Stabilization of homopolyatomic cations of iodine in anhydrous hydrogen fluoride

Abstract

1669very well with the lower ligand field states and it seems unlikely that relaxation to those states could account for the observed ligand substitution products. Focusing on the ligand substitution products from the rhodo ion in chloride-containing solutions, both with and without oxygen, it is interesting to note that the yield of the aquo pentaammine and aquo erythro ions varies from oxygenated to deoxygenated solutions, whereas the yield of the chloro erythro ion is independent of oxygen.Due to the lability of Cr(I1) systems it is reasonable to suggest that the increase in the yield of the bridge cleavage product in oxygenated systems is in some way related to the charge-transfer process. The fact that some aquo pentaammine is formed in the absence of oxygen supports the suggestion made above that the Cr(I1) that is formed in the charge-transfer process is quickly reoxidized to Cr(II1) by geminate recombination with the chloride radical in the ion pair. The invariance of the chloro erythro yield suggests that it arises from a state whose reactivity is unaffected by the presence or absence of oxygen. We propose that at least two states, the charge-transfer state and the L3 state, are involved in the 254-nm photolysis and that the chloro erythro product arises solely from the L3 state, while the aquo pentaammine and aquo erythro products arise at least from the charge-transfer state and perhaps from both states. Given that no bridge cleavage is observed in L, and Lz, it is tempting to suggest that all of the aquo pentaammine arises from the charge-transfer state but that some of the aquo erythro arises from the L3 state.The general conclusions reached here about the nature of the states involved in the photochemistry following 254-nm excitation are further supported by recent preliminary experiments on the rhodo ion following excitation at 249 and 195 nm using KrF and ArF rare-gas-halide lasers. Although it has proven difficult to determine quantum yields from these experiments, due to problemswith measuring the intensities of the very intense laser pulses, we have measured relative amounts of photoproducts in several experiments. The following trends have been observed:1. The photochemistry observed at 249 nm is similar to that observed at 254 nm except that the yield of Cr(VI), relative to that of the other products, has increased by 20-30% and the ratio of aquo pentaammine to aquo erythro has also increased.2. At 195 nm, where, in nitrate media, photochemistry of the nitrate ion is expected to be important, the ratio of nitrite formed to Cr(V1) is greater than 20/1.These results are consistent with preparation of a state at 249 nm that is more charge transfer and less L3 in character than that prepared at 254 nm and with reactions at 254 nm in which nitrate photochemistry is of minimal importance. ConclusionThe production of Cr(V1) species from the charge-transfer photolysis has been quantified and an ion-pair model proposed to explain the observations. The yield of Cr(V1) should parallel the yield of Cr(I1...

On the Commonality of Speciation of Inorganic Solutes in Superacids, Strong Bases, Molten Salts, and Water

“…[19] This is the only such study in HF that has been reported. However, virtually all of the pioneering work on generation in solution of cations of iodine, bromine, sulfur, selenium, and tellurium had emanated earlier from Gillespie's group at McMaster University, Ontario.…”

“…Electrophilic cations which are stable in strongly acidic solutions require very weakly nucleophilic counter-ions to be stabilised in the solid state. Using Gillespie's spectral data to identify iodine cations in HF solutions, Besida and O'Donnell [19] determined the acidity thresholds at which polyiodine cations were formed in HF solutions. They treated excess of iodine with controlled amounts of elemental F 2 in HF solutions ranging from basic to strongly acidic.…”

“…[2e] Homopolyatomic nonmetal cations are susceptible to step-wise disproportionation reactions on gradual addition of base to solutions of the cations in superacids. Quantitative investigation [19] has shown that with increasing basicity, the cation I 2 ϩ in HFϪSbF 5 disproportionates firstly to I 3 ϩ and IF 5 , Equation (9), then to I 5 ϩ and IF 5 , Equation (10), and finally to I 2 and IF 5 , Equation (11):…”

Homopolyatomic and heteropolyatomic halogen cations

“…Sodium fluoride and the Lewis acids NbF5, TaFs, and SbF5 have been used to fix the levels of basicity and acidity in the solvent anhydrous HF in order to establish the acidity thresholds above which the cations Is+, 13+, and I,+ can be generated in solution [49]. Addition of an excess of the base Fcauses disproportionation of each of the cations to I2 and IF5.…”

Elemental Iodine or Diphenyl Diselenide in the [Bis(trifluoroacetoxy)iodo]benzene‐Mediated Conversion of Alkynes into 1,2‐Diketones

“…The reduced efficiency of the reactions carried out with iodine could also probably be explained by the fact that when elemental iodine is treated with PIFA a series homopolyatomic iodine‐containing cations can be produced together with the expected I + species, these are particularly stable in the presence of Lewis acids,16 but are ineffective in the desired reactions.…”