Molecular spin frustration in the [Fe4O2]8+ core: synthesis, structure, and magnetochemistry of tetranuclear iron-oxo complex [Fe4O2(O2CR)7(bpy)2](C1O4) (R = Me, Ph)

Abstract

The structural, spectroscopic, and magnetochemical characteristics of a new tetranuclear iron-oxo complex are reported. [Fe402(02CCH3)7(bpy)2](C104>y4CH2Cl2-H20 (l) crystallizes in the monoclinic space group C2/c with a = 27.261 (10) A, b = 11.789 (4) Á, c = 16.439 (5) A, ß = 118.27 (2)°, V = 4653.19 Á3, and Z = 4. The structure was refined with 2646 reflections having F > 2.33a(F), giving final R factors of 0.0644 and 0.0688 for R and Rw, respectively. The [Fe402]8+ core of the cation is structurally similar to other [M402]8+ (M = Mn, Fe) complexes which have been previously reported.The core structure consists of a tetranuclear bis^-O) cluster disposed in a "butterfly" arrangement. Two different Fe-O(oxide) bridge distances of 1.819 ( 5) Á (wing-body) and 1.926 ( 5) Á (body-body) are observed. These differences are reflected in the Mossbauer spectrum of the complex, which analyzes as two quadrupole-split doublets in the range of 100-300 K. Each of the doublets has parameters characteristic of high-spin Fe(III) ions.NMR spectra are reported for two [Fe402]8+ complexes. Assignments for all resonances were made on the basis of chemical shift data for two related complexes and one deuterated complex as well as measurements of spin-lattice (T¡) relaxation times. The magnetic susceptibility of complex 1 was measured in the range of 5.01-277.4 K. The effective moment per molecule decreases gradually from 4.20 µ at 277.4 K to 0.82 µ at 5.01 K, indicating a diamagnetic 5 = 0 ground state. A detailed theoretical analysis of the susceptibility data using a spin Hamiltonian approach gives a value for the "wing-body" Fe-Fe magnetic exchange interaction parameter of Jwb = -45 cm'1. It was interesting to find that the "body-body" interaction Jbb is indeterminate and can only be described as being more positive than -15 cm"1. The lack of definition of Jbb is due to spin frustration, where the relative magnitudes of the antiferromagnetic Jwb and 7bb interactions result in a net alignment of the spin vectors on the two body dioxo bridge core Fem ions. The significance of these results as they pertain to exchange coupling in iron-oxo proteins is discussed.

Iron(III)‐Pivalate‐Based Complexes with Tetranuclear {Fe4(μ3‐O)2}8+ Cores and N‐Donor Ligands: Formation of Cluster and Polymeric Architectures

“…[18] but also in ref. [16,[19][20][21][22][23] . We have summarized several characteristic data of these compounds in [22] and [L 2 Fe 4 (μ 3 -O) 2 (Ph 2 C(OH)CO 2 ) 3 (sao) 2 ] (ClO 4 ), [25] in which L = 1,4,7-trimethyl-1,4,7-triazacyclononane and H 2 sao = salicylaldoxime, are the exceptions from this family.…”

Trovacenyl-based organometallic triradicals: Spin frustration, competing interactions and redox splitting

“…It should be noted that both fits are unique solutions and that no other solution fit the data as wetl, in contrast to tases studied by Iwamura [31] and Hendrickson [34]. The experimental data points of 4 could be fitted best with J= -0.68(1) cm -t anda = 1, meaning that the coupling is antiferromagnetic and that 4 shows the effect of spin frustration (twofold degenerate spin ground state [Edoublet, 1 -= Edoublet, 2 = 0]).…”

Magnetic Behavior and Antibacterial Activity of Iron (Iii) Complexes

“…The complexes were synthesized according to the reported procedure by McCusker, et al 14 . To an orange solution of FeCl 3 ·6H 2 O (2.67 mmol) in ethanol (50 mL) was treated with sodium acetate (6.63 mmol) and the respective ligand (1.43 mmol).…”

“…The expression for the molar paramagnetic susceptibility, χ M derived by using the Van Vleck equation 14 .The solid line in the Figure 6 represent the result obtained from fitting to the experimental data using a least-square fitting routine with the EPR determined g value of 1.9 as a constant parameter. The best fit was found with J a = -16.20 cm -1 and J b = -9.78 cm -1 , with R= 6.22x10 -3 An examination of the Table 1, in which the magnetic properties of other complexes of this kind are tabulated reveals that, J b constant is much less than J a constant.…”