DOI: 10.1021/cg100568a
A New Class of Easily Generated TCNQ2--Based Coordination Polymers
2010, Vol. 10 2860–2862
Brendan F. Abrahams,* Robert W. Elliott, Timothy A. Hudson, and Richard Robson* School of Chemistry, University of Melbourne, Victoria 3010, Australia Received April 28, 2010
ABSTRACT: New types of coordination polymers containing [M(TCNQ)] sheets in which the TCNQ component is present as the little known dianion TCNQ2- are obtained in a very simple manner using readily available TCNQH2 (i.e. 1,4-(NC)2CH 3 C6H4 3 CH(CN)2) as the starting material. Above and below the metal centers in the sheets, a range of pyridine derivatives can be attached, some terminal and some acting as pillars linking sheet to sheet to form a 3D coordination network. The following compounds, generally in solvated form, were isolated and structurally characterized;[M(TCNQ)(pyridine)2] (M=Mn or Zn), [M(TCNQ)(quinoline)2] (M=Co or Zn), [Mn(TCNQ)(4-methylpyridine)2], [Zn(TCNQ)(4-phenylpyridine)2], [Zn(TCNQ)(isoquinoline)2], [Zn(TCNQ)(nicotinamide)2], [M(TCNQ)(bipy)] (M= Mn, Fe, Zn, Cd, and bipy =4,40 -bipyridine, which links sheet to sheet to generate 3D coordination polymers), [Zn(TCNQ)(bpe)] (bpe = 1,2-bis(4-pyridyl)ethylene), and [Zn(CH3OH)(TCNQ)(Obip)1/2] (Obip = 4,40 -bipyridine di-Noxide). The TCNQH2/TCNQ2- approach opens the way to numerous new types of crystalline and structurally characterizable TCNQbased networks (and not just the sheet structures that are the focus of this preliminary report) that may lead to solids with unusual and useful electronic/magnetic properties.
Derivatives of tetracyanoquinodimethane, I, (hereafter TCNQ) have been the focus of much research because of the promise they hold for interesting magnetic/electronic properties arising from the ready accessibility of the radical anion TCNQ•-;1 indeed, a complex of TCNQ with tetrathiafulvalene was the first material to be described as an “organic metal”.2 In previous preparations of TCNQ-coordination polymers, either TCNQ0 or TCNQ•- has been used as the starting material, often generating ill-defined, inhomogeneous products; the number of crystalline, structurally characterized examples is consequently small.3 Evidence presented below strongly supports the proposition that the use of the “hydrogenated” version of TCNQ, viz. 1,4-(NC)2 3 CH 3 C6H4 3 CH 3 (CN)2, structure II (hereafter TCNQH2), as the starting material, will open the way to many new geometrical and topological types of TCNQbased coordination networks; it is clear to us on the basis of recent results that enormous scope exists here. The first example of a crystallographically characterized TCNQ2- salt was reported by Miller and co-workers in 1987.4 TCNQH2 is easily obtained from TCNQ and is air stable,5 but in solution the derived TCNQ2- is air sensitive.6 We speculated that the dianion might be stabilized against such air oxidation if it were generated in the presence of metal ions to which it can bind. Stabilization of this kind does indeed appear to be operative, for we have isolated in a very simple manner not only numerous products containing [M2þ(TCNQ2-)]0 sheets, which form the core of the present report, but also others with a 3D rather than a 2D metal/TCNQ connectivity.7 Advantages that might be expected to arise from the “high” charge on the ligand of minus two are (a) it should make accessible many additional types of as yet unknown anionic coordination networks of composition [(Mnþ)x(TCNQ2-)y]z-, in which case the choice of countercation could afford a means of controlling the network structure, and (b) the TCNQ2- dianion may interact with metal cations more strongly than does either TCNQ•- or TCNQ0, thereby yielding more robust, more crystalline, and more easily *To whom correspondence should be addressed. B.F.A. E-mail:
[email protected]. Telephone: þ61 3 8344 0341. Fax: þ61 3 9347 5180. R.R. E-mail:
[email protected]. Telephone: þ61 3 8344 6469. Fax: þ61 3 9347 5180. pubs.acs.org/crystal
Published on Web 06/04/2010
characterizable coordination polymers. Results to date support these suppositions.
An eminently reasonable objective for the longer term is to subject well characterized coordination polymers of TCNQ2- to oxidative intercalation so as to generate materials in which the initial connectivity remains intact but in which the TCNQ2- component has been oxidized to the radical anion state (TCNQ•-) or to mixed states such as (TCNQ2-)x(TCNQ•-)y or (TCNQ0)m(TCNQ•-)n; such products would be very significantly different from any TCNQ-based materials reported to date, and their properties could be unprecedented. Coordination polymers possessing channels appear particularly well suited to such intercalation. Reaction at room temperature between TCNQH2 in DMF and a mixture of Mn(NO3)2 and pyridine in methanol yields solvated crystals which contain [Mn(TCNQ)(pyridine)2] sheets of the type shown in Figure 1a.8a Each TCNQ2- ligand is attached to four Mn2þ centers located at the corners of a rectangle of edges r 2010 American Chemical Society
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Figure 3. Two fragments of adjacent [Zn(TCNQ)] sheets connected by an inclined Obip ligand. A methanol ligand is attached to each Zn center trans to the Obip oxygen donor.
Figure 1. (a) A [Mn(TCNQ)(pyridine)2] sheet. (b) Interdigitation between [Mn(TCNQ)(pyridine)2] sheets with close face-to-face pyridinepyridine contacts. (c) Interdigitation between [Zn(TCNQ)(4-phenylpyridine)2] sheets with close face-to-face phenyl-pyridyl contacts.
Figure 2. View of the [Mn(TCNQ)(bipy)] 3D coordination network.
7.373 A˚ and 11.227 A˚. The [Mn(TCNQ)(pyridine)2] sheets interdigitate, as shown in Figure 1b, making pyridine-pyridine π contacts of ca. 3.7 A˚. Crystalline solids with interdigitating sheet structures closely related to that just described and with compositions as listed below are similarly and equally easily obtained; [Zn(TCNQ)(pyridine)2],8b [M(TCNQ)(quinoline)2] (M = Co or Zn),8c [M(TCNQ)(4-methylpyridine)2] (M=Cd or Mn),8d
[Zn(TCNQ)(4-phenylpyridine)2],8e and [Zn(TCNQ)(nicotinamide)2].8f Not surprisingly, the 4-phenylpyridine component of [(Zn)(TCNQ)(4-phenylpyridine)2] significantly increases the sheet-sheet separation (relative to that in [Zn(TCNQ)(pyridine)2]), with the phenyl ring of one ligand making close π-π contact with the pyridyl ring of its neighbor (see Figure 1c). The [Zn(TCNQ)(nicotinamide)2] sheets interact with their neighbors by amide-to-amide double hydrogen bonds in the manner schematically represented in III, as was intended. 4,40 -Bipyridine (bipy) and 1,2-bis(4-pyridyl)ethylene (bpe) are able to act as “pillars”, linking sheet to sheet, as shown for the [Mn(TCNQ)(bipy)] 3D coordination polymer in Figure 2.8g Similar bipy-pillared 3D coordination networks are obtained with FeII, CoII, ZnII, and CdII, and related bpe-pillared structures are seen with ZnII 8h,9 and CdII.8i The νCN bands in the IR spectra of the compounds reported here (see the Supporting Information) are consistent with the formal charge of minus 2 on the TCNQ component.10 The connectivity within the sheets in the pillared 3D networks differs in an interesting manner from that in the sheets with terminal, nonbridging ligands such as pyridine. In the latter case, as can be seen in Figure 1a and as is shown schematically in IVa, the “methane C to methane C” axes of all the TCNQ components are parallel, whereas in the pillared structures the orientation of these axes alternates in the manner shown schematically in IVb. It will be appreciated that the four metal centers attached to each TCNQ2- unit in the arrangement seen in IVa are at the corners of a rectangle with two very significantly different edges whereas in the arrangement in IVb the four are at the corners of a square (or very nearly a square, since the four metal centers are not exactly coplanar). The fact that little energy is required to bend the M.N.C.C moieties from linearity makes possible the very different arrangements seen in IVa and IVb. When 4,40 -bipyridine di-N-oxide (Obip) is used to link [Zn(TCNQ)] sheets together, another interesting variant is observed.8j N-Oxide donors, of course, prefer to coordinate to metals with a pronounced bend at the oxygen center, so much so in the present case that the pyridine rings, rather than being roughly perpendicular to the average [Zn(TCNQ)] plane (as seen for example in Figure 1a), adopt an orientation closer to parallel with the nearby TCNQ2- unit, as can be seen in Figure 3. The pyridine rings consequently make close contact with the TCNQ2cyano groups (closest Cpyr 3 3 3 CCN = 3.035 A˚). Recently, we reported a number of metal-free TCNQ2- derivatives, in some of which donor/acceptor interactions between the TCNQ2-, which acted as the donor component, and various acceptors led to
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strong visible absorption, giving rise to intense colors.10 The Obip ligand would be expected to show acceptor properties, particularly so when it is attached to two electron withdrawing cations; it is not surprising, therefore, given the close contact between the Obip and TCNQ2- components, that the compound is deep red, which is to be contrasted with the pale yellow color of the [Zn(TCNQ)(bipy)] compound. In summary, it is clear that very many variations on the themes presented in this preliminary report may be played, using different metal centers, different terminal ligands, and different pillaring ligands. The TCNQH2/TCNQ2- approach will undoubtedly open the way to many new types of TCNQ-based networks. Whereas the TCNQ components of previously reported TCNQbased coordination polymers have generally carried an average charge of zero to minus one and generally have been involved in close π-π contacts, the TCNQ2- component in the networks reported here is “isolated” from such π-π contacts and is therefore accessible to reagents subsequently introduced into the network, e.g. e-acceptors. A venerable route to materials with enhanced electrical conductivities is the intercalation of oxidants or reductants into solid starting materials, for example, the tungsten bronzes with metal-like conductivity and superconducting C60M3 (M = K, Rb, or Cs) are generated thus. It is difficult to imagine a class of solids better disposed to undergo redox intercalation than channeled coordination networks. As mentioned earlier, oxidative intercalation into already crystalline and structurally characterized coordination networks provided by the TCNQH2 route could afford materials in which the initial connectivity remains intact but in which the TCNQ2- component has been oxidized. Given the fact that TCNQ maintains its planarity in the -2, -1, and 0 oxidation states and appears to be reasonably stable in all of these oxidation levels, we believe the prospects are good for generating mixed states such as (TCNQ2-)x(TCNQ•-)y or (TCNQ0)m(TCNQ•-)n in single crystal to single crystal transformations with appropriate anions occupying the channels. Depending on the nature of the metal component;for example whether it contains unpaired electrons or is itself redox active or both;the properties of such materials could be fascinating. Acknowledgment. The authors gratefully acknowledge support from the Australian Research Council and the Australian Synchrotron. Supporting Information Available: Syntheses, TGA, crystallographic details, and crystallographic information files (CIF). This material is available free of charge via the Internet at http://pubs.acs.org.
References (1) (a) Melby, L. R.; Harder, R. J.; Hertler, W. R.; Mahler, W.; Benson, R. E.; Mochel, W. E. J. Am. Chem. Soc. 1962, 84, 3374. (b) Hertler, W. R.; Mahler, W.; Melby, L. R.; Miller, J. S.; Putscher, R. E.; Webster, O. W. Mol. Cryst. Liq. Cryst. 1989, 171, 205. (2) Ferraris, J.; Cowan, D. O.; Walatka, V. V.; Perlstein, J. H. J. Am. Chem. Soc. 1973, 95, 948. (3) (a) Heintz, R. A.; Zhao, H.; Ouyang, X.; Grandinetti, G.; Cowen, J.; Dunbar, K. R. Inorg. Chem. 1999, 38, 144. (b) Zhao, H.; Heintz, R. A.; Ouyang, X.; Grandinetti, G.; Dunbar, K. R.; Campana, C. F.; Rogers, R. D. Chem. Mater. 1999, 11, 736. (c) Miyasaka, H.; CamposFernandez, C. S.; Clerac, R.; Dunbar, K. R. Angew. Chem., Int. Ed. 2000, 39, 3831. (d) O'Kane, S. A.; Clerac, R.; Zhao, H.; Ouyang, X.; Galan-Mascaros, J. R.; Heintz, R.; Dunbar, K. R. J. Solid State Chem. 2000, 152, 159. (e) Zhao, H.; Bazile, M. J.; Galan-Mascaros, J. R.; Dunbar, K. R. Angew. Chem., Int. Ed. 2003, 42, 1015. (f) Lopez, N.; Zhao, H.; Prosvirin, A. V.; Chouai, A.; Shatruk, M.; Dunbar, K. R. Chem. Commun. 2007, 4611. (4) Miller, J. S.; Zhang, J. H.; Reiff, W. M.; Dixon, D. A.; Preston, L. D.; Reis, A. H., Jr.; Gebert, E.; Extine, M.; Troup, J.; Epstein, A. J.; Ward, M. D. J. Phys. Chem. 1987, 91, 4344. (5) Acker, D. S.; Hertler, W. R. J. Am. Chem. Soc. 1962, 84, 3370. (6) Suchanski, M. R.; Van Duyne, R. P. J. Am. Chem. Soc. 1976, 98, 250. (7) Abrahams, B. F.; Hudson, T. A.; Robson, R. Cryst. Growth Des. 2008, 8, 1123.
Abrahams et al. (8) (a) All structures were solved and refined using SHELX-9711 within the WinGX12 suite of programs. The SQUEEZE routine within PLATON13 was employed in structures in which the solvent could not be satisfactorily modeled. Crystal data and refinement details for [Mn(TCNQ)(pyridine)2] 3 2MeOH: C24H22MnN6O2, Mr 481.42, monoclinic, C2/m, a=15.725(3) A˚, b=7.4496(8) A˚, c=11.3104(16) A˚, β=108.603(17)°, V=1255.7(3) A˚3, Z=2, μ=4.526 mm-1, T=130(2) K, no. of measured (and independent) reflections 2037 (1199), wR2 (all data)=0.1750, R1 [I>2σ(I)]=0.0688. (b) Crystal data and refinement details for [Zn(TCNQ)(pyridine)2] 3 1/2MeOH: C22.50H16N6O0.50Zn, Mr 443.78, monoclinic, C2/m, a = 15.5974(12) A˚, b = 7.3732(6) A˚, c=11.2273(16) A˚, β=109.061(10)°, V=1220.4(2) A˚3, Z=2, T=130(2) K, no. of measured (and independent) reflections 3715 (3715), wR2 (all data) = 0.1879, R1 [I > 2σ(I)] = 0.0699. (c) Crystal data for [Zn(TCNQ)(quinoline)2]DMF: C33H25N7OZn, Mr 600.97, monoclinic, C2/c, a = 23.6373(14) A˚, b = 15.9425(10) A˚, c=7.3340(4) A˚, β=106.397(5)°, V=2651.3(3) A˚3, Z=4, μ=1.628 mm-1, T=130(2) K, no. of measured (and independent) reflections 4810 (2423), wR2 (all data)=0.1522, R1 [I > 2σ(I)]=0.0550. On the basis of cell dimensions, [Co(TCNQ)(quinoline)2]DMF is isostructural; a=23.626(6) A˚, b= 15.870(5) A˚, c=7.296(3) A˚, β=106.54(3)°, V=2922.2(10) A˚3. (d) Crystal data and refinement details for [Cd(TCNQ)(4-methylpyridine)2] 3 2MeOH: C26H26CdN6O2, Mr 566.93, monoclinic, C2/m, a = 18.622(5) A˚, b=7.6404(8) A˚, c=10.749(3) A˚, β=122.27(3)°, V=1293.2(5) A˚3, Z=2, μ=7.037 mm-1, T=130(2) K, no. of measured (and independent) reflections 2213 (1328), wR2 (all data) = 0.2165, R1 [I > 2σ(I)]=0.0816. On the basis of cell dimensions [Mn(TCNQ)(4methylpyridine)2] 3 MeOH is isostructural; a = 19.165(14) A˚, b = 7.5148(12) A˚, c=10.743(7) A˚, β=122.94(11)°, V = 1298.5(8) A˚3. (e) Crystal data and refinement details for [Zn(TCNQ)(4-phenylpyridine)2] 3 2MeOH: C36H30N6O2Zn, Mr 644.03, monoclinic, P21/n, a = 10.9343(3) A˚, b=7.3954(2) A˚, c = 22.5187(6) A˚, β=93.059(3)°, V= 1818.35(9) A˚3, Z=2, μ=1.231 mm-1, T=130(2) K, no. of measured (and independent) reflections 6871 (3431), wR2 (all data) =0.0741, R1 [I > 2σ(I)]=0.0742. (f) Crystal data and refinement details for [Zn(TCNQ)(nicotinamide)2]DMF: C27H23N9O3Zn, Mr 586.91, monoclinic, C2/c, a = 23.985(6) A˚, b = 15.449(4) A˚, c = 7.340(2) A˚, β = 107.60(2)°, V = 2592.5(12) A˚3, Z =4, μ = 0.997 mm-1, λ = 0.77373 A˚ (data collected at the Australian Synchrotron), T = 100(2) K, no. of measured (and independent) reflections 13147 (2016), wR2 (all data) =0.2303, R1 [I > 2σ(I)] =0.0919. (g) Crystal data and refinement details for [Mn2(TCNQ)2(bipy)2] 3 13MeOH: C57H76Mn2N12O13, Mr 1247.18, tetragonal, P4/ncc, a = 17.2551(4) A˚, c = 23.1856(7) A˚, V=6903.2(3) A˚3, Z = 4, μ=3.500 mm-1, T=130(2) K, no. of measured (and independent) reflections 13482 (3421), wR2 (all data)=0.1336, R1 [I>2σ(I)]=0.0517. On the basis of cell dimensions, [M2(TCNQ)2(bipy)2] 3 13MeOH (M = Fe, Co, Zn, and Cd) are isostructural; M=Fe, a=17.3026(7) A˚, c=22.938(2) A˚, V=6867(2) A˚3; M=Co, a=17.2405(12) A˚, c=22.704(4) A˚, V=6748(1) A˚3; M=Zn, a = 17.3927(2) A˚, c = 22.8122(5) A˚, V = 6900.8(5) A˚3; M = Cd: a=17.5029(4) A˚, c=23.4820(6) A˚, V= 7193.8(5) A˚3. (h) Crystal data and refinement details for [Zn(TCNQ)(bpe)] 3 4DMF: C36H42N10O4Zn, Mr 744.17, monoclinic, P2/m, a=10.9623(9) A˚, b=7.3937(6) A˚, c=12.6331(14) A˚, β=109.510(11)°, V=965.15(15) A˚3, Z=1, μ= 1.295 mm-1, T = 130(2) K, no. of measured (and independent) reflections 3262 (1968), wR2 (all data) = 0.1367, R1 [I > 2σ(I)] = 0.0527. (i) Crystal data and refinement details for [Cd(TCNQ)(bpe)] 3 8MeOH: C32H46CdN6O8, Mr 755.16, monoclinic, P21/c, a = 14.0082(7) A˚, b=12.4871(4) A˚, c=12.3464(6) A˚, β = 113.763(6)°, V= 1976.56(18) A˚3, Z=2, μ=4.844 mm-1, T = 130(2) K, no. of measured (and independent) reflections 7269 (3808), wR2 (all data) = 0.1595, R1 [I > 2σ(I)] = 0.0692. (j) Crystal data for [Zn2(TCNQ)2(Obip)(MeOH)2](DMF)2: C42H38N12O6Zn2, Mr 937.58, monoclinic, P21/n, a=7.83660(10) A˚, b = 17.4153(2) A˚, c = 14.7632(2) A˚, β = 95.4390(10)°, V = 2005.76(4) A˚3, Z = 2, μ = 2.022 mm-1, T = 130(2) K, no. of measured (and independent) reflections 8098 (3605), wR2 (all data) = 0.0777, R1 [I > 2σ(I)] = 0.0302. (9) The following paper reported a TCNQ2--containing compound, obtained inadvertently from TCNQ•-, of composition [Zn2þ(TCNQ2-)(4,40 -bipyridine)] with the same 3D network structure: Shimomura, S.; Matsuda, R.; Tsujino, T.; Kamamura, T.; Kitagawa, S. J. Am. Chem. Soc. 2006, 128, 16416. (10) Hudson, T. A.; Robson, R. Cryst. Growth Des. 2009, 9, 1658. (11) Sheldrick, G. M. SHELX-97, Program for Crystal Structure Analysis; University of Gottingen: Germany, 1997. (12) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837. (13) Spek, A. L. PLATON, A Multipurpose Crystallographic Tool; Utrecht University: Utrecht, The Netherlands, 2005.
