Channel-containing structures generated from linear coordination polymer chains containing N,N′ -bidentate ligands and Cu–Cu dimetal units

Solid State Sciences 7 (2005) 1083–1095 www.elsevier.com/locate/ssscie

Channel-containing structures generated from linear coordination polymer chains containing N ,N
-bidentate ligands and Cu–Cu dimetal units Andrea M. Goforth, Kathrine Gerth, Mark D. Smith, Sandra Shotwell 1 , Uwe H.F. Bunz 1 , Hans-Conrad zur Loye ∗ Department of Chemistry and Biochemistry, The University of South Carolina, Columbia, SC 29208, USA Received 2 December 2004; received in revised form 12 January 2005; accepted 1 March 2005 Available online 6 June 2005

Abstract Four new one-dimensional coordination polymers containing the dimetal cluster Cu2 (OAc)4 have been synthesized by reacting Cu(OAc)2 · H2 O with two different N ,N
-bidentate ligands. Reaction of the flexible ligand, 1,2-bis(4-pyridyl)ethane (L1 ), with the copper starting material produced two, co-crystallizing coordination polymers: catena-Poly[Cu2 (OAc)4 (L1 )] · 2H2 O (1) and catena-Poly[Cu2 (OAc)4 (L1 )]. In the solid state, 1 (monoclinic, C2/c, a = 24.9471(17) Å, b = 13.3539(9) Å, c = 8.8050(6) Å, β = 93.6480(10)◦ , V = 2927.4(3) Å3 , Z = 4) features linear chains which are organized into layers. These layers stack along the crystallographic c-axis forming small hexagonal channels occupied by the solvent of crystallization. Compound 2 (triclinic, P-1, a = 7.6263(6) Å, b = 8.5283(6) Å, c = 9.8633(6) Å, α = 74.1070(10)◦ , β = 68.2160(10)◦ , γ = 74.0090(10)◦ , V = 561.96(7) Å3 , Z = 1) also features linear chains of the coordination polymer, but differs from 1 in that the chains are packed so as to leave no significant channels. Reaction of the rigid ligand, 1,4-bis(4-pyridyl)buta-1,3-diyne (L2 ), with the copper starting material also afforded two co-crystallizing coordination polymers: catena-Poly[Cu2 (OAc)4 (L2 )] (3) and catenaPoly[Cu2 (OAc)4 (L2 )] · solvents (4). 3 (monoclinic, P21 /m, a = 9.8065(9) Å, b = 12.3793(11) Å, c = 9.9408(9) Å, β = 107.6009(17)◦ , V = 1150.29(18) Å3 , Z = 2), like 2, features linear chains and contains no significant solvent accessible void space. 4 (monoclinic, C2/c, a = 28.9810(16) Å, b = 12.9301(7) Å, c = 8.6954(5) Å, β = 98.8010(10)◦ , V = 3220.0(3) Å3 , Z = 4) also consists of linear chains of the coordination polymer. However, the overall topology of 4 is identical to that of 1, with the generated hexagonal channels containing crystallographically unidentifiable solvents of crystallization. Compounds 1 and 2 and compounds 3 and 4 are pairs of polymorphic coordination polymers neglecting the solvents of crystallization in 1 and 4. The compounds, which represent four new examples of coordination polymers containing dimetal units, have been characterized by IR, elemental analysis, and thermogravimetric analysis in addition to X-ray crystallography.  2005 Elsevier SAS. All rights reserved. Keywords: Coordination polymers; Copper dimers; N ,N
-bidentate ligands; Dimetal building blocks; Polymorphic coordination polymers; Twinned crystal

1. Introduction

* Corresponding author. Hans-Conrad zur Loye, Department of Chemistry and Biochemistry, The University of South Carolina, 631 Sumter Street, Columbia, SC 29208, USA. Tel.: +1 (803) 777-6916; Fax: +1 (803) 777-8508. E-mail address: [email protected] (H.-C. zur Loye). 1 New address since August 2003: Department of Chemistry, Georgia Institute of Technology, Atlanta, GA 30332, USA.

1293-2558/$ – see front matter  2005 Elsevier SAS. All rights reserved. doi:10.1016/j.solidstatesciences.2005.03.006

The field of inorganic/organic coordination polymers has received much recent attention because many such materials exhibit encouraging potential for application in areas such as catalysis, non-linear optics, gas separation or storage, magnetic materials, and molecular recognition [1–7]. Researchers in this field have been extremely successful in the preparation of a large number of coordination polymers with a wide variety of structural motifs from diverse metals and organic linkers [8–23]. At present, the topology and

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properties of such materials are not easily predicted. However, some fundamental aspects of the coordination chemistry, such as the identity, oxidation state, and coordination preference of the metal center or the relative flexibility of the organic linker, can nonetheless be utilized to direct the product architecture. Additionally, the use of organic or metal-containing building blocks exhibiting certain physical or chemical properties is often fruitful as those same properties frequently become the properties of the hybrid inorganic/organic architecture [24–26]. In the long run, strategies of this type may allow the prediction of topology and properties for this class of materials. Previous research in this area has demonstrated that the most efficient synthetic route to inorganic/organic coordination polymers is via the direct chemical combination of functional inorganic and organic components [8–23]. In terms of the organic component, the most useful class of ligands has been the N ,N
-bidentate ligands. This class of ligands has provided remarkable structural diversity in the field of coordination polymers due to the varying extent of flexibility in these organics. So far, several rigid N -donor bidentate ligands (e.g., 4,4
-bipyridine, 1,4-bis(4pyridyl)ethene, and 1,4-bis(4-pyridyl)ethyne) as well as several flexible N -donor bidentate ligands (e.g., 1,4-bis(4pyridyl)ethane, 1,4-bis(3-pyridyl)-2,3-diaza-1,3-butadiene, and 2,5-bis(3-pyridyl)-3,4-diaza-2,4-hexadiene) have been used by us and others to construct coordination polymers exhibiting a variety of structural motifs [8–10,27–33]. In terms of the inorganic component, the majority of the research carried out so far has focused on the use of mononuclear coordination centers. Coordination polymers and oligomers containing dimetal units have not been as extensively explored, although numerous bridged dimetal units containing copper, rhodium, molybdenum, and ruthenium are known [34–42]. Recently, two reviews summarizing one-dimensional coordination polymers based on tetracarboxylate-bridged dimetal units have appeared in the literature [34,35]. Bridged dimetal clusters represent useful linear building blocks as they possess two Lewis acid binding sites that readily bond to Lewis bases such as those found in the N ,N
-bidentate type ligands. Polymeric systems containing dimetal clusters are of interest as they may display interesting spectroscopic or magnetic properties generated from the synergistic effect between two or more metal centers [43]. Herein, we wish to report four new one-dimensional coordination polymers containing Cu–Cu dimetal units and N,N
-bidentate ligands, namely catena-Poly[Cu2 (OAc)4 (L1 )] · 2H2 O (1), catena-Poly[Cu2 (OAc)4 (L1 )] (2), catenaPoly[Cu2 (OAc)4 (L2 )] (3), and catena-Poly[Cu2 (OAc)4 (L2 )] · solvents (4) which were generated by direct chemical combination of Cu(OAc)2 · H2 O with 1,2-bis(4-pyridyl)ethane (L1 ) or 1,4-bis(4-pyridyl)buta-1,3-diyne (L2 ), respectively (Fig. 1). Though the combination of a linear bidentate ligand with a linear dimetal unit is anticipated to result in the formation of 1D coordination polymer chains, it is unex-

Fig. 1. Flexible (L1 ) and rigid (L2 ) N ,N
-bidentate ligands.

pected that the arrangement of such chains in the solid state may produce a channel-containing material. In this paper we describe two materials in which 1D coordination polymer chains generate 3D channel-containing materials.

2. Experimental 2.1. Materials and methods Cu(OAc)2 · H2 O (Johnson Matthey, reagent grade) and 1,2-bis(4-pyridyl)ethane (Aldrich, 99%) were purchased and used without further purification. 1,4-bis(4-pyridyl)buta-1,3diyne was synthesized according to the published literature procedure [44]. Elemental analyses were performed by Desert Analytics (Tucson, AZ). TGA measurements were carried out on a TA Instruments SDT 2960 DTA-TGA apparatus in a flowing He atmosphere using a heating rate of 10 ◦ C/min. Infrared (IR) samples were prepared by intimately grinding the samples with KBr for diffuse reflectance measurement, and spectra were collected in the 400–4000 cm−1 range using a Shimadzu 8400 FT-IR spectrometer. 2.1.1. Preparation of catena-Poly[Cu2 (OAc)4 (L1 )] · 2H2 O (1) and catena-Poly[Cu2 (OAc)4 (L1 )] (2) 1,2-bis(4-pyridyl)ethane (L1 ) (29.4 mg, 0.16 mmol) was dissolved in 2 ml of CH2 Cl2 , and a neat 1 ml layer of methanol was carefully layered on top of the ligandcontaining solution. On top of the neat methanol layer was placed a methanol solution (2 ml) of Cu(OAc)2 · H2 O (20.9 mg, 0.10 mmol). Diffusion of the two solutions into one another at room temperature over the course of one week produced 1 and 2 as green and blue-green co-crystallizing solids. Because it was not possible to easily separate the two crystalline materials, measurements other than the crystallographic analyses were made on samples containing both 1 and 2. The yield, based on Cu(OAc)2 ·H2 O, is 36% assuming that 100% of the solid product is the product of greater molar

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mass (1). Crystals of 1 lose solvent of crystallization upon standing in air for several days, as evidenced by the loss of transparency and cracking of the crystals. A suitable single crystal of each compound was selected for the X-ray crystallographic analyses. IR (KBr, cm−1 ): ν = 3425(m), 3055(m), 2934(m), 2870, 2766, 2446, 2361, 1960, 1869, 1612(s), 1558, 1501, 1429(s), 1348(m), 1225(m), 1076(m), 1016(m), 935, 881, 833(m), 812(m), 781, 735, 681(s), 629(m). Anal. calcd. for 1 (anhydrous) and 2: C, 43.87%; H, 4.42%; N, 5.12%. Found: C, 44.14%; H, 4.39%; N, 5.21%. 2.1.2. Preparation of catena-Poly[Cu2 (OAc)4 (L2 )] (3) and catena-Poly[Cu2 (OAc)4 (L2 )] · solvents (4) 1,4-bis(4-pyridyl)buta-1,3-diyne (L2 ) (31.1 mg, 0.15 mmol) was dissolved in 7 ml CH2 Cl2 . A neat 2 ml layer of methanol was placed on top of the ligand-containing solution, and a solution of Cu(OAc)2 · H2 O (30.4 mg, 0.15 mmol) dissolved in methanol (7 ml) was carefully placed on top of the methanol layer. Diffusion of the two solutions into one another over the course of one week resulted in the formation of blue-green and green single crystals of 3 and 4. The yield of crystals of 3 and 4, based on Cu(OAc)2 · H2 O and assuming that 100% of the crystalline product is the product of greater molar mass (4, vide infra), was 73%. A suitable single crystal of each compound was selected for X-ray crystallographic analyses. Crystals of 4 rapidly lose solvents of crystallization as evidenced by loss of transparency upon removal from the mother liquor. Because of difficulty in separating the two co-crystallizing coordination polymers, measurements other than the single crystal analyses were made on samples containing both 3 and 4. IR (KBr, cm−1 ) for desolvated 3 and 4: ν = 3055(m), 2934(m), 2343(m), 2166, 1597(s), 1533, 1491, 1425(s), 1346(m), 1225(m), 1207, 1096, 1050(m), 1015(m), 833(m), 785(m), 681(m), 627(m). Anal. calcd. for desolvated 3 and 4: C, 46.56%; H, 3.55; N, 4.94. Found: C, 46.34%; H, 3.48%; N, 4.90%. 2.1.3. Single crystal structure determination Suitable single crystals of 1, 2, 3, and 4 were selected and mounted on the end of thin glass fibers for data collection. X-ray intensity data were measured at 293(2) K (1), 294(1) K (2), 190(2) K (3), or 150(2) K (4) on a Bruker SMART APEX CCD-based diffractometer (Mo Kα radiation, λ = 0.71073 Å) [45]. The structure solution and refinement of 3 is particularly noteworthy, due to twinning in the crystals, and is discussed following descriptions of the crystallographic solutions of 1, 2, and 4. For 1, 2, and 4, the raw data frames were integrated into reflection intensity files with the Bruker SAINT+ program [45], which also applied corrections for Lorentz and polarization effects. Final unit cell parameters are based on the least-squares refinement of all reflections from each data set with I > 5(σ )I (4642 for 1, 4053 for 2, and 9153 for 4). Analysis of all three data sets showed negligible crystal decay during data collection. An empirical absorption correction based on the multiple measurement of equiva-

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lent reflections was applied with the program SADABS [45] to each data set. The structures were solved by a combination of direct methods and difference Fourier syntheses and were refined by full-matrix least-squares against F 2 using the SHELXTL software package [46]. For 1 and 4, the space group C2/c was confirmed by successful solution and refinement of the data sets. The centrosymmetric space group P-1 was determined for compound 2. For 1, the asymmetric unit consists of one Cu, two acetate groups, half a ligand, and a water molecule disordered over three positions. The site occupation factors for the three positions (O1s, 0.60; O2s, 0.20; O3s, 0.20) were set manually to give reasonable thermal parameters. Though reasonable positions for hydrogen atoms on the three disordered solvent water sites could be located in the Fourier difference map, their coordinates were fixed during refinement and should be regarded as approximate. For this reason, no attempt was made to identify a hydrogen-bonding network involving the solvent waters. Eventually, all non-hydrogen atoms were refined with anisotropic displacement parameters; hydrogen atoms were placed in idealized positions and refined using a riding model except for the solvent H atoms mentioned above. The packing of the [Cu2 (OAc)4 (C12 H12 N2 )] chains gives rise to infinite channels running parallel to the [001] direction. The channels constitute 28.5% of the total unit cell volume (834.3 Å3 /2927.4 Å3 ) [47]. Crystal data for 1 is summarized in Table 1. Atomic coordinates and equivalent isotropic displacement parameters for the compound are given in Table 2. Selected bond lengths and angles for 1 are given in Table 6. For 2, the asymmetric unit contains half of a Cu2 (OAc)4 grouping and half of a 1,2-bis(4-pyridyl)ethane ligand. Both species are located on inversion centers. All non-hydrogen atoms were refined with anisotropic displacement parameters. Hydrogen atoms were placed in geometrically idealized positions and included as riding atoms. The inflated displacement ellipsoids for atom C6 of the ligand and the elongated ellipsoids for atoms of the pyridyl ring indicate minor disorder affecting the ligand. This could not be modeled successfully. A C3–C6 = 1.50 Å distance restraint was necessary to compensate for the disorder effects. Crystal data for 2 is summarized in Table 1. Atomic coordinates and equivalent isotropic displacement parameters for the compound are given in Table 3. Selected bond lengths and angles for 2 are given in Table 7. For 4, the asymmetric unit consists of one Cu center, two acetate groups, and one ligand. These atoms were refined anisotropically with their associated hydrogen atoms included in idealized positions as riding atoms. The packing of the [Cu2 (OAc)4 (C14 H8 N2 )] chains gives rise to infinite channels running parallel to the [001] direction. The channels constitute 34.3% of the total unit cell volume (1105.2 Å3 /3220.04 Å3 ) [47] and contain many diffusely distributed electron density peaks due to disordered solvent. No reasonable disorder model could be achieved for these species, and they were therefore treated as variable occu-

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Table 1 Crystallographic data for 1, 2, 3, and 4 Formula

Cu2 C20 H28 N2 O10 , 1

C20 H24 Cu2 N2 O8 , 2

Cu2 C22 H20 N2 O8 , 3

Cu2 C22 H20 N2 O12 , 4

Formula weight 583.52 547.49 567.48 631.48 Crystal system Monoclinic Triclinic Monoclinic Monoclinic C2/c Space group C2/c P-1 P21 /m a (Å) 24.9471(17) 7.6263(6) 9.8065(9) 28.9810(16) b (Å) 13.3539(9) 8.5283(6) 12.3793(11) 12.9301(7) c (Å) 8.8050(6) 9.8633(7) 9.9408(9) 8.6954(5) 90 74.1070(10) 90 90 α (◦ ) 93.6480(10) 68.2160(10) 107.6009(17) 98.8010(10) β (◦ ) γ (◦ ) 90 74.0090(10) 90 90 V (Å3 ) 2927.4(3) 561.96(7) 1150.29(18) 3220.0(3) Z value 4 1 2 4 1.324 1.618 1.638 1.303 ρ calc. (Mg/m3 ) µ (mm−1 ) 1.499 1.940 1.899 1.373 Temperature (K) 293(2) 294(1) 190(2) 150(2) Reflections collected 11156 4684 9089 11602 Independent reflections 3638 1982 9089 2850 GOFa 0.996 1.085 1.012 1.152 Residuals:b R1 , wR 2 I > 2σ (I ) 0.0512, 0.1415 0.0388, 0.1011 0.0395, 0.0854 0.0399, 0.1325 all data 0.0651, 0.1480 0.0405, 0.1029 0.0493, 0.0885 0.0412, 0.1339 Residual electron density max and min (e Å−3 ) 0.672 and −0.312 0.833 and −0.782 0.780 and −0.392 0.716 and −0.395 a GOF = {
[w(F 2 − F 2 )2 ]/(n − p)}1/2 (n means no. refl.; p means refined parameters), w = 1/[σ 2 (F 2 ) + (aP )2 + bP ], where P = [2F 2 + o c o c max(Fo2 , 0)]/3.



b R = ||Fo | − |Fc ||/ |Fo |, wR2 = { [Fo2 − Fc2 )2 ]/ [w(Fo2 )]2 }1/2 . 1 Table 2 Atomic coordinates (×104 ) and equivalent isotropic displacement parameters (Å2 × 103 ) for 1 Cu(1) C(1) C(2) C(3) C(4) C(5) C(6) C(7) C(8) C(9) C(10) N(1) O(1) O(2) O(3) O(4) O(1S) O(2S) O(3S)

x

y

z

2071(1) 979(2) 587(1) 635(1) 1083(1) 1464(1) 207(1) 2983(2) 3256(2) 2870(2) 3071(2) 1415(1) 2516(1) 3250(1) 2433(1) 3159(1) 4332(4) 4819(16) 4316(19)

2179(1) 2044(3) 1673(3) 727(3) 188(3) 620(3) 281(3) 2769(3) 2962(3) 740(3) −326(3) 1526(2) 2459(2) 2940(2) 878(2) 1412(2) 2013(12) 821(16) 530(20)

9187(1) 7293(4) 6289(4) 5704(3) 6170(4) 7194(4) 4606(4) 7597(4) 6136(5) 10260(4) 10401(7) 7757(3) 7471(3) 8827(3) 9544(3) 10884(3) 9081(15) 1460(40) 3210(80)

Table 3 Atomic coordinates (×104 ) and equivalent isotropic displacement parameters (Å2 × 103 ) for 2

U (eq) 40(1) 51(1) 52(1) 44(1) 46(1) 44(1) 54(1) 51(1) 74(1) 55(1) 95(2) 42(1) 59(1) 65(1) 62(1) 64(1) 258(8) 190(14) 390(40)

U (eq) is defined as one third of the trace of the orthogonalized U ij tensor.

pancy oxygen atoms. Initially, the solvent peak occupancies were allowed to refine; subsequently all solvent peaks were refined with a fixed common isotropic displacement parameter of Ueq = 0.10 Å2 with occupancies fixed near the final refined values. H atoms were not located or calculated for these species. Crystal data for 4 is summarized in Table 1. Atomic coordinates and equivalent isotropic displacement

Cu(1) C(1) C(2) C(3) C(4) C(5) C(6) C(7) C(8) C(9) C(10) N(1) O(1) O(2) O(3) O(4)

x

y

z

U (eq)

1538(1) 4603(5) 6351(7) 7811(7) 7268(7) 5499(6) 9764(8) 1531(5) 2528(6) −1489(5) −2433(6) 4169(4) 2439(4) −141(4) 177(4) −2411(4)

4114(1) 3020(6) 2384(7) 1411(7) 1066(7) 1785(6) 899(7) 4443(5) 4214(6) 2422(4) 928(5) 2764(4) 3783(4) 5294(4) 2246(3) 3733(3)

4193(1) 1380(4) 459(5) 1012(6) 2570(6) 3414(5) 13(7) 7013(4) 8128(5) 6129(4) 6731(5) 2841(3) 5902(3) 7261(3) 5211(3) 6588(3)

33(1) 49(1) 69(1) 73(2) 79(2) 55(1) 86(2) 39(1) 57(1) 37(1) 54(1) 36(1) 50(1) 51(1) 50(1) 46(1)

U (eq) is defined as one third of the trace of the orthogonalized U ij tensor.

parameters for the compound are given in Table 5. Selected bond lengths and angles for 4 are given in Table 9. For 3, examination of area detector intensity data frames from several crystals revealed diffraction patterns containing single spots and split spots. All crystals could be indexed to an apparent primitive monoclinic cell of a = 9.94 Å, b = 12.39 Å, c = 47.00 Å, β = 96.04◦ . However, a large number of reflections were left unindexed. Eventually, the program GEMINI [48] was used to identify the crystals as

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Table 4 Atomic coordinates (×104 ) and equivalent isotropic displacement parameters (Å2 × 103 ) for 3 Cu(1) Cu(2) C(1) C(2) C(3) C(4) C(5) C(6) C(7) C(8) C(9) C(10) C(11) C(12) C(21) C(22) C(23) C(24) N(1) N(2) O(1) O(2) O(3) O(4)

x

y

z

U (eq)

6536(1) 9238(1) 3875(3) 2452(3) 1413(3) 1863(3) 3312(3) −74(3) −1346(3) −2784(3) −4043(3) −5545(3) −6313(2) −7760(2) 8332(2) 8600(2) 7469(2) 7244(2) 4310(2) −8479(2) 7064(1) 9397(1) 6392(1) 8724(1)

2500 2500 2500 2500 2500 2500 2500 2500 2500 2500 2500 2500 1533(2) 1576(2) 1044(2) 188(2) 1034(2) 144(2) 2500 2500 1371(1) 1382(1) 1373(1) 1373(1)

3260(1) 4661(1) 651(3) −140(3) 522(3) 2005(3) 2713(3) −232(3) −834(3) −1495(3) −2122(3) −2840(3) −3212(2) −3896(2) 2326(2) 1363(2) 5577(2) 6515(2) 2070(3) −4241(2) 2093(2) 3301(2) 4617(2) 5813(2)

22(1) 21(1) 26(1) 27(1) 20(1) 24(1) 22(1) 24(1) 23(1) 24(1) 27(1) 24(1) 24(1) 25(1) 23(1) 35(1) 23(1) 31(1) 19(1) 20(1) 33(1) 28(1) 30(1) 30(1)

U (eq) is defined as one third of the trace of the orthogonalized U ij tensor.

Table 5 Atomic coordinates (×104 ) and equivalent isotropic displacement parameters (Å2 × 103 ) for 4 Cu(1) C(1) C(2) C(3) C(4) C(5) C(6) C(7) C(8) C(9) C(10) C(11) N(1) O(1) O(2) O(3) O(4) O(1S) O(2S) O(3S) O(4S) O(5S) O(6S) O(7S)

x

y

z

U (eq)

2870(1) 3833(1) 4192(1) 4163(1) 3774(1) 3433(1) 4520(1) 4825(1) 2902(1) 3123(2) 2836(1) 3027(2) 3459(1) 3133(1) 2501(1) 3077(1) 2447(1) 4016(3) 4961(4) 4339(5) 4286(7) 4303(8) 4321(11) 4629(11)

2841(1) 2862(2) 3197(3) 4177(3) 4778(2) 4378(2) 4534(3) 4829(3) 2848(2) 3083(3) 692(2) −392(3) 3437(2) 3044(2) 2486(2) 1394(2) 815(2) 1679(8) 1206(9) 2515(12) 245(15) 236(18) 200(20) 1900(20)

4472(1) 3333(4) 2580(4) 1898(3) 2032(3) 2811(3) 1068(4) 381(4) 7746(3) 9389(4) 5113(4) 5160(6) 3459(3) 6673(3) 7556(2) 4652(3) 5522(3) 7310(11) 1744(12) 7752(15) 3180(20) 1770(30) 4280(40) 8200(40)

21(1) 36(1) 39(1) 29(1) 28(1) 26(1) 36(1) 37(1) 29(1) 47(1) 31(1) 57(1) 26(1) 49(1) 37(1) 41(1) 43(1) 100 100 100 100 100 100 100

U (eq) is defined as one third of the trace of the orthogonalized U ij tensor.

non-merohedral twins with two domains, to determine orientation matrices (unit cells) for both components, and to prepare an HKLF 5 format reflection file for twin refinement in SHELX. X-ray intensity data covering the full sphere of

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Table 6 Selected interatomic distances (Å) and bond angles (◦ ) with esds () for 1 Cu–O(1) Cu–O(3) Cu–N C(3)–C(6) O(1)–Cu–O(3) O(2)a –Cu–O(3) O(1)–Cu–N O(3)–Cu–N O(1)–Cu–Cua O(3)–Cu–Cua N–Cu–Cua

1.967(2) 1.974(3) 2.181(2) 1.515(4) 90.85(13) 89.67(13) 94.13(10) 93.36(11) 82.91(8) 81.49(7) 173.99(8)

Cu–O(2)a Cu–O(4)a Cu–Cua C(6)–C(6)b O(1)–Cu–O(4)a O(2)a –Cu–O(4)a O(2)a –Cu–N O(4)a –Cu–N O(2)a –Cu–Cua O(4)a –Cu–Cua C(3)–C(6)–C6b

1.975(3) 1.966(3) 2.6424(7) 1.484(6) 88.36(13) 88.41(13) 98.51(10) 99.09(11) 84.61(8) 86.08(8) 112.5(3)

Symmetry transformations used to generate equivalent atoms: a −x + 1/2, −y + 1/2, −z + 2; b −x, −y, −z + 1. Table 7 Selected interatomic distances (Å) and bond angles (◦ ) with esds () for 2 Cu(1)–O(1) Cu(1)–O(3) Cu(1)–N(1) C(3)–C(6) O(1)–Cu(1)–O(2)a O(1)–Cu(1)–O(4)a O(2)a –Cu(1)–O(4)a O(1)–Cu(1)–N(1) O(3)–Cu(1)–N(1) O(1)–Cu(1)–Cu(1)a O(3)–Cu(1)–Cu(1)a N(1)–Cu(1)–Cu(1)a

1.971(3) 1.971(3) 2.170(3) 1.472(6) 167.99(11) 89.07(13) 90.01(13) 95.79(11) 98.23(11) 83.04(8) 84.93(8) 176.64(8)

Cu(1)–O(2)a Cu(1)–O(4)a Cu(1)–Cu(1)a C(6)–C(6)b O(1)–Cu(1)–O(3) O(2)a –Cu(1)–O(3) O(3)–Cu(1)–O(4)a O(2)a –Cu(1)–N(1) O(4)a –Cu(1)–N(1) O(2)a –Cu(1)–Cu(1)a O(4)a –Cu(1)–Cu(1)a C(3)–C(6)–C(6)b

1.971(3) 1.981(3) 2.6298(7) 1.481(11) 89.94(13) 88.48(13) 168.05(10) 96.22(11) 93.71(11) 84.97(8) 83.13(7) 112.4(6)

Symmetry transformations used to generate equivalent atoms: a −x, −y + 1, −z + 1; b −x + 2, −y, −z. Table 8 Selected interatomic distances (Å) and bond angles (◦ ) with esds () for 3 Cu(1)–O(1) 1.9826(15) Cu(2)–O(2) 1.9733(14) Cu(1)–N(1) 2.146(2) Cu(1)–Cu(2) 2.5933(5) C(6)–C(7) 1.210(4) C(8)–C(9) 1.203(4) 89.70(9) O(1)–Cu(1)–O(1)a O(2)–Cu(2)–O(2)a 89.03(9) O(1)–Cu(1)–N(1) 64.56(6) O(3)–Cu(1)–N(1) 96.05(7) O(1)–Cu(1)–Cu(2) 84.81(4) O(3)–Cu(1)–Cu(2) 84.59(4) N(1)–Cu(1)–Cu(2) 179.10(7)

Cu(1)–O(3) 1.9745(15) Cu(2)–O(4) 1.9642(15) Cu(2)–N(2)b 2.174(2) C(3)–C(6) 1.423(4) C(7)–C(8) 1.364(4) C(9)–C(10) 1.429(4) O(1)–Cu(1)–O(3) 89.23(6) O(2)–Cu(2)–O(4) 89.34(6) O(2)–Cu(2)–N(2)b 93.49(6) O(4)–Cu(2)–N(2)b 96.57(6) O(2)–Cu(2)–Cu(1) 84.92(4) O(4)–Cu(2)–Cu(1) 84.99(4) N(2)b –Cu(2)–Cu(1) 179.10(7)

Symmetry transformations used to generate equivalent atoms: a x, −y + 1/2, z; b x + 2, y, z − 1.

reciprocal space were measured in ω scan mode at φ settings of 0, 120, and 240◦ . Using raw data frames from all three runs, 816 strong reflections were threshholded into a reflection array. Of these, 498 were indexed to twin component 1 (primitive monoclinic unit cell parameters: a = 9.80 Å, b = 9.94 Å, c = 12.38 Å, β = 107.70◦ ), and 316 of the remaining 318 were indexed to component 2, with similar

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Table 9 Selected interatomic distances (Å) and bond angles (◦ ) with esds () for 4 Cu–O(1) Cu–O(3) Cu–N C(3)–C(6) C(7)–C(7) O(1)–Cu–O(3) O(2)a –Cu–O(3) O(1)–Cu–N O(3)–Cu–N O(1)–Cu–Cua O(3)–Cu–Cua N–Cu–Cua

1.966(2) 1.962(2) 2.178(2) 1.427(4) 1.368(6) 90.85(13) 89.67(13) 94.13(10) 93.36(11) 82.91(8) 81.49(7) 173.99(8)

Cu–O(2)a Cu–O(4)a Cu–Cua C(6)–C(7) O(1)–Cu–O(4)a O(2)a –Cu–O(4)a O(2)a –Cu–N O(4)a –Cu–N O(2)a –Cu–Cua O(4)a –Cu–Cua C(3)–C(6)–C6b

1.966(2) 1.966(2) 2.6139(6) 1.201(5) 88.36(13) 88.41(13) 98.51(10) 99.09(11) 84.61(8) 86.08(8) 112.5(3)

Symmetry transformations used to generate equivalent atoms: a −x + 1/2, −y + 1/2, −z + 2; b −x, −y, −z + 1.

cell dimensions. The two unindexed reflections apparently belong to neither component and may be due to a third component or to an attached crystallite. The twin element is a 180◦ rotation around the reciprocal [100] direction, as determined by GEMINI. The twin law is, by rows, (1 0 0.6 / 0 −1 0 / 0 0 −1). Using the two orientation matrices so determined, the raw intensity data for each component was integrated with SAINT+ [45], which also applied corrections for Lorentz and polarization effects. An empirical absorption correction based on the multiple measurement of equivalent reflections was applied to each component with the program SADABS [45]. Two reflection files were created, containing reflections suffering from varying degrees of overlap with reflections from the complementary component. Due to the specific lattice metrics, the twinning causes the reciprocal lattices of the two domains to coincide exactly for the l = 5n (n = 0, 1 . . .) layers of reciprocal space. Partial overlap occurs when l = ±2, ±3, ±7 and ±8 (i.e., l = 5n ± 2, 5n ± 3). Reflections are non-overlapped when l = ±1, ±4 and ±6 (l = 5n ± 1, 5n ± 4, 5n ± 6). The orientation of the reciprocal lattices of the two twin components is shown schematically in Fig. 2. For an initial solution of the structure, only overlap-free data from component 1 was used. Systematic absences indicated the space groups P21 or P21 /m. The structure was readily solved in P21 /m by direct methods and subsequent difference Fourier syntheses. For refinement of the data, an HKLF 5 file was constructed with GEMINI, assigning separate batch scale factors (BASF parameters in SHELX) to the three groups of reflections (completely, partially, and non-overlapped). In total, 5356 reflections suffer from complete or partial overlap, and 3750 reflections are completely free of overlap. With this treatment of the data, refinement of the initial structural model converged rapidly to R1 (F) = 0.0395, wR2 (F2) = 0.0854 (I > 2σ (I )). Refinement was carried out by full-matrix least-squares against F 2 , using the SHELXTL software package [46]. The final unit cell parameters are based on the least-squares refinement of 4771 reflections with I > 5(σ )I from the major component. All atoms, except the acetate groups and part of one pyridyl ring (C11–C12, C11A–C12A), of the one-

dimensional chains in 3 reside on a crystallographic mirror plane. All non-hydrogen atoms were refined with anisotropic displacement parameters. Hydrogen atoms were placed in geometrically idealized positions and refined as standard riding atoms. Crystal data for 3 is summarized in Table 1. Atomic coordinates and equivalent isotropic displacement parameters for the compound are given in Table 4. Table 8 lists selected bond lengths and angles for 3.

3. Results and discussion 3.1. Compound 1 The reaction of 1,2-bis(4-pyridyl)ethane (L1 ) with Cu(OAc)2 · H2 O yielded blue-green and green crystals of 1 and 2 in 36% yield. X-ray crystallographic analysis of 1 revealed for the compound an infinite, one-dimensional zig-zag chain motif, a fragment of which is shown in Fig. 3. In 1, both the binuclear Cu2 (OAc)4 cluster core and the ligand (L1 ) reside on crystallographic inversion centers. The asymmetric unit therefore consists of one Cu2+ , two acetate groups, and half a ligand. In addition, the asymmetric unit contains one water molecule of crystallization that is disordered over three positions (O1s, 0.60; O2s, 0.20; O3s, 0.20). The Cu–Cu dimetal unit is bridged by four acetate ligands, with one oxygen donor from each ligand contributing to a CuO4 square plane about each copper center. The four Cu–O bond lengths are in the range 1.966(3) to 1.975(3) Å (average = 1.971 Å), and are typical of those found in other copper acetate-containing coordination polymers [49]. A nitrogen donor from L1 occupies the apical position of the copper coordination sphere. The Cu–N bond length is 2.181(2) Å and is comparable to Cu–N bond lengths in many other pyridyl ligated copper systems [50–54]. The Cu–Cu distance in 1 is 2.6424(7) Å, which is well within the range of Cu–Cu distances reported for other copper carboxylate dimers having N -donor apical ligands [50–54]. However, this distance is slightly longer than the Cu–Cu distance reported for Cu(OAc)2 · H2 O (Cu– Cu = 2.6164 Å) where water ligands, rather than nitrogen donor ligands, occupy the apical ligand positions [55]. In the solid state, compound 1 adopts an infinite 1D linear chain motif, with pairs of copper dimers linked by bidentate L1 ligands. Despite the possibility of free rotation about the C–C single bond, the ligand adopts a “z” shape with a C3–C6–C6B angle of 112.5(3)◦ and the pyridyl rings lying in parallel planes. The shortest intrachain Cu–Cu separation between successive dimetal units is about 13.6 Å and the shortest interchain Cu–Cu separation is about 8.8 Å. When 1 is viewed along the c-axis, two sets of crystallographically identical chains become apparent. These two sets of chains appear to run approximately in the [−110] and [110] directions but are not strictly in the ab plane. There is approximately a 35◦ angle between the direction of propagation of the chains and the a-axis when the structure is viewed along the b-axis. The two sets of chains form

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Fig. 2. Orientation of the reciprocal lattices of the two twin components of 2. Reflections from domain 1 are shown in red; domain 2, blue. Completely overlapped reflections from both domains are shown in green.

Fig. 3. Chain fragment of 1 highlighting the copper coordination environment and atom labeling scheme. Displacement ellipsoids drawn at the 40% probability level.

two separate, alternating layers as shown in Fig. 4. Stacking of these layers along the crystallographic c-axis generates hexagonal shaped channels (Fig. 5); and the compound has a solvent accessible void volume of 28.5%. The channels contain disordered water molecules of crystallization, which may be involved in a hydrogen-bonding network with the coordination polymer chains. However, no attempt was made to specify this network because of the solvent disorder. 3.2. Compound 2 Reaction of 1,2-bis(4-pyridyl)ethane (L1 ) with Cu(OAc)2 · H2 O also afforded green crystals of 2 in addition to blue-green crystals of the channel-containing structure (1). In 2, both the ligand and the dimetal building unit are located on crystallographic inversion centers. As in 1, onedimensional chains of the coordination polymer 2 are constructed by alternation of the linear, bidentate ligand with the linear dimetal building unit, which utilizes its two linearly opposed Lewis acid sites to bind to two different ligands. A fragment of the linear coordination polymer chains of 2 is shown in Fig. 6. Chains of the coordination polymer are observed to zig-zag as they propagate due to the anti con-

formation of the ligand pyridyl groups relative to the ethane C–C bond. The C3–C6–C6B angle observed in 2 (112.4(6)◦ ) is the same as the corresponding angle in 1. The Cu2 (OAc)4 core in 2 is also the same as that found in 1, with Cu–O and Cu–N distances in the normal ranges (average Cu–O distance is 1.974 Å, Cu–N distance is 2.170(3) Å). The Cu–Cu distance in 2 is 2.6298(7) Å, a distance which is slightly shorter than the corresponding distance in 1 (2.6424 Å) but still slightly longer than the Cu–Cu distance in Cu(OAc)2 · H2 O (2.6264 Å). For 2, the shortest interchain Cu–Cu distance is 6.683 Å and the shortest intrachain Cu–Cu separation between successive dimetal units is 11.157 Å. Whereas solvent-containing channels are observed in compound 1, the crystal packing in 2 leaves no significant solvent accessible channels. Neglecting the presence of the solvent of crystallization in 1, compounds 1 and 2 may be considered polymorphs. 3.3. Compound 3 The reaction of 1,4-bis(4-pyridyl)buta-1,3-diyne (L2 ) with Cu(OAc)2 · H2 O yielded blue-green crystals of 3 and 4 as co-crystallizing products. X-ray crystallographic analysis

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Fig. 4. View of 1 along the crystallographic c-axis showing two adjacent layers of 1D chains. Copper atoms are shown as green spheres; C, yellow; O, red; N, blue.

Fig. 5. Space filling model of 1 projected along the c-axis and highlighting the solvent accessible hexagonal channels. Copper atoms are shown as green spheres; C, yellow; H, white; O, red; N, blue. Water guest molecules are omitted for clarity.

of 3 revealed for the compound an infinite one-dimensional linear chain motif, a fragment of which is shown in Fig. 8. In 3, all atoms except the acetate groups and part of one pyridyl ring (C11–C12 and those designated A, related by a mirror plane) reside on a crystallographic mirror plane. The asymmetric unit therefore consists of two Cu2+ , two

acetate ligands, and most of one L2 ligand. The Cu2 (OAc)4 cluster core is the same in 3 as it is in 1 and 2 with Cu– O bond lengths in the range 1.9642(15)–1.9826(15) Å in 3 (average = 1.974 Å), similar to those found for 1 and 2. The Cu–Cu distance in 3 is 2.5933(5) Å, which is slightly shorter than that found in 1, 2, and the Cu(OAc)2 · H2 O starting

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Fig. 6. Chain fragment of 2 highlighting the Cu2+ coordination environment and atom numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.

Fig. 7. [100] view of the crystal packing in 2. Copper atoms shown as green spheres; C, yellow; O, red; N, blue.

material. The two Cu–N distances in 3 are 2.146(2) Å and 2.174(2) Å (average = 2.160 Å) for Cu(1)–N(1) and Cu(2)– N(2) respectively, and are well within the reported range for pyridyl ligated copper systems. In the solid state, compound 3 adopts an infinite 1D linear chain motif, with pairs of copper dimers linked by bidentate L2 ligands, each of which has a 90◦ dihedral angle between its two pyridyl rings. When viewed along the crystallographic a-axis, the 1D chains appear to run parallel to

the c-axis in the [001] direction. When viewed along the baxis however, it is apparent that there is approximately an 80◦ angle between the c-axis and the direction of propagation of the chains. The crystal packing viewed along the crystallographic a-axis is shown in Fig. 9. The shortest intrachain Cu–Cu separation between successive dimetal units is about 16.5 Å and the shortest interchain Cu–Cu separation is about 6.4 Å. No significant solvent accessible channels are observed for 3.

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Fig. 8. Chain fragment of 3 highlighting the copper coordination environment and atom labeling scheme. Displacement ellipsoids drawn at the 50% probability level.

Fig. 9. [100] view of the crystal packing in 3. Copper atoms are shown as green spheres; C, yellow; O, red; N, blue.

3.4. Compound 4 The reaction of 1,4-bis(4-pyridyl)buta-1,3-diyne (L2 ) and Cu(OAc)2 · H2 O also yielded blue-green crystals of 4 in addition to crystals of 3. The X-ray crystallographic analysis of 4 revealed that the compound consists of infinite, linear 1D coordination polymer chains. A fragment of one such chain is shown in Fig. 10. As in 1, the asymmetric unit of 4 consists of one Cu2+ , two acetate groups, and one ligand; and the compound crystallizes in the same space group as 1 (monoclinic, C2/c). Compound 4 also contains disordered solvents of crystallization in hexagonal channels generated from the packing of the coordination polymer chains, and compounds 1 and 4 are therefore isostructural. The identity of the crystallization solvent could not conclusively be determined for 4 due to rapid solvent loss when the crystals are

removed from the mother liquor. The dinuclear Cu2 (OAc)4 cluster core of 4 is the same as that found in 1, 2, and 3, with Cu–O bond distances (1.962(2)–1.966(2) Å) in the typical range. The coordination environment about a single copper atom is the same as that found in 3, with an equatorial square plane of oxygen atoms from the µ2 -bridging acetate groups and an apical nitrogen donor belonging to L2 . The Cu–N distance of 2.178(2) Å and the Cu–Cu distance of 2.6193(2) Å are similar to the corresponding distances in 1, 2, and 3. In the solid state, compound 4 adopts an infinite, 1D linear chain motif with successive pairs of copper dimers linked by bidentate L2 ligands. Whereas the pyridyl rings of a single L2 are perpendicular to one another in 3, these rings are coplanar in 4. This conformational flexibility observed for L2 is surprising given its high degree of conjugation. For 4,

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Fig. 10. Chain fragment of 4 highlighting the copper coordination environment and atom labeling scheme. Displacement ellipsoids are drawn at the 50% probability level.

Fig. 11. View of 4 along the crystallographic c-axis showing two adjacent layers of 1D chains. Copper atoms are shown as green spheres; C, yellow; O, red; N, small, blue spheres. Variable occupancy oxygen atoms are shown as large blue spheres.

the shortest intrachain Cu–Cu separation between successive dimetal units is 16.5 Å and the shortest interchain Cu–Cu separation is 7.1 Å. Interestingly, compounds 1 and 4, although based on a different linker ligand, are isostructural. The hexagonal channels generated from the packing of the two sets of crystallographically identical chains (Fig. 11) provide a solvent accessible void volume of 34.3% in 4. This increase relative to 1 is a function of ligand length as indicated by the intrachain Cu–Cu separations.

While compounds 1 and 4 are isostructural, compounds 1 and 2 and compounds 3 and 4 are polymorphic neglecting the presence of solvents of crystallization in 1 and 4. It is well known that certain kinetic factors, such as crystallization conditions, concentration of reagents, and rate of reactant diffusion, can be adjusted to produce polymorphic coordination compounds [56,57]. In fact we have discussed the formation of supramolecular isomers in other systems, where slight differences in the reaction conditions can give rise to isomers that can be as different as molecular vs. poly-

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meric [58]. In the present case, preliminary studies indicate that the concentration of the reagents may be adjusted to produce the polymorphic compounds in different relative ratios, with the use of less concentrated solutions leading to a greater relative quantity of the denser structure (thermodynamic product) and the use of more concentrated solutions leading to a greater relative quantity of the channelcontaining structure (kinetic product).

polymers when linear bidentate ligands are employed. Furthermore, we have shown that the packing of the 1D coordination polymer chains can generate 3D channel-containing materials under the appropriate synthetic conditions. Ongoing studies suggest that the formation of “open”, channelcontaining structures rather than condensed structures may be related to certain kinetic factors, such as the concentration of the reagents employed in synthesis.

3.5. Thermal analyses Supplementary material 650 ◦ C

Upon heating compounds 1 and 2 to in a flowing He (65 cc/min) atmosphere, three successive weight loss intervals were observed. The first, occurring over the temperature interval from 30–160 ◦ C, corresponded to a weight loss of 5.4% and is attributed to the loss of the water solvent of crystallization from compound 1 (theoretical for 1, 6.2%). The observation that the solvent of crystallization is easily lost from compound 1 at low temperatures is consistent with the results of elemental analysis. Following the first weight loss, two consecutive weight losses, corresponding to decomposition of the coordination polymers, occur over the temperature region 160–540 ◦ C. At 540 ◦ C, 27.6% of the weight remains, consistent with the formation of two moles of CuO per mole of coordination polymer (theoretical for 1, 27.3%; theoretical for 2, 29.06%). The identity of the decomposition product as copper(II) oxide was confirmed by X-ray powder diffraction measurements. Thermal decomposition of 3 and 4 proceeded differently from the thermal decomposition of 1 and 2. For 3 and 4, only a single step weight loss, corresponding to decomposition of the coordination polymers, was observed when the compounds were heated under He (70 cc/min) to 1200 ◦ C. The observation of a single step weight loss is consistent with the results of the elemental analysis, which suggest that the solvent of crystallization is readily lost from crystals of 4. In fact, visual observation also suggests that the crystallization solvent is readily lost as crystals of 4 turn opaque immediately upon removal from the mother liquor. Decomposition of the polymers began at about 200 ◦ C and continued until a weight loss plateau was observed at about 1100 ◦ C and 28.16 weight percent. This is consistent with the formation of two moles CuO per mole of coordination polymer (theoretical for 3 and desolvated 4, 28.03%). 3.6. Conclusions Four coordination polymers constructed from N ,N
bidentate ligands and copper acetate dimetal units have been synthesized and structurally characterized. These four compounds are new examples of a rapidly growing number of coordination polymers generated from dimetal carboxylate building blocks. This study demonstrates that such building blocks, which have linearly opposed Lewis acid binding sites, are ideal for the formation of 1D chain coordination

CCDC 229559-61 and CCDC 259782 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge at http://www.ccdc.cam.ac.uk/ conts/retrieving.html [or from the Cambridge Crystallographic Data Centre (CCDC), 12 Union Road, Cambridge CB2 1EZ, U.K.; fax: +44(0)1223-336033; e-mail: deposit@ ccdc.cam.ac.uk].

Acknowledgements We gratefully acknowledge financial support from the South Carolina NSF/EPSCoR/BRIN program, award # R02-104, and the National Science Foundation, award CHE0314164. K.G. gratefully acknowledges support through the University of South Carolina NSF REU Program, CHE: 0139143.

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