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 344

(a) (b) (c)

Figure9.14 X-raystructuresof1,2,3-dithiazolylradicals(a) 91 ,(b) 92 ,and(c) 93 .

A total of four 1,2,3-dithiazolyl radicals have been structurally characterized - each of which adopts a
different structure type (Figure 9.14). 2,3-Naphtho-fused derivative 91 has a cis -cofacial dimer structure
(Figure 9.14a) - albeit one in which the two rings are tilted significantly, as evidenced by the disparate
S-S inter-radical distances of 3.053 and 3.309 A 176 - while the tricyclic species 92 adopts a cofacial but
centrosymmetric dimer structure (Figure 9.14b), in which each of the two inter-radical S-S contacts (3.23 A)
involve the dithiazole S2 and the thiadiazole S (Figure 9.13b). 177 The (pentafluorophenyl)(chloro)radical
93 has a twisted (“gauche”) structure (Figure 9.14c) with an intradimer S-S contact distance of 3.299 A, 173
and isothiazole-substituted radical 94 is monomeric and adopts a slipped stacked structure. 174 In all of

the dimerized derivatives, it is noteworthy that the S-S distances between rings are generally longer than
the corresponding S-S interactions in other kinds of thiazyl radical dimers.

π

Cl

Cl

C 6 F 5

N

N S

S

N

S

S S

S

S S

S

N N

N

N

Cl S

N

N

Cl

91 92 93 94

Oakley has attempted to incorporate selenium and even tellurium into the 1,2,3-dithiazolyl frame-
work. The 1,2-naphtho-fused radicals 95a-c - in which one or both of the sulfur atoms is replaced by
selenium - could all be synthesized and spectroscopically characterized; the introduction of selenium in
either or both chalcogen positions (E 1 ,E 2 ) appears to have minor consequences for the radicals' overall
electronic structure, but isolation of the selenium radicals was thwarted by their thermal instability. 176
The same comparative features are true for the benzo fused selenium radical 96a . 178 Attempts to gen-
erate tellurium-based radical 96b failed, possibly because the corresponding tellurathiazolium cation is
strongly associated in solid state and solution. Indeed, while the electrochemical reduction of the thiasele-
nazolium cation ( 96a + ) follows closely the behavior of the analogous benzo-1,2,3-dithiazolium cation, the
corresponding thiatellurazolium cation 96b + is irreversibly reduced at much higher potentials. 178

a E 1 =S,E 2 =Se
b E 1 =Se,E 2 =S
c E 1 =E 2 =Se

E 1
E 2

S

a E=Se
b E=Te

E

N N

96

95