group P2,,,; a =14.828(2). h = 11.513(1), c =16.637(2)A. 0 =112.735(4). V = 2619.5(5) A', 2 = 4 , pidlid =1.373 gem-,; p = 4.25 m m -' ; max. absorption correction factor l.60:20max =115,24';Cu,,radiation; T = 298K:O-28scan;reflectionscollectedjunique!used, 3767/3579 (R,,, = 0.0219)/3577; parameters refined, 352; Rl!xR2 [2794 reflections with I > 2a/], 0.0576/0.1579; GOF = 1.029; [ A / GI,,, = 0.003; [A&JAp]*," 0.373/ -0.308 eA-3, structure solution and refinement with the programs SHELXS-86 and SHELXL-93: H atoms of 1.10phenanthroline were located by difference maps and refined isotropically, the rest were introduced at calculated positions as riding on bonded atoms; all non-H atoms refined anisotropically (except atoms of the solvent methanol which refined isotropically with occupancy fixed at 10.5. Crystallographic data (excluding structure factors) for the structure reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC-179-98. Copies of the data can be obtained free of charge on application to The Director, CCDC, 12 Union Road.

This review describes recent advances in the development of thiazyl radicals, particularly dithiadiazolyl (RCNSSN) and dithiazolyl (RCSNSCR) as molecule-based materials. Particular emphasis is placed on their potential applications as molecular conductors, magnets and switchable materials and incorporates an overview of the structure-property relationships required in these molecular systems.

1,3-Diphenyl-7-trifluoromethyl-1,4-dihydro-1,2,4-benzotriazin-4-yl (4), prepared in high yield via the catalytic oxidation of the corresponding amidrazone 5 by using Pd/C (1.6 mol %) and 1,8-diazabicyclo[5.4.0]undec-7-ene (0.1 equiv) in air, is stable in dichloromethane solutions in the presence of MnO(2) and KMnO(4). Furthermore, radical 4 is thermally stable well past its melting point (160-161 °C) with a decomposition onset temperature of 288 °C. X-ray studies show that radical 4 packs in equidistant slipped π-stacks along the a axis. Cyclic voltammetry shows two fully reversible waves, corresponding to the -1/0, 0/+1 processes. EPR studies indicate that the spin density is mainly delocalized on the triazinyl fragment of the heterocycle. Magnetic susceptibility measurements in the 5-300 K region showed that the radical obeys Curie-Weiss behavior down to 10 K (C = 0.376 emu·K·mol(-1) and θ = +1.41 K) consistent with weak ferromagnetic interactions between S = 1/2 radicals. Subsequent fitting of the magnetic data to a 1D ferromagnetic chain model provided an excellent fit (g = 2.00, J/k = +1.49 K) down to 10 K but failed to reproduce the subsequent decrease in χT at lower temperatures, which has been ascribed to the onset of weaker antiferromagnetic interactions between ferromagnetic chains.

The synthesis and characterisation of the dodecanuclear nickel complex, [Ni12(02CMe)12(~hp)12(H20)6(THF)6] (where chp = the anion of 6-chloro-2-pyridone) is described; structure determination shows formation of a metallocycle, while magnetic studies indicate ferromagnetic coupling between the nickel(ii) ions within the complex leading to a high spin multiplicity in the ground state.

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In 1928 Heisenberg proposed [1] that bulk ferromagnetic order would only ever be achieved in systems containing heavy atoms, that is, metals, their oxides, and related derivatives. Indeed it was not until 1991 that the first organic ferromagnet was reported; the b-polymorph of the para-nitrophenyl nitronyl nitroxide radical (p-NPNN, 1; Scheme 1) was shown to order below 0.6 K. [2] Since then a number of other purely organic radicals have been found to undergo bulk ferromagnetic order, although the majority order below 1 K. Exceptions include the radical cation salts [C 60 ][TDAE] [3] (TDAE = tetrakis(dimethylamino)ethylene) and [BBDTA]-GaCl 4 [4](3; BBDTA = benzobis(1,3,2-dithiazolyl), which order as ferromagnets at 16 and 6.7 K, respectively. Of the neutral radicals, only the nitroxide-based diradical DOTM-DAA (2; DOTMDAA = N,N'-dioxy-1,3,5,7-tetramethyl-2,6diazaadamantane) orders ferromagnetically above 1 K (T c = 1.48 K), [5] although the dithiadiazolyl radical p-NCC 6 F 4 CNSSNC (4) orders as a weak ferromagnet at 36 K under ambient pressure, [6] the highest reported temperature for magnetic ordering in an organic radical. We have sought to prepare new dithiadiazolyl radicals, closely related to 4, in which small structural changes may lead to new magnetically ordered systems. Here we report the structure and magnetic properties of 5, which is only the second neutral organic radical to order as a ferromagnet above 1 K.

Al(C6F5)3/R3P [R = tert-butyl (tBu), mesityl (Mes), naphthyl (Nap)] frustrated Lewis pairs react with N2O to form species having the formula R3P(N2O)Al(C6F5)3, which react with additional alane to generate proposed frustrated radical ion pairs formulated as [R3P·][(μ-O·)(Al(C6F5)3)2] that can activate C-H bonds. For R = tBu, C-H activation of a tBu group affords [tBu2PMe(C(CH2)Me)][(μ-OH)(Al(C6F5)3)2]. In the case of R = Mes, the radical cation salt [Mes3P·][(μ-HO)(Al(C6F5)3)2] is isolated, while for R = Nap, the activation of toluene and bromobenzene gives [(Nap)3PCH2Ph][(μ-OH)(Al(C6F5)3)2] and [(Nap)3PC6H4Br][(μ-HO)(Al(C6F5)3)2], respectively.

A two-step route to 1,3-disubstituted benzo- and pyrido-fused 1,2,4-triazinyl radicals is presented. The route involves the N'-(2-nitroarylation) of easily prepared N'-(het)arylhydrazides via nucleophilic aromatic substitution of 1-halo-2-nitroarenes, which in most cases gives N'-(het)aryl-N'-[2-nitro(het)aryl]hydrazides in good yields. Mild reduction of the nitro group followed by an acid-mediated cyclodehydration gives the fused triazines, which upon alkali treatment afford the desired radicals. Fifteen examples of radicals are presented bearing a range of substituents at N-1, C-3, and C-7, including the pyrid-2-yl and 8-aza analogues. This route to the N'-(het)aryl-N'-[2-nitro(het)aryl]hydrazides, which works well with benzo- and picolinohydrazides, required a modification for aceto- and trifluoroacetohydrazides that involved a multistep synthesis of asymmetrically 1,1-diaryl-substituted hydrazines.