Effect of N-Donor Ligands and Metal Ions on the Coordination

Mar 14, 2016 - Complex 1 displays a tfz-d topology with (3,8)-connected structure, and the Schläfli symbol is (43)2(46.618.84). Complex 2 shows a 4-c...
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Effect of N‑Donor Ligands and Metal Ions on the Coordination Polymers Based on a Semirigid Carboxylic Acid Ligand: Structures Analysis, Magnetic Properties, and Photoluminescence Xiu-Yan Dong,† Chang-Dai Si,*,†,§ Yan Fan,† Dong-Cheng Hu,† Xiao-Qiang Yao,† Yun-Xia Yang,† and Jia-Cheng Liu*,†,‡ †

College of Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou 730070, P. R. China State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, P. R. China § College of Chemical Engineering and Technology, Tianshui Normal University, Tianshui 741001, P. R. China ‡

S Supporting Information *

ABSTRACT: Seven novel coordination polymers derived from the 3-(3′,5′-dicarboxylphenoxy)phthalic acid (H4L) ligand have been constructed under similar synthesized conditions with Co(II), Zn(II), Cd(II) ions in the presence of N-donor ancillary ligands, namely, [Co2(HL)(4,4′-bipy)(μ3OH)(μ2-H2O)]n (1), [Co2(L)(dpa)2]n (2), {[Co2(L)(4,4′bibp)(H2O)4]·H2O}n (3), [Co2(L)(dib)2]n (4), [Co2(L)(bix)1.5]n (5), [Zn2(L)(bix)1.5]n (6), and {[Cd2(L)(bix)0.5(H2O)]·2H2O}n (7). The various topologies of the structures have been generated by adjusting the N-donor ligands and the central metal ions. Complex 1 displays a tfz-d topology with (3,8)connected structure, and the Schläfli symbol is (43)2(46.618.84). Complex 2 shows a 4-connected structure of sod topology with a Schläfli symbol of (42.64), forming a three-dimensional (3D) 2-fold interpenetrating structure. Complex 3 presents a novel (3,3,4)-connected topology with a Schläfli symbol of (63.83)(63)(83) and shows 2D → 3D supramolecular structure through C− H···O hydrogen bonds. Complex 4 features a four-connected structure of Nbo topology. Complex 5 and 6 are defined as the same novel (4,4,5)-connected topology with a Schläfli symbol of (4.5.6.83)(42.53.6)(43.53.62.72). In addition, complex 7 can be simplified as a (3,8)-connected tfz-d topology with a Schläfli symbol of (43)2(46.618.84). The contrast of 1−5 reveals that the ancillary ligands have key roles in adjusting the crystal structures, and the contrast of 5−7 indicates the central metal ions’ influences. Moreover, the magnetic properties of 1−5 and the fluorescence properties of 6 and 7 are discussed.

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INTRODUCTION The research of coordination polymers (CPs) has evolved continuously in recent years, which is attributed to the CP’s appealing nature of structural and topological novelty,1−3 as well as properties in magnetism,4,5 catalysis,6−8 nonlinear optics,9−11 ion exchange,12,13 and so on. In order to control the structural architectures and tune the properties of CPs through rational design, many researchers have adopted various synthetic strategies to obtain the desired CPs.14−16 Although the great progress has been achieved on the theoretical aspects and experiment area,17−20 it is still a great challenge to explore various factors that influence the final target crystalline products, such as the organic ligand, metal ion, ratio of reactants, solvent, pH value, temperature, and the nature of the anion.21−26 Generally, building CP materials with good structure and application potential mainly depend on the configuration and coordination group of the ligands and the characteristics of metal ions. In particular, the conformational flexibility of the ligand is an important factor that should be considered in the design of the targeted CPs, because the linker could adopt various conformations in the crystallization and that further leads to structural isomerism. © XXXX American Chemical Society

In this work, we chose 3-(3′,5′-dicarboxylphenoxy)phthalic acid (H4L) as the main ligand and five N-donor as the ancillary ligands based on the following design (Scheme 1). First, H4L is a semirigid V-shaped polycarboxylate ligand, which has superior coordinating ability and variable conformations justified by our group, so it is very efficient for construction of CPs as an organic building unit.41 However, it is believed that the CPs containing H4L with various structures and properties could still be obtained by changing ancillary ligands and metal ions.27 Second, the varying spacers of ancillary N-donor ligands will result in forming of different voids,28,29 and also N-donor ligands have certain influences on the coordination mode of carboxylate acid.30−32 Apart from the impacts of ancillary ligands, metal cations’ influence is also the focus of these issues,33−40 while other conditions are the same; employing various metal cations would get different structures. And the effect of the metal Received: December 8, 2015 Revised: March 9, 2016

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DOI: 10.1021/acs.cgd.5b01734 Cryst. Growth Des. XXXX, XXX, XXX−XXX

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Scheme 1. Synthesis Scheme of Complexes 1−7

Table 1. Crystal Data and Structure Refinement for Complexes 1−7 complex

1

2

3

4

5

6

7

formula F.W. cryst system space group a/Å b/Å c/Å α/° β/° γ/° V (Å3) Dc (g/cm3) Z F(000) GOF R1 [I > 2σ(I)]a wR2 [I > 2σ(I)]b

C26H18Co2N2O11 652.28 triclinic P1̅ 9.393(4) 12.318(5) 13.170(5) 113.035(6) 106.733(6) 96.040(6) 1301.2(9) 1.665 2 660 1.093 0.0384 0.1028

C36H24Co2N6O9 802.47 triclinic P1̅ 8.625(4) 14.964(7) 15.404(8) 61.850(8) 77.690(8) 82.307(8) 1711.4(15) 1.557 2 816 1.076 0.0514 0.1415

C32H26Co2N2O14 780.41 monoclinic C2/c 36.136(4) 9.6648(11) 22.323(3) 90.00 123.205(2) 90.00 6523.3(13) 1.589 8 3184 1.055 0.0398 0.1059

C40H26Co2N8O9 880.55 orthorhombic P212121 10.523(3) 14.711(4) 23.163(6) 90.00 90.00 90.00 3585.6(16) 1.631 4 1792 1.070 0.0472 0.1168

C37H27N6O9Co2 817.51 triclinic P1̅ 12.664(6) 13.004(6) 13.129(6) 89.829(7) 62.953(7) 72.347(7) 1811.6(14) 1.499 2 834 1.032 0.0504 0.1275

C37H27N6O9Zn2 830.39 triclinic P1̅ 12.5985(16) 12.9183(16) 13.0604(17) 90.108(2) 116.673(2) 107.752(2) 1784.8(4) 1.545 2 846 1.094 0.0469 0.1502

C23H19Cd2N2O12 740.20 triclinic P1̅ 10.6765(5) 11.1706(6) 12.2603(6) 63.7200(10) 67.6980(10) 84.2230(10) 1208.99(10) 2.033 2 726 1.073 0.0189 0.0468

a

R1 = Σ∥F0| − |Fc∥/Σ|F0|. bwR2 = |Σw(|F0|2 − |Fc|2)|/Σ|w(F0)2|1/2, where w = 1/[σ2(F02) + (aP)2 + bP]. P = (F02 + 2Fc2)/3. urements were collected by a Quantum Design MPMS(SQUID)-XL magnetometer under a field of 1000 G. Synthesis of [Co2(HL)(4,4′-bipy)(μ3-OH)(μ2-H2O)]n (1). A mixture of Co(OAc)2·4H2O (40 mg, 0.16 mmol), H4L (27.7 mg, 0.08 mmol), 4,4′-bipy (12.5 mg, 0.08 mmol), and H2O (8 mL) was placed in a 25 mL Teflon-lined autoclave and heated to 140 °C for 3 days, when the mixture cooled to room temperature, Purple block-shaped crystals of 1 were obtained in 71% yield (based on H4L). Anal. Calcd for C26H18N2O11Co2 (652.28): C, 47.87; H, 2.78; N, 4.29%. Found: C, 47.92; H, 2.65; N, 4.27%. IR (cm−1, KBr): 3606(m), 3348(w), 3095(m), 1961(w), 1936(w), 1608(s), 1586(s), 1476(m), 1413(s), 1370(s), 1261(s), 1228(m), 1151(m), 1098(m), 1067(m), 1004(s), 916(s), 848(m), 814(s),766(s), 690(s), 632(s). Synthesis of [Co2(L)(dpa)2]n (2). The synthesis of 2 used the same condition as with 1 except that 4,4′-bipy was replaced by dpa. Purple crystals of 2 were collected with yield 32% based on Co. Anal. Calcd for C36H24Co2N6O9 (802.47): C, 53.88; H, 3.01; N, 10.47%. Found: C, 53.75; H, 3.13; N, 10.51%. IR (cm−1, KBr): 3454(m), 3172(w), 2922(w), 1633(m), 1599(s), 1526(s), 1489(w), 1446(m), 1384(m), 1354(m), 1238(m), 1213(s), 1107(w), 1061(m), 1024(s), 848(s),815(s), 771(m), 729(m). Synthesis of {[Co2(L)(4,4′-bibp)(H2O)4]·H2O}n (3). The synthesis of 3 used the same condition as with 1 except that 4,4′-bipy was replaced by 4,4′-bibp. Purple crystals were obtained with yield 29% based on Co. Anal. Calcd for C32H26Co2N2O14 (780.41): C, 49.25; H, 3.36; N, 3.59%. Found: C, 50.9; H, 3.28; N, 3.62%. IR (cm−1, KBr): 3451(s), 3124(m), 2921(s), 2873(m), 1581(s), 1533(m), 1424(w), 1377(s), 1303(s), 1278(w), 1186(w), 1129(s), 1011(w), 987(w), 932(w), 869(m), 831(m), 767(m), 747(m), 721(m), 683(s),638(m).

cations on the coordination mode of carboxylate acid and the frameworks can be observed. Inspired by these ideas, we build five complexes (1−5) by using the N-donor ligands as the structure-linking agents in the H4L-CoII synthesis system, namely, [Co2(HL1)(4,4′-bipy)(μ3OH)(μ2-H2O)]n (1), [Co2(L)(dpa)2]n (2), {[Co2(L)(4,4′bibp)(H2O)4]·H2O}n (3), [Co2(L)(dib)2]n (4), and [Co2(L)(bix)1.5]n (5). And introducing ZnII, CdII into the H4L-bix synthesis system, 6 and 7 were synthesized, namely, [Zn2(L)(bix)1.5]n (6), and {[Cd2(L)(bix)0.5(H2O)]·2H2O}n (7). The topological analyses of the seven complexes and the effects of ancillary ligands and Co(II), Zn(II), and Cd(II) ions on the framework of CPs have been researched in detail. Moreover, the magnetic properties of complexes 1−5 and the fluorescence properties of 6 and 7 have been investigated.

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EXPERIMENTAL SECTION

Materials and Physical Measurements. The ligand 3-(3′,5′dicarboxylphenoxy)phthalic acid (H4L) was obtained according to the literature.41 Other chemicals and solvents were purchased directly and without further purification. The elemental analyses were determined using a VxRio EL Instrument. The infrared (IR) spectra (4000−400 cm−1) were taken in KBr pellets on an FTS 3000 (the United States DIGILAB) spectrometer. Thermogravimetric analysis (TGA) was performed on a PerkinElmer TG-7 analyzer in the temperature range 25−800 °C with a heating rate of 10 °C/min under N2 atmosphere. Powder X-ray diffraction (PXRD) data were collected on a Philips PW 1710-BASED diffractometer. Temperature-dependent magnetic measB

DOI: 10.1021/acs.cgd.5b01734 Cryst. Growth Des. XXXX, XXX, XXX−XXX

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Figure 1. (a) Coordination environment of Co(II) ion in 1 (hydrogen atoms are omitted for clarity). Symmetry codes: A, −x, 1 − y, −z; B, −x, −y, −z; C, x, 1 + y, z; D, 1 + x, 1 − y, 1 − z. (b) The view of 2D network formed by L ligands. (c) The 3D supermolecular framework. (d) The 3D topology of the complex 1. methods and refined by full-matrix least-squares based on F2 using the SHELXL-97.44 Non-hydrogen atoms were refined with anisotropic, and the hydrogen atoms were included in the final refinement by using geometrical restrains and refined isotropically using the riding model. Table 1 shows the crystallographic crystal parameters and data collection for complexes 1−7. Crucial angles [deg] and bond distances [Å] are listed in Table S1 (Supporting Information), while hydrogen bonds of 3 were shown in Figure S2 (Supporting Information). The CCDC reference number lists: 1060397 (1), 1060390 (2), 1060392 (3), 1060389 (4), 1060396 (5), 1060394 (6), and 1440086 (7).

Synthesis of [Co2(L)(dib)2]n (4). The synthesis of 4 used the same condition as with 1 except that 4,4′-bipy was replaced by dib. Purple crystals were collected with yield 49% based on Co. Anal. Calcd for C40H26N8O9Co2 (880.55): C, 54.56; H, 2.98; N, 12.73%. Found: C, 54.49; H, 3.12; N, 12.60%. IR (cm−1, KBr): 3445(w), 3115(s), 2925(w), 2666(w), 1582(m), 1554(s), 1530(s), 1474(w), 1447(m), 1399(m), 1372(s), 1303(m), 1255(s), 1124(s), 1072(s), 1014(m), 960(m), 921(w), 833(s), 779(s), 763(m),734(s), 657(s). Synthesis of [Co2(L)(bix)1.5]n (5). The synthesis of 5 used the same condition as with 1 except that 4,4′-bipy was replaced by bix. Purple crystals were collected with yield 52% based on Co. Anal. Calcd for C37H27N6O9Co2 (817.51): C, 54.36; H, 3.33; N, 10.28%. Found: C, 54.31; H, 3.30; N, 10.31%. IR (cm−1, KBr): 3621(m), 3516(w), 3391(w), 3239(w), 3118(s), 1571(s), 1476(m), 1409(m), 1379(s), 1240(s), 1089(s), 1001(m), 951(m), 869(m), 812(s), 752(s), 655(m), 619(w). Synthesis of [Zn2(L)(bix)1.5]n (6). The synthesis of 6 used the same condition as with 5 except that Co(OAc)2·4H2O was replaced by Zn(NO3)2·6H2O. Colorless crystals of 6 were obtained with yield 59% based on Zn. Anal. Calcd for C37H27N6O9Zn2 (830.39): C, 53.52; H, 3.28; N, 10.12%. Found: C, 53.62; H, 3.28; N, 10.04%. IR (cm−1, KBr): 3620(m), 3512(w), 3235(w), 3120(s), 3071(m), 1575(s), 1533(w), 1381(m), 1347(s), 1242(s), 1091(s),1001(m), 950(m), 923(m), 812(s), 753(s), 656(m), 619(w). Synthesis of {[Cd2(L)(bix)0.5(H2O)]·2H2O}n (7). The synthesis of 7 used the same condition as with 5 except that Co(OAc)2·4H2O was replaced by Cd(NO3)2·4H2O. Colorless crystals were collected with yield 56% based on Cd. Anal. Calcd for C23H19Cd2N2O12 (740.20): C, 37.32; H, 2.59; N, 3.78%. Found: C, 37.36; H, 2.65; N, 3.76%. IR (cm−1, KBr): 3526(w), 3367(m), 3242(m), 3122(m), 2488(w), 2237(m), 1956(m), 1804(m),1613(m), 1517(m), 1456(m),1392(m), 1297(m), 1250(s), 1201(s), 1167(m), 1120(s), 1088(s), 1072(w), 1010(s), 996(s), 943(s), 898(s), 843(m), 818(s), 766(s), 723(s), 698(m), 650(s), 623(m), 614(w). X-ray Crystallography. Single-crystal X-ray diffraction data of the complexes 1−7 were collected on a Bruker Smart Apex CCD diffractometer (Mo−Kα, λ = 0.71073 Å) with graphite-monochromated at 20 ± 1 °C. The diffraction data were integrated and intensity corrections for the Lorentz and polarization effects were performed by using the SAINT program.42 All absorption corrections were applied using SADABS program.43 All structures were solved by direct

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RESULTS AND DISCUSSION Crystal Structure of [Co2(HL)(4,4′-bipy)(μ3-OH)(μ2H2O)]n (1). The result of single crystal X-ray diffraction analysis showed that complex 1 crystallized in the triclinic P1̅ space group (Table 1). There are two independent Co(II) atoms, one HL3− ligand, one hydroxyl group, one 4,4′-bipy ligand, and one coordination water in the asymmetric unit. As depicted in Figure 1a, Co1 and Co2 are all six-coordinated in distorted octahedral coordination geometries, but the Co1 and Co2 coordination environments are a little distinct from each other. Co1 coordinates with one N atom (N2) from 4,4′-bipy ligand, two O atoms (O2, O9B) from two different HL3− ligands, two O atoms (O11, O11A) from two different hydroxyl groups, and one O atom (O10) from coordination water. Co2 is surrounded by one N atom (N1D) from the 4,4′-bipy ligand, three O atoms (O1, O6, O8C) from two different HL3− ligands, one O atom (O11) from one hydroxyl group and O atom (O10A) from coordination water. The Co−O bond lengths vary from 2.044(2)−2.333(2) Å, and the Co−N ones are 2.129(2) and 2.135(2) Å (Table S1, Supporting Information), which are in the normal ranges in both cases. Four crystallographically distinct Co(II) ions are bound together by two hydroxyl groups, two μ2-water molecule and four carboxylate groups to form a tetranuclear [Co4(μ3OH)2(μ2-H2O)2(COO)4]2+ unit (Figure S6, Supporting Information). The distances of intermetallic which are spanned by the μ3 -O groups are 3.5336(11), 3.1379(13), and C

DOI: 10.1021/acs.cgd.5b01734 Cryst. Growth Des. XXXX, XXX, XXX−XXX

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Figure 2. (a) Coordination environment of the Co(II) ion in 2 (hydrogen atoms are omitted for clarity). Symmetry codes: A, 1 − x, −y, −z; B, 2 − x, −y, 1 − z; C, 1 − x, 1 − y, −z; D, −1 + x, y, 1 + z. (b) 1D ladder-like structure formed by L ligands (c) The view of 2D network formed by L and dpa ligands. (d) The 3D supermolecular framework. (e) The 3D 2-fold interpenetrating framework. (f) The 3D topology of the complex 2.

Given that different bridging angles of ligands might have an effect on the structure, thus dpa instead of 4,4′-bipy participated in the Co(II)-semirigid carboxylic acid (H4L) system, complex 2 was isolated. The independent unit of 2 is composed of one L4− anion, two independent Co(II) ions, and two dpa ligands (Figure 2a). As depicted in Figure 2a, Co1 is four-coordinated by two N atoms (N1, N4B) from two different dpa ligands and two O atoms (O2A, O6) from two different L4− ligands forming a tetrahedral geometry with Co1− O lengths of 1.920(4) and 1.924(3) Å, and the Co1−N distances are 2.027(4) and 2.055(3) Å. However, Co2 is fivecoordinated with square-pyramidal coordination geometry by two N atoms (N2D, N3) from the pyridyl ring of the different dpa, three O atoms (O3C, O7, O8) coming from two distinct L4− ligands ligands with Co2−O lengths extending from 2.000(3) to 2.361(4) Å, and the Co2−N bond distance is 2.071(4) Å (Table S1, Supporting Information). The Co(II) atoms are joined by double L4− ligands to result in the Co2L2 22-membered and Co2L2 24-membered cycle with a diameter approximately 7.2 and 10.2 Å in 2. Two strands of L4− are held together by Co(II) atoms and wrapped around each other to form a double chain with a Co−Co distance of 7.231(4) Å (Co1−Co1) 10.253(4) Å (Co2−Co2) (Figure 2b). Adjacent 1D double chains are linked by dpa ligands to construct the unusual 2D network (Figure 2c), which are pillared by the other dpa to form a 3D framework, and the distance of adjacent layers is 11.49 Å (Figure 2d). Large

3.2232(13) Å for Co2···Co1, Co2···Co1A, and Co1···Co1A, respectively, and two neighboring tetranuclear units via two bridging 4,4′-bipy ligands, forming the 1D chain structure (Figure S1, Supporting Information). If the connection of 4,4′bipy ligands is ignored, each tetranuclear unit is shrouded within six HL3− anions, each of which is connected with three tetranuclear units (Figure S3a, Supporting Information). A 2D layer can be formed by the HL3− anions connecting with the tetranuclear units (Figure 1b), which also can be acquired a 3D framework by the 4,4′-bipy ligands (Figure 1c). Topological analysis can get a better insight into the structure of 1.45,46 As mentioned above, each HL3− ligand is neighbored by three tetranuclear [Co4(μ3-OH)2(μ2-H2O)2(COO)4]2+ units which can be viewed as a three-connector, while the tetranuclear [Co4(μ3OOH)2(μ2-H2O)2(COO)4]2+ units can be considered as eight-connected nodes (Figure S3a, Supporting Information). Thus, the 3D framework acquired can be simplified as a (3,8)-connected net with (43)2(46.618. 84) topology (Figure 1d). Crystal Structure of 2−5. In order to research the effect of N-donor ligands on the Co(II)-semirigid carboxylic acid (H4L) system, the same synthetic procedure was repeated substituting 4,4′-bipy by dpa, 4,4′-bibp, dib, and bix as auxiliary N-donor ligands. Inspired by these ideas, we can use the auxiliary ligands, as the structure-directing agents, to form the other four different structures of 2−5. D

DOI: 10.1021/acs.cgd.5b01734 Cryst. Growth Des. XXXX, XXX, XXX−XXX

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Figure 3. (a) Coordination environment of Co(II) ion in 3 (hydrogen atoms and water molecules are omitted for clarity). Symmetry codes: A, x, 2 − y, −0.5 + z; B, x, 1 − y, −0.5 + z; C, 0.5 − x, 0.5 − y, 1 − z; D, 0.5 − x, 0.5 − y, −z. (b) The view of 2D network formed by L ligands. (c) The 2D double layer network formed by 4,4′-bibp ligands and the 2D network showed in b. (d) The 3D supermolecular structure. (e) The 3D topology of the complex 3. (f) The detail of the hydrogen bonds among coordinated water molecules and uncoordinated carboxylate groups between the adjacent 2D layers in 3.

fashion as μ 4 -η 1 :η 0 :η 1 :η 0 :η 1 :η 0 :η 1 :η 0 coordination mode (Scheme S1c, Supporting Information), leading to a 2D wavelike grid layer (Figure 3b). The 4,4′-bibp ligands play bridging linkers role, and the N atoms coordinate with the Co1 ions of the 2D layer to construct a “sandwich” 2D double layer network (Figure 3c). Through H-bonding between −OH of the coordinated water and the free carboxylate O of L4− ligand from adjacent layers, those 2D layers are stacked along the baxis, forming a polycatenated 3D supramolecular framework (Figure 3d,f). The topological approach is used to simplify the 3D framework for better learning of the structure. Obviously, the metal centers and L4− ligands can be regarded as threeconnected nodes and four-connected nodes (Figure S3c, Supporting Information); therefore, the whole structure can be seen as a (3,3,4)-connected topological network with a Schläfli symbol of (63.83)(63)(83), which is a novel topology (Figure 3e). Compared with 1, the longer linear ligand dib was introduced instead of 4,4′-bipy to investigate the effect of ligand length on the structure; complex 4 with a 3D framework was obtained which crystallized in the orthorhombic system with space group P212121. The result of single crystal X-ray diffraction analysis revealed that the asymmetric unit of 4 consists of one molecule of [Co2(L)(dib)2]. As depicted in

vacancies exist in the 3D framework, and through the interpenetration, the large cavities are completely filled,47,48 forming a 2-fold interpenetrating 3D framework (Figure 2e). To simplify the framework, Co1, Co2, and L4− ligands in mode 1b (Scheme S1, Supporting Information) can all be regarded as four-connectors (Figure S3b, Supporting Information). Thus, the structure of 2 is a four-connected uninodal 3D framework with as depicted in Figure 2f. The Point Schläfli symbol for the net is (42.64) calculated by the TOPOS program. How about the other longer ligands displacing the 4,4′-bipy of 1? Can they retain a similar network or not? When 4,4′-bibp was introduced in the reactions mentioned above, an entirely different framework of complex 3 was obtained. One [Co2(L)(4,4′-bibp)(H2O)4]·H2O molecule is the only component element for the asymmetric unit of 3. As illustrated in Figure 3a, Co1 is six-coordinated in an octahedral coordination environment, defined by two N atoms from two different 4,4′bibp ligands, and four O atoms from one individual L4− anions and three coordination water molecules, while Co2 is fourcoordinated, surrounded by four O atoms from three different L4− anions and one coordination water molecule, forming a distorted tetrahedral coordination. The Co−O are in the ranges of 1.965(3)−2.162(3) Å, and the Co−N bond distances are 2.132(3) and 2.136(3) Å, respectively. The four carboxylate groups of the L4− anions bind to the metal ions in the same E

DOI: 10.1021/acs.cgd.5b01734 Cryst. Growth Des. XXXX, XXX, XXX−XXX

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Figure 4. (a) Coordination environment of Co(II) ion in 4 (hydrogen atoms are omitted for clarity). Symmetry codes: A, 1.5 − x, −y, −0.5 + z; B, −1 + x, y, z; C, −0.5 + x, 0.5 −y, −z; D, −0.5 + x, −0.5 − y, −z. (b) The view of 2D network formed by L ligands. (c) The 3D supermolecular structure. (d) The 3D topology of the complex 4. (e−g) right- and left-handed helix chains.

complexes and take into account the coordination property of the auxiliary ligand, bix was introduced as an auxiliary ligand; complex 5 with a novel structure was obtained as expected. As shown in Figure 5a, the asymmetric unit of 5 consists of one [Co2(L)(bix)1.5] molecule. Although both Co1 and Co2 are four-coordinated in distorted tetrahedral coordination geometries, their coordination environments are completely different. Co1 is coordinated by three O atoms from three individual L4− anions and one N atom from a bix ligand, while Co2 is surrounded by two O atoms from two individual L4− anions and two N atoms from two individual bix ligands. The Co−O and Co−N bond distances are in the ranges of 1.954(3)−2.003(3) and 2.003(4)−2.046(4) Å, respectively. The ligand of L4− in 5 is fully deprotonated and acts as one μ5η1:η1:η1:η0:η1:η0:η1:η0 (Scheme S1e, Supporting Information) coordination mode to coordinate with five Co(II) ions via five dentate atoms. If the connection of bix ligands is ignored, the Co1 and Co2 ions are bridged alternately by the above L4− ligands to form a 2D layer structure along the ab plane. It is worth noting that the two crystallographic independent bix ligands show different coordination modes represented by type A (side by side) and type B (side to side). In this 2D layer, the Co1 atoms of the binuclear Co(II) unit are linked the neighbored Co2 atoms of the binuclear Co(II) unit by the bix ligand as type A along the b direction (the distance of center of binuclear Co(II) unit is 10.234 Å), resulting in a novel 2D layer (Figure 5b). Better insight into these 2D layer frameworks can

Figure 4a, each Co(II) atom is surrounded by three O atoms of carboxylate groups (Co−O = 1.967(4)−2.302(4) Å) provided by two L4− ligands and two N atoms (Co−N = 2.028(5)− 2.053(5) Å) from the imidazole ring of the different dib, to give geometries between square pyramid and trigonal bipyramid (τ = 0.47 for Co1, τ = 0.42 for Co2). In complex 4, Each L4− ligand with mode d (Scheme S1d, Supporting Information) adopts a μ4-bridging mode to connect four Co(II) atoms. If the connection of dib ligands are ignored, L4− ligands connect Co(II) atoms to form a 2D network (Figure 4b), in which two of the four carboxylate groups is in μ1-η1:η0-monodentate, and the rest are both in μ1-η1:η1 fashion. Adjacent 2D networks are linked by dib ligands through their coordinated nitrogen atoms to form one 3D framework, as seen in Figure 4c. It is particular to find that the Co(II) ions linked by the dib ligands to form right- and left-handed helix chains with a pitch of 14.711 Å, the helix chains alternately arrange in right- and left-handed sequences, and the whole sheet show no chirality (Figure 4e−g). TOPOS analysis reveals that the 3D framework of 4 can be rationalized to a four-connected new net with point symbol of {64.82} (Figure 4d), where the L4− ligand can be considered as a four-connected node, and each Co1 and Co2 metal center is also considered as four-connected, respectively, during simplification (Figure S3d, Supporting Information). To further investigate the influence of the length and bridging angle of ligand on the structural adjustment of the F

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Figure 5. (a) Coordination environment of Co(II) ion in 5 (hydrogen atoms are omitted for clarity). Symmetry codes: A, −1 + x, y, 1 + z; B, 1 − x, −y, 2 − z; C, −1 + x, −1 + y, 1 + z; D, 1 − x, 1 − y, 2 − z; E, 3 − x, −y, 1 − z. (b) The view of 2D network formed by L ligands. (c) The 3D supermolecular structure. (d) Schematic diagram of 2D network. (e) The 3D topology of the complex 5. (f) Schematic diagram of 3D network.

Figure 6. (a) Coordination environment of Cd(II) ion in 7 (hydrogen atoms and water molecules are omitted for clarity). Symmetry codes: A, x, y, −1 + z; B, 1 + x, y, −1 + z; C, 1 + x, y, z; D, 2 − x, −y, 3 − z; E x, y, 1 + z; F, 1 − x, 1 − y, 1 − z. (b) The view of 2D network formed by L ligands. (c) The 3D supermolecular structure. (d) The 3D topology of the complex 7. G

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According to the structural descriptions above, it can be seen that the auxiliary N-donor ligands uniformly behave as binodal linkers to connect the metal centers in 1−7, and also among these complexes, the main caboxylate ligands H4L are completely deprotonated except three deprotonated carboxylic (HL3−) in 1, which was confirmed by the crystal structure analysis and IR spectral data. And the carboxylate groups show different coordination modes in 1−7, namely, μ 5 η1:η1:η1:η1:η1:η0 in 1, μ4-η1:η1:η1:η0:η1:η0:η1:η0 in 2, μ4η1:η0:η1:η0:η1:η0:η1:η0 in 3, μ4-η1:η1:η1:η1:η1:η0:η1:η0 in 4, μ5η1:η1:η1:η0:η1:η0:η1:η0 in 5 and 6, and μ7-η1:η2:η1:η2:η1:η1:η1:η1 in 7 (Scheme S1, Supporting Information). How can this phenomenon be explained? The reason is that the solution pH is varied by regulating of the neutral auxiliary ligands.49 Under the same conditions, 4,4′-bipy only enables three carboxyl deprotonations, while dpa, dib, 4,4′-bibp, and bix can fully make four carboxyl deprotonations. In addition, all of complexes 1−7 show 3D structures with different topologies. Comparing the syntheses of 1 and 5, the same Co(II) ion and L4− anions were used, and multinuclear subunits are observed in the two complexes (1: tetranuclear, 5: binuclear). However, the final structures and topologies are not alike, which could be due to the different neutral auxiliary ligands. On the other hand, the preparation of complexes 2, 3, and 4 were similar to the synthesis of 1 but with different auxiliary ligands. However, the structure of 3 is absolutely different from other complexes, which could be ascribed to the length of the ancillary ligands increasing, forming a double 2D layer which can be further connected together by H-bond interaction. In the case of 2 and 4, the L4− anions link with the metal centers form 2D layers, and the 2D layers are connected by ancillary ligands with pyridyl and imidazole groups from different directions to obtain different 3D structures. As we know, the central metals have certain effects on the final structures of the CPs. When we just displace the central metals Co(II) of complex 5 by Zn(II) and Cd(II), complexes 6 (the same as 5) and 7 were obtained. Complex 7 implies the central metals’ effect on the complex structures. Compared with 5, the complex 7 has an additional bridging coordinated carboxylate group and the semirigid N-donor adopted the only one type to further bridge the 2D layer by Cd-L4−, resulting in a 3D supramolecular framework. On the basis of these structures it may be concluded that the ancillary ligands have a significant effect on the coordination modes of H4L (semirigid carboxylic acid) and the final structures. So, we can come to the conclusion that the rational adjustment of N-donor ligands is a feasible method to get the perfect structure of the coordination frameworks. Magnetic Properties. The magnetic susceptibility measurements were investigated in the range of 2−300 K. For complex 1, the χMT value is 6.60 at 300 K, which is larger than two high-spin Co(II) ions (3.75 cm3 K mol−1, S = 3/2, g = 2.0). When the temperature is lowered, the χMT value continuously decreases to 0.16 cm3 K mol−1 at 2.0 K, which shows the presence of antiferromagnetic coupling between octahedral Co(II) ions. With decreasing temperatures, it is notable that the χM value undergoes a steep decrease in 6−27 K (Figure 7).50 The reciprocal susceptibilities (1/χM) of 1 obeys the Curie− Weiss law with θ = −67.72 K and C = 8.06 cm3·K·mol−1 above 32 K (Figure 7 inset). In the light of the structure of 1, each tetranuclear cobalt cluster has four different magnetic exchange pathways: J1 (one μ3-OH and one μ1,3-carboxylate groups bridge), J1′ (one μ2-

be accessed by the schematic diagram as shown in Figure 5d. These layered structures are pillared by another bix ligand to complete the 3D connectivity (Figure 5c, f). To simplify the framework, Co1 atoms, Co2 atoms, and L4− ligand can be regarded as three-, three-, and five-connectors (Figure S3e, Supporting Information). Thus, the resulting structure of 5 is a (4,4,5)-connected three-nodal 3D net with a Schläfli symbol of (4.5.6.83)(42.53.6)(43.53.62.72), as depicted in Figure 5e. Crystal Structure of [Zn2(L)(bix)1.5]n (6) and {[Cd2(L)(bix)0.5(H2O)]·2H2O}n (7). To investigate the effect of the bridging-angles and spacer length of N-donor ligands as the structure-directing agents on the structures of the Co(II)semirigid carboxylic acid (H4L) system, 4,4′-bipy, dpa, 4,4′bibp, dib, and bix as ancillary N-donor ligands in 1−5. On considering the influence of the nature of metal centers, we replaced Co(II) cation of the bix-Co(II)-semirigid carboxylic acid (H4L) system by Zn(II) and Cd(II) cations under the same conditions. On the basis of this strategy, could we get a similar structure as 5? When the Zn(II) cations was introduced into the aforementioned reactions, one completely similar framework of complex 6 was obtained (Figure S4, Supporting Information). Further when Cd(II) instead of Co(II) was introduced into the synthesis of 5 under the same reaction conditions, beyond our expectation, another kind of 7 was obtained. The asymmetric unit of 7 is composed of one [Cd 2 (L)(bix)0.5(H2O)] molecule and two lattice water molecules (Figure 6a). The two Cd(II) atoms present five-coordinated and adopt trigonal bipyramidal and pyramidal coordination geometry, respectively. The Cd−O bond distances range from 2.193(16) to 2.462(15) Å, and the Cd2−N1 bond distances are 2.194(2) Å, respectively, which are all in the normal range. In this structure, the 2D double-fold layers are constructed by the connection between Cd(II) ions and L4− anions, in which tetranuclear {Cd4(COO)6}2+ clusters are formed by carboxylate groups of L4− anions and are arranged alternately (Figure 6b, Figure S5, Supporting Information). Cd2 and Cd2A ions are related to each other by coordinating with two N atoms of the bix ligand, and so the 2D layers are linked into a 3D framework (Figure 6c). Although the synthesis reaction conditions were the same as with 5 but the structure is not alike, the bridging bix ligand was observed just by type B (side to side) in complex 7. Each {Cd4(COO)6}2+ cluster is connected by two bix ligands and six carboxylate groups from three L4− linkers, so {Cd4(COO)6}2+ cluster is considered as an eight-connected node (Figure S3f, Supporting Information). The L4− ligands acted as a 3-connected node. Through simplification, this framework can be considered as a binodal (3,8)-connected tfz-d topological network with the point symbol of (43)2(46.618.84) (Figure 6d). Effects of N-Donor Ancillary Ligand and Central Metal Ion on the Structure. With the attraction of coordination chemistry to design and synthesis of novel multidimensional CPs with appealing functionality, the selection of suitable organic ligands with different flexibility and length is an important key factor. In this work, we selected the semirigid carboxylic acid (H4L) as the main ligand, and used N-donor ligands (4,4′-bipy, dpa, 4,4′-bibp, dib, and bix) as the auxiliary ligands, with the purpose of exploring the effect of N-donor ligands on the synthesis and framework of target CPs. H

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Then those decreased quickly to 3.42 and 2.44 cm3 K mol−1 at 2 K for 2 and 3. It is notable that the χMT value has an increasing to a value of 4.24 cm3 K mol−1 at 20 K for 4 and finally decreases quickly to 2.89 cm3 K mol−1 at 2 K, and the magnetic behavior of 4 is remarkable, representative of a weak ferromagnetic interaction resulting from spin canting admixture in a strong single-ion behavior.59−61 These results reveal that the antiferromagnetic interaction between neighboring Co(II) ions exists in the three complexes at the high temperature region. And at low temperature the decrease of the magnetization for Co(II) complexes was determined mainly by the contribution of the orbital momentum or zero-field splitting effects of the single Co(II) ion.58,62 The magnetic susceptibilities (1/χM) obey the Curie−Weiss law in the temperature range for 2−4, giving a negative Weiss constant θ = −2.90 K and C = 5.22 cm3·K·mol−1 for 2, θ = −3.67 K and C = 3.66 cm3·K·mol−1 for 3, as well as θ = −3.08 K and C = 4.69 cm3 ·K·mol−1 for 4, confirming the antiferromagnetic interaction again in the three complexes (Figures S7−S9 inset, Supporting Information). 2−4 are all typical mononuclear Co(II) complexes, the coordinated environment of Co(II) ions is different (four and five-coordinated in 2, four and six-coordinated in 3, and fivecoordinated in 4), and with the lack of an appropriate analytical expression for an mononuclear model of these complicated system, we judged the magnetic behavior of complexes 2−4 by a phenomenological approach.57,58

Figure 7. Plots of χMT and χM vs T for 1 between 2 to 300 K. Inset: temperature dependence of χM−1. The red solid lines represent the fitting results.

H2O, one μ3-OH, and one μ1,3-carboxylate group bridge), J2 (two μ3-OH bridge), and J3; however, the value of J3 can be negligible owing to the longer Co2···Co2A distance of 5.85(22) Å.51 Though J1 and J1′ have a double bridge and triple bridge, respectively, their distances of Co(II) ions are similar; we approximately take as J1′ ≈ J1, and J3 as zero.52 Consequently, the tetranuclear cobalt cluster of 1 can be considered as a parallelogram-shaped model, which contains two different magnetic exchange pathways: J1 and J2 (Figure S6, Supporting Information). Thus, the expression of spin Hamiltonian is given as follows.53,54

χM T = A exp( −E1/kT ) + B exp(−E2 /kT )

H = −2J1(SCo1SCo2 + SCo2SCo1A + SCo1ASCo2A

The best fit was obtained in the temperature range 2−300 K for 2−3 and 21−300 K for 4, and the values are shown in Table S2 (Supporting Information). For 2, A + B = 5.24 cm3 K mol−1, which is close to Curie constant C (5.22 cm3·K·mol−1), E1/k = 14.66 K, and −E2/k = −0.28 K (corresponding to J = −0.14 cm−1). For 3, A + B = 3.72 cm3 K mol−1, which is close to Curie constant C (3.66 cm3·K·mol−1), E1/k = 28.3 K, and −E2/k = −0.35 K (corresponding to J = −0.18 cm−1). For 4, A + B = 4.81 cm3 K mol−1, which is close to Curie constant C (4.69 cm3·K·mol−1), E1/k = 119.4 K, and −E2/k = −1.15 K (corresponding to J = −0.58 cm−1). The values of E2/k are small, indicating that a very weak antiferromagnetic interaction exists, which corresponds to the antiferromagnetic exchange between Co(II) magnetic centers in similar Co(II) complexes.63−65 χMT is equal to 4.55 cm3 K mol−1 at 300 K for 5, which is higher than 3.76 cm3 K mol−1 for two uncoupled CoII ions (S = 3/2, g = 2.0), indicating that there is an nonignorable effect of spin−orbital coupling (Figure 8). Additionally, the syn-anti carboxylate bridges would account for the increased χMT when the temperature is decreased, suggesting ferromagnetic interactions between the Co(II) ions.66 In the case of the carboxylate bridge of the Co(II) ions forming an isolated spin dimer system, the magnetic susceptibility data were fitted with the intermolecular magnetic couping constants zJ′ taken into account (Figure S10, Supporting Information); the following spin Hamiltonian was postulated.67,68

+ SCo2ASCo1) − 2J2 SCo1SCo1A

The analysis of the magnetic susceptibility is according to the equation: χ ′Co4 = (2Ng 2β 2 /kT )[A/B]

Because of the phenomenon of polymetallic complexes with a singlet ground state is often observed, and considering the effect of the presence of a very small amount of noncoupled species in the sample, which is not intrinsic to the complex.55 The χCo4 may be corrected as follows: χCo4 = (1 − ρ)(2Ng 2β 2 /kT )[A/B] + ρ(5Ng 2β 2 /kT )

in which ρ is the molar fraction of noncoupled species, the parameters N, k, β, and T have their usual meanings, and A and B are given in Supporting Information. A fit to the data confirms antiferromagnetic interactions, with g = 2.02(3), J1 = −5.72(3) cm−1, J2 = −4.9(1) cm−1, R = 6.45 × 10−4 (R = Σ[(χMT)obsd − (χMT)calcd]2/Σ[(χMT)obsd]2), and ρ = 0.021. Most likely, the Co−O−Co angles can offer the potential to address magnetic behaviors pertaining to the tetranuclear cobalt cluster.53,54 The J value is consistent with the cobalt complexes, in which the neighboring Co(II) ions are connected by the μ3− OH and μ1,3-carboxylate group.56,58 The magnetic susceptibility measurements of 2−4 were investigated in the range of 2−300 K, and the changing tendencies for temperature dependence are similar. The χMT value at 300 K is 5.20 for 2, 3.61 for 3, and 4.31 for 4 (Figures S7−S9, Supporting Information), which are all larger than magnetically isolated spin-only Co(II) ions (1.88 cm3 K mol−1, S = 3/2, g = 2.0). When the temperature is down, the χMT value falls slowly until about 45, 60, 21 K for 2, 3, and 4, respectively.

H = λL · S The {Co2} expression of the magnetic susceptibility is χ ′M = (2Nβ 2g 2 /kT )[3 + exp(− 25J /9kT )]−1 I

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tion). As we know, due to the existence of the electronwithdrawing substituents, the organic carboxylate anions almost have no contribution to emissions.70 In order to study the emission nature, the free bix ligand was researched for luminescent property. The free bix ligand shows a strong emission peak (λem = 366 nm) upon excitation at 293 nm. The complex 6 exhibits an emission at 334 nm (λex = 316 nm), while complex 7 displays emissions at 336 nm (λex = 306 nm), respectively. Obviously, the N-donor bix ligand has a remarkable contribution to the emissions of the complexes. The emission bands of complexes 6 and 7 exhibit blue shifts compared with the free bix ligand, which is probably due to the ligand-to-metal charge-transfer transition (LMCT) involving the bix ligand, Zn(II) and Cd(II) ions.71−73 PXRD and Thermogravimetric Analysis. Powder X-ray diffractions (PXRD) were adopted for checking the phase purity of the samples 1−7 in the solid state. The results showed that the measured PXRD patterns correspond to the simulated patterns generated from the singlecrystal diffraction data, which indicates a pure phase of solid state sample (Figure S12, Supporting Information). The thermogravimetric (TG) analysis was also investigated for those seven complexes in N2 atmosphere. The TG data are shown in Figure S13 (Supporting Information). For 1, the weight loss between 120 and 200 °C is consistent with the loss of coordinated water molecules (obsd 5.7%, calcd 5.5%), and then the structure decomposed at 390 °C. For 2, because of no lattice and coordinated water molecules, the weight hardly changed before 420 °C. Above 710 °C, weight remaining corresponds to the formation of CoO, which is 18.7% (calcd 18.7%). The TG for complex 3 shows a first weight loss near 160 °C, which corresponds to the loss of the H2O molecules, and upon further heating, the structure is stable up to 400 °C and then has a sharp weight loss between 400 and 580 °C owing to the collapse of the structure. Complex 4 is similar to 2 and exhibits a thermal stability up to 400 °C, and then the structure starts collapsing, the remaining weight of 28.7% at 800 °C. Complex 5 has no weight change before 400 °C, and then a sharp weight loss is observed between 400 and 580°C owing to the collapse of the structure. TG analysis curve of 6 have the same trend with 5. For complex 7, the first weight loss is 6.3% (calcd 7.3%) owing to the loss of lattice and coordinated water molecules from 200 to 250°C and above 396°C the structure collapse, the remaining weight is 32.1%.

Figure 8. Plots of magnetic susceptibility in the forms of χMT and χM−1 vs T for 5 between 1.9 to 300 K. The red solid lines represent the fitting results.

χM = χ ′M /[1 − (2zJ ′/Ng 2β 2)χ ′M ]

The best fit was obtained with g = 4.90(4), J = 2.17(4) cm−1, zJ′ = −0.24(8) K, and R = 3.88 × 10−4 (R = Σ[(χMT)obsd − (χMT)calcd]2/Σ[(χMT)obsd]2), confirming the existence of the effect of spin−orbital coupling and the dominant weak ferromagnetic interaction between Co(II) in 5. zJ′ is regarded as the interdimer interaction. In addition, the magnetic susceptibility data obeys Curie−Weiss law, giving θ = 1.3(1) K and C = 4.52 cm3 K mol−1 in 2−300 K, further suggesting a weak ferromagnetic interaction. The J values is slightly smaller than that reported previously in other similar complexes.66 In order to further investigate the magnetic behavior of 5, the field dependence of the magnetization has been performed at 2, 3, and 5 K with the field range from 0 to 70 kOe. In the Mmol/ NμB vs H plots (Figure 9), the Mmol/NμB values increased

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CONCLUSION The self-assembly reactions of the H4L ligand with a series of N-donor ligands and Co(II), Zn(II), Cd(II) cations have produced seven different CPs under similar conditions. Under the influence of N-donor ligands and the metal ions, complexes 1 and 7 have similar 3D structures of tfz-d topology. Complex 2 shows an interpenetrating structure of sod topology. Complex 3 exhibits a unique double 2D layer network, and then shows 2D → 3D structure through C-H···O hydrogen bonds. Complex 4 features a four-connected structure of Nbo topology. Complexes 5 and 6 are defined as the same novel topology. Additionally, the magnetic character (for 1−5) and fluorescence (for 6 and 7) were investigated to elaborate the relationship between structures and properties. This work provides a feasible way to modify the structures of CPs by Ndonor ligands and central metal ions for their potential applications.

Figure 9. Plots of Mmol/NμB vs H at 2, 3, and 5 K, respectively.

gradually until 70 kOe. The maximum values are 4.83, 4.79, and 4.59 μB at 2, 3, and 5 K, respectively, which are lower than the saturated magnetization value 6.0 μB for ferromagnetic or paramagnetic Co(II) ions, consistent with the magnetic anisotropy of Co(II) ions.69 Luminescence Properties. Owing to the excellent luminescence properties of Zn(II) and Cd(II) complexes, the solid-state fluorescent properties of the two complexes (6 and 7) were investigated at room temperature, and the photoluminescent spectra of free H4L and bix were also obtained under the same conditions (Figure S11, Supporting InformaJ

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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.5b01734. Tables with bond lengths and angles, magnetic properties of 2−4, luminescence spectrum, PXRD patterns, TG curves, and topological structures (PDF) Accession Codes

CCDC 1060389−1060390, 1060392, 1060394, 1060396− 1060397, and 1440086 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

*E-mail: [email protected]. *E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by grants from the Natural Science Foundation of China (Nos. 21461023 and 21361023), Fundamental Research Funds for the Gansu Universities.

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DOI: 10.1021/acs.cgd.5b01734 Cryst. Growth Des. XXXX, XXX, XXX−XXX