Supramolecular Isomerism and Polyrotaxane-Based Two

Nov 21, 2016 - Department of Materials Science and Engineering, National ... *E-mail: [email protected] (S.S.L.)., *E-mail: [email protected] (J.D.).,...
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Supramolecular Isomerism and Polyrotaxane-Based TwoDimensional Coordination Polymers In-Hyeok Park,† Huiyeong Ju,† Tun Seng Herng,‡,§ Yunji Kang,† Shim Sung Lee,*,† Jun Ding,*,‡ and Jagadese J. Vittal*,§ †

Department of Chemistry and Research Institute of Natural Science, Gyeongsang National University, Jinju 52828, South Korea Department of Materials Science and Engineering, National University of Singapore, 119260, Singapore § Department of Chemistry, National University of Singapore, 3 Science Drive 3, 117543, Singapore ‡

S Supporting Information *

ABSTRACT: Different types of structural connectivities, topologies, and geometrical variations are possible for a given formula unit in coordination polymers (CPs) and metal−organic frameworks (MOFs) structures. This is termed supramolecular isomerism, similar to the isomerism observed in coordination complexes and organic molecules. The supramolecular isomers may exhibit different physical properties and chemical reactivities. Herein a bent dicarboxylate (sdb), a long dipyridyl spacer ligand (bpeb), and Co(II) have been used to construct two-dimensional (2D) sheets made of wheels and axles. Depending upon the experimental conditions used, seven CPs (1−7) which have the same repeating unit [Co2(bpeb)(sdb)2] based on a paddlewheel structure have been isolated: a non-interpenetrated 2D sheet (1), two distortional supramolecular isomers (2 and 3), one mutually inclined interpenetrated three-dimensional structure (4), two other compounds isotypical to 2 but with two different guest solvents (5 and 6), and finally 7, a polymorph of 2. It is rather intriguing that such a simple composition can exhibit such diverse solid state structures. The magnetic properties of 2 and 3 have been discussed.

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INTRODUCTION Wheel-shaped cyclodextrins have been used to construct a variety of mechanically interlocked architectures including rotaxanes.1,2 Correspondingly, wheels formed by two bent spacer ligands with two metal ions and axles made by linear spacer coligands have been used to assemble a variety of entangled structures including polyrotaxanes.3−13 The twodimensional (2D) coordination polymers (CPs) containing polyrotaxane structures can be designed and constructed from bent dipyridyl ligands and linear dicarboxylates or vice versa.14−23 For the given formula, the nodes, comprising metal ions or metal ion aggregates, can be connected in different ways to the spacer ligands to furnish different structures and topologies, leading to supramolecular isomerism in CPs. Zaworotko extended the concept of isomerism observed in coordination complexes to coordination polymers.24,25 A number of new examples for supramolecular isomerism nowadays are emerging.26−44 Recently, we have shown that four different types of supramolecular isomers from 2D CP [Zn2(bpeb)(sdb)2] (sdb = 4,4′-sulfonyldibenzoate and bpeb = 1,4-bis[2-(4′-pyridyl)ethenyl] benzene), made up of rings and rectangular voids, can be constructed by changing the experimental conditions.40 These include a non-interpenetrating 2D sheet, a parallel/ diagonal interpenetrating framework forming a three-dimensional (3D) structure, and two other forms arising from polyrotaxane structures containing 2D → 2D entanglement. © XXXX American Chemical Society

The two polyrotaxane structures have different photoreactivity and sensing of nitro-aromatic compounds. They have different conformations and relative orientations of the bpeb ligands in the 2-fold entanglements and are designated as distortional supramolecular isomers as depicted in Scheme 1. Nonetheless, it is not clear whether such supramolecular structures can be extended to other transition metal ions. Formation of the supramolecular isomers in other systems may help to advance our knowledge in these types of interesting entanglements. Hence we perused our interest to synthesize similar entangled structures with Co(II) and successfully isolated seven 2D CPs having the same paddlewheel repeating unit [Co2(bpeb)(sdb)2]. Of these 1 has a non-interpenetrating structure, 2 and 3 are distortional supramolecular isomers, 4 is mutually inclined doubly interpenetrated, 5 and 6 are isotypical to 2 but with two different guest solvents, and 7 is a polymorph of 2. Of these 4− 6 were obtained concomitantly with 3 during the synthesis. The details are discussed below.

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RESULTS AND DISCUSSION Syntheses of CPs 1−7. Seven 2D CPs (1−7) have been synthesized from the solvothermal reactions of Co(NO3)2· 6H2O, bpeb, and H2sdb in the equimolar ratio at 120 °C, but Received: September 27, 2016 Revised: November 1, 2016

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mide (DMA) respectively in the presence of dimethyl sulfoxide (DMSO)/water produced 2 and 3 cleanly. Furthermore, there is no change in the products isolated, when CoCl2 or Co(ClO4)2·6H2O salts were used instead of Co(NO3)2·6H2O in the synthesis of 2 and 3. Non-interpenetrated dark green crystals of 1 were formed when water was avoided in the solvent combination used to prepare 3. When benzene or toluene was added to the solvent mixture of DMA/H2O/ DMSO, mutually inclined interpenetrated 4 was crystallized along with 3 concomitantly. Furthermore, with addition of 1,4dichlorobenzene (dcb) or 1,4-dibromobenzene (dbb) to DMA/H2O/DMSO, 5 and 6 were obtained in minor yields along with 3. Apart from the inclusion of the guest solvents dcb and dbb, 5 and 6 are essentially isotypical to 2. It may be noted that replacing DMA by DMF under these conditions did not yield 4−6. A new polymorph of 2, namely, 7, was obtained when pyrene was added during the synthesis of 2, but it was not retained in the solid. The details of the syntheses of 1−7 are shown in Scheme 2. The solid-state structures as determined by single-crystal Xray diffraction techniques show that 1−7 have the same connectivity with small variations in their geometrical parameters (Table 1). Basically the paddlewheel repeating units, [Co2(O2C−C)4] are connected by two sdb angular ligands on each side to form a large square shaped necklace-like one-dimensional (1D) chain (Figure 1a). These are further linked by the linear spacer ligand bpeb through the axial positions of Co(II) atoms in the paddlewheel building block to form a layer containing square and rectangular voids (Figure 1b). The large square formed by [Co2(sdb)4/2] acts as a wheel, and the bpeb ligand from the neighboring 2D CP acts as an axle yielding 2D → 2D entangled polyrotaxane motifs in 2 and 3 (Figure 1c,d). Interestingly, 2 and 3 obtained from DMF and DMA respectively are distortional supramolecular isomers which are isotypical to the reported Zn(II) analogues.40 On the contrary, mutually inclined 2-fold interpenetration of the 2D CPs occurs in 4 (Figure 1e). The structures of 5 and 6 are isotypical to 2 with the guest dcb and dbb occluded in the lattice. Some of the unique features of the individual structures are briefly discussed below. [Co2(bpeb)(sdb)2]·1.5DMA·1.5H2O (1). The compound 1 with a non-interpenetrated 2D structure crystallized in triclinic space group P1̅ with Z = 1. The asymmetric unit has half of the repeating formula [Co2(bpeb)(sdb)2]. Crystallographic inversion is present in the middle of the paddlewheel, benzene ring in bpeb and [Co2(sdb)2]. The [Co2(sdb)2] has a diamond shape with a distance of 8.60 Å and angles of 82° and 98°. The rectangular ring formed by [Co2(bpeb)]2 has a dimension of 11.28 × 22.79 Å. Despite these “empty” spaces, there is no entanglement or interpenetration observed. All the sheets are aligned approximately in the (101) plane, and the adjacent sheets are staggered along the direction in which bpeb ligands are propagated such that each Co2(bpeb)2 rectangle is interdigitated by two adjacent sdb ligands from both sides. Hence interpenetration is completely prevented as displayed in Figure 2. It is presumed to be a kinetic product. Although the cell parameters are similar to the Zn(II) analogue, it is not isotypical. However, this type of packing generates a total potential solvent accessible volume of 735.0 Å3, which is 32.5% of the unit cell volume.45,46 Further, the empty space has been partially occupied by highly disordered DMA and water molecules but not DMSO which was also used in the synthesis.

Scheme 1. Distortional Supramolecular Isomers Arising from the Relative Orientations of the Spacer Ligands in Polyrotaxane 2D Co(II) CPsa

a

Pink: bent dicarboxylate; blue: dipyridyl spacer; orange: Co(II).

the solvent and/or guest employed in each reaction is slightly different. Details of the synthetic conditions for 1−7 and their structural comparison are shown in Scheme 2. Only 1−3 and 7 were obtained in pure form, while 4−6 were formed concomitantly with 3. The solvent used in the reaction influences the formation of different supramolecular isomers. For example, dimethylformamide (DMF) and dimethylacetaScheme 2. Syntheses of the Supramolecular Isomers 1−7 and Their Structural Comparison

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formula formula weight crystal system space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z Dcalc (g/cm3) μ (mm−1) 2θmax (deg) reflections collected independent reflections goodness-of-fit on F2 R1, wR2 [I > 2σ(I)] R1, wR2 (all data)

2 C51H39Co2N3O13S2 1083.83 triclinic P1̅ 9.3536(2) 11.1983(3) 12.9445(3) 101.712(1) 107.031(1) 106.779(1) 1178.39(5) 1 1.527 0.864 52.00 18747 4619 [Rint = 0.0303] 1.045 0.0372, 0.0917 0.0414, 0.0938

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C54H47Co2N3.50O15S 1166.93 triclinic P1̅ 10.057(2) 12.984(3) 13.034(3) 81.59(3) 83.99(3) 84.68(3) 1669.2(6) 1 1.161 0.616 52.00 27304 6565 [Rint = 0.1401] 1.083 0.0740, 0.2281 0.0852, 0.2366

3 C52H45Co2N3O15S2 1133.89 triclinic P1̅ 12.5334(11) 12.6843(11) 18.4328(17) 77.004(6) 89.015(6) 89.225(6) 2854.8(4) 2 1.319 0.719 52.00 36634 10605 [Rint = 0.1450] 1.109 0.1559, 0.3553 0.2459, 0.3916

Table 1. Crystallographic Data and Refinement Parameters of 1−7 C96H114Co4N6O35S4 2275.89 monoclinic C2/c 16.2102(8) 18.9338(10) 21.0696(12) 90 104.203(4) 90 6269.0(6) 2 1.206 0.657 52.00 31309 5954 [Rint = 0.1226] 1.191 0.1026, 0.2827 0.1216, 0.2980

4 C54H36Cl2Co2N2O12S2 1157.73 triclinic P1̅ 9.4423(2) 11.4577(2) 12.8767(3) 102.295(1) 107.397(1) 107.399(1) 1196.57(4) 1 1.607 0.962 52.00 19148 4705 [Rint = 0.0344] 1.059 0.0421, 0.1234 0.0469, 0.1273

5 C54H36Br2Co2N2O12S2 1246.65 triclinic P1̅ 9.4861(3) 11.4601(3) 12.9104(4) 102.547(2) 107.725(2) 107.200(2) 1202.08(6) 1 1.722 2.509 52.00 19735 4719 [Rint = 0.0686] 1.072 0.0634, 0.1731 0.0881, 0.1890

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C51H39Co2N3O13S2 1083.83 triclinic P1̅ 13.5546(5) 15.2868(6) 18.7777(7) 96.991(2) 99.964(2) 110.606(2) 3515.9(2) 3 1.536 0.868 55.00 61515 16089 [Rint = 0.0709] 0.954 0.0831, 0.2366 0.1819, 0.2884

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Figure 3. (a) Front view and (b) side view of the 2-fold entanglement forming a polyrotaxane structure in 2. (c) Trans,trans,transconformation of bpeb in 2. Figure 1. (a) A view of the necklace-like 1D chain part in 1−7. (b) A single 2D sheet as observed in 1. 2D supramolecular isomers showing different types of entanglements in polyrotaxanes (c) 2 and (d) 3. (e) Two-fold interpenetrated structure in 4.

Figure 4. (a) Front view and (b) side view of the 2-fold entanglement forming the polyrotaxane structure in 3. (c) Trans,cis,transconformation of bpeb in 3. Figure 2. A view of the packing showing how the interpenetration is avoided in 1.

4.306 Å but not too close as revealed by the rotational disorder in one of the pyridyl groups. Although isotypical to Zn(II) compound,40 3 was found to be photoinert as observed other Co(II) MOFs.47,48 In 3, the bpeb ligand has trans,cis,transconformation (Figure 4c). The PLATON calculation45,46 shows that the total potential solvent accessible volume is 927.0 Å3 which is 32.5% of the unit cell volume. Further, the empty space has been partially occupied by highly disordered DMA and water molecules but not DMSO which was also used in the synthesis. [Co2(bpeb)(sdb)2]·0.5DMA·2H2O (4). Another supramolecular isomer 4 crystallized in the monoclinic space group C2/ c with Z = 4. Its asymmetric unit contains half of the formula unit, and it also has a crystallographic inversion in the paddlewheel building unit. The dimension of the distorted square formed by Co2(sdb)2 linkages is 8.578 × 8.594 Å. A parallelogram with an angle of 103° is formed if the centers of the Co(II) atoms across sdb ligands and bpeb ligand are connected to produce dimensions of 12.463 × 22.703 Å. The 2D layer structure is doubly interpenetrated to furnish 3D structure utilizing the rectangular voids, as shown in Figure 5. The parallel diagonal inclined interpenetrated 4 has a total potential solvent area volume45,46 of 2540.0 Å3, which is 40.5% of the unit cell volume. The empty voids were partially occupied by highly disordered DMF and water molecules.

[Co2(bpeb)(sdb)2]·DMF (2). The dark green blocks of [Co2(bpeb)(sdb)2]·DMF (2) crystallized in triclinic space group P1̅ with Z = 1. Crystallographic inversion center is present at the centers of the paddlewheel structure and benzene ring of bpeb ligand. The framework in 2 adopts a doubly entangled 2D structure (Figure 3a−c). The bpeb ligand has trans,trans,trans-conformation (Figure 3c). The center of the benzene ring of the bpeb ligand from the neighboring 2D framework sits in the middle of the [Co2(sdb)2] square in a complementary manner (Figure 3a,b). The total potential solvent accessible volume of 171.0 Å3, which is 14.5% of the unit cell volume, was calculated by the PLATON.45,46 Further, the empty space has been partially occupied by a DMF solvent used in the synthesis. Overall, this is isomorphous and isotypical to the Zn(II) analogue.40 [Co2(bpeb)(sdb)2]·DMA·H2O (3). The crystal structure of 3 shown in Figure 4 is isotypical to the corresponding Zn(II) analogue.40 One formula unit is present in the asymmetric unit for triclinic space group P1̅ with Z = 2. Similar to 2, this also forms a polyrotaxane type entangled structure as displayed in Figure 4. However, the relative orientations between the adjacent bpeb ligands from the adjacent 2D sheets are different to make 2 and 3 unique supramolecular isomers. The slipstacked alignment brings one pair of the olefin bonds closer to D

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Magnetic Property. The magnetic properties of the polycrystalline samples of the two distortional isomers 2 and 3 have been measured on a SQUID magnetometer under an applied field of 5000 Oe in the temperature range of 2−350 K. The temperature dependence magnetic susceptibility in the form of χMT versus T is shown in Figure 6.

Figure 5. (a) Top view and (b) side view of the packing showing the mutually inclined 2-fold interpenetrated structure of 4.

The main 2D structures of both [Co2(bpeb)(sdb)2]·dcb (5) and [Co2(bpeb)(sdb)2]·dbb (6) are essentially isotypical to 2, but the voids are partially filled with dcb and ddb respectively (Scheme 2 and Figure S10). Hence they are not discussed here further. [Co2(bpeb)(sdb)2]·DMF (7). Addition of pyrene in the synthesis of 2 allowed the isolation of 7 as a polymorph of 2, but the pyrene was not retained in the crystal lattice. Interestingly both 2 and 7 crystallized in the triclinic space group with the same composition, but Z = 3 in the case of 7. This means 7 has 1.5 formula units in the asymmetric unit (Figure S11a) with half the formula unit is close to the crystallographic inversion center. Apart from this, there is not much difference in the structure. Trans,trans,trans-conformation of bpeb was present in both 7 and 2. The PLATON calculation45,46 reveals that the total potential solvent accessible volume 503 Å3 (14.5% of the unit cell volume) is similar to that found in 2. Only supramolecular isomerism dominates in CPs and MOFs, and occurrence of polymorphism in coordination polymeric structure is not common.49−55 During the synthesis, 4−6 were formed concomitantly, and probably all are kinetic products and their relative energies of formation are very close to each other. Such concomitant occurrence of supramolecular isomers has been noted during synthesis.56−59 To our surprise 2 and 3 were isolated in pure form, and they have distinct solid state structures. Both have the same connectivity with a subtle difference in the displacement of the adjacent bpeb axles in the entangled structure responsible for the formation of rotaxane formation. The existence of different types of isomerism in CPs and MOFs was first realized by Zaworotko.24,25 The term “supramolecular isomerism” was used to describe the presence of more than one superstructure for a given molecular component.24,25,60,61 Other types of isomerism such as conformational and structural supramolecular isomerism were also encountered in extended and infinite structures.24,52,62−64 Here 2 and 3 have the same connectivity, dimensionality, and topology, but structurally they are distinct and different from each other. Hence the term “distortional supramolecular isomers” has been coined for this type of isomers.40 There seems to be a parallel behavior between polymorphism and supramolecular isomerism. Now it is an appropriate time to state, similar to the provocative statement of McCrone on polymorphism, that “every coordination polymeric architecture can have different supramolecular isomers and that, in general, the number of forms known for the given CP is proportional to the time and energy spent in research on that CP”.65

Figure 6. Temperature dependence of χMT for 2 and 3, measured at 500 Oe from 2 to 350 K. The samples are fitted according to a spin Hamiltonian by the PHI program with g = 2.02 (solid lines).

For 3, as the temperature decreases from 350 K, χmT decreases continuously from 1.47 cm3 K mol−1 at 350 K to 0.017 cm3 K mol−1 at 30 K. Below this temperature χMT is constant until 2 K. Similarly, χMT of 2 decreases continuously from 1.79 cm3 K mol−1 at 350 K to 0.023 cm3 K mol−1 at 30 K. Such a behavior is associated with the antiferromagnetic exchange coupling between the Co(II) ions. The value of χMT, 1.65 cm3 K mol−1 at 300 K is lower than the expected 1.87 cm3 K mol−1 for spin only high spin Co(II) ions (S = 3/2 and g = 2). This is caused by an unquenched orbital contribution arising from the 4Tıg ground state of Co(II).66−68 The magnetic susceptibility data were fitted according to a spin Hamiltonian by the PHI66 program with g = 2.02 in the temperature range of 2−350 K. The best fitted data yielded the exchange integral J of −55.302 cm−1 for 2 and −64.183 cm−1 for 3 respectively. The 2 exhibited a temperature independent paramagnetic (TIP) component of 1.0 × 10−4 cm3 K mol−1, while 3 has a TIP of 1.4 × 10−4 cm3 K mol−1. These results indicate that antiferromagnetic interaction exists within the Co(II) dimer unit.69−74 2 and 3 shows axial zero field splitting (ZFS) parameter (D) of 4.69 and 4.49 cm−1, respectively, with the rhombic ZFS parameter (E) of ±0.056 cm−1. The parameters indicate the presence of magnetic anisotropy as expected for the Co(II) atom with square-pyramidal geometry. The magnetic properties have been investigated for a number of CPs containing paddlewheel based Co(II) dimers. These dimers have weak Co(II)···Co(II) interactions with distances around 2.8 Å. The exchange interaction is usually large giving rise to mainly antiferromagnetic interactions between the metal pairs.6,75−80 The magnetic moment reported for the paddlewheel based Co(II) dimers are in the range of 1.4−6.85 μB. Interestingly in a similar 2D → 2D entangled polyrotaxane framework, a value of 1.87 cm3 K mol−1 was observed at 300 E

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IR (KBr pellet, cm−1): 3447, 3098, 2930, 1678, 1633, 1608, 1568, 1408, 1299, 1161, 1136, 1101, 1015, 972, 872, 837, 778, 741, 722, 621, 576, and 557. Preparation of [Co2(bpeb)(sdb)2]·DMA·2H2O (3). A mixture of bpeb (19.9 mg, 0.070 mmol), H2sdb (20.4 mg, 0.070 mmol), and Co(NO3)2·6H2O (22.1 mg, 0.072 mmol) dissolved in DMA (3 mL), H2O (1 mL), and DMSO (0.5 mL) was placed in a 5 mL glass tube, and then 0.1 M NaOH solution (0.15 mL) was added. The tube was sealed and kept at 120 °C for 48 h, followed by cooling to room temperature over 8 h. Dark blue needle-shaped crystals 3 suitable for X-ray analysis were obtained. Anal. Calcd for the bulk, [C52.8H44.8Co2N3.2O14.2S2] as [Co2(bpeb)(sdb)2]·1.2DMA·H2O: C, 55.96; H, 3.98; N, 3.95; S, 5.66. Found: C, 55.55; H, 4.02; N, 4.40; S, 6.17%. IR (KBr pellet, cm−1): 3421, 3038, 2933, 1636, 1609, 1567, 1409, 1407, 1299, 1164, 1101, 1015, 968, 871, 834, 778, 739, 722, 694, 583, 556, and 509. Preparation of [Co2(bpeb)(sdb)2]·0.5DMA·2H2O (4). A mixture of bpeb (20.1 mg, 0.071 mmol), H2sdb (21.7 mg, 0.071 mmol), and Co(NO3)2·6H2O (20.6 mg, 0.071 mmol) dissolved in DMA (3 mL), H2O (1 mL), DMSO (0.5 mL), and benzene (1 mL) was placed in a 5 mL glass tube, and then 0.1 M NaOH solution (0.15 mL) was added. The tube was sealed and kept at 120 °C for 48 h, followed by cooling to room temperature over 8 h. A mixture of dark blue needle-shaped crystals 4 (major) and dark blue block-shaped crystals 3 (minor) suitable for X-ray analysis was obtained. Preparation of [Co2(bpeb)(sdb)2]·dcb (5). A mixture of bpeb (19.9 mg, 0.070 mmol), H2sdb (20.4 mg, 0.070 mmol), and Co(NO3)2·6H2O (22.1 mg, 0.072 mmol) dissolved in DMA (3 mL), H2O (1 mL), DMSO (0.5 mL), and 1,4-dichlorobenzene (dcb, 1 mL) was placed in a 5 mL glass tube, and then 0.1 M NaOH solution (0.15 mL) was added. The tube was sealed and kept at 120 °C for 48 h, followed by cooling to room temperature over 8 h. A mixture of dark blue needle-shaped crystals 3 (major) and dark blue block-shaped crystals 5 (3⊃BzCl, minor) suitable for X-ray analysis was obtained. Preparation of [Co2(bpeb)(sdb)2]·dbb (6). A mixture of bpeb (19.9 mg, 0.070 mmol), H2sdb (20.4 mg, 0.070 mmol), and Co(NO3)2·6H2O (22.1 mg, 0.072 mmol) dissolved in DMA (3 mL), H2O (1 mL), DMSO (0.5 mL), and 1,4-dibromobenzene (dbb, 1 mL) was placed in a 5 mL glass tube, and then 0.1 M NaOH solution (0.15 mL) was added. The tube was sealed and kept at 120 °C for 48 h, followed by cooling to room temperature over 8 h. A mixture of dark blue needle-shaped crystals 3 (major) and dark blue block-shaped crystals 6 (3⊃BzBr, minor) suitable for X-ray analysis was obtained. Preparation of [Co2(bpeb)(sdb)2]·DMF (7). A mixture of bpeb (20.1 mg, 0.071 mmol), H2sdb (21.7 mg, 0.071 mmol), and Co(NO3)2·6H2O (20.6 mg, 0.071 mmol) dissolved in DMF (3 mL), H2O (1 mL), DMSO (0.5 mL), and pyrene (14.3 mg, 0.071 mmol) was placed in a 5 mL glass tube, and then 0.1 M NaOH solution (0.15 mL) was added. The tube was sealed and kept at 120 °C for 48 h, followed by cooling to room temperature over 8 h. Dark blue blockshaped crystals 7 suitable for X-ray analysis were obtained. Crystallographic Structure Determinations. Crystal data for 1−7 at 173 K were collected on a Bruker SMART APEX II ULTRA diffractometer equipped with graphite monochromated Mo Kα radiation (λ = 0.71073 Å) generated by a rotating anode. Data collection, data reduction, and absorption correction were carried out using the software package of APEX2.83 All of the calculations for the structure determination were carried out using the SHELXTL package.84 Relevant crystal data collection and refinement data for the crystal structures of 1−7 are summarized in Table 1. Powder X-ray Diffraction (PXRD) Studies. The homogeneity of 2 and 3 was also confirmed by the PXRD patterns (Figures S1 and S2). In 1, the PXRD patterns were not matched. Hence, the cell parameters of single crystals of 1 were checked by single crystal X-ray diffraction (SC-XRD) for more 20 times, which supports the purity of the single crystal. However, during the sample preparation of PXRD by grinding the single crystals, solvent would have been lost and caused a change in the phase of the compound which gave a new PXRD pattern. The solvent molecules were removed by grinding in 1.

K.6 Although 2 and 3 are distinct structures, the structural changes and distortions that occur in the long-range have no effect on the magnetic properties.

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CONCLUSION In summary, we have synthesized seven supramolecular isomers and polymorphic forms from Co(II), a bent dicarboxylate, sdb, and a long spacer ligand, bpeb, under different experimental conditions. Solid state structures as determined by the single crystal X-ray diffraction techniques reveal that all these structures are built from 2D sheets. Interestingly, all have the same repeating unit [Co2(bpeb)(sdb)2] based on paddlewheel structures and rings formed by Co2(sdb)2 squares and axles. In all the structures, the bpeb ligand has trans,trans,transconformation except in 3 which has trans,cis,trans-conformation. In compounds 2 and 3 the wheel and axle joined together yielding a polyrotaxane structure. Two different relative alignments of the bpeb axles generate distortional supramolecular isomers. On the contrary, a non-interpenetrated 2D sheet and a mutually inclined 2-fold interpenetrated 3D structure were also formed in this series of structures. Addition of pyrene in the synthesis yielded a polymorphic modification of 2, whereas the additives were retained as guests in 5 and 6. Previously the Zn(II) analogues of 2 and 3 showed photoreactivity.40 Here we found all the Co(II) compounds to be photoinactive. Photoreactivity of compounds of transition metal ions is poorly understood as some exhibited photoreactivity, while others were not. More theoretical understanding is needed to understand this phenomena.81 The variable magnetic studies revealed that both 2 and 3 are antiferromagnetic in the temperature region 3−350 K.

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EXPERIMENTAL SECTION

General. All chemicals were purchased from commercial sources and used as received. All solvents used were of reagent grade. The bpeb ligand was synthesized by the reported procedure.82 Elemental analyses were carried out on a LECO CHNS-932 elemental analyzer. Thermogravimetric analyses were recorded in a TA Instruments TGAQ50 thermogravimetric analyzer. Samples were heated at a constant rate of 5 °C min−1 from room temperature to 700 °C and at a continuous flow nitrogen atmosphere. The Fourier transform infrared (FT-IR) spectra were recorded using Thermo Fisher Scientific Nicolet iS 10 FT-IR spectrometer with KBr pellets. Preparation of [Co2(bpeb)(sdb)2]·1.5DMA·1.5H2O (1). A mixture of bpeb (19.9 mg, 0.070 mmol), H2sdb (20.4 mg, 0.070 mmol), and Co(NO3)2·6H2O (22.1 mg, 0.072 mmol) dissolved in DMF (3 mL) and DMSO (0.5 mL) was placed in a 5 mL glass tube, and then 0.1 M NaOH solution (0.15 mL) was added. The tube was sealed and kept at 120 °C for 48 h, followed by cooling to room temperature over 8 h. Dark blue block-shaped crystals 1 suitable for Xray analysis were obtained. Anal. Calcd for the bulk [C61.6H66.6Co2N5.4O17.4S2] as [Co2(bpeb)(sdb)2]·3.4DMA·2H2O: C, 55.09; H, 5.00; N, 5.63; S, 4.78. Found: C, 55.15; H, 4.96; N, 5.73; S, 4.81. IR (KBr pellet, cm−1): 2932, 1650, 1609, 1571, 1499, 1404, 1325, 1301, 1163, 1136, 1100, 1072, 1035, 1011, 961, 873, 843, 781, and 739. Preparation of [Co2(bpeb)(sdb)2]·DMF (2). A mixture of bpeb (20.1 mg, 0.071 mmol), H2sdb (21.7 mg, 0.071 mmol), and Co(NO3)2·6H2O (20.6 mg, 0.071 mmol) dissolved in DMF (3 mL), H2O (1 mL), and DMSO (0.5 mL) was placed in a 5 mL glass tube, and then 0.1 M NaOH solution (0.15 mL) was added. The tube was sealed and kept at 120 °C for 48 h, followed by cooling to room temperature over 8 h. Dark blue block-shaped crystals 2 suitable for Xray analysis were obtained. Anal. Calcd for the bulk, [C50.1H36.9Co2N2.7O12.7S2] as [Co2(bpeb)(sdb)2]·0.7DMF: C, 56.66; H, 3.50; N, 3.56; S, 6.04. Found: C, 56.60; H, 3.60; N, 3.97; S, 6.65%. F

DOI: 10.1021/acs.cgd.6b01431 Cryst. Growth Des. XXXX, XXX, XXX−XXX

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Magnetic Studies. A superconducting quantum interference device (SQUID) magnetometer MPMS was used for the magnetic characterization. A powder sample with a weight of 5−10 mg was sealed in a plastic capsule. Magnetic moment was measured in the temperature range of 2−350 K. The empty plastic capsule exhibited diamagnetism, and its magnetic moment was measured for correction. After correction of diamagnetic signal of plastic capsule and sample holder, diamagnetism of monomer, and paramagnetic contamination (for example free radical), magnetic susceptibility was fitted using the PHI66 program by means of an isotropic spin Hamiltonian (SH) accounting for the exchange coupling (Heisonberg−Dirac−van Vleck Hamitonian) and ZFS.

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H = Hex + HZee + HCF

→⎯ ⎯→ Hex = −2J12 S1 S2 2

→ ⎯ HZee = μB ∑ SigiB ⃗ i=1

HCF =

⎡

∑ Di⎢Sz2, i − ⎣

⎤ E 1 Si(Si + 1) + i (Sx2, i − Sy2, i)⎥ 3 Di ⎦

D: axial ZFS parameter; F: rhombic ZFS parameter; S⃗: spin vector; B⃗ : μB : Bohr magneton. magnetic field vector; g: g-factor; ⎯→

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ASSOCIATED CONTENT

S Supporting Information *

These materials are available free of charge via the Internet at The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.cgd.6b01431. PXRD patterns, TGA curves, IR spectra, crystallographic refinements, crystal structures, photograph of crystals (PDF) Accession Codes

CCDC 1500542−1500548 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] (S.S.L.). *E-mail: [email protected] (J.D.). *E-mail: [email protected] (J.J.V.). ORCID

Jagadese J. Vittal: 0000-0001-8302-0733 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the NRF (2012R1A4A1027750), South Korea, the Ministry of Education, Singapore through NUS FRC Grant R-143-000-604-112, and National Research Foundation through NRF-CRP Grant No. 10-2012-03.

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H

DOI: 10.1021/acs.cgd.6b01431 Cryst. Growth Des. XXXX, XXX, XXX−XXX