Interaction of 1,2,5-Chalcogenadiazole Derivatives with Thiophenolate: Hypercoordination with Formation of Interchalcogen Bond versus Reduction to Radical Anion

Abstract

According to the DFT calculations, [1,2,5]thiadiazolo[3,4-c][1,2,5]thiadiazole (4), [1,2,5]selenadiazolo[3,4-c][1,2,5]thiadiazole (5), 3,4-dicyano-1,2,5-thiadiazole (6), and 3,4-dicyano-1,2,5-selenadiazole (7) have nearly the same positive electron affinity (EA). Under the CV conditions they readily produce long-lived π-delocalized radical anions (π-RAs) characterized by EPR. Whereas 4 and 5 were chemically reduced into the π-RAs with thiophenolate (PhS(-)), 6 did not react and 7 formed a product of hypercoordination at the Se center (9) isolated in the form of the thermally stable salt [K(18-crown-6)][9] (10). The latter type of reactivity has never been observed previously for any 1,2,5-chalcogenadiazole derivatives. The X-ray structure of salt 10 revealed that the Se-S distance in the anion 9 (2.722 Å) is ca. 0.5 Å longer than the sum of the covalent radii of these atoms but ca. 1 Å shorter than the sum of their van der Waals radii. According to the QTAIM and NBO analysis, the Se-S bond in 9 can be considered a donor-acceptor bond whose formation leads to transfer of ca. 40% of negative charge from PhS(-) onto the heterocycle. For various PhS(-)/1,2,5-chalcogenadiazole reaction systems, thermodynamics and kinetics were theoretically studied to rationalize the interchalcogen hypercoordination vs reduction to π-RA dichotomy. It is predicted that interaction between PhS(-) and 3,4-dicyano-1,2,5-telluradiazole (12), whose EA slightly exceeds that of 6 and 7, will lead to hypercoordinate anion (17) with the interchalcogen Te-S bond being stronger than the Se-S bond observed in anion 9.

[1,2,5]Selenadiazolo[3,4‐b]pyrazines: Synthesis from 3,4‐Diamino‐1,2,5‐selena­diazole and Generation of Persistent Radical Anions

“…According to XRD (Figures 1 and 2), geometries of the selenadiazole rings of 6 and 5a,g are quite similar. For 6 ( Figure 1), the geometry of the selenadiazole moiety is similar to that reported for 3,4-R2-1,2,5-selenadiazoles (9a, R = Ph [24] ; 9b, R = CN [25] ). In 5a,g, the Se-N (1.786 and 1.806 Å), C-N (1.321 and 1.327 Å) and C-C (1.436 Å) distances have typical values and are statistically indistinguishable in the two compounds.…”

Molecular Structure of Tetrakis(1,2,5-thiadiazolo)-porphyrazinatozinc(II) in Gaseous Phase

“…It can be seen that the values of structural parameters produced by the analysis of GED data for both compounds existing in gas phase -the macrocyclic complex [ZnTTDPz] and the dinitrile C 4 N 4 Sare in satisfactory agreement with the available single crystal X-ray diffraction data. [6,13] The results of GED refinement and DFT calculations show that the [ZnTTDPz] molecule has a planar structure of D 4h symmetry in the gas phase. This indicates that the displacement of the Zn atom out of plane of the molecule found in the crystal structure of [ZnTTDPz] is caused by intermolecular interactions or more exactly by «the (M ... N g ) coordination bonding» as it previously was reported by Awaga et al…”

“…At the same time it is longer by ~0.04 Å than in the gas-phase [ZnPc]. [13] The Zn-N difference between [ZnTTDPz] and [ZnPc] reflects the effect of expansion of the macrocyclic core observed when external benzene rings in the phthalocyanines are replaced by heterocyclic 1,2,5-thiadiazole moieties in TTDPz macrocycle. It should be noted that the expansion of the macrocyclic core is accompanied by rearrangement of all DFT r e X-ray [6] r Parameter GED r h1…”

“…DFT r e X-ray [13] r Bond distances Bond distances assigned to the C 4 N 4 S molecular species -1,2,5-thiadiazole-3,4-dicarbonitrile which presents in the vapor together with…”

“…In contrast with the above-mentioned [ZnTTDPz] molecule the GED geometry of the dinitrile molecule C 4 N 4 S in gas phase is similar to the X-Ray geometry in a crystalline state. [13] Investigation of gas-phase behavior of other porphyrazine analogues with fused 1,2,5-thiadiazole rings is in progress.…”