Dithiadiazolyl radicals

Regular jc-stack Peierls distorted 7E-stack p-type doping (a) (b) (c) 

There has been considerable interest in the magnetic behaviour of thiazyl radicals because of the discovery of long-range magnetic order in derivatives of 2. 

The dimerisation energy for derivatives of 2 (ca. 35 kJ mol-1) is considerable, particularly in relation to the strength of intermolecular forces and some persistence is required in order to isolate derivatives of 2 which do not form 7T —7r dimers in the solid state. A survey of the monomeric derivatives has been published recently.26 Since the spin density distribution in 2 is rather insensitive to chemical tuning, approaches to inhibit dimerisation rely exclusively on structural modifications, which affect the nature of the intermolecular forces. Inclusion of sterically demanding groups, such as 13, 14 and 15 has proved partially successful (in the case of the diradical 14 one ring is involved in formation of a dimer, while the other retains its open shell character). 

Dithiadiazolyl radical 18 has recently been reported to order as a ferromag-net below 1.3 K.33 The application of pressure also leads to an increase in 

Another approach has been to include strongly-structure directing groups e.g. 

N02 interactions successfully compete with the favourable 7r -7r dimerisation process. 

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Electron diffraction studies provide valuable information about structures in the gas phase. Consequently, this method is important for chalcogen-nitrogen compounds that are liquids or gases at room temperature. The application of this technique has provided evidence for the monomeric structures of the 1,2,3,5-dithiadiazolyl radical [CEsCNSSN] (3.3) and the 1,3,2-dithiazolyl [CEsCSNSCCEs] (3.4), a... 

In solution, the phenyl derivative 12.29 (R = Ph) is fluxional. The mechanism of the fluxional process has been shown by an N NMR investigation of a partially N-labelled sample, Le., PhCN2 N3S3 ( N = 99% N), to involve a series of 1,3-nitrogen shifts (Section 4.8.4). Thermolysis or photolysis of 12.29 generates the corresponding 1,2,3,5-dithiadiazolyl radicals [RCNaSa]". ... 

Figure 3 Four modes of association of 1,2,3,5-dithiadiazolyl radicals (2)...

Dithiadiazolyl radicals are considered to be organic molecular magnets and conductors and therefore chemists display increasing interest. Treatment of... 

Figure 3.10 EPR spectra of (a) 1,3,2-dithiazolyl and (b) 1,2,3,5-dithiadiazolyl radicals both absorption and first-derivative spectra are shown.

When R = Bu or a polyfluorinated aryl group (4-XCgF4, X = Br, CN, NO2), the 1,2,3,5-dithiadiazolyl radicals [RCN2S2] exist as monomers, whose magnetic properties are of particular interest. The tert-butyl derivative 5.5 is an unusual example of a liquid that is paramagnetic at room temperature the... 

The preparation of 1,2,3,5-dithiadiazolyl radicals by rearrangement of the isomeric 1,3,2,4-dithiadiazolyl radicals in solution [86CC140 87CC69 92JCS(D)1277] will be described more fully in Section XXI.A.l. In the case of some multi-l,2,3,5-dithiadiazolyl radicals, this reaction occurs in the solid state on thermolysis (Section XXIII.G.3). However, this route is not a common preparative technique, since these radicals are more conveniently prepared by direct reduction of 2+ salts, as described in Section VII.B. 

Isotropic ESR Data for Substituted 1,2,3,5-Dithiadiazolyl Radicals (All Coupling Constants in Milli-Teslas)... 

Aryl derivatives of 23 are readily degraded with chlorine to dithiatriazines 94 with the rate being dependent on the aryl substituent. The phenyl derivative of 23 undergoes nucleophilic attack by triphenylphosphine or triphenylarsine and is transformed into the monocyclic eight-membered imino compound 95, which has weak transannular S-S bonds (Scheme 2). Thermolysis and photolysis of compounds 23 affords the corresponding 1,2,3,5-dithiadiazolyl radicals. The trifluoromethyl derivative of 23 (R = Cp3) is astonishingly stable and does not react with bromine, chlorine, sulfuryl chloride, or (Cp3)2NO. To date, no explanation has been found <2003EJI3211>. 

The stability of the 1,3,2,4-dithiadiazolyl radical is extremely sensitive to substituent and is susceptible to both thermal and photochemical isomerisation to the thermodynamically more stable 1,2,3,5-dithiadiazolyl radical (Section 12.1.1.1) via a bimolecular rearrangement." In a number of other instances the radicals appear indefinitely stable in dilute solution, but decomposition appears to occur at high concentrations. As a consequence few 1,3,2,4-dithiadiazolyl radicals have been isolated in the solid state. Of these the phenyl-ene-bridged fe/5(l,3,2,4-dithiadiazolyl) adopts a n -n dimeric structure in the solid state" while the mixed l,2,3,5-/l,3,2,4-fcw(dithiadiazolyl) has recently been reported (Figure 8)." This too adopts a n n bonding mode," although the dimers exhibit an unexpected behaviour with two sets of n -n interactions between 2 and 3 rather than the symmetric 2/2 and 3/3 dimer. 

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