Some investigations of S5N5+ compounds; X-ray crystal structure of [S5N5]Cl

Abstract

Aluminium chloride is removed from cyclopenta(azathienium) tetrachloroaluminate by tetrahydrofuran to give pure [S₅N₅]Cl and this reacts with aqueous tetrafluoroboric acid to give [S₅N₅][BF₄]. Cyclic voltammograms of [S₅N₅]Cl in liquid SO₂ show reduction of S₅N₅⁺at E_p/2^red= 0.34 V vs. a saturated calomel electrode; the process is reversible. Cyclic voltammograms of [S₅N₅][BF₄] in MeCN were more complex and a mechanism for this electroreduction is proposed. Electrodeposition of (SN)_X on platinum-foil and on (SN)_x-film cathodes was achieved by potentiostatic electrolysis. [S₅N₅]Cl crystallizes in the monoclinic space group C2/c, with a= 7.98(1), b= 14.37(1), c = 7.30(1)Å, β=97.15(5)°, and Z= 4.1 366 Observed reflections were refined to R= 0.054. The mean bond angles are NSN 111.3 and SNS 140.2°. Three of the five unique S–N distances are 158.2 pm but two [S(2)–N(2) 156.5, S(3)–N(3) 159.8 pm] are affected by short S ⋯ Cl contacts [3.277(1) and 3.148(1)Å at S(2) and 3.243(1) and 3.279(1)Å at S(3)]. Strain in the azulene-shaped cation arising from cation-anion interactions can be detected by comparing bond distances and angles with the strain-free values deduced from either bond distance–bond angle correlation functions or MNDO calculations.