I) cations.
In complex 1, two independent trans–trans conformations of the ligand L1 are present. The N1-containing one bridges adjacent Ag1 cations to form a curving chain along the c-axis (Fig. 2), in which the nearest Ag Ag distance is 7.554(2) Å. Meanwhile, the N4-containing one links two Ag2 cations, producing a 14-membered macrometallacyclic ring, in which the Ag Ag separation is 3.797(1) Å. Subsequently, the weakly coordinated Cl2-containing perchlorate anion connects the two types of motifs, leading to the formation of a layer structure (Fig. 2). Moreover, the terminal coordinated Cl1-containing perchlorate anions forms intermolecular hydrogen bonding interactions (Table S2) with the amine groups (N2–H2N), which result in a 3-D supramolecular network, as shown in Fig. S1. Differing from the ligand L1, the two L2 ligands in complex 2 exhibit different cis–trans and trans–trans conformations. The Ag1 and Ag2 cations are alternately connected by the two ligands to generate curving chains along the c-axis, which then link through the weak Ag Ag interactions (3.358(1) Å) and p p stacking interactions between the N3- and N6-containing pyridyl rings (the centroid-to-centroid distance being 3.663(1) Å) to a form double chain involving 38-membered macrometallacyclic rings (Fig. 3a). Adjacent double chains are further connected into a layer motif through C–H O interactions (C16–H16 O2 = 3.263(1) Å, \C–H p = 127.0°) (Fig. S2) [16]. The N–H O interactions between Cl2-containing perchlorate anions and the amine groups (N2–H2N) extend adjacent layers into a 3-D porous supramolecular network (Fig. S3, Table S2), with the 1-D channels filled by free MeCN molecules (Fig. 3b). Furthermore, p p stacking interactions
between the N1- and N4-containing pyridyl rings are detected, with the centroid-to-centroid distance being 3.567(9) Å, which strengthens the stability of the 3-D supramolecular network. 3.2.2. Structural description of [Ag(L)(NO3)]n [L = L1 (3) and L2 (4)] Single-crystal X-ray analyses indicate that complexes 3 and 4 possess a similar composition, with the molecular structure comprising of one Ag(I) cation, one ligand L (L indicating L1 or L2) and one nitrate anion (Fig. 4). The Ag(I) cations in the two complexes are all five-coordinated, except for the two longer contacts (2.828(8)–2.963(6) Å) to oxygen atoms of nitrate anions in complex 3. Despite of the similarity of the two complexes, they exhibit diverse architectures with the alteration of the two unsymmetrical bis(pyridyl) ligands and the different coordination modes of the nitrate anion. For complex 3, as shown in Fig. 5, two adjacent L1 ligands act in the cis–cis conformation and cooperatively coordinate to two Ag(I) cations, producing a 14-membered macrometallacyclic ring with the Ag Ag separation being 4.678(1) Å (Ag Agi), in which the aliphatic N2–H2N group forms a hydrogen bonding interaction with the atom O3 of the nitrate anion. The binuclear units are further linked together through two weakly coordinated nitrate anions, generating a chain structure along the a-axis (Fig. 5) with the shortest adjacent Ag Ag separation being 4.352(2) Å (Ag Agii). Meanwhile, C–H p interactions (C1–H1 p, 3.581(6) Å, \C–H p = 132.8°) between the p electron density of the N3-containing pyridyl ring and the adjacent pyridine CH are observed [16], which further strengthen the stability of the chain
Fig. 2. Layer structure of complex 1 formed by curving chains (grey) and the 14-membered macrometallacyclic rings (black).
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Fig. 3. (a) Double chain in complex 2 involving 38-membered macrometallacyclic rings. (b) Porous supramolecular network of complex 2 with 1-D channels filled by free MeCN molecules in the space-filling mode.
Fig. 4. Perspective view of the asymmetric unit of complexes 3 and 4 showing the coordination environment around the Ag(I) cations.
(Fig. 5). Moreover, another group of C–H p interactions (C10– H10 p, 3.801(8) Å, \C–H p = 143.9°) between the p electron density of the N1-containing pyridyl ring and the adjacent CH group [16] connect adjacent chains to generate a layer structure, as shown in Fig. S4.
The ligand L2 in complex 4 adopts the cis–trans conformation and bridges adjacent Ag(I) cations to form a linear chain along the diagonal ab plane (Fig. 6), in which the distance between subsequent Ag(I) cations is 12.218(1) Å. Meanwhile, the nitrate anions in the present complex connect adjacent Ag(I) cations in a l2
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43
Fig. 5. Infinite chain structure in complex 3 comprising of 14-membered macrometallacyclic rings.
(j1O1:j1O2:j1O3) bridging mode, thus generating a helical chain with the Ag Ag distance being 6.058(1) Å. Subsequently, the combination of the two types of chains results in the formation of a double layer structure along the bc plane (Fig. 6), in which C–H p interactions (C6–H6A p, 3.484(6) Å, \C–H p = 137.1°) between the p electron density of the N3-containing pyridyl ring and adjacent methylene group are observed [16]. Moreover, p p stacking interactions between the N1-containing pyridyl rings are also detected with the centroid-to-centroid distance being 3.657(3) Å, which extend the adjacent layers into a 3-D supramolecular network, as shown in Fig. S5. 3.2.3. Structural description of [Ag(L)(NO3)(PPh3)]n [L = L3 (5), L4 (6)] As the case of complexes 3 and 4, complexes 5 and 6 also possess a similar composition, with the molecular structure comprising of one Ag(I) cation, one ligand L (L indicating L3 or L4), one nitrate anion and one PPh3 molecule (Fig. 7). The Ag(I) cations in the two complexes exhibit diverse coordination spheres, with the coordination numbers being 4 and 5 owing to the different coordination modes of the nitrate anion. Moreover, these two complexes exhibit diverse architectures with the alteration of the two unsymmetrical bis(pyridyl) ligands. The ligands L3 and L4 of the two complexes present a similar cis–trans conformation and bridge adjacent Ag(I) cations to form different zig-zag chains along the b-axis (complex 5, Fig. 8a) and a curving chain along the c-axis (complex 6, Fig. 8b), in which the nearest Ag Ag distances are 10.112(4) and 9.222(5) Å, respectively. Furthermore, the terminal coordinated nitrate anions in the two complexes form intermolecular hydrogen bonding interactions with the amine groups (Table S2), which results in a brick wall shaped layer in complex 5 and a (4,4) layer motif in complex 6, as shown in Fig. 9a and b. Therefore, the introduction of the PPh3 molecule gives rise to more architectures. 3.3. Influence of the anions on the architectures From the aforementioned descriptions, the nature of the inorganic anions plays an important role in the structural diversities of the six complexes, owing to their different coordination abilities. For the nitrate-containing complexes 3–6, the stronger coordinating nitrate anion is involved in the coordination environment of the Ag(I) cations and allows the Ag(I) cations in the four complexes to exhibit diverse coordination spheres with the coordination numbers varying from 3 to 5. The nitrate anion can coordinate to the Ag(I) cation in monodentate, chelating and even more intricate l2-j3 modes, thus defining the dinuclear unit in complex 3, zig-zag chain motif in complex 5, curving chain motif in complex 6 and double layer structure in complex 4. By comparison, the perchlorate anion exhibits a weak coordination ability, and all the Ag(I) cations in the perchlorate-containing complexes 1 and 2 exhibit
Fig. 6. Double layer structure in complex 4 constructing from linear –Ag–L2– and helical –Ag–NO3– chains.
a linear coordination geometry with two coordinated N atoms from L1 and L2. Thus, complexes 1 and 2 only present curving chain motifs.
3.4. Influence of the ligands on the crystal structures Except for the inorganic anions, the crystal structures of the six complexes are also influenced by the conformations and the different positions of the pyridyl N atoms in the four positional isomeric unsymmetrical bis(pyridyl) ligands. Table 2 lists the conformations of the four bis(pyridyl) ligands in the present six complexes. Owing to the flexibility of the four ligands, the two pyridyl rings can rotate freely around the unsymmetrical –CH2–NH– spacer with different angles to form cis- and trans-conformations (Scheme 2), which exhibit a special ability to coordinate to metal centers, leading to interestingly structural motifs. For complexes 1 and 3, the ligand L1 exhibits different cis-cis and trans–trans conformations, which then results in different architectures (curving chain and dinuclear unit in complex 1; dinuclear unit in complex 3), without considering the coordination of the inorganic anions. Similarly, the ligand L2 exhibits different cis–trans conformations in complex 4 and cis–trans and trans–trans conformations in complex 2. The conformational differences directly result in the formation of linear and curving chains in the two complexes. Differing from the above two ligands, the ligands L3 and L4 in complexes 5 and 6 act in the same cis–trans conformation with similar dihedral angles and axis angles (Table 2), which leads to the diverse zig-zag chain in
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Fig. 7. Perspective view of the asymmetric unit of complexes 5 and 6 showing the coordination environment around the Ag(I) cations.
Fig. 8. (a) Zig-zag chain in complex 5. (b) Curving chain in complex 6.
complex 5 and curving chain in complex 6. Furthermore, the coordination of the PPh3 molecule also limits the extension of the dimension. For the same ligand, the cis–cis conformation can only lead to a dinuclear unit, while the cis–trans and trans–trans conformations can lead to the formation of various chain motifs. Moreover, the different positions of the pyridyl N atoms in the four positional isomeric unsymmetrical bis(pyridyl) ligands can cause subtle differences in these complexes. As observed in Table 2, with the change of the positions of the pyridyl N atoms, the Ag Ag separations show a regular increase, with the sequence of L1, L3, L4 and L2. Meanwhile, for the same conformation of one ligand, a small axis angle results in a longer AgAg separation, such as the ligand L1 in complex 1, and the ligand L2 in complexes 2 and 4. Therefore, the conformations and the different positions of the pyridyl N atoms in the four positional isomeric unsymmetrical bis(pyridyl) ligands play crucial roles on the structural diversities of these complexes. 3.5. Luminescent properties The luminescent properties of complexes 1–6 and the four free ligands in the solid-state at room temperature were investigated, in which the emission spectrum of the ligand L2 has been reported
in our previous work [17]. As shown in Fig. 10, the four free ligands present an emission maximum at 463, 420, 428 and 402 nm upon excitation at 384, 352, 372 and 361 nm, respectively, which could probably be attributed to the p⁄–p transitions. Upon different excitation (exmax = 340 nm for 1, 341 nm for 2, 392 nm for 3, and 339 nm for 4), complexes 1–4 exhibit an emission maximum at 456, 402, 460 and 410 nm, respectively. In contrast to the emissions of their corresponding free ligands, the luminescent emission band for the above four complexes can probably be assigned to intraligand (IL) p–p⁄ transitions (Fig. 10) [18]. Moreover, it is interesting to note that the emission intensities for these four complexes present a regular increase with the sequence of free ligands, nitrate-containing complexes and perchlorate-containing complexes. The increasing intensity of the complexes is probably attributable to the coordination of the ligand to the Ag(I) cation, which effectively restricts the flexibility and increases the rigidity of the free ligands, thus reducing the loss of energy [19]. Especially, the sharp increase of emission intensity for the perchlorate-containing complexes could be ascribed to the p p interactions in these complexes, as well as the abundant electrons in the delocalized P58 of ClO4 (delocalized P46 in NO3 ), which makes it more preferable to increase the chance of intraligand charge transfer and the quantum efficiency [19].
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Fig. 9. (a) Brick wall shaped layer of complex 5 extended by N–H O interactions. The PPh3 molecules are omitted for clarity. (b) (4,4)-Layer of complex 6 extended by N–H O interactions. The PPh3 molecules are omitted for clarity.
Table 2 Conformations of the four flexible unsymmetrical bis(pyridyl) ligands. Ligands
Complexes
Conformationsa
Dihedral angles (°)
Axis anglesb (°)
M(II) M(II) distances (Å)
L1
1
L2
3 2
L3 L4
4 5 6
trans–trans trans–trans cis–cis cis–trans trans–trans cis–trans cis–trans cis–trans
48.95 63.38 71.04 89.71 83.69 79.22 74.11 70.18
40.52 83.41 15.97 67.70 74.83 23.89 72.80 84.33
7.554(2) 3.797(1) 4.678(1) 7.606(3) 10.696(3) 12.218(1) 10.112(4) 9.222(5)
(N1) (N4) (N1) (N1)
a The former are defined by the position of the pyridine ring: located on the opposite side of the –CH2–NH– line is trans while the same side is cis; the latter are defined by the orientation of the N atoms in the pyridine ring: pointed in the opposite direction is trans while the same direction is cis. b Axis angle refers to the angle between the two Ag–N bonds of the same ligand.
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Scheme 2. Diverse conformations of the four unsymmetrical bis(pyridyl) ligands in complexes 1–6.
Fig. 10. Normalized emission spectra of the free ligands L1–L4 and complexes 1–6 in the solid-state at room temperature.
As is the case in complexes 1–4, the emission maximum at 424 and 398 nm upon a different excitation of 374 and 363 nm for complexes 5 and 6 respectively can also probably be assigned to the intraligand (IL) p–p⁄ transitions because of their resemblance to the emission spectra (Fig. 10) [18]. Their stronger emission intensities may be attributed to coordination of the ligands to the Ag(I) cations and the influence of the introduced PPh3 molecule on the freedom of the flexible ligands. The bulky PPh3 molecules restrain the twisted degrees of the flexible ligands (L3 and L4) and reduce the loss of energy via radiationless decay of the intraligand emission excited state, which cause the enhancement of the fluorescence intensity.
salts leads to the formation of six Ag(I)-bis(pyridyl) complexes, which exhibit structural diversities of macrometallacycle, curving and zig-zag chain, as well as double layer. The four ligands in the six complexes present diverse cis–cis, cis–trans and trans–trans conformations. The stronger coordination ability of the nitrate anion can extend adjacent Ag(I) cations into more intricate architectures. Therefore, the variation of these structures can be mainly attributed to the nature of the inorganic anions and the conformations of the four flexible unsymmetrical bis(pyridyl) ligands. Moreover, solid-state luminescent properties demonstrate that the emission intensities of the perchlorate-containing complexes are stronger than those of the nitrate-containing complexes.
4. Conclusions
Acknowledgements
In conclusion, the self-assembly of four flexible unsymmetrical bis(pyridyl) ligands, PPh3 and different AgX (X = NO3 and ClO4 )
This work is financial supported by the Key Project of Natural Science Foundation of Heilongjiang Province (No. ZD200903), Key
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Project of the Education bureau of Heilongjiang Province (Nos. 12511z023, and 2011CJHB006), and the Innovation team of the Education bureau of Heilongjiang Province (No. 2010td03). We thank the University of Heilongjiang (Hdtd2010-04) for supporting this study. Appendix A. Supplementary data CCDC reference numbers 917106–917111 contains the supplementary crystallographic data for paper. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/ retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336 033; or e-mail: [email protected]. Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.poly.2013.04.041. References [1] (a) L. Applegarth, N. Clark, A.C. Richardson, A.D.M. Parker, I. RadosavljevicEvans, A.E. Goeta, J.A.K. Howard, J.W. Steed, Chem. Commun. (2005) 5423; (b) L.R. Hanton, A.G. Young, Cryst. Growth Des. 6 (2006) 833; (c) T.J. Burchell, D.J. Eisler, R.J. Puddephatt, Cryst. Growth Des. 6 (2006) 974. [2] (a) H.C. Chen, H.L. Hu, Z.K. Chan, C.W. Yeh, H.W. Jia, C.P. Wu, J.D. Chen, J.C. Wang, Cryst. Growth Des. 7 (2007) 698; (b) V.J. Catalano, A.L. Moore, Inorg. Chem. 44 (2005) 6558; (c) Y. Zheng, J.R. Li, M. Du, R.Q. Zou, X.H. Bu, Cryst. Growth Des. 5 (2005) 215. [3] (a) C. He, C.Y. Duan, C.J. Fang, J. Chem. Soc., Dalton Trans. (2000) 2419; (b) B. Schmaltz, A. Jouaiti, M.W. Hosseini, A.D. Cian, Chem. Commun. (2001) 1242; (c) R. Horikoshi, T. Mochida, N. Maki, S. Yamada, H. Moriyama, J. Chem. Soc., Dalton Trans. (2002) 28. [4] M. Maekawa, H. Konaka, Y. Suenaga, T. Kuroda-Sowa, M. Munakata, J. Chem. Soc., Dalton Trans. (2000) 4160. [5] (a) A.R. Kennedy, K.G. Brown, G. Duncan, J.B. Kirkhouse, M. Kittner, C. Major, C.J. McHugh, P. Murdoch, W.E. Smith, New J. Chem. 29 (2005) 826; (b) H.C. Wu, P. Thanasekaran, C.H. Tsai, J.Y. Wu, S.M. Huang, Y.S. Wen, K.L. Lu, Inorg. Chem. 45 (2006) 295; (c) Y.B. Dong, H.Y. Wang, J.P. Ma, R.Q. Huang, Cryst. Growth Des. 5 (2005) 789. [6] G.J. Halder, S.M. Neville, C.J. Kepert, CrystEngComm 7 (2005) 266. [7] A.N. Khlobystov, A.J. Blake, N.R. Champness, D.A. Lemenovskii, A.G. Majouga, N.V. Zyk, M. Schröder, Coord. Chem. Rev. 222 (2001) 155. [8] A.J. Blake, N.R. Brooks, N.R. Champness, M. Crew, A. Deveson, D. Fenske, D.H. Gregory, L.R. Hanton, P. Hubberstey, M. Schröder, Chem. Commun. (2001) 1432.
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