Abstract: The conjugate acids of benzo-2,1,3-selena- and
benzo-2,1,3-telluradiazole are the simplest members of the family of
N-substituted chalcogenadiazolium cations. Four crystalline phases that in
principle contain such molecular ions were isolated and structurally
characterized:
C_{6}H_{4}(NH)_{2}TeCl_{2},
[C_{6}H_{5}(NH)]_{3}[C_{6}H_{4}(NH)_{2}TeCl_{4}]Cl,
C_{6}H_{4}N(NH)SeCl and
C_{6}H_{4}N(NH)SeCl · 1/2
[H_{5}O_{2}]Cl. The stepwise protonation
of benzo-2,1,3-teluradiazole in DMSO solution was monitored by
^{1}H NMR, providing an estimate of the basicity of this
molecule relative to pyridine. While most of the structures are consistent with
the chalcogen in oxidation state II, the molecular geometry of
C_{6}H_{4}(NH)_{2}TeCl_{4}
is suggestive of oxidation state IV. The relationship between the two
structural types was examined with DFT calculations.
