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Micromodulation: induction of intramolecular electron transfer by solvate molecule dynamics in the iron acetato oxo methylpyridine mixed-valence complex [Fe3O(O2CCH3)6(3-Me-py)3](solvate)

Cited 79 time in Web of Science Cited 68 time in Scopus
Authors
Oh, Seung Mo; Wilson, Scott R.; Hendrickson, David N.; Woehler, Scott E.; Wittebort, Richard J.; Inniss, Daryl; Strouse, Charles E.
Issue Date
1987-02
Publisher
American Chemical Society
Citation
J. Am. Chem. Soc. 1987, 109, 1073
Abstract
The oxo-centered, trinuclear, mixed-valence iron acetate complexes [Fe30(02CCH3)6(3-Me-py)w3h]e.reS S, = CH,CN (I), toluene (Z), 3-methylpyridine (3), and benzene (4), have been prepared, and the intramolecular electron transfer
properties in the solid state have been studied. It is found that the rate of electron transfer is dramatically influenced by changing
the solvate molecule. The complex 1 crystallizes in the monoclinic space group P2,/c with 4 molecules in a unit cell which
has dimensions a = 12.760 ( 5 ) A, b = 26.233 (1 1) A, c = 14.819 ( 5 ) A, and /3 = 116.20 (3)'. Compound 2 crystallizes in
the triclinic space group Pi with 2 = 2, a = 13.056 (4) A, b = 15.902 (3) A, c = 12.896 (2) A, a = 102.82 (2)O, /3 = 118.96
(Z)', and y = 70.02 (2)'. The complex 3, isostructural with 2, was characterized in the triclinic space group Al with Z =
4: at 128 K, a = 12.964 ( 5 ) A, b = 12.976 (4) A, c = 29.293 (9) A, a = 84.01 ( 1 ) O , /3 = 94.41 (l)', and y = 121.76 (1)';
at 298 K, a = 13.114 (4) A, 6 = 13.052 (4) A, c = 30.054 ( 5 ) A, a = 85.81 (4)', /3 = 95.23 (4)', and y = 120.99 ( 5 ) ' . The
complex 1 has valence-trapped electronic states from 120 to 298 K on the Mossbauer time scale, and non-equivalent metal
sites are seen in its single-crystal X-ray structure. The other three complexes are isostructural as indicated by the single-crystal
X-ray structures of 2 and 3 and by a comparison of room-temperature powder X-ray diffraction patterns determined for all
three complexes. The three complexes 2, 3, and 4 also exhibit similar Mossbauer spectra. At temperatures below - 100 K
there are two doublets in the area ratio of two (high-spin Fell') to one (high-spin Fe"). Increasing the sample temperature
of 2, 3, and 4 above - 100 K leads to the appearance of a third average-valence doublet with a small spectral area. Eventually
the spectrum changes upon increasing the temperature to become a single-average doublet. The X-ray structural work for
3 carried out at 298 and 128 K shows that the dimensions of the Fe30 triangular complex change appreciably with temperature.
The Fe, triangle of 3 at 128 K is asymmetric with three inequivalent Fe ions; the triangle becomes more equilateral at the
higher temperature. The solid-state packing arrangement of 2, 3, and presumably 4 consists of Fe30 units arranged twodimensionally
in layers with the solvate molecule located in an open space made by three neighboring Fe30 molecules. In
the case of 1 CH3CN molecules are sandwiched between pairs of Fe30 molecules. The Fe30 complexes in 2 and 3 adopt a
symmetric conformation with all three 3-methylpyridine ligands approximately perpendicular to the Fe30 plane, while in 1
two of the 3-methylpyridine ligands are parallel to the Fe30 plane. The effects of conformation on the charge distribution
and intramolecular electron-transfer rate are discussed in light of these and previously reported results. Intramolecular electron
transfer is slow in 1 because the environment about the Fe30 complexes in 1 leads to an asymmetric complex with inequivalent
iron ions. This inequivalence introduces appreciable potential-energy barriers for intramolecular electron transfer. In the
case of 2,3, and 4 it is suggested that an order-disorder phase transition involving motion of the solvate molecules influences
the rate of intramolecular electron transfer. A single-crystal 2H NMR study of 2 with perdeuterated toluene shows that at
293 K the toluene solvate molecules are involved in two motions. There is a twofold ring flip about the para axis, and the
toluene solvate molecule is jumping between two lattice positions. Variable-temperature (290 to 140 K) 2H NMR data are
presented for a microcrystalline sample of 2 with perdeuterated toluene to show that, while the solvate molecule motion has
not completely stopped by 140 K, the motion has slowed down considerably.
ISSN
0002-7863 (print)
1520-5126 (online)
Language
English
URI
http://hdl.handle.net/10371/5633
DOI
https://doi.org/10.1021/ja00238a015

https://doi.org/10.1021/ja00238a015
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College of Engineering/Engineering Practice School (공과대학/대학원)Dept. of Chemical and Biological Engineering (화학생물공학부)Journal Papers (저널논문_화학생물공학부)
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