The Synthesis and Characterization of Stable Radicals Containing the Thiazyl (SN) Fragment and Their Use as Building Blocks for Advanced Functional Materials - Stable Radicals: Fundamentals and Applied Aspects of Odd-Electron Compounds - page 370

y

100 [0.0, 3.0] [3.0, 3.0]

3.0

0

x

2.5

− 100

2.0

− 200

0.0

1.5

0.5

1.0

1.0

1.5

2.0 0.5

0.0

2.5

[0.0, 0.0] [3.0, 0.0]

3.0

(a) (b)

Figure 9.31 (a) Surface plot of calculated intermolecular magnetic exchange (J π ) between two π stacked

bis(dithiazolyl) radicals 97a (R 1 = H) as a function of displacement of the two radicals along x and y

vectors. (b) Definition of x and y displacement vectors. 223 (Reprinted with permission from [223]. Copyright
2009 American Chemical Society.) A full-colour version of this figure appears in the Colour Plate section of
this topic.

R 2 =

and Rassat's adamantyl dinitroxide, which has the highest T C among all nitroxides. 250 Among non-nitroxide
radicals, the radical ion salt C 60 + • TDAE − (TDAE

tetrakis(dimethylamino)ethylene) deserves mention
as the material with the highest T C (16 K) for a material based exclusively on first row elements. 251
The magnetically ordered thiazyl-based radicals are listed in Table 9.3. A diverse range of molecular
structure types are represented, and the magnetic ordering temperatures are generally much higher than
is typically found for the nitroxide-based magnets. The first reported magnetically ordered thiazyl radical
was Rawson's cyano-substituted perfluorphenyl 1,2,3,5-dithiadiazolyl 155 . 252 This discovery generated a
great deal of interest, not only as the first example of a thiazyl radical to magnetically order, but also
because the ordering temperature of 36 K was over an order of magnitude higher than the previous record
for neutral radical magnets. The magnetically ordered state in this system is actually antiferromagnetic , but
one in which the ordering is canted - a phenomenon which arises when the antiferromagnetic alignment
of spins in two sublattices is not entirely antiparallel. As a result, the material does exhibit spontaneous
magnetization below T C but the magnetization is much smaller than would be expected for ferromagnetic
ordering. The only other magnetically ordered dithiadiazolyl is the p -nitro-perfluorophenyl analogue 156
which orders ferromagnetically below 1.3 K 118
There are a few 1,3,2-dithiazolyl radical based magnets. Benzo-1,3,2-dithiazolyl 69 was initially charac-
terized as a (diamagnetic)

=

dimer at room temperature. 165 The discovery of magnetic bistability in other
1,3,2-dithiazolyls prompted a subsequent investigation of the high temperature magnetic behavior of 69 . 253
Indeed this radical undergoes a phase transition to a paramagnetic state at 346 K and reforms the diamag-
netic state upon cooling to

π

270 K. However, upon rapid cooling the paramagnetic state (of unknown solid
state structure) remains stable all the way down to 11 K, whereupon antiferromagnetic ordering sets in.
Awaga has also investigated the magnetic properties of salts of the benzobis(1,3,2-dithiazole) radical
cation, 80 + .TheGaCl 4 − 254,255

∼

and FeCl 4 − 256 salts initially crystallize as solvates (acetonitrile and acetone,