摘要:
1,2,3,5-Dithiadiazolyls and 1,2,3,5-diselenadiazolyls; stacking and packing of p-dimers Leanne Beer,a A. Wallace Cordes,b Daniel J. T. Myles,a Richard T. Oakley*a and Nicholas J. Taylora a Department of Chemistry, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1. E-mail: oakley@sciborg.uwaterloo.ca b Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, Arkansas 72701, USA Received 19th June 2000, Accepted 29th June 2000, Published 11th July 2000 1,2,3,5-Dithiadiazolyl and 1,2,3,5-diselenadiazolyl radicals bearing a 2,5-difluorophenyl substituent crystallize as p-stacked dimers. In the S-compound the dimer stacks adopt a pinwheel arrangement about a 41 axis with a series of close trans-columnar S---S contacts. In the Se-compound the dimer stacks are packed in a non-centric dovetailed arrangement. The preference for the latter pattern is dictated by structure-making intermolecular F---Se contacts.Recent studies into the effects of steric bulk of the 4- substituent on the properties of dithiadiazolyls have revealed structures in which p-stacking and even dimerization is suppressed.13 Under such circumstances the much weaker interactions between radical centers can give rise to interesting magnetic phenomena.1,14 But in those cases where p-stacked structures prevail there is a strong and inescapable correlation between solid state structure and magnetic susceptibility; diamagnetism and dimerization go hand in hand. Within this context we were intrigued by the recent report that the dithiadiazolyl 1 is diamagnetic over the temperature range 5–300 K, and yet possesses a uniformly spaced (undimerized) p-stacked structure.15 These apparently conflicting observations reminded us of a special crystallographic situation we have seen before.We have therefore prepared and fully characterized compound 1, along with its selenium analogue 2, in order to clarify the structure–property relationships for these two systems. Structural analysis of 1 and 2 establishes that both radicals form p-dimers (at room temperature) with similar molecular features. The crystal structures are, however, very different. The differences arise from the effects of supramolecular dipolar F---Se interactions in 2. The syntheses of 1 and 2 build off the standard amidine methodology16 that we developed for dithia- and diselenadiazolyls (Scheme 1).Thus the reaction of 2,5- difluorobenzonitrile with lithium hexamethyldisilylamide, followed by treatment of the intermediate N-lithio derivative with chlorotrimethylsilane afforded the persilylated amidine 3. Cyclization of this material with (i) excess sulfur monochloride or (ii) selenium dichloride yielded the corresponding dithiadiazolylium or Introduction Interest in the potential applications of 1,2,3,5- dithiadiazolyl radicals in molecular magnets,1 conductors2 and thin film devices3 has led to extensive research into the relationships between molecular structure, solid state structure and transport properties.4 Within the context of molecular conductor design, strong intermolecular electronic interactions are desirable, and many mono-,5 di- ,3,6–8 and tri-functional9 derivatives have been prepared with a view to generating closely packed p-stacks in which orbital overlap along and between the stacks is maximized.Ideally, such systems would conform to the Haddon model10 for a neutral radical conductor. In practice, however, most p-stacked dithiadiazolyls have highly onedimensional electronic structures, and suffer from a charge density wave (CDW) driven or Peierls instability, i.e., a tendency for the radicals to dimerize.11 Such structures are diamagnetic. At elevated temperatures, the weak intermolecular S–S "bonds" of p-stacked dithiadiazolyls uncouple, oftentimes with a dramatic enhancement in magnetic susceptibility.6,7 These magnetic changes, however, are not accompanied by any significant increase in conductivity, indicating that the liberated spins are not charge carriers.Within a simple band model of electronic structure these observations can be rationalized in terms of the collapse of intermolecular overlap as the radicals separate. As a consequence the band width is insufficient to offset the coulombic barrier to charge transfer (U) and the materials fall into Mott insulating states.2 Dimerization of p-stacked dithiadiazolyls can be suppressed, and conductivity enhanced, by p-type doping, e.g., by oxidation with halogens.12 As a result the level of filling of the associated energy band is no longer commensurate with dimerization.More importantly the value of U, which is a maximum for a half-filled energy band, is reduced. But in the absence of doping, the energetics of charge transfer between neutral dithiadiazolyls imposes limits on their utility as conductive materials. DOI: 10.1039/b004875p CrystEngComm, 2000, 20 Results and discussiondiselenadiazolylium chloride. This was reduced, with Zn in SO2(l) (E = S), and with triphenylantimony in CH3CN (E = Se), to the radical 1 or 2, respectively. Purification and crystal growth of both compounds was effected by fractional sublimation in vacuo. Crystal data for the two compounds are provided in Table 1. Scheme 1 Table 1 Crystal, data collectiona and refinement parameters for 1 and 2 Compound Formula MCrystal system Space group a/Å b/Å c/Å b/° V/Å3 ZT/K Linear absorption coefficient/mm–1 Measured reflections Unique reflections R for merging Reflections in refinement R(F), Rw(F) R(F2), Rw(F2) R(F) for I > 2 s (I) GOF Largest D/ s Final difference map/e Å–3 0.00 –0.20, +0.21 a Data were collected at 293 K on Siemens P4 (for 1) and Rigaku Mercury CCD diffractometers with graphitemonochromated Mo-Ka radiation ( l = 0.71073 Å) using w scans.The structure was solved by direct methods and refined by full-matrix least-squares analyses. The fluorine positions in 1 were refined with a disorder model (79/21 in the F1,2 ring and 54/46 in the F3,4 ring).Crystals of 2 are prone to twinning; several were examined before finding one that was relatively untwinned. Even then the mosaicity was twice its normal value and there was evidence for non-merohedral twinning (random orientation of twin components). The high R-factor is in part due to this twinning, which precluded anisotropic refinement of C and N atoms. Click here for full crystallographic data (CCDC no. 1350/26). Crystals of the dithiadiazolyl 1 consist of p-dimers (Fig. 1, left) with a mean intradimer S---S contact of 3.16(4) Å; the S–S, S–N and N–C distances are all normal for this class of compound. The diselanadiazolyl 2 dimerizes in a similar fashion (Fig. 1, right), with a mean intradimer Se---Se contact of 3.295(14) Å; the intramolecular distances are normal for this class of compound.The dihedral angles between the CN2S2/CN2Se2 rings and phenyl rings, 21.16(2) and 18.29(5)° for 1, 21.7(4) and 23.1(4)° for 2, are similar. Both dimers form superimposed p-stacks (Fig. 2), with mean interdimer contacts of 4.04(4) Å (for S---S) and 4.026(13) Å (for Se---Se). Fig. 1 ORTEP drawings (30% ellipsoids) of the dimers of 1 (left) and 2 (right), with atom numbering. The fluorine atoms in 1 are disordered; only the higher occupancy positions are shown. Mean intradimer S---S = 3.16(4) Å and Se---Se = 3.295(14) Å. 1 2C7F2H3N2Se2 311.0 Monoclinic C7F2H3N2S2 217.2 Tetragonal I41/a P21 7.305(3) 11.121(4) 11.198(4) 111.44(2) 846.8(6) 4293 8.63 30.214(2) —7.1829(1) —6556.3(11) 32 293 0.63 3011 2885 0.014 2885 —0.070, 0.093 0.038 0.88 6568 1574 0.07 1574 0.098, 0.098 —0.054 1.58 0.00 –1.18, +1.08Fig.2 Stacked p-dimers of 1 (left) and 2 (right). Mean interdimer contacts are S---S = 4.04(4) Å and Se---Se = 4.026(13) Å. Fig. 3 Packing of dimers of 1 in the xy plane, showing the pinwheel arrangement of four dimers about the 41 axes. Click image or here to view the 3D crystal structure of a single pinwheel array. Within the tetragonal unit cell of 1 there are four pinwheellike arrays of p-dimers (Fig. 3). Each of these pinwheel patterns, wrapped about a 41 axis, generates a spiral staircase arrangement of intermolecular S---S interactions (Fig.4). Overall this motif is strikingly similar to that observed for the bifunctional 1,3-phenylene bridged diradicals 4 (E = S and Se).6 As described here, the crystal structure of 1 differs from that previously reported17 in several respects, paramount of which is a doubling of the unit cell repeat along the stacking direction, i.e., a, and a doubling of the size of the bc plane. Over the years, in our structural studies on dithiadiazolyl radicals, we have encountered a number of cases of p-stacked dimers exhibiting superlattices. Many of these we were unable to solve. In other cases, such as this one, we have been successful in identifying both the correct lattice parameters and the corresponding space group. In the case of compound 4 (E = S), for example, it was possible to achieve a satisfactory refinement using a model of evenly spaced (undimerized) radicals, but the observation that the material was diamagnetic forced us to re-examine the X-ray data, and eventually to establish the existence of a dimerized rather than an undimerized p-stack.Insofar as the magnetic susceptibility measurements on 1 indicate that it is diamagnetic up to 300 K, the solid state structure must be such that the spins are paired, i.e., the radicals are dimerized. The present data confirm that structure–property relationship. Fig. 4 Spiral staircase of S---S contacts around the 41 axis in the structure of 1. For purposes of clarity only the innermost sulfur of each pinwheel is shown; d1 = 3.578, d2 = 3.517, d3 = 3.587 and d4 = 3.554 Å.Given the similarities between the two structures of 4 (E = S, Se)18 we expected that the structures of 1 and 2 would follow suit. However, while 2 also adopts a stacked p- dimer structure, the packing pattern of the stacks is quite different to that found for 1. Instead of forming four-fold pinwheel arrays, the stacks are assembled into interlocking dovetailed arrays (Fig. 5) similar to those observed for cyanophenyl substituted diselenadiazolyls in general, and 2-cyanophenyl-diselenadiazolyl 5 in particular. The structure of the latter compound (Fig. 6) also belongs to the space group P21 and consists of stacks of cofacial p-dimers linked by dipolar CN---Se interactions which serve as structure making "supramolecular synthons".19 In compound 2 the 2-fluoro substituent plays the role of structure maker.That these groups are important in 2, but apparently not in 1, can be ascribed to the fact that dipolar F---Se interactions are likely to be stronger than F---S interactions; selenium is a stronger Lewis acid. Fig. 5 Packing of dimers of 2, viewed down the x axis, showing the lateral Se---Se contacts and Se---F interactions. The two in-register Se---Se contacts are 3.745 and 3.904 Å. Click image or here to view the 3D crystal structure of the packing of dimers of 2.Fig. 6 Packing of dimers of 5, viewed down the x axis, showing the lateral Se---Se contacts and Se---NC interactions. The two out-ofregister Se---Se contacts are 4.040 and 4.066 Å.Click image or here to view the 3D crystal structure of the packing of dimers of 5. Adjacent stacks in 2 are in-register and the F---Se interactions fall into two four-way groups (Fig. 7); F2 bridges to four selenium atoms within the same dimer unit, while F4 links to four selenium atoms in two separate dimers. This arrangement is in contrast to 5, where adjacent stacks are out-of-register (Fig. 8), and the CN---Se interactions link a nitrile to two seleniums within a single heterocyclic ring. Conclusions In summary, we have confirmed that the solid state structure of 1 is consistent with the previously reported magnetic properties. The crystal structure consists of superimposed p-dimer stacks clustered about a 41 axis.The resulting 4-fold pinwheels exhibit a spiral staircase array of intermolecular S---S contacts. Compound 2 also forms superimposed p-dimer stacks but, as a result of the expected preference of selenium to form structure-making dipolar interactions with halogens, the stacks are interlocked into a (non-centric) dovetailed arrangement in which Se---F interactions are maximized. Fig. 7 In-register alignment of p-dimer stacks in 2, showing the four-way structure making dipolar Se---F interactions. The contacts range from 3.212 to 3.559 Å (Se---F2), and from 2.966 to 3.673 Å (Se---F4). Fig. 8 Out-of-register alignment of p-dimer stacks in 5, showing the two-way structure making dipolar Se---NC interactions. The contacts are 2.971/3.162 Å (Se---N5), and 3.172/2.962 Å (Se--- N6).The tendency of the crystal structures of diselenadiazolyls bearing ortho-substituted phenyl groups to be dictated by halogen-to-Se (or nitrile-to-Se) interactions suggests new opportunities for the design of diselenadiazolyls with specific solid state structures, and hence desirable magnetic and/or non-linear optical properties. Experimental section General procedures 2,5-Difluorobenzonitrile, selenium powder, chlorine gas, sulfur monochloride, triphenylantimony, zinc powder and chlorotrimethylsilane were obtained commercially and used as received. Acetonitrile was purified by distillation from P2O5 and toluene by distillation from sodium. Commercial LiN(SiMe3)2 was converted into its mono-etherate in order to facilitate amidine synthesis.16 All reactions were performed under an atmosphere of nitrogen.Fractional sublimations of radicals were performed in an ATS series 3210 three-zone tube furnace, mounted horizontally and linked to a series 1400 temperature control system. Elemental analyses were performed by MHW Laboratories, Phoenix, AZ. Infrared spectra were recorded (at 2 cm–1 resolution on Nujol mulls) on a Nicolet Avatar FTIR spectrometer. 1H NMR spectra were recorded at 250 MHz on a Bruker AM 250NMR spectrometer. Preparation of 2,5-difluorobenzene-[N,N,N�- tris(trimethylsilyl)carboximideamide] 3 Solid LiN(SiMe3)2·Et2O (8.80 g, 3.6 mmol) was added to a solution of 2,5-difluorobenzonitrile (5.00 g, 3.6 mmol) in 75 mL toluene.The resultant mixture was stirred at room temperature for 3 h, and excess Me3SiCl (5.0, 4.6 mmol) added via syringe. The mixture was gently refluxed for 16 h, cooled, filtered, and the filtrate concentrated in vacuo to leave a brown oil that was vacuum distilled at 100–102 °C, 10–1 Torr to yield 3 as a colourless liquid (6.00 g, 1.6 mol, 44%) which solidified at room temperature. The product was recrystallized, for analytical purposes, from hot CH3CN, as colourless needles, mp 158–160 °C. Anal. calc. for C16H30F2N2Si3: C, 51.57; H, 8.11; N, 10.82%. Found: C, 51.45; H, 8.11; N, 7.52%. 1H NMR ( d, CDCl3) 6.7–7.0 (m, 3H), 0.045 (s, 54H). IR (2000–400 cm–1) 1640(s),1485(m), 1300(w), 1247(s), 1187(m), 1121(w), 1083(w), 1006(m), 912(m), 876(m), 850(vs), 761, 691(m), 624(w) cm–1.Preparation of 2,5-difluorobenzene-(1,2,3,5- dithiadiazolyl) 1 Excess sulfur monochloride (3.4 g, 25 mmol) was injected, via syringe, into a slurry of the persilylated amidine 3 (2.03 g, 5.4 mmol) in 20 mL acetonitrile and the mixture stirred and heated under gentle reflux for 30 min. The mixture was cooled and the crude dithiadiazolylium chloride [1][Cl] filtered off, washed with 2 × 20 mL CH3CN, and dried in vacuo. This orange solid (1.12 g, 4.4 mmol) was reduced in an h-cell by zinc powder in 10 mL SO2(l) for 2 h. The dark brown solution was filtered, and the SO2 removed to leave a black solid, from which the product 1 was purified by vacuum sublimation at 60 °C, 10–1 Torr.The crude product (0.300 g, 1.4 mmol, 25% based on 3) was purified by sublimation (over several days) in a sealed tube (10–2 Torr) along a temperature gradient of 45–35 °C to yield black lustrous needles of 1, mp 77–80 °C. IR (2000–400 cm–1): 1592(w), 1496(m), 1351(s), 1296(m), 1258(m), 1235(m), 1186(s), 1128 (s), 1084(s), 968(s), 878(s), 820(s), 797(s), 774(m), 757(s), 652(m), 557(s), 531(s), 499(s), 457(m), 421(m) cm–1. Anal. calc. for C7H3F2N2S2: C, 38.70; 1.39; N, 12.89%. Found: C, 39.12; H, 0.99; N, 12.89%. Preparation of 2,5-difluorobenzene-(1,2,3,5- diselenadiazolyl) 2 The persilylated amidine 3 (1.89 g, 5.1 mmol) was added portionwise, as a solid, to a solution of SeCl2 prepared in situ by the reaction of SeCl4 (1.12 g, 5.1 mmol) and elemental selenium (0.40 g, 5.1 mmol) in 75 mL CH3CN. The resulting dark red slurry was heated under reflux for 2 h, then cooled and filtered.The crude diselenadiazolylium chloride [2][Cl] was washed with 3 × 40 mL CH3CN, dried in vacuo (1.4 g), and immediately reduced with Ph3Sb (0.70 g, 2.3 mmol) in 50 mL CH3CN at reflux for 30 min. The red solution was cooled to 0 °C, and bronze microcrystals of 2 filtered off. The crude product (1.17 g, 3.8 mmol, 74% based on 3) was purified by sublimation (over 10 days) in a sealed tube (10–2 Torr) along a temperature gradient of 45– 35 °C to yield bronze needles of 2, mp 63–67 °C. IR (2000–400 cm–1): 1598(m), 1377(s), 1328(s), 1279(m), 1248(m), 1182(s), 1128(m), 1082(m), 957(m), 886(s), 872(vs), 782(s), 746(s), 717(w), 706(w), 691(s), 629(m), 550(w), 525(w) cm–1.Anal. calc. for C7H3F2N2Se2: C, 27.03; H, 0.97; N, 9.01%. Found: C, 27.16; H, 0.81; N, 9.20%. Acknowledgements We thank the Natural Science and Engineering Research Council of Canada and the State of Arkansas for financial support. References 1 (a) A. J. Banister, N. Bricklebank, I. Lavender, J. M. Rawson, C. I. Gregory, B. K. Tanner, W. Clegg, M. R. J. Elsegood and F. Palacio, Angew. Chem., Int. Ed. Engl., 1996, 35, 2533; (b) G. Antorrena, J. E. Davies, M. Hartley, F. Palacio, J. M. Rawson, J. N. Smith and A. Steiner, Chem. Commun., 1999, 1393. 2 (a) A. W. Cordes, R. C. Haddon and R. T. Oakley, in The Chemistry of Inorganic Ring Systems, ed. R. Steudel, Elsevier, Amsterdam, 1992, p.295; (b) A. W. Cordes, R. C. Haddon and R. T. Oakley, Adv. Mater., 1994, 6, 798. 3 A. W. Cordes, R. C. Haddon, C. D. MacKinnon, R. T. Oakley, G. W. Patenaude, R. W. Reed, T. Rietveld and K. E. Vajda, Inorg. Chem., 1996, 35, 7626. 4 (a) A. J. Banister and J. M. Rawson, in The Chemistry of Inorganic Ring Systems, ed. R. Steudel, Elsevier, Amsterdam, 1992, p. 323; (b) A. J. Banister and J. M. Rawson, Adv. Heterocycl. Chem., 1995, 62, 137; (c) T. Torroba, J. Prakt. Chem., 1999, 341, 99. 5 (a) A. W. Cordes, C. M. Chamchoumis, R. G. Hicks, R. T. Oakley, K. M. Young and R. C. Haddon, Can. J. Chem., 1992, 70, 919; (b) W. M. Davis, R. G. Hicks, R. T. Oakley, B. Zhao and N. J. Taylor. Can. J. Chem., 1993, 71, 180; (c) A.W. Cordes, R. C. Haddon, R. G. Hicks, R. T. Oakley and T. T. M. Palstra, Inorg. Chem., 1992, 31, 1802. 6 (a) M. P. Andrews, A. W. Cordes, D. C. Douglass, R. M. Fleming, S. H. Glarum, R. C. Haddon, P. Marsh, R. T. Oakley, T. T. M. Palstra, L. F. Schneemeyer, G. W. Trucks, R. Tycko, J. V. Waszczak, K. M. Young and N. M. Zimmerman, J. Am. Chem. Soc., 1991, 113, 3559; (b) A. W. Cordes, R. C. Haddon, R. G. Hicks, D. K. Kennepohl, R. T. Oakley, T. T. M. Palstra, L. F. Schneemeyer, S. R. Scott and J. V. Waszczak, Chem. Mater., 1993, 5, 820. 7 R. A. Beckman, R. T. Boeré, K. H. Moock and M. Parvez, Can. J. Chem., 1998, 76, 85. 8 A. W. Cordes, R. C. Haddon, R. T. Oakley, L. F. Schneemeyer, J. Waszczak, K. M. Young and N. M. Zimmerman, J.Am. Chem. Soc., 1991, 113, 582. 9 (a) A. W. Cordes, R. C. Haddon, R. G. Hicks, R. T. Oakley, T. T. M. Palstra, L. F. Schneemeyer and J. V. Waszczak, J. Am. Chem. Soc., 1992, 114, 5000; (b) A. W. Cordes, R. C. Haddon, R. G. Hicks, D. K. Kennepohl, R. T. Oakley, L. F. Schneemeyer and J. V. Waszczak. Inorg. Chem., 1993, 32, 1554. 10 R. C. Haddon, Nature, 1975, 256, 394. 11 R. E. Peierls, Quantum Theory of Solids, Oxford University Press, London, 1953, p. 108. 12 (a) C. D. Bryan, A. W. Cordes, R. C. Haddon, R. G. Hicks, D. K. Kennepohl, C. D. MacKinnon, R. T. Oakley, T. T. M. Palstra, A. S. Perel, S. R. Scott, L. F. Schneemeyer and J. V. Waszczak, J. Am. Chem. Soc., 1994, 116, 1205; (b) C. D. Bryan, A. W. Cordes, R. M. Fleming, N.A. George, S. H. Glarum, R. C. Haddon, C. D. MacKinnon, R. T. Oakley, T. T. M. Palstra, A. S. Perel, L. F. Schneemeyer and J. V. Waszczak, J. Am. Chem. Soc., 1995, 117, 6880; (c) A. W. Cordes, N. A. George, R. C. Haddon, D. K. Kennepohl, R. T. Oakley, T. T. M. Palstra and R. W. Reed. Chem. Mater., 1996, 8, 2774; (d) C. D. Bryan, A. W. Cordes, J. D. Goddard, R. C. Haddon, R. G. Hicks, C. D. MacKinnon, R. C. Mawhinney, R. T. Oakley, T. T. M. Palstra and A. S. Perel. J. Am. Chem. Soc., 1996, 118, 330. 13 T. M. Barclay, A. W. Cordes, N. A. George, R. C. Haddon, M. E. Itkis and R. T. Oakley, Chem. Commun., 1999, 2269. 14 A. J. Banister, N. Bricklebank, W. Clegg, M. R. J. Elsegood, C. I. Gregory, I. Lavender, J. M. Rawson and B. K. Tanner, J. Chem. Soc., Chem. Commun., 1995, 679. 15 A. J. Banister, A. S. Batsanov, O. G. Dawe, P. L. Herbertson, J. A. K. Howard, S. Lynn, I. May, J. N. B. Smith, J. M. Rawson, T. E. Rogers, B. K. Tanner, G. Antorrena and F. Palacio, J. Chem. Soc., Dalton. Trans., 1997, 2539. 16 R. T. Boeré, R.G. Hicks and R. T. Oakley, Inorg. Synth., 1997, 31, 94. 17 In the earlier work crystals of 1 were reported to belong (at T = 150(2) K) to the tetragonal space group P4/n,with a = 21.289(1), c = 3.544(3) Å, V = 1604(3) Å3, Z = 8. While differences are to be expected between low temperature and room temperature data sets, any superlattice effects should be more accentuated at low temperature. 18 For this latter system, a second (unstacked) phase has also been observed. See A. W. Cordes, R. C. Haddon, R. G. Hicks, R. T. Oakley, T. T. M. Palstra, L. F. Schneemeyer and J. V. Waszczak, J. Am. Chem. Soc., 1992, 114, 1729. 19 D. S. Reddy, Y. E. Ovchinnikov, O. V. Shishkin, Y. T. Struchkov and G. R. Desiraju, J. Am. Chem. Soc. 1996, 118, 4085. CrystEngComm © The Royal Society of Chemistry 2000
ISSN:1466-8033
DOI:10.1039/b004875p
出版商:RSC
年代:2000
数据来源: RSC