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Copper halide clusters and polymers supported by bipodal heteroelemental ligands
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Polyhedron 27 (2008) 1463–1470 www.elsevier.com/locate/poly
Copper halide clusters and polymers supported by bipodal heteroelemental ligands Christian R. Samanamu´, Peter M. Lococo, William D. Woodul, Anne F. Richards * Department of Chemistry, Texas Christian University, Box 298860, Fort Worth, TX 76129, United States Received 30 August 2007; accepted 15 January 2008 Available online 4 March 2008
Abstract The flexible, multi dentate, heteroelemental, dipodal ligands; bis(2pyridylthio)methane, (PyS)2CH2 (Py = pyridyl = C5H4N), (PymS)2CH2, bis(2pyrimidylthio)methane, and bipyrimidyldisulfide, (PymS)2 (Pym = pyrimidine, C4H3N2), were reacted with a series of copper precursors to determine whether monomeric compounds, cubane clusters or polymeric chains would be obtained. Copper(II) chloride, copper(I) cyanide and copper(I) thiocyanate afforded infinite polymeric chains while copper(I) iodide afforded tetranuclear clusters supported by two ligand molecules. All products were characterized in the solid-state by X-ray crystallography. Ó 2008 Elsevier Ltd. All rights reserved. Keywords: Copper; X-ray crystallography; Dipodal flexible ligands
1. Introduction Heteroelemental donor ligands containing nitrogen and sulfur have found numerous useful properties in the coordination chemistry of copper and copper organic frameworks [1,2]. Previous research has found that the interaction of pyridyl nucleophiles with Cu(I) halides often afford tetranuclear cubane clusters, Cu4X4L4 (X = halide, L = ligand) clusters [3]. These clusters have shown promising photophysical properties attributed to Cu–Cu interactions [4,5]. Sulfur containing ligands that are derivatives of heterocyclic thiones, are of biological interest as the active site in copper ‘blue’ proteins involves sulfur/nitrogen coordination [6]. Furthermore, Cu(I) has shown diverse results with sulfur containing ligands, for example, Cu(I) can react with pyridine-2-thiolate (pyt) to form the hexanuclear complex [Cu6(lpyt)6] [7,8]. Given the potential in these areas, we were interested in using the heteroelemental dipodal ligands: (PyS)2CH2 (Py = pyridyl, C5H4N), (PymS)2CH2 and (PymS)2 (Pym = C4H3N2) to explore
*
Corresponding author. Tel.: +1 817 257 6220; fax: +1 817 257 5851. E-mail address: [email protected] (A.F. Richards).
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the outcome of reactions with copper precursors to determine whether these ligands would lead to the formation of cubane clusters, polymeric structures or monomeric compounds [1–3,8,9]. These ligands were purposefully selected because of their flexible nature and the presence of both sulfur and nitrogen donor atoms for metal center coordination. In free bis(pyridylthio)methane the two aromatic ligands are essentially planar and they adopt a transoid configuration that minimizes unfavourable electronic interactions between the lone pairs of the sulfur and nitrogens [10]. On coordination to metal centers the molecule is able to rotate, it is this rotation that allows the molecule to open up for bridged coordination or wrap around a metal center and use its multiple donor atoms for coordination. Fig. 1 depicts how these ligands have a plethora of coordination modes that can lead to multiple structural outcomes. We were particularly interested in using copper cyanide and thiocyanide precursors for cluster or framework syntheses. These ambidentate ligands behave as pseudo halides that can coordinate end on, or end-to-end. Unlike their halide counterparts they have been less utilized for creating infinite polymeric chains, but can afford frameworks that display varying degrees of interpenetration [11]. A further
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Fig. 1. Coordination modes of (PyS)2CH2, (PymS)2CH2 and (PymS)2.
Fig. 2. Products 1–5 from the reactions of (PyS)2CH2, (PymS)2CH2 and (PymS)2 with copper halides and pseudo halides.
advantage of these precursors is that they provide the opportunity for anion incorporation, which promotes the isolation of uncharged motifs that have accessible channels for possible small molecule adsorption. Traditionally, the synthesis of copper polymers has involved high temperature reactions as it was believed this was required to form metastable phases that would not be accessible at lower temperatures [2b,12]. For example, the reaction of CuSCN with 1,2,-bis(4pyridyl)bipyridylethane (bpa), to form the infinite polymer [Cu(SCN)2bpa]1, involves vacuum synthesis at 180 °C [11c]. On the other hand, slow diffusion or co-crystallization techniques have yielded polymeric chains, but usually in low yields [11a,13]. Instead of these typical methods, we wished to investigate synthetic routes that employ mild conditions and result in air stable products that can be isolated in moderate yields, thus allowing exploration of their further chemistry. Experimentally it was determined that reaction of the copper precursor and ligand in acetonitrile, followed by over night heating to 70–100 °C, afforded a series of copper complexes that vary structurally depending on the copper precursor selected.
Compounds 1–5, Fig. 2, were isolated at ambient conditions as thermally stable crystalline materials, in moderate to high yield. Here in we report the results of the investigation of (PyS)2CH2, (PymS)2CH2 and (PymS)2 with copper halides and pseudo halides. 2. Experimental The synthesis of (PyS)2CH2 [14] and (PymS)2CH2 [15] were performed according to the published procedure. (PymS)2 was prepared through modification of the literature procedure1.
1 2-Mercaptopyrimidine (1.68 g, 15 mmol) was added to a stirred solution of potassium hydroxide (0.84 g, 15 mmol) in ethanol (60 mL). The mixture was warmed to reflux and then bromoform (1.3 mL, 15 mmol) was added drop-wise. The resultant mixture was refluxed for 24 h. After adding water (90 mL), the mixture was left to stand overnight. The yellow precipitate was filtered off and washed with cold ethanol and cold water giving a brown solid that was recrystallized from hot ethanol and water (1.30 g).
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Table 1 Crystal data for all complexes Compound name
1
2
3
4
5
Chemical formula Formula weight Crystal system Space group T (K) ˚) a (A ˚) b (A ˚) c (A a (°) b (°) c (°) ˚ 3) V (A Z F(0 0 0) Reflections collected Independent reflections (Rint) Data/restraint/parameter R indices, all data
C9H8Cl2CuN4S2 370.75 monoclinic P2(1)/c 223(2) 10.5531(11) 11.7012(12) 12.3481(10) 90 118.280(6) 90 1342.8(2) 4 740 8333 3184 (0.0362) 3184/0/163 R1 = 0.0519, wR2 = 0.0808 R1 = 0.0328, wR2 = 0.0727 0.457 and 0.395
C12H10CuN3S2 323.89 orthorhombic P2(1)2(1)2(1) 223(2) 8.7016(11) 10.3863(13) 14.6171(19) 90 90 90 1321.1(3) 4 656 7776 3098 (0.0291) 3098/0/164 R1 = 0.0408, wR2 = 0.0640 R1 = 0.0292, wR2 = 0.0594 0.419 and 0.230
C22H20Cu4I4N4S4 1230.42 triclinic P 1 223(2) 8.9760(13) 9.2164(13) 10.4439(15) 70.630(2) 88.535(2) 76.640(2) 791.8(2) 1 572 4612 3498 (0.0162) 3498/0/172 R1 = 0.0396, wR2 = 0.0917 R1 = 0.0333, wR2 = 0.0868 1.703 and 1.310
C16H12Cu4I4N8S4 1206.34 monoclinic P2(1)/c 213(2) 10.6418(9) 10.8611(9) 13.5162(8) 90 113.183(5) 90 1436.08(19) 2 1112 7375 2578 (0.1782) 2578/0/163 R1 = 0.0728, wR2 = 0.1724 R1 = 0.0693, wR2 = 0.1678 3.169 and 3.700
C9H6CuN5S3 343.91 monoclinic P2(1)/c 223(2) 8.4826(7) 13.9955(12) 11.1165(9) 90 110.7400(10) 90 1234.21(18) 4 688 11 855 2226 (0.0276) 2226/0/163 R1 = 0.0302, wR2 = 0.0676 R1 = 0.0242, wR2 = 0.0623 0.501 and 0.350
Final R indices [I > 2r(I)] Largest difference peak and ˚ 3) hole (e A
All chemicals were purchased from Aldrich or Acros and used as received. Melting points were preformed on a Meltemp apparatus under ambient conditions. In a typical experiment, the ligand and copper salt in a 1:1 mol ratio were dissolved in acetonitrile and heated to between 80 and 90 °C for 12 h. Grease free Teflon sealed Schlenk flasks were employed to avoid grease contamination and to allow heating of a sealed system. All crystals were obtained from slow evaporation of the solution at room temperature. Crystal data were collected with a Bruker SMART 1000 diffractometer using graphite monochromated molybde˚ ). Crystals were attached to num radiation (k = 0.7107 A glass fibers using paratone oil and data were collected at 60 °C. The data were corrected for absorption. Structures were solved by direct methods using the SHELXS-97 [16,17] program and refined via full-matrix least squares [16,17]. Crystal data for all compounds are given in Table 1.
2.1. Synthesis of 1: [(PymS)2CH2Cu(lCl)Cl]1 In a grease free Schlenk flask, 5 mL of acetonitrile, CuCl2 2H2O (0.04 g, 0.23 mmol) and (PymS)2CH2 (0.05 g, 0.21 mmol) were added together. The reaction mixture was heated at 100 °C for 14 h. After 14 h, the green colored reaction mixture was gravity filtered to remove insoluble impurities. The solution was kept at room temperature for 2 days, during which time large, teal green crystals, suitable for single crystal analysis were isolated. M.Pt. decomposes at 150–152 °C, yield: 0.045 g (51% with respect to CuCl2 2H2O) IR (KBr pellet, t cm1): 2956.1 (s), 2923.8 (s), 2855.3 (s), 1614.9 (m), 1578.7 (m), 1461.9
(m), 1449.8 (m), 1386.0 (m), 1181.4 (m), 817.5 (m), UV– Vis (CH3CN): k max (nm) = 254, 311, 462. 2.2. Synthesis of 2: [(PyS)2CH2CuCN]1 In a grease free Schlenk flask, 5 mL of acetonitrile, CuCN (0.035 g, 0.391 mmol) and (PymS)2CH2 (0.1 g, 0.391 mmol) were mixed. The reaction mixture was stirred at 80–100 °C for 14 h. After cooling to room temperature the colorless solution was gravity filtered to remove insoluble particles. The solution was stored overnight at room temperature, yielding colorless single crystals of 2. M.Pt. 72–74 °C, yield: 0.049 g (39% with respect to CuCN), IR (KBr pellet, t cm1): 2361.0 (s), 1578.2 (s), 1554.7 (s), 1465.4 (m), 1455.1 (m), 1411.7 (m), 1337.3 (m), 1285.9 (m), 1214.1 (m), 1143.4 (m), 1123.5 (m), 1040.8 (m), 986.5 (m), 755.0 (m), 740.0 (m), 714.0 (m), 1H NMR (300 MHz, CD3CN, 25 °C): 5.01 (s, 2H), 7.13 (t, 2H), 7.26 (d, 2H), 7.62 (t, 2H), 8.49 (d, 2H). UV–Vis (CH3CN): k max (nm) = 250, 290. 2.3. Synthesis of 3: [(PyS)2CH2Cu2I2]2 CuI (0.1 g, 0.53 mmol) and (PyS)2CH2 (0.03 g, 0.12 mmol) were dissolved in 5 mL of acetonitrile. The solution was stirred for 14 h at 80–90 °C. Following filtration, storage of the solution at room temperature afforded pale yellow crystals of 3 suitable for X-ray diffraction. M.Pt. decomposes at 145–147 °C, yield: 0.30 g (45% with respect to CuI), IR (KBr pellet, t cm1): 2960.0 (s), 2927.8 (s), 2854.2 (m), 1449.8 (m), 1413.5 (m), 1373.3 (m), 1260.5 (m), 797.4 (s), 765.2 (s), 749.1 (m), 1H NMR
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(300 MHz, CD3CN, 25 °C): 5.02 (s, 2H), 7.14 (t, 2H), 7.28 (d, 2H), 7.63 (t, 2H), 8.49 (d, 2H). UV–Vis (CH3CN): k max (nm): 209, 245, 360. 2.4. Synthesis of 4: [(PymS)2Cu2I2]2 CuI (0.1 g, 0.52 mmol) and (PymS)2 (0.18 g, 0.52 mmol) were dissolved in 5 mL CH3CN and heated to 70–80 °C for 14 h. After filtration of the yellow solution and storage at room temperature for 5 days, suitable X-ray quality yellow crystals of compound 4 were isolated. M.Pt. 175–177 °C, yield: 0.34 g (50% with respect to CuI) IR (KBr pellet, t cm1): 2359.3 (s), 1640.2 (s), 1425.6 (m), 1376.0 (m), 1196.4 (m), 1167.2 (m), 822.6 (m), 804.9 (s), 774.1 (m), 766.9 (m), 744.4 (m), 629.0 (m), 448.5 (m), 1H NMR (300 MHz, CD3CN, 25 °C): 7.25 (t, 2H), 8.61 (d, 4H). UV–Vis (CH3CN): k max (nm) = 209, 242, 359. 2.5. Synthesis of 5: [(PymS)2CuSCN]1 5 mL of acetonitrile, CuSCN (0.04 g, 0.33 mmol) and (PymS)2 (0.1 g, 0.29 mmol) were added together in a grease free Schlenk flask. The reaction mixture was stirred for 14 h at 90–100 °C. The colorless solution was filtered to remove a cloudy precipitate. Slow evaporation of the colorless solution at room temperature afforded colorless crystals of 5. M.Pt. 112–115 °C, yield: 0.037 g (30% with respect to CuSCN), IR (KBr pellet, t cm1): 2110.1 (s), 2066.9 (s), 1550.9 (m), 1427.2 (m), 1375.6 (m), 1196.6 (m), 1169.4 (m), 817.6 (m), 767.1 (w), 743.6 (m), 629.1 (m), 1H NMR (300 MHz, CD3CN, 25 °C): 6.91 (t, 2H), 6.94 (t, 2H), 8.10 (d, H), 8.30 (d, 4H). UV–Vis (CH3CN): k max = 236 nm. 3. Results and discussion The reaction of (bispyrimidylthio)methane with CuCl2 afforded teal paramagnetic crystals of the complex [(PymS)2CH2CuCl2]1 as shown in Scheme 1. Experimentally it was determined that the choice of solvent is important. Attempts using tetrahydrofuran, benzonitrile, ethanol, water or toluene were all unsuccessful and no coordination of the ligand to the metal was observed. For all reactions acetonitrile was used as the solvent.
Scheme 1. Synthesis of [(PymS)2CH2Cu(lCl)Cl]n.
Fig. 3. Diagram of the asymmetric crystallographic unit and the polymeric structural motif. Thermal ellipsoids shown at 30% probability ˚) level, hydrogen atoms are omitted for clarity. Selected bond lengths (A and angles (°): Cu(1)–N(1) 2.049(2), Cl(1)–Cu(1)–N(1) 93.04(6), N(3)– Cu(1)–Cl(2) 88.11(7), Cl(1)–Cu(1)–Cl(1a) 85.97(3).
The overall structural motif can be described as twodimensional sheet with the interchain linkage provided by the organic ligand. The X-ray crystal structure of 1 is exhibited in Fig. 3. The geometry around each copper atom is five coordinate corresponding to distorted trigonal bypyrimidal geometry. The ligand bridges the copper centers. Every copper atom is coordinated to two nitrogen atoms, N(1) and N(3), from pyrimidine groups provided by two different ligand molecules. Making up the remaining two coordination sites on copper are chloride atoms, Cl(1) bridges two copper centers (l2) while the other remains terminal. The bond lengths of the chlorides vary only slightly, the ˚ comterminal chloride has a Cu–Cl distance of 2.2468(8) A ˚ pared to the bridged Cu–Cl distance of 2.2822(7) A. Compound 1 can be compared to a previously reported structure [CuCl2(l-dpds)] (dpds = dipyridyl disulfide) (A) [18], Fig. 4, that was isolated from the similar reaction of bis(2pyridylthio)methane with CuCl2.
Fig. 4. Structurally similar molecule to (1), from the reaction of CuCl2 with bptm [18].
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Comparison of the structures of [CuCl2(l-dpds)] with [(PymS)2CH2Cu(lCl)Cl]1 (1) reveals distinct differences that likely arise from the different experimental procedures. [CuCl2(l-dpds)] was formed from the slow diffusion of methanol solution of copper(II) chloride and the ligand. The main difference between the two structures is that in A the chloride atoms do not bridge, instead they retain their trans geometry yielding an infinite helical chain. The bridging halides in complex 1 help minimize the distance between the pyridyl layers, by constraining the geometry. ˚ (between corresponding The Pym–Pym distance is 3.697 A aromatic carbons), which is relatively short and so should allow p–p stacking, however the arrangement of the pyrimidyl rings are slightly twisted. Comparison of the bond lengths and angles between [CuCl2(l-dpds)] and 1 show good similarity, and are detailed in Table 2. Polymer 1 is soluble in common organic solvents and is relatively thermally stable, melting to a green liquid at 150– 152 °C. The UV–Vis spectrum of 1 showed broad adsorptions between 250 and 470 nm which are assigned as Cu– ligand charge transfer transitions. Luminescence measurements were attempted in acetonitrile at room temperature, but no meaningful data could be obtained. In an attempt to further develop polymeric networks, the reaction of (PyS)2CH2 with CuCN was performed, Scheme 2. CuCN has limited solubility in acetonitrile, but the reaction proceeds as a suspension, however the lower yield of the product (39%) is due to the lower solubility of the metal salt. Colorless crystals of 2 (Fig. 5) were isolated at room temperature and crystallize in the orthorhombic, chiral space group, P2(1)2(1)2(1). Solid-state X-ray analysis revealed the ambidentate CN ligand bridges each copper center and is coordinated to a nitrogen atom of the pyridyl group from bis(bipyridylthio)methane. This results in each copper center having two cyanide groups, giving rise to distorted trigonal planar geometry. The C–N distance of
Table 2 ˚ ) between complexes [CuCl2(l-dpds)] Comparison of the bond lengths (A [18] and (1)
Cu–N(1) Cu–N(2) for A, N(3) for 1 Cu–Cl(1) Cu–Cl(2)
[CuCl2 (l-dpds)] (A)
[(PymS)2CH2 Cu(lCl)Cl]1 (1)
2.047(3) 2.045(1)
2.049(2) 2.038(2)
2.2840(9) 2.261(1)
2.2822(7) 2.2468(8)
Scheme 2. Synthesis of 2, [(PyS)2CH2CuCN]1.
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Fig. 5. Crystallographic analysis of 2 [CuCN(PyS)2CH2]1. Ellipsoids are shown at 30% probability level with hydrogen atoms omitted for clarity. ˚ ) and angles (°) of 2: Cu(1)–N(2) 2.034(2), Cu(1)– Selected bond lengths (A C(12) 1.872(3), C(12)–N(3) 1.154(3), N(2)–Cu(1)–C(12) 120.93(10), N(3)– C(12)– Cu(1) 174.9(2), Cu(1)–Cu(1a) 4.933.
˚ is typical of the C–N bond in cyanide [11,19]. 1.154(3) A ˚ . Each Cu(I) The distance between Cu centers is 4.933 A atom has distorted trigonal planar geometry with angles of 125.43(10)°, 113.25(9)° and 120.93(10)°. Three coordinate distorted trigonal planar geometry is a characteristic of Cu(I) cyanide structures, for example in KCu(CN)2 [20]. The geometry around the Cu(1)–C(12)–N(3) ligand is close to linear, with an angle of 174.9(2). Infrared spectroscopy exhibited the distinctive CN stretch at 2361 cm1 that is within the range expected for a bridged CN ligand [11f,19,20]. Proton NMR on 2 showed the proton signals shifted downfield when compared with the free ligand [10]. This was observed in the spectra of complexes 2–5 suggesting that the structure is retained in solution when the crystalline material is redissolved. Bond lengths and angles of 2 show good agreement with other Py–CuCN complexes, for example [(CuCN)2[CuCN]2(l-4-40 bipy)] has a Cu–CN bond length of ˚ and a Cu–N(Py) bond length of 2.069(2) A ˚ 1.862(3) A [21]. Within the polymeric network of 2 the distance between the aromatic layers (i.e. from C(1)–C(1a) or ˚ [22]. S(1)–S(1a)) is 8.702 A Having successfully isolated polymeric chains from copper(II) chloride and copper(I) cyanide, we wished to extend the series and examine if polymeric chains would be isolated using copper(I) iodide. Using similar reaction conditions as were used for the formation of 1 and 2 (PyS)2CH2 and (PymS)2 were reacted with CuI (Scheme 3). Complexes 3 and 4 show structural similarity, both feature the Cu4I4 core which can be described as a ‘ladder type’ arrangement that is well documented common for copper halides [3]. The four copper atoms and four iodine atoms form parallelograms, with Cu–Cu distances of ˚ and 2.862 A ˚ between the two copper atoms in 3 2.849 A ˚ in 4. This can be compared with and 3.038 and 2.657 A ˚ and the the Cu–Cu distance in metallic copper of 2.556 A ˚ Van der Waals radius of copper at 2.80 A [23] and is a typical value for discrete Cu–I ladder structures [24]. Complex 3 is analogous to the Cu(I) bromide compound isolated by
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Scheme 3. Reactions of copper(I) iodide with (PyS)2CH2 and (PymS)2.
Garcı´a-Martı´nez and co-workers [10] from the reaction of (PyS)2CH2 with Cu(I)Br, however, unlike their copper cluster, complex 3 was the major reaction product and was isolated in 67% yield. Complex 3 crystallizes as yellow triclinic crystals (Fig. 6) space group P 1, while complex 4 crystallizes as yellow monoclinic crystals, space group, P21/c (Fig. 7). Single crystal X-ray analysis of complex 3 reveals that two different bonding arrangements occur around the copper centers, but both adopt distorted tetrahedral geometries. Cu(1) is coordinated to the pyridyl nitrogen (N1) and two bridging iodides, I(1) and I(2). The second copper center, Cu(2), has coordination to a pyridyl nitrogen atom N(2), a sulfur atom from the ligand, S(1) and two bridging iodides, I(1) and I(2). Thus, the ligand bridges two copper centers. The iodide atoms bridge the copper atoms in l3 and l2 modes. The two copper centers have distorted tetrahedral geometry with angles ranging from 102.43(2)° to 118.11(11)° for Cu(1) and 100.48(12)° to 116.68(4)° around Cu(2). The Cu–I bridges are found to be slightly asymmet˚ , Cu(1)–Cu(I2A) = 2.6776(8) A ˚, ric, Cu(1)–I(1) = 2.7257 A but this is not uncommon for bridged halides and can be compared to [Cu4(L1)2I4] (L1 = bis(6-methyl-2 pyridyl methyl sulfide)) that has bond lengths of 2.586(1)– ˚ for the bridged iodides, a Cu–N distance of 2.652(1) A ˚ ˚ [25,26]. 2.031(3) A and a Cu–S distance of 2.570(1) A
Fig. 6. Crystal structure of complex 3, thermal ellipsoids at 30% probability level, hydrogen atoms are omitted for clarity. Key bond ˚ ) and angles (°): Cu(1)–I(1) 2.7257(7), Cu(1)–I(2) 2.6776(8), lengths (A Cu(2)–N(2) 2.079(4), Cu(2)–I(2) 2.5693(8), Cu(1)–N(1) 2.071(4), Cu(2)– S(1) 2.3010(14), N(1)–Cu(1)–I(2) 107.67(11), N(1)–Cu(1)–I(1) 104.82(11), I(1)–Cu(1)–I(2a) 106.91(2), S(1)–Cu(2)–I(2) 116.68(4), N(2)–Cu(2)–I(1a) 100.48(12).
Fig. 7. X-ray crystal structure of [(PymS)2Cu2I2]2, complex 4, thermal ellipsoids at 30% probability level. Hydrogen atoms are omitted for ˚ ) and angles (°): Cu(1)–N(1) 2.053(7), Cu(2)– clarity. Key bond lengths (A N(3a) 2.061(7), Cu(1)–S(2) 2.421(2), Cu(1)–I(1) 2.5612(11), N(1)–Cu(1)– I(2) 114.1(2), I(1)–Cu(1)–S(2) 106.20(6), N(1)–Cu(1)–Cu(2) 172.1(2), N(1)–Cu(1)–S(2) 85.97(19).
Unlike the analogous bromide compound, complex 3 has no hydrogen bonding existing between the CH2 group and the iodides [10]. This is possibly due to the lower electronegativity of the iodine versus bromine, and the larger size between the atoms, therefore a polymeric chain of clusters does not form. Solution luminescent measurements in acetonitrile were performed on 3 and 4 but no luminescence was recorded, it is possible that low temperature solid-state measurements are required. PymS–SPym was prepared serendipitously in high yield from the attempted synthesis of (PymS)3CH. Despite this not being the desired product, it could be reproducibly prepared in high yield1. The reaction of (PymS)2 with CuI (Scheme 3) afforded monoclinic yellow crystals of compound 4 in high yield, Fig. 7. The solid-state analysis reveals a dimeric structure that features a tetrameric core of copper atoms. Each ligand chelates one copper atom through S(1) and N(1) atoms and coordinates to another Cu(2) through another nitrogen atom, thus bridging between the two. An average ˚ [26], the Cu– Cu–S bond is reported to be around 2.67 A ˚ S distance of 2.421(2) A is significantly shorter than this distance, and is attributed to the steric constraints of the ligand. It is noteworthy to mention that complex 4 appears to be thermally robust in the solid-state and in solution, however, attempts to use the similar system, PyS–SPy, for framework synthesis resulted in cleavage of the S–C aromatic bond and formation of elemental sulfur. To continue the series the reaction of CuCN with (PymS)2 was performed, however no crystalline product could be isolated. Exchange of copper cyanide for copper
Scheme 4. Synthesis of 5 from the reaction of (PymS)2 with CuSCN.
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4. Conclusion We have shown that copper(II) chloride, copper(I) iodide and copper pseudo halides can be used in conjunction with flexible heteroelemental organic linkers to form polymers that can incorporate the anion into the framework. This type of preparation is a versatile useful approach for construction of neutral polymeric frameworks that offer potential for further reactions and framework growth, because of the availability of uncoordinated donor atoms present. Future work will explore the further chemistry of these polymers and will focus on expanding the chemistry of the dipodal ligands for further polymeric materials. Acknowledgement The Welch Foundation (Grant Number P0176) TCURCAF and TCU-SERC are thanked for financial support. Appendix A. Supplementary material
Fig. 8. Crystal structure of [(PymS)2CuSCN]1 (5) asymmetric unit and polymeric network. Thermal ellipsoids at 30% probability and hydrogen ˚ ) and angles (°): atoms are omitted for clarity. Selected bond lengths (A Cu(1)–N(3) 2.1580(19), Cu(1)–S(3) 2.3957(7), Cu(1)–N(2) 2.036(2), Cu(1)– N(5) 1.918(2), S(1)–C(1) 1.785(2), S(3)–C(9) 1.656(3), N(2)–Cu(1)–S(3) 96.95(6), N(5)–Cu(1)–S(3) 115.80(7), N(2)–Cu(1)–N(3) 105.77(8).
CCDC 647083, 647084, 647085, 647086 and 647087 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via http:// www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033, or email: [email protected]. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.poly.2008.01.005. References
thiocyanate, afforded colorless crystals of an infinite twodimensional polymeric material 5, Scheme 4 and Fig. 8. Use of copper(I) thiocyanate has not been well explored for use in metal organic framework construction, in part because of its limited solubility in organic solvents [11]. We were drawn to this precursor, given our success with copper cyanide, and because this copper salt exists as polymeric [Cu(SCN)]1 [27]. Polymer 5 crystallizes in the monoclinic space group P21/c and the X-ray analysis shows that each copper is tetrahedrally coordinated to two nitrogen atoms from two different ligands, sulfur and nitrogen atoms from the thiocyanate group. Complex 5 forms a two-dimensional network. The geometry around the thiocyanate group is nearly linear, with the S–C„N angle of 178.3(2)°, and a ˚ . The bond lengths and angles Cu–Cu separation of 5.559 A in 5 compare well with that of [Cu(SCN)(pyz)]1, that has ˚ and 1.940(4) A ˚, Cu–S and Cu–N bonds of 2.349(2) A respectively [11g]. Infrared spectroscopy of polymer 5 exhibited CN stretches at 2110.1 and 2066.9 cm1 and at 767.1 cm1, associated with the S–C stretch and these values compare well with other reported polymeric structures [11].
[1] (a) For selected examples see: P.C. Healy, C. Pakawatchai, R.I. Papasergio, V.A. Patrick, A.H. White, Inorg. Chem. 23 (1984) 3769; (b) S. Hong, Y. Zou, D. Moon, M.S. Lah, Chem. Commun. (2007) 1707; (c) B. Lucchese, K.J. Humphreys, D.H. Lee, C.D. Incarnto, R.D. Sommer, A.L. Rheingold, K.D. Karlin, Inorg. Chem. 43 (2004) 5987; (d) R. Kappoor, A. Katanna, P. Venugpalan, P. Kappor, M. Corbella, M. Rodrigues, I. Romero, A. Klobert, Inorg. Chem. 43 (2004) 6699; (e) For the use of sulfur containing ligands see:S. Oae, Organic Sulfur Chemistry: Structure and Mechanism, CRC Press, Boca Raton, 1991; (f) S. Oae, T. Okuyama (Eds.), Organic Sulfur Chemistry: Biological Aspects, CRC Press, Boca Raton, 1992. [2] (a) For selected examples see: L. Hou, W.-J. Shi, Y.-G. Yin, S.W. Ng, Inorg. Chem. 44 (2005) 7825; (b) D.J. Chesnut, A. Kusnetzow, R.R. Birge, J. Zubieta, Inorg. Chem. 38 (1999) 2663; (c) S.L. James, Coord. Chem. Rev. 32 (2003) 276, and references therein; (d) J.A. Cabeza, A. Llamazares, V. Riera, R. Trivedi, Organometallics 17 (1998) 550; (e) A. Paulo, A. Domingos, I. Santos, J. Chem. Soc., Dalton Trans. (1999) 3735; (f) L. Dahlenburg, M. Ku¨hnlein, Eur. J. Inorg. Chem. (2000) 2117. [3] (a) Selected Examples include: C.L. Raston, A.H. White, J. Chem. Soc., Dalton. (1976) 2153;
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Polyhedron 27 (2008) 1463–1470 www.elsevier.com/locate/poly
Copper halide clusters and polymers supported by bipodal heteroelemental ligands Christian R. Samanamu´, Peter M. Lococo, William D. Woodul, Anne F. Richards * Department of Chemistry, Texas Christian University, Box 298860, Fort Worth, TX 76129, United States Received 30 August 2007; accepted 15 January 2008 Available online 4 March 2008
Abstract The flexible, multi dentate, heteroelemental, dipodal ligands; bis(2pyridylthio)methane, (PyS)2CH2 (Py = pyridyl = C5H4N), (PymS)2CH2, bis(2pyrimidylthio)methane, and bipyrimidyldisulfide, (PymS)2 (Pym = pyrimidine, C4H3N2), were reacted with a series of copper precursors to determine whether monomeric compounds, cubane clusters or polymeric chains would be obtained. Copper(II) chloride, copper(I) cyanide and copper(I) thiocyanate afforded infinite polymeric chains while copper(I) iodide afforded tetranuclear clusters supported by two ligand molecules. All products were characterized in the solid-state by X-ray crystallography. Ó 2008 Elsevier Ltd. All rights reserved. Keywords: Copper; X-ray crystallography; Dipodal flexible ligands
1. Introduction Heteroelemental donor ligands containing nitrogen and sulfur have found numerous useful properties in the coordination chemistry of copper and copper organic frameworks [1,2]. Previous research has found that the interaction of pyridyl nucleophiles with Cu(I) halides often afford tetranuclear cubane clusters, Cu4X4L4 (X = halide, L = ligand) clusters [3]. These clusters have shown promising photophysical properties attributed to Cu–Cu interactions [4,5]. Sulfur containing ligands that are derivatives of heterocyclic thiones, are of biological interest as the active site in copper ‘blue’ proteins involves sulfur/nitrogen coordination [6]. Furthermore, Cu(I) has shown diverse results with sulfur containing ligands, for example, Cu(I) can react with pyridine-2-thiolate (pyt) to form the hexanuclear complex [Cu6(lpyt)6] [7,8]. Given the potential in these areas, we were interested in using the heteroelemental dipodal ligands: (PyS)2CH2 (Py = pyridyl, C5H4N), (PymS)2CH2 and (PymS)2 (Pym = C4H3N2) to explore
*
Corresponding author. Tel.: +1 817 257 6220; fax: +1 817 257 5851. E-mail address: [email protected] (A.F. Richards).
0277-5387/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2008.01.005
the outcome of reactions with copper precursors to determine whether these ligands would lead to the formation of cubane clusters, polymeric structures or monomeric compounds [1–3,8,9]. These ligands were purposefully selected because of their flexible nature and the presence of both sulfur and nitrogen donor atoms for metal center coordination. In free bis(pyridylthio)methane the two aromatic ligands are essentially planar and they adopt a transoid configuration that minimizes unfavourable electronic interactions between the lone pairs of the sulfur and nitrogens [10]. On coordination to metal centers the molecule is able to rotate, it is this rotation that allows the molecule to open up for bridged coordination or wrap around a metal center and use its multiple donor atoms for coordination. Fig. 1 depicts how these ligands have a plethora of coordination modes that can lead to multiple structural outcomes. We were particularly interested in using copper cyanide and thiocyanide precursors for cluster or framework syntheses. These ambidentate ligands behave as pseudo halides that can coordinate end on, or end-to-end. Unlike their halide counterparts they have been less utilized for creating infinite polymeric chains, but can afford frameworks that display varying degrees of interpenetration [11]. A further
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Fig. 1. Coordination modes of (PyS)2CH2, (PymS)2CH2 and (PymS)2.
Fig. 2. Products 1–5 from the reactions of (PyS)2CH2, (PymS)2CH2 and (PymS)2 with copper halides and pseudo halides.
advantage of these precursors is that they provide the opportunity for anion incorporation, which promotes the isolation of uncharged motifs that have accessible channels for possible small molecule adsorption. Traditionally, the synthesis of copper polymers has involved high temperature reactions as it was believed this was required to form metastable phases that would not be accessible at lower temperatures [2b,12]. For example, the reaction of CuSCN with 1,2,-bis(4pyridyl)bipyridylethane (bpa), to form the infinite polymer [Cu(SCN)2bpa]1, involves vacuum synthesis at 180 °C [11c]. On the other hand, slow diffusion or co-crystallization techniques have yielded polymeric chains, but usually in low yields [11a,13]. Instead of these typical methods, we wished to investigate synthetic routes that employ mild conditions and result in air stable products that can be isolated in moderate yields, thus allowing exploration of their further chemistry. Experimentally it was determined that reaction of the copper precursor and ligand in acetonitrile, followed by over night heating to 70–100 °C, afforded a series of copper complexes that vary structurally depending on the copper precursor selected.
Compounds 1–5, Fig. 2, were isolated at ambient conditions as thermally stable crystalline materials, in moderate to high yield. Here in we report the results of the investigation of (PyS)2CH2, (PymS)2CH2 and (PymS)2 with copper halides and pseudo halides. 2. Experimental The synthesis of (PyS)2CH2 [14] and (PymS)2CH2 [15] were performed according to the published procedure. (PymS)2 was prepared through modification of the literature procedure1.
1 2-Mercaptopyrimidine (1.68 g, 15 mmol) was added to a stirred solution of potassium hydroxide (0.84 g, 15 mmol) in ethanol (60 mL). The mixture was warmed to reflux and then bromoform (1.3 mL, 15 mmol) was added drop-wise. The resultant mixture was refluxed for 24 h. After adding water (90 mL), the mixture was left to stand overnight. The yellow precipitate was filtered off and washed with cold ethanol and cold water giving a brown solid that was recrystallized from hot ethanol and water (1.30 g).
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Table 1 Crystal data for all complexes Compound name
1
2
3
4
5
Chemical formula Formula weight Crystal system Space group T (K) ˚) a (A ˚) b (A ˚) c (A a (°) b (°) c (°) ˚ 3) V (A Z F(0 0 0) Reflections collected Independent reflections (Rint) Data/restraint/parameter R indices, all data
C9H8Cl2CuN4S2 370.75 monoclinic P2(1)/c 223(2) 10.5531(11) 11.7012(12) 12.3481(10) 90 118.280(6) 90 1342.8(2) 4 740 8333 3184 (0.0362) 3184/0/163 R1 = 0.0519, wR2 = 0.0808 R1 = 0.0328, wR2 = 0.0727 0.457 and 0.395
C12H10CuN3S2 323.89 orthorhombic P2(1)2(1)2(1) 223(2) 8.7016(11) 10.3863(13) 14.6171(19) 90 90 90 1321.1(3) 4 656 7776 3098 (0.0291) 3098/0/164 R1 = 0.0408, wR2 = 0.0640 R1 = 0.0292, wR2 = 0.0594 0.419 and 0.230
C22H20Cu4I4N4S4 1230.42 triclinic P 1 223(2) 8.9760(13) 9.2164(13) 10.4439(15) 70.630(2) 88.535(2) 76.640(2) 791.8(2) 1 572 4612 3498 (0.0162) 3498/0/172 R1 = 0.0396, wR2 = 0.0917 R1 = 0.0333, wR2 = 0.0868 1.703 and 1.310
C16H12Cu4I4N8S4 1206.34 monoclinic P2(1)/c 213(2) 10.6418(9) 10.8611(9) 13.5162(8) 90 113.183(5) 90 1436.08(19) 2 1112 7375 2578 (0.1782) 2578/0/163 R1 = 0.0728, wR2 = 0.1724 R1 = 0.0693, wR2 = 0.1678 3.169 and 3.700
C9H6CuN5S3 343.91 monoclinic P2(1)/c 223(2) 8.4826(7) 13.9955(12) 11.1165(9) 90 110.7400(10) 90 1234.21(18) 4 688 11 855 2226 (0.0276) 2226/0/163 R1 = 0.0302, wR2 = 0.0676 R1 = 0.0242, wR2 = 0.0623 0.501 and 0.350
Final R indices [I > 2r(I)] Largest difference peak and ˚ 3) hole (e A
All chemicals were purchased from Aldrich or Acros and used as received. Melting points were preformed on a Meltemp apparatus under ambient conditions. In a typical experiment, the ligand and copper salt in a 1:1 mol ratio were dissolved in acetonitrile and heated to between 80 and 90 °C for 12 h. Grease free Teflon sealed Schlenk flasks were employed to avoid grease contamination and to allow heating of a sealed system. All crystals were obtained from slow evaporation of the solution at room temperature. Crystal data were collected with a Bruker SMART 1000 diffractometer using graphite monochromated molybde˚ ). Crystals were attached to num radiation (k = 0.7107 A glass fibers using paratone oil and data were collected at 60 °C. The data were corrected for absorption. Structures were solved by direct methods using the SHELXS-97 [16,17] program and refined via full-matrix least squares [16,17]. Crystal data for all compounds are given in Table 1.
2.1. Synthesis of 1: [(PymS)2CH2Cu(lCl)Cl]1 In a grease free Schlenk flask, 5 mL of acetonitrile, CuCl2 2H2O (0.04 g, 0.23 mmol) and (PymS)2CH2 (0.05 g, 0.21 mmol) were added together. The reaction mixture was heated at 100 °C for 14 h. After 14 h, the green colored reaction mixture was gravity filtered to remove insoluble impurities. The solution was kept at room temperature for 2 days, during which time large, teal green crystals, suitable for single crystal analysis were isolated. M.Pt. decomposes at 150–152 °C, yield: 0.045 g (51% with respect to CuCl2 2H2O) IR (KBr pellet, t cm1): 2956.1 (s), 2923.8 (s), 2855.3 (s), 1614.9 (m), 1578.7 (m), 1461.9
(m), 1449.8 (m), 1386.0 (m), 1181.4 (m), 817.5 (m), UV– Vis (CH3CN): k max (nm) = 254, 311, 462. 2.2. Synthesis of 2: [(PyS)2CH2CuCN]1 In a grease free Schlenk flask, 5 mL of acetonitrile, CuCN (0.035 g, 0.391 mmol) and (PymS)2CH2 (0.1 g, 0.391 mmol) were mixed. The reaction mixture was stirred at 80–100 °C for 14 h. After cooling to room temperature the colorless solution was gravity filtered to remove insoluble particles. The solution was stored overnight at room temperature, yielding colorless single crystals of 2. M.Pt. 72–74 °C, yield: 0.049 g (39% with respect to CuCN), IR (KBr pellet, t cm1): 2361.0 (s), 1578.2 (s), 1554.7 (s), 1465.4 (m), 1455.1 (m), 1411.7 (m), 1337.3 (m), 1285.9 (m), 1214.1 (m), 1143.4 (m), 1123.5 (m), 1040.8 (m), 986.5 (m), 755.0 (m), 740.0 (m), 714.0 (m), 1H NMR (300 MHz, CD3CN, 25 °C): 5.01 (s, 2H), 7.13 (t, 2H), 7.26 (d, 2H), 7.62 (t, 2H), 8.49 (d, 2H). UV–Vis (CH3CN): k max (nm) = 250, 290. 2.3. Synthesis of 3: [(PyS)2CH2Cu2I2]2 CuI (0.1 g, 0.53 mmol) and (PyS)2CH2 (0.03 g, 0.12 mmol) were dissolved in 5 mL of acetonitrile. The solution was stirred for 14 h at 80–90 °C. Following filtration, storage of the solution at room temperature afforded pale yellow crystals of 3 suitable for X-ray diffraction. M.Pt. decomposes at 145–147 °C, yield: 0.30 g (45% with respect to CuI), IR (KBr pellet, t cm1): 2960.0 (s), 2927.8 (s), 2854.2 (m), 1449.8 (m), 1413.5 (m), 1373.3 (m), 1260.5 (m), 797.4 (s), 765.2 (s), 749.1 (m), 1H NMR
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(300 MHz, CD3CN, 25 °C): 5.02 (s, 2H), 7.14 (t, 2H), 7.28 (d, 2H), 7.63 (t, 2H), 8.49 (d, 2H). UV–Vis (CH3CN): k max (nm): 209, 245, 360. 2.4. Synthesis of 4: [(PymS)2Cu2I2]2 CuI (0.1 g, 0.52 mmol) and (PymS)2 (0.18 g, 0.52 mmol) were dissolved in 5 mL CH3CN and heated to 70–80 °C for 14 h. After filtration of the yellow solution and storage at room temperature for 5 days, suitable X-ray quality yellow crystals of compound 4 were isolated. M.Pt. 175–177 °C, yield: 0.34 g (50% with respect to CuI) IR (KBr pellet, t cm1): 2359.3 (s), 1640.2 (s), 1425.6 (m), 1376.0 (m), 1196.4 (m), 1167.2 (m), 822.6 (m), 804.9 (s), 774.1 (m), 766.9 (m), 744.4 (m), 629.0 (m), 448.5 (m), 1H NMR (300 MHz, CD3CN, 25 °C): 7.25 (t, 2H), 8.61 (d, 4H). UV–Vis (CH3CN): k max (nm) = 209, 242, 359. 2.5. Synthesis of 5: [(PymS)2CuSCN]1 5 mL of acetonitrile, CuSCN (0.04 g, 0.33 mmol) and (PymS)2 (0.1 g, 0.29 mmol) were added together in a grease free Schlenk flask. The reaction mixture was stirred for 14 h at 90–100 °C. The colorless solution was filtered to remove a cloudy precipitate. Slow evaporation of the colorless solution at room temperature afforded colorless crystals of 5. M.Pt. 112–115 °C, yield: 0.037 g (30% with respect to CuSCN), IR (KBr pellet, t cm1): 2110.1 (s), 2066.9 (s), 1550.9 (m), 1427.2 (m), 1375.6 (m), 1196.6 (m), 1169.4 (m), 817.6 (m), 767.1 (w), 743.6 (m), 629.1 (m), 1H NMR (300 MHz, CD3CN, 25 °C): 6.91 (t, 2H), 6.94 (t, 2H), 8.10 (d, H), 8.30 (d, 4H). UV–Vis (CH3CN): k max = 236 nm. 3. Results and discussion The reaction of (bispyrimidylthio)methane with CuCl2 afforded teal paramagnetic crystals of the complex [(PymS)2CH2CuCl2]1 as shown in Scheme 1. Experimentally it was determined that the choice of solvent is important. Attempts using tetrahydrofuran, benzonitrile, ethanol, water or toluene were all unsuccessful and no coordination of the ligand to the metal was observed. For all reactions acetonitrile was used as the solvent.
Scheme 1. Synthesis of [(PymS)2CH2Cu(lCl)Cl]n.
Fig. 3. Diagram of the asymmetric crystallographic unit and the polymeric structural motif. Thermal ellipsoids shown at 30% probability ˚) level, hydrogen atoms are omitted for clarity. Selected bond lengths (A and angles (°): Cu(1)–N(1) 2.049(2), Cl(1)–Cu(1)–N(1) 93.04(6), N(3)– Cu(1)–Cl(2) 88.11(7), Cl(1)–Cu(1)–Cl(1a) 85.97(3).
The overall structural motif can be described as twodimensional sheet with the interchain linkage provided by the organic ligand. The X-ray crystal structure of 1 is exhibited in Fig. 3. The geometry around each copper atom is five coordinate corresponding to distorted trigonal bypyrimidal geometry. The ligand bridges the copper centers. Every copper atom is coordinated to two nitrogen atoms, N(1) and N(3), from pyrimidine groups provided by two different ligand molecules. Making up the remaining two coordination sites on copper are chloride atoms, Cl(1) bridges two copper centers (l2) while the other remains terminal. The bond lengths of the chlorides vary only slightly, the ˚ comterminal chloride has a Cu–Cl distance of 2.2468(8) A ˚ pared to the bridged Cu–Cl distance of 2.2822(7) A. Compound 1 can be compared to a previously reported structure [CuCl2(l-dpds)] (dpds = dipyridyl disulfide) (A) [18], Fig. 4, that was isolated from the similar reaction of bis(2pyridylthio)methane with CuCl2.
Fig. 4. Structurally similar molecule to (1), from the reaction of CuCl2 with bptm [18].
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Comparison of the structures of [CuCl2(l-dpds)] with [(PymS)2CH2Cu(lCl)Cl]1 (1) reveals distinct differences that likely arise from the different experimental procedures. [CuCl2(l-dpds)] was formed from the slow diffusion of methanol solution of copper(II) chloride and the ligand. The main difference between the two structures is that in A the chloride atoms do not bridge, instead they retain their trans geometry yielding an infinite helical chain. The bridging halides in complex 1 help minimize the distance between the pyridyl layers, by constraining the geometry. ˚ (between corresponding The Pym–Pym distance is 3.697 A aromatic carbons), which is relatively short and so should allow p–p stacking, however the arrangement of the pyrimidyl rings are slightly twisted. Comparison of the bond lengths and angles between [CuCl2(l-dpds)] and 1 show good similarity, and are detailed in Table 2. Polymer 1 is soluble in common organic solvents and is relatively thermally stable, melting to a green liquid at 150– 152 °C. The UV–Vis spectrum of 1 showed broad adsorptions between 250 and 470 nm which are assigned as Cu– ligand charge transfer transitions. Luminescence measurements were attempted in acetonitrile at room temperature, but no meaningful data could be obtained. In an attempt to further develop polymeric networks, the reaction of (PyS)2CH2 with CuCN was performed, Scheme 2. CuCN has limited solubility in acetonitrile, but the reaction proceeds as a suspension, however the lower yield of the product (39%) is due to the lower solubility of the metal salt. Colorless crystals of 2 (Fig. 5) were isolated at room temperature and crystallize in the orthorhombic, chiral space group, P2(1)2(1)2(1). Solid-state X-ray analysis revealed the ambidentate CN ligand bridges each copper center and is coordinated to a nitrogen atom of the pyridyl group from bis(bipyridylthio)methane. This results in each copper center having two cyanide groups, giving rise to distorted trigonal planar geometry. The C–N distance of
Table 2 ˚ ) between complexes [CuCl2(l-dpds)] Comparison of the bond lengths (A [18] and (1)
Cu–N(1) Cu–N(2) for A, N(3) for 1 Cu–Cl(1) Cu–Cl(2)
[CuCl2 (l-dpds)] (A)
[(PymS)2CH2 Cu(lCl)Cl]1 (1)
2.047(3) 2.045(1)
2.049(2) 2.038(2)
2.2840(9) 2.261(1)
2.2822(7) 2.2468(8)
Scheme 2. Synthesis of 2, [(PyS)2CH2CuCN]1.
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Fig. 5. Crystallographic analysis of 2 [CuCN(PyS)2CH2]1. Ellipsoids are shown at 30% probability level with hydrogen atoms omitted for clarity. ˚ ) and angles (°) of 2: Cu(1)–N(2) 2.034(2), Cu(1)– Selected bond lengths (A C(12) 1.872(3), C(12)–N(3) 1.154(3), N(2)–Cu(1)–C(12) 120.93(10), N(3)– C(12)– Cu(1) 174.9(2), Cu(1)–Cu(1a) 4.933.
˚ is typical of the C–N bond in cyanide [11,19]. 1.154(3) A ˚ . Each Cu(I) The distance between Cu centers is 4.933 A atom has distorted trigonal planar geometry with angles of 125.43(10)°, 113.25(9)° and 120.93(10)°. Three coordinate distorted trigonal planar geometry is a characteristic of Cu(I) cyanide structures, for example in KCu(CN)2 [20]. The geometry around the Cu(1)–C(12)–N(3) ligand is close to linear, with an angle of 174.9(2). Infrared spectroscopy exhibited the distinctive CN stretch at 2361 cm1 that is within the range expected for a bridged CN ligand [11f,19,20]. Proton NMR on 2 showed the proton signals shifted downfield when compared with the free ligand [10]. This was observed in the spectra of complexes 2–5 suggesting that the structure is retained in solution when the crystalline material is redissolved. Bond lengths and angles of 2 show good agreement with other Py–CuCN complexes, for example [(CuCN)2[CuCN]2(l-4-40 bipy)] has a Cu–CN bond length of ˚ and a Cu–N(Py) bond length of 2.069(2) A ˚ 1.862(3) A [21]. Within the polymeric network of 2 the distance between the aromatic layers (i.e. from C(1)–C(1a) or ˚ [22]. S(1)–S(1a)) is 8.702 A Having successfully isolated polymeric chains from copper(II) chloride and copper(I) cyanide, we wished to extend the series and examine if polymeric chains would be isolated using copper(I) iodide. Using similar reaction conditions as were used for the formation of 1 and 2 (PyS)2CH2 and (PymS)2 were reacted with CuI (Scheme 3). Complexes 3 and 4 show structural similarity, both feature the Cu4I4 core which can be described as a ‘ladder type’ arrangement that is well documented common for copper halides [3]. The four copper atoms and four iodine atoms form parallelograms, with Cu–Cu distances of ˚ and 2.862 A ˚ between the two copper atoms in 3 2.849 A ˚ in 4. This can be compared with and 3.038 and 2.657 A ˚ and the the Cu–Cu distance in metallic copper of 2.556 A ˚ Van der Waals radius of copper at 2.80 A [23] and is a typical value for discrete Cu–I ladder structures [24]. Complex 3 is analogous to the Cu(I) bromide compound isolated by
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Scheme 3. Reactions of copper(I) iodide with (PyS)2CH2 and (PymS)2.
Garcı´a-Martı´nez and co-workers [10] from the reaction of (PyS)2CH2 with Cu(I)Br, however, unlike their copper cluster, complex 3 was the major reaction product and was isolated in 67% yield. Complex 3 crystallizes as yellow triclinic crystals (Fig. 6) space group P 1, while complex 4 crystallizes as yellow monoclinic crystals, space group, P21/c (Fig. 7). Single crystal X-ray analysis of complex 3 reveals that two different bonding arrangements occur around the copper centers, but both adopt distorted tetrahedral geometries. Cu(1) is coordinated to the pyridyl nitrogen (N1) and two bridging iodides, I(1) and I(2). The second copper center, Cu(2), has coordination to a pyridyl nitrogen atom N(2), a sulfur atom from the ligand, S(1) and two bridging iodides, I(1) and I(2). Thus, the ligand bridges two copper centers. The iodide atoms bridge the copper atoms in l3 and l2 modes. The two copper centers have distorted tetrahedral geometry with angles ranging from 102.43(2)° to 118.11(11)° for Cu(1) and 100.48(12)° to 116.68(4)° around Cu(2). The Cu–I bridges are found to be slightly asymmet˚ , Cu(1)–Cu(I2A) = 2.6776(8) A ˚, ric, Cu(1)–I(1) = 2.7257 A but this is not uncommon for bridged halides and can be compared to [Cu4(L1)2I4] (L1 = bis(6-methyl-2 pyridyl methyl sulfide)) that has bond lengths of 2.586(1)– ˚ for the bridged iodides, a Cu–N distance of 2.652(1) A ˚ ˚ [25,26]. 2.031(3) A and a Cu–S distance of 2.570(1) A
Fig. 6. Crystal structure of complex 3, thermal ellipsoids at 30% probability level, hydrogen atoms are omitted for clarity. Key bond ˚ ) and angles (°): Cu(1)–I(1) 2.7257(7), Cu(1)–I(2) 2.6776(8), lengths (A Cu(2)–N(2) 2.079(4), Cu(2)–I(2) 2.5693(8), Cu(1)–N(1) 2.071(4), Cu(2)– S(1) 2.3010(14), N(1)–Cu(1)–I(2) 107.67(11), N(1)–Cu(1)–I(1) 104.82(11), I(1)–Cu(1)–I(2a) 106.91(2), S(1)–Cu(2)–I(2) 116.68(4), N(2)–Cu(2)–I(1a) 100.48(12).
Fig. 7. X-ray crystal structure of [(PymS)2Cu2I2]2, complex 4, thermal ellipsoids at 30% probability level. Hydrogen atoms are omitted for ˚ ) and angles (°): Cu(1)–N(1) 2.053(7), Cu(2)– clarity. Key bond lengths (A N(3a) 2.061(7), Cu(1)–S(2) 2.421(2), Cu(1)–I(1) 2.5612(11), N(1)–Cu(1)– I(2) 114.1(2), I(1)–Cu(1)–S(2) 106.20(6), N(1)–Cu(1)–Cu(2) 172.1(2), N(1)–Cu(1)–S(2) 85.97(19).
Unlike the analogous bromide compound, complex 3 has no hydrogen bonding existing between the CH2 group and the iodides [10]. This is possibly due to the lower electronegativity of the iodine versus bromine, and the larger size between the atoms, therefore a polymeric chain of clusters does not form. Solution luminescent measurements in acetonitrile were performed on 3 and 4 but no luminescence was recorded, it is possible that low temperature solid-state measurements are required. PymS–SPym was prepared serendipitously in high yield from the attempted synthesis of (PymS)3CH. Despite this not being the desired product, it could be reproducibly prepared in high yield1. The reaction of (PymS)2 with CuI (Scheme 3) afforded monoclinic yellow crystals of compound 4 in high yield, Fig. 7. The solid-state analysis reveals a dimeric structure that features a tetrameric core of copper atoms. Each ligand chelates one copper atom through S(1) and N(1) atoms and coordinates to another Cu(2) through another nitrogen atom, thus bridging between the two. An average ˚ [26], the Cu– Cu–S bond is reported to be around 2.67 A ˚ S distance of 2.421(2) A is significantly shorter than this distance, and is attributed to the steric constraints of the ligand. It is noteworthy to mention that complex 4 appears to be thermally robust in the solid-state and in solution, however, attempts to use the similar system, PyS–SPy, for framework synthesis resulted in cleavage of the S–C aromatic bond and formation of elemental sulfur. To continue the series the reaction of CuCN with (PymS)2 was performed, however no crystalline product could be isolated. Exchange of copper cyanide for copper
Scheme 4. Synthesis of 5 from the reaction of (PymS)2 with CuSCN.
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4. Conclusion We have shown that copper(II) chloride, copper(I) iodide and copper pseudo halides can be used in conjunction with flexible heteroelemental organic linkers to form polymers that can incorporate the anion into the framework. This type of preparation is a versatile useful approach for construction of neutral polymeric frameworks that offer potential for further reactions and framework growth, because of the availability of uncoordinated donor atoms present. Future work will explore the further chemistry of these polymers and will focus on expanding the chemistry of the dipodal ligands for further polymeric materials. Acknowledgement The Welch Foundation (Grant Number P0176) TCURCAF and TCU-SERC are thanked for financial support. Appendix A. Supplementary material
Fig. 8. Crystal structure of [(PymS)2CuSCN]1 (5) asymmetric unit and polymeric network. Thermal ellipsoids at 30% probability and hydrogen ˚ ) and angles (°): atoms are omitted for clarity. Selected bond lengths (A Cu(1)–N(3) 2.1580(19), Cu(1)–S(3) 2.3957(7), Cu(1)–N(2) 2.036(2), Cu(1)– N(5) 1.918(2), S(1)–C(1) 1.785(2), S(3)–C(9) 1.656(3), N(2)–Cu(1)–S(3) 96.95(6), N(5)–Cu(1)–S(3) 115.80(7), N(2)–Cu(1)–N(3) 105.77(8).
CCDC 647083, 647084, 647085, 647086 and 647087 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via http:// www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033, or email: [email protected]. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.poly.2008.01.005. References
thiocyanate, afforded colorless crystals of an infinite twodimensional polymeric material 5, Scheme 4 and Fig. 8. Use of copper(I) thiocyanate has not been well explored for use in metal organic framework construction, in part because of its limited solubility in organic solvents [11]. We were drawn to this precursor, given our success with copper cyanide, and because this copper salt exists as polymeric [Cu(SCN)]1 [27]. Polymer 5 crystallizes in the monoclinic space group P21/c and the X-ray analysis shows that each copper is tetrahedrally coordinated to two nitrogen atoms from two different ligands, sulfur and nitrogen atoms from the thiocyanate group. Complex 5 forms a two-dimensional network. The geometry around the thiocyanate group is nearly linear, with the S–C„N angle of 178.3(2)°, and a ˚ . The bond lengths and angles Cu–Cu separation of 5.559 A in 5 compare well with that of [Cu(SCN)(pyz)]1, that has ˚ and 1.940(4) A ˚, Cu–S and Cu–N bonds of 2.349(2) A respectively [11g]. Infrared spectroscopy of polymer 5 exhibited CN stretches at 2110.1 and 2066.9 cm1 and at 767.1 cm1, associated with the S–C stretch and these values compare well with other reported polymeric structures [11].
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