Journal ArticleThe search for ferromagnetic organic compounds and polymers is the focus of contemporary research.1 - 5 Polymerization of di-iminoxyl diacetylene monomers has been suggested as a means to prepare a high spin potentially  ferromagnetically coupled polymers3 and the thermal, photochemical, and glow discharge treatment of 4,4'-(butadiynel, 1,4-diyl)-bis-(2,2,6,6-tetramethyl-4-hydroxypiperidin-l-oxyl)  (1-oxyl) (1) was reported to form a black polymer of which some samples exhibit field dependent magnetization corresponding to an 'insignificant' amount (0.1%) of a ferromagnet.3,4 Later,  Cao and co-workers reported 0.7% for thermally treated (1).

Miller, Joel Steven

Wiley, Douglas W.

English

The University of Utah: J. Willard Marriott Digital Library

Structural and Magnetic Characterization of a- and fJ-2,4-Hexadiyne-1,6-diyl Bis(2,2,5,5-tetramethyl-1-oxyl-3-pyrroline-3-carboxylatel and its Thermal Degradation Product Douglas W. Wiley, Joseph C. Calabrese, and Joel S. Miller Central Research and Development, E.I. du Pont de Nemours and Co. Inc., Experimental Station 328, Wilmington, DE 19880-0328, U.S.A.t Two polymorphs of the titled diradical have been characterized by X-ray diffraction, vibrational spectroscopies, and magnetic susceptibility; its radiation or thermal induced polymerization has not been achieved. The search for ferromagnetic organic compounds and poly-mers is the focus of contemporary research. 1-5 Poly-merization of di-iminoxyl diacetylene monomers has been suggested as a means to prepare a high spin potentially ferromagnetically coupled polymers3 and the thermal, photo-chemical, and glow discharge treatment of 4,4' -(butadiyne-1 ,4-diyl)-bis-(2,2,6 ,6-tetramethy 1-4-hydroxypiperidin-1-oxy I) (1) was reported to form a black polymer of which some samples exhibit field dependent magnetization corresponding to an 'insignificant' amount (0.1 %) of a ferromagnet .3,4 Later , Ca? and co-workers reported 0.7% for thermally treated (1) .5 'Ibis c~emistry attempts to take advantage of the fact that -;:ne dlyne~ crystallize in such a manner that enables thermal , p O~oc~emlcal, or X-ray induced topochemical poly-~enzatJon to form a single crystal polymer or polydiynes in a ~e cry~tal matrix.6 Cao and co-workers also reported that , he~adlyne-1,6-diyl bis(2,2,5 ,5-tetramethyl-1-oxyl-3-PYJ:r0hne-3-carboxylate) (2) exhibits a spontaneous magneti-~~~n of 88.5 emuG/mol and a coercive field of 455 G (1 G = 1 6~ T).5 The saturation magnetization is characterization of a Ovcb.eff~ct; an order of magnitude greater than reported by _ Illmkov and co-workers.3 t Contribution No. 5117. As part of our continued interest in molecular based ferromagnetic materials ,la,4 we have prepared (2) in an effort to verify and elucidate its ferromagnetic behaviour after polymerization. Compound (2) was synthesized by the con-OH (1 ) (2) 1524 1. CHEM. SOC., CHEM. COMMUN. , I989 Tv (C)-~ I 3200 I 2900 I 2600 I 2300 I 2000 500 I 1700 I 1400 I 1100 800 Wavenumber/cm - 1 Figure 1. I.r. spectra of (2). (a) (2) ex (KBr) ; (b) (2) ~ (KBr) ; and (c) (2) in CCI4. densation of 2,4-hexadiyne-l,6-diol with 2,2,5,5-tetramethyl-l-oxyl-3-pyrrolinecarboxylic acid and two polymorphs were isolated.* Crystals of the <x-phase were usually obtained during recrystallizations of the pure material without seeding. Recrystallizations with seeding of the hot solutions most often afforded the ~-phase as rectangular blocks. Both crystals were yellow to orange-yellow in colour depending on their thick-ness. The crystals of the two phases were isolated and identified by their appearance and their quite different i.T. spectra , Figure l.§ In KBr and Nujol , the <x-phase had a :I: A solution of 2,4-hexadiyne-1 ,6-diol (10 mmole) , 2,2,5,5-tetramethyl-1-oxyl-3-pyrrolinecarboxylic acid (21 mmole) , dicyclo-hexyldicarbodianhydride (21 mmole) , and 4-dimethylpyridine (1.5 mmol) in 150 ml tetrahydrofuran (THF) was stirred overnight. Filtration of the insoluble dicyclohexylurea and removal of the solvent gave crude product which was roughly purified by passing through a 70 x 45 mm silica column using 3: 2 light ether: EtOAc (93% yield). Purification by multiple flash chromatography gave material which showed only one spot by t.1.c . on silica . Development with phospho-molybdic acid gave a much more sensitive analysis than using u.v . on fluorescent plates. X-ray quality crystals were obtained from recry-stallization from either hexane or i-hexane . § Identical elemental analysis and fast atom bombardment (f.a.b.) mass spectra were obtained for both phases . The La .b. mass spectra have an anomolous parent peak at 442 .10. [The f.a.b. usually is P + 1; apparently, the material loses an electron more easily than the conventional addition of H +]. U.V. spectra (in hexane) : Amax (cm- I ) (E) (M- I cm- I) 46300 (26060) , 40 820sh (3650) , 38460sh (1920) , and 25640 (145) . unique sharp peak at 3084 cm- I along with a characteristic 5-peak pattern between 900 and 970 and sharp single peaks at 769 m and 548 mw em-I. The ~-phase had many of the absorptions split or showing shoulders including the strong 0=0 peak at 1727 cm- 1 and a different 5-peak pattern between 900 and 970 em-I. In CCI4 , both phases had identical spectra with Vc=o 1731 s, Vc=c 1629 m, VN- O 1290 ms , and Vc- o 1185 ms and 1050 s em-I. The Raman spectra (solid) had a strong G:C peak at 2263 em- I. The solid state e.s.r. spectra of both <x and ~ monomers consists of a single line at -3400 G with f...H = 12 G , consistent with an unoriented powder pattern for isolated nitroxide spins. The molecular structures of (2) <x and (2) ~ I I have essentially II Crystal data: ex-C24H30N20 6, m.p. = 104--105 °C, M = 442.51 , monoclinic space grouy P21/n (No. 14) , a = 5.867 (3) A, b = 21.894 (3) A , c = 9.711 (3) A, ~ = 96.18 (2t , U = 1240.2 A\ Z = 2, T = -70 °C, Dc = 1.185 g cm- 3, f!(Mo-K,,) = 0.80 cm- I , R = 6.6%, Rw = 6.6% for 873 unique reflections (l >3a!) to emax = 52° on a Enraf-Nonius CAD4 diffractometer. Crystal data : ~-C24H30N206 ' m.p. = 108-109 °C, M = 442.51 , monoclinic space group P2l/n (No. 14) , a = 8.152 (2) A , b = 33.763 (4) A , c = 9.192 (2) A, ~ = 104.59 (1)°, U = 2448.4 A3, Z = 4, T = -70 °C, Dc = 1.200 g cm- 3, f!(Mo-K,,) = 0.81 cm- I , R = 4.7% , Rw = 5.1 % for 3235 unique reflections (I > 3a!) to em a x = 55° on a Enraf-Nonius CAD4 diffractometer. Atomic co-ordinates , bond lengths and angles, and thermal parameters have been deposited at the Cambridge Crystallographic Data Centre . See Notice to Authors, Issue No. 1. J . CHEM. SOC., CHEM. COMMUN ., 1989 \ I Figure 2. Stereoview of the molecular conformation tor the IX-and ~-phases of 2,4-hexadiyne-l ,6-diyl bis(2,2,5,5-tetramethyl-l-oxyl-3-pyrroline-3-carboxylate) , (2) IX (solid bonds) and (2) ~ (dashed bonds) . equivalent bond distances with the average C:C, CC-CC, and NO bonds of 1.186, 1.380, and 1.279 A, respectively. These values are typical of di-iminoxyl diacetylenes. 4,6 The major difference between the pair of phases is their relative conformation around the linear hexadiyne fragment. The a:-phase consists of half the molecule lying on an inversion centre with both pyrroline carboxylate groups essentially trans to each other, whereas the ~-phase has these groups asymmet-rically arranged, Figure 2. The packing motif of the two phases are similar with the linear hexadiynes aligned in a herringbone fashion. The closest interdiyne separations in the IX-phase for the I-carbon of the butadiyne portion of one molecule to the 4- and ~-carbons of the butadiyne portion of the nearest neighbour-mg aligned molecule are 4.14 and 4.42 A, respectively . In the ~-phase, the nearly eclipsed pyrroline carboxylate groups allow a pairing of near neighbours resulting in a somewhat closer approach between the hexadiyne carbons (3.93 and 4.40 A, respectively) . In neither case are the butadiyne atoms close enough to support topchemical polymerization.6 1!te molar magnetic susceptibility corrected for the diamag-netI~ Core correction, XM , between 2-320 K was fit by the Cune-Weiss expression, XM = C/(T - 8), where the paramet-ersare: 8 = 2.54K, C = 0.75 emuKlmoland 8 = -2.87 K, C = 1525 0.74 emuKlmol for IX- and ~-phases , respectively . The effective moment , !leff' is 1.73 ± O.01!lB per NO group, or 2.44 ± 0.01 !lB per molecule for both phases. These values are consistent with two independent S = 112 spins. For both phases , the magnetic moment is essentially temperature independent down to 2 K. Similar data are not reported by Cao and co-workers.5 Careful analyses of the field dependent magnetization for magnetic field up to 19.5 kG for several samples showed that any ferromagnetic impurities are present in less than 2 p.p.m. by weight of equivalent iron . The thermal behaviours of both phases were studied with differential scanning calorimetry (DSC) and thermal gravime-tric analysis (TGA) . Neither phase under nitrogen showed any rapid change below their melting points. Upon melting, an exothermic reaction set in accompanied by darkening with no weight loss until ca. 140-160 °C. From these temperatures to a break around 170-180 °c, there was an endothermic weight loss of 2.5-4% . Above this the measurements indicated a steady decomposition with 35-40% weight loss by 250-300 °C. No additional information was gained by chang-ing the rate of heating (range 2 to 20 °C/min) . In order to induce topochemical polymerization, we have studied the effects of both radiation and heat. The IX and ~ monomers were subjected to y-ray, electron beam, and u.v. irradiations. ~ No change was noted for either y-ray or electron beam irradiations. Some darkening was observed after 72 h exposure to u.v. radiation. The magnetic susceptibility measurements showed a reduced moment of 2.16 !lB per original monomer unit. Longer exposure (162 h) caused additional darkening and the moment reducing to 2.09 !lB' Thermal treatment of (2) was carried out either under TGA conditions in N2 or in Pyrex tubes under vacuum. Isothermal calorimetry on both phases at 90 °C for 10 h under N2 showed essentially no weight loss , slight darkening , and a decrease in !leff to 2.35 !lB per original monomer unit. At 95 °C for 55 h , there was more darkening, 2.2% weight loss and a further decrease in the moment to 1.69 !lB ' Experiments carried out in Pyrex tubes were placed in a temperature controlled small tube heater. At 90 °C for 12 days , the quite dark solids showed a decrease in moment to 0.89 !lB' When samples were heated at 99 °c overnight , an amorphous dark melt resulted which still had !len = 1.69 !lB' In both the radiated and heated samples, no anomalous behaviour as reported by Ca05 was observed in the temperature dependence of the magnetic moment over the range of 1.5-300 K. In conclusion , the IX- and ~-2 ,4-hexadiyne-1,6-diyl bis-(2,2,5 ,5-tetramethyl-1-oxyl-3-carboxylate) (2) diacetylene monomer is a well behaved magnetic system comprised of a pair of independent doublets without evidence for a significant triplet. Since the SpillS on this diacetylene monomer couple only extremely weakly , it seems unlikely that should the desired single crystal polymer form that it would possess spin coupling that could lead to high spin or ferromagnetic behaviour. A preferred model diacetylene monomer should have a spin coupled triplet ground state as well as the ideal solid state structure enabling topochemical polymerization. The magnetic data of both phases of (2) as well as their thermal degradation products do not provide evidence that any polymeric or organic material present possesses ferromag-netic coupling or ferromagnetic behaviour. ~ The y-ray irradiation (2.5 Mrad) from a 6OCO source was carried out by Neutron Products Inc., Dickerson, MD and electron beam irradiation (5 Mrad) was performed by Electron TechnologIes Corp., South Windsor, CT. The u.v. source was a 450 watt medIUm pressure mercury arc lamp. In all cases sample temperatures did not exceed 6O-65 °C. 1526 We thank A. P. Berry, B. Chase, P. J. Krusic, W. Marshall, R. S. McLean, S. Riggs, and H. Williams for assistance in these studies. Received, 25th April 1989; Com. 9101761E References 1 (a) J. S. Miller, A. J. Epstein, and W. M. Reiff, Chern. Rev., 1988, 88,201; J. S. Miller and A. J. Epstein, NA TO Adv. Sc. Inst., Ser. B, 1987,168, 159-174; J. S. Miller, A. J. Epstein, and W. M. Reiff, Ace. Chern. Res., 1988,23,114; J. S. Miller and A. J. Epstein, Adv. Org. Chern., 1989, in the press; (b) K. Hoh and K. Takai, Mol. Crysl. Liq. Cryst., 1985, 125,251; (c) H. Iwamura, Pure & Appl. 1. CHEM. SOC., CHEM. COMMUN., 1989 Chern., 1986,58,187; (d) R. Breslow, Mol. Cryst. Liq. Cryst., 1985. 1~,Ul. . 2 J. B. Torrance, P. S. Bagus, I. Johannsen, A. Nazzal, S. S. p. Parkin, and P. Batail, 1. Appl. Phys., 1988, 63, 2962; A. A. Ovchinnikov and V. N. Spector, Syn. Met" 1988,27, B615. 3 Yu. V. Korshak, T. V. Medvedeva, A. A. Ovchinnikov, and V. N. Specktor, Nature, 1987,326,370. 4 J. S. Miller, D. T. Glatzhofer, R. Laversanne, S. Chittipeddi, P. Vaca, T. B. Brill, M. D. Timken, C. J. O'Connor, J. H. Zhang, J. C. Calabrese, and A. J. Epstein, submitted for publication. 5 Y. Cao, P. Wang, Z. Hu, S. Ki, L. Zhang, and J. Zhao, Solid State Cornrnun., 1988,68,817; Syn. Met., 1988,27, B625. 6 H. Bassler, Adv. Poly. Sci., 1984, 63, 1; R. H. Baughman, and R. R. Chance, Ann. N. Y. Acad. Sci., 1978,313,705; NATO Adv. Sc. Ins!., Ser. E: App. Sc., eds. D. Bloor and R. R. Chance, 1985, p.102. 

Structural and magnetic characterization of  a- and B-2,4-hexadiyne-1,6-diyl Bis(2,2,5,5-tetramethyl-1-oxyl-3-pyrroline-3-carboxylate) and its thermal degradation product

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Structural and magnetic characterization of a- and B-2,4-hexadiyne-1,6-diyl Bis(2,2,5,5-tetramethyl-1-oxyl-3-pyrroline-3-carboxylate) and its thermal degradation product

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