Synthesis, structures and luminescent studies of five metal coordination compounds with a pyridine-containing tripodal ligand

Polyhedron 87 (2015) 369–376

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Synthesis, structures and luminescent studies of five metal coordination compounds with a pyridine-containing tripodal ligand Zhao-Peng Qi a,b,⇑, Jiao-Jiao Sun a, Yan-Su Lan a, Pei-Yu Li a, Lei Xu a, Peng Wan a a b

School of Chemistry and Chemical Engineering, Huangshan University, Huangshan 245041, China State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, China

a r t i c l e

i n f o

Article history: Received 7 October 2014 Accepted 28 November 2014 Available online 17 December 2014 Keywords: Tripodal ligand Coordination compound 1D chain Structure Luminescence

a b s t r a c t Five new coordination compounds, [Ag2(L3)2](ClO4)2 (1), [Zn(L3)(Cl)](ClO4)H2O (2) [Zn2(L3)(Cl)4] (3), [Cu(L3)(Cl)](Cl)2H2O (4) and [Cd(L3)(Cl)(H2O)](ClO4)H2O (5), with the tripodal ligand N1-(2-aminoethyl)-N1-pyridin-3-ylmethyl-ethane- 1,2-diamine (L3) have been synthesized. Interestingly, coordination compound 1 shows a dinuclear structure, coordination compounds 2, 4 and 5 display 1D zig-zag chain structures, and coordination compound 3 exhibits an uncommon 1D chain structure. The results showed that the metal ions and anions have a distinct impact on the frameworks of the coordination compounds. The photoluminescent properties of the ligand and coordination compounds were also investigated. Ó 2014 Elsevier Ltd. All rights reserved.

1. Introduction

2. Experimental

The design and assembly of coordination polymers with welldefined structures and valuable properties, such as magnetism, luminescence, catalysis, gas adsorption, etc., has attracted more attention in the field of supramolecular chemistry and crystal engineering in recent years [1–3]. However, how to rationally control desired structures with potential applications is still a great challenge, and many efforts have been made by chemists to investigate the detailed assembly process, including the coordination preference of metal ions, the bonding conformation of the ligands and other factors [2–5]. Previously, we have concentrated our attention on polyamine ligands for their extensive use in the construction of diverse frameworks with well-defined properties [4–7]. For example, recently we have designed two isomeric ligands (L3 and L4), which are found to be agile in assembling mononuclear [Ni(L3)2](ClO4)2 (10 ), onedimensional (1D) zig-zag [Cu(L3)(H2O)](ClO4)2 (20 ) and ladder structures [Cu2(L4)2(Cl)](ClO4)32H2O, etc. [7a]. To further investigate the assembly process and as an extension of our work, we utilized ligand L3 to synthesize five coordination compounds, namely [Ag2(L3)2](ClO4)2 (1), [Zn(L3)(Cl)](ClO4)H2O (2) [Zn2(L3)(Cl)4] (3), [Cu(L3)(Cl)](Cl)2H2O (4) and [Cd(L3)(Cl)(H2O)](ClO4)H2O (5), and investigated their photoluminescent properties (Scheme 1).

2.1. Materials and measurements

⇑ Corresponding author at: School of Chemistry and Chemical Engineering, Huangshan University, Huangshan 245041, China. Fax: +86 559 2546554. E-mail address: [email protected] (Z.-P. Qi). http://dx.doi.org/10.1016/j.poly.2014.11.037 0277-5387/Ó 2014 Elsevier Ltd. All rights reserved.

All commercially available chemicals were of reagent grade and used as received without further purification. L33HCl was obtained as described previously [7a]. Elemental analyses for C, H and N were made on a Perkin-Elmer 240C elemental analyzer. Powder X-ray diffraction (PXRD) measurements were performed on a Bruker D8 X-ray diffractometer using Cu Ka radiation (k = 1.5406 Å), in which the X-ray tube was operated at 40 kV and 40 mA. Infrared (IR) spectra were recorded on a Nicolet 380 FT-IR spectrophotometer using KBr pellets. Luminescence spectra for the samples were measured at room temperature on a Hitachi F-4500 spectrofluorometer with a xenon arc lamp as the light source. In the measurements of emission and excitation spectra, the pass width was 2.5 nm. 2.2. Synthesis of the coordination compounds 2.2.1. Synthesis of [Ag2(L3)2](ClO4)2 (1) An aqueous solution (3 ml) of L3 (0.0097 g, 0.05 mmol) was added to an aqueous solution (3 ml) of AgClO4 (0.0103 g, 0.05 mmol), and acetonitrile (3 ml) was added to dissolve the precipitate that formed. The solution was filtered about 15 min later and the filtrate was evaporated slowly in air over several days to give colorless crystals. Yield: 50%. Anal. Calc. for C20H36Cl2Ag2N8O8: C, 29.91; H, 4.52; N, 13.95. Found: C, 30.03; H, 4.61; N, 13.84%. IR

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(KBr, cm1): 3329 (s), 2939 (m), 2823 (m), 1583 (s), 1474 (m), 1425 (m), 1320 (w), 1126 (vs), 1087 (vs), 872 (w), 714 (m), 630 (s). 2.2.2. Synthesis of [Zn(L3)(Cl)](ClO4)H2O (2) An aqueous solution (3 ml) of L33HCl (0.0151 g, 0.05 mmol) was added to an aqueous solution (3 ml) of Zn(ClO4)26H2O (0.0177 g, 0.05 mmol), the resulting solution was adjusted to pH ca. 9 with 0.5 M NaOH while stirring and then acetonitrile (5 ml) was added. The solution was filtered about 15 min later and the filtrate was evaporated slowly in air over several days to give colorless block crystals. Yield: 60%. Anal. Calc. for C10H20Cl2ZnN4O5: C, 29.11; H, 4.89; N, 13.58. Found: C, 29.06; H, 4.95; N, 13.50%. IR (KBr, cm1): 3331 (s), 3251 (s), 2957 (m), 2892 (m), 1598 (s), 1487 (m), 1466 (w), 1435 (m), 1335 (m), 1089 (vs), 953 (m), 892 (w), 624 (m). 2.2.3. Synthesis of [Zn2(L3)(Cl)4] (3) Coordination compound 3 was acquired as colorless crystals by the same method as for 1, except that ZnCl2 was used instead of AgClO4. Crystals 3 could also be obtained by the same method as for 2, except using ZnCl2 instead of Zn(ClO4)26H2O. Yield: 45%. Anal. Calc. for C10H18Zn2N4Cl4: C, 25.73; H, 3.89; N, 12.00. Found: C, 25.82; H, 4.01; N, 11.94%. IR (KBr, cm1): 3314 (s), 3268 (s), 3339 (s), 3155 (m), 2918 (w), 2878 (w), 2850 (w), 1606 (s), 1584 (s), 1470 (s), 1435 (s), 1356 (w), 1121 (s), 1058 (vs), 1003 (s), 956 (s), 888 (m), 810 (m), 657 (m). 2.2.4. Synthesis of [Cu(L3)(Cl)](Cl)2H2O (4) Coordination compound 4 was obtained as blue plate crystals by the same method as for 3, except that CuCl22H2O was used. Yield: 54%. Anal. Calc. for C10H22Cl2CuN4O2: C, 32.93; H, 6.08; N, 15.36. Found: C, 32.80; H, 6.15; N, 15.47%. IR (KBr, cm1): 3468 (s), 3361 (s), 1627 (s), 1384 (s), 1092 (m), 1055 (m), 614 (m). 2.2.5. Synthesis of [Cd(L3)(Cl)(H2O)](ClO4)H2O (5) Coordination compound 5 was obtained as colorless crystals by the same method as for 2, except that Cd(ClO4)26H2O was used instead of of Zn(ClO4)26H2O. Yield: 60%. Anal. Calc. for C10H22Cl2CdN4O6: C, 25.15; H, 4.64; N, 11.73. Found: C, 25.01; H, 4.77; N, 11.86%. IR (KBr, cm1): 3349 (s), 3241 (s), 3143 (m), 2931 (w), 2872 (w), 1592 (m), 1469 (w), 1428 (w), 1143 (s), 1107 (vs), 1090 (vs), 949 (w), 887 (w), 626 (m). Caution! Perchlorate salts of metal coordination compounds with organic ligands are potentially explosive. Only small amounts of the materials should be prepared and the samples should be handled with caution.

H2N

N

1’

NH2

1 2’

N

2 3 4 5 Scheme 1. Schematic drawing for the formation of coordination compounds 1–5 with the ligand L3.

2.3. X-ray crystallography The unit cell parameters were determined and the data were collected at 293 K with a Bruker SMART CCD system equipped with monochromated Mo Ka radiation (k = 0.71073 Å) for 1–5. Empirical absorption corrections were applied to the data using the SADABS program. Structures of 1–5 were solved by direct methods and refined by full-matrix least-squares on F2 using the SHELXL-97 programs [8]. All the non-hydrogen atoms were refined anisotropically on F2 by full-matrix least-squares techniques. The hydrogen atoms were generated geometrically. Crystallographic data for 1–5 are listed in Table 1. Selected bond lengths and angles for coordination compounds 1–5 are listed in Table 2. The hydrogen-bonding data are listed in Table S1 (Supporting Information).

3. Results and discussion 3.1. Description of the crystal structures of coordination compounds 1–5 3.1.1. [Ag2(L3)2](ClO4)2 (1) Colorless block crystals of 1 could be obtained by evaporation of an aqueous solution containing L3 and AgClO4. As shown in Fig. 1a, the asymmetric unit of 1 consists of two similar Ag(I) atoms, and each Ag(I) atom is coordinated by three amino nitrogen atoms from one L3 ligand and one pyridine nitrogen atom from another

Table 1 Crystallographic data for coordination compounds 1–5. Compound

1

2

3

Empirical formula Formula weight Crystal system Space group a (Å) b (Å) c (Å) a (°) b (°) c (°) V (Å3) Z Dcalc (g cm3) l (mm1) Rint R1 (I > 2r(I))a wR2 (all data)b Goodness-of-fit (GOF) on F2

C20H36Cl2Ag2N8O8 803.21 monoclinic P21 9.4711(18) 14.270(3) 11.590(2) 90.00 99.221(2) 90.00 1546.2(5) 2 1.725 1.493 0.0203 0.0262 0.0699 1.034

C10H20Cl2ZnN4O5 412.59 monoclinic P21/c 12.374(15) 9.454(12) 16.286(15) 90.00 117.76(5) 90.00 1686(3) 4 1.626 1.799 0.0199 0.0327 0.0958 1.091

C10H18Zn2N4Cl4 466.82 orthorhombic Pbca 10.1178(12) 16.4130(19) 21.150(2) 90.00 90.00 90.00 3512.2(7) 8 1.766 3.334 0.0899 0.0395 0.1086 1.075

Compound 4 Empirical formula C10H22Cl2CuN4O2 Formula weight 364.76 Crystal system monoclinic Space group P21/c a (Å) 10.455(2) b (Å) 9.661(2) c (Å) 15.788(3) a (°) 90.00 b (°) 105.612(2) c (°) 90.00 3 V (Å ) 1535.9(6) Z 4 Dcalc (g cm3) 1.577 l (mm1) 1.773 Rint 0.0183 R1 (I > 2r(I))a 0.0284 b wR2 (all data) 0.0760 2 Goodness-of-fit (GOF) on F 1.094 P P a R1 = ||Fo|  |Fc||/ |Fo|. P P b wR2 = | w(|Fo|2  |Fc|2)|/ |w(Fo)2|1/2.

5 C10H22Cl2CdN4O6 477.63 orthorhombic Pca21 16.408(3) 9.2370(18) 23.627(5) 90.00 90.00 90.00 3580.9(12) 8 1.772 1.550 0.0959 0.0340 0.0783 1.025

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Table 2 Selected bond lengths (Å) and angles (°) for coordination compounds 1–5. 1 Ag1–N1 Ag1–N3 Ag2–N5 Ag2–N7 N1–Ag1–N2 N1–Ag1–N8 N2–Ag1–N8 N4–Ag2–N5 N4–Ag2–N7 N5–Ag2–N7

2.363(5) 2.288(4) 2.499(4) 2.263(4) 75.39(15) 110.20(16) 131.68(14) 75.06(17) 115.07(16) 146.86(16)

Ag1–N2 Ag2–N4 Ag2–N6 Ag1–N8 N1–Ag1–N3 N2–Ag1–N3 N3–Ag1–N8 N4–Ag2–N6 N5–Ag2–N6 N6–Ag2–N7

2 Zn1–N1 Zn1–N3 Zn1–Cl1 N1–Zn1–N2 N1–Zn1–N4#1 N2–Zn1–N4#1 N1–Zn1–Cl1 N3–Zn1–Cl1

2.045(3) 2.056(3) 2.274(2) 81.04(12) 90.32(13) 167.43(9) 118.61(13) 119.55(11)

Zn1–N2 Zn1–N4#1

3 Zn1–N1 Zn1–N3 Zn1–Cl2 Zn2–Cl2 Zn2–Cl4 N1–Zn1–N2 N2–Zn1–N3 N2–Zn1–Cl1 N1–Zn1–Cl2 N3–Zn1–Cl2 N4–Zn2–Cl2#2 N4–Zn2–Cl4#2 Cl2–Zn2–Cl4

2.015(3) 2.020(3) 2.6838(12) 2.2754(11) 2.2176(11) 82.25(10) 81.92(10) 100.13(7) 94.01(8) 89.12(8) 106.97(8) 104.49(8) 113.34(5)

Zn1–N2 Zn1–Cl1 Zn2–N4#2 Zn2–Cl3 N1–Zn1–N3 N1–Zn1–Cl1 N3–Zn1–Cl1 N2–Zn1–Cl2 Cl1–Zn1–Cl2 N4–Zn2–Cl3#2 Cl2–Zn2–Cl3 Cl3–Zn2–Cl4

122.66(14) 113.88(10) 123.05(10) 166.26(8) 93.48(3) 105.69(8) 107.22(4) 118.29(5)

4 Cu1–N1 Cu1–N3 Cu1–Cl1 N1–Cu1–N2 N1–Cu1–N4 N2–Cu1–N4 N1–Cu1–Cl1 N3–Cu1–Cl1

2.004(2) 2.002(2) 2.4776(9) 84.34(8) 96.10(8) #3 167.63(8) #3 99.77(7) 105.79(7)

Cu1–N2 Cu1–N4

2.1139(19) 2.075(2) #3

N1–Cu1–N3 N2–Cu1–N3 N3–Cu1–N4 N2–Cu1–Cl1 N4–Cu1–Cl1

153.48(9) 83.65(8) 90.77(8) #3 101.83(6) 90.30(6) #3

5 Cd1–N1 Cd1–N3 Cd1–O1 Cd2–N5 Cd2–N7 Cd2–O2 N1–Cd1–N2 N1–Cd1–N4#4 N2–Cd1–O1 N4–Cd1–O1#4 N2–Cd1–N4#4 N1–Cd1–Cl1 N3–Cd1–Cl1 O1–Cd1–Cl1 N5–Cd2–N7 N5–Cd2–O2 N7–Cd2–O2 N6–Cd2–N7 N7–Cd2–N8#5 N6–Cd2–Cl2 N8–Cd2–Cl2#5

2.341(5) 2.320(8) 2.492(4) 2.351(8) 2.337(5) 2.478(4) 75.93(16) 104.65(17) 91.95(15) 88.29(15) 164.83(19) 92.54(17) 165.5(2) 84.38(14) 99.2(3) 82.6(3) 166.03(15) 75.36(16) 105.82(16) 99.72(14) 96.63(15)

Cd1–N2 Cd1–N4#4 Cd1–Cl1 Cd2–N6 Cd2–N8#5 Cd2–Cl2 N1–Cd1–N3 N1–Cd1–O1 N3–Cd1–O1 N2–Cd1–N3 N3–Cd1–N4#4 N2–Cd1–Cl1 N4–Cd1–Cl1#4 N5–Cd2–N6 N5–Cd2–N8#5 N6–Cd2–O2 N8–Cd2–O2#5 N6–Cd2–N8#5 N5–Cd2–Cl2 N7–Cd2–Cl2 O2–Cd2–Cl2

2.442(5) 2.344(4) 2.521(3) 2.471(5) 2.348(4) 2.518(3) 98.7(3) 166.98(16) 82.7(3) 76.0(2) 89.0(2) 98.15(14) 96.97(15) 75.2(2) 88.5(2) 91.86(15) 88.04(15) 163.6(2) 165.3(2) 92.66(17) 83.82(16)

N1–Zn1–N3 N2–Zn1–N3 N3–Zn1–N4#1 N2–Zn1–Cl1 N4–Zn1–Cl1#1

2.516(4) 2.363(5) 2.326(5) 2.222(3) 116.60(18) 76.23(17) 130.82(14) 118.3(2) 74.72(17) 119.61(18) 2.328(3) 2.241(3) 120.72(14) 80.93(12) 95.91(12) 97.85(9) 94.29(9) 2.304(3) 2.2256(10) 2.063(3) 2.2772(10)

Symmetry transformation used to generate equivalent atoms: #1 x, 1/2  y, 1/2 + z; #2 1/2  x, 2  y, 1/2 + z; #3 x, 3/2  y, 1/2 + z; #4 1/2 + x, 1  y, z; #5 1/2 + x, 2 – y, z.

L3 ligand, with a distorted tetrahedral coordination geometry. All the bond distances and bond angles around the Ag(I) atoms are in the normal ranges, from 2.222(3) to 2.516(4) Å and 74.72(17)°

Fig. 1. (a) The coordination environment of the Ag(I) atoms in 1 with the ellipsoids drawn at 30% probability; the hydrogen atoms are omitted for clarity. (b) The topological representation of the dinuclear structure of 1. (c) The 3D structure of 1.

to 146.86(16)° [2d,2e]. Selected bond distances and angles are summarized in Table 2. In addition, two L3 ligands and two Ag(I) atoms are bridged by pyridine nitrogen atoms to form a dinuclear 12-membered macrocyclic ring unit (Fig. 1a and b). The dinuclear units are further linked by rich hydrogen bonds, like N3– H3A  O8, N4–H4A  O1, N4–H4D  O7 with N  O distances of 3.255(9), 3.096(9) and 3.198(15) Å, and N1–H1D  N7 with an N  N distance of 3.391(7) Å to form the 3D structure (Fig. 1c, Table S1). The perchlorate anions are located among the dinuclear macrocyclic units, acting as counteranions to balance the electronic neutrality of the crystal, as well as providing O atoms for the hydrogen bonds.

3.1.2. [Zn(L3)(Cl)](ClO4)H2O (2) When a solution of L33HCl and Zn(ClO4)26H2O was adjusted to pH ca. 9, coordination compound 2 was formed, which crystallizes in the monoclinic space group P21/c. The Zn(II) atom is coordinated by three nitrogen atoms from one L3 ligand, one pyridine N4 atom from another L3 ligand and one chloride anion, with a distorted trigonal bipyramid coordination geometry, as indicated by an index s

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Fig. 2. (a) The coordination environment of the Zn(II) atom in 2 with the ellipsoids drawn at 30% probability; the hydrogen atoms are omitted for clarity. (b) Infinite 1D zigzag chain of 2. (c) The topological representation of the 1D zig-zag chain of 2. (d) The 3D structure of 2.

value of 0.78, as defined by Addison et al.: s = 0 for an ideal square pyramid and s = 1 for a perfect trigonal bipyramid [9] (Fig. 2a). The average Zn–N separation is 2.167(4) Å and the Zn–Cl bond distance is 2.274(2) Å. Adjacent Zn(II) atoms are joined by pyridine N4 atoms of L3 ligands to form a 1D zig-zag chain (Fig. 2b and c). The 3D structure of 2 is formed with the support of N1–H1A   O3 (3.080(6) Å), N3–H3D  O2 (3.263(7) Å) and N3–H3  Cl1

(3.325(5) Å) hydrogen bonds, and water molecules are fixed on the 1D chains by N1–H1D  O1 W hydrogen bonds with a distance of 3.095(7) Å (Table S1). It should be noted that although the 1D chain structure of coordination compound 2 is similar to our lately reported Cu(II) coordination compound 20 [7a], the fifth coordination site of the Zn(II) atom in 2 is a chloride anion rather than an H2O molecule, as in

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Fig. 3. (a) The coordination environment of the Zn(II) atoms in 3 with the ellipsoids drawn at 30% probability; the hydrogen atoms are omitted for clarity. (b) Infinite uncommon 1D chain of 3. (c) The topological representation of the 1D ladder of 3. (d) The 3D structure of 3.

20 , and also the space group is different, monoclinic P21/c in 2 and orthorhombic Pna21 in 20 , which indicates that the metal ions have a great influence on the formation of coordination compounds.

3.1.3. [Zn2(L3)(Cl)4] (3) From the above results, it was found that the perchlorate anions remain uncoordinated and act as counteranions to keep the charge

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Fig. 4. (a) The coordination environment of the Cu(II) atom in 4 with the ellipsoids drawn at 30% probability; the hydrogen atoms are omitted for clarity. (b) Infinite 1D zigzag chain of 4. (c) The topological representation of the 1D zig-zag chain of 4.

neutrality of the coordination compounds. To investigate the influence of the anions on the structure, ZnCl2 was selected instead of Zn(ClO4)26H2O, and a new compound 3 was obtained. As shown in Fig. 3a, there are two different Zn(II) atoms; the Zn1 atom is five-coordinated by three amino nitrogen atoms from the L3 ligand and two chloride anions with a distorted trigonal bipyramidal coordination geometry, as indicated by an index s value of 0.73 [9], while Zn2 is four-coordinated by one pyridine N4 atom from the L3 ligand and three chloride anions, with a distorted tetrahedral coordination geometry. The Zn(II) atoms are bridged by Cl2 atoms and also pyridine N4 atoms of L3 ligands to form an uncommon 1D chain structure (Fig. 3b and c). Further, 1D chains are packed with the help of N1–H1A  Cl1 (3.304(3) Å), N1–H1D  Cl3 (3.508(3) Å), and N3–H3A  Cl1 (3.286(3) Å) hydrogen bonds to form a 3D structure (Fig. 3d). 3.1.4. [Cu(L3)(Cl)](Cl)2H2O (4) To further investigate the influence of metal ions on the formation of coordination compounds, CuCl22H2O was used instead of ZnCl2 in coordination compound 3, and the blue coordination compound 4 was isolated. Structure analysis revealed that it forms a similar 1D chain like 2 and 20 , rather than 3, and the fifth coordination site of the Cu(II) atom is one chloride anion, like that of 2 but not 20 (Fig. 4a–c). However, the coordination environment around the Cu(II) atom is a distorted square pyramidal geometry with a s value of 0.24 [9], which is similar to 20 but different from 2. Meanwhile,

the counteranions and crystalline water amounts of coordination compounds 2, 20 and 4 are different from each other [7a]. The crystalline water molecules and uncoordinated chloride anions are located on the 1D chains by fN3–H3A  O1W (2.989(4) Å), C3– H3C  O2W (3.457(4) Å) and N1–H1A  Cl2 (3.386(2) Å) hydrogen bonds. The above results further indicate that the metal ions and anions have a great influence on the assembly of coordination compounds. 3.1.5. [Cd(L3)(Cl)(H2O)](ClO4)H2O (5) When Cd(ClO4)26H2O was introduced into the reaction system instead of Zn(ClO4)26H2O as for coordination compound 2, the new colorless coordination compound 5 was obtained. As shown in Fig. 5a, there are two similar Cd(II) centers, and each Cd(II) atom exhibits a distorted octahedral arrangement and is six-coordinated by three amino nitrogen atoms from one L3 ligand, one chloride anion, one water molecule and one pyridine nitrogen atom from another L3 ligand. Similarly, the adjacent Cd(II) atoms are bridged by pyridine nitrogens to form 1D zig-zag chains (Fig. 5b and c). In addition, the 1D chains are packed sequentially with abundant N3–H3A  O8 (3.071(9) Å), N3–H3D  O5 (3.213(12) Å), N5–H5D  O7 (3.222(13) Å) and N7–H7C  Cl1 (3.295(6) Å) hydrogen bonds to form a 3D structure (Fig. 5d). The uncoordinated perchlorate anions and water molecules, which serve as oxygen donors in hydrogen bonds, are located in the vacancy of the frameworks.

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Fig. 5. (a) The coordination environment of the Cd(II) atoms in 5 with the ellipsoids drawn at 30% probability; the hydrogen atoms are omitted for clarity. (b) Infinite 1D zigzag chains of 5. (c) The topological representation of the 1D zig-zag chains of 5. (d) The 3D structure of 5.

3.2. PXRD characterization

3.3. Photoluminescent properties

To investigate whether the crystal structures are representative of the bulk samples, powder X-ray diffraction (PXRD) experiments were performed for crystalline samples 1–5. All the diffraction peaks in both the experimental and simulated patterns of the corresponding coordination compounds are consistent with each other (Fig. S1), indicating that the measured single crystals and the bulk compounds are the same.

Metal-organic coordination compounds with a d10 closed-shell electronic configuration were found to show excellent photoluminescent properties, and have been used as fluorescence-emitting materials [10]. Consequently, the photoluminescent properties of the ligand L33HCl and coordination compounds 1–3 and 5 were studied with emission and excitation pass widths of 2.5 nm in the solid state at room temperature. As shown in Fig. 6, L33HCl

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(2011SQRL141, 2013SQRL088ZD), and the Project of Huangshan University (2013xkjq008).

Relative Intensity (a.u.)

2

Appendix A. Supplementary data

4000

5

2000

CCDC 1027687–1027691 contain the supplementary crystallographic data for coordination compounds 1–5. 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) 1223336-033; 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.2014.11.037.

3

L3·3HCl 1

0 200

250

300

350

400

References 450

500

Wavelength (nm) Fig. 6. The emission and excitation spectra of the ligand and related coordination compounds.

exhibits a weak emission maxima at about 390 nm on excitation at 240 nm. Coordination compound 1 shows similar but much weaker emission maxima at about 395 nm on excitation at 240 nm. Therefore, we can presume that the luminescence of Ag(I) compound 1 may mainly originate from the intraligand p– p⁄ or n–p⁄ fluorescence [10]. In addition, Zn(II) compounds 2 and 3 have similar stronger and significantly red shifted emission bands compared to the ligand and 1 (426 nm with kex = 264 nm for 2, 423 nm with kex = 270 nm for 3), and Cd(II) compound 5 exhibits a stronger emission maxima at about 392 nm when excited at 274 nm. The luminescence of the Zn(II) and Cd(II) compounds 2, 3 and 5 should probably be assigned to ligand-to-metal charge transfer (LMCT) and intraligand p–p⁄ or n–p⁄ fluorescence [10]. The difference of the intensity and band shift may result from different metal centers and conformations of the ligands, as well as weak interactions in the crystalline lattice, which may affect the rigidity of the ligand edifice and the energy transfer involved in the luminescence [10]. 4. Conclusions In summary, five new coordination compounds with a pyridinecontaining tripodal ligand were prepared. It was found that the ligand is versatile to assembly compounds from mononuclear (10 ), dinuclear (1) and various 1D zig-zag chains (20 , 2, 4, and 5) to a 1D uncommon chain structure (3) (Scheme 1). The results showed that the metal ions and anions have a distinct impact on the structures of the coordination compounds. Further studies indicated that coordination compounds 3, 5 and especially 2 might be good candidates as fluorescence-emitting materials. Acknowledgements This work was financially supported by Science Foundation for Excellent Youth Scholars of Higher Education of Anhui Province

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