Theoretical Studies of 1,2,3,5-Dithiadiazolylium Heterocycles

Theoretical calculations have been performed by several workers on the RCNSSN+ cation (R = H, H2N, Cl) in order to rationalize the nature of UV/visible spectra (85JST1 86IC2119 89JA6147 see also Section 

Modification of such orbitals by substituent groups occurs readily, most conspicuously for substituents possessing lone-pairs, e.g., H2N— and Cl— (85JST1) these lone pairs affect the lowest energy electronic transitions and therefore the colors of these materials in solution (see Section 

Several comparative studies of molecular structure in 2+ and 2 rings have been undertaken [89JCS(D)2229 90JCS(D)2793 91JCS(D)1105 92CBR148 92MI2] frontier orbitals have proved very helpful in rationalizing differences in both structure (e.g., S—S bond distances) and reactivity. 

Some 7r-donor anions (such as S3N3 ), which interact out-of-plane with the 2+ cation, facilitate charge transfer into the 7r-based unoccupied molecular orbital which is of a2 symmetry and therefore antibonding with respect to both dss and dSN (see Fig. 4a). Consequently, salts of this type exhibit longer SS bonds than salts of weakly interacting anions such as AsF6 . Similarly, complete reduction of 2+ to 2 produces partial occupancy of the same a2 orbital and thus dss in (2 )2 is greater than in 2+ (Fig. 4b). In the extreme, when filled metal orbitals donate electron density into the 

Until recently, the dithiadiazolylium rings have not been conveniently studied by nmr because of the low natural abundance of S = 1/2 isotopes [33S 0.76%,, 5N 0.37%, and 13C 1.1% (80MI1)] and the poor resolution often associated with 14N nmr. However, with improvements in nmr technology, a few data have become available (Table II). Nuclear magnetic resonances for substituent groups generally show a shift to low field (rela- 

---