Infrared spectra, structures, and force constants of the matrix-isolated thiazyl halides CISN and BrSN

Abstract

Pyrolysis of the tetrathiatriazyl halide S₄N₃⁺X^– at low pressures furnishes the corresponding thiazyl halide XSN where X = Cl or Br but not where X = I. Infrared spectra of both CISN and BrSN suspended in argon matrices at 15 K are reported. Isotopic variations at all three atomic positions in CISN and at two positions in BrSN verify the molecular identity and indicate, through normal co-ordinate analysis, that both molecules are bent with ∠CISN = 117 ± 3° and ∠BrSN = 118 ± 3°(allowance being made for anharmonicity corrections). The force constant k_SN diminishes from 1070·9 N m^–1 for FSN through 1009·5 N m^–1 for CISN to 987·5 N m^–1 for BrSN. This trend, together with the relatively small k_SX values for all three molecules, is rationalised in a simple molecular orbital treatment which invites comparisons with molecules in the series XNO and XEEX (E = O or S).