From One-Dimensional, Two-Dimensional to Three-Dimensional

Article pubs.acs.org/crystal

From One-Dimensional, Two-Dimensional to Three-Dimensional Entangled Architectures with Polythreading Feature: Synthesis, Structures, and Properties Xian-Ying Duan*,† and Mei-Lin Wei‡ †

Institute of Chemistry, Henan Academy of Sciences, Zhengzhou 450002, P. R. China School of Chemistry and Chemical Engineering, Henan Normal University, Xinxiang, 453007, P.R. China

‡

S Supporting Information *

ABSTRACT: Under hydrothermal conditions, eight coordination polymers, namely, [Zn(H2L)(bpn)]n (1) and [Co(H2L)(bpn)]n (2), [Co(H2L)(bpe)]2·bpe·H2O}n (3), {[Mn2(H2L)(bpa)(H2O)3]·bpa· 4H2O}n (4), {[Zn(H2L)(bpe)]·H2O}n (5), {[Zn(H2L)(bpa)]· H2O}n (6), {[Cd(L)0.5(bime)(H2O)]2·2H2O}n (7), and {[Ni2(L)(bime)(H2O)2]·H2O}n (8) [H4L= methylenediisophthalic acid; bpn = 4,4′-azopyridine; bpe = 1, 2-bis(4-pyridyl)ethylene; bpa = 1, 2bis(4-pyridyl)ethane; bime = 1,2-ethanediylbis(imidazole)] have been prepared based on mixed ligands. The result of X-ray crystallographic analyses indicates all the complexes have a polythreading feature. In complexes 1−2, one-dimensional (1D) [M2(H2L)]∞ polygrids are threaded by R66 hydrogen bonds formed by protonated carboxylates of H2L2− from adjacent chains. Complexes 3−4 have 1D + zero-dimensional (0D) → 1D pseudo-polyrotaxane character, in which 1D [M2(H2L)]∞ polygrids are threaded by free bpe/bpa. Complexes 5−6 are two-dimensional (2D) → 2D 2-fold parallel interpenetration structures with (6, 3) topology. 0D [M2(H2L)] grids of 5−6 are threaded by coordinated bpe/bpa from the other identical network. The structures display polyrotaxane and polycatenane character. Complex 7 is three-dimensional (3D) → 3D 4-fold parallel interpenetration. One-dimensional polygrids [M(L)2]∞ are threaded by coordinated bime from two other identical networks. They exhibit polyrotaxane, polycatenane, and helical character. When separated grids are threaded by coordinated bime from the same 3D network (8), a self-penetrated motif is formed. Related luminescent, thermogravimetric, and magnetic properties of these complexes are investigated here.

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INTRODUCTION Various intriguing architectures and potential properties as functional solid materials are two interests in the research of coordination polymer frameworks,1,2 since they are a breakthrough in the solid state for scientists from various fields. Entanglement networks are of interest in biology and molecular devices,3−7 of which polythreaded coordination networks are analogous of rotaxanes or pseudorotaxanes, with the feature loops penetrated by threads, as defined by Batten and Robson.8−10 When the shortest circuits within the network are penetrated by rods of the same network, a self-penetrating feature is formed. If the circuits are penetrated by rods of a different network, a polythreaded feature will be formed. Until now, a lot of entangled architectures have been reported, while the modulation of an entangled motif with tailored structures and properties is still a long pursued issue, which is more closely related to versatile chemical environments.11−17 In the assembly of novel coordination complexes, ligands often serve as important building units. Their specific symmetry and rigidity/flexibility are crucial to control and adjust the final architectures. The mixed-ligand synthetic strategy is rationally proposed, in which the preferred research © XXXX American Chemical Society

is focused on polycarboxylate acids and N-donor ligands. This is due to their ability to incorporate the virtues of different functional groups and to easily obtain controlled architecture by subtle change.18−23 Therefore, exploration of the essential factors in such sa tructural assembly may provide further insights into designing new hybrid crystalline materials. For the tetracarboxlyate ligands, they not only are appealing in the aspect of establishing fascinating architectures24−28 but have also been proven to be useful ligands in orienting adsorption properties29 and heterogeneous asymmetric catalysis,30 etc. The existence of −CH2− groups in the semirigid polycarboxylate (methylenediisophthalic acid) can form loops or rings which are beneficial for the assembly of polyrotaxaneand polycatenate-like motifs. And it can adopt various conformations via bending, stretching, or twisting depending on the coordination environment of the metal center and the competition and cooperation of different coligands. Meanwhile, continuing our interest in the structures and properties of the Received: October 31, 2016 Revised: January 4, 2017

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DOI: 10.1021/acs.cgd.6b01591 Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design

Article

1587(m), 1442(w), 1415(m), 1385(m), 1329(w), 1288(m), 1223(w), 1134(w), 1108(w), 989(w), 842(w), 798(w), 782(w), 763(w), 706(w), 618(w), 569(w), 535(w), 469(w), 426(vw), 414(vw). {[Co(H2L)(bpe)]2·bpe·H2O}n (3). A mixture of 0.1 mM H4L, 0.1 mM bpe, 0.2 mM Co(NO3)2·6H2O, one drop of triethylamine (Et3N), methanol (2 mL), and H2O (8 mL) was sealed in a 25 mL Teflonlined autoclave by heating at 120 °C for 3 days. Purple single crystals were collected in 53% yield on the basis of cobalt. Anal. Calcd for C70H52Co2N6O17 C, 61.50; H, 3.83; N, 6.15; Found: C, 61.57; H, 3.79; N, 6.18. IR (KBr cm−1): 3413(s), 1609(s), 1576(m), 1537(m), 1458(m), 1428(m), 1404(m), 1373(s), 1298(w), 1208(w), 1108(w), 1062(w), 1023(m), 972(m), 909(w), 842(m), 782(m), 714(m), 643(w), 551(m), 497(w), 467(w), 446(w). {[Mn2(H2L)(bpa)(H2O)3]·bpa·4H2O}n (4). 4 was synthesized hydrothermally in a 25 mL Teflon-lined autoclave by heating a mixture of 0.1 mM H4L, 0.1 mM bpa, 0.2 mM Mn(CH3COO)2·4H2O, methanol (2 mL), and H2O (8 mL) at 120 °C for 3 days. Light yellow single crystals were collected in 47% yield on the basis of manganese. Anal. Calcd for C70H70Mn2N6O23: C, 57.07; H, 4.79; N, 5.70; Found: C, 57.10; H, 4.81; N, 5.73. IR (KBr cm−1): 3370(s), 2543(m), 2154(m), 2044(m), 1954(m), 1691(m), 1620(s), 1582(s), 1552(s), 1506(m), 1441(s), 1401(s), 1368(s), 1233(w), 1209(w), 1134(w), 1098(w), 1062(w), 1022(w), 985(w), 960(w), 938(w), 912(w), 825(m), 784(m), 767(m), 713(m), 701(m), 647(w), 583(w), 548(w), 533(w), 514(w), 454(w), 432(w). {[Zn(H2L)(bpe)]·H2O}n (5). 5 was synthesized hydrothermally in a 25 mL Teflon-lined autoclave by heating a mixture of 0.1 mM H4L, 0.1 mM bpe, 0.2 mM Zn(NO3)2·6H2O, one drop of Et3N, methanol (2 mL), and H2O (8 mL) at 120 °C for 3 days. Light brown single crystals were collected in 85% yield on the basis of zinc. Anal. Calcd for C29H22N2O9Zn: C, 57.30; H, 3.65; N, 4.61; Found: C, 57.24; H, 3.60; N, 4.55. IR (KBr, cm−1): 3443(s), 2926(w), 2565(w), 1715(m), 1689(m), 1644(m), 1616(s), 1580(m), 1508(w), 1437(m), 1395(s), 1306(m), 1274(m), 1227(w), 1201(m), 1106(w), 1072(w), 1031(m), 978(w), 957(w), 933(w), 914(w), 832(w), 799(w), 763(m), 707(w), 684(w), 643(w), 575(w), 551(m), 450(w). {[Zn(H2L)(bpa)]·H2O}n (6). 6 was synthesized as the same method as 5, using bpa instead of bpe. Anal. Calcd for C29H24N2O9Zn: C, 57.11; H, 3.97; N, 4.59; Zn, 10.72; Found: C, 57.15; H, 3.85; N, 4.62; Zn, 10.77. IR (KBr cm−1): 3430(s), 1712(m), 1638(s), 1616(s), 1565(m), 1512(w), 1441(m), 1392(s), 1230(w), 1202(w), 1121(w), 1036(w), 997(w), 784(m), 718(m), 650(w), 618(w), 580(w), 541(w), 511(w), 469(w), 441(w). {[Cd(L)0.5(bime)(H2O)]2·2H2O}n (7). 7 was synthesized hydrothermally in a 25 mL Teflon-lined autoclave by heating a mixture of 0.1 mM H4L, 0.1 mM bime, 0.2 mM Cd(NO3)2·4H2O, 0.02 mM NaOH, and H2O (10 mL) at 120 °C for 3 days. White single crystals were collected in 60% yield on the basis of cadmium. Anal. Calcd for C25H26Cd2N4O12: C, 37.57; H, 3.28; N,7.01. Found: C, 37.34; H, 3.35; N, 6.98. IR(KBr cm−1): 3446(s), 3127(m), 1607(s), 1532(s), 1446(s), 1375(s), 1320(w), 1298(w), 1246(m), 1114(m), 1093(m), 1033(w), 1007(w), 946(w), 919(w), 892(w), 857(w), 824(m), 797(w), 770(w), 742(m), 711(m), 683(w), 656(w), 637(w), 585(w), 562(w), 511(e), 494(w), 429(m). [Ni2(L)(bime)(H2O)2·H2O]n (8). 8 was synthesized hydrothermally in a 25 mL Teflon-lined autoclave by heating a 10 mL aqueous mixture of 0.1 mM H4L, 0.1 mM bime, 0.2 mM Ni(NO3)2·6H2O and one drop of Et3N at 120 °C for 3 days. Green single crystals were collected in 65% yield on the basis of nickel. Elemental analysis calcd (%) for C25H24N4Ni2O11: C, 44.56; H, 3.59; N, 8.31; found: C 44.52, H 3.53, N 8.31. IR (KBr, cm−1): 3413(m), 3120(m), 2955(w), 1610(m), 1587(m), 1532(s), 1451(s), 1420(m), 1389(s), 1319(m), 1298(m), 1244(m), 1170(w), 1112(m), 1089(m), 1032(m), 941(w), 906(w), 852(w), 819(w), 801(w), 777(w), 753(w), 722(w), 705(w), 683(w), 689(w), 629(w), 573(w), 527(w), 493(w), 427(w). General X-ray Crystallography. Single crystals of all the complexes suitable for X-ray analysis were used on a Bruker SMART APEX CCD diffractometer using graphite-monochromatized Mo Kα radiation (λ = 0.71073 Å) at room temperature using the ωscan technique. Lorentz polarization and absorption corrections were

entangled architectures, and to further investigate the influence of coligands in detail, we choose bis-N-containing ligands (such as bispyridyl, bisimidazol) with two atoms (−CHCH−, −NN−, −CH2−CH2−, etc.) separating the N-containing ring (Scheme 1). On the basis of the mixed ligands, we have Scheme 1. Auxiliary N-Donor Ligands

successfully synthesized eight entangled coordination complexes with interesting polythreading features, [Zn(H2L)(bpn)]n (1) and [Co(H2L)(bpn)]n (2), {[Co(H2L)(bpe)]2· bpe·H2O}n (3), {[Mn2(H2L)(bpa)(H2O)3]·bpa·4H2O}n (4), {[Zn(H2L)(bpe)]·H2O}n (5), {[Zn(H2L)(bpa)]·H2O}n (6), {[Cd(L)0.5(bime)(H2O)]2·2H2O}n (7), and {[Ni2(L)(bime)(H2O)2]2·2H2O}n (8) [bpn = 4,4′-azopyridine; bpe = 1,2bis(4-pyridyl)ethylene; bpa = 1,2-bis(4-pyridyl)ethane; bime = 1,2-ethanediylbis(imidazole)]. The effects of the conformations of H4L ligand, the subtle difference of coligands, and the coordination geometry of the metal ions on the assembly of frameworks are unraveled in detail.

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EXPERIMENTAL SECTION

General Materials and Methods. H4L was synthesized according to the literature.31 All the other starting materials were of reagent quality and obtained from commercial sources without further purification. The ligands bpn and bime (bpn = 4,4′-azopyridine, bime = 1,2-ethanediylbis(imidazole)) were prepared by previously reported procedures.32,33 Elemental analyses were performed on a PerkinElmer 240C elemental analyzer. The IR spectra were obtained using KBr disks methods on a VECTOR 22 spectrometer. The luminescent spectra for the solid samples were recorded at room temperature on an Aminco Bowman Series 2 spectrophotometer with a xenon arc lamp as the light source. Thermal analyses were performed on a TGA V5.1A Dupont 2100 instrument from room temperature to 800 °C with a heating rate of 20 °C/min in a nitrogen environment. The variable temperature magnetic susceptibilities were measured on polycrystalline samples with a Quantum Design MPMS SQUID susceptometer. Powder X-ray diffraction patterns (PXRD) were recorded on a RigakuD/max-RA rotating anode X-ray diffractometer with graphite monochromatic Cu Kα (λ = 1.542 Å) radiation at room temperature. [Zn(H2L)(bpn)]n (1). 1 was synthesized hydrothermally in a 25 mL Teflon-lined autoclave by heating a mixture of 0.1 mM H4L, 0.1 mM bpn, 0.2 mM Zn(NO3)2·6H2O and H2O (10 mL) at 120 °C for 3 days. Brick red crystals were collected in 43% yield on the basis of zinc. Anal. Calcd for C27H18N4O8Zn C, 54.79; H, 3.07; N, 9.47. Found: C, 54.77; H, 3.04; N, 9.50. IR(KBr cm−1). 3103(w), 1689(s), 1652(s), 1613(m), 1596(m), 1445(m), 1420(s), 1390(s), 1327(m), 1280(s), 1223(m), 1131(w), 1104(w), 1052(w), 1030(w), 942(w), 911(w), 876(w), 843(m), 795(w), 762(m), 704(m), 673(w), 583(w), 568(m), 544(w), 524(w), 478(w), 449(m). [Co(H2L)(bpn)]n (2). 2 was synthesized as the same method as 1, using Co(NO3)2·6H2O instead of Zn(NO3)2·4H2O. Purple black crystals were collected in 51% yield on the basis of cobalt. Anal. Calcd for C27H18N4O8Co C, 55.40; H, 3.10; N, 9.57. Found: C, 55.40; H, 3.12; N, 9.54. IR(KBr cm−1), 3100(w), 1690(m), 1639(m), 1619(m), B



Article

Table 1. Crystal Data and Structure Refinements for Complexes 1−8 1

2

3

4

formula fw crystal system space group a/Å b/Å c/Å α/° β/° γ/° V/Å3 Z T/K Dcalcd (g cm−3) F(000) GOF on F2 μ/mm−1 tot/indpndt reflens Rint R1/ wR2 (I > 2σ(I)) residues (e·Å3)

C27H18N4O8Zn 591.82 triclinic P1̅ 8.475(3) 10.398(3) 14.965(5) 92.453(5) 100.883(4) 103.056(4) 1256.4(7) 2 291(2) 1.564 604 1.078 1.038 6869/4845 0.0308 0.0589, 0.1264 0.623, −0.672 5

C27H18CoN4O8 585.38 triclinic P1̅ 8.4580(12) 10.3513(15) 14.910(2) 92.135(3) 100.904(3) 102.716(3) 1246.1(3) 2 291(2) 1.560 598 1.061 0.750 6748/4787 0.0300 0.0581, 0.1319 0.353, −0.388 6

C70H52Co2N6O17 1367.04 triclinic P1̅ 11.1083(19) 12.2425(12) 12.6558(15) 112.5050(10) 92.372(2) 94.8060(10) 1579.4(4) 1 291(2) 1.437 704.0 1.090 0.603 8704/6079 0.0299 0.0593, 0.1359 0.341, −0.394 7

C70H70Mn2N6O23 1473.20 monoclinic P2/c 12.0723(16) 11.4985(15) 26.758(3) 90.00 112.883(5) 90.00 3422.0(7) 2 291(2) 1.430 1532 1.016 0.453 17977/6670 0.0491 0.0546, 0.1210 0.389, −0.329 8

formula fw crystal system space group a/Å b/Å c/Å α/° β/° γ/° V/Å3 Z T/K Dcalcd (g cm−3) F(000) GOF on F2 μ/mm−1 tot/indpndt reflens Rint R1/wR2 (I > 2σ(I)) residues (e·Å3)

C29H22ZnN2O9 607.86 triclinic P1̅ 9.5191(6) 11.6397(8) 13.1784(9) 111.9020(10) 96.587(2) 96.7610(10) 1325.26(15) 2 291(2) 1.523 624 1.069 0.987 7314/5120 0.0293 0.0609, 0.1567 0.999, −1.062

C29H24ZnN2O9 609.89 triclinic P1̅ 8.6145(12) 12.2931(18) 13.3532(19) 73.566(3) 81.690(2) 86.428(3) 1341.7(3) 2 292(2) 1.510 628 0.987 0.975 7257/5141 0.0274 0.0438, 0.0939 0.499, −0.256

C25H26Cd2N4O12 799.30 monoclinic C2/c 24.091(6) 8.691(2) 17.568(4) 90.00 132.095(4) 90.00 2729.2(12) 4 291(2) 1.945 1584 1.003 1.632 7083/2676 0.0237 0.0343, 0.0873 0.469, −0.992

C25H24N4Ni2O11 673.86 monoclinic C2/c 24.323(3) 8.6917(11) 16.704(2) 90.00 132.227(2) 90.00 2614.9(6) 4 293(2) 1.712 1384 1.108 1.511 6769/2578 0.0720 0.0613, 0.1363 0.866, −0.385

applied. The structures were solved by direct methods and refined with the full-matrix least-squares technique using the SHELXS-97 and SHELXL-97 programs.34−36 Anisotropic thermal parameters were assigned to all non-hydrogen atoms. Crystal data and details of the structural determination for complexes 1−8 are summarized in Table 1.

position is occupied by N atom from bpn. The Zn−O bond distances are within the range of 2.028(2)−2.062(3) Å, and the dimeric [Zn2(CO2)4] unit has a paddlewheel37 structure with Zn···Zn 2.9453(16) Å. One-dimensional infinite [Zn2(H2L)2]∞ chains (Figure 1b) are formed by dimeric [Zn2(CO2)4] units connected via two bis-mono carboxylates in trans position of H2L2−. Moreover, each metal in the dimeric unit bears a terminally bonded bpn ligand at the axis orientation in the a direction (Figure 1b,d). The dangling bpn groups are disposed in a mutual anti orientation with respect to the chain in an inclined manner that paves the way for enclathration. In a 1D [Zn2(H2L)2(bpn)2]∞ chain, the combination of adjacent dimeric units with two H2L2− ligands gives a 24-member molecular grid. In the a direction, these polygrids are crossed by R66 O(carboxyl)−H···O(carboxyl) hydrogen bond (Figure 1c) from two adjacent chains. These weak hydrogen

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RESULTS AND DISCUSSION Preparation of Complexes. All the complexes were prepared under hydrothermal conditions. Their structures are described as follows. Crystal Structures of [Zn(H2L) (bpn)]n 1 and [Co(H2L) (bpn)]n 2. The result of X-ray diffraction analyses indicates that complex 1 crystallizes in the monoclinic P1̅ space group, and it is a one-dimensional (1D) infinite chain. As shown in Figure 1a, the metal Zn2+ lies in a distorted square-pyramidal geometry formed by four O atoms of four H2L2− ligands, while the apical C



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Figure 1. (a) Molecular structure of 1. Hydrogen atoms are omitted for clarity. (Symmetry code: #1 1 − x, 1 − y, −z; #2 x, 1 + y, z; #3 1 − x, −y, −z; #4 x, −1 + y, z). (b) View of 1D [Zn2(H2L)(bpn)]∞ chain with paddle-wheel dimeric zinc unit in 1. (c) View of grids penetrated by R66 hydrogen bonds from adjacent chains. (d) Schematic view of topology considering the R66 hydrogen bonds.

Figure 2. (a) Molecular structure of complex 3. Hydrogen atoms and free water molecules are omitted for clarity (#1 1 − x, −y, 1 − z; #2 2 − x, −y, 1 − z; #3 1 + x, y, z; #4 −1 + x, y, z). (b) Representation of 1D dimeric [Co2(H2L)(bpe)]∞ chain with free bpe through the grid in 3. (c) Schematic representation of the structure in 3.

2D supramolecular layers are stacked in an AB motif to be three-dimensional (3D) architecture. Complex 2 [Co(H2L)(bpn)]n shares a similar structure with 1 except the dimeric unit is somewhat distorted (Figure S1). Crystal Structures of {[Co(H2L)(bpe)]2·bpe·H2O}n 3 and {[Mn2(H2L)(bpa)(H2O)3]·bpa·4H2O}n 4. The X-ray diffraction analysis reveals that complex 3 crystallizes in the monoclinic P1̅ space group and consists of two components: neutral 1D [Co2(H2L)2(bpe)2]∞ chain and free bpe. As shown in Figure

interactions also help to form two 2-fold parallel interpenetration two-dimensional (2D) layers because the polygrids in one layer are threaded by rods (formed by hydrogen bonds) of the other layer and vice versa. These layers show polyrotaxane and polycatenane characters. Each 2D layer can be simplified to be 2D (3,4)-connected net (Figure 1d) with the short schläfli symbol38 of (4.62)2(426282) when taken C7 and dimeric unit as 3-connected and 4-connected nodes. The D



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Figure 3. (a) Molecular structure of 5. Hydrogen atoms and free water molecules are omitted for clarity (#1 −1 − x, 2 − y, 1 − z; #2 1 − x, 2 − y, 1 − z; #3 −x, 1 − y, 2 − z). (b, c) View of the 2D net and 2-fold interpenetration of these nets. (d) Schematic representation of the 2-fold interpenetrating nets in 5.

and then in the a and b direction, these grids are extended by bis-coordinated bpe with Zn1···Zn1 distances 13.30, 13.35 Å to be 2D layers of (6, 3) topology (Figure 3b). In the 68-member hexagon meshes, two edges are from [Zn2(H2L)2] grids and four edges are built from four bpe ligands, and zinc centers act as four-connected node. As indicated in Figure 3c, two (6, 3) layers give parallel interpenetration because the loops in one layer are threaded by rods of the other layer and vice versa. The 2-fold sheets can also be described as formed by interconnected parallel 1D polyrotaxane chains, and then the coordinated bpe ligand is present within [Zn2(H2L)2] grids. Two such grids interpenetrate as the manner represented schematically in Figure 3c, generating polyrotaxane columns. In addition, Figure 3c,d also shows the polycatenane character. Therefore, this complex is 2D 2-fold interpenetration (2D + 2D → 2D) showing rarely reported both polyrotaxane and polycatenane.4 Adjacent 2D layers are arranged in AB mode, which are stacked to form a 3D supramolecular structure. Crystal Structure of {[Cd(L)0.5(bime)(H2O)]2·2H2O}n 7. Determination by X-ray crystallography shows that complex 7 crystallizes in the monoclinic space group C2/c and contains one unique CdII atom, one L4− anion, and one bime ligand (Figure 4a). Cd1 is coordinated by four O atoms from two different L4− ligands, one N atom from one bime ligand, and one O atom from coordinating water molecule, showing a distorted triangular prismic geometry {CdNO5}. The Cd1−O distances are in the normal range: 2.2285(3)−2.389(3) Å, and the Cd1−N distance has the shortest value 2.175(4) Å. As illustrated in Figure 4b, in the ac plane, L4− connects four Cd centers to show a 1D [Cd2L]∞ chain, comprising one 24member grid [Cd2L2] with the cross dimensions 6.52 × 7.93 Å. It contains two distorted helices with 21 screw axis, in which CdII linked by trans-carboxylates of L4− ligands, with the screw pitch of 17.933 Å. Because two helical chains with opposite handness coexist, [Cd2L]∞ chain is achiral. View of the uvw [1

2a, the Co1 center lies in a distorted octahedron geometry formed by five O atoms of four H2L2− ligands and one N atom of bpe. The Co−O bond distances are within the range of 2.020(2)−2.352(2) Å, and the Co···Co distance in the paddlewheel [Co2(CO2)4] unit is 2.91 Å, which is longer than the metal···metal distances measured in other Co2(RCOO)4 complexes.39−41 Such a chain is similar to complex 1, and the coordination modes of trans-carboxylates on H2L2− in [Co2(CO2)4] units are connected by monochelating and bis-mono coordination modes. And bpe ligands are at the apical of paddlewheel to form a 1D infinite [Co2(H2L)2(bpe)2]∞ chain (Figure 2b). Different from 1, the 24-member molecular polygrids are penetrated by free bpe. If we regard each molecular grid as a wheel, and each distinct bpe as an axle, the nature of the entanglement in this complex can be described as a novel armed pseudo-polyprotaxane structure (Figure 2b,c), 1D + 0D → 1D, which has seldom been reported in systems of coordination polymers. {[Mn2(H2L)(bpa)(H2O)3]·bpa·4H2O}n 4 shares the similar structure with 3 except that the dimeric units are different (Figure S2). Crystal Structures of {[Zn(H2L)(bpe)]·H2O}n 5 and {[Zn(H2L)(bpa)]·H2O}n 6. Complexes 5−6 share a similar structure and only 5 is described. Complex 5 crystallizes in the space group P1̅, and the structure is made up of a 2D infinite {[Zn(H2L)(bpe)]}n sheet. As shown in Figure 3a, Zn1 is tetrahedrally coordinated by two O from two H2L2−, two N from two bpe. The Zn−O distances are in the range of 1.945(3)−2.053(3) Å, and although O2 and O7#1 are not coordinated to Zn1, the bond distances Zn1···O2 (2.726 Å), Zn1···O7#1 (2.795 Å) are smaller than the sum of the van der Waals radii (2.9−3.0 Å) and is thus indicative of weak secondary bonding.42−45 By trans-carboxylates of two H2L2− ligands, two Zn1 centers are joined together to produce a 24member [Zn2(H2L)2] grid with Zn1···Zn1 separation 11.20 Å, E



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Figure 4. (a) The asymmetric unit of 7. Solvent water molecules and hydrogen atoms are omitted for clarity. (Symmetrical code: #1: 0.5 + x, 0.5 − y, 0.5 + z; #2 −0.5 + x, 0.5 − y, −0.5 + z.) (b) View of the helical chain in the achiral 1D [Cd2L]∞ chain in the b direction in 7. (c) Project view of 1fold net of complex 7. (d) Representation of the 4-fold interpenetration framework and topology. Left: Polyrotaxane representation of 1D [Cd2L]∞ chain in a 1-fold net is interpenetrated by other two nets. Right: Catenane representation.

Figure 5. Topological view of the 3D 4-fold (3, 4)-connected network of complex 7.

0 1] axis, four orientation of bisdentate trans-bime is arranged with C2 symmetry around the 1D [Cd2L]∞ chain. Then, adjacent 1D chains are joined together by bime to form a 3D porous framework with the rhombic void 22.36 × 38.56 Å (Figure 4c), in which the dihedral angle in a larger rhombic void along the uvw [1 0 1] axis is 58.95°, as well as the cross angle of two bime orientations around the 1D [Cd2L]∞ chain. Because of the large void in this porous framework, 4-fold interpenetration came into being (Figure 4d).

Detailed investigation of the structure reveals that each 24member grid [Cd2L2] in one single 3D network is threaded by the rod of one bime ligand, and each 1D [Cd2L2]∞ chain is threaded by two other 3D identical networks (Figure 4d right), showing the polyrotaxane and polycatenane character. A higher dimensional array of complexes with polyrotaxane and polycatanexane character is a great challenge. Reported examples mostly are 1D → 2D or 3D, 2D → 2D or 3D. Three-dimensiona; polyrotaxane frameworks are quite rare.10,13 F



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Figure 6. Coordination environment of Ni1 and L4− ligand in complex 8. The hydrogen atoms and free water molecules are omitted for clarity. #1: x, −y + 1, z − 1/2; #2: −x + 1/2, −y + 1/2, −z + 1; #3: x, 1 − y, z + 1/2; #4: −x + 1, −y + 2, −z + 1. (b) View of 1D nanotube [Ni4(L)2]∞ connected by bime ligands with 1D [Ni(CO2)]∞ helical chain. The [Ni4(L)2] grids are penetrated by coordinated bime ligands, displaying selfpenetrating character. (c) Schematic view of the self-penetrating chain. (d) View of the whole 3D framework.

As far as we know, compound 7 represents the first 3D → 3D coordination polymer with polyrotaxane, polycatanexane, and helical character. Although the structure is 4-fold interpenetrated (3D + 3D → 3D), still there is a void located with two included crystal water molecules per unit. The minor porosity is closer to the potential solvent volume calculated in this complex in the absence of the water of crystallization as 238.5 Å3 (8.7% of the cell unit volume 2729.4 Å3).46 Topologically, considering the coordination modes of L4−, which linked four CdII, it can be viewed as a 4-connected node, and C7 is viewed as a 3-connected node; thus as seen in Figure 5, the 3D (3, 4) topology has a short Schläfli symbol of (4 × 102)2(42.104). Crystal Structure of {[Ni2(L)(bime)(H2O)2]·H2O}n 8. X-ray analysis revealed that complex 8 crystallizes in the monoclinic centrosymmetric space group C2/c, and the asymmetric unit consists of one independent NiII center, a half L4−, a half bime, one coordinated and a half solvated water molecules (Figure 6a). The octahedrally coordinated Ni atom is directly ligated by two O atoms from one chelating carboxylate group, two O from two bis-mono carboxylate groups, one N atom from one bime, and one O from one water molecule. The Ni−O bond lengths range over 1.993(3)−2.189(4) Å, and the Ni−N bond distance is 2.000(4) Å. These values are comparable to those of related complexes.20,47 As shown in Figure 6b, the 1D metalcarboxylate [Ni(−OCO−)]∞ helical chain is shaped by the nonlinear flexibility around the center between bis-mono carboxylates (O3−C9−

O4) and Ni atoms. The winding axis corresponds to the b axis with a pitch length of 8.69 Å. Such chains show C2 symmetry with 21 rotation axis. The dihedral angle between the carboxylate (O3−C9−O4) and the attached benzene ring is 42.34°, and this effectively contributes to the helical formation. The adjacent Ni···Ni separation of this chain is 5.47 Å. Then, in the bc plane, two [Ni(CO2)]∞ chains are further linked through chelating carboxylates of two L4− ligands with C2 symmetry axis along the b axis to form the nanotube [Ni4(L)2]∞ (Figure 6d). Noticeably, each L4− is C2 symmetry through the methylene group as a center point. In this way, the observed 3D open framework is formed. Coordinated bime ligands thread the [Ni4(L)2] girds of nanotube [Ni4(L)2]∞ to exhibit a selfpenetrating feature48 (Figure 6b right and Figure 6c), with Ni··· Ni distance of 11.42 Å. This complex represents the seldom reported binodal self-penetrating networks with helix. The 3D framework can be seen as a (4, 6)-connected network with a Schläfli symbol of (42.63.8)2(44.62.74.84.9) (L4− is 6-connected node, and Ni is 4-coonected node) (Figure 7). The structure is similar to the reported.27 As we can see that in all complexes, the 24-member grid formed by metal ions and H4L ligand can be penetrated by hydrogen bonds, neutral ligands, polymers, etc. And 1D chains with polygrids (1−2) are threaded by hydrogen bonds formed by protonated carboxylates from H2L2−. One-dimensional chains with polygrids (3−4) are threaded by free N-donor ligands. A 2D layer with separate grids (5−6) and a 3D framework with 1D polygrids 7 are 2-fold and 4-fold G



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class of polythreading (extended systems that “cannot be disentangled”),4 and all are interpenetrated with polyrotaxane and polycatenane character. Complexes 3−4 have the second class of polythreading (extended systems that can be disentangled) with two distinct situations and polythreading with finite components, providing new polythreaded examples. For the polythreading feature, with the −CH2− group in H4L, it is easy to form a holder part suitable to be threaded. In complexes 1−2, since the holder is penetrated by hydrogen bonds, only π···π stacking interactions exist between the aryl rings of H4L and the pyridine ring of coordinated dangling bpn from adjacent chains. In complexes 3−7, many kinds of weak interactions exist between the holder and penetrating part (Figure S3), and they are found not only between H atoms of −(CHm)2− and L but also between H of N-donor ligands (imidazole or pyridine) and L. It is clear that the existence of suitable H atoms in the ring and the bridge of N-donor ligands is important to construct frameworks with polyrotaxane features. For 3 and 6 Mn(Zn)/H4L/bpa, 4 and 5 Co(Zn)/H4L/bpe, their differences are dominated by the nature coordination geometry of metal ions; that is, Mn/Co is apt to be octahedrally coordinated, and Zn is apt to be tetrahedrally coordinated. The structural difference of 7−8 Ni(Cd)/H4L/bime is also very related to the nature of metal ions. For complexes 5−6 Zn/ H4L/bpe(bpa), their structures are similar. This implies that coligands do not influence the final architecture, and the reason may be that coligands are too similar. As for complexes 1, 5, and 6, Zn/H4L/bpn(bpe, bpa), 2 and 3 Co/H4L/bpn(bpe),

Figure 7. Topological view of 3D (4, 6)-connected network with selfpenetrating feature of 8.

interpenetration, respectively, and the related grids are penetrated by coordinated N-donor ligands from identical polymer. In complexes 5, 6, 8, the grids are separated, whereas in complexes 1, 2, 3, 4, and 7, the grids are a 1D infinite chain. Moreover, there are binuclear units in complexes 1−4, mononuclear units in 5−7, and 1D metal-carboxylate chain in 8. Helix is only found in complexes 7−8. Prepared under hydrothermal conditions, all parts of complexes are neutral. They have much in common: all have polythreading features. Complexes 1−2 and 5−8 have the first

Figure 8. (a−c) Fluorescence spectra of complexes 5, 6, and 7 in the solid state at room temperature (dash lines represent the excitation spectra). H



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Figure 9. Temperature dependence of the χmT and χm−1 values for 2, 3, 4, and 8 (a−d).

the cationic threading part. (4) The polyrotaxane parts of 3−4 are 1D linear chain with symmetry, while the previous examples are more complicated, that is, a 1D chiral double chain in Mn/ H4L/bpa and 2D symmetric layer in the Co/H4L/bpe system, respectively. (5) The separated threading motifs of 3−4 are organic molecules rather than the reported coordination cations of previous examples. (6) After threading, all dimensions of the previous final architectures are increased. Such phenomena are not observed in 3−4. (7) Moreover, the auxiliary N-containing ligands of 3−4 coordinate with metal centers of the polyrotaxane part, while they do not in previous examples. We think that the structural difference is likely related to the synthetic method. Complexes 3−4 are prepared under hydrothermal conditions, while the reported complexes are prepared at room temperature. It may be the same reason for the structural difference in the Zn/H4L/bpe system. Complex 5 is prepared under routine hydrothermal conditions, while the reported complex [Zn2(L)2(bpe)]n·3H2O49 is prepared under nitrogen atmosphere, using a DMF/HCl mixed solvent. As for the final architecture, complex 5 is 2D interpenentration with polyrotaxane and polycatenane character, and the reported example is a 3D pillar-layer framework, in which the 3D [Zn2(L)2] layer is pillared by slipped bpe ligands. IR and Luminescent Properties. In KBr pellets, the solid state IR spectra of complexes 1−7 (Figure S4) show strong absorption bands between 1350 and 1630 cm−1 that can be assigned to coordinated carboxylate groups.50 There are no absorption bands in the area 1720−1650 cm−1, which proves the complete deprotonation of the carboxyl groups in 7−8, while the absorption peaks of other complexes could be clearly observed.

their structural differences are very related to the coligands, and the reason is possibly the hydrogen absence in the −NN− of bpn compared to −CHCH− of bpe, −CH2−CH2− of bpa. With trans-carboxylates coordinating of H2L2− with metal centers, in 1−6, the dihedral angle between the pair of phenyl rings of H2L2− is 87.43, 87.28°, 80.60, 74.82, 63.91, 79.67°. In the grid, the −CH2− separations of H2L2− are 10.53, 10.53, 10.28, 10.97, 9.58, 10.59 Å, respectively. In 7−8, with four carboxylates of L4− coordinated with metal centers, the dihedral angle is 85.01, 81.81°, respectively. Four aryl rings are extended as far as possible with −CH2− separation 11.65, 11.33 Å, respectively. Because of the repulsions of the phenyl rings, compared to the ideal bond angle (109.5°) surrounding a tetrahedral C atoms, such an angle is 113.34, 115.52° in 1−2, 113.93, 112.69° in 3−4, 117.07, 115.01° in 5−6, and 111.8° in 7, 114.06° in 8, all showing some deviation. The linear bis-N donor ligands in 1−2 are monodentate; in 3−4, they are not only as monodentate, but also free; in 5−8, they are all bidentate. All this may be helpful for the polythreading feature. In addition, comparing these complexes on the results of the work and those for the reported compounds using the same mixed ligands24,49 is interesting. In the Co/H4L/bpe and Mn/ H4L/bpa system, all complexes have a polythreading feature. However, (1) the structures of 3−4 are similar, showing 1D ⊂ 0D + 1D, while in previously reported complexes, they differ greatly (3D2− ⊂ 2[1D2+] + 2D6− in the Co/H4L/bpe system, 2D4− ⊂ 0D2+ + 2[1D3−] in the Mn/H4L/bpa system. (2) The structures of 3−4 are symmetric. In previous Co/H4L/bpe and Mn/H4L/bpa systems, their structures are symmetric and chiral, respectively). (3) The motifs of 3−4 are all neutral, while in previous examples, the polythreading and the polyrotaxane motifs are ionic, including the negative polyrotaxane part and I



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Weiss law [χm = C/(T − θ)] with a Curie constant of C = 4.25 and 5.48 emu K mol−1, and a Weiss constant θ = −6.30 and −10.81 K, which further confirms the antiferromagnetic interaction between the Co(II) ions. For compound 4, the χmT value at 300 K is 8.15 emu K mol−1 (Figure 9c), which is somewhat lower than the expected value of χmT 8.75 emu K mol−1 for two Mn(II) S = 5/2 uncoupled spins with g = 2.0. This is a signal of antiferromagnetic couplings between Mn(II) ions. Upon lowering the temperature, the χmT value consecutively drops to the minimum value of 2.37 emu K mol−1 at 2 K. The temperature dependence χm−1 obeyed the Curie−Weiss law with C = 8.49 emu K mol−1, θ = −9.56 K, and the negative value of θ also confirms the presence of antiferromagnetic interactions between Mn(II) ions. For compound 8, as shown in Figure 9d, at 300 K, χmT is 1.295 emu K mol−1 per nickel(II) and remains nearly constant until 60 K; below this temperature, the χmT value increases continuously to a maximum of 1.518 emu K mol−1, indicating the overall ferromagnetic coupling in 8. Upon further cooling below 4.0 K, the χmT values decrease to 1.323 emu K mol−1 at 1.8 K, which is probably due to the antiferromagnetic interactions through L4− or bime ligands. The χm−1 vs T curve is almost linear in the whole temperature range. The data were therefore analyzed by the Curie−Weiss law, which led to the parameters C = 1.284 emu K mol−1 and θ = 0.189 K, corresponding to the parameter g = 2.210. The very small positive θ value may indicate the rather weak ferromagnetic interactions of between the Ni(II) ions.53

Considering the luminescent properties of d10 metal complexes, in the solid state, the photoluminescent spectra of compounds 1, 5, 6, and 7 were studied at room temperature (Figure 8). Complex 1 does not show luminescent properties. For 5 and 7, they exhibit moderate yellow-green emission peaks at ca. 480 nm and a shoulder at ca. 525 nm upon excitation at 350 nm. The spectra of complex 6 displays strong blue fluorescent emission peaks at 360, 380 nm with a shoulder at 402 nm when excited at 339 nm. These characteristic peaks result from the π−π* transition of the ligand H4L. Although complexes 5−6 share a similar structure, complex 6 showed more intense emissions compared with complex 5, and this may be a result of the effective increase in rigidity for complex 5 (bpe in 5 is more rigid bpa in 6). The reason is probably that the photoluminescence behavior is closely associated with the metal ions and the ligands coordinated around them.51,52 Complex 6 may be suitable as excellent candidates of fluorescent materials comparing to 5 and 7. Powder X-ray Diffraction. The powder diffraction patterns of compounds 1−8 are given by Figure S5. The experimental PXRD patterns and the synthesized PXRD patterns match perfectly, which indicates that the compounds are pure phase. Thermogravimetric Analyses and N2 Uptake Property. Complexes 1−8 are stable in air and retain the crystalline integrity at ambient conditions. Thermal gravimetric analyses (TGA) under nitrogen atmosphere were carried out to examine the thermal stability (Figure S6). Since complexes 1−2 do not have solvent molecules, 1 does not lose weight until 230 °C and 2 until 290 °C. Complex 3 shows two continuative steps of weight loss, and complex 4 shows three steps of weight loss to lose lattice and coordination solvent molecules. For complexes 5−6, with the loss of free water molecules, the TG curve exhibits one weight loss. TG analyses of 7 show that the lattice and coordinated water molecules are easily lost upon heating in the range from room temperature to 150 °C. The remaining framework is stable up to 460 °C. And when evacuated at 100, 150, 300 °C for 2 h in air, similar XRD peaks of complex 7 (Figure S7) indicate that the framework is intact. The TG curve of complex 8 displays the weight loss gradually with an increases of temperature before 400 °C. Then the framework began to collapse. Because of the porous structure of complex 7, the adsorption and desorption isotherm of N2 were collected under 77 K to check the porosity. As shown in Figure S8, complex 7 exhibits a type II adsorption isotherm, suggesting only surface adsorption, and absorbs 25.4 cm3g−1 at 77 K. The BET surface area is 38 m2 g−1, and the Langmuir surface area is 113 m2 g−1. Magnetic Properties. The solid-state, variable-temperature magnetic susceptibilities of crystalline samples of 2, 3, 4, and 8 were investigated from 1.8 to 300 K at 2 kOe applied (Figure 9). Both compounds 2−3 are binuclear structures, and they show similar magnetic properties. The magnetic susceptibilities of 2−3 versus temperature are shown in Figure 9a,b, and the χmT values at 300 K are 4.21 and 5.33 emu K mol−1, which are much greater than the calculated spin-only value (3.75 emu K mol−1) for two Co(II) ions with S = 3/2 (g = 2). This high experimental χmT value may be due to the significant orbital contribution of the Co(II) ions. As the temperature decreases, the values of χmT decrease continuously and reach a value of 2.91 and 2.47 at 2 K. The results suggest that these compounds exhibit antiferromagnetic behavior. The temperature dependence of the reciprocal susceptibility (χm−1) follows the Curie−

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CONCLUSION In summary, based on mixed ligands, interesting entangled networks with polythreading feature have been reported in this paper, in which circurts/grids are formed by a divalent metal center and H4L ligand. The grids are penetrated by hydrogen bonds, free N-donor ligands, and coordinated N-donor ligands from an identical net or the same net. Therefore, interesting 1D, 2D to 3D architectures come into being. The result of this study demonstrated that the rational selection of organic ligands with specific conformation and geometry is an effective approach for the construction of entangled coordination complexes with a polythreading motif. The structural variations are much related to the N-donor ligands and the nature of metal cations as well. This work shows a natural synergy in structural diversity of the resultant architectures.

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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.6b01591. Additional figures showing the structures of 2 and 4, weak interactions in the polythreading grids of complexes 1−8, IR spectra, TG figures, PXRD of complexes 1−8, and N2 sorption isotherm of complex 7 (PDF) Accession Codes

CCDC 1513114−1513121 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. J



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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Fax: (86)-371-65718110. ORCID

Xian-Ying Duan: 0000-0001-8535-6329 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank the National Natural Science Foundation of China [Grant Number 21501047], [Grant Number 21171050].

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