Coordination Networks from Zero-Dimensional Metallomacrocycle

DOI: 10.1021/cg100093n

Coordination Networks from Zero-Dimensional Metallomacrocycle, One-Dimensional Chain to Two-Dimensional Sheet Based on a Ditopic Diiminopyridine Ligand and Group 12 Metals

2010, Vol. 10 2331–2341

Jin Yang,† Biao Wu,*,†,‡ Fuyu Zhuge,‡ Jianjun Liang,‡ Chuandong Jia,‡ Yao-Yu Wang,§ Ning Tang,*,† Xiao-Juan Yang,*,†,‡ and Qi-Zhen Shi§ †

State Key Laboratory of Applied Organic Chemistry, College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, China, ‡State Key Laboratory for Oxo Synthesis & Selective Oxidation, Lanzhou Institute of Chemical Physics, CAS, Lanzhou 730000, China, and § College of Chemistry and Materials Science, Northwest University, Xi’an 710069, China Received January 21, 2010; Revised Manuscript Received April 12, 2010

ABSTRACT: The reaction of a ditopic diiminopyridine ligand 2,6-bis(1-(2,6-diisopropyl-4-(pyridin-3-yl)phenylimino)ethyl)pyridine (L) with group 12 metal salts in various solvent systems afforded 12 metal-organic coordination complexes, including zero-dimensional (0D) metallomacrocycle, one-dimensional (1D) chain, and two-dimensional (2D) network structures: [Zn4Cl8L2] 3 2C7H8 3 2CH3COCH3 3 3H2O (1a), {[Zn2Cl4L] 3 2CH3OH 3 2CHCl3 3 2H2O}n (1b), {[ZnCl2L] 3 0.5CH2Cl2 3 0.5H2O}n (1c), {[ZnBr2L] 3 CH2Cl2}n (2), [ZnI2L]n (3), {[Zn(NO3)2L2 3 2C7H8]}n (4), {[CdCl2L2] 3 2CH2Cl2}n (5), {[Cd(NO3)2L2] 3 CH2Cl2}n (6), {[Cd(ClO4)2L2] 3 CH2Cl2}n (7), {[Hg4(μ2-L2)(μ2-Cl2)(μ-HgCl2)Cl6] 3 2H2O}n (8), {[HgBr2L] 3 CH3CN 3 0.5CH2Cl2}n (9), and {[HgI2L] 3 0.5CH2Cl2}n (10). In these complexes, the semirigid ligand L exhibits four kinds of coordination modes [(syn, syn, syn), (syn, syn, anti), (anti, anti, syn), (anti, anti, anti)], leading to the formation of various supramolecular structures. Complex 1a is a tetranuclear metallomacrocycle. 1b contains 1D zigzag chains propagating along two different directions, which further pack into a noninterpenetrated three-dimensional (3D) framework by hydrogen-bonding interactions. Complexes 1c, 2, 3, 9, and 10 exhibit a 1D helical chain structure, while 4, 5, 6, and 7 are 1D looped-chain coordination polymers. Complex 8 displays an unprecedented pentanuclear Hg(II)-based 2D network with both HgCl2 and Hg2Cl2 bridges. It is noteworthy that 1a and 1b are supramolecular isomers formed in different solvent systems. The effects of the solvent, metal center, and anion on the different conformations adopted by the ligand and the structure of the products have been discussed. Additionally, the luminescent properties of the complexes have been investigated in the solid state, which display increased ligand-based fluorescence emission at room temperature.

Introduction Metal-organic frameworks (MOFs) from self-assembly of metal ions and multifunctional ligands have developed rapidly in recent years because of their fascinating structural topologies and potential applications as functional materials in the fields of catalysis, gas absorption, chirality, magnetism, nonlinear optics, and luminescence.1,2 In order to obtain MOFs with desirable structures and properties, many attempts have been made using different strategies.3 It is well-known that the supramolecular structures of MOFs are dependent on a number of parameters such as the nature of the metal-ligand bonds, coordination geometries of the metal centers, the ligating topologies of the ligands used, the metal-ligand ratio, the counterions and the experimental conditions such as solvent, temperature, and crystallization method. However, the key to successful design of intriguing MOFs should be the proper choice of metal center with preferred coordination geometries and intelligent ligand design.4 The group 12 metal ions Zn2þ, Cd2þ, and Hg2þ, because of their flexible coordination environment, can form complexes with variable geometries from tetrahedral, trigonal bipyramidal, or square pyramidal to octahedral and often lead to severe distortion from the ideal polyhedron, thus resulting in rich varieties in the construction of coordination polymers and networks.5 On the other hand, in the past decades, numerous multidentate ligands with an “arm-spacer-arm” type *Corresponding authors. E-mail: [email protected] (B.W.); tangn@ lzu.edu.cn (N.T.); [email protected] (X.-J.Y.). r 2010 American Chemical Society

structural feature have been used to construct a variety of zerodimensional (0D) to three-dimensional (3D) supramolecular assemblies, because their flexibility affords great opportunities for the formation of novel topologies and, potentially, for modulation and functionalization of the assembled structures.6,7 It should also be noted that the solvent system used in the assembly process can significantly influence the structures of the coordination polymers, especially when the conformation of the ligand is sensitive to the solution environment.8 The diiminopyridine ligands are known for their applications in catalysis.9 Because of the possibility of attaching functional groups on different positions of diiminopyridines, such ligands can be readily modified with suitable functionalities and geometries for the purpose of constructing various metal coordination complexes. We have recently designed a new terminal pyridine-functionalized diiminopyridine ligand, 2,6-bis(1-(2,6-diisopropyl-4-(pyridin-3-yl)-phenylimino)ethyl)-pyridine (L), which was found to form different structures with cobalt(II) salts.10 Herein we report a series of metal-organic coordination architectures assembled by the ligand L and a range of group 12 zinc(II), cadmium(II), mercury(II) salts. The complexes include a 0D metallomacrocycle [Zn4Cl8L2] 3 2C7H8 3 2CH3COCH3 3 3H2O (1a), one-dimensional (1D) zigzag chain {[Zn2Cl4L] 3 2CH3OH 3 2CHCl3 3 2H2O}n (1b), 1D helical chains, {[ZnCl2L] 3 0.5CH2Cl2 3 0.5H2O}n (1c), {[ZnBr2L] 3 CH2Cl2}n (2), [ZnI2L]n (3), {[HgBr2L] 3 CH3CN 3 0.5CH2Cl2}n (9), and {[HgI2L] 3 0.5CH2Cl2}n (10), 1D looped chains, {[Zn(NO3)2L2 3 2C7H8]}n (4), {[CdCl2L2] 3 2CH2Cl2}n (5), {[Cd(NO3)2L2] 3 CH2Cl2}n (6), {[Cd(ClO4)2L2] 3 CH2Cl2}n (7), and a 2D network Published on Web 04/20/2010

pubs.acs.org/crystal

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Crystal Growth & Design, Vol. 10, No. 5, 2010

Scheme 1. Observed Coordination Modes of Ligand L in Complexes 1-10a

a The first and second assignments, syn or anti, are the orientation of the diiminopyridyl moiety, while the third one represents the relative orientation of the two terminal pyridyl rings.

{[Hg4(μ2-L2)(μ2-Cl2)(μ-HgCl2)Cl6] 3 2H2O}n (8). In these compounds, the ligand L exhibits four conformations as illustrated in Scheme 1. This study aims to understand how the resulting coordination networks can be manipulated by varying the conformation of the ligand, coordination geometry of the metal, and structure of the anion and by utilizing various solvent systems. Experimental Section General Procedures. All the starting chemicals were of analytical reagent grade and were used as received. 2,6-Diisopropyl-4-bromoaniline11a and 3-pyridylboroxin11b,c were prepared by literature methods. 2,6-Diisopropyl-4-(3-pyridyl)aniline was prepared by using the Suzuki coupling as described before.12 The ligand L was prepared by a condensation reaction according to literature methods for related compounds.10,13 Elemental analyses were performed on an Elementar VarioEL instrument. IR spectra were recorded on a Bruker IFS 120HR spectrometer as KBr disks. Powder X-ray diffraction (PXRD) data were collected on a Philips X’Pert PRO SUPER diffractometer with Cu KR radiation (λ = 1.54187 A˚). Fluorescent emission spectra for the solid samples were recorded on a HITACHI F-7000 luminescence spectrometer at room temperature. Synthesis of 2,6-Bis(1-(2,6-diisopropyl-4-(pyridin-3-yl)phenylimino)ethyl)pyridine (L). A solution of 2,6-diacetylpyridine (0.33 g, 2.0 mmol), 2,6-diisopropyl-4-(3-pyridyl)aniline (1.02 g, 4.0 mmol), and p-toluenesulfonic acid (0.02 g) in toluene (20 mL) was refluxed for 3 days with azeotropic removal of water using a Dean-Stark trap. The reaction mixture was then cooled to room temperature, and the solvent was removed in vacuo. The crude product was purified by column chromatography on silica gel with petroleum ether/ethyl acetate. L was obtained as a yellow powder in an 80% yield. m.p.: 308-309 °C. Anal. Calc for C43H49N5: C, 81.22; H, 7.77; N, 11.01%. Found: C, 81.01; H, 7.56; N, 11.21%. ESI-MS: m/z 319.0 ([M þ 2H]2þ), 636.9 ([M þ H]þ). IR (KBr, cm-1): 2961, 2928, 2868, 1642 (νCdN), 1571, 1456, 1431,1365, 1183, 1116, 1076, 1020, 881, 824, 800. 1H NMR (400 MHz, CDCl3, δ ppm): 1.23 (t, 24H, J=5.2 Hz,

Yang et al. CHMe2), 2.35 (s, 6H, NdCMe), 2.84 (m, 4H, J = 5.2 Hz, CHMe2), 7.36-7.38 (m, 2H, Py-H5), 7.40 (s, 4H, Ar-H), 7.94 (dt, 2H, J=2.0, 3.6 Hz, Py-H4), 7.98 (t, 1H, J=8.0 Hz, Py-H40 ), 8.53 (d, 2H, J=8.0 Hz, Py-H30 ), 8.58 (dd, 2H, J=1.6, 3.2 Hz, Py-H6), 8.91 (d, 2H, J=1.6 Hz, Py-H2). 13C NMR (100.6 MHz, CDCl3, δ ppm): 17.31, 22.84, 23.22, 28.50, 122.02, 122.40, 123.39, 133.04, 134.01, 136.67, 136.97, 137.34, 146.70, 147.85, 148.27, 155.05, 167.18. Synthesis of [Zn4Cl8L2] 3 2C7H8 3 2CH3COCH3 3 3H2O (1a). A solution of the ligand L (31.8 mg, 0.05 mmol) in CH2Cl2 (2 mL, bottom), a buffer layer of acetone/toluene/CH2Cl2 (v/v/v 1:1:1, 6 mL, middle), and a solution of ZnCl2 (6.8 mg, 0.05 mmol) in acetone (2 mL, top) were in turn placed carefully into a glass tube. Yellow crystals of the product were obtained after the mixture was allowed to stand for approximately two weeks at room temperature. Yield: 34.8 mg, 70%. Anal. Calc for Zn4Cl8L2 3 7H2O: C, 53.16; H, 5.81; N, 7.21%. Found: C, 53.02; H, 5.68; N, 7.05%. IR (KBr, cm-1): 2963, 2927, 2868, 1636 (νCdN), 1592, 1465, 1439, 1370, 1298, 1257, 1205, 1193, 1107, 816, 714. Synthesis of catena-{[Zn2Cl4L] 3 2CH3OH 3 2CHCl3 3 2H2O}n (1b). In a similar manner, a solution of the ligand L (31.8 mg, 0.05 mmol) in CHCl3 (2 mL), a buffer layer of CH3OH/toluene/CHCl3 (v/v/v 1:1:1, 6 mL), and a solution of ZnCl2 (27.2 mg, 0.20 mmol) in CH3OH (2 mL) were in turn placed carefully into a glass tube. The mixture was allowed to diffuse at room temperature and yellow crystals of 1b were obtained after two weeks. Yield: 38.1 mg, 84%. Anal. Calc for Zn2Cl4L 3 CHCl3 3 CH3OH: C, 50.99; H, 5.14; N, 6.61%. Found: C, 51.24; H, 5.42; N, 6.59%. IR (KBr, cm-1): 2963, 2928, 2868, 1638 (νCdN), 1592, 1463, 1438, 1368, 1256, 1190, 1107, 1069, 814. Synthesis of catena-{[ZnCl2L] 3 0.5CH2Cl2 3 0.5H2O}n (1c). In a similar manner, a solution of the ligand L (31.8 mg, 0.05 mmol) in CH2Cl2 (2 mL), a buffer layer of CH3CN/toluene/CH2Cl2 (v/v/v 1:1:1, 6 mL), and a solution of ZnCl2 (6.8 mg, 0.05 mmol) in CH3CN (2 mL) were in turn placed carefully into a glass tube. Yellow crystals were obtained after 10 days. Yield: 21.2 mg, 55%. Anal. Calc for ZnCl2L: C, 66.88; H, 6.40; N, 9.07%. Found: C, 66.58; H, 6.38; N, 9.03%. IR (KBr, cm-1): 2960, 2867, 1635 (νCdN), 1603, 1573, 1457, 1441, 1364, 1297, 1257, 1185, 1114, 801, 700. Synthesis of catena-{[ZnBr2L] 3 CH2Cl2}n (2). The synthesis of 2 was similar to that of 1c, except that ZnBr2 (22.5 mg, 0.10 mmol) was used instead of ZnCl2. Yield: 32.2 mg, 75%. Anal. Calc for ZnBr2L 3 0.5CH2Cl2: C, 57.82; H, 5.58; N, 7.75%. Found: C, 58.03; H, 5.67; N, 7.84%. IR (KBr, cm-1): 2960, 2928, 2868, 1645 (νCdN), 1601, 1578, 1460, 1439, 1365, 1255, 1187, 1111, 1068, 802, 700. Synthesis of catena-[ZnI2L]n (3). The synthesis of 3 was similar to that of 1c, except that ZnI2 (31.9 mg, 0.10 mmol) was used instead of ZnCl2. Yield: 37.2 mg, 78%. Anal. Calc for ZnI2L: C, 54.08; H, 5.17; N, 7.33%. Found: C, 54.37; H, 4.92; N, 7.19%. IR (KBr, cm-1): 2959, 2928, 2867, 1643 (νCdN), 1603, 1573, 1457, 1438, 1364, 1297, 1186, 1116, 1069, 802, 700. Synthesis of catena-{[Zn(NO3)2L2 3 2C7H8]}n (4). The synthesis of 4 was similar to that of 1c, except that Zn(NO3)2 3 6H2O (29.8 mg, 0.20 mmol) was used instead of ZnCl2. Yield: 23.6 mg, 60%. Anal. Calc for Zn(NO3)2L2: C, 70.69; H, 6.76; N, 11.50%. Found: C, 70.33; H, 6.68; N, 11.31%. IR (KBr, cm-1): 2960, 1644 (νCdN), 1603, 1575, 1458, 1438, 1366, 1298, 1252, 1186, 1118, 1035, 882, 806, 710. Synthesis of catena-{[CdCl2L2] 3 2CH2Cl2}n (5). A solution of the ligand L (31.8 mg, 0.05 mmol) in CH2Cl2 (2 mL), a buffer layer of CH3OH/toluene/CH2Cl2 (v/v/v 1:1:1, 6 mL), and a solution of CdCl2 3 2.5H2O (22.8 mg, 0.10 mmol) in CH3OH (2 mL) were in turn placed carefully into a glass tube. Yellow crystals were obtained after diffusion of the solutions for 10 days at room temperature. Yield: 20.7 mg, 55%. Anal. Calc for CdCl2L2 3 1.5CH2Cl2: C, 70.12; H, 6.84; N, 9.51%. Found: C, 70.23; H, 6.65; N, 9.24%. IR (KBr, cm-1): 2959, 2930, 2868, 1645 (νCdN), 1604, 1573, 1456, 1434, 1365, 1288, 1253, 1186, 1118, 1040, 882, 806, 710. Synthesis of catena-{[Cd(NO3)2L2] 3 CH2Cl2}n (6). In a manner similar to that for 1c, a solution of the ligand L (31.8 mg, 0.05 mmol) in CH2Cl2 (2 mL), a buffer layer of CH3CN/toluene/CH2Cl2 (v/v/v 1:1:1, 6 mL), and a solution of Cd(NO3)2 3 4H2O (30.9 mg, 0.10 mmol) in CH3CN (2 mL) were in turn placed in a glass tube carefully. Yellow crystals of 6 were obtained after 10 days. Yield: 23.7 mg, 60%. Anal. Calc for Cd(NO3)2L2 3 2H2O: C, 66.89; H, 6.66; N,

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Table 1. Crystallographic Data for Compounds 1-10 formula fw crystal system space group a/A˚ b/A˚ c/A˚ R/deg β/deg γ/deg V/A˚3 Z Dcalc/g cm-3 F(000) μ/mm-1 GOF R1; wR2 [I > 2σ(I )] R1; wR2 (all data) formula fw crystal system space group a/A˚ b/A˚ c/A˚ R/deg β/deg γ/deg V/A˚3 Z Dcalc/g cm-3 F(000) μ/mm-1 GOF R1; wR2 [I > 2σ(I )] R1; wR2 (all data)

1a

1b

1c

2

3

4

C106H132Cl8N10O5Zn4 2171.30 triclinic h P1 13.825(4) 14.017(4) 16.710(5) 68.684(3) 74.647(4) 74.865(4) 2859.4(14) 1 1.261 1134 1.067 1.021 0.0527, 0.1500 0.0813, 0.1704

C47H63Cl10N5O4Zn2 1247.26 orthorhombic Pna2(1) 15.003(3) 31.085(6) 13.095(3) 90.00 90.00 90.00 6107(2) 4 1.356 2568 1.265 0.995 0.0617, 0.1517 0.1121, 0.1805

C87H102Cl6N10OZn2 1647.23 triclinic P1 8.753(11) 16.52(2) 16.82(2) 103.068(15) 94.392(17) 98.362(16) 2329(5) 1 1.175 864 0.733 0.985 0.0789, 0.2046 0.1504, 0.2440

C44H51Br2Cl2N5Zn 945.99 triclinic P1 8.8613(8) 16.8356(15) 17.2240(16) 104.2870(10) 93.0740(10) 99.4770(10) 2444.1(4) 2 1.285 968 2.279 0.943 0.0623, 0.1474 0.1490, 0.1882

C43H49I2N5Zn 955.04 triclinic P1 8.799(2) 17.294(4) 17.334(4) 106.025(3) 92.531(3) 99.213(3) 2491.6(10) 2 1.273 956 1.761 1.007 0.0621, 0.1772 0.1425, 0.2231

C100H114N12O6Zn 1645.40 triclinic P1 9.3232(19) 13.392(3) 19.236(4) 99.65(3) 93.16(3) 99.26(3) 2328.6(9) 1 1.173 876 0.323 1.044 0.0687, 0.1732 0.1204, 0.2087

5

6

7

8

9

10

C88H102CdCl6N10 1624.90 triclinic P1 9.162(3) 13.885(4) 19.359(5) 79.078(4) 88.870(4) 80.669(4) 2386.0(12) 1 1.131 850 0.441 1.051 0.0723, 0.1933 0.1132, 0.2216

C87H100CdCl2N12O6 1593.09 triclinic P1 9.1844(18) 13.608(3) 19.550(4) 99.927(3) 92.104(3) 98.862(3) 2373.0(9) 1 1.115 836 0.338 1.114 0.0615, 0.1768 0.0808, 0.1922

C87H100CdCl4N10O8 1667.97 triclinic P1 9.623(2) 13.519(3) 19.238(4) 98.790(3) 92.299(3) 99.514(3) 2433.8(9) 1 1.138 872 0.387 1.005 0.0704, 0.1826 0.1069, 0.2096

C86H102Cl10Hg5N10O2 2665.23 orthorhombic Cmcm 23.076(6) 21.216(6) 23.340(7) 90.00 90.00 90.00 11427(6) 4 1.549 5096 6.969 1.035 0.0555, 0.1519 0.1064, 0.1852

C91H106Br4Cl2Hg2N12 2159.60 triclinic P1 9.253(13) 15.35(2) 20.68(4) 107.41(3) 91.73(3) 105.227(19) 2684(8) 1 1.336 1070 4.437 0.921 0.0594, 0.1338 0.1406, 0.1622

C87H100Cl2Hg2I4N10 2265.45 triclinic P1 8.671(6) 17.105(11) 17.134(11) 106.475(10) 100.111(10) 91.359(11) 2392(3) 1 1.573 1098 4.596 1.034 0.0515, 0.1368 0.0606, 0.1426

10.88%. Found: C, 66.67; H, 6.61; N, 10.60%. IR (KBr, cm-1): 2964, 2928, 2869, 1642 (νCdN), 1575, 1463, 1436, 1367, 1288, 1201, 1183, 1109, 1022, 883, 814, 708. Synthesis of catena-{[Cd(ClO4)2L2] 3 CH2Cl2}n (7). The synthesis of 7 was similar to that of 6, except that Cd(ClO4)2 3 6H2O (41.9 mg, 0.10 mmol) was used instead of Cd(NO3)2 3 4H2O. Yield: 23.7 mg, 60%. Anal. Calc for Cd(ClO4)2L2 3 2H2O: C, 63.80; H, 6.35; N, 8.65%. Found: C, 63.58; H, 6.37; N, 8.43%. IR (KBr, cm-1): 2960, 2927, 2870, 1740, 1644 (νCdN), 1603, 1574, 1459, 1436, 1365, 1298, 1250, 1138, 1028, 930, 805, 708. Synthesis of catena-{[Hg4(μ2-L2)(μ2-Cl2)(μ-HgCl2)Cl6] 3 2H2O}n (8). The synthesis of 8 was similar to that of 1c: a solution of the ligand L (31.8 mg, 0.05 mmol) in CH2Cl2 (2 mL), a buffer layer of CH3CN/toluene/CH2Cl2 (v/v/v 1:1:1, 6 mL), and a solution of HgCl2 (27.2 mg, 0.20 mmol) in CH3CN (2 mL) were in turn placed in a glass tube carefully. Diffusion of the reactants at room temperature for a week gave yellow crystals of the product 8. Yield: 43.3 mg, 75%. Anal. Calc for Hg5Cl10L2 3 2H2O: C, 38.75; H, 3.86; N, 5.26%. Found: C, 38.65; H, 3.64; N, 5.12%. IR (KBr, cm-1): 2960, 2924, 2865, 1635 (νCdN), 1604, 1590, 1459, 1439, 1400, 1364, 1305, 1249, 1228, 1202, 1189, 1105, 1069, 881, 812, 700. Synthesis of catena-{[HgBr2L] 3 CH3CN 3 0.5CH2Cl2}n (9). The synthesis of 9 was similar to that of 8, except that HgBr2 (36.1 mg, 0.10 mmol) was used instead of HgCl2. Yield: 49.8 mg, 50%. Anal. Calc for HgBr2L 3 CH2Cl2: C, 48.88; H, 4.75; N, 6.48%. Found: C, 48.75; H, 4.55; N, 6.72%. IR (KBr, cm-1): 2962, 2927, 2867, 1644 (νCdN), 1574, 1460, 1437, 1366, 1296, 1250, 1188, 1105, 1033, 881, 806, 704. Synthesis of catena-{[HgI2L] 3 0.5CH2Cl2}n (10). The synthesis of 10 was similar to that of 8, except that HgI2 (45.5 mg, 0.10 mmol) was used instead of HgCl2. Yield: 27.3 mg, 50%. Anal. Calc for HgI2L 3 2H2O: C, 45.85; H, 4.74; N, 6.22%. Found: C, 45.75; H, 4.37; N, 5.92%. IR (KBr, cm-1): 2958, 2927, 2866, 1644 (νCdN),

1601, 1573, 1456, 1435, 1364, 1296, 1250, 1184, 1119, 1104, 1033, 881, 803, 703. X-ray Crystallography. Diffraction data for 1-10 were collected at 293 K on a Bruker Apex II CCD area detector equipped with graphite-monochromated Mo KR radiation (λ = 0.71073 A˚). Empirical absorption corrections were applied using the SADABS program. The structures were solved by the direct method and refined by the full-matrix least-squares method on F2, with all non-hydrogen atoms refined with anisotropic thermal parameters. All hydrogen atoms attached to carbon atoms were placed in calculated positions and refined using the riding model. All calculations were carried out with the SHELXTL crystallographic software. Compound 1c crystallized in poor quality. The weak reflections cause a low observed/ unique reflection ratio, which results in low completeness of the data set (0.868), and gives insufficient strong reflections to support full refinement of all non-hydrogen atoms. No H atoms were added for the crystal water molecules due to the imposed crystallographic symmetry or disorder. A summary of the crystallographic data, data collection, and refinement parameters for compounds 1-10 are provided in Table 1, and the selected bond lengths are listed in Tables 2-5.

Results and Discussion Synthesis and Characterization of the Complexes. As shown in Scheme 1, the ligand L contains two terminal pyridyl arms and one diiminopyridine spacer. The joints between the terminal pyridyl ring and the neighboring phenyl ring and between the middle pyridyl ring and the imino bond are C-C bonds which allow the two arms and the spacer to rotate freely. This type of semirigidity endows the ligand with the flexibility to take

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Yang et al.

Table 2. Selected Bond Distances (A˚) and Angles (deg) for 1a and 1ba

Table 4. Selected Bond Distances (A˚) and Angles (deg) for 4-7a

Complex 1a

Complex 4

Zn(1)-N(2) 2.289(3) Zn(1)-N(4) 2.318(3) Zn(1)-Cl(2) 2.2353(14) Zn(2)-N(5A) 2.068(3) Zn(2)-Cl(4) 2.2050(17) Cl(2)-Zn(1)-Cl(1) 117.63(7) Cl(1)-Zn(1)-N(2) 96.73(9) N(5A)-Zn(2)-N(1) 103.63(13)

Zn(1)-N(3) Zn(1)-Cl(1) Zn(2)-N1 Zn(2)-Cl(3) N(3)-Zn(1)-Cl(1) N(4)-Zn(1)-N(2) Cl(3)-Zn(2)-Cl(4) N(1)-Zn(2)-Cl(3)

2.099(3) 2.1971(15) 2.051(3) 2.2081(14) 141.91(10) 140.10(12) 124.77(7) 107.25(11)

Zn(1)-N(1) Zn(1)-O(1) N(5A)-Zn(1)-N(1)

2.174(3) 2.181(3) 90.45(12)

Cd(1)-N(1) Cd(1)-Cl(1) N(1)-Cd(1)-N(5A)

2.389(5) 2.6043(15) 85.80(15)

a

2.374(5) 2.352(5) 2.229(2) 2.056(7) 2.208(3) 116.79(11) 101.23(15) 103.0(3)

Zn(1)-N(3) Zn(1)-Cl(2) Zn(2)-N(1) Zn(2)-Cl(3) N(3)-Zn(1)-Cl(1) N(4)-Zn(1)-N(2) Cl(3)-Zn(2)-Cl(4) N(1)-Zn(2)-Cl(3)

Cd(1)-N(1) Cd(1)-O(1) N(1)-Cd(1)-N(5A)

2.324(3) 2.323(4) 87.92(12)

Cd(1)-N(1) Cd(1)-O(1) N(1)-Cd(1)-N(5A)

2.322(4) 2.351(4) 90.40(15)

Complex 1c Zn(1)-N(5A) Zn(1)-Cl(2) N(5A)-Zn(1)-Cl(1) Cl(1)-Zn(1)-Cl(2)

2.058(6) 2.194(3) 111.10(17) 122.08(11)

Complex 2 Zn(1)-N(1) 2.066(6) Zn(1)-Br(1) 2.3259(11) N(5)-Zn(1)-N(1) 99.8(2) N(1)-Zn(1)-Br(2) 104.57(15)

Zn(1)-N(5) 2.062(5) Zn(1)-Br(2) 2.3558(12) N(5)-Zn(1)-Br(1) 108.86(15) Br(1)-Zn(1)-Br(2) 121.22(5)

Complex 3 Zn(1)-N(1) 2.071(5) Zn(1)-I(1) 2.5534(11) N(5A)-Zn(1)-N(1) 100.4(2) N(1)-Zn(1)-I(2) 111.15(14)

Zn(1)-N(5A) 2.052(6) Zn(1)-I(2) 2.5109(11) N(5A)-Zn(1)-I(1) 109.67(15) I(2)-Zn(1)-I(1) 121.82(4)

2.492(7) 2.560(3) 91.5(2) 96.58(19)

Hg(1)-N(5A) Hg(1)-Br(2) N(1)-Hg(1)-Br(2) Br(2)-Hg(1)-Br(1)

2.484(8) 2.530(4) 102.07(19) 147.71(8)

Complex 10 Hg(1)-N(1) 2.391(6) Hg(1)-I(1) 2.5977(14) N(5A)-Hg(1)-N(1) 88.4(2) N(5A)-Hg(1)-I(1) 105.80(17)

Hg(1)-N(5A) 2.375(6) Hg(1)-I(2) 2.5591(17) N(1)-Hg(1)-I(2) 108.92(14) I(2)-Hg(1)-I(1) 140.65(4)

a Symmetry codes: 1c, 3, 10: A 1 þ x, -1 þ y, -1 þ z; 9: A -1 þ x, 1 þ y, 1 þ z.

on different conformations, which may play a crucial role in shaping up the final supramolecular architecture. Therefore, reaction of this ligand with the same metal ion may result in different structures depending on the conformation adopted by the ligand. Indeed, three different complexes were obtained from the reaction of ZnCl2 with ligand L: a tetranuclear macrocycle (1a), a 1D zigzag chain (1b), and a 1D helical chain (1c). The resulting structures are closely tied to the reaction conditions employed, especially to the solvent system. The 0D tetranuclear complex 1a was isolated as a pure compound from an acetone-toluene-CH2Cl2 mixed-solvent system by using a ZnCl2:L ratio of 2:1. The 1D zigzag chain structure 1b was obtained by layer-separation diffusion in an MeOH-toluene-CHCl3

Cd(1)-N(5A) O(1)-Cd(1)-N(1) O(1)-Cd(1)-N(5A)

2.344(4) 89.30(15) 93.51(16)

Cd(1)-N(5A) O(1)-Cd(1)-N(1) O(1)-Cd(1)-N(5A)

2.321(4) 91.52(16) 92.38(17)

a Symmetry codes: 4: A 1 - x, 1 - y, -z; 5: A -x, 1 - y, 1 - z; 6: A 2 - x, 1 - y, 1 - z; 7: A 1 - x, -y, 2 - z.

Table 5. Selected Bond Distances (A˚) and Angles (deg) for 8a Hg(1)-N(3) Hg(1)-Cl(1) Hg(2)-Cl(2) Hg(3)-Cl(4) Hg(3)-N(1) Cl(1)-Hg(1)-Cl(2) N(3)-Hg(1)-Cl(1) Cl(2)-Hg(2)-Cl(3) Cl(3)-Hg(2)-Cl(3A) Cl(5)-Hg(3)-N(1) Cl(4)-Hg(3)-Cl(5B) a

Complex 9 Hg(1)-N(1) Hg(1)-Br(1) N(5A)-Hg(1)-N(1) N(5A)-Hg(1)-Br(1)

2.412(4) 89.19(12) 91.01(11)

Complex 7

Table 3. Selected Bond Distances (A˚) and Angles (deg) for 1c, 2, 3, 9, and 10a 2.032(6) 2.179(3) 98.2(2) 108.07(16)

Cd(1)-N(5A) N(1)-Cd(1)-Cl(1) N(5A)-Cd(1)-Cl(1)

Complex 6 2.055(6) 2.213(2) 2.066(6) 2.230(3) 115.9(2) 146.9(2) 122.65(12) 104.4(2)

Symmetry codes: 1a: A - x, 1 - y, 1 - z; 1b: A 1.5 - x, -0.5 þ y, 0.5 þ z.

Zn(1)-N(1) Zn(1)-Cl(1) N(5A)-Zn(1)-N(1) Cl(1)-Zn(1)-N(1)

2.144(3) 89.61(12) 90.66(13)

Complex 5

Complex 1b Zn(1)-N(2) Zn(1)-N(4) Zn(1)-Cl(1) Zn(2)-N(5A) Zn(2)-Cl(4) Cl(2)-Zn(1)-Cl(1) Cl(1)-Zn(1)-N(2) N(5A)-Zn(2)-N(1)

Zn(1)-N(5A) N(5A)-Zn(1)-O(1) N(1)-Zn(1)-O(1)

2.302(12) 2.346(5) 2.663(5) 2.363(6) 2.529(10) 110.5(2) 153.9(4) 101.78(10) 143.0(3) 90.7(3) 108.2(3)

Hg(1)-N(2) 2.474(8) Hg(1)-Cl(2) 2.554(5) Hg(2)-Cl(3) 2.369(5) Hg(3)-Cl(5) 2.443(6) Hg(3)-Cl(5B) 2.819(7) N(3)-Hg(1)-Cl(2) 95.6(3) Cl(2)-Hg(2)-Cl(2A) 99.9(2) Hg(1)-Cl(2)-Hg(2) 112.54(19) Cl(4)-Hg(3)-Cl(5) 162.5(3) Cl(4)-Hg(3)-N(1) 89.2(3) Cl(5)-Hg(3)-Cl(5B) 89.3(2)

Symmetry code: A -x, y, 0.5 - z; B x, -y, 1 - z.

system with an excess of ZnCl2, while complex 1c was crystallized from a CH3CN-toluene-CH2Cl2 solution. In these three complexes, 1a and 1b have a Zn:L ratio of 2:1, while 1c shows the 1:1 mode even when an excess of metal ion was used, indicating that the product depends mainly on the solvent system rather than the metal-to-ligand ratio. Furthermore, in order to study the influence of metal ions and anions on the structure of the complexes, reactions of the ligand with ZnX2 (X = Br-, I-, NO3-), CdX2 (X = Cl-, NO3-, ClO4-), and HgX2 (X = Cl-, Br-, I-) were carried out in different solvent systems, and complexes 2-4, 5-7, and 8-10, respectively, were successfully isolated. Considering the structural diversity of complexes 1a, 1b, and 1c with the same metal salt (ZnCl2), it was expected that reaction of L with other metal salts may also result in different structures on the basis of the conformation adopted by the ligand. However, attempts to adjust the solvent property or the metal-to-ligand ratio yielded either no crystalline products or only the same complexes mentioned above. Thus, a total of five different types of complexes were obtained from the reaction of the d10 metal with L (Scheme 2). Complexes 1a and 1b are supramolecular isomers (Zn:L = 2:1), and complexes 1c, 2, 3, 9, and 10 have the same M(II):L composition of 1:1. For 4, 5, 6, and 7, an M(II):L ratio of 1:2 was achieved, while for complex 8, the Hg(II):L ratio is 5:2. In the latter case, although the starting Hg(II):L ratio was varied in the reaction, the same complex 8 was exclusively obtained. The phase purity of these complexes was convincingly established by X-ray powder diffraction measurements (Figure S1 in the

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Scheme 2. Illustration of the Different Conformations and Linking Modes of L in the Coordination Networks

Figure 1. The M4L2 metallocycle in 1a showing the coordination geometries of two types of Zn(II) ions. (a) top view; (b) side view. Hydrogen atoms and solvent molecules are omitted for clarity (symmetry code: A -x, 1 - y, 1 - z).

Supporting Information). The solid-state structures of the 12 complexes 1a, 1b, 1c, and 2-10 are described below. Crystal Structures. Structure of the Metallomacrocycle [Zn4Cl8L2] 3 2C7H8 3 2CH3COCH3 3 3H2O (1a). X-ray singlecrystal diffraction analysis reveals that complex 1a features a 0D tetranuclear macrocycle structure that crystallizes in the triclinic space group P1. The conformation of L is close to the type “A” with a “syn, syn, syn” orientation (Scheme 1); that is, the central diiminopyridyl moiety is in the tridentate chelate fasion (syn, syn), and the two terminal pyridyl N donors point to the same direction (syn). As shown in Figure 1a,b, the basic building block is a centro-symmetric macrocycle. Two ligands bridge two zinc atoms through the terminal pyridyl groups, resulting in a Zn2L2-type metallocyclic motif, while the remaining two sites of the tetrahedral Zn(2) center are occupied by chloride ions. Meanwhile, the middle tridentate diiminopyridine moieties also coordinate to Zn2þ ions and finally a Zn4L2-type metallocyclic complex is formed (Figure 1a) with the distances of two corresponding

Zn(1) 3 3 3 Zn(1A) being 10.625 A˚ and Zn(2) 3 3 3 Zn(2A) 18.090 A˚. In the inside of the macrocycle, the Zn(1) atom is fivecoordinated by the tridentate diiminopyridyl moiety and two Cl atoms in a square pyramidal geometry, with Cl(2) occupying the apical position, as in similar complexes with 2,6-bis(1-(2,6-diisopropylphenylimino)ethyl)pyridine.14 The Zn(1)-N(imino) distances (2.289(3) and 2.318(3) A˚) are noticeably longer than the Zn(1)-N(pyridyl) bond length (2.099(3) A˚) (Table 1). The coordinated terminal pyridyl group acts as a bridge between two Zn atoms, facilitating the formation of the M2L2 metallocycle.2b In addition, the middle diiminopyridyl moiety chelates to the Zn center with a “V” shape, yielding the remarkably large discrete Zn4L2 metallomacrocycle. Structure of catena-{[Zn2Cl4L] 3 2CH3OH 3 2CHCl3 3 2H2O}n (1b). Complex 1b (space group Pna2(1)) consists of 1D zigzag polymeric chains. The conformation of L is close to the type “B” with a “syn, syn, anti” orientation (Scheme 1). Compared to 1a, it is noteworthy that the two terminal coordinating pyridyl groups of ligand L in 1b adopt the anti arrangement and point in opposite directions acting as a bridge between two Zn(II) ions to form a 1D polymeric chain (Figure 2a), while in 1a the two terminal pyridyls are in the “syn” conformation and lead to a 0D metallocycle. Thus, complex 1b can be regarded as a ring-opening isomer of 1a. One of the Zn center, Zn(1), is five-coordinated by three nitrogen atoms of the tridentate diiminopyridyl moiety and two Cl atoms. The geometry at Zn(1) can be best described as distorted trigonal bipyramidal with the pyridyl nitrogen atom and the two Cl atoms forming the equatorial plane. The other zinc center, Zn(2), is four-coordinated by two terminal pyridyl groups and two Cl atoms with a distorted tetrahedral geometry. From the viewpoint of chain packing, the 1D zigzag chains of complex 1b are aligned in a corner-in-corner fashion along two different directions, [0 1 1] and [0 1 1]. Consequently, two equivalent sets of layers containing parallel zigzag chains are formed in the (0 1 1) and (0 1 1) planes, respectively. The dihedral angle between the two sets of layers is 45.69°. As shown in Figure 2c, these 1D chains with different orientations stack in an ...ABAB... fashion to form a porous structure with large open channels along the a axis. The adjacent chains are linked via C-H 3 3 3 Cl hydrogen bonding interactions from a methyl group and a pyridyl CH to the two coordinated Clions.15 The separation of two chains is ca. 15.0 A˚ (Figure 2b).

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Figure 2. (a) 1D chain structure in 1b showing the coordination geometries of two Zn(II) ions. (b) Hydrogen bonds between the chains in the same layer (dashed lines). (c, d) View of the chain packing in 1b. Colors are used to distinguish chains along different propagating directions. Symmetry code: A 1.5 - x, -0.5 þ y, 0.5 þ z.

An alternative view of the overall chain packing in 1b is shown in Figure 2d. The chains propagating along different directions are alternately arranged in separate layers parallel to the (1 0 0) plane and the chains in the same layer are aligned in a parallel and corner-in-corner fashion. Neighboring chains in different directions are also linked by C-H 3 3 3 Cl hydrogen bonds as that between the parallel chains from the same layer. Thus, the resulting structure of 1b can be described as a noninterpenetrated 3D framework constructed by 1D zigzag chains. Structures of catena-{[ZnCl2L] 3 0.5CH2Cl2 3 0.5H2O }n (1c), catena-{[ZnBr2L] 3 CH2Cl2}n (2), catena-[ZnI2L]n (3), catena{[HgBr2L] 3 CH3CN 3 0.5CH2Cl2}n (9) and catena-{[HgI2L] 3 0.5CH2Cl2}n (10). Since the solvent can have significant effects on the coordination between the ligand L and metal ion, we also used other solvent systems in the reactions of L and group 12 metals. Through a layer-separation diffusion of ZnCl2 and L in the ternary solvent CH3CN-toluene-CH2Cl2 in an ambient environment, pale-yellow, needle-shaped crystals of complex 1c were obtained. To further examine the impact of the anions on the self-assembled structures, the reaction of the ligand L with ZnBr2 or ZnI2 under similar conditions was carried out and complexes 2 and 3 were isolated. Furthermore, the reaction of ligand L with HgBr2 or HgI2 gave complexes 9 and 10. X-ray single-crystal diffraction reveals that complexes 1c, 2, 3, 9, and 10 are isostructural (Tables 1 and 3), so only complex 2 is described in detail.

In complex 2, the ligand L has a quasi linear shape with a conformation close to type “C” (“anti, anti, syn”, Scheme 1) and bridges two Zn(II) ions using its two terminal pyridyl groups to give a 1D helical chain structure with a pitch of 24.104 A˚ (Figure 3a). The metal atom adopts a distorted tetrahedral geometry by coordinating to two pyridyl N donors of two ligands and two bromide ions. Interestingly, compared with complexes 1a and 1b, in complex 2 only the terminal pyridyl nitrogen donors (N1 and N5) coordinate to the metal center, while the potential tridentate diiminopyridyl moiety adopts the “anti, anti” orientation and does not participate in the coordination to metal. The P and M helices are arranged alternately and linked through π-π stacking interactions between the terminal pyridyl rings, and the whole compound is racemic. The stacking pyridyl rings are parallel to each other (dihedral angle 0.0°) with a centroidcentroid separation of 3.650 A˚ (Figure 3b).16 Furthermore, such double stranded chains are parallel to each other and are linked by C-H 3 3 3 π interations between the C(22)H(22A) from the middle pyridyl group and the phenyl ring [C(6)-C(11)] from another chain (the CH to centroid distance is 2.722 A˚).17 Taking into account these C-H 3 3 3 π interactions, the resulting structure of 2 can be described as a polymeric 2D sheet architecture (Figure 3c). Structure of catena-{[Zn(NO3)2L2 3 2C7H8]}n (4). When ligand L was reacted with zinc(II) nitrate, complex 4 was isolated. The skeletal structure of 4 consists of Zn(II) ions

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Figure 3. (a) 1D chain structure of 2 showing the coordination geometry of the Zn(II) ion. (b) Perspective view of the racemic helical chains in 2. (c) C-H 3 3 3 π and π 3 3 3 π interactions between the chains (dashed lines).

and L in a 1:2 molar ratio. The conformation of L is close to the type “D” with the “anti, anti, anti” orientation (Scheme 1) in which only the terminal pyridyl groups are involved in metal-coordination, while the central diiminopyridyl moiety is free. This conformation is also adopted by the free ligand.10 The zinc atom in complex 4 is six-coordinated rather than four- or five-coordinated as observed in complexes 1-3. As illustrated in Figure 4a, each zinc(II) center has an octahedral environment and is coordinated by four terminal pyridyl groups of four ligands with Zn-N bond lengths in the range of 2.144(3)-2.174(3) A˚. The two axial positions are occupied by two monodentate NO3- ions with a Zn-O bond length of 2.181(3) A˚ (Table 4). Two ligands link two zinc atoms to form a 44-membered metallomacrocycle with a Zn 3 3 3 Zn distance of 21.518 A˚. The macrocycles are linked by the Zn centers to give a 1D polymeric chain which interdigitates in the bc plane, so the structure can be best described as a looped-chain 1D coordination polymer. These 1D chains are further linked by C-H 3 3 3 π interactions to form a layer structure similar to that in complex 2 (Figure 4b). All the 1D chains stack along the a direction, forming ellipsoidal channels with dimensions of ca. 21.5 10.2 A˚2 where solvent toluene molecules are located as shown in Figure 4c. Structures of {[CdCl2L2] 3 2CH2Cl2}n (5), {[Cd(NO3)2L2] 3 CH2Cl2}n (6), {[Cd(ClO4)2L2] 3 CH2Cl2}n (7). The reaction of ligand L with CdCl2, Cd(NO3)2, or Cd(ClO4)2 gave complexes 5, 6, and 7. The structures of the three complexes are isostructural where the Cd(II) center has a similar coordination environment as that in 4 except that different coordinated anions occupy the axial positions. Each Cd(II) center displays a distorted octahedral environment, being coordinated by four terminal pyridyl groups from four ligand molecules and two chloride (5), nitrate (6), or perchlorate (7) ions, respectively (Figure 5). Notably, although the anions are different (Cl-, NO3-, and ClO4-), they all serve as monodentate auxiliary ligands in 5, 6, and 7. This also indicates that complexes 5, 6, and 7 (1D looped-chain) are metal-directed assemblies in which the anion does not show significant effects

Figure 4. (a) One macrocycle in 4 showing the coordination geometry of Zn(II) ion. (b) View of the 2D layer connected by C-H 3 3 3 π interactions between the 1D looped-chains. (c) Channels along the a axis. Hydrogen atoms and solvents are omitted for clarity. Symmetry code: A 1 - x, 1 - y, -z.

Figure 5. 1D macrocyclic chain structure in 5, 6, and 7 showing the similar coordination geometry of Cd(II) ion. Hydrogen atoms and solvent molecules are omitted for clarity. Symmetry codes: B -x, 1-y, -1-z; C 2-x, 1-y, 1-z; D 1-x, -y, 2-z.

on the structure. Such a structure was also obtained previously for cobalt(II) complexes of L.10 Structure of catena-{[Hg4(μ2-L2)(μ2-Cl2)(μ-HgCl2)Cl6] 3 2H2O}n (8). In addition to the above-mentioned zinc chloride and cadmium chloride complexes, mercury chloride was also tested to investigate the influence of metal ion on the structure of the assemblies. Complex 8 was obtained by the reaction of L with mercury chloride. The ligand adopts the

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Figure 6. (a) The coordination environments of three different types of Hg(II) ion in complex 8. (b) 1D zigzag chain in the bc plane. (c) 2D network linked by Hg2Cl2 and HgCl2 bridges in the ac plane. (d) Open channels in 8 along the c axis formed by alternately arranged macrocycles. (e) A schematic view of the 2D network, with orange lines representing the ligands (one ligand is shown in the stick style), red nodes representing the Hg(II) centers, and green ones the bridging Cl atoms. The terminal Cl atoms are omitted for clarity. Symmetry codes: A -x, y, 0.5 - z; B x, -y, 1 - z; C x, y, 0.5 - z; D 1 - x, y, 0.5 - z.

type “A” conformation. There are three different Hg(II) ions in complex 8 (space group Cmcm) as shown in Figure 6a. In the middle part of the ligand, the Hg(1) center is five-coordinated by the three nitrogen atoms of the diiminopyridyl moiety and two Cl atoms. The geometry at the Hg(1) center can be described as a square pyramid with Cl(2) occupying the apical position. The four basal atoms [N(2), N(3), N(2C), Cl(1)] are coplanar (deviations within 0.026 A˚), and the Hg atom lies 0.538 A˚ out of this plane. The two Hg-Cl bonds at Hg(1) are noticeably asymmetric, with that to the apical chloride being significantly longer (Hg(1)-Cl(2) at 2.554(5) A˚) than that to its basal counterpart (Hg(1)-Cl(1) at 2.346(5) A˚), probably as a consequence to satisfy the apical chloride serving as a bridging ligand. Two of the five-coordinate [Hg(1)Cl2L] units are linked by an HgCl2 bridge to form a centro-symmetric trinuclear unit. The second type of mercury center, Hg(2), in the HgCl2 bridge adopts a distorted tetrahedral geometry by coordinating to four chloride atoms, two bridging and two terminal. The bridging Hg-Cl distance (2.663(5) A˚ for Hg(2)-Cl(2)) is longer than the terminal (2.369(5) A˚ for Hg(2)-Cl(3)). The Cl-Hg-Cl bond angles around the bridging HgCl2 fall in the range 99.9(2)-143.0(3)°. The third type of Hg(II) ion, Hg(3), displays a square pyramidal geometry comprised of two terminal pyridyl groups from two ligands and three chloride ions, two bridging and one terminal, with one of the bridging chlorides Cl(5B) occupying the apical position. The Hg-Cl bond lengths are in the

range of 2.364(6)-2.819(7) A˚, among which two μ2-chloride ions are bound to two square pyramidal Hg(II) ions forming a rectangular HgCl2Hg cycle [Cl(5)-Hg(3)-Cl(5B), 89.3(2)° and Hg(3)-Cl(5)-Hg(3B), 90.7(2)°]. The dimeric bridging units HgCl2Hg act as four-connected junctions and are joined to each other via four L ligands. The dihedral angle between the terminal pyridyl ring and the rectangular plane is 84.19°. The Hg 3 3 3 Hg distance is short (ca. 3.753 A˚) and close to those observed in other structures with mercurophilic interactions, but is not as short as the sum of the van der Waals radii of Hg(II) of 3.41 A˚.18 The Hg-Cl (bridging) distances (2.444(6) and 2.819(7) A˚) are longer than the Hg-Cl (terminal) distance (2.364(6) A˚) as expected (Table 5), the latter indicating a strong Hg-Cl bond. However, it should be noted that one of the two Hg-Cl (bridging) bonds is 0.375 A˚ shorter than the other. Most of the HgCl2Hg bridges reported in the literature are either symmetrical with two equivalent Hg-Cl distances of about 2.8 A˚, or highly unsymmetrical with one short bond of 2.3 A˚ and one weak contact (>3.0 A˚); thus, complex 8 has an intermediate asymmetry in this aspect.19 These three kinds of coordinatively different Hg(II) atoms are bridged by ligand L to form an infinite 2D network that extends in the crystallographic ac plane. Although many halide-bridged mercury-based structures have been reported in the literature and the formation of Hg2X2 bridges is ubiquitous in the structural chemistry of mercury halides,20 a complex like 8 that has three kinds of coordination modes for mercury atoms and displays both

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HgCl2 and Hg2Cl2 bridges is, to the best of our knowledge, not yet known. As mentioned above, in complex 8, the ligand adopts a conformation close to type “A” (Scheme 1) as in complex 1a. The dinuclear μ2-chloro bridged Hg2Cl2 units link two L molecules through the terminal pyridyl nitrogen atoms to form a 1D looped chain of 36-membered macrocycles propagating along the c axis with two types of Hg 3 3 3 Hg distances of 14.465 (Hg1 3 3 3 Hg1D) and 15.057 A˚ (Hg3 3 3 3 Hg3D), respectively. The looped chains are further linked by the mononuclear HgCl2 bridges through the middle diiminopyridyl moiety in the a direction to form a polymeric 2D net in the ac plane (Figure 6c). It is different from the structure of complexes 4-7 in which the macrocycles are linked by sixcoordinate metal ions directly. Interestingly, this compound differs also from a cobalt(II/III) complex of L, in which the same 1D looped chain of 36-membered macrocycles are formed, but the central diiminopyridyl-coordinated Co atoms are not further linked by Cl bridges in the other direction, thus remaining an overall 1D structure.10 It is also noteworthy that, although complex 8 is a 2D network in the ac plane, open channels are formed along the c direction (see Figure 6d). An alternative view of the overall chain packing in 8 is shown in Figure 6e. The most significant structural feature of 8 is that the loop-containing 2D layers with three different kinds of rings are inextricably entangled in an unprecedented manner. The torsional polygonal ring is a 48-membered macrocycle with the composition of Hg10(1/2 L)4Cl6. The second kind of ring is a rhomboid 36-membered macrocycle, which is formed by Hg2L2, while the dinuclear μ2-chloro bridged Hg2Cl2 unit is a rectangle ring. The neighboring torsional polygonal rings are linked by the dinuclear Hg2Cl2 units along the a axis and the neighboring rhombus rings are linked by the Hg2Cl2 units along the c axis. Thus, the resultant entangled framework could equally well be considered to be formed by interconnected different rings in the ac plane. A PLATON calculation shows that the effective volume for inclusion in 8 is about 2290.4 A˚3 per unit cell, comprising 20.0% of the crystal volume. The Effects of Solvent, Metal Center and Anion on the Structure of the Complexes. The above structural analyses of complexes 1-10 reveal that the semirigid ligand L can adopt four possible conformations, “A”, “B”, “C”, and “D”, as depicted in Scheme 1, to participate in coordination with metal ions to construct a variety of coordination frameworks. In complexes 1a, 1b, and 8, the tridentate diiminopyridyl moiety adopts the “syn, syn” orientation with the conformation “A” or “B”, and the ligand L acts as a pentadentate ligand where all five potential coordination sites coordinate to metal ions. However, in other complexes, the diiminopyridyl moiety adopts the “anti, anti” orientation with the conformation “C” or “D” in which only the terminal pyridyl groups are involved in metal coordination, leaving the stretched diiminopyridyl moiety free from metal ions. The structural diversity is closely related to the nature of the metal ions with different coordination tendencies. Meanwhile, the properties of the solvent systems (coordinating ability, polarity) and the anions (coordinating ability, size, and shape) also play important roles in governing the structure of such metal-organic coordination architectures. Among the d10 metal ions, the Zn(II) ion exhibited variable coordination geometries from 4-coordinate tetrahedral, 5-coordinate square pyramidal and trigonal bipyramidal,


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Table 6. Solid-State Photoluminescent Data for the Ligand L and Compounds 1-10 ligand/complex

λex (nm)

L 1a 1b 1c 2 3 4 5 6 7 8 9 10

533 501 510 510 489 497 500 474 470 475 496 500 500

λem (nm) 625 617 603 604 580 588 590 564 560 567 589 593 593

649 625 626 605 613 616 590 586 591 612 616 616

to 6-coordinate octahedral, while the Cd(II) ion was in favor of 6-coordinate octahedral geometry and the Hg(II) ion preferred the 4-coordinate tetrahedral and 5-coordinate trigonal bipyramidal geometries in this work. Thus, although complexes 1a, 1b, 1c, 5, and 8 contain the same anion (Cl-), the Zn(II), Cd(II), and Hg(II) ions show differentiable coordination behaviors and result in distinct structural features. However, in some cases (the isostructural complexes of 1c, 2, 3, 9, and 10, 1D helical chain, and 4-7, 1D looped chain) the structure can also display some tolerance to the metal center and its local coordination environment. The solvent systems used show crucial effects on the structure of the final product, as in the cases of the ZnCl2 complexes 1a, 1b, and 1c. This may be the result that the polarity and coordinating ability of the solvent can interfere the coordination behavior of the metal ion (such as competition between the solvent and ligand) during the metal coordination process. On the other hand, the counteranion may also affect the assembly of the coordination architectures. Although all the counteranions studied in this work display strong coordination tendencies to metal ions, the different coordination modes of them lead to variable architectures. For example, in the HgX2-complexes 8-10 which contain different halide ions, the Cl- ions in 8 coordinate to Hg(II) in the bridging mode to form a 2D network. In contrast, in 9 and 10, the heavier anions (Br-, I-) coordinate to the metal center in the terminal fashion and result in 1D helical chains. It should be noted that the formation of different structural topologies may be directed by multiple factors synergistically; thus, a combination of the metal, anion and solvent effects should be considered in the construction of coordination networks. Luminescent Properties. Metal-organic coordination polymers, especially those with d10 metal centers, have been reported to be able to affect the emission wavelength and intensity of the organic material through metal coordination.21 In this work, the photoluminescent properties of complexes 1-10 have been explored at room temperature in the solid state, and their photoluminescent characteristics are summarized in Table 6. The emission spectrum of the ligand L shows emission maxima at 625 and 649 nm (λex = 533 nm) due to the intraligand π-π* transition (Figure 7). The chromophore of this ligand is mainly the diiminopyridyl moiety and the aromatic rings (pyridyl and phenyl), and the combination of the pyridyl and phenyl rings results in a significant red shift of the emission wavelength of the ligand L compared with the 2,6-bis(1-(2,6-diisopropylphenylimino)ethyl)pyridine ligand (λem = 475 nm).14

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Conclusions In this paper, we report 12 metal-organic coordination architectures of a ditopic diiminopyridine ligand L with group 12 metal Zn(II), Cd(II), and Hg(II) ions. The compounds are structurally diverse, including five main structural motifs: 0D metallomacrocycle, 1D zigzag chain, 1D helical chain, 1D looped-chain, and 2D network. In the complexes, the ligand L shows four different conformation modes, which are responsible for the various structural topologies. This study clearly demonstrates that the solvent system, the metal ion, and anion play important roles in determining the coordination modes of the metal centers, resulting in different building blocks in the assembly of the supramolecular structures. Photoluminescent studies indicate that the complexes exhibit enhanced and blue-shifted solid-state fluorescence at room temperature compared with ligand L. Acknowledgment. This work was supported by the “Bairen Jihua” project of the Chinese Academy of Sciences. Supporting Information Available: The powder X-ray diffraction patterns of complexes 1-10 and the X-ray crystallographic files in CIF format. This material is available free of charge via the Internet at http://pubs.acs.org.

References

Figure 7. Emission spectra of L and 1-10 in the solid-state at room temperature.

The emission spectra of complexes 1-10 (Figure 7) closely resemble that of the ligand L with enhanced intensities and significant blue shifts, which may be assigned to the ligandbased (π-π*) fluorescence.22 The highest occupied molecular orbital (HOMO) is presumably associated with the π-bonding orbital from the pyridyl and phenyl ring of the ligand L, and the lowest unoccupied molecular orbital (LUMO) may be dominated by the ligand π* character rather than M-X σ* orbital, because heteroatoms in an aromatic ligand can effectively decrease the π and π* orbital energies.23 The blue shifts for compounds 1-10 compared to the free ligand (Table 6) can be tentatively ascribed to the coordination of the pyridyl groups to metal ions which may increase the HOMO-LUMO energy gap, and the enhancement of luminescence intensity is perhaps a result of the metal-ligand coordination which effectively increases the rigidity of the ligand and reduces the nonradiative decay of the intraligand (π-π*) excited state.24

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