PREPARATION AND CHARACTERIZATION OF (SENSNS)N(ASF6)2 CONTAINING THE ELECTRON-RICH AROMATIC 6-PI SENSNS2+ (N = 1) AND 7-PI SENSNS.(+) (N = 2)

Attempted syntheses of SeNSAsF6 from the reactions of SNAsF6 with Se8(AsF6)2 (4:1) or Se (1:1) gave (SeNSNS)n(AsF6)2 (n = 1 and 2), Se4(AsF6)2 and trace amounts of SeNSNe(AsF6)2 and (Se/SNSNSe)2(AsF6)2. The formation of (SeNSNS)n(AsF6)2 (n = 1 and 2) as the major product is consistent with generation of a SeNS+ intermediate which undergoes a concerted symmetry-allowed cycloaddition reaction with SN+ to give SeNSN2+. The crystal structure of SeNSN(AsF6)2 consists of disordered SeNSN2+ cations and AsF6- anions, that of (SeNSN)2(AsF6)2 consists of AsF6-anions and two independent disordered SeNSNS.+ radical cations weakly linked into a non-centrosymmetric dimer by two long Se ... S bonds [3.12(4), 3.09(2); 3.32(5), 3.16(6) angstrom]. The structure of (Se/SNSNSe)2(AsF6)2 Contains a 50:50 mixture of disordered SeNSNSe.+ and SeNSN.+ radical cations joined by two long Se/S . . . Se bonds (3.077(3), 3.138(3) angstrom]. There are significant interionic interactions in all the salts. The Se-77 [-60-degrees-C, delta(Me2Se) = 2422 nu = 10.4 Hz] and N-14 NMR [room temperature (r.t.), delta(MeNO2) = 68.9, nu = 446 Hz] spectra of SeNSNS2+ are consistent with a delocalised 6pi ring structure. The SeNSN2+ cation readily reacts with CCl3F to give ClSeNSNAsF6 the identity of which was confirmed by the determination of its crystal structure. The ESR spectrum of SeNSNS+ in SO2 solution at r.t. (g = 2.026, broad) and the spectrum of powdered SeNSNS.+ in frozen SO2 at -160-degrees-C were similar to but not identical with those of SeNSeNe.+, SeNSNSe.+ and SNSNS.+ indicative of a planar 7pi system.