Extreme environmental sensitivity of the rate of intramolecular electron transfer in mixed-valence 1',1'''-dibenzylbiferrocenium triiodide

Abstract

The extreme sensitivity of the rate of intramolecular electron transfer for the mixed-valence 1',1"'-dibenzylbiferrocenium cation to different environments is explored. Two different crystalline morphologies of 1',1"'-dibenzylbiferronium triiodide (1) could be identified by their different crystal habits (needle and plate-like crystals). They are structurally characterized by single-crystal and powder X-ray diffraction techniques. The single-crystal X-ray structure of a parallelepiped (needle) crystal of 1 at 298 K shows that this polymorph crystallizes in the triclinic space group Pi. The unit cell parameters are a = 9.900 (1) A, b = 9.962 (1) A, c = 10.193 (2) A, CY = 112.97 (2)O, @ = 114.50 (I)O, and y = 97.80 (1)O with Z = 1. The structure is also reported for the same crystal at 135 K. An analysis of the full sphere of data again indicates Pi as the appropriate space group with unit cell constants a = 9.782 (2) A, b = 9.930 (1) A, c = 10.108 (2) A, CY = 113.08 (2)O, @ = 114.08 and y = 98.06 (1)' with 2 = 1. Refinements were carried out with 2990 (6a) and 3315 (6a) observed reflections at 298 and 135 K, respectively, to give R = 0.026 and R, = 0.037 at 298 K and R = 0.025 and R, = 0.038 at 135 K. Both the mixed-valence l', 1"'-dibenzylbiferrocenium cation and triiodide anion are centrosymmetric at both temperatures. The two crystallographically equivalent metallocene moieties of the cation have dimensions intermediate between those of Fe" and Fell' metallocenes. The packing of 1 consists of weakly interacting 1',1"'-dibenzylbiferronium cations forming chains which are surrounded by and separated from other similar chains by the triiodide anions. The 296 K single-crystal X-ray structure of the plate-like crystals of complex 1 show that this pol morph crystallizes in the monoclinic space group P2,/n. The unit cell parameters are a = 22.286 (9) A, b = 19.413 (10) 1, c = 22.840 ( 5 ) A, and @ = 98.55 (3)O with Z = 12. Refinementwas carried out with 4486 (6a) observed reflections to give R = 0.089 and R, = 0.131. There are three different l',l"'dibenzylbiferrocenium cations and three different Ipanions in the asymmetric unit. There is not crystallographically imposed symmetry for any of the cations or anions. The temperature dependencies of the S7Fe Mossbauer spectra of the Pi and P2,/n polymorphs of complex 1 differ widely. A sample of needle crystallites has a Mossbauer spectrum characteristic of a valence detrapped mixed-valence species down to a temperature of 25 K. On the other hand, a sample of the P 2 , / n plate-like crystals exhibits a Mhsbauer spectrum characteristic of a valence-trapped species which remains trapped even at 300 K. It was surprising to find that mild grinding of the needle crystallites produces a valence-trapped Mossbauer signal in addition to the valence detrapped signal. Appreciable amounts of the trapped species persist for the ground Pi needles even up to 300 K. At 7 K, the EPR spectrum of a recrystallized microcrystalline sample of 1 consists of the superposition of three signals: t...

Polytriazolium poly(ionic liquid) bearing triiodide anions: Synthesis, basic properties and electrochemical behaviors

“…The change in the solubility of the iodide PIL in acetone after the treatment of I 2 indicated that triiodide-based PILs were successfully synthesized, which was further identified by elemental analysis (Table S2). As reported, triiodide anions exist in an isolation state in solutions because they are electronically more stable instead of I 2 -Ipair in solvents, [37,38] we believe that the delocalized negative charge in triiodide vs iodide leads to weakened interaction of anions with hydrogens in the 1,2,4-triazolium heterocycle ring, which eventually results in shielding of those acidic protons. The boiling point of iodine is 184 o C, close to the observed decomposition temperature, at which iodine leaves the system and drives the equilibrium to the decomposition side.…”

1,4‐Diethynylbenzene‐Bridged [Cp*(dppe)Fe]n+ Units: Effect of 2,5‐Ethynyl Groups on the Chemical and Electronic Properties

“…[75] Many years ago, a similar behavior was also reported by Hendrickson for the 1',1'''-dibenzylbiferrocenium triiodide monocation. [76][77][78][79] Indeed, a polycrystalline sample can be regarded as a solid solution containing population of various conformers of the same molecules. In the case of complex p-1(PF 6 ) the relative conformation of the bridging ligand and the metal centers switches the magnitude of the electronic coupling between the metal centers yielding population of trapped and detrapped mixed-valence species at the spectroscopic time scale.…”

Pronounced effects of grinding on rates of intramolecular electron transfer in mixed-valence 1′,2′,1‴,2‴-tetranaphthylmethyl- and 1′,3′,1‴,3‴-tetranaphthylmethyl-biferrocenium triiodides

“…The influence of grinding sample on physical properties has been well studied for spin crossover transitions [27]. In the case of mixed-valenced biferrocenium salts, Hendrickson found a reduction of the electron-transfer rate in mixed-valence 1?,1 §-dibenzylbiferrocenium triiodide (3p, n 0/1) as a result of mechanical grinding [21]. A change in valence for a transition-metal complex is generally accompanied by the coordination sphere reorganization.…”

“…In the case of a binuclear mixed-valence biferrocenium cation, the value of g tensor anisotropy (Dg0/g jj (/g Þ ) can be used as a rough estimate of the nature of the electronic ground state of the cation. Here, we are interested in studying the influence of grinding on the electronic ground state by EPR technique [21].…”

“…It has been shown that there is an evenÁ/odd character in the number of carbon atoms of the substituents in the relationship between the crystal structure and the mixed-valenced state. The third strategy is the use of the derivatives attached to a planar substituent 3pÁ/q [13,21]. The 2-phenylethyl and 4phenylbutyl derivatives of 3p show the valence detrapping electronic state at temperature of 300 and 160 K, respectively.…”