This anion (“ANN-eye-on”) is reduced in the most common redox couple for dye-sensitized solar cells. For 10 points each:
[10h] Name this hyper·valent anion used as a model system for three-center, four-electron bonding. Thio·sulfate reduces this ion, dissociating one of its covalent bonds, in a common colori·metric redox titration.
ANSWER: tri·iodide [or I3-- (“I-three-minus”); reject “iodide”]
[10e] Hyper·valent species like tri·iodide violate this basic principle of chemical bonding. According to this rule, the sum of lone pairs and bonding pairs of electrons on every main-group atom is four.
ANSWER: octet rule
[10m] Photo·chemists use tri·iodide to simulate the hyper·valent transition state of this organic reaction mechanism. In this concerted mechanism, donation of a lone pair into a sigma-star orbital coincides with leaving group departure.
ANSWER: SN2 [or bimolecular nucleophilic substitution; prompt on substitution or nucleophilic substitution]
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