Two-Dimensional and Three-Dimensional Coordination Polymers of

Article pubs.acs.org/crystal

Two-Dimensional and Three-Dimensional Coordination Polymers of Hexakis(4-cyanophenyl)[3]radialene: The Role of Stoichiometry and Kinetics Courtney A. Hollis,† Stuart R. Batten,‡ and Christopher J. Sumby*,† †

School of Chemistry & Physics, The University of Adelaide, Adelaide, South Australia 5005, Australia School of Chemistry, Monash University, Clayton, Victoria 3800, Australia

‡

S Supporting Information *

ABSTRACT: Hexakis(4-cyanophenyl)[3]radialene (1) is a hexadentate ligand that has previously been shown to form isomorphous honeycomb two-dimensional (2-D) coordination polymers {[Ag(1)](X)·2(CH3NO2)}n (X = ClO4, 2a; X = PF6, 2b) upon reaction with AgClO4 and AgPF6. Within these coordination polymers, close contacts were observed between the anions and the electron-deficient [3]radialene core. Here the synthesis and characterization of four new coordination polymers of 1 and copper(I), {[Cu2(1)2](X)2·Y(CH3NO2)}n (X = BF4, Y = 20, 4a; X = PF6, Y = 14, 4b) and {[Cu(1)](X)·2(CH3NO2)}n (X = BF4, 5a; X = PF6, 5b), are reported, along with two further examples of the (6,3) network {[Ag(1)](X)·2(CH3NO2)}n (X = BF4, 2c; X = SbF6, 2d), and an 8-fold interpenetrated (10,3)-b net formed from 1 and AgClO4, {[Ag3(1)](ClO4)3·CH3NO2}n (3). Coordination polymers 2a−2d were synthesized using low ratios of ligand to metal, 1:1 to 1:3, whereas other examples described herein (compounds 3, 4, and 5) were obtained via the use of a considerably higher ligand-to-metal salt ratio, in the range of 1:6 to 1:18. Reaction of 1 with [Cu(CH3CN)4]BF4 and [Cu(CH3CN)4]PF6 gave isostructural coordination polymers. In each experiment, a three-dimensional (3-D) network with a (4.62)(42.6)(43.66.86) topology (4a and 4b) formed first, while a honeycomb two-dimensional (2-D) coordination polymer, with a fully cross-linked bilayer (5a and 5b) crystallized second. Unlike the case for the Ag(I) coordination polymers, the rate of crystallization rather than the stoichiometry of the reactions dictated the structure of the final product for the Cu(I) compounds. The presence of radialene−anion interactions within these coordination polymers is also discussed, with anion-π interactions being observed to be of lesser significance relative to weak C− H···anion hydrogen bonding.

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INTRODUCTION

many coordination polymers, predominantly containing silver(I) and copper(I) due to the soft neutral nitrile donors, have been reported.6−12 In contrast, the coordination chemistry of nonaromatic cross-conjugated polynitrile ligands has received limited attention.13 [3]Radialenes are cyclic cross-conjugated molecules characterized by a propane ring core and three exocyclic double bonds.14,15 Functionalized hexaaryl and hexa-heteroaryl derivatives of the parent [3]radialene (Figure 1a) make attractive

Coordination polymers are infinite one-, two-, and threedimensional (1-, 2-, and 3-D) networks composed of metal ion (nodes) and organic ligands (linkers).1−4 Access to a virtually endless structural diversity for such materials can be achieved by employing varying metal salt and linker combinations. These components can also imbue the framework with useful properties such as magnetism, conduction, and porosity.2−5 The multitopic organic bridging ligands used to form coordination polymers can contain a range of Lewis basic donors; these are commonly N-heterocyclic, carboxylate, and nitrile donors.1 The coordination chemistry of linearly conjugated polynitrile ligands has been widely studied, and © XXXX American Chemical Society

Received: January 7, 2013 Revised: April 27, 2013

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dx.doi.org/10.1021/cg400036x | Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design

Article

coordination polymers.17 Hexa(4-pyridyl)[3]radialene has also been observed to act as a 4-connecting bridging ligand in a 3-D coordination polymer with AgClO4,18 while two isomorphous (6,3) networks were obtained upon reaction of hexakis(4cyanophenyl)[3]radialene (1) (Figure 1c) with AgClO4 (2a) and AgPF6 (2b) (Scheme 1).13 In both of these materials, 1 acts as a 3-connecting tetradentate ligand. The dianion of hexacyano[3]radialene has also been observed to form a range of 1-D and 2-D coordination polymers with various transition metals including manganese(II), iron(II), and cobalt(II).19,20 Within these structures, the ligand is hypodentate, exhibiting bidentate or tridentate coordination. Within the 2-D coordination polymers 2a and 2b, close contacts have been observed between the anions and the [3]radialene core.13 This was posited to be due to the electron deficiency of 1, which undergoes two stepwise reductions to form the dianion.15 A recent computational and mass spectroscopic study of nitrile functionalized hexaaryl[3]radialenes has shown that they possess properties conducive to the formation of anion-π interactions, namely, a large negative quadropole moment and regions of positive electrostatic potential.21 Short contacts, indicative of anion-π interactions, involving hexaaryl[3]radialenes were first observed in the M6L2 cage of hexa(2-pyridyl)[3]radialene, which exhibits

Figure 1. The structures of (a) the parent [3]radialene; (b) hexa(2pyridyl)[3]radialene (X = N, Y = CH) and hexa(4-pyridyl) [3]radialene (X = CH, Y = N); and (c) hexakis(4-cyanophenyl) [3]radialene (1).

ligands for use in coordination polymers due to their propellerlike 3-D structures, interesting optical properties, and potential to display a variety of coordination modes. For example, three modes of coordination with silver(I) have been observed for hexa(2-pyridyl)[3]radialene (Figure 1b); hexadentate in a discrete M6L2 cage,16 and pentadentate or tetradentate in 1-D

Scheme 1. Synthesis, Coordination Mode, and Formulae for the Coordination Polymers Reported

B



Article

Table 1. Crystal Data and X-ray Experimental Data for 1·4(CH3NO2), 2c, 2d, and 3 compound

1·4(CH3NO2)

2c

2d

3

empirical formula formula weight radiation source crystal system space group a (Å) b (Å) c (Å) α (°) β (°) γ (°) volume (Å3) Z Dcalc (Mg/m3) absorption coefficient (mm−1) F(000) crystal size (mm3) theta range for data (°) reflections collected independent reflections [R(int)] completeness to theta full (%) observed reflections [I > 2σ(I)] data/restraints/parameters goodness-of-fit on F2 R1 [I > 2σ(I)] wR2 (all data) largest diff peak and hole (e Å−3)

C52H36N10O8 928.91 Mo Kα monoclinic P21/c 9.4964(11) 19.218(2) 26.352(3) 90 98.503(6) 90 4756.4(10) 4 1.297 0.091 1928 0.50 × 0.37 × 0.22 1.32−28.89 88392 12409 [0.0357] 99.8 9184 12409/0/662 1.048 0.0813 0.2580 1.77 and −1.21

C50H30N8O4Ag1B1F4 1001.50 Mo Kα triclinic P1̅ 9.3749(6) 15.3886(11) 17.2299(11) 112.269(7) 98.944(5) 102.439(6) 2167.6(2) 2 1.534 0.540 1012 0.30 × 0.16 × 0.09 2.65−29.35 48646 10494 [0.0604] 99.5 7506 10494/3/665 1.041 0.0660 0.1944 1.39 and −0.80

C50H30N8O4Ag1Sb1F6 1150.44 Synchrotron triclinic P1̅ 9.6360(19) 15.622(3) 17.308(3) 110.70(3) 101.45(3) 103.66(3) 2251.5(7) 2 1.697 1.117 1140 0.25 × 0.13 × 0.05 1.32−29.10 35950 10215 [0.0498] 91.7 7930 10215/10/705 1.067 0.0652 0.2090 1.32 and −1.59

C49H27N7O14Ag3Cl3 1367.76 Synchrotron orthorhombic Pnna 28.799(6) 30.905(6) 15.631(3) 90 90 90 13912(5) 8 1.306 1.006 5392 0.10 × 0.03 × 0.01 1.46−24.19 150585 11121 [0.0937] 99.5 7088 11121/0/515 1.287 0.1107 0.3522 1.53 and −0.91

Table 2. Crystal Data and X-ray Experimental Data for 4a, 5a, 4b, and 5b compound

4a

4b

5a

5b

empirical formula formula weight radiation source crystal system space group a (Å) b (Å) c (Å) α (°) β (°) γ (°) volume (Å3) Z Dcalc (Mg/m3) absorption coefficient (mm−1) F(000) crystal size (mm3) theta range for data (°) reflections collected independent reflections [R(int)] completeness to theta full (%) observed reflections [I > 2σ(I)] data/restraints/parameters goodness-of-fit on F2 R1 [I > 2σ(I)] wR2 (all data) largest diff peak and hole (e Å−3)

C116H108N32O40Cu2B2F8 2891.04 Synchrotron orthorhombic Pbca 23.470(5) 22.051(4) 52.645(10) 90 90 90 27246(9) 8 1.410 0.414 11904 1.8 × 1.4 × 1.2 1.16−25.00 310511 23961 [0.0644] 99.8 20159 23961/0/1131 1.021 0.0765 0.2338 0.85 and −0.85

C110H90N26O28Cu2P2F12 2641.10 Synchrotron orthorhombic Pbca 23.653(5) 23.737(4) 51.930(10) 90 90 90 29156(10) 8 1.203 0.399 10816 1.6 × 1.3 × 1.1 1.16−28.86 174567 25220 [0.1581] 96.2 13060 25220/3/901 1.086 0.1336 0.3590 1.09 and −1.18

C50H30N8O4Cu1B1F4 957.17 Synchrotron triclinic P1̅ 9.6110(19) 14.831(3) 16.740(3) 74.76(3) 75.04(3) 81.55(3) 2216.2(8) 2 1.434 0.566 976 0.42 × 0.25 × 0.20 1.30−27.83 67800 10293 [0.0652] 99.2 9118 10293/1/681 1.050 0.0738 0.1909 1.11 and −1.84

C50H30N8O4Cu1P1F6 1015.33 Synchrotron triclinic P1̅ 9.776(2) 15.018(3) 16.673(3) 74.51(3) 76.80(3) 78.27(3) 2270.0(8) 2 1.485 0.597 1032 0.40 × 0.22 × 0.18 1.29−28.89 77974 11750 [0.0411] 99.4 10609 11750/3/652 1.038 0.0495 0.1311 1.04 and −1.18

a very close contact (2.67 Å) between the core and a fluoride anion.16 However, in that case, the fluoride anion is trapped

within a positively charged cage and coordinated by three of the six silver(I) atoms, so the short anion-π contact is supported by C



Article

Synthesis of Coordination Polymers. {[Ag(1)](BF 4 )·2(CH3NO2)}n (2c). A solution of 1 (5.0 mg, 0.0073 mmol) in CH3NO2 (2 mL) was combined in a vial with a solution of AgBF4 (1.4 mg, 0.0073 mmol) in CH3NO2 (0.5 mL). Slow evaporation of the solvent led to precipitation of 2c as bright red, diamond-shaped crystals (2.0 mg, 27%) that were suitable for X-ray crystallography. Analysis calcd for 2c: C48H24N6Ag1B1F4·1.5CH3NO2 C 61.22, H 2.96, N 10.82; found C 61.19, H 2.87, N 10.64; FT-IR υmax/cm−1: 2228 (CN str., vs), 1048 (B−F str., vs, b). Carrying out the reaction with a 1:AgBF4 ratio in the range from 1:1 to 1:3 gave the same product. Additional Refinement Details for 2c. There is disorder of the tetrafluoroborate anion, the silver(I) metal atom, and one nitromethane solvate molecule. All are refined with different occupancies over two major positions. Four restraints were used to maintain chemically sensible bond lengths in the tetrafluoroborate anion. {[Ag(1)](SbF6)·2(CH3NO2)}n (2d). A solution of 1 (5.0 mg, 0.0073 mmol) in CH3NO2 (2 mL) was combined in a vial with a solution of AgSbF6 (2.4 mg, 0.0073 mmol) in CH3NO2 (0.5 mL). Precipitation occurred immediately, and the precipitate was redissolved via addition of CH3CN (2 drops). Slow evaporation of the solvent led to precipitation of 2d as bright red, diamond-shaped crystals (3.2 mg, 38%) that were suitable for X-ray crystallography. Analysis calcd for 2d: C48H24N6Ag1Sb1F6·1.5CH3NO2 C 53.09, H 2.57, N 9.38; found C 53.01, H 2.37, N 9.34; FT-IR υmax/cm−1: 2226 (CN str., vs), 654 (Sb−F str., vs). Carrying out the reaction with a 1:AgSbF6 ratio in the range from 1:1 to 1:3 gave the same product. Additional Refinement Details for 2d. There is disorder of the hexafluoroantimonate anion and the silver metal atom. Both are modeled over two major positions. Four restraints were used to maintain chemically sensible bond lengths in the nitromethane solvate molecules and ISOR commands (six restraints) were used to allow two atoms of a nitromethane solvate molecule to be refined anisotropically. {[Ag3(1)](ClO4)3·CH3NO2}n (3). A solution of 1 (5.0 mg, 0.0073 mmol) in CH3NO2 (3 mL) was combined in a vial with a solution of AgClO4 (15 mg, 0.073 mmol) in CH3NO2 (0.5 mL). Precipitation occurred immediately and the precipitate was removed via filtration. Slow evaporation of the remaining mixture, over approximately one month, led to precipitation of 3 as very small, dark red, rod-shaped crystals (trace quantities) suitable for X-ray crystallography. Analysis calcd for initial precipitate C48H24N6Cl3O12Ag3 C 44.12, H 1.85, N 6.43; found C 43.97, H 2.50, N 5.78; FT-IR υmax/cm−1 of initial precipitate: 2247 (CN str. vs), 1599, 1498, 1406, 1277, 1059 (Cl−O str. vs, b), 1018, 928, 838, 767; FT-IR υmax/cm−1 of 3: 2257 (CN str. vs), 1651, 1604, 1501, 1406, 1279, 1052 (Cl−O str. vs, b), 1019, 927, 842, 757. Additional Refinement Details for 3. The structure has large, solvent-accessible voids. These contained a number of diffuse electron density peaks that could not be adequately identified and refined as solvent. The SQUEEZE routine of PLATON31 was applied to the collected data, which resulted in significant reductions in R1 and wR2 and an improvement in the GOF. R1, wR2, and GOF before SQUEEZE routine: 23.5%, 64.3%, and 3.18; after SQUEEZE routine: 11.1%, 35.2%, and 1.29. The contents of the solvent region calculated from the result of SQUEEZE routine (3 ClO4− and 1 CH3NO2 per asymmetric unit) are represented in the unit cell contents in crystal data. {[Cu2(1)2](BF4)2·20(CH3NO2)}n (4a) and {[Cu(1)](BF4)·2(CH3NO2)}n (5a). A solution of 1 (5.0 mg, 0.0073 mmol) in CH3NO2 (3 mL) was combined in a vial with a solution of [Cu(CH3CN)4]BF4 (41.4 mg, 0.131 mmol) also in CH3NO2 (0.5 mL). Precipitation occurred immediately and the precipitate was redissolved via addition of CH3CN (2 drops). Slow evaporation of the solvent led to precipitation of 4a first as bright red, octahedral crystals (trace quantities) that were solvent dependent, and 5a second as bright orange block-shaped crystals (2.9 mg, 41%) that were air stable. Crystals suitable for X-ray crystallography were obtained for both products. Carrying out the reaction with a 1:[Cu(CH3CN)4]BF4 ratio in the range from 1:6 to 1:18 gave the same two products. 4a (5.6 mg, 53%) can be recovered as the sole product by seeding a 1:6 1:[Cu(CH3CN)4]BF4 ratio CH3NO2 solution with crystals of 4a. However, seeding of an identical

other bonding constraints. Likewise, the anion-π interactions seen in polymers 2a and 2b may be due to crystal packing effects, and furthermore, these anion-π interactions are always supported by anion-hydrogen bonding interactions with the phenyl protons.13 Thus, the relative significance of these weak interactions is yet to be fully determined, and additional examples of coordination polymers containing 1 may provide further insight. To date hexaaryl[3]radialenes have only been shown to form coordination complexes with silver(I). This may be due to the versatility of silver(I) and its multiple coordination geometries, which include linear, T-shaped, tetrahedral, and octahedral.22−25 This contribution outlines the synthesis and characterization of four coordination polymers of 1 and copper(I): two 3-D networks with the formulas {[Cu2(1)2](X)2·Y(CH3NO2)}n (X = BF4, Y = 20, 4a; X = PF6, Y = 14, 4b) and two honeycomb 2-D coordination polymers with a fully cross-linked bilayer, {[Cu(1)](X)·2(CH3NO2)}n (X = BF4, 5a; X = PF6, 5b), as well as two further examples of the (6,3) 2-D net {[Ag(1)](X)·2(CH3NO2)}n (X = BF4, 2c; X = SbF6, 2d), and an interesting 8-fold interpenetrated (10,3)-b net formed from 1 and AgClO4, {[Ag3(1)](ClO4)3·CH3NO2}n (3). Where possible, radialene-anion interactions within these structures are discussed.

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EXPERIMENTAL SECTION

General Procedures. Infrared spectra were recorded using a Perkin-Elmer Spectrum 100 FT-IR spectrometer with universal attenuated total reflectance (ATR) sampling accessory. The Campbell microanalytical laboratory at the University of Otago performed elemental analyses. Unless otherwise stated, reagents were obtained from commercial sources and used as received. Compound 1 was prepared as previously described.26 X-ray Crystallography. Crystals were mounted under oil on a nylon loop, and X-ray diffraction data were collected with Mo Kα radiation (λ = 0.71073 Å) using an Oxford Diffraction X-Calibur diffractometer fitted with an Eos CCD detector, a Bruker-AXS single crystal diffraction system fitted with an Apex II CCD detector, or with synchrotron radiation (λ = 0.7107 Å) using the Macromolecular Crystallography beamline (MX1) at the Australian Synchrotron (see Tables 1 and 2).27 Crystals of 4a and 4b were extremely sensitive to solvent loss, and manipulation or removal from solvent rapidly led to loss of crystallinity. Thus, large crystals were used, as noted in Table 2 and 3, but the data collection was only conducted on a small portion of the crystal. The nominal beam size at the sample (horizontal × vertical) on MX1 is 130 × 90 μm. The data sets were corrected for absorption, and the structures were solved by direct methods using SHELXS-9728 and refined by full-matrix least-squares on F2 by SHELXL-97,29 interfaced through the program X-Seed.30 In general, all non-hydrogen atoms were refined anisotropically, and hydrogen atoms were included as invariants at geometrically estimated positions. CCDC 915960−915967 contain the supplementary crystallographic data for these structures. This data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac. uk/data_request/cif. Tables 1 and 2 provide crystal data and X-ray experimental data for all structures. Crystals of Hexakis(4-cyanophenyl)[3]radialene·4(CH3NO2) (1·4(CH3NO2)). A solution of 1 (5.0 mg, 0.0073 mmol) in CH3NO2 (2 mL) was allowed to evaporate for approximately one week to yield 1·4(CH3NO2) as diamond-shaped, orange crystals (2.9 mg, 43%) that were suitable for X-ray crystallography. Analysis calcd for 1·4(CH3NO2): C48H24N6.CH3NO2 C 78.90, H 3.66, N 13.15; found, C 79.45, H 3.50, N 12.97%; FT-IR υmax/cm−1: 2224 (CN str., vs), 1598 (CC, str., vs), 1556 and 1379 (N−O, str.). Additional Refinement Details for 1·4(CH3NO2). There is disorder of one of the nitromethane solvent molecules, and this was modeled over two major positions (0:65:0:35). D



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solution with 5a leads to equal formation of both products. Analysis calcd for 4a: C48H24N6BF4Cu C 69.04, H 2.90, N 10.06; found C 65.19, H 2.93, N 9.56; FT-IR υmax/cm−1: 2247 (CN str., vs), 2225 (CN str., vs), 1052 (B−F str., vs, b). 1H NMR (300 MHz, CD3CN) digestion of 4a: δ 4.31 (s, 30H, CH3NO2), 6.92 (d, 12H, [J = 9.0 Hz], H3 and H5), 7.25 (d, 12H, [J = 9.0 Hz], H2 and H6). Additional Refinement Details for 4a. The structure has large, solvent-accessible voids. These contained a number of diffuse electron density peaks that could not be adequately identified and refined as solvent. The SQUEEZE routine of PLATON31 was applied to the collected data, which resulted in significant reductions in R1 and wR2 and an improvement in the GOF. R1, wR2, and GOF before SQUEEZE routine: 30.3%, 69.2%, and 3.78; after SQUEEZE routine: 7.7%, 23.4%, and 1.02. The contents of the solvent region calculated from the result of SQUEEZE routine (20 CH3NO2 per asymmetric unit) are represented in the unit cell contents in crystal data. This was corroborated by NMR spectroscopy. Analysis calcd for 5a: C48H24N6BF4Cu C 69.04, H 2.90, N 10.06; found C 59.48, H 2.96, N 10.40; FT-IR υmax/cm−1: 2246 (CN str., vs), 2223 (CN str., vs), 1052 (B−F str., vs, b). Additional Refinement Details for 5a. There is disorder of the tetrafluoroborate anion and one of the nitromethane solvent molecules. Both are modeled over two major positions. One restraint was used to maintain a chemically sensible bond length for one N−O bond in the nitromethane molecule. {[Cu2(1)2](PF6)2·14(CH3NO2)}n (4b) and {[Cu(1)](PF6)·2(CH3NO2)}n (5b). A solution of 1 (5.0 mg, 0.0073 mmol) in CH3NO2 (3 mL) was combined in a vial with a solution of [Cu(CH3CN)4]PF6 (16.3 mg, 0.044 mmol) in CH3NO2 (0.5 mL). Precipitation occurred immediately and the precipitate was redissolved via addition of CH3CN (2 drops). Slow evaporation of the solvent led to precipitation of 4b first as bright red, octahedral crystals (trace quantities) that were solvent dependent, and 5b second as bright orange block-shaped crystals (3.0 mg, 40%) that were air stable. Crystals suitable for X-ray crystallography were obtained for both products. Carrying out the reaction with a 1:[Cu(CH3CN)4]PF6 ratio in the range from 1:6 to 1:18 gave the same two products. 4b (5.1 mg, 53%) can be recovered as the sole product via seeding of a 1:6 1:[Cu(CH3CN)4]PF6 ratio CH3NO2 solution. However, seeding of an identical solution with 5b leads to equal formation of both products. Analysis calcd for 4b: C48H24N6PF6Cu C 64.54, H 2.71, N 9.41; found C 55.09, H 2.88, N 9.72; FT-IR υmax/cm−1: 2248 (CN str., vs), 2224 (CN str., vs), 829 (P−F str., vs). 1H NMR (300 MHz, CD3CN) digestion of 4b: δ 4.31 (s, 21H, CH3NO2), 6.92 (d, 12H, [J = 9.0 Hz], H3 and H5), 7.25 (d, 12H, [J = 9.0 Hz], H2 and H6). Additional Refinement Details for 4b. The structure has large, solvent-accessible voids. These contained a number of diffuse electron density peaks that could not be adequately identified and refined as solvent. The SQUEEZE routine of PLATON31 was applied to the collected data, which resulted in significant reductions in R1 and wR2 and an improvement in the GOF. R1, wR2, and GOF before SQUEEZE routine: 37.9%, 74.2%, and 3.16; after SQUEEZE routine: 13.3%, 35.8%, and 1.08. The contents of the solvent region calculated from the result of the SQUEEZE routine (2 PF6− and 32 CH3NO2 per asymmetric unit) did not correspond with the crystal solvent content determined via 1H NMR digestion (14 CH3NO2 per asymmetric unit). In this case, the 1H NMR digestion value is represented in the unit cell contents of the crystal data as it correlates better with that of the isomorphous structure 4a. Three restraints were used to maintain chemically sensible bond lengths within radialene core. Complex 4b was very weakly diffracting and as such the data was omitted above 42° to provide a reasonable completeness for the data. As a consequence, limited discussion of the structural parameters will be made. Analysis calcd for 5b: C48H24N6PF6Cu C 64.54, H 2.71, N 9.41; found C 60.68, H 2.76, N 9.56; FT-IR υmax/cm−1: 2246 (CN str., vs), 2223 (CN str., vs), 822 (P−F str., vs). Additional Refinement Details for 5b. There is disorder of one of the nitromethane solvent molecules, and this is modeled over two major positions. Three restraints were used to maintain chemically sensible bond lengths within the nitromethane molecule.

Article

RESULTS AND DISCUSSION

The 2-D coordination polymers 2a and 2b mentioned earlier are the only examples of coordination polymers featuring crossconjugated polynitrile ligands reported thus far. They were synthesized via slow evaporation of nitromethane solutions of the ligand and metal salt in 1:1 to 1:3 ratios.13 Scheme 1 shows the coordination mode and empirical formulas for these two structures and those of the new polymers reported herein. Polymers 2a and 2b, as well as the other coordination polymers reported here, were obtained from solutions of nitromethane (with minimal acetonitrile where initial precipitation occurred). Therefore, crystals of a nitromethane solvate of 1, 1·4(CH3NO2), were prepared to allow comparison of the structure of the radialene within coordination polymers to the noncoordinated ligand structure. The compound crystallizes in the monoclinic space group P21/c with one molecule of 1 and four nitromethane solvate molecules in the asymmetric unit. As expected, the [3]radialene core is planar and the “arms” extend in a double-bladed propeller conformation with torsion angles of ca. 38° on average, which is common for hexaaryl[3]radialenes and similar to that observed in a dichloromethane solvate of 1.13,16−18,32 Bond lengths and angles about the central core are consistent with a [3]radialene derivative with the C−C bonds of the propane ring ranging from 1.428(2) to 1.432(3) Å and the exocyclic double bonds ranging from 1.357(2) to 1.361(3) Å. In the extended packing of this structure, there are two nitromethane solvate molecules which are positioned above and below the [3]radialene core. One is situated almost directly over the core and exhibits close contacts between an oxygen atom and a core carbon atom of 3.40 Å and between the same oxygen atom and an exocyclic carbon atom of 3.30 Å. A single hydrogen bond is also present between the first nitromethane molecule and a radialene aryl hydrogen atom with a bond length of 2.52 Å. The second nitromethane molecule is situated slightly off center with respect to the [3]radialene core and so only exhibits a close contact between an oxygen atom and an exocyclic carbon atom of 3.21 Å. Complexes 2c and 2d were prepared via slow evaporation of nitromethane solutions of 1 with AgBF 4 and AgSbF 6 respectively in ratios of 1:1 to 1:3 (2d required 2 drops of acetonitrile to solubilize the initially formed precipitate). These structures (Figure 2a) are isomorphous with 2a and 2b and further emphasize that the cationic coordination polymer units are not affected by the change in anion. As the isomorphs 2a and 2b have been previously described in detail,13 structural description of 2c and 2d is unnecessary; however, radialeneanion interactions within these polymers will be discussed. The tetrahedral tetrafluoroborate anion in structure 2c is disordered over two positions like that of the tetrahedral perchlorate anion in 2a. This seems to be due to the anion residing in a binding pocket which is better suited for octahedral anions. The tetrafluoroborate anion forms six weak C−H···Fanion hydrogen bonds with the four [3]radialene ligands surrounding it (Figure 2b). The anion forms two hydrogen bonds with the [3]radialene ligand directly below it, in layer A (shown in blue), with C−H···Fanion distances of 2.59 and 2.61 Å (Table 4). Two more hydrogen bonding interactions are observed between the anion and the ligand above it, in layer A2 (also shown in blue), with C−H···Fanion distances of 2.49 and 2.76 Å. Lastly, the disordered tetrafluoroborate anion is also involved in hydrogen bonding interactions with the two E



Article

phate anion and so can be involved in a greater number of hydrogen bonding interactions. The hexafluoroantimonate anion exhibits 13 hydrogen bonding interactions with the four [3]radialene ligands surrounding it in the structure. The closest and most plentiful of these interactions involve the [3]radialene ligand directly below the anion (layer A). Five anion hydrogen bonding interactions with C−H···F anion distances in the range of 2.35−2.84 Å can be observed. Three hydrogen bonds between the anion and the [3]radialene ligand above it, in layer A2, with C−H···Fanion distances of 2.61, 2.74, and 2.86 Å are also present. Four hydrogen bonds between the anion and the adjacent [3]radialene ligands (layer B) with C−H···Fanion distances between 2.67 and 2.86 Å can also be seen in Figure 2c. As in previous structures the hexafluoroantimonate anion sits almost directly over the core of the [3]radialene ligand. Considering the major component of the disordered anion, the closest radialene centroid anion distance is 3.55 Å which occurs between the hexafluoroantimonate anion (a fluorine atom) and [3]radialene situated in layer A. Similar to previous structures with anions containing fluorine, 2b and 2c, this is slightly outside the limit of the ∑vdw + 0.2 Å of carbon and fluorine (3.37 Å). Again, closer contacts are observed between the anion and the radialene core with π···F anion distances to the same ligand of 3.21 Å to a ring carbon and 3.08 Å to an exocyclic carbon, respectively. These interactions are the closest so far observed between a fluorine atom of a polyatomic anion and the [3]radialene core. The angles between the centroid of the major component of the disordered anion and the [3]radialene core plane are 81.48, 93.04, and 95.47° respectively. These are all within the range required for a significant anion-π interaction of 90 ± 10°. Structure determination of coordination polymers of 1 and silver salts from solutions with higher ligand to metal ratios than 1:3 has proven difficult with most compounds preferentially precipitating as amorphous solids. However, slow evaporation of a solution of 1 with 10 equivalents of AgClO4 in nitromethane, after the initial precipitate has been removed, yielded very small, dark red, rod-shaped crystals. These crystals were only suitable for X-ray crystallography using synchrotron radiation. Complex 3, {[Ag 3 (1)](ClO4)3·CH3NO2}n, is a 3-D coordination polymer of (10,3)b topology and crystallizes in the orthorhombic space group Pnna with an asymmetric unit that contains one molecule of the ligand and three silver atoms (two fully occupied positions and two with site occupancies of 0.5, Scheme 1). Unfortunately the anion and solvent molecules within the structure were disordered. Due to the disorder the anions and solvent molecules could not be located in their entirety and the SQUEEZE routine of PLATON was applied to the data.31 The crystals were only obtained in trace quantities, approximately four or five individual crystals per vial, so enough material for elemental analysis was unable to be readily obtained. However, analysis of the initial noncrystalline precipitate, which constituted the bulk of the isolated material, gave a reasonably good fit (within 0.65%) to the formula derived from the crystal structure (excluding solvent); this increases the metal−ligand ratio in the filtrate which, upon slow evaporation, gives 3. The IR absorption for the nitrile stretch of the crystals (2257 cm−1) differed to that of the precipitate (2247 cm−1), although there are a number of other well correlated peaks within the IR spectrum. In complex 3 the silver atoms have a near linear geometry and are coordinated to nitrogen donor atoms of two radialene

Figure 2. (a) A representation of the honeycomb 2-D coordination polymer in 2a−2d. Perspective views of the packing of (b) 2c and (c) 2d showing the disordered anions in the pocket formed by four molecules of 1. Both disorder components of the anion are shown; the fluorine atoms of the minor component are shown in yellow. Radialene phenyl C−H···Fanion hydrogen bonds are shown as dashed lines.

[3]radialene ligands adjacent to it, in layer B (shown in green), with C−H···Fanion distances of 2.57 and 2.64 Å respectively. In structure 2c the closest radialene centroid anion distance is 3.42 Å, which occurs between a fluorine atom of the tetrafluoroborate anion and [3]radialene situated in layer A. This is slightly outside the ∑vdw + 0.2 Å (3.37 Å), although the closest radialene core π···F anion distances to the same ligand are 3.45 Å to a ring carbon and 3.34 Å to an exocyclic carbon, respectively. This is consistent with the π-system of the [3]radialene core being localized along the exocyclic double bonds and not delocalized around the core.21 The angles between the centroid of the anion and the [3]radialene core plane are 74.04, 97.69, and 98.03°, which is outside of the desired range of 90 ± 10°.33,34 This shows that the tetrafluoroborate anion is not sitting directly over the core of the [3]radialene. The geometry of the anion is also not as expected from computational results21 with only one peripheral fluorine atom directed toward the core instead of three oxygen atoms as observed for the perchlorate anion in 2a. Similar disorder is observed for compound 2d (Figure 2c), which may be related to the size of the anion; the hexafluoroantimonate anion is larger than the hexafluorophosF



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Table 3. Selected Bond Lengths and Angles for Compounds 1−5 compound 1·4(CH3NO2) 2a 2b 2c 2d 3

4a 4b 5a 5b

M−N≡C (Å) bond lengthsa

N−M−N angles (deg)a

range/average of torsion angles (deg)b

2.244(3) − 2.403(5) Ag1 2.234(4) − 2.388(4) Ag1 2.230(4) − 2.391(4) Ag1 2.206(6) − 2.418(6) Ag1 2.091(7) Ag1 2.159(7) Ag2 2.113(6) and 2.167(8) Ag3 2.067(7) and 2.101(7) Ag4 1.950(3) − 2.008(3) Cu1 1.945(3) − 2.016(3) Cu2 1.9273(17) − 1.990(6) Cu1 1.915(6) − 2.047(4) Cu2 1.912(3) − 2.125(4) Cu1 1.9162(18) − 2.168(2) Cu1

85.54(14) − 129.48(14) Ag1 87.92(15) − 130.41(15) Ag1 88.21(16) − 129.22(19) Ag1 87.4(2) − 125.9(2) Ag1 170.7(5) Ag1 171.8(5) Ag2 172.0(3) Ag3 171.2(4) Ag4 104.60(13) − 115.52(12) Cu1 97.55(12) − 121.03(12) Cu2 103.66(9) − 115.30(16) Cu1 96.45(18) − 124.6(2) Cu2 92.89(14) − 125.58(13) Cu1 92.98(8) − 126.07(8) Cu1

31.3 36.3 37.9 36.2 37.5 34.7

− − − − − −

45.8/37.7 45.5/40.0 46.0/40.9 47.1/39.7 45.7/40.2 48.7/42.1

27.1 32.0 35.0 34.6 31.0 34.8

− − − − − −

46.1/38.8 46.6/38.2 64.3/42.9 42.1/38.1 52.9/40.9 52.5/42.3

[3]radialene [3]radialene [3]radialene [3]radialene

1 2 1 2

range/average of displacement (Å)c 0.730 0.269 0.179 0.328 0.192 0.480

− − − − − −

1.337/1.023 1.138/0.698 1.074/0.717 1.159/0.718 1.128/0.773 1.594/0.962

0.779 0.163 0.025 0.136 0.047 0.099

− − − − − −

1.613/1.118 1.472/1.033 2.709/1.198 2.143/1.002 1.531/0.748 1.614/0.741

[3]radialene [3]radialene [3]radialene [3]radialene

1 2 1 2

a c

Range for each crystallographically unique metal atom. bTorsion angles around the arms of each crystallographically unique [3]radialene ligand. Displacement of the N donor atom from the plane of the [3]radialene core.

Figure 3. (a) The (10,3)-b net motif of structure 3, and (b) (10,3)-b net extended in three dimensions. (c) A representation of the 8-fold interpenetrated structure of 3 with one network showing the molecular structure and the other seven simplified for clarity (the [3]radialene centroid is treated as a node and the silver(I) centers are topologically trivial), and (d) the 1-D channels viewed along the b-axis.

lengths of the central cyclopropane ring are in the range of

ligands. The Ag−N bond lengths in structure 3 range from 2.067(7) to 2.159(7) Å. In contrast to all previously reported coordination polymers of 1, here all six of the nitrile donor atoms are coordinated to silver atoms. The radialene core of 1 exhibits bond lengths which are consistent with those of other [3]radialenes reported in the literature.13,16−18,35 The bond

1.438(8) to 1.450(7) Å and the exocyclic double bonds range from 1.328(8) to 1.375(8) Å. In complex 3 the torsion angles around the “arms” of the [3]radialene averages 41.8° with the ligands taking on a propeller conformation, which is common G



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Figure 4. (a) The 2-D layered packing of 5a and 5b with layer A in blue and layer B in green. Hydrogen atoms and solvent molecules were removed for clarity. Perspective views of (b) 5a showing where the tetrafluoroborate anion resides within the structure (the major component of the disordered tetrafluoroborate anion is shown in blue and the minor component in yellow) and (c) 5b showing where the hexafluorophosphate anion resides within the polymer. Radialene phenyl C−H···anion hydrogen bonds are shown as dashed red lines.

{[Cu2(1)2](PF6)2·14(CH3NO2)}n 4b, and {[Cu(1)](PF6)·2(CH3NO2)}n 5b, were characterized by elemental analysis, IR spectroscopy, and X-ray crystallography. Elemental analysis of these complexes repeatedly produced low carbon values. As only a small number of the larger crystals, 4a, were present in the mixture they were able to be separated manually from the smaller crystals, 5a. These were then dried to constant weight under a vacuum. The initial analysis of these solvent free samples gave carbon values which were out by a significant margin (11.85% for 5a and 9.20% for 4a, for example), although the hydrogen and nitrogen values were within 1% of the calculated percentages. Seeding nitromethane solutions of a 1:6 ratio of 1/copper salt with crystals of 4a or 4b led to formation of only these species which allowed for easier isolation and analysis. Unfortunately, seeding of the same solutions with 5a and 5b still resulted in mixtures of both crystal forms in each sample. Upon separation of the initial mixtures, it was noted that some blue copper(II) salts had begun precipitating, which were postulated to be the reason for the low carbon values. The copper(II) salts were removed by suspending the crystals of 5a and 5b on a mixture of dichloromethane and dibromomethane; the contaminants remained at the bottom of the vial. These crystals and the samples of 4a and 4b grown by seeding were dried to constant weight under a vacuum prior to analysis but, even with this careful isolation and drying of the samples, the carbon values were still low (% difference between the calculated and experimental values: 4a 3.85%, 5a 9.56%, 4b 9.45%, 5b 3.86%). However, the hydrogen and nitrogen values were now within 0.4% (0.5% for 4a). It is known that samples which contain phosphorus may not combust successfully and give low carbon values although this does not explain why the BF4 analogues also analyze with low carbon. Incomplete combustion of the

for hexaaryl[3]radialenes.16−18,35 Selected bond lengths and angles are summarized in Table 3. The (10,3)-b net is composed of 1 acting as a three connecting node, while the two-coordinate silver centers are topologically trivial. A ring of 10 radialene ligands is formed (Figure 3a) which then extends into three dimensions (Figure 3b). This 3-D structure is 8-fold interpenetrated (Figure 3c) to form a dense network with 1-D pores running down the b-axis (Figure 3d). The pores along the b-axis are filled with disordered perchlorate anions and nitromethane solvate molecules. As these were unable to be modeled, radialeneanion interactions within this structure were not examined. The (10,3) net is the most frequently encountered 3-connected 3-D net and the (10,3)-b subtype is a common variation.1 The majority of (10,3)-b nets reported in the literature are 2-fold interpenetrated36−38 however there are examples of 4-fold39 and 8-fold40 interpenetration. Weak silver−silver interactions are present between adjacent interpenetrated nets within structure 3 with a Ag−Ag distance of 3.34 Å, which is within the sum of the van der Waals radii for silver (3.44 Å).41 Dissolution of 1 in nitromethane followed by addition of nitromethane solutions of [Cu(CH3CN)4]BF4 and [Cu(CH3CN)4]PF6 in stoichiometries ranging from 1:6 to 1:18 leads to immediate precipitation of an orange solid. Addition of two drops of acetonitrile effectively redissolved the precipitate. In each case, slow evaporation of the red solutions yielded two different crystal morphologies. In both cases first to form were large red octahedra followed by smaller orange block-shaped crystals. The variation in physical appearance of these crystals belied a dramatic difference in stability, the large red crystals being inherently solvent dependent and the smaller orange crystals being air stable. All of the complexes, {[Cu2(1)2](BF4)2·20(CH3NO2)}n 4a, {[Cu(1)](BF4)·2(CH3NO2)}n 5a, H



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Table 4. Close Solvent (Nitromethane) and Anion Contacts for Compounds 1·4(CH3NO2), 2a−2d, 4a, 5a, and 5b compound

anion

anion atom to [3] radialene centroid (Å)

anion atom to [3] radialene core carbon (Å)

anion atom to [3] radialene hydrogen (Å)

1·4(CH3NO2) 2a13

ClO4−

2b13

PF6−

2c

BF4−

2d

SbF6−

4a

BF4−

5a

BF4−

5b

PF6−

3.35 centroid···O 3.47 centroid···F 3.42 centroid···F 3.54 centroid···F

3.41 ring C 3.26 exocyclic C 3.34 exocyclic C 3.37 ring C

2.47−2.86 six contacts 2.37−2.83 six contacts 2.49−2.76 six contacts 2.35−2.86 13 contacts 2.43−2.85 six contacts 2.35−2.87 eight contacts 2.37−2.84 nine contacts

CH3NO2 atom to [3]radialene centroid (Å)

CH3NO2 atom to [3] radialene core carbon (Å)

CH3NO2 atom to [3]radialene hydrogen (Å)

3.70 centroid···O

3.21 exocyclic C

2.52−2.82 11 contacts 2.62−2.83 six contacts 2.24−2.91 nine contacts 2.51−2.91 eight contacts 2.36−2.82 six contacts

3.38 centroid···O 3.64 centroid···O

3.30 exocyclic C 3.45 ring C

2.43−2.91 six contacts 2.40−2.72 six contacts

[3]radialenes reported in the literature.13,16−18,35 The bond lengths of the central cyclopropane ring are in the range of 1.432(4)−1.439(3) Å and the exocyclic double bonds range from 1.348(4) to 1.356(4) Å. In complexes 5a and 5b the torsion angles around the “arms” of the [3]radialene average 41.6° with the ligands taking on the typical propeller conformation.16−18,35 In the extended structure, each radialene ligand coordinates to four copper cations; with three of these cations it forms a (6,3) sheet, layer A, which is cross-linked by the fourth copper cation to a second sheet, B, directly below it (Figure 4a) to create an A-B bilayer. All the 3-connecting nodes are bridged to create a 4-connected 2-D bilayer. Layer B, shown in green, has its [3]radialene units in the opposite orientation, related by a center of inversion, to those of A, shown in blue, and is also offset so that its [3]radialene units do not reside directly below those of A. The bilayer, A-B, is then packed in the extended crystalline lattice with additional bilayers to give an A-B A-B repeating structure. The anions reside between the layers A and B but not directly above or below the [3]radialene core of 1. The structures of 5a and 5b are topologically similar to a coordination polymer of copper(I) with the polynitrile ligand dicyanamide (dca) and 4,4′-bipyridine (bipy), which has the formula [Cu4(dca)4(bipy)(CH3CN)2]n.44 This structure also consists of pairs of (6,3) sheets which are bridged to create a 2D bilayer; however only half of the 3-connecting nodes are bridged to form a 3,4-connected net rather than a 4-connected net like in the case of 5a and 5b. Furthermore, in the case of [Cu4(dca)4(bipy)(CH3CN)2]n, the 2-D sheets are 4-fold interpenetrated in such a fashion to produce an overall 3-D entangled structure.44 Structures 5a and 5b are reminiscent of the four isomorphous honeycomb 2-D coordination polymers of 1 and silver, 2a−2d. The defining feature of 2a−2d, which is not observed in 5a/5b and gives rise to the structural differences between them, is the chelation of a silver atom by two nitrile groups on adjacent “arms” of the [3]radialene ligand. Because of this chelating binding mode in 2a−2d, the [3]radialene acts as a three-connecting node as opposed to a four-connecting node; thus the equivalent layers A and B in the silver structures are not physically connected. Chelation is not observed in the

ligand is another possibility; a number of examples in the literature have reported low carbon values in elemental analyses due to incomplete combustion of highly unsaturated arene structures.41 However, this has not been an issue in previous elemental analyses of hexaaryl[3]radialene complexes13 nor in the silver(I) coordination polymers reported herein. On the basis of these points, a possible reason for the low carbon percentages in these samples is the formation of metal carbides which persist after combustion is complete,42 although this problem has not been previously observed for copper(I) salts. The IR spectra of 4a and 5a correlate well except for one extra significant peak in 5a (1551 cm−1). 4b and 5b also have very similar IR spectra and the spectra of all four complexes exhibit two CN stretches (approximately 2247 and 2224 cm−1) for the coordinated and uncoordinated nitrile groups. The structures of complexes 5a and 5b are 2-D coordination polymers (Figure 4). Both coordination polymers crystallize in the triclinic space group P1̅, with an asymmetric unit that contains one molecule of the ligand, one copper atom, one anion, and two nitromethane solvate molecules. The structures were refined with some disorder problems of the tetrafluoroborate anion in compound 5a and one of the nitromethane solvate molecules in both compounds. The crystal structures are isomorphous and the cationic coordination polymers in the two structures are isostructural. In both structures the copper atom has a distorted tetrahedral coordination geometry with bond angles in the range 92.89(14)−126.07(8)°. The fourcoordinate geometry index, τ4, developed by Houser and coworkers states that a value of one for τ4 suggests a tetrahedral geometry and a value of zero a square planar geometry.43 The τ4 values for the copper atoms in 5a and 5b are 0.84 and 0.83 respectively. The coordination environment of the copper involves monodentate binding by nitrogen donor atoms from three ligands within the same plane and one ligand in a different plane to connect four different ligands in total. The Cu−N bond lengths in structures 5a and 5b range from 1.912(3) to 2.168(2) Å. Within both coordination polymers 1 is hypodentate; only four out of six ligand donor atoms coordinate to the copper cation. This coordination mode has been observed previously in quite a few coordination polymers of hexaaryl[3]radialenes.13,17,18 The radialene core exhibits bond lengths which are consistent with those of other I



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Figure 5. (a) The asymmetric unit of 4a. (b) Local coordination environments of metals and ligands in 4a (and also 4b). For clarity, the crystallographically distinct metal ions and ligands are colored differently. Hydrogen atoms and anions are omitted for clarity. (c) The overall network topology of 4a and 4b. Red nodes represent the Cu2 moieties, while the green and blue nodes represent the three-connecting ligands (colors are consistent with b). (d) A stick representation of the structure of 4a showing the channels parallel to the b-axis.

analogue, {[Cu2(1)2](BF4)2·20(CH3NO2)}n 4a, via rapid selection of a suitable crystal and immediate mounting within a cryostream at 150 K. Data were also obtained from the hexafluorophosphate analogue, {[Cu 2 (1) 2 ](PF 6 ) 2 ·14(CH3NO2)}n 4b, in a similar manner; however it is of considerably lower quality. Structures 4a and 4b are 3-D coordination polymers which crystallize in the orthorhombic space group Pbca, with an asymmetric unit that contains two molecules of the ligand, two copper atoms, and in the case of 4a, two tetrafluoroborate anions (three positions, two with site occupancies of 0.5, Figure 5a). There was a large amount of disorder in both structures due to large solvent-filled channels (∼11.4 by 8.4 Å) which run along the b-axis (Figure 5d). Because of this disorder, the solvent molecules in 4a could not be located in their entirety, and the SQUEEZE routine of PLATON was applied to the data.31 In the case of 4b both the anion and solvent molecules were unable to be located, and the SQUEEZE routine of PLATON was used again.31 The structures of 4a and 4b are complicated 3-D coordination polymers containing two crystallographically unique molecules of 1 and two crystallographically unique Cu(I) ions. Only 4a will be described in significant detail with comparison to 4b where appropriate. Each Cu(I) ion coordinates in a tetrahedral arrangement to four molecules of 1, and both molecules of 1 each coordinate to four Cu(I) ions (Figure 5b). In these structures, the copper atoms have a tetrahedral coordination geometry with bond angles in the range 96.55−124.50°. The τ4 values for the copper atoms in 4a are 0.87 and 0.96, and those in 4b are 0.85 and 0.96, revealing

copper polymers, 5a and 5b, due to the smaller ionic radius of Cu+, 91 pm, compared to that of Ag+, 129 pm.45 In the structures of 5a and 5b, the anions reside between the layers A and B but not directly above or below the [3]radialene core of 1. Within the silver polymers, 2a−2d, the anions sit almost directly above and below the radialene core of the 2-D polymer layers which are more separated than layers A and B in the copper polymers. This allows for a closer approach of the anions to the [3]radialene core, such that both radialene πanion interactions and phenyl C−H···anion hydrogen bonds are observed. Within structure 5a, the tetrafluoroborate anion is disordered over two positions with an occupancy of ca. 0.63:0.37 (Figure 4b). No short contacts with the radialene core are observed; however a number of anion hydrogen bonding interactions are present. The shortest interactions are those between the tetrafluoroborate anion and the [3]radialene ligand directly below it in layer A of the A-B bilayer (Table 4). In a similar manner, the hexafluorophosphate anion in complex 5b does not reside directly above the [3]radialene core and as such no anion-π interactions are observed. Again, a number of anion hydrogen bonding interactions are present between the anion and the four [3]radialene ligands which surround it in the polymer (Figure 4c and Table 4). The large red octahedral-shaped crystals of 4a and 4b, which crystallized first from the reaction mixture, proved particularly difficult to investigate. Size was not an issue as they were much larger than the orange block-shaped crystals of 5a and 5b and so could be easily separated. Their inherent instability was readily observed upon removal from the mother liquor, but diffraction data were obtained from the tetrafluoroborate J



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radialene phenyl C−H···Fanion hydrogen bonds are seen for each of the tetrafluoroborate anions. This is because the anions are located in the large channels within the structure. The first anion exhibits three radialene phenyl C−H···Fanion hydrogen bonds with two different ligands with bond lengths of 2.43, 2.47, and 2.71 Å (Figure 6a). The second anion has two hydrogen bonds to the same [3]radialene ligand with C− H···Fanion distances of 2.46 and 2.85 Å (Figure 6b), while the third anion only has one significant anion hydrogen bond which has a C−H···Fanion distance of 2.64 Å (Figure 6c). Unlike the silver(I) structures, the copper(I) coordination polymers have not shown any evidence of anion-π interactions involving the [3]radialene.

that one copper atom has a more distorted tetrahedral geometry than the other. Both copper centers involve monodentate binding by nitrile donor atoms from four different ligands. The Cu−N bond lengths in these structures range from 1.912(9) to 2.016(3) Å. As in coordination polymers 5a and 5b, 1 is hypodentate; only four out of six ligand donor atoms coordinate to the copper cations. The radialene core of both molecules of 1 within the asymmetric unit exhibit bond lengths which are consistent with those of other [3]radialenes reported in the literature.13,16−18,35 The bond lengths of the central cyclopropane rings in complex 4a are in the range of 1.429(4)− 1.449(4) Å, and the exocyclic double bonds range from 1.345(4) to 1.361(4) Å. In complex 4a, the torsion angles around the “arms” of the [3]radialenes average 38.5° with the ligands taking on a propeller conformation, which is common for hexaaryl[3]radialenes.13,16−18,35 Within the structures of 4a and 4b distinct pairs of Cu(I) ions, composed of the two unique metal ions, are observed. These pairs are connected by two molecules of 1, again one of each type. The metal ions in this pair also coordinate once to four other molecules of 1 (two of each type) to give the 3-D network. If this pair of metal ions is considered as a sixconnecting node, and each ligand considered as threeconnecting nodes (each coordinates to three Cu2 pairs), then the structure has a network with (4.62)(42.6)(43.66.86) topology (the two three-connecting nodes are inequivalent), as shown in Figure 5c. This topology is closely related to (but distinct from) the brk net found on the RCSR database.46 Within the asymmetric unit of 4a, there are two tetrafluoroborate anions over three positions, two of which are 50% occupied. These anions are surrounded by five different [3]radialene ligands within the structure and form interactions with four of these (Figure 6). Yet again no anion-π interactions are observed as the anions do not reside above the core of any of the [3]radialenes. Only a small number of

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CONCLUSIONS

We have previously shown that with low Ag:1 stoichiometries (1:1−3:1) the electron-deficient [3]radialene 1 forms (6,3) 2-D coordination polymers in which only four of the nitrile donors are coordinated to silver atoms. Using AgClO4 and increasing the Ag:1 ratio dramatically to 10:1 allow the isolation of an 8fold interpenetrated (10,3)-b net, {[Ag3(1)](ClO4)3·CH3NO2}n (3), whereby 1 acts as a hexadentate ligand. Such high Ag:L ratios appear to be necessary to facilitate utilization of all six donors of 1. In contrast, the Cu(I) containing structures {[Cu2(1)2](BF4)2·20(CH3NO2)}n 4a, {[Cu(1)](BF 4 )·2(CH 3 NO 2 )} n 5a, {[Cu 2 (1) 2 ](PF 6 ) 2 ·14(CH3NO2)}n 4b, and {[Cu(1)](PF6)·2(CH3NO2)}n 5b all form from reactions undertaken with Cu:1 stoichiometries in the range of 6:1 to 18:1. In both reactions, the two structures isolated (either 4a and 5a, or 4b and 5b) have the same stoichiometry of Cu:1 despite being formed at different stages of the slow evaporation process. In this case, the more open, metastable products (4a and 4b) appear to form first  these are particularly solvent dependent  and over time the denser, close-packed and stable structures of 5a and 5b form. This observation was supported by the fact that only 4a and 4b could be formed exclusively from seeding reactions; when 5a and 5b were added to a reaction mixture the more rapidly formed compounds 4a and 4b are isolated as well as 5a and 5b. Within the coordination polymers of [3]radialenes previously reported, close contacts were observed between the anions and the [3]radialene core. Here we sought further examples of such phenomena in new structures. In two isomorphous examples of the 2-D coordination polymer {[Ag(1)](X)·2(CH3NO2)}n (X = BF4, 2c; X = SbF6, 2d) close contacts indicative of anion-π interactions were observed between the anions and the [3]radialene core. However, in the 8-fold interpenetrated (10,3)-b net 3 and compound 4b the anions were too disordered to be located and in the other three copper(I) structures the anions did not reside near the [3]radialene core of 1. For 5a and 5b this appears to be due to packing effects where the smaller metallic radii does not allow a chelating coordination mode for 1 and the Cu(I) center has a greater preference for tetrahedral coordination which favors a 2-D coordination polymer with a fully cross-linked bilayer. Thus, it appears crystal packing dominates the observation of anion-π interactions or C−H···anion hydrogen bonds in coordination polymers of the [3]radialene 1.

Figure 6. Three perspective views showing the environment around the (a) first, (b) second, and (c) third crystallographically unique tetrafluoroborate anions in structure 4a. Radialene phenyl C−H···Fanion hydrogen bonds are shown as dashed lines. K



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Article

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ASSOCIATED CONTENT

S Supporting Information *

A combined cif for compounds 1·4(CH3NO2), 2c, 2d, 3, 4a, 4b, 5a, and 5b. This information is available free of charge via the Internet at http://pubs.acs.org/.

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AUTHOR INFORMATION

Corresponding Author

*Phone: +61 8 8313 7406. Fax: +61 8 8313 4358. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank Prof. Michaele Hardie, University of Leeds, for helpful discussions. The Australian Research Council (ARC) is acknowledged for a Future Fellowships to C.J.S. (FT0991910) and S.R.B. (FT0991840), and for funding this research through DP0773011. The ARC is also acknowledged for funding the Bragg Crystallography Facility (LE0989336). Prof. Lyall Hanton at the University of Otago is acknowledged for providing access to facilities for X-ray structure determination. The Australian Synchrotron is thanked for funding travel and access to the MX1 beamline through the Australian Synchrotron Access Program. The views expressed herein are those of the authors and are not necessarily those of the owner or operator of the Australian Synchrotron.

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