The duodecet rule

Hypervalence: A Useful Concept or One That Should Be Gracefully Retired?

In this essay the origins of the term hypervalence and its application in p-block element chemistry are considered and it is argued that the term should now be consigned to the graveyard of concepts that no longer afford any discernible value or insight, certainly from an educational perspective. In contrast, the educational merits of the octet rule are also examined where it is concluded that this rule does have significant pedagogical value, albeit mostly within the ambit of introductory level explanations. For a few of the chosen exemplar compounds, a selection of orbital-based analyses, at different levels of sophistication, are also considered, and their values appraised together with a brief survey of some of the more general computational studies which have been employed in relation to this topic.

Synthesis of [N(CH3)4]2O3SOSO2(s) and [N(CH3)4]2[(O2SO)2SO2]·SO2(s) containing (SO4)(SO2)x(2-) x = 1, 2, members of a new class of sulfur oxydianions

One mole equivalent of SO2 reversibly reacts with [N(CH3)4]2SO4(s) to give [N(CH3)4]2S2O6(s) (1) containing the [O3SOSO2](2-), shown by Raman and IR to be an isomer of the [O3SSO3](2-) dianion. The experimental and calculated (B3PW91/6-311+G(3df)) vibrational spectra are in excellent agreement, and the IR spectrum is similar to that of the isoelectronic O3ClOClO2. Crystals of [N(CH3)4]2(O2SO)2SO2·SO2 (2) were isolated from solutions of [N(CH3)4]2SO4 in liquid SO2. The X-ray structure showed that 2 contained the [(O2SO)2SO2](2-) dianion. The characterized N(CH3)4(+) salts 1 and 2 are the first two members of the (SO4)(SO2)x(2-) class of sulfur oxydianions analogous to the well-known small cation salts of the SO4(SO3)x(2-) polysulfates.