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Slow magnetic relaxation and electron delocalization in an S = 9/2 iron(II/III) complex with two crystallographically inequivalent iron sites
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Image of FIG. 1.
FIG. 1.

Crystal structure of [Fe2 L(μ-OAc)2]ClO4, 1. The hydrogen atoms have been omitted for clarity and the two perchlorate anions are each half-occupied.

Image of FIG. 2.
FIG. 2.

The temperature dependence of χ M T of 1 measured in an applied dc field of 0.02 T, black, and 1 T, red. The black and red solid lines are a fit below 20 K with g = 1.91 and 1.92 and D 9/2 = −1.04 and −0.76 cm−1, and between 20 and 300 K with B = 950 cm−1, J = −32(2) cm−1, and g = 1.90(1). Inset: The corresponding temperature dependence of 1/χ M of 1 with a linear Curie-Weiss law fit between 2 and 300 K. The results obtained at 0.02 and 1 T are superimposed upon each other.

Image of FIG. 3.
FIG. 3.

The low-temperature magnetization of 1 obtained at the indicated applied dc fields. The black lines represent fits of the magnetization. Inset: the dc magnetization of 1 measured at 2 K.

Image of FIG. 4.
FIG. 4.

The variable-frequency out-of-phase ac magnetic susceptibility of 1, measured at 1.74 K, black, 1.8 K, red, 1.9 K, green, 2.0 K, blue, and 2.1 K, magenta. Inset: An Arrhenius plot of the relaxation time. The solid red line corresponds to a linear fit with U eff = 9.8 cm−1.

Image of FIG. 5.
FIG. 5.

The iron-57 Mössbauer spectra of 1 obtained at the indicated temperatures. The black solid line is the result of the fit described in the text and the supplementary material (Ref. 32) The red and blue solid lines are the two spectral components in the fit and are tentatively assigned to Fe(1) and Fe(2), respectively.

Image of FIG. 6.
FIG. 6.

Possible relaxation path shown as red arrows between the |9/2> and |−9/2> states via excited states within the 10-fold multiplet ground state of 1.

Image of FIG. 7.
FIG. 7.

The temperature dependence of the observed average hyperfine field, circles, and of the average hyperfine field calculated, solid line, for a Boltzmann population of the left or right branch of the |m t > states shown in Fig. 6.

Image of FIG. 8.
FIG. 8.

An Arrhenius plot of the logarthim of the relaxation frequency in 1, where the red and blue points correspond to low and high temperature regimes.

Image of FIG. 9.
FIG. 9.

Intervalent charge transfer absorption band in 1 measured in chloroform, blue; dichloromethane, red; nitrobenzene, black; acetone, green; acetonitrile, magenta; dimethylformamide, cyan; and dimethylsulfoxide, purple. The first five solvents lead to very similar absorption bands.

Image of FIG. 10.
FIG. 10.

Cyclic voltamogram of 1 measured in acetonitrile.

Image of Chart a1.
Chart a1.

The macrocyclic ligands, H2 L and H2 L 1 , used in the preparation of 1, left, and 2, right, respectively.


Generic image for table
Table I.

Crystallographic results for 1.

Generic image for table
Table II.

Bond distances, in Å, and bond angles, in deg, for 1 and a comparison with 2.

Generic image for table
Table III.

Mössbauer spectral parameters for 1.a


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Slow magnetic relaxation and electron delocalization in an S = 9/2 iron(II/III) complex with two crystallographically inequivalent iron sites