Structural Diversities and Fluorescent and Photocatalytic Properties of

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Structural Diversities, Fluorescent and Photocatalytic Properties of a Series of CuII Coordination Polymers Constructed from Flexible Bis-pyridyl-bis-amide Ligands with Different Spacer Length and Different Aromatic Carboxylates Xiuli Wang, Jian Luan, Fangfang Sui, Hongyan Lin, Guocheng Liu, and Chuang Xu Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/cg400538c • Publication Date (Web): 14 Jun 2013 Downloaded from http://pubs.acs.org on June 24, 2013

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Crystal Growth & Design

Structural Diversities, Fluorescent and Photocatalytic Properties of a Series of CuII Coordination Polymers Constructed from Flexible Bis-pyridyl-bis-amide Ligands with Different Spacer Length and Different Aromatic Carboxylates Xiu-Li Wang,∗ Jian Luan, Fang-Fang Sui, Hong-Yan Lin, Guo-Cheng Liu, and Chuang Xu Department of Chemistry, Bohai University, Liaoning Province Silicon Materials Engineering Technology Research Centre, Jinzhou 121000, P. R. China

ABSTRACT Thirteen new CuII coordination polymers, namely, [Cu(3-dppa)(1,3,5-HBTC)] (1), [Cu(3-dpha)(1,3,5-HBTC)(H2O)]·H2O (2), [Cu3(3-dpsea)(1,3,5-BTC)2(H2O)5]·4H2O (3),

[Cu(3-dpba)(1,2-BDC)]·H2O

[Cu(3-dpsea)(1,2-BDC)]·H2O

(6),

(4),

[Cu(3-dpha)(1,2-BDC)]

(5),

[Cu2(3-dpyp)(1,3-BDC)2(H2O)4]·3H2O

(7),

[Cu(3-dppa)(1,3-BDC)(H2O)]·2H2O (8), [Cu(3-dppia)(1,3-BDC)(H2O)2]·2H2O (9), [Cu2(3-dpsea)2(1,3-BDC)2(H2O)2]·7H2O (10), [Cu(3-dpba)(1,4-NDC)]·3H2O (11), [Cu(3-dpyh)(1,4-NDC)(H2O)]·3H2O (12), [Cu(3-dpyh)0.5(1,4-NDC)]·H2O (13), have been

purposefully

synthesized

under

hydrothermal

conditions

[3-dppa

=

N,N'-di(3-pyridyl)propanediamide, 3-dpba = N,N'-di(3-pyridyl)butanediamide, 3-dpha =

N,N'-di(3-pyridyl)hexanedioicdiamide,

pimelicdiamide,

3-dpsea

=

3-dppia

=

N,N'-di(3-pyridyl)

N,N'-di(3-pyridyl)sebacicdiamide,

3-dpyp

=

N,N'-di(3-pyridinecarboxamide)-1,3-propane,

3-dpyh

=

N,N'-di(3-pyridinecarboxamide)-1,6-hexane,

1,3,5-H3BTC

=

1,3,5-benzenetricarboxylic acid, 1,2-H2BDC = 1,2-benzenedicarboxylic 1,3-H2BDC

=

1,3-benzenedicarboxylic

acid

and

acid,

1,4-H2NDC

=

1,4-naphthalenedicarboxylic acid]. Complexes 1-3 based on the same auxiliary ligand ∗ Corresponding author. Tel: +86-416-3400158 E-mail address: [email protected] (X.-L. Wang) 1

ACS Paragon Plus Environment


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show various structures. Complex 1 features a 1D ∞-like double-chain structure, which consists of [Cu-1,3,5-HBTC]n chain and [Cu-3-dppa]n meso-helical chain. Complex 2 possesses a (2,4) undulated honeycomb (hcb) net. Complex 3 is a 3-fold interpenetrating 3D framework, which shows trinodal (2,3,3)-connected topology with the Schläfli symbol of (10·122)2(103)2(12). Complexes 4–6 with 1,2-BDC as secondary ligand exhibit different 2D layer structures. Complex 4 exhibits a 2D (2,4)-connected (4·124·14)(4) net. Complexes 5 and 6 have similar structures and show 2D networks with undulated sql topology. For complexes 7–10 based on 1,3-BDC secondary ligand, complex 7 shows a 1D zigzag chain, while complexes 8–10 have similar wave-like 2D structures. When 1,4-NDC was used as the auxiliary ligand, complex 11 is a 2D puckered (4,4) network, complex 12 reveals a 4-connected topology with the point symbol of (44·62), while complex 13 exhibits a 3-fold interpenetrating 3D α-Po framework. The structural diversity indicates that the bis-pyridyl-bis-amide

ligands

with

different

spacers

and

the

aromatic

polycarboxylates play important roles in tuning the dimensionalities and structures of the title complexes. The fluorescent and photocatalytic properties for 1–13 have also been investigated in detail.

INTRODUCTION Coordination polymers (CPs) have attracted great interest in recent years due to their diverse structures and potential applications in gas adsorption, separation, luminescence and catalysis.1 It is well known that the construction of CPs is dependent on several factors, such as organic ligand, geometric requirement of the metal ion, temperature, pH, and solvent system.2 Among these factors, the organic ligands play an important role in tuning the coordination frameworks and topologies of CPs.3 Bis-pyridyl-bis-amide as a kind of excellent organic ligands, which possess not only various coordination atoms and strong coodination ability, but also abundant potential hydrogen bond sites for hydrogen bonding interaction, have attracted great interest in the construction of CPs.4 For example, Chen et al.4a have reported an 2


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interpenetrating diamondoid network with an unusual 12-fold [6+6] mode based on copper sulfate and N,N'-di(4-pyridyl)adipoamide. Furthermore, by using the N1,N4-bis(pyridin-3-ylmethyl)naphthalene-1,4-dicarboxamide ligand, a self-catenated network containing unprecedented 0D + 2D → 2D polycatenation array has been obtained by Luo’s group4d. Our group has prepared a series of CuII/CoII/CdII CPs derived

from

the

rigid

bis-pyridyl-bis-amide

ligands

N,N'-bis(4/3-pyridinecarboxamide)-1,4-benzene (4-bpcb/3-bpcb)5, or the semi-rigid N,N'-bis(pyridin-3-yl)cyclohexane-1,4-dicarboxamide

(3-bpcd)

and

bis(3-pyridylformyl)piperazine (3-bpfp)6, and different aromatic polycarboxylates mixed ligands. Compared with the rigid or semi-rigid bis-pyridyl-bis-amide, the flexible bis-pyridyl-bis-amide ligands with different -(CH2)n- backbone have attracted more attention recently, because they can bend and twist with large degree to satisfy the coordination request of metal ions. To the best of our knowledge, the reports

on

the

CPs

constructed

with

flexible

bis-pyridyl-bis-amide

and

polycarboxylates mixed ligands are still limited.7 On the other hand, the development of photocatalysis as applied, in particular, to organic pollutants concentration abatement or removal from wastewater under ultraviolet light has received great research attention in catalysis field.8 A new emerging application of CPs is photocatalysis, and some CPs have been demonstrated to be efficient photocatalysts on the green degradation of organic pollutants.9 However, such kinds of application of CPs on ultraviolet-light-driven photocatalysis are just beginning to emerge.10 How to achieve inexpensive, stable and efficient CPs photocatalysts is still a big challenge. Considering that the flexible bis-pyridyl-bis-amide ligands may supply the charge transfer excited state to oxygenate water molecules to generate the •OH radicals, which have potential photocatalytic activity to degrade some other orgainc dyes,11 in this

work,

seven

flexible

N,N'-di(3-pyridyl)propanediamide (3-dpba),

bis-pyridyl-bis-amide (3-dppa),

N,N'-di(3-pyridyl)hexanedioicdiamide

pimelicdiamide

(3-dppia),

ligands

(Scheme

1):

N,N'-di(3-pyridyl)butanediamide (3-dpha),

N,N'-di(3-pyridyl)

N,N'-di(3-pyridyl)sebacicdiamide 3


(3-dpsea),


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N,N'-bis(3-pyridinecarboxamide)-1,3-propane

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(3-dpyp),

and

N,N'-bis(3-pyridinecarboxamide)-1,6-hexane (3-dpyh) have been selected as the main ligands combining with polycarboxylates to construct CuII CPs, aiming for investigating their effect on the final structures and the photocatalytic properties of target CPs. To the best of our knowledge, only a few examples based on the bis-pyridyl-bis-amide ligands has been reported as the photocatalyst.7b, 11 As a result, thirteen CuII CPs based on seven flexible bis-pyridyl-bis-amide and four polycarboxylates mixed ligands, namely, [Cu(3-dppa)(1,3,5-HBTC)] (1), [Cu(3-dpha)(1,3,5-HBTC)(H2O)]·H2O (2), [Cu3(3-dpsea)(1,3,5-BTC)2(H2O)5]·4H2O (3),

[Cu(3-dpba)(1,2-BDC)]·H2O

[Cu(3-dpsea)(1,2-BDC)]·H2O

(6),

(4),

[Cu(3-dpha)(1,2-BDC)]

[Cu2(3-dpyp)(1,3-BDC)2(H2O)4]·3H2O

(5), (7),

[Cu(3-dppa)(1,3-BDC)(H2O)]·2H2O (8), [Cu(3-dppia)(1,3-BDC)(H2O)2]·2H2O (9), [Cu2(3-dpsea)2(1,3-BDC)2(H2O)2]·7H2O (10), [Cu(3-dpba)(1,4-NDC)]·3H2O (11), [Cu(3-dpyh)(1,4-NDC)(H2O)]·3H2O (12), [Cu(3-dpyh)0.5(1,4-NDC)]·H2O (13), have been designed and synthesized under hydrothermal conditions [1,3,5-H3BTC = 1,3,5-benzenetricarboxylic acid, 1,2-H2BDC = 1,2-benzenedicarboxylic 1,3-H2BDC

=

1,3-benzenedicarboxylic

acid

and

1,4-H2NDC

acid, =

1,4-naphthalenedicarboxylic acid]. All the complexes were characterized by single crystal X-ray crystallography, IR spectroscopy, powder X-ray diffraction (PXRD), elemental analysis, and thermogravimetric (TG) analysis. In addition, the fluorescent and photocatalytic properties of complexes 1-13 have been investigated. Insert Scheme 1 EXPERIMENTAL SECTION Materials and Methods. The bis-pyridyl-bis-amide ligands were prepared according to the reported procedure.4c, 12 All other reagents and solvents for syntheses were purchased from commercial sources and used as received without further purification.

4


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Physical Measurements. The elemental analyses (C, H and N) were carried out on a Perkin-Elmer 240C elemental analyzer. FT-IR spectra (KBr pellets) were taken on a Varian 640 FT-IR spectrometer. The fluorescence properties of the ligands and complexes were measured on a Hitachi F-4500 fluorescence/phosphorescence spectrophotometer at room temperature. Powder X-ray diffraction (PXRD) investigations were carried out with a Ultima IV with D/teX Ultra diffractometer at 40 kV, 40 mA with Cu Kα (λ = 1.5406 Å) radiation. Thermogravimetric analyses (TGA) were performed on a SDT 2960 Simultaneous DSC-TGA instrument under flowing N2 atmosphere with a heating rate of 10 °C · min-1. UV-Vis absorption spectra were obtained using a SP-1900 UV-Vis spectrophotometer. X-Ray crystallography. Crystallographic data for complexes 1–13 were collected on a Bruker SMART APEX II with Mo Kα (λ = 0.71073 Å) by ω and θ scan mode. All the structures were solved by direct methods and refined on F2 by full-matrix least squares using the SHELXTL package.13 For complexes 1–13, the crystal parameters, data collection, and refinement results are summarized in Table 1-2. Selected bond distances and bond angles are listed in Table S1–S13. Hydrogen bonding geometries of complexes 1, 2, 4, 5, and 8-12 are summarized in Table S14. CCDC 919483-919495 for complexes 1–13 contain the supplementary crystallographic data in this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Insert Table 1 and Table 2 Synthesis of [Cu(3-dppa)(1,3,5-HBTC)] (1) The mixture of CuCl2·2H2O (0.034 g, 0.2 mmol), 1,3,5-H3BTC (0.030 g, 0.15 mmol), 3-dppa (0.027 g, 0.1 mmol), H2O (12 mL) and NaOH (0.019 g, 0.48 mmol) was stirred for 30 min in air, then transferred and sealed in a 25ml Teflon reactor, which was heated at 120 °C for 4 days. After slow cooling to room temperature, purple block crystals of 1 were obtained in 29% yield based on Cu. C22H16CuN4O8 (527.93): calcd. C 50.01, H 3.03, N 10.61; found C 50.05, H 3.08, N 10.57. IR (KBr, cm-1): 3215 (w), 2362 (w), 1701 (s), 1656 (m), 1616

5



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(s), 1523 (s), 1475 (s), 1421 (s), 1357 (s), 1217 (m), 1164 (m), 1002 (m), 945 (m), 752 (m), 509 (w). Synthesis of [Cu(3-dpha)(1,3,5-HBTC)(H2O)]·H2O (2) The synthesis method of 2 is similar to that of 1 except for ligand 3-dpha (0.031 g, 0.1 mmol) as the substitute of 3-dppa, and different amount of NaOH (0.017 g, 0.42 mmol) was added to adjust the systematic pH. Blue block crystals of 2 were obtained in 28% yield based on Cu. C25H26CuN4O10 (606.04): calcd. C 49.50, H 4.29, N 9.24; found C 49.51, H 4.26, N 9.26. IR (KBr, cm-1): 3433 (m), 2923 (w), 2364 (w), 1870 (w), 1702 (s), 1665 (s), 1628 (s), 1568 (s), 1541 (s), 1475 (m), 1425 (s), 1363 (s), 1230 (m), 1192 (m), 998 (m), 808 (w), 769 (w), 582 (w). Synthesis of [Cu3(3-dpsea)(1,3,5-BTC)2(H2O)5]·4H2O (3) The synthesis process of 3 is similar to that of 1 except that ligand 3-dpsea (0.036 g, 0.1 mmol) was used as the substitute of 3-dppa, and different amount of NaOH (0.018 g, 0.45 mmol) was added to adjust the systematic pH. Blue block crystals of 3 were obtained in 25% yield based on Cu. C38H50Cu3N4O23 (1121.44): calcd. C 40.66, H 4.46, N 4.99; found C 40.64, H 4.47, N 4.95. IR (KBr, cm-1): 3363 (w), 2850 (w), 2360 (w), 1685 (m), 1616 (s), 1541 (s), 1473 (m), 1429 (s), 1363 (s), 1213 (m), 1147 (w), 1079 (w), 966 (w), 729 (m), 669 (m), 569 (w). Synthesis of [Cu(3-dpba)(1,2-BDC)]·H2O (4) The mixture of CuCl2·2H2O (0.034 g, 0.2 mmol), 1,2-H2BDC (0.025 g, 0.15 mmol), 3-dpba (0.030 g, 0.1 mmol), H2O (12 mL), and NaOH (0.019 g, 0.48 mmol) was stirred for 30 min in air, then transferred and sealed in a 25ml Teflon reactor, which was heated at 120 °C for 4 days. After slow cooling to room temperature, blue block crystals of 4 were obtained in a 30% yield based on Cu. C22H20CuN4O7 (515.96): calcd. C 51.17, H 3.88, N 10.85; found C 51.12, H 3.90, N 10.84. IR (KBr, cm-1): 3309 (w), 2362 (m), 1651 (m), 1558 (s), 1481 (s), 1419 (m), 1384 (s), 1290 (s), 1164 (m), 1091 (w), 889 (m), 806 (m), 750 (w), 536 (w). Synthesis of [Cu(3-dpha)(1,2-BDC)] (5) The synthesis method of 5 is similar to that of 4 except for ligand 3-dpha (0.031 g, 0.1 mmol) as the substitute of 3-dpba, and different amount of NaOH (0.016 g, 0.40 mmol) was added to adjust the systematic 6


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pH. Blue block crystals of 5 were obtained in 34% yield based on Cu. C24H22CuN4O6 (526.00): calcd. C 54.75, H 4.18, N 10.65; found C 54.78, H 4.16, N 10.68. IR (KBr, cm-1): 3432 (w), 3297 (w), 2360 (w), 1654 (m), 1600 (m), 1583 (s), 1531 (s), 1488 (m), 1425 (s), 1386 (s), 1322 (m), 1247 (m), 1153 (m), 1153 (m), 821 (m), 757 (m), 701 (w), 619 (w), 507 (w). Synthesis of [Cu(3-dpsea)(1,2-BDC)]·H2O (6) The synthesis method of 6 is also similar to that of 4 except that ligand 3-dpsea (0.036 g, 0.1 mmol) was used instead of 3-dpba, and different amount of NaOH (0.018 g, 0.45 mmol) was added to adjust the systematic pH. Blue block crystals of 6 were collected in 35% yield based on Cu. C28H32CuN4O7 (600.12): calcd. C 55.99, H 5.33, N 9.33; found C 55.94, H 5.31, N 9.35. IR (KBr, cm-1): 3269 (w), 2374 (w), 1664 (s), 1622 (m), 1554 (s), 1485 (s), 1431 (s), 1386 (s), 1278 (m), 1174 (m), 1010 (w), 873 (w), 775 (w), 696 (w), 567 (m). Synthesis

of [Cu2(3-dpyp)(1,3-BDC)2(H2O)4]·3H2O

(7) The mixture

of

CuCl2·2H2O (0.034 g, 0.2 mmol), 1,3-H2BDC (0.025 g, 0.15 mmol), 3-dpyp (0.029 g, 0.1 mmol), H2O (12 mL), and NaOH (0.016 g, 0.40 mmol) was stirred for 30 min in air, then transferred and sealed in a 25ml Teflon reactor, which was heated at 120 °C for 4 days. After slow cooling to room temperature, blue block crystals of 7 were obtained in 30% yield based on Cu. C31H38Cu2N4O17 (865.73): calcd. C 42.97, H 4.39, N 6.47; found C 42.96, H 4.40, N 6.45. IR (KBr, cm-1): 3292 (w), 2360 (w), 1654 (s), 1620 (s), 1562 (s), 1479 (m), 1436 (s), 1388 (s), 1367 (s), 1272 (w), 1201 (w), 1164 (w), 1074 (w), 748 (m), 721 (m), 661 (w), 582 (w). Synthesis of [Cu(3-dppa)(1,3-BDC)(H2O)]·2H2O (8) The synthesis method of 8 is similar to that of 7 except for ligand 3-dppa (0.027 g, 0.1 mmol) as the substitute of 3-dpyp, and different amount of NaOH (0.018 g, 0.45 mmol) was added to adjust the systematic pH. Blue block crystals of 8 were obtained in 34% yield based on Cu. C21H22CuN4O9 (537.97): calcd. C 46.84, H 4.09, N 10.41; found C 48.83, H 4.07, N 10.40. IR (KBr, cm-1): 3217 (w), 2364 (w), 1666 (m), 1606 (s), 1587 (m), 1556 (s), 1523 (s), 1481 (m), 1427 (s), 1396 (s), 1367 (s), 1326 (m), 1274 (m), 1163 (m), 1105 (w), 806 (m), 744 (m), 653 (m), 505 (w).

7



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Synthesis of [Cu(3-dppia)(1,3-BDC)(H2O)2]·2H2O (9) The synthesis method of 9 is also similar to that of 7 except that ligand 3-dppia (0.031 g, 0.1 mmol) was used instead of 3-dpyp, and different amount of NaOH (0.019 g, 0.46 mmol) was added to adjust the systematic pH. Blue block crystals of 9 were collected in 31% yield based on Cu. C25H32CuN4O10 (612.09): calcd. C 49.02, H 5.23, N 9.15; found C 49.05, H 5.25, N 9.12. IR (KBr, cm-1): 3379 (w), 2362 (w), 1681 (m), 1612 (m), 1556 (s), 1502 (m), 1483 (s), 1431 (m), 1375 (s), 1213 (m), 1191 (m), 1031 (m), 923 (w), 810 (w), 750 (w), 609 (w), 569 (w). Synthesis of [Cu2(3-dpsea)2(1,3-BDC)2(H2O)2]·7H2O (10) The synthesis method of 10 is similar to that of 7 except for ligand 3-dpsea (0.036 g, 0.1 mmol) as the substitute of 3-dpyp, and different amount of NaOH (0.018 g, 0.45 mmol) was added to adjust the systematic pH. Blue block crystals of 10 were collected in 35% yield based on Cu. C56H78Cu2N8O21 (1326.34): calcd. C 50.67, H 5.88, N 8.44; found C 50.62, H 5.87, N 8.42. IR 4(KBr, cm-1): 3271 (w), 2923 (w), 2356 (w), 1650 (s), 1608 (s), 1556 (s), 1485 (s), 1408 (m), 1373 (s), 1346 (s), 1245 (m), 1195 (m), 995 (w), 864 (w), 698 (m), 592 (w). Synthesis of [Cu(3-dpba)(1,4-NDC)]·3H2O (11) The mixture of CuCl2·2H2O (0.034 g, 0.2 mmol), 1,4-H2NDC (0.032 g, 0.15 mmol), 3-dpba (0.030 g, 0.1 mmol), H2O (8.4 mL), and NaOH (0.014 g, 0.36 mmol) was stirred for 30 min in air, then transferred and sealed in a 25ml Teflon reactor, which was heated at 120 °C for 6 days. After slow cooling to room temperature, blue block crystals of 11 were collected in 25% yield based on Cu. C26H26CuN4O9 (602.05): calcd. C 51.83, H 4.32, N 9.30; found C 51.86, H 4.31, N 9.35. IR (KBr, cm-1): 3442 (w), 2360 (w), 1697 (m), 1650 (s), 1616 (m), 1558 (s), 1546 (m), 1477 (m), 1419 (m), 1361 (s), 1325 (m), 1211 (m), 1161 (m), 946 (w), 785 (w), 694 (m), 584 (w). Synthesis of [Cu(3-dpyh)(1,4-NDC)(H2O)]·3H2O (12) The synthesis method of 12 is similar to that of 11 except for ligand 3-dpyh (0.033 g, 0.1 mmol) as the substitute of 3-dpba, and different amount of NaOH (0.013 g, 0.34 mmol) was added to adjust the systematic pH. Blue block crystals of 12 were collected in 27% yield based on Cu. C30H36CuN4O10 (676.17): calcd. C 53.24, H 5.32, N 8.28; found C 53.22, 8


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H 5.30, N 8.29. IR (KBr, cm-1): 3413 (w), 2935 (w), 2356 (w), 1652 (s), 1606 (s), 1558 (s), 1510 (m), 1473 (m), 1458 (m), 1400 (m), 1357 (s), 1315 (m), 1257 (w), 1164 (w), 1033 (w), 954 (w), 800 (m), 700 (m), 655 (w), 586 (w). Synthesis of [Cu(3-dpyh)0.5(1,4-NDC)]·H2O (13) The synthesis method of 13 is similar to that of 12 except for different amount of NaOH (0.016 g, 0.40 mmol) was added to adjust the systematic pH. Green block crystals of 13 were collected in 32% yield based on Cu. C21H19CuN2O6 (458.92): calcd. C 54.91, H 4.14, N 6.10; found C 54.93, H 4.11, N 6.13. IR (KBr, cm-1): 3344 (w), 2937 (w), 2358 (w), 1641 (s), 1606 (m), 1575 (m), 1521 (w), 1458 (m), 1400 (s), 1352 (s), 1282 (m), 1259 (m), 1126 (m), 1029 (m), 975 (w), 862 (w), 788 (m), 665 (w), 594 (w).

RESULTS AND DISCUSSION Structure Description of 1. The crystal structure of 1 with the coordination environment of CuII centers is depicted in Figure 1a. Each CuII atom is four-coordinated by two pyridyl N atoms from two 3-dppa with the Cu-N distances of 2.081(2) and 2.0757(19) Å, and two O atoms from two 1,3,5-HBTC anions with the Cu-O distances of 1.9368(14) and 1.9182(13) Å, showing a distorted tetrahedral geometry. In 1, the two carboxyl groups of 1,3,5-HBTC adopt µ1-η1:η0 coordination mode and the third one was protonated. The neighboring CuII ions are linked by pairs of 1,3,5-HBTC and 3-dppa ligands to form an infrequent 1D ∞-like chain with the Cu···Cu distance of 10.38 Å (Figure 1b, Figure S1), in which the 1,3,5-HBTC shows a bis(monodentate) bridging mode and the 3-dppa ligand exhibits a µ2-bridging mode (Table 3). It is noted that the [Cu-3-dppa]n chain displays a meso-helical feature (Figure 1c). As shown in Figure S2, the adjacent 1D ∞-like chains are further connected by hydrogen-bonding interactions [N4···O7 = 2.7876 Å] between the amide groups from adjacent 1D chains to give a 3D supramolecular framework. Insert Figure 1 Structure Description of 2. Compared with complex 1, a longer 3-dpha was used as the substitute of 3-dppa in 2, a 2D network was obtained. As illustrated in Figure 9



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2a, the square-pyramidal CuII ion is coordinated by two symmetry-related oxygen atoms (O1, O3) from two 1,3,5-HBTC anions, two nitrogen atoms (N1, N3) from two 3-dpha, and one coordinated water molecule with the Cu-O and Cu-N bond distances of 1.918(3), 1.930(3), 2.052(4), 2.076(4), and 2.380(3) Å, respectively. In 2, the 1,3,5-HBTC anion shows a similar “V” shaped bis(monodentate) bridging coordination mode to that in 1 (Table 3), which connects the adjacent CuII ions to form a single-strand helix chain with the Cu···Cu separation of 9.80 Å (Figure 2b). The third carboxyl group of 1,3,5-HBTC was also protonated, which is same as that in 1. The 3-dpha displays a µ2-bridging mode connecting the CuII ions to build a [Cu-3-dpha]n meso-helical chain with Cu···Cu distance of 15.31 Å (Figure 2c). Adjacent [Cu-3-dpha]n meso-helical chains were linked by 1,3,5-HBTC anions to form a 2D (2,4) undulated net, as shown in Figure 2d and Figure S3. In this 2D layer, every two 3-dpha and two 1,3,5-HBTC anions are connected by four CuII ions to construct a chair conformational [Cu4(3-dpha)2(1,3,5-BTC)2] hexagonal ring. The ring diameters, defined as the distance between two symmetry-related opposing CuII ions, range from 11.26 to 24.17 Å. In addition, the adjacent 2D layers are connected by N4–H4A···O2W [3.0737 Å] hydrogen-bonding interactions to produce a 3D supramolecular framework (Figure S4). Insert Figure 2 Structure Description of 3. The asymmetric unit of 3 contains three CuII ions, one 3-dpsea ligand, two 1,3,5-BTC anions, five coordinated water molecules, and four lattice water molecules. There are two crystallographically independent CuII ions in the

crystal

structure

of

3.

Cu1

ions

possesses

typical

five-coordinated

square-pyramidal geometry {CuO5}, as depicted in Figure 3a, which is coordinated by two oxygen atoms from two different 1,3,5-BTC anions [Cu1-O5 and Cu1-O5#1, 1.950(3) Å] and three oxygen atom from three coordinated water molecules [Cu1-O1W = 2.192(5), Cu1-O2W and Cu1-O2W#1, 1.982(3) Å]. Cu2 is coordinated by two oxygen atoms from two different 1,3,5-BTC anions [Cu1-O2 = 1.942(3), Cu1-O3 = 1.974(3) Å], one oxygen atom from one coordinated water molecule 10


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[Cu1-O3W = 1.980(3) Å], and one nitrogen atom from one 3-dpsea ligand [Cu1-N2 = 2.015(4) Å], showing a distorted tetrahedral arrangement {CuNO3}. All the carboxyl groups from 1,3,5-BTC anion are deprotonated and adopt µ1-η1:η0 mode (Table 3), which link the CuII ions to generate a 2D sheet (Figure 3b). Further, the sheets are extended by µ2-bridging 3-dpsea ligands via Cu–N bonds to yield a complicated 3D framework (Figure S5). In order to better understand the whole structure, we can simplify the intricate structure as node-and-connecting nets. The 1,3,5-BTC anions can be assigned to three-connectors, while the Cu1/Cu2 ions can be considered as two-/three-connectors, and the 3-dpsea ligands can be viewed as linkers. Thus, the structure of 3 can be simplified as a trinodal (2,3,3)-connected topology with the Schläfli symbol of (10·122)2(103)2(12) (Figure 3c). Three identical nets interpenetrate each other giving rise to a 3-fold interpenetrating framework (Figure 3e). As shown in Figures 3d, the 3-fold interpenetrating 3D framework generated by the interlaced 2D layers is different from the interpenetrating framework formed by non-interpenetrating 2D layers in our previous work14, which may broaden insight into the CPs related to the interpenetrating framework. Insert Figure 3 Structure Description of 4. The asymmetric unit of 4 contains one CuII ion, one 3-dpba ligand, one 1,2-BDC anion, and one lattice water molecule. Each CuII ion is four-coordinated by two N atoms from two 3-dpba ligands [Cu1–N1 = 1.990(7) Å and Cu1–N2 = 2.001(7) Å], two carboxyl oxygen atoms from two different 1,2-BDC anions [Cu1–O1 = 1.970(6) Å and Cu1–O3 = 1.994(6) Å] in a distorted tetrahedral environment (Figure 4a). Adjacent CuII ions are linked by µ2-bridging 3-dpba ligands to yield a 1D helical chain (Figure 4b). The 1D helical chains in perpendicular direction are further connected by the 1,2-BDC anions to form an uncommon 2D network (Figure 4c). The Cu···Cu separations bridged by 1,2-BDC anions and 3-dpba ligands are 5.60 and 10.88 Å, respectively. Topologically, the CuII ions can be defined as 4-connected nodes, the 1,2-BDC anions can be considered as 2-connected nodes, and the 3-dpba ligands can be regarded as linkers. Thus, the structure of 4 can be 11



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described as a (2,4)-connected (4·124·14)(4) net (Figure 4d). In addition, the O1W atom from the lattice water molecule is a hydrogen bond donor and acceptor, which extends the 2D layer into a 3D supramolecular architecture through intermolecular O1W–H1WA···O1 and N5–H5B···O1W hydrogen-bonding interactions [2.8315 and 2.9651 Å] (Figure S6). Insert Figure 4

Structure Description of 5 and 6. Compared with complex 4, the longer 3-dpha and 3-dpsea ligands with four and eight -(CH2)- spacers were employed in 5 and 6, respectively. The structures of omplexes 5 and 6 are very similar, therefore only the structure of 6 is described here in detail. The structure of complex 5 are shown in Figures S7-S10 in the Supporting Information. As shown in Figure 5a, the asymmetric unit of 6 contains one CuII ion, one 1,2-BDC anion, one 3-dpsea ligand and one lattice water molecule. The CuII ion adopts a tetrahedral coordination geometry, coordinated by two carboxylic O atoms from two 1,2-BDC anions (Cu1-O1 and Cu1-O1#1, 2.0069(19) Å) and two N atoms from two 3-dpsea ligands (Cu1-N1 and Cu1-N1#1, 1.997(2) Å). The 3-dpsea ligand adopts a µ2-bridging mode with the dihedral angle between the two pyridine rings of 0 °. Each 3-dpsea ligand bridges the adjacent CuII ions to yield wavelike meso-helical chains (Figure 5b) with a Cu···Cu distance of 21.51 Å, which are further linked by 1,2-BDC anions to form a 2D layer (Figure 5d). Interestingly, the 1,2-BDC anion connect adjacent CuII ions to generate a 1D helical chain (Figure 5c). The 2D layer can also be considered as an undulated sql net by repeating the [Cu4(3-dpsea)2(1,2-BDC)2] unit (Figure 5e). Notably, the [Cu4(3-dpsea)2(1,2-BDC)2] unit has a square window with dimension of 18.11×26.33 Å2. These 2D layers are further extended by π−π stacking interactions [values of the shortest centroid−centroid distance and offset angle of 3.5730 Å and 0 °, respectively] to a 3D supramolecular structure (Figure S11). Insert Figure 5

12


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Structure Description of 7. As shown in Figure 6a, complex 7 contains two CuII ions, two 1,3-BDC anions, one 3-dpyp ligand, four coordinated water molecules and three lattice water molecules. The CuII center is five-coordinated by two carboxylic oxygen atoms from two 1,3-BDC anions (Cu1-O1 = 1.9563(19), Cu1-O3 = 1.9622(18) Å), one nitrogen atom from 3-dpyp ligand (Cu1-N1 = 2.015(2) Å), and two oxygen atoms from coordinated water molecules (Cu1-O1W = 2.331(2), Cu1-O2W = 1.9540(18) Å), showing a distorted square-pyramidal coordination geometry. The 1,3-BDC show bis(monodentate) bridging coordination mode, connecting adjacent CuII ions to form a 1D [Cu-1,3-BDC]n zigzag chain with the Cu···Cu separation of 7.95 Å (Figure S12). The 3-dpyp ligand exhibits a bidentate coordination mode with a “U-shape” conformation, attaching to one side of the [Cu-1,3-BDC]n zigzag chain to build a binuclear ring (Figure 6b). The chains are extended into 2D layers through two kinds of π-π stacking interactions, one is between aromatic rings from adjacent chains with a centroid−centroid distance of 3.7968 Å and offset angle of 0 °, and the other is between pyridine rings from adjacent chains with a centroid−centroid distance of 3.5549 Å and offset angle of 0 ° (Figure S13). Insert Figure 6 Structure Description of 8-10. In order to investigate the influence of flexible N-donor ligands with different spacers on the structures, three kinds of flexible bis-pyridyl-bis-amide ligands with different –(CH2)n– length (n = 1, 5, 8) were used in complexes 8-10. Structural analyses indicate that the final networks of the three complexes are very similar, as shown in Figures 7-10, so complex 8 is discussed here as an example. The asymmetric unit of 8 contains one CuII ion, one 3-dppa ligand, one 1,3-BDC anion, one coordinated water molecules and two lattice water molecules (Figure 7). The CuII ion is five-coordinated by two carboxylic oxygen atoms from two 1,3-BDC anions (Cu1-O1 = 1.9646(17), Cu1-O4 = 1.9777(17) Å), two nitrogen atoms from two different 3-dppa ligands (Cu1-N1 = 2.026(2), Cu1-N4 = 2.0342 Å), and one oxygen atom from coordinated water molecule (Cu1-O1W = 2.319(2) Å) in a 13



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distorted square-pyramidal geometry. As shown in Figure 8, the 3-dppa ligands connect adjacent CuII ions to form a wave-like chain. Each 1,3-BDC anion also links two CuII centers with its two carboxylic groups in a monodentate mode to generate a 1D helical chain (Figure 9). The two kinds of chains crossed to yield a 2D (4,4) network through sharing the central CuII atoms (Figure 10 and Figure S14). The 2D sheets are further extended into a 3D supramolecular architecture by the hydrogen bonding interaction between the nitrogen atoms from amide groups and carboxyl oxygen atoms (N2–H2A···O2, 2.9256 Å) (Figure S15). Insert Figure 7 Insert Figure 8 Insert Figure 9 Insert Figure 10 Structure Description of 11. Single-crystal X-ray structural analysis shows that the asymmetric unit of 11 contains one CuII ion, one 1,4-NDC anion, one 3-dpba ligand, and three lattice water molecules. As illustrated in Figure 11a, the distorted tetrahedral CuII ion is coordinated by two oxygen atoms (O1, O1#1) from two 1,4-NDC anions and two nitrogen atoms (N1, N1#1) from two distinct 3-dpba with the Cu-O and Cu-N bond distances of 1.980(5) and 2.006(6) Å, respectively. In 11, the 3-dpba adopts a bidentate mode to coordinate with two adjacent CuII ions, forming a 1D helical chain with the Cu···Cu separation of 8.96 Å (Figure 11b). The 1,4-NDC anions adopt bis(monodentate) bridging mode linking adjacent CuII ions to form a meso-helix with the Cu···Cu separation of 10.91 Å (Figure 11c), which are further connected by 3-dpba ligands to give a 2D puckered (4,4) network (Figure 11d). In order to simplify the 2D network of complex 11, the CuII ions can be considered as connecting nodes, and the ligands 1, 4-NDC and 3-dpba can be regarded as spacers, which suggests the 4-connected sql topology (Figure 11e). In addition, the adjacent 2D layers are interconnected by three kinds of N2–H2A···O1W [2.9529 Å], O1W–H1WA···O2W

[2.9773

Å],

and

O2W–H2WA···O2

14


[2.8762

Å]

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hydrogen-bonding interactions that further extend the crystal structure to a 3D supramolecular framework (Figure S16). Insert Figure 11 Structure Description of 12. When the 3-dpba ligand in 11 was replaced by the longer 3-dpyh ligand, a 2D undulated layer of 12 was obtained. The asymmetric unit of 12 contains one crystallographically independent CuII ion, one 1,4-NDC anion, one 3-dpyh ligand, one coordinated water molecule, and three lattice water molecules. As shown in Figure 12a, the CuII center is five-coordinated by two carboxylic oxygen atoms from two individual 1,4-NDC anions [Cu1-O1 = 1.949(2), Cu1-O6 = 1.982(2) Å], two nitrogen atoms from two different 3-dpyh ligands [Cu1-N1 = 2.024(3), Cu1-N2 = 2.029(3) Å], and one oxygen atom from one coordinated water molecule [Cu1-O1W = 2.307(3) Å], displaying a distorted square-pyramidal coordination geometry. Each 1,4-NDC anion adopting bis(monodentate) coordination mode links two adjacent CuII ions to afford a 1D linear chain (Figure S17). If 1,4-NDC anions are neglected, CuII ions are bridged by 3-dpyh ligands to form a 1D Ω-like chain (Figure 12b). The two types of chains are linked to generate a 2D undulated layer through sharing the central CuII atoms. Notably, the 2D network has two kinds of large rectangular windows with approximate dimensions of 20.83×21.02 Å2 for A and 21.55×22.44 Å2 for B, which built up by four CuII atoms, two 3-dpyh ligands, and two 1,4-NDC anions (Figure 12c). For convenience, if Cu1 ions are viewed as 4-connected nodes, 1,4-NDC anions and 3-dpyh ligands are viewed as linkers, the undulated layer can be described as a 4-connected sql topology with the point symbol of (44·62) (Figure 12d). In addition, there exist hydrogen-bonding interactions associated with oxygen atom (O13) of 3-dpyh ligands and oxygen atom (O1W) from coordinated water molecule (O13···O1W distance of 2.7443 Å) between the adjacent layers, which extend the 2D undulated layers to a 3D supramolecular architecture (Figure S18). Insert Figure 12

15



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Structure Description of 13. In order to investigate the influence of pH on the ultimate structures, different pH was adjusted to construct complex 13. The asymmetric unit of 13 contains one CuII ion, half a 1,4-NDC anion, one 3-dpyh ligand, and one lattice water molecule. As shown in Figure 13a, the CuII center is coordinated by four carboxyl oxygen atoms from four 1,4-NDC anions and one nitrogen atom from one 3-dpyh ligand to give a {CuO4N} square-pyramidal geometry [Cu1-O2 = 1.9636(14), Cu1-O3 = 1.9676(14), Cu1-O4 = 1.9785(15), Cu1-O5 = 1.9708(14), and Cu1-N1 = 2.2170(16) Å]. Each 1,4-NDC anion coordinates to four CuII ions in the bis(bidentate) bridging coordination mode (Table 3). As a result, two CuII ions and four carboxyl groups constitute a bimetallic [Cu2(CO2)4] unit. Each bimetallic unit connects four 1,4-NDC anions, and in turn each 1,4-NDC anion links two bimetallic units to give a 2D sheet, showing a window with dimension of 14.34 Å ×16.27 Å (Figure 13b). The 3-dpyh ligands bridge the adjacent sheets in the bidentate bridging coordination mode to generate a 3D framework (Figure 13c). From the topological view, if each [Cu2(CO2)4] unit is considered as a 4-connected node and the 1,4-NDC anion and 3-dpyh ligand are considered as linkers, the structure of 13 is an α-Po network with the dimensional size of 10.84 Å×10.84 Å×24.75 Å. In order to minimize the big void cavities and stabilize the framework, the potential voids formed by a single 3D framework show incorporation of another identical network, thus giving a 3-fold interpenetrating 3D framework (Figure 13d). Insert Figure 13 Influence of the flexible bis-pyridyl-bis-amide ligands with different spacer length, polycarboxylic anions, and the pH on the dimensionalities of the coordination

polymers.

In

this

work,

we

selected

seven

flexible

bis-pyridyl-bis-amide ligands 3-dppa, 3-dpba, 3-dpha, 3-dppia, 3-dpsea, 3-dpyp, and 3-dpyh to assemble with CuII ion and polycarboxylates, intending to observe their effect on the structures of the coordination polymers. For complexes 1-3 constructed from the same auxiliary ligand 1,3,5-H3BTC and different bis-pyridyl-bis-amide ligands (3-dppa in 1, 3-dpha in 2, 3-dpsea in 3), complex 1 showed a 1D ∞-like chain, 16


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complex 2 exhibited 2D sheet structure, and complex 3 is a 3D 3-fold interpenetrating framework. It is the different -(CH2)n- (n = 1, 4, and 8) spacers of bis-pyridyl-bis-amide ligands that lead to the various structures of these complexes from 1D chain to 2D sheet, and to 3D frameworks, in which the Cu···Cu distance are 10.38 Å for 1, 15.31 Å for 2, and 21.07 Å for 3 by the connection of ligands 3-dppa, 3-dpha and 3-dpsea. The results indicate that the spacer length of the bis-pyridyl-bis-amide ligands show great effects on the dimensionality of the complexes (Figure 14). Complexes 4-6 are based on the same secondary ligand 1,3-H2BDC and different flexible bis-pyridyl-bis-amide ligands with -(CH2)n- (n = 2, 4, and 8) spacers. In complex 4, the µ2-bridging 3-dpba ligands are linked by adjacent CuII ions to yield a 1D helical chain. Finally, a (2,4)-connected (4·124·14)(4) 2D network was obtained. When the 3-dpba ligand was replaced by the longer 3-dpha and 3-dpsea in complexes 5-6, the meso-helical chains of [Cu-3-dpha]n and [Cu-3-dpsea]n were obtained, respectively. The complexes 5-6 show similar undulated sql networks, but exhibit different square windows with dimensions of 14.57×21.94 Å2 for 5 and 18.11×26.33 Å2 for 6. These results reveal that the spacer length associated the number of -CH2group of the bis-pyridyl-bis-amide ligands greatly affects not only the dimensionality but also the size of loop subunits of the complexes. As expected, the spacer lengths of the flexible bis-pyridyl-bis-amide ligands also show significant effect on the architectures of the complexes 7-10 based on the 1,3-BDC auxiliary ligand, which is similar to that of complexes 4-6. The complex 7 showed a 1D chain, in which 3-dpyp exhibits a “U-shape” conformation. Complexes 8-10 have similar 2D layer, but display different square window with dimensions of 13.01×19.58 Å2, 8.71×24.10 Å2, and 17.62×28.90 Å2, respectively. Complexes 11–13 based on the same 1,4-NDC anion also exhibit the effect of length and conformation of bis-pyridyl-bis-amide ligands on the dimensionality of target complexes. As described above, 11 and 12 exhibit different 2D networks, in which the 3-dpba and 3-dpyh show µ2-bridging mode with the different dihedral angles (64.86 ° in 11 and 0.61 ° in 12) among two pyridyl rings within each bis-pyridyl-bis-amide ligand, while 17



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in complex 13, the 3-dpyh adopts a µ2-bridging mode with the corresponding dihedral angle of 0 °, resulting in the formation of a 3D 3-fold interpenetrating framework. On the other hand, the polycarboxylate anions also play important role in the formation of the structures based on the same bis-pyridyl-bis-amide ligand. Complexes 1 and 8, 2 and 5, 4 and 11, as well as 3, 6, and 10, exhibit the effect of the number and position of the carboxyl groups on the resultant structures. Compared with dicarboxylate anions, the 1,3,5-BTC anion has an extra carboxyl group. Usually, the additional carboxyl group can increase the connection number of the ligand, which further results in different structure motifs. Take complexes 3 and 6 for example, each 1,3,5-BTC anion as a 3-connected node bridges the CuII ions to yield a 2D layer in 3, while each 1,2-BDC anion links the CuII ions to generate a 1D helical chain in 6. The 2D layers in 3 are further linked by the 3-dpsea ligands to form a 3D 3-fold interpenetrating framework, whereas, in 6, the chains are further connected by the 3-dpsea ligands to furnish a 2D network. Obviously, the number of the carboxyl group show an important influence on the structures of the complexes. While complexes 6 and 10 show effect of the position of carboxyl groups on the structures. Although the 1,2-BDC and 1,3-BDC anions serve as dicarboxylates with the rigid benzene ring spacers, the two carboxyl groups are located in the 1,2- and 1,3-position with the angles of 60° and 120°, respectively. As a result, the 1,2-BDC anions link the adjacent CuII ions to construct a 1D helical chain, while 1,3-BDC anions connect the adjacent CuII ions to form a 1D linear chain. The different 1D Cu-dicarboxylate chains finally result in the different 2D networks in 6 and 10. Furthermore, the pH plays an important role in the formation of the structures. For complexes 1-3, when the pH value was adjusted to about 6.0, two carboxyl groups of 1,3,5-H3BTC were deprotonated, which connected CuII ions to form 1D [Cu-1,3,5-HBTC]n chains in complexes 1 and 2. When the pH was increased to about 7.0, all the three carboxyl groups of 1,3,5-H3BTC were deprotonated and coordinated with CuII ions, resulting in a 2D [Cu-1,3,5-BTC]n layer in 3. Meanwhile, for complexes 12 and 13 based on the same 3-dpyh ligand and 1,4-NDC anion, when the pH value was adjusted to about 5.5 in 12, each carboxyl group of 1,4-NDC anion 18


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adopts µ1-η1:η0 mode to coordinate with CuII ions, resulting in the formation of a 2D layer. However, when the pH was increased to about 7.0, each carboxyl group of 1,4-NDC anion shows µ1-η1:η1 mode in 13, leading to a 3D 3-fold interpenetrating network. In a word, the structural differences show that the flexible bis-pyridyl-bis-amide ligands with different spacer lengths, polycarboxylic anions, and the pH have great influences on the assembly and structures of the final complexes. Insert Figure 14 IR spectra of complexes 1–13 The IR spectra of complexes 1–13 are determined in the frequency range of 500-4000 cm-1, as shown in Figure S19. The strong peaks at 1616 and 1217 cm-1 for 1, 1628 and 1230 cm-1 for 2, 1616 and 1213 cm-1 for 3, 1649 and 1290 cm-1 for 4, 1600 and 1247 cm-1 for 5, 1622 and 1278 cm-1 for 6, 1620 and 1272 cm-1 for 7, 1606 and 1274 cm-1 for 8, 1612 and 1213 cm-1 for 9, 1608 and 1245 cm-1 for 10, 1616 and 1211 cm-1 for 11, 1606 and 1257 cm-1 for 12, 1606 and 1259 cm-1 for 13, may be attributed to the asymmetric and symmetric vibrations of carboxyl groups.15 The bands around 1656 cm-1 for 1, 1665 cm-1 for 2, 1685 cm-1 for 3, 1651 cm-1 for 4, 1654 cm-1 for 5, 1664 cm-1 for 6, 1654 cm-1 for 7, 1666 cm-1 for 8, 1681 cm-1 for 9, 1650 cm-1 for 10, 1650 cm-1 for 11, 1652 cm-1 for 12, and 1641 cm-1 for 13, are characteristic of the carbonyl groups.16 The presence of the characteristic bands at 1523, 1475, 1421, 1357 cm-1 for 1, 1541, 1477, 1425, 1363 cm-1 for 2, 1541, 1473, 1429, 1363 cm-1 for 3, 1558, 1481, 1419, 1384 cm-1 for 4, 1531, 1488, 1425, 1386 cm-1 for 5, 1554, 1485, 1431, 1386 cm-1 for 6, 1562, 1479, 1436, 1388 cm-1 for 7, 1523, 1481, 1427, 1367 cm-1 for 8, 1556, 1483, 1431, 1375 cm-1 for 9, 1556, 1485, 1408, 1373 cm-1 for 10, 1558, 1477, 1419, 1361 cm-1 for 11, 1558, 1458, 1400, 1357 cm-1 for 12, 1521, 1458, 1400, 1352 cm-1 for 13, suggest the νC-N stretching vibrations of the pyridyl ring of the bis-pyridyl-bis-amide ligands.16 For complexes 2–4 and 6-13, the strong absorption peaks observed at 3433, 3363, 3309, 3269, 3292, 3217, 3379, 3271, 3442, 3413, and 3344 cm–1 indicate the presence of –OH groups of water molecules, respectively.15 19



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The bands at 1701 and 1702 cm-1 are assigned to stretching and bending vibrations of –COOH groups for complexes 1 and 2, respectively.15 Powder X-ray diffraction and Thermal analyses The powder X-ray diffraction (PXRD) patterns for complexes 1-13 are presented in Figure S20. The as-synthesized patterns are in good agreement with the corresponding simulated ones, indicating the phase purities of the samples. To fully characterize the complexes in terms of thermal stability, the thermal behaviors of 1-13 were examined by TGA. The experiments were performed on samples consisting of numerous single crystals under N2 atmosphere with a heating rate of 10 oC/min (Figure S21). For complexes 1 and 5, the weight loss corresponding to the release of organic ligands is observed from 234 to 545 °C for 1, and 140 to 474 °C for 5. The remaining residues are assigned to the CuO (obsd. 15.52%, calcd. 15.15% for 1, and obsd. 15.23%, calcd. 15.21% for 5). The TGA curves of 2-4 show that the first weight losses from room temperature to 101, 105, 107 °C correspond to the loss of water molecules (obsd. 6.19, 14.03, 3.85%, calcd. 5.94, 14.45, 3.49%), respectively. The second weight losses of 80.82, 64.76, 80.88% (calcd. 80.86, 64.15, 81.00%) in the temperature ranges of 323-543, 171-522, 150-464 °C can be assigned to the release of organic ligands, leading to the formation of CuO as the residues (obsd. 12.99, 21.21, 15.27%, calcd. 13.20, 21.40, 15.51%). Complexes 6-10 show two steps of weight losses. The first weight losses of 3.29, 14.19, 9.94, 11.96, 12.12% in the range of 32-130, 53-151, 45-143, 55-129, 41-126 °C are consistent with the removal of lattice or/and coordination water molecules (calcd. 3.00, 14.55, 10.04, 11.76, 12.21%). The second steps from 242-608, 244-529, 217-693, 373-624, 221-695 °C can be attributed to the release of the organic ligands. The remaining weights correspond to CuO residue (obsd. 13.12, 9.76, 14.53, 13.11, 11.98%, calcd. 13.33, 9.24, 14.87, 13.07, 12.06%). As expected, in the TGA curves of complexes 11-13, the weight losses in the ranges of 40-140, 26-111, 30-95 °C correspond to the departure of lattice or/and coordination water molecules (obsd. 9.13, 10.33, 3.62%, calcd. 8.97, 10.65, 3.92%). The removals of the organic components occur in the ranges of 20


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184-672, 208-505, 269-587 °C, respectively. The remaining residues corresponding to the formation of CuO are 13.26, 11.59, 17.29% (calcd. 13.29, 11.83, 17.43%), respectively. Fluorescent property The fluorescent properties of the CuII complexes 1-13, together with the free ligands were studied in the solid state at room temperature. The emission spectra of the complexes and the free organic ligands are depicted in Figure 15. The free 3-dppa, 3-dpha, 3-dpsea, 3-dpba, 3-dpyp, 3-dppia, and 3-dpyh display intense emission bands with the maxima at 455 nm, 385 nm, 397 nm, 447 nm, 389 nm, 398 nm, and 398 nm upon excitation at 320 nm, respectively, which may be ascribed to the π*→π transitions.17 As strong electron withdrawing groups, carboxylate ligands almost have no significant contribution to the fluorescent emission.17a, 18 Thus, the emission of the coordination polymers is mainly associated with the presence of the N-donor ligands.18 For complexes 1 and 8, the emission peaks at 399 nm are found (λex = 320 nm), which is blue-shifted 56 nm as compared with the free 3-dppa ligand. Complexes 2 and 5 exhibit intense emission bands at 400 nm for 2, and 404 nm for 5 with excitation band at 320 nm, which are red-shifted (15 nm for 2 and 19 nm for 5) comparing with the free 3-dpha. Complexes 3, 6 and 10 show intense emission bands with the maxima at ca. 400, 396 and 396 nm upon excitation at 320 nm, which are similar to that of 3-dpsea (λex = 320 nm). For complexes 4 and 11, the emission bands are highly blue-shifted (48 nm) compared to the free 3-dpba. As for 7, the emission peak exhibits an obviously red shift (about 31 nm) with respect to the free 3-dpyp. The emission band of 9 appears at 398 nm, which is same as that of free 3-dppia. Complexes 12-13 based on the same organic ligands show different emission peaks (397 nm for 12 and 384 nm for 13). As is known, CuII complexes do not contain d10 metal centers, but a series of fluorescent CuII complexes have been reported.18 Density functional theory calculation indicates that the fluorescence of CuII coordination complexes may be mainly attributed to the coupling of ligand-to-metal charge transfer (LMCT) and 21



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ligand-to-ligand charge-transfer (LLCT).19 Thus the emission bands of the title CuII complexes may also be assigned to the LMCT or the LLCT as previously reported.18a, 18c, 20

The reduction of emission intensity and shift of the emission peaks in complexes

1-2, 4-5, 7-8, 10-11 and 13 may be attributed to the coordination of ligands to the CuII center, which enhances the loss of energy through a radiationless pathway, and may be assigned to the LMCT.18c, 20 The emission bands of complexes 3, 6, 9, 10 or 12 are very similar to that of free 3-dpsea/3-dppia/3-dpyh ligands, which can probably be assigned to the LLCT of 3-dpsea/3-dppia/3-dpyh.18a As described above, the intensity or position or shape of emission peaks in complexes 1-13 are different from each other, which may be ascribed to the different coordination fashions of organic ligands and their different components and architectures.18 Insert Figure 15 Photocatalytic property Photocatalysts have attracted much attention due to their potential applications in purifying water and air by thoroughly decomposing organic pollutants.8a, 22 Herein, methylene blue (MB), as a model of dye contaminant, was selected for evaluating the activities of photocatalysts in the purification of wastewater. We have investigated the photocatalytic performances of complexes 1−13 for the photodegradation of MB under UV irradiation. Complexes 3 and 13 have good photocatalytic activities. However, no obviously photocatalytic behavior was observed for complexes 2 and 4. The results suggest that the more extended networks may aid in the transport of excited holes/electrons to the surface to initiate the photocatalytic decomposition reaction with MB.10b Thus, the structural characters of complexes, such as the number of the coordinated water molecules, the coordination environments of the central metals, the extent of the conjugation, and the sizes of the metal−oxygen clusters, are the main factor that influences their photocatalytic activities.9b, 10b, 23 As is known, in the presence of UV light, there is an electron transfer from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular 22


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orbital (LUMO). The HOMO is mainly contributed by oxygen and/or nitrogen 2p bonding orbitals (valence band) and the LUMO by empty Cu orbitals (conduction band), charge transfer actually takes place from oxygen and (or) nitrogen to Cu on photoexcitation. The HOMO strongly demands one electron to return to its stable state.10a, 24 Therefore, one electron was captured from water molecules, which was oxygenated into the ·OH active species. Then the ·OH radicals could cleave MB effectively to complete the photocatalytic process.10a, 24 As shown in Figure 16 and Figure S22, the absorption peaks of MB decreased obviously along with the reaction time. In addition, the concentrations of MB (C) versus reaction time (t) of complexes 1−13 are plotted in Figure 17. It can be seen that the photocatalytic activities increase from 5% (without any catalyst) to 56% for 3, and 67% for 13 after 2 h of irradiation. In addition, the photocatalytic performance of 3 and

13

were

better

than

that

of

a

highly

connected

framework

[Cu5(H2L)2(btb)2(OH)2]·3H2O [btb = 1,4-bis(1,2,4-triazol-1-yl)butane and H6L = 2,4,6-trimethylbenzene-1,3,5-tris(methylenephosphonic acid)] for the decomposition of MB under UV irradiation.10d For complex 13, approximately 67% of MB was decomposed after 120 min, whereas 59% of MB was degraded after 120 min for [Cu5(H2L)2(btb)2(OH)2]·3H2O. These results suggest that complexes 3 and 13 may be good candidates for photocatalytic degradation of MB. In order to investigate the stability of complexes 1−13 as photocatalysts, we repeated the IR patterns of complexes 1−13 after the photocatalytic experiments, and the IR spectra and PXRD are almost identical with those of the as-prepared samples (Figure S19 and Figure S20). Control experiments were carried out for the title complexes. The CuCl2·2H2O, seven flexible bis-pyridyl-bis-amide ligands, and four aromatic carboxylates were added to the MB solution under UV irradiation, respectively. However, they did not show observable photocatalytic activities. In addition, no obvious MB degradation was observed in the dark. The results indicate that some title complexes may be good candidates for the photocatalytic degradation of MB, which would have potential photocatalytic activity in the redution of some other organic dyes. 23



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In order to evaluate reproducible ability of the title complexes, the repeated photocatalysis experiment was also studied with a constant MB concentration. Take complexes 3 and 13 for examples. After each cycle of MB photodegradation, the photocatalysts were filtered, washed with distilled water under stirring for 120 min, then filtered again. After drying in air, the recyclable samples were obtained. As shown in Figure S23, there is no significant reduction of decolorization rate when the photocatalyst is used for five times in the same photodegradation process. The result indicated that the photocatalysis of 3 and 13 have good reproducibilities. After photocatalysis, the IR spectra and PXRD of photocatalysts 3 and 13 were nearly identical to those of the original complexes(Figure S19 and Figure S20), implying that complexes 3 and 13 are stable potential photocatalysts. Insert Figure 16 Insert Figure 17 CONCLUSION Thirteen new CuII coordination polymers were successfully synthesized under hydrothermal conditions through variation of the bis-pyridyl-bis-amide and polycarboxylate ligands. The title complexes display versatile coordination features with 1D, 2D, and 3D frameworks. The structural diversities of the title complexes indicate that the flexible bis-pyridyl-bis-amide ligands not only are good candidates for the construction of coordination polymers, but also play an important role in tuning the structures of the title complexes. Moreover, the polycarboxylates also greatly contributes to the structural diversities of the final frameworks. The fluorescent and photocatalytic behaviors of 1−13 imply that complexes 3 and 13 may be good candidates for photoactive materials.

ASSOCIATED CONTENT Supporting Information X-ray crystallographic data in CIF format, selected bond lengths and angles, structure illustrations for complexes 1-13, IR spectra of complexes 1–13, 24


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thermogravimetric analysis (TGA) for complexes 1-13, photocatalytic properties for complexes 1-13. These materials are available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] (X.-L.W.). Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS The supports of the National Natural Science Foundation of China (No. 20871022, 21171025), New Century Excellent Talents in University (NCET-09-0853), the Natural Science Foundation of Liaoning Province (No. 201102003) and Program of Innovative Research Team in University of Liaoning Province (LT2012020) are gratefully acknowledged.

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For Table of Contents Use Only

Structural Diversities, Fluorescent and Photocatalytic Properties of a Series of CuII Coordination Polymers Constructed from Flexible Bis-pyridyl-bis-amide Ligands with Different Spacer Length and Different Aromatic Carboxylates Xiu-Li Wang,∗ Jian Luan, Fang-Fang Sui, Hong-Yan Lin, Guo-Cheng Liu, and Chuang Xu

Thirteen CuII coordination polymers based on seven flexible bis-pyridyl-bis-amide ligands and four polycarboxylates have been hydrothermally synthesized. The structural diversity indicates that the N-donor ligands with different spacers and the polycarboxylates play important roles in tuning the dimensionality and structures of the title complexes. The fluorescent and photocatalytic properties of complexes 1–13 have also been investigated.

∗ Corresponding author. Tel: +86-416-3400158 E-mail address: [email protected] (X.-L. Wang) 29



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Figure Captions Figure 1 (a) Coordination environment of the CuII ion in 1 (50% probability displacement ellipsoids). (b) View of the 1D ∞-like double-chain. (c) View of the 1D [Cu-3-dppa]n meso-helical chain. Figure 2 (a) Coordination environment of the CuII ion in 2 (50% probability displacement ellipsoids). (b) View of the 1D [Cu-1,3,5-HBTC]n helical chain. (c) View of the 1D [Cu-3-dpha]n meso-helical chain. (d) View of the 2D wave layer Figure 3 (a) Coordination environment of the CuII ion in 3 (50% probability displacement ellipsoids). (b) View of the 2D sheet. (c) View of the 3D network (d) Schematic representation of 3-fold interpenetrating framework of 3. Figure 4 (a) Coordination environment of the CuII ion in 4 (50% probability displacement ellipsoids). (b) The 3-dpba ligands linking the CuII ions into a 1D helical chain. (c) The [Cu-3-dpba]n helices are extended to a 2D layer by the 1,2-BDC anions. (d) Schematic representation of (2,4)-connected (4·124·14)(4) net. Figure 5 (a) Coordination environment of the CuII ion in 6 (50% probability displacement ellipsoids). (b) View of the 1D meso-helical [Cu-3-dpba]n chain. (c) View of the 1D helical [Cu-1,2-BDC]n chain (d) The 2D undulated net of 6. (e) Schematic representation sql net of 6. Figure 6 (a) Coordination environment of the CuII ion in 7 (50% probability displacement ellipsoids). (b) View of the 1D chain of 7. Figure 7 Coordination environments of the CuII ions in 8-10 (50% probability displacement ellipsoids). Figure 8 View of the 1D [Cu-3-dppa]n chain for 8, [Cu-3-dppia]n chain for 9, [Cu-3-dpsea]n chain for 10. Figure 9 View of the 1D [Cu-1,3-BDC]n chains of 8-10. Figure 10 The 2D nets of 8-10. Figure 11 (a) Coordination environment of the CuII ion in 11 (50% probability 1


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displacement ellipsoids). (b) View of the 1D [Cu-3-dpba]n helical chain. (c) View of the 1D [Cu-1,4-NDC]n meso-helical chain. (d) The 2D net of 11. (e) Schematic representation sql net of 11. Figure 12 (a) Coordination environment of the CuII ion in 12 (50% probability displacement ellipsoids). (b) View of 1D [Cu-3-dyph]n meso-helical chain. (c) View of the 2D undulated layer. (d) Simplification of the structure to an undulated 44-sql layer. Figure 13 Coordination environment of the CuII ion in 13 (50% probability displacement ellipsoids). (b) View of the 2D layer. (c) View of the 3D network. (d) Schematic representation of 3-fold interpenetrating α-Po framework of 13. Figure 14 Influence of the flexible bis-pyridyl-bis-amide ligands and polycarboxylic anions on the structures of the coordination polymers Figure 15 Solid-state photoluminescent emission spectra of free ligands and complexes 1–13 at room temperature. Figure 16 Absorption spectra of the MB solution during the decomposition reaction under UV irradiation with the presence of complexes 3 and 13. Figure 17 Photocatalytic decomposition rates of MB solution under UV irradiation with the use of the title compounds and no crystal in the same conditions. Scheme 1 Seven flexible bis-pyridyl-bis-amide ligands used in this paper.

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Figures

Fig.1

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Fig.2

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Fig.3

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Fig.4

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Fig.5

Fig.6

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Fig.7

Fig.8

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Fig.9

Fig. 10

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Fig.11

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Fig.12

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Fig.13

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Fig. 14

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Fig. 15

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Fig. 16

Fig. 17

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Scheme 1

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Structural Diversities and Fluorescent and Photocatalytic Properties of

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