J . Org. Chem. 1995,60,2092-2098
2092
Crystal Structures and Magnetic Properties of Nitronyl Nitroxide and Imino Nitroxide Radicals Attached to Thieno[S,%b]-and Thieno[2,3-b]thiophene Rings Takeyuki Akita, Yasuhiro Mazaki, and Keiji Kobayashi* Department
of
Chemistry, College of Arts and Sciences, The University of Tokyo, Komaba, Meguro-ku, Tokyo 153, Japan
Noboru Koga and Hiizu Iwamura Department of Chemistry, Graduate School of Science, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113, Japan Received July 27, 1994@
Nitronyl nitroxide (ONC=NO) and imino nitroxide (NCNO) free radicals joined to isomeric thieno[3,2-b]thiophene and thieno[2,3-blthiophene, respectively, were prepared and their crystal structures and magnetic properties were investigated. In all crystals of four free radical species, the ONC-NO moieties are in the same plane as the thienothiophene ring. The coplanarity is associated with the extremely short intramolecular contact between the oxygen atom in the NO group and the sulfur atom in the thienothiophene ring. The free radicals attached to thieno[3,2-blthiophene are arranged in a chain structure with short intermolecular NO-S contacts, while the free radicals linked to thieno[2,3-blthiophenes make dimers with a face-to-face pairing by the use of the NO-S contacts. Among four radical species, thieno[3,2-blthiophene-sub~tituted nitronyl nitroxide exhibits a weak ferromagnetic interaction (J = +0.11 W ~ BH, = -2JSiSj) below 40 K as revealed by a SQUID susceptometer, while others are antiferromagnetic.
A number of organic free radicals are currently under investigation in the solid state for their magnetic properties in general and ferromagnetism in particular.' Several of their radical crystals have been found to exhibit ferromagnetic intermolecular interactions. Among those, nitronyl nitroxide radicals substituted with various aromatic rings are of great interest as highlighted by the discovery of rare organic ferromagnet in p-nitrophenyl nitronyl nitroxide crystak2 Commonly in these organic solids, the intermolecular interaction between the nitroxide group of one molecule and the substituent aromatic moiety of the adjacent molecule, rather than the direct one between the NO groups, plays critical roles for their bulk magnetic properties. In an effort to increase intermolecular interactions, nitrogen heteroaromatics have been incorporated in the nitronyl nitroxide radicals. Relevant examples of such nitrogen heterorings are ~ y r i d i n e ,pyridinium ~ salt: q ~ i n o l i n epyrimidine,6 ,~ and 1,2,4-triazole7derivatives. In contrast, the nitroxide radicals joined with sulfur heterocycles have never been investigated.8 The intermolecular interactions between the sulfur and the oxygen of the NO group are anticipated to work as spin-coupling
pathways in the solid state. In this paper we report the structural characterization and magnetic properties of two closely related nitronyl nitroxide (ONC=NO) and imino nitroxide (NCNO) free radicals, 4,4,5,5-tetramethyl-3-oxo-l-oxylimidazolin-2-yl (lN,2N) and 4,4,5,5tetramethyl-l-oxylimidazolin-2-yl(1I, 211,each of which is substituted at the 2-position with the isomeric thienothiophenes ,thieno[3,2-blthiopheneand thieno[2,3blthiophene, respectively. The constituent thienothiophene moieties are isomeric to each other with similar molecular size and shape and different only in the topology of n conjugation. Therefore, these materials would provide direct insight into magnetostructural relations in the crystalline state, particularly, if isostructural crystals are ~ b t a i n e d .Although ~ such a case was not realized, we could deduce characteristic features of the spin interaction between the NO group and the sulfur atom as well as their effects on the bulk magnetic properties.
Results and Discussion
Abstract published in Advance ACS Abstracts, March 1, 1995. (1)(a) Miller, J. S.; Epstein, A. J. Angew. Chem., Znt. Ed. Engl. 1994, 33,385. (b) Iwamura, H. Adu. Pliys. Org. Chem. 1990,26,179. ( c ) Dougherty, D. A. Acc. Chem. Res. 1991,24,88.
Crystal Structures. Crystal and molecular structures of the four radical species were studied by singlecrystal X-ray diffractions. Crystal data are summarized in Table 1. The selected bond lengths and angles are listed in Table 2.20 In all the crystals studied, the ON-C-NO moieties that bear the radical center are in the same plane as the thienothiophene ring. As a result of coplanarity of the thienothiophene ring and the ON-C-NO fragment, one
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(8) After the submission of this manuscript, an investigation of the magnetic properties of nitrene species attached to thiophene rings was published see: Ling, C.; Lahti, P. M. J.Am. Chem. SOC.1994,116, 8784. Recently Iwamura et al. have also investigated the carbene species linked to thiophene rings; unpublished results. (9)A unique example of the isomorphic crystals including thieno[3,2-blthiophene and thieno[2,3-b]thiophene frameworks has recently been reported; see: Hayashi, N.; Mazaki, Y.; Kobayashi, K. J . Chem. Soc., Chem. Commun. 1994,2351.
@
(2) (a) Turek, P.; Nozawa, K.; Shiomi, D.; Awaga, K.; Inabe, T.; Maruyama, Y.; Kinoshita, M. Chem. Phys. Lett. 1991,180,327. (b) Takahashi, M.; Turek, P.; Nakazawa, Y.; Tamura, M.; Nozawa, K.; Shiomi, D.; Ishikawa, M.; Kinoshita, M. Phys. Rev. Lett. 1991,67,746. (3)Awaga, K.; Inabe, T.; Maruyama, Y. Chem. Phys. Lett. 1992,190, 349. (4) Awaga, K.; Inabe, T.; Nakamura, T.; Matsumoto, M.; Maruyama, Y. Mol. Cryst. Liq. Cryst. 1993,232,69. ( 5 )Sugano, T.; Tamura, M.; Goto, T.; Kato, R.; Kinoshita, M.; Sasaki, Y.; Ohashi, Y.; Kurmoo, M.; Day, P. Mol. Cryst. Liq. Cryst. 1993,232, 61
(6) Lanfrance de Panthou, F.; Luneau, D.; Laugier, J.; Rey, P. J .
Am. Chem. SOC.1993,115,9095.
(7)Pei, Y.; Kahn, 0.;Aebersold, M. A.; Ouahab, L.; Le Berre, F.; Pardi, L.;Tholence, J. L. Adu. Mater. 1994,6,681.
0022-3263/95/1960-2092$09.00/00 1995 American Chemical Society
Properties of Nitronyl Nitroxide and Imino Nitroxide
J. Org. Chem., Vol. 60,No. 7,1995 2093
Table 1. Crystal Data and Experimental Parameters of X-ray Crystal Analyses of lN,11, 2N,and 21 formula M crystal system space group a,A b,
A
c, A
deg
v, A3
z
D,g cm-3 scan mode 26 range, deg no. of reflections measured no. of reflections used in refinement F > 2 . 5 ~ no. of parameters refined R(I)
RdI)
1N
11
2N
Cdd202Sz 295.37 monoclinic P211a 12.560(4) 13.853(7) 8.676(3) 105 62(2) 1454(1) 4 1.350 wl20 4-55 3754 2171 277 0.068 0.076
Ci3Hi5N20iS2 279 37 monoclinic P2 1In 17.12115) 10.661(3) 16.467i4) 109.5812i 2832(1) 8 1.311 0126 4-55 7094 4129 446 0.084
Ci3Hi5Nz0& 295.37 monoclinic P2& 31.6911 t 9.04015) 13.459
