Syntheses, Structural Evolutions, and Properties of Cd(II) Coordination

Apr 13, 2017 - interconnection of a [Cd-H2L2+]n pcu net and [SO4 ... different coordination modes and join adjacent Cd(II) cations together with L mol...
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Syntheses, Structural Evolutions, and Properties of Cd(II) Coordination Polymers Induced by Bis(pyridyl) Ligand with Chelated or Protonated Spacer and Diverse Counteranions Fa-Yuan Ge, Xin Ma, Dan-Dan Guo, Li-Na Zhu, Zhao-Peng Deng,* Li-Hua Huo, and Shan Gao* Key Laboratory of Functional Inorganic Material Chemistry, Ministry of Education, School of Chemistry and Materials Science, Heilongjiang University, Harbin 150080, People’s Republic of China S Supporting Information *

ABSTRACT: Hydrothermal reaction of Cd(II) metal salts, diverse organic acids, as well as flexible bis(pyridyl) ligand leads to the formation of 10 complexes, namely, [Cd2LCl4]n (1), [Cd(H2L)(SO4)2(H2O)2]n·6nH2O (2), [CdL(malonate)]n·5nH2O (3), [Cd2L(malonate)Cl2(H2O)]n·nH2O (4), [Cd2(H2L)(succinate)3]n·4nH2O (5), [Cd2L(fumarate)2(H2O)2]n·2nH2O (6), [Cd2L(m-BDC2−)2]n·2nH2O (7), [Cd2(L)(p-BDC2−)2(H2O)3]n·3nH2O (8), [Cd3(L)2(p-BDC2−)3(H2O)4]n·nH2O (9), and [Cd3(H2L)(p-BDC2−)2(SO4)2(H2O)3]n·2nH2O (10) (L = N,N′-bis(pyridin-3-ylmethyl)ethane-1,2diamine, m-BDC2− = m-benzene dicarboxylate dianion, p-BDC2− = p-benzene dicarboxylate dianion), which have been characterized by elemental analysis, infrared, thermogravimetric analysis, PL, powder and single-crystal X-ray diffraction. Structural analyses indicate that the diverse coordination modes of the bis(pyridyl) ligand with a chelated or protonated spacer, the feature of different inorganic and organic anions, can effectively influence the topological structures of these complexes. Complex 1 presents a three-dimensional (3D) hybrid network which is accomplished by the interconnection of adjacent Cd(II) cations through L molecules and μ2-Cl− anions. Complex 2 exhibits an interesting pseudo 2-fold interpenetrated network formed by the interconnection of a [Cd-H2L2+]n pcu net and [SO42+-H2O]n pcu net. In complexes 3 and 4, adjacent Cd(II) cations are all bridged by dicarboxylate and L to generate a sql layer. In contrast, complex 5 presents 3-fold parallel interpenetrated sql layer owing to the protonated spacer of H2L2+ cation which extends the size of the quadrate window. The organic dicarboxylates in complexes 6 and 7 present more abundant coordination modes which join adjacent Cd(II) cations together with L molecules, thus giving rise to a different 3D framework with sra and snk topology. The p-BDC2− dianions in complexes 8, 9, and 10 present different coordination modes and join adjacent Cd(II) cations together with L molecules and H2L2+ cations to form a diverse ladder chain, tfc and new (44.611)(66) topology. Luminescent investigation reveals that the emission maximum of these 10 complexes varies from 376 to 450 nm.

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INTRODUCTION Metal−organic coordination polymers (MOCPs) assembled from metal cations or clusters and multitopic organic ligands have aroused a high degree of attention and offer numerous opportunities to modify properties related to gas storage,1−4 separation,5 luminescence,6−8 catalysis,9,10 sensors,11,12 and so forth.13−15 Aside from the metal cations or clusters, welldesigned ligands that have a specific structure directing feature are a key factor for constructing new multifunctional MOCPs with novel topological structures and structure-related properties.16,17 In this sense, bis(pyridyl) molecules with specific coordination directivity have proven to be a class of excellent ligands by virtue of the multiple and changeable spacers, such as aliphatic hydrocarbon, amide, ether, aliphatic amine, and so on.18−25 However, these previous reports mainly concern the length, rigidity-flexibility, as well as the type of spacers, and only a few works pay attention to the coordination and protonation of the spacers. In 2015, our group24 reported eight Ag(I) complexes that show macrocyclic dinuclear, helical, layered, and © XXXX American Chemical Society

three-dimensional (3D) microporous networks, in which the spacer of N,N′-bis(pyridine-n-ylmethyl)propane-1,3-diamine (n = 2, 3, or 4) coordinated to the Ag(I) center in chelating mode. Interestingly, one of these complexes presents one-dimensional (1D) cationic channel structures with the spacer being protonated. One year later, Wu and co-workers25 employed 1,2-bis(4-pyridylmethylamino)ethane to react with Zn(ClO4)2 and generated three chiral MOCPs, in which the spacers all coordinate to the Zn(II) cations to form a chain, layer, and 3D microporous framework. The bis(pyridyl) ligand can capture additional metal cations as a node with the chelated spacer to form novel topological structures. Meanwhile, the aliphatic amine spacers could be protonated and form a large window which then capture solvents or anions as guests to give rise to host−guest frameworks or induce the formation of interReceived: February 4, 2017 Revised: April 11, 2017 Published: April 13, 2017 A

DOI: 10.1021/acs.cgd.7b00174 Cryst. Growth Des. XXXX, XXX, XXX−XXX

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Scheme 1. Schematic Representation of L and Various Organic Acids Used in This Work

are mainly influenced by the coordination modes of L or H2L2+ cation and the features of different inorganic and organic anions. With the chelated spacer, complex 1 presents a 3D hybrid network, while complexes 3 and 4 present an sql layer. Meanwhile, complexes 6, 7, 8, and 9 present an sra net, snk net, ladder chain, and tfc net. In contrast, the protonated spacer makes complexes 2, 5, and 10 present an interesting 2-fold interpenetrated pcu net, 3-fold parallel interpenetrated sql layer, as well as new (44.611)(66) topology. Moreover, infrared (IR) spectroscopy, thermogravimetric analyses (TGA), powder X-ray diffraction (PXRD), and PL of these 10 complexes are also investigated in the solid state.

penetrating frameworks. Therefore, modulating the architectures and properties of MOCPs through the rational design of bis(pyridyl) molecules with chelated or protonated spacers would be challenging and interesting work. In view of these points, we synthesized a bis(pyridyl) ligand with symmetric −NH−CH2−CH2−NH− spacer, namely, N,N′-bis(pyridin-3-ylmethyl)ethane-1,2-diamine (L, Scheme 1),26 which possesses the following three features: (i) the two pyridyl N atoms exhibit specific coordination directivity toward metal cations; (ii) the spacer could coordinate to metal cations in chelating mode, forming a stable five-membered ring and then modulating the topological structures of target complexes; (iii) owing to the stronger alkalinity of the ethylenediamine unit than the pyridine unit (Pkb1 of ethylenediamine, 4.07; Pkb of pyridine, 8.80), it can be first protonated to prevent its coordination to metal cations and further induce the formation of interpenetrated networks. Meanwhile, the bis(pyridyl) ligands with aliphatic diamine spacers can coordinate to metal cations in neutral form or cationic form after the spacers are protonated. Therefore, the features of counteranions, such as size, length, rigidity-flexibility, and coordination modes, would be another important factor in modulating the topological structures of target complexes. Usually, the counteranions play two kinds of roles in such systems, i.e., acting as anion templates in porous channels of the cationic frameworks27,28 and serving as coordinated anions to achieve novel architectures and topologies in neutral frameworks. In comparison with the first role, the second one will be more effective in structure regulation and control, especially for the complexes containing the same metal cations.29,30 The Cd(II) cation is often chosen as the metal center owing to its multiple coordination numbers that vary from 4 to 8 and potential optical properties.31 The large ionic radius can accommodate more bridging ligands to form MOCPs with a higher dimension and novel topological structures. Meanwhile, Cd(II)-based MOCPs are always considered as prospective luminescent materials since the closed shell d10 electronic configuration of Cd(II) cation.31 Accordingly, in this work, five selected organic acids (Scheme 1), malonic acid, succinic acid, fumaric acid, mbenzene dicarboxylic acid (m-H2BDC), and p-benzene dicarboxylic acid (p-H2BDC), with different structure features used to react with L and Cd(II) salts. Then, 10 complexes, namely, [Cd2LCl4]n (1), [Cd(H2L)(SO4)2(H2O)2]n·6nH2O (2), [CdL(malonate)] n ·5nH 2 O (3), [Cd 2 L(malonate)Cl2(H2O)]n·nH2O (4), [Cd2(H2L)(succinate)3]n·4nH2O (5), [Cd2L(fumarate)2(H2O)2]n·2nH2O (6), [Cd2L(m-BDC2−)2]n· 2nH 2 O (7), [Cd 2 (L)(p-BDC 2− ) 2 (H 2 O) 3 ] n ·3nH 2 O (8), [Cd3(L)2(p-BDC2−)3(H2O)4]n·nH2O (9), and [Cd3(H2L)(pBDC2−)2(SO4)2(H2O)3]n·2nH2O (10), were obtained and structurally characterized. The structures of the 10 complexes

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EXPERIMENTAL SECTION

General Procedures. All chemicals and solvents were of A. R. grade and used without further purification in the syntheses. The L ligand was synthesized following the reported process.26 Elemental analyses were carried out with a Vario MICRO from Elementar Analysensysteme GmbH, and the IR spectra were recorded from KBr pellets in the range of 4000−400 cm−1 on a Bruker Equinox 55 FT-IR spectrometer. PXRD patterns for the nine complexes were measured at 293 K on a Bruker D8 diffractometer (Cu Kα, λ = 1.54059 Å). TGA were carried out on a PerkinElmer TG/DTA 6300 thermal analyzer under flowing N2 atmosphere, with a heating rate of 10 °C min−1. Luminescence spectra were measured on a PerkinElmer LS 55 luminescence spectrometer. Synthesis of Complex 1. An aqueous solution of CdCl2·2.5H2O (10 mmol, 2.28 g) was added to a solution of L (10 mmol, 2.42 g) in MeOH followed by stirring at room temperature for 30 min. Then, the mixture was sealed in a 50 mL Teflon-lined stainless steel vessel and heated at 70 °C for 2 days. Colorless crystals of 1 suitable for X-ray diffraction were isolated after being cooled slowly to room temperature. Yield: 83% (based on Cd). Elemental analysis calcd (%) for C14H18N4Cl4Cd2: C 27.61, H 2.98, N 9.20; found: C 27.58, H 3.03, N 9.24. IR (ν/cm−1): 3253s, 3059w, 2948w, 2879w, 1579s, 1536s, 1476m, 1434m, 1382m, 1345m, 1228m. Synthesis of Complex 2. A similar procedure as complex 1 was employed to prepare complex 2 by changing the metal salt to CdSO4·8/3H2O (10 mmol, 2.57 g). The mixture was sealed in a 50 mL Teflon-lined stainless steel vessel and heated at 110 °C for 3 days. Colorless crystals of 2 suitable for X-ray diffraction were isolated after being cooled slowly to room temperature. Yield: 81% (based on Cd). Elemental analysis calcd (%) for C14H36CdN4O16S2: C 24.26, H 5.24, N 8.08; found: C 24.23, H 5.19, N 8.05. IR (ν/cm−1): 3424m, 3289m, 3185m, 3054w, 2934w, 2863w, 1602s, 1540s, 1479m, 1438m, 1388m, 1332m, 1122m. Synthesis of Complex 3. A mixture of Cd(NO3)·4H2O (10 mmol, 3.08 g), L (10 mmol, 2.42 g), malonic acid (10 mmol, 1.04 g), NaOH (10 mmol, 0.4 g), and deionized water (25 mL) were sealed in a 50 mL Teflon-lined stainless steel vessel and heated at 70 °C for 2 days. Colorless crystals of 3 suitable for X-ray diffraction were isolated after being cooled slowly to room temperature. Yield: 76% (based on Cd). Elemental analysis calcd (%) for C17H30CdN4O9: C 37.34, H 5.53, N B

DOI: 10.1021/acs.cgd.7b00174 Cryst. Growth Des. XXXX, XXX, XXX−XXX

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Table 1. Crystal Data and Structure Refinement Parameters of Complexes 1−10 complex

1

2

3

4

5

empirical formula formula weight space group a/Å b/Å c/Å α/deg β/deg γ/deg V/Å3 Z Dc/g cm−3 μ (Mo Kα)/mm−1 F(000) reflections collected unique reflections parameters R (int) GOFa on F2 final Rb indices [I ≥ 2σ(I)]

C14H18Cd2Cl4N4 608.92 P21/c 9.9596(3) 13.0370(3) 15.8902(6) 90.00 94.832(4) 90.00 2055.92(11) 4 1.967 2.592 1176 7264 4704 223 0.0301 1.033 R1 = 0.0364 wR2 = 0.0676

C14H36CdN4O16S2 692.99 P1̅ 7.7330(6) 11.4007(7) 15.7294(10) 107.245(6) 93.587(6) 90.235(6) 1321.41(16) 2 1.742 1.063 712 7816 6028 394 0.0235 1.040 R1 = 0.0468 wR2 = 0.1030

C17H30CdN4O9 546.85 P21/c 13.9242(6) 11.2000(4) 17.2396(7) 90.00 104.642(4) 90.00 2601.21(18) 4 1.396 0.887 1120 9290 5949 286 0.0256 1.087 R1 = 0.0695 wR2 = 0.2179 wR2 = 0.0596 8

C17H23Cd2Cl2N4O6 675.11 Pbcn 12.7261(3) 15.8899(4) 24.2914(5) 90.00 90.00 90.00 4912.11(19) 8 1.820 1.987 2632 10919 5655 287 0.0280 1.092 R1 = 0.0471 wR2 = 0.1155

C26H40Cd2N4O16 889.42 P21/c 10.2580(3) 21.2756(8) 15.5224(4) 90.00 98.517(2) 90.00 3350.31(18) 4 1.763 1.347 1792 12602 7684 469 0.0296 1.043 R1 = 0.0620 wR2 = 0.1562

complex

6

7

empirical formula formula weight space group a/Å b/Å c/Å α/deg β/deg γ/deg V/Å3 Z Dc/g m−3 μ (Mo Kα)/mm−1 F(000) reflections collected unique reflections parameters R (int) GOF on F2 final R indices [I ≥ 2σ(I)]

C22H30Cd2N4O12 767.27 P1̅ 8.7999(5) 10.8475(7) 16.8132(11) 76.600(6) 82.105(5) 90.135(5) 1545.48(17) 2 1.640 1.436 756 9244 7040 369 0.0203 1.070 R1 = 0.0459 wR2 = 0.1297

C30H30Cd2N4O10 831.38 C2/c 35.986(2) 10.1738(4) 18.9084(11) 90.00 117.988(8) 90.00 6113.1(6) 8 1.807 1.456 3312 111217 6994 433 0.0265 1.093 R1 = 0.0356 wR2 = 0.0821 wR2 = 0.0596

C30H38Cd2N4O14 903.44 P1̅ 9.1999(5) 12.7795(8) 15.6184(8) 84.607(5) 83.267(5) 83.843(5) 1806.90(18) 2 1.661 1.247 908 12093 8249 478 0.0293 1.014 R1 = 0.0537 wR2 = 0.1338

9

10

C45H49Cd3N6O17 1283.10 P1̅ 10.3192(3) 11.7329(5) 20.8700(7) 90.369(3) 90.187(3) 100.927(3) 2480.92(15) 2 1.718 1.351 1282 14774 11305 686 0.0281 1.047 R1 = 0.0498 wR2 = 0.1310

C30H38Cd3N4O21S2 1191.96 C2/c 12.4871(3) 18.9997(7) 16.0690(3) 90.00 92.444(2) 90.00 3808.93(19) 4 2.079 1.862 2360 7420 4359 294 0.0311 1.076 R1 = 0.0501 wR2 = 0.0996

GOF = {∑w((F02 − Fc2)2)/(n − p)}1/2, where n = number of reflections and p = total number of parameters refined. bR = ∑∥F0|−|Fc∥/∑|F0|, wR = {∑w(F02 − Fc2)2/∑w(F02)2}1/2.

a

10.25; found: C 37.30, H 5.49, N 10.22. IR (ν/cm−1): 3432s, 3237s, 3054w, 2925w, 2879w, 1641m, 1552s, 1486m, 1432m, 1376s, 1267m. Synthesis of Complex 4. A similar procedure as complex 3 was employed to prepare complex 4 by changing the metal salt to CdCl2· 2.5H2O (10 mmol, 2.28 g). Colorless crystals of 4 suitable for X-ray diffraction were isolated after being cooled slowly to room temperature. Yield: 77% (based on Cd). Elemental analysis calcd (%) for C17H23Cd2Cl2N4O6: C 30.24, H 3.43, N 8.30; found: C 30.23, H 3.40, N 8.29. IR (ν/cm−1): 3444m, 3237m, 3062w, 2925w, 2875w, 1646m, 1587m, 1556m, 1484m, 1436m, 1373s, 1259m. Synthesis of Complex 5. A similar procedure as complex 3 was employed to prepare complex 5 by changing the metal salt and organic acid to CdSO4·8/3H2O (10 mmol, 2.57 g) and succinic acid (10 mmol,

1.18 g). Colorless crystals of 5 suitable for X-ray diffraction were isolated after being cooled slowly to room temperature. Yield: 80% (based on Cd). Elemental analysis calcd (%) for C26H40Cd2N4O16: C 35.11, H 4.53, N 6.30; found: C 35.14, H 4.57, N 6.26. IR (ν/cm−1): 3446m, 3243m, 3198m, 3042w, 2925w, 2877w, 1642m, 1585s, 1550s, 1486m, 1432m, 1380s, 1267m. Synthesis of Complex 6. A similar procedure as complex 3 was employed to prepare complex 6 by changing the organic acid to fumaric acid (10 mmol, 1.16 g). Colorless crystals of 6 suitable for Xray diffraction were isolated after being cooled slowly to room temperature. This complex can also be synthesized by using CdCl2. Yield: 85% (based on Cd). Elemental analysis calcd (%) for C22H30Cd2N4O12: C 34.44, H 3.94, N 7.30; found: C 34.42, H 3.99, C

DOI: 10.1021/acs.cgd.7b00174 Cryst. Growth Des. XXXX, XXX, XXX−XXX

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Figure 1. 3D hybrid network (right) of 1 formed by the linkage of organic one side zipper chain (middle) and inorganic (4,4) layers (left). Different Cd(II) cations and polyhedral were denoted as different colors. N 7.28. IR (ν/cm−1): 3401m, 3239m, 3048w, 2931w, 2871w, 1644m, 1572s, 1482m, 1434m, 1386s, 1215m. Synthesis of Complex 7. A similar procedure as for complex 3 was employed to prepare complex 7 by changing the organic acid to mbenzene dicarboxylic acid (10 mmol, 1.66 g). The mixture was sealed in a 50 mL Teflon-lined stainless steel vessel and heated at 130 °C for 3 days. Colorless crystals of 7 suitable for X-ray diffraction were isolated after being cooled slowly to room temperature. This complex can also be synthesized by using CdCl2. Yield: 83% (based on Cd). Elemental analysis calcd (%) for C30H30Cd2N4O10: C 43.34, H 3.64, N 6.74; found: C 43.30, H 3.62, N 6.77. IR (ν/cm−1): 3442m, 3289m, 3185m, 3064w, 2935w, 2863w, 1610s, 1540s, 1479m, 1440m, 1386s, 1338s, 1271m. Synthesis of Complex 8. A mixture of Cd(NO3)·4H2O (10 mmol, 3.08 g), L (10 mmol, 2.42 g), p-benzene dicarboxylic acid (10 mmol, 1.66 g), NaOH (20 mmol, 0.8 g), and deionized water (25 mL) were sealed in a 50 mL Teflon-lined stainless steel vessel and heated at 110 °C for 3 days. Colorless crystals of 8 suitable for X-ray diffraction were isolated after being cooled slowly to room temperature. Yield: 76% (based on Cd). Elemental analysis calcd (%) for C30H38Cd2N4O14: C 39.88, H 4.24, N 6.20; found: C 39.85, H 4.28, N 6.22. IR (ν/cm−1): 3390m, 3218m, 3054w, 2948w, 2869w, 1625m, 1571s, 1537m, 1422m, 1388s, 1361s, 1292m, 1230m. Synthesis of Complex 9. A similar procedure as for complex 8 was employed to prepare complex 9 by changing the metal salt to CdCl2· 2.5H2O (10 mmol, 2.28 g). Colorless crystals of 9 suitable for X-ray diffraction were isolated after being cooled slowly to room temperature. Yield: 85% (based on Cd). Elemental analysis calcd (%) for C45H49Cd3N6O17: C 42.12, H 3.85, N 6.55; found: C 42.08, H 3.88, N 6.51. IR (ν/cm−1): 3480m, 3198m, 3052w, 2933w, 2881w, 1615m, 1561s, 1506m, 1436m, 1382s, 1295m, 1249m. Synthesis of Complex 10. A similar procedure as for complex 8 was employed to prepare complex 10 by changing the metal salt to CdSO4·8/3H2O (10 mmol, 2.57 g). Colorless crystals of 10 suitable for X-ray diffraction were isolated after being cooled slowly to room temperature. Yield: 82% (based on Cd). Elemental analysis calcd (%) for C30H38Cd3N4O21S2: C 30.23, H 3.21, N 4.70; found: C 30.20, H 3.24, N 4.68. IR (ν/cm−1): 3479m, 3200m, 3059w, 2927w, 2871w, 1677m, 1621m, 1563s, 1540m, 1508m, 1482m, 1438m, 1392s, 1297m, 1135m. X-ray Crystallographic Measurements. Table 1 provides a summary of the crystal data, data collection, and refinement parameters for the complexes 1−10. All diffraction data were collected at 295 K on a Xcalibur Eos diffractometer with graphite monochromatized Mo-Kα (λ = 0.71073 Å) radiation in ω scan mode. Absorption corrections were applied using a multiscan technique. All structures were solved by direct method and difference Fourier syntheses, and refined by full-matrix least-squares techniques. Non-hydrogen atoms were refined with anisotropic temperature parameters except for the highly disordered O2w in complex 4 and O3w, O4w in complex 6, which were just refined isotropically. And as a result, the H atoms on these O atoms cannot be found in difference

Fourier maps, which led to a series of B-level alerts. Furthermore, the missed H atoms were directly added into the final formula. During the refinement, the coordinated and free −NH−CH2−CH2−NH− spacers of two different L ligands in 9 are disordered over two sites with the occupancies of the two disordered parts being 0.6:0.4 and 0.5:0.5, respectively. The hydrogen atoms attached to carbons in these 10 complexes, N3 in complex 8 and the disordered N6, N6′ in complex 9 were placed in calculated positions with C−H = 0.93 Å (aromatic and ethylene H atoms), C−H = 0.97 Å (methylene H atoms), N−H = 0.86 Å, refined with the riding model approximation and assigned Uiso(H) = 1.5Ueq (N) or 1.2Ueq (C) of their respective parent atoms. The H atoms on lattice water molecules O1w−O5w in 3, O1w and O2w in 8, and O3w in 9 were determined by WinGX according to the orientation of corresponding hydrogen bonds and subsequently fixed (AFIX 3) with their thermal parameters set to Uiso(H) = 1.2Ueq(O). The other hydrogen atoms of nitrogen atoms and water molecules in 1−2 and 4−10 were located in difference Fourier maps and were also refined in the riding model approximation, with N−H and O−H distance restraint (0.86(1) or 0.85(1) Å) and Uiso(H) = 1.5Ueq(N, O). All calculations were carried out with the SHELXTL-97 program. 32 The CCDC reference numbers are 1526178−1526187 for these nine complexes. Selected bond lengths and hydrogen bonding parameters for these complexes are listed in Table S1 and Table S2 (Supporting Information).

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RESULTS AND DISCUSSION Syntheses. With the aim to investigate the influence of coordination modes of N-donor ligand and the features of counteranions on the structures of coordination complexes, we synthesized a bis(pyridyl) ligand (L mentioned above) with a chelated spacer that is capable of being protonated which was then used to react with different Cd(II) salts as well as diverse organic acids under hydrothermal conditions. At the beginning of our experiment, different Cd(II) salts were employed to react with L, and then, crystals of complexes 1 and 2 were obtained at 70 and 110 °C with high quality and yield owing to the stronger coordination ability of Cl− and SO42− anions.33,34 It is interesting to note that the spacer of L in complex 2 is protonated which gives rise to the formation of a 2-fold interpenetrated pcu net. In comparison, the spacer of L in complex 1 coordinates to Cd(II) cation in chelated mode. For the sake of obtaining new complexes with interesting topological structures, naturally, various organic carboxylic acids are introduced to partially or fully replace the inorganic anions. Therefore, five types of organic acids with different length and rigidity-flexibility were added to the former systems individually. For the aliphatic carboxylic acids, the crystals could be obtained at lower temperature of 70 °C. However, for the aromatic carboxylic acids, the reaction temperature should be D

DOI: 10.1021/acs.cgd.7b00174 Cryst. Growth Des. XXXX, XXX, XXX−XXX

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Figure 2. (a) The pcu network (down) formed by the interconnection of zigzag chains (top) through C−H···π and π···π interactions (green dashed lines). (b) The pcu network formed by the interconnection of [(S1O42−)2(H2O)6] and [(S2O42−)2(H2O)6] clusters through hydrogen bonds (black dashed lines). (c) The 3D supramolecular network of 2 with the lattice water molecules being denoted as green balls. Hydrogen bonds were omitted for clarity. (d) Schematic representation of the pseudo 2-fold interpenetrated pcu network.

increased to higher temperature of 110 and 130 °C to obtain high quality crystals. Single X-ray diffraction analyses indicate that the inorganic anions are fully replaced by the organic anions in most of complexes except for complexes 4 and 10. The left Cl− and SO42− anions in these two complexes are responsible for the charge balance and structure regulation. Nevertheless, these results demonstrate that the organic anions exhibit a stronger coordination ability in comparison with the aforementioned inorganic anions. Comparison of these 10 complexes reveals that CdSO4 as a reactant could easily bring out the protonation of the spacer that further resulta in novel topological structures in complexes 2, 5, and 10. Structure Description of Complexes 1 and 2. Complex 1 contains two six-coordinated Cd(II) cations, one L molecule and four Cl− anions (Figure S1, Supporting Information) in the molecular structure. As shown in Figure 1, one [(Cd1)2(μ2Cl2)2] unit joins adjacent two identical [(Cd1)(Cd2)(μ2Cl3)(μ2-Cl4)] units to form a “chair cluster”, which further connects adjacent four clusters through μ2-Cl1− anions, thus forming a (4,4) layer motif in the bc plane. Furthermore, L molecules coordinate to Cd(II) cations with both pyridyl and aliphatic N atoms and extend adjacent Cd(II) cations into one side zipper chain (Figure 1). The combination of the (4,4) layers and one side zipper chains gives rise to the formation of a 3D inorganic−organic hybrid network (Figure 1).

When the cadmium(II) salt was changed into CdSO4, a new complex 2 is obtained. As shown in Figure S1 (Supporting Information), the molecular structure of complex 2 is composed of one six-coordinated Cd(II) cation, one doubly protonated H2L2+ cation, two terminal sulfate anions, two coordinated water molecules, and six lattice water molecules. The spacer of L here is protonated and then forms H2L2+ cations. Such a hydrogenated ligand presents pseudorigidity and joins adjacent Cd(II) cations with pyridyl N atoms to form a zigzag chain structure along the c-axis (Figure 2a), which is definitely different from the one side zipper chain structure in complex 1. Leaving the sulfate anions and water molecules aside, C−H···π and π···π interactions among adjacent −CH2− groups and pyridyl rings of H2L2+ cations extend adjacent chains into a 3D supramolecular pcu network with 1D open rhombic channels along the a-axis (Figure 2a). The channels are filled by above neglected sulfate anions and water molecules. Interestingly, the interconnection of these sulfate anions and water molecules through hydrogen bonds also affords a 3D supramolecular pcu network (Figure 2b), which could be understood in the following manner. As shown in Figure 2b, the two crystallographically unique sulfate anions form two types of tapes with different lattice water molecules, which involve different [(SO42−)2(H2O)6] clusters consisting of three water molecules and one sulfate anion, as well as their E

DOI: 10.1021/acs.cgd.7b00174 Cryst. Growth Des. XXXX, XXX, XXX−XXX

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Figure 3. Wavelike sql layers (b) of 3 (a) and 4 (c) incorporating right- and left-handed helical chains. The π···π interactions between opposite pyridyl rings were denoted as green dashed lines. (d) Illustration of the different coordination modes of malonate dianions in 3 (left) and 4 (right).

centrosymmetric equivalents. The [(S1O42−)2(H2O)6] cluster involving O6w, O7w, and O8w exhibits a cage-shaped configuration, while the [(S2O42−)2(H2O)6] cluster involving O3w, O4w, and O5w shows looped configuration. Both types of [(SO42−)2(H2O)6] clusters are expanded by the R24(8) motifs to form hydrogen-bonding tapes. Then, the atoms H3w1 form hydrogen bonds with atoms O1 which connect different adjacent tapes into a hydrogen-bonding layer motif (Figure S2, Supporting Information). Furthermore, the coordinated O1w molecules act as the “hydrogen-bonding bridge” to extend adjacent layers into the final 3D supramolecular pcu network by considering each R24(8) motif as 4-connected nodes. Then, the two aforementioned types of pcu networks interpenetrate with each other to form a pseudo 2-fold interpenetrated network as illustrated in Figure 2c,d. Structure Description of Complexes 3 and 4. As shown in Figure S1 (Supporting Information), these two complexes have different contents in their molecular structures. For complex 3, its molecular structure consists of one sevencoordinated Cd(II) cation, one L molecule, one malonate dianion, and five lattice water molecules. The molecular structure of complex 4 comprises two crystallographically independent Cd(II) cations, one L molecule, one malonate dianions, two Cl− anions, one coordinated water molecule, and one lattice water molecule. The Cd1 and Cd2 cations adopt distinct seven- and six-coordinated coordination spheres, respectively. Different from complex 1, the pyridyl N4 atom of ligand L in these two complexes does not involve the coordination sphere of the Cd(II) cation. Instead, it forms hydrogen bonds with free or coordinated water molecules (Table S2, Supporting Information). The malonate dianions in complex 3 act in bis-bidentate chelate mode and connect adjacent Cd(II) cations to form alternate left- and right-handed helical chains with a pitch of 11.200 Å corresponding to the length of the b-axis (Figure 3a). Furthermore, the L molecules connect these left- and right-handed helical chains to form a wavelike sql layer with the Cd(II) cations being viewed as 4connected nodes (Figure 3b). Strong π···π interactions are observed between the opposite N1-containing pyridyl rings with the centroid-to-centroid distance being 3.445(2) Å. Aside from the Cd2 cations and Cl− anions, complex 4 possesses a

similar sql layer with that of complex 3, as evidenced by the same coordinated and uncoordinated pyridyl groups (Figure S1, Supporting Information), similar left- and right-handed helical chains (the pitch of 12.726 Å corresponding to the length of the a-axis) (Figure 3c), as well as the considerable π···π interactions between the coordinated pyridyl rings (the centroid-to-centroid distance being 3.698(2) Å). Due to the coordination of Cd2 cation, however, the dihedral angle between two carboxyl groups and the distance between O2 and O3 atoms (Figure 3d) in the malonate dianion sharply drop to 41.3° and 2.815(5) Å from those of 87.6° and 3.245(4) Å in complex 3. With these changes, the malonate dianions adopt a different μ3 (κ2O1: κ1O2: κ2O3: κ1O4) bridging mode. Meanwhile, the μ2-Cl bridged Cd2 dinuclear units fill in the rhombic grid, which generate distinct rod-shaped secondary building units (SBUs) (Figure S3b, Supporting Information). Moreover, the uncoordinated pyridyl rings in complex 3 arrange along the two sides of the layers in parallel mode, which provide the chance for the formation of continuous π···π interactions. The centroid-to-centroid distances are 3.601(2) (interlamellar) and 3.661(3) Å (intralamellar). Highly disordered water molecules reside in the interspaces between adjacent layers (Figure S3a, Supporting Information). In contrast, the layers in this complex 4 are nearly flat with the uncoordinated pyridyl rings arranging along the two sides of the layers in vertical mode (Figure S3c, Supporting Information). Similarly, the lattice water molecules also reside in the interspaces between adjacent layers. Structure Description of Complex 5. The ligand L in complex 5 is protonated to form H2L2+ cations which act as pseudorigid linkers to join adjacent Cd(II) cations together with longer succinate dianions, forming a novel 3-fold parallel interpenetrated sql layer. Single-crystal X-ray analysis reveals that its molecular structure consists of two crystallographically independent Cd(II) cations, one doubly protonated H2L2+ cation, three succinate dianions, and four lattice waters (Figure S1, Supporting Information). The Cd1 and Cd2 cations locate in six-coordinated and seven-coordinated environments, respectively. Remarkably, the three succinate dianions here exhibit different coordination modes and play different roles in constructing the structure of complex 5. As shown in Figure 4, F

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Figure 4. Left: The sql layer of 5 formed by the interconnection of [Cd2(suc)2] SBUs through succinate dianions (green balls) and H2L2+ cations. Right: Three-fold parallel interpenetrated sql layers.

Figure 5. (a) Top: Zig-zag chain structure extended by different fumarate dianions. Down: Layer structure extended by π···π interactions between adjacent snake-shaped chains. (b) The 3D covalent framework of 6. (c) Schematic representation of the sra topology. The different Cd(II) cations in the 4-c nodes were denoted as different colors.

Figure 6. (a) Top: Two types of ladder chains formed by different m-BDC2− dianions and different Cd(II) cations (green and sky blue balls). Down: Layer structure extended by π···π interactions between adjacent chains. (b) The 3D covalent framework of 7. (c) Schematic representation of the snk topology. The different Cd(II) cations in the 4-c nodes were denoted as different colors.

lattice water molecules through O/N−H···O hydrogen bonds to give rise to 3D supramolecular network (Figure S4, Supporting Information). Structure Description of Complex 6. Complex 6 was obtained under similar experimental conditions for preparing complex 5 except for using rigid fumaric acid instead of the flexible succinic acid. The molecular structure of complex 6 contains two seven-coordinated Cd(II) cations, one L molecule, one and two half crystallographically independent fumarate dianions, two coordinated water molecules, and two lattice water molecules (Figure S1, Supporting Information). The three different fumarate dianions present the same bis-

two of succinate dianions exhibit the same bis-bidentate chelate mode and connect two Cd(II) cations to form dinuclear [Cd2(suc)2] SBU with the Cd1···Cd2 distance of 6.383(1) Å. Then, adjacent dinuclear SBUs are further linked by the third succinate dianions in different bidentate chelate modes and monodentate modes and H2L2+ cations to form an sql layer in the ac plane containing large parallelogram-shaped windows with the diagonal Cd···Cd distances of ca. 25 × 16 Å2. Such windows are large enough to be simultaneously threaded by the other two identical windows, thus leading to the 3-fold parallel interpenetrated sql layer without available space (Figure 4). Moreover, adjacent interpenetrated layers are extended by the G

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Figure 7. Two types of layers in 8 formed by the interconnection of ladder chains through hydrogen bonds.

Figure 8. (a) Layer and chain structures formed by the interconnection of different p-BDC2− dianions and different Cd(II) cations. (b) The macrocycle and short stick formed by the interconnection of different L molecules and different Cd(II) cations. (c) The 3D covalent framework of 9. (d) Schematic representation of the tfc topology.

fumarate dianions and L can be looked at as linkers. Therefore, the whole structure of complex 6 can thus be represented to a sra topology with the Schläfli symbol of (42.63.8). Structure Description of Complex 7. X-ray crystallography reveals that there are two seven-coordinated Cd(II) cations, one L molecule, two m-BDC2− dianions, and two lattice water in the molecular structure of complex 7 (Figure S1, Supporting Information). As observed in complex 6, two adjacent types of Cd(II) cations are connected by L molecules to give rise to a chain structure, which is further extended by the π···π interactions between N1/N4-containing pyridyl rings with the centroid-to-centroid distance being 3.816(1) Å into a layer motif (Figure 6a). Meanwhile, the two different m-BDC2− dianions act in the same μ3 (κ1O: κ1O: κ1O: κ2O) coordination mode to bridge different Cd(II) cations into two kinds of ladder chains parallel to the crystallographic b-axis (Figure 6a).

bidentate chelated mode and connect adjacent different Cd(II) cations to form a zigzag chain, which could be denoted as [-fumA-Cd1-fumB-Cd1-fumA-Cd2-fumC-Cd2-] (A, B, and C are used to distinguish different fumarate dianions) (Figure 5a). Meanwhile, the two types of Cd(II) cations are also connected by the L molecules to generate a snake-shaped chain (Figure 5a). It should be noted that weak π···π interactions between the two opposite pyridyl rings in adjacent parallel chains are observed with the centroid-to-centroid distance of 3.968(2) Å, which affords the formation of a supramolecular layer structure in the ab plane. Then, the intercrossing of zigzag chains and supramolecular layers generates a 3D covalent framework by sharing Cd(II) cations (Figure 5a). To further understand the complicated framework of complex 6, topological analysis35 was carried out. As shown in Figure 5b, each seven-coordinated Cd(II) cations can be simplified as 4-connect nodes, and H

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Figure 9. (a) Single 3D porous framework. (b) Perspective view of the 2-fold interpenetrated network in 10. (c) Schematic representation of the 2fold interpenetrated pcu network. (d) The 3D framework formed by the interconnection of two identical networks through L molecules. (e) Schematic representation of the (44.611)(66) topology.

extending adjacent ladder chains into two types of layers (Figure 7). Furthermore, interconnection of the two types of layers gives rise to a 3D supramolecular network (Figure S5, Supporting Information). The molecular structure of complex 9 is composed of three crystallographically unique seven-coordinated Cd(II) cations, one and a half L molecules, two and two half p-BDC2− dianions, four coordinated water molecules, and one lattice water molecule. It is noteworthy that both L molecules and pBDC2− dianions present different coordination modes to connect adjacent Cd(II) cations into a intricate 3D framework. For clarity, the four p-BDC2− dianions are signed as pBDC2−(I), p-BDC2−(II), p-BDC2−(III), and p-BDC2−(IV), while the two L molecules are denoted as La and Lb (Figure 8a,b). The p-BDC2−(I) dianions connect adjacent Cd1 cations in the μ4 (κ1O: κ2O: κ1O: κ2O) coordination mode to generate a chain structure along the a-axis. Meanwhile, two p-BDC2−(II) and one p-BDC2−(III) dianions connect two Cd2 cations with the same μ2 (κ1O: κ1O: κ1O: κ1O) coordination mode to form finite “Z” shaped motifs, which join adjacent chains, giving rise to a layer structure (Figure 8a). The p-BDC2−(IV) dianions present the μ2 (κ1O: κ1O: κ1O: κ0O) coordination mode and join adjacent Cd3 cations to form another chain structure (Figure 8a), which fill in the channels defined by the packing of adjacent layers (Figure S6, Supporting Information). Two La molecules coordinate to two Cd1 cations with the flexible spacers chelating to two Cd3 cations, forming a 26-membered macrocycle. In contrast, the Lb molecules only coordinate to

Furthermore, the two types of ladder chains support adjacent layers to construct a complicated 3D framework (Figure 6a). A better insight into the nature of the intricate framework can be achieved by the application of a topological approach,35 reducing multidimensional structures to simple node and connection nets. As discussed above, each dinuclear Cd(II) SBU can be regarded as 6-connected nodes, and m-BDC2− dianions and L are both considered as linkers. According to the simplification principle, the resulting structure of complex 7 is a 6-connected snk net with a Schläfli symbol of (410.52.63) (Figure 6b). Structure Description of Complexes 8−10. The reaction of different Cd(II) salts with L and p-H2BDC leads to the formation of three different complexes 8−10. As shown in Figure S1 (Supporting Information), the molecular structure of complex 8 contains two crystallographically unique Cd(II) cations, one L molecule, two p-BDC2− dianions, three coordinated water molecules, and three lattice water molecules. The Cd1 and Cd2 cations adopt distinct six- and sevencoordinated coordination spheres, respectively. The two different p-BDC2−(I) dianions alternately connect adjacent Cd1 and Cd2 cations in different μ2 (κ1O: κ1O: κ1O) and μ2 (κ1O: κ1O: κ1O: κ1O) coordination modes to generate chain structures, which are further joined by L in the same coordination mode as that in complexes 3 and 4 into a ladder chain (Figure 7). The two coordinated O2w and O3w molecules form hydrogen bonds (Table S2, Supporting Information) with coordinated carboxyl O atoms, thus I

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Figure 10. Diverse coordination modes of L and H2L2+ in 1−10.

channels along the a-axis with dimensions of windows being ca. 16 × 11 Å2. The channels are too large to accommodate the other identical nets, causing the 2-fold interpenetrated pcu net by self-clathration (Figure 9b,c). According to the classification defined by Blatov et al.,36 the present interpenetrated network belongs to Class Ia, where only one interpenetration vector can be found. An analysis by ToposPro package35 reveals that one pcu net is related to the other one by a single translation vector, [1/2, 1/2, 0] of 11.37 Å. The H2L2+ cations join the two identical networks at the points of Cd3 cations, thus extending the 2-fold interpenetrated pcu net into the aforementioned intricate 3D framework (Figure 9d). From the view of topology, each dinuclear unit and Cd3 cations can be respectively regarded as 6- and 4-connected nodes, and each p-BDC2− dianion and H2L2+ cation can be regarded as the same linkers. Therefore, an analysis by ToposPro package35 reveals that the network of this complex present a new topology as displayed in Figure 9e with the Schläfli symbol of (44.611)(66). Moreover, strong π···π interactions are formed between the pyridyl groups with the centroid-to-centroid distance being 3.601(2) Å. Coordination Modes of the Bis(pyridyl) Ligands. As stated before, the present bis(pyridyl) ligand may either coordinate to metal cations in chelating mode or be protonated to form supramolecular interactions through the modulation of experimental conditions. Therefore, this ligand can exhibit diverse coordination modes, which then play a crucial role during the assembly of coordination complexes. As shown in Figure 10, when the spacer coordinates to Cd(II) cation, ligand L presents three types of coordination modes. Mode I is observed in complexes 1, 6, 7, and 9, in which the ligands L coordinate to Cd(II) cations with the two aliphatic N atoms in chelating mode and two pyridyl N atoms in monodentate mode. Subsequently, these four complexes exhibit intricate 3D frameworks with diverse topologies. Significantly, the mode I in complex 9 is somewhat different from those in the other three complexes. The two pyridyl N atoms coordinate to Cd(II) cations in the same direction. Hence, two ligands L coordinate to four Cd(II) cations to

two Cd2 cations with the pyridyl N atoms to generate a short stick (Figure 8b). Then, the macrocycles and short sticks cohere the aforementioned layers and −Cd3−p-BDC2−(IV)− chains to afford the formation of the intricate 3D framework by sharing Cd(II) cations (Figure 8c). From the topological viewpoint, the dinuclear Cd12O2 units and Cd2 cations can be respectively regarded as 4- and 3-connected nodes, and each pBDC2− dianion and L molecule can be regarded as the same linkers. Therefore, an analysis by ToposPro package35 reveals that the network can thus be represented as a tfc net as displayed in Figure 8d with the Schläfli symbol of (85.10)(83). Different from the former two complexes, ligand L is protonated to form a H2L2+ cation. Meanwhile, the SO42− dianion is found to be involved in the coordination spheres of Cd(II) cations and comprises the molecular structure of complex 10 together with three crystallographically unique Cd(II) cations, half a double protonated H2L2+ cation, two half p-BDC2− dianions, one and a half coordinated water molecules, as well as one lattice water molecule (Figure S1, Supporting Information). It should be noted that all the three Cd(II) cations locate at different special positions with half occupancy. Different from any Cd(II) cations in the former eight complexes, all the Cd(II) cations here exhibit distinct coordination spheres with the coordination numbers varying from six to eight, which are further bridged by L, sulfate dianions and p-BDC2− dianions to form intricate 3D framework (Figure 9c). Alternatively, this framework can be understood in the following manner. The sulfate dianions join adjacent Cd1 and Cd2 cations though O5, O6, and O7 atoms to generate dinuclear units, which are further connected by two types of pBDC2− dianions to generate a (4,4) layer structure (Figure S7, Supporting Information). The Cd3 cations act as linker to connect these layers through the left O8 atoms of sulfate anions to form a 3D porous framework as illustrated in Figure 9a. Therefore, the sulfate dianions here adopt the interesting μ3 (κ1O: κ1O: κ1O: κ1O) bridging mode. By considering the dinuclear units as 6-connected nodes, this framework can be represented to be a pcu net with the Schläfli symbol of (412.63). It should be noted that the porous framework include elliptic J

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Figure 11. Diverse coordination modes of various counteranions in 3−10.

into the rhombic grid. For this reason, the Cl− anions here only act in μ2- and terminal coordination modes to furnish a dinuclear unit in the rhombic grid. Despite the fact that complex 5 also presents an sql layer, the flexible coordination mode of succinate dianions extend the single Cd(II) center into a large [Cd2(succinate)2] node (Figure 4) and the rigid coordination mode of succinate dianions and H2L2+ cations causes large windows, thus leading to the formation of a 3-fold parallel interpenetrated sql layer. The fumarate dianion in complex 6 only shows a simple bis-bidentate chelated mode. Nevertheless, three different fumarate dianions in such coordination modes join adjacent Cd(II) cations together with L in mode I to form an sra topological framework. In contrast to the aliphatic carboxylates, the aromatic carboxylates possess more abundant π-electrons and larger conjugated system. Therefore, aromatic carboxylates may present more coordination modes when they coordinate to the metal cations. In this sense, m-BDC2− dianions in complex 7 adopt μ3 (κ1O: κ1O: κ1O: κ2O) coordination modes which extend single Cd(II) cations into an snk net. The p-BDC2− dianions in complexes 8−10 exhibit three types of coordination modes and join Cd(II) cations with other bridging ligands to form diverse structures. In complex 8, the p-BDC2− dianions with the first two coordination modes connect adjacent Cd(II) cations to generate ladder chain structure. The same two coordination modes are also observed in complex 9. However, this complex presents obviously distinct tfc net owing to the attendance of the third intricate coordination mode. The p-BDC2− dianions in complex 10 only present the first type of coordination mode. Fortunately, the μ3 (κ1O: κ1O: κ1O: κ1O) bridging mode of SO42− anion supplies powerful assistance to generate a novel (44.611)(66) net with high connected nodes. Furthermore, the Cd(II) cations exhibit higher seven- and eight-coordinated spheres in complexes 3−10 than those of six-coordinated spheres in complexes 1 and 2, which could be ascribed to the abundant coordination modes and strong chelating effect of carboxylate groups. IR Spectroscopy. The IR spectra of complexes 3−10 exhibiting no CO vibration band of organic carboxylic acid at around 1700 cm−1 confirm the completely deprotonation of the carboxyl groups.37,38 The peaks observed at the range of 1677− 1610 cm−1 for these complexes are assigned to the stretching bands of νas(COO−), while the peaks observed at the range of

generate macrocycle instead of the chain structure in complexes 1, 6, and 7. Meanwhile, the other L in complex 9 shows a different mode III, in which the two neutral aliphatic N atoms do not involve in the coordination sphere. Only the two pyridyl N atoms coordinate to two Cd(II) cations to form a short stick. Then, the combination of the two types of coordination modes leads to the intricate 3D tfc net in complex 9. Mode II is observed in complexes 3, 4, and 8, which coordinate to the Cd(II) cations with two chelating aliphatic N atoms and one pyridyl N atom. The other pyridyl N atom is involved the formation of hydrogen bonds instead of coordination. Therefore, only double chain (8) and layer structures (3 and 4) are formed in these three complexes. When the spacer of L is protonated, the two aliphatic N atoms could not take part in the coordination sphere of Cd(II) cations. In such a case, the protonated ligand can act as a pseudo rigid ligand to result in novel structures. Therefore, a pseudo 2-fold interpenetrated pcu net in complex 2, 3-fold parallel interpenetrated sql layer in complex 5, as well as novel (44.611)(66) net constructed from 2fold interpenetrated pcu net in complex 10 are obtained. From the former comparison, the ligands with protonated spacers tend to induce the formation of an interpenetrated network. Structural Diversities Tuned by Different Counteranions. In addition to the coordination modes of ligand L and H2L2+ cations, the features of different counteranions are also the key factors in determining the structures of the resultant complexes. Totally, the features mainly cover the following three aspects: i.e., size, length, and rigidity-flexibility, as well as coordination mode of the anions. For the small global Cl− anion in complex 1, each Cd(II) cations can be surrounded by three or five Cl− anions (Figure S1, Supporting Information). Thus, a layer structure could be easily obtained by the bridging of Cl− anions. However, the larger tetrahedral SO42− anion in complex 2 only acts as a terminal coordination ligand that leads to the formation of a 3D supramolecular pcu net with the left three O atoms. In contrast to the inorganic anions, the organic anions exhibit more abundant coordination modes as shown in Figure 11. For complexes 3 and 4, although the malonate dianions present different coordination modes, they all exhibit an sql layer structure due to the similar coordination mode of L. The additional chelated coordination of two O atoms from different carboxyl groups in complex 4 has no contribution to the extension of dimension but captures second Cd(II) cations K

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Figure 12. PXRD pattern (a) and TG curve (b) of complex 5.

Figure 13. (a−c) Emission spectra of the 10 complexes in the solid state at room temperature.

1392−1373 cm−1 can be assigned to the stretching bands of νs(COO−). The peaks falling in the range of 1602−1422 cm−1 are ascribed to the skeletal vibration of phenyl and pyridyl rings. The stretching bands of the νC−N and νC−N in all complexes appear in the range of 1345−1215 cm−1 in the IR spectra. The characteristic vibrations of sulfate anions in complexes 2 and 10 are observed at 1122 and 1135 cm−1, respectively, which indicate the different coordination modes of sulfate anions in the two complexes. The absorptions observed at 3253 cm−1 for 1, 3289, 3185 cm−1 for 2, 3237 cm−1 for 3, 3237 cm−1 for 4, 3243, 3198 cm−1 for 5, 3239 cm−1 for 6, 3289, 3185 cm−1 for 7, 3218 cm−1 for 8, 3198 cm−1 for 9, 3200 cm−1 for 10 can be attributed to the νN−H stretching band of the spacer of −NH− CH2−CH2−NH− in L ligand. In addition, the broad bands in the area of 3480 to 3390 cm−1 represent O−H stretching modes within the free and coordinated water molecules or the formation of hydrogen-bonding interactions in the nine complexes, respectively. Powder X-ray Diffraction and Thermogravimetric Analyses (TGA). The formation and purity of these nine complexes were confirmed by comparison of their experimental PXRD patterns with the reference powder diffractogram (calculated on the basis of single-crystal X-ray diffraction data). As illustrated in Figure 12 and Figure S8 (Supporting Information), the experimental patterns of these nine complexes are nearly consistent with their simulated ones, which indicate that the single crystal structures are really representative of the bulk of the corresponding samples. And

the differences in intensity are due to the preferred orientation of the powder samples. The stabilities of these complexes were analyzed on crystalline samples by TGA from room temperature to 900 °C at a rate of 10 °C min−1, under N2 atmosphere. As illustrated in Figure 12 and Figure S9 (Supporting Information), for the anhydrous complex 1, there is no marked weight loss until 234 °C, at which the inorganic−organic hybrid framework subsequently collapses. At 660 °C, a CdO residue of 42.24% (calcd 42.18%) is obtained. And the hydrous compounds 2−10 exhibit at least two weight loss steps. The first step corresponds to the release of various coordinated or lattice water molecules with the observed weight loss of 20.47% in 2 (72−133 °C), 16.33% in 3 (70−130 °C), 5.02% in 4 (65− 149 °C), 7.92% in 5 (61−136 °C), 9.23% in 6 (74−126 °C), 4.18% in 7 (68−146 °C), 10.96% in 8 (64−124 °C), 6.82% in 9 (80−195 °C), and 5.06% in 10 (78−142 °C) being reasonably close to their calculated value (20.08% in 2, 16.46% in 3, 5.33% in 4, 8.10% in 5, 9.39% in 6, 4.33% in 7, 11.96% in 8, 7.02% in 9, and 5.43% in 10). Then, the following weight losses for these eight complexes indicate the decomposition of the resulting solvent-free frameworks. All of the residual components are corresponding to CdO with different percentages (obsrd: 18.63%; calcd: 18.53% for 2, obsrd: 23.48%; calcd: 23.61% for 3, obsrd: 38.63%; calcd: 38.91% for 4, obsrd:28.87%; calcd: 28.88% for 5, obsrd: 33.30%; calcd: 33.47% for 6, obsrd: 30.74%; calcd: 30.89% for 7, obsrd: 27.88%; calcd: 28.43% for 8, obsrd: 30.02%; calcd: 29.97% for 9 and obsrd: 32.43%; calcd: 32.21% for 10). Interestingly, complex 4 exhibits higher L

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frameworks simultaneously, complexes 7, 9, and 10 show stronger emission intensity than that of complex 8 which possesses a ladder chain structure. In particular, complex 10 presents the strongest emission intensity which is also attributed to the reason as explained for complex 2.

thermal stability than 3 owing to the involvement of the bridging inorganic anions. This is mainly attributed to the fact that the coordination of the Cl− anions increases the rigidity of the framework of 4. Luminescent Properties. Cd(II)-containing MOCPs have attracted great interest for their potential applications based on photochemical properties.31 Therefore, the luminescent properties of these 10 complexes, the free L ligands, as well as the free m-H2BDC and p-H2BDC were investigated in the solid state at room temperature. As shown in Figure S10 (Supporting Information), the free L ligands, m-H2BDC and p-H2BDC molecules exhibit emission maxima at 460, 382, and 393 nm upon excitation at 395, 340, and 346 nm, respectively. These values are nearly close to the reported values in previous work.26,29,30 Upon excitation at 340, 320, 390, 330, 390, 395, 312, 327, 326, and 353 nm, complexes 1−10 exhibit emission maxima at 420, 380 and 420, 451, 432, 447, 444, 431, 399, 436, and 386 nm, respectively (Figure 13). In comparison with the emission of free L and m-H2BDC/p-H2BDC molecules, the origin of the emissive behavior of these complexes is plausibly ascribed to ligand-to-ligand charge transfer (LLCT) or intraligand (IL) π*−π transitions within the molecular orbitals of the pyridyl rings of the L and the phenyl rings of the m-H2BDC/p-H2BDC ligands owing to the fact that the electrochemically inert Cd(II) cation is difficult to oxidize or reduce; that is, metal-to-ligand charge transfer (MLCT) and ligand-to-metal charge transfer (LMCT) are impossible essentially.29,30 Meanwhile, the emission maxima of these 10 complexes show varying degrees of shift. The differences in the band positions of these complexes might be related to the different coordination environments of Cd(II) cations, diverse conformations of L ligands, or the degree of π-electron overlap of the multitopic organic linkers in their structures.39 In view of the different content the 10 complexes involved, their luminescent behaviors are discussed in groups, that is, group I (complexes 1 and 2), group II (complexes 3−6), and group III (complexes 7−10). In group I, the emission intensity of complex 2 at 420 nm is obviously stronger than that of complex 1, which is attributed to the fact that the delocalized Π58 of SO42− offers more electrons. Such results may improve the energy level of HOMO in aromatic rings and subsequently decrease the energy gap between HOMO and LUMO, thus increasing the chance of intraligand charging transfer.40 Furthermore, the emission peak at 380 nm in complex 2 is ascribed to the massive C−H···π and π···π interactions involved in its structures that are beneficial for the electron transfer. Complexes 3−6 in group II present similar emission spectra except for minor distinction in emission intensity. The decreasing of emission intensity from complexes 3 and 4 to 5, 6 could be ascribed to the increase of the carbochain. Usually, the thermal vibrations intensify with the increasing of carbochain, which then make partial excited electrons quench through the nonradioactive transition, thus leading to the decline of emission intensity.41 Particular attention should be devoted to the larger blue shift of 28 nm toward L in complex 4. The main reason is the coordination of Cl− anions that strength the rigidity of structure and further decreases the energy loss. For group III, the aromatic carboxylates they contained are beneficial for the electron transfer through π···π interactions. Therefore, this group presents stronger emission intensity than the former two groups. Taking into account the rigid 3D

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CONCLUSIONS In summary, 10 complexes assembled from different Cd(II) salts, L, as well as various organic acids have been synthesized and characterized. The chelated coordination and protonation of spacer lead to the formation of diverse coordination modes of L and H2L2+, which then join adjacent Cd(II) cations together with different inorganic and organic anions in multiple coordination modes, forming multiple chains, sql layer, 3-fold parallel interpenetrated sql layer, 3D hybrid network, 3D sra, snk, tfc and (44.611)(66) nets. It is interesting to note that the ligand containing protonated spacer tends to induce the formation of an interpenetrated network. Luminescence analysis indicates that complex 10 exhibits strong purple solid state emission at room temperature. The results of this work may promote the development of MOCPs assembled from bis(pyridyl) ligands with chelated or protonated spacers.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.cgd.7b00174. Additional figures, PXRD patterns, TG curves, emission spectra of ligands (PDF) Accession Codes

CCDC 1526178−1526187 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Authors

*(Z.-P.D.) E-mail: [email protected]. *(S.G.) E-mail: [email protected]. ORCID

Li-Hua Huo: 0000-0003-1725-0148 Shan Gao: 0000-0001-6370-4994 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work is financial supported by the National Natural Science Foundation of China (51302067), Specialized Research Fund for the Doctoral Program of Higher Education of China (20132301120002), the Project of Natural Science Foundation of Heilongjiang Province (No. B2015007), the Scientific and Technological Innovation Talents of Harbin (2016RAQXJ005), and the Innovation team of Education bureau of Heilongjiang Province (2013td002). We thank the Key Laboratory of Functional Inorganic Material Chemistry, Ministry of Education, Heilongjiang University for supporting this study. M

DOI: 10.1021/acs.cgd.7b00174 Cryst. Growth Des. XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.cgd.7b00174 Cryst. Growth Des. XXXX, XXX, XXX−XXX