High-Yield Syntheses and Reactivity Studies of Fe₁₀“Ferric Wheels”: Structural, Magnetic, and Computational Characterization of a Star-Shaped Fe₈Complex

Abstract

Convenient, high-yield routes have been developed to [Fe 10(OMe) 20(O 2CR) 10] ( 1) "ferric wheels" involving the alcoholysis of [Fe 3O(O 2CR) 6(H 2O) 3] (+) salts in MeOH in the presence of NEt 3. Reactivity studies have established [Fe 10(OMe) 20(O 2CMe) 10] ( 1a) to undergo clean carboxylate substitution with a variety of other RCO 2H groups to the corresponding [Fe 10(OMe) 20(O 2CR) 10] product. In contrast, the reaction with phenol causes a nuclearity change to give a smaller [Fe 8(OH) 4(OPh) 8(O 2CR) 12] ( 2) wheel. Similarly, reactions of [Fe 10(OMe) 20(O 2CR) 10] with the bidentate chelate ethylenediamine (en) cause a structural change to give either [Fe 8O 5(O 2CMe) 8(en) 8](ClO 4) 6 ( 3) or [Fe 2O(O 2CBu (t))(en) 4](NO 3) 3 ( 4), depending on conditions. Complex 3 possesses a "Christmas-star" Fe 8 topology comprising a central planar [Fe 4(mu 4-O)] (10+) square subunit edge-fused to four oxide-centered [Fe 3(mu 3-O)] (7+) triangular units. Variable-temperature, solid-state dc and ac magnetization studies on complexes 1a- 4 in the 5.0-300 K range established that all the complexes possess an S = 0 ground state. The magnetic susceptibility data for 4 were fit to the theoretical chi M versus T expression derived by the use of an isotropic Heisenberg spin Hamiltonian and the Van Vleck equation, and this revealed an antiferromagnetic exchange parameter with a value of J = -107.7(5) cm (-1). This value is consistent with that predicted by a previously published magnetostructural relationship. Theoretically computed values of the exchange constants in 3 were obtained with the ZILSH method, and the pattern of spin frustration within its core and the origin of its S = 0 ground state have been analyzed in detail.

Fluorescent Naphthalene Diols as Bridging Ligands in LnIII Cluster Chemistry: Synthetic, Structural, Magnetic, and Photophysical Characterization of LnIII8 “Christmas Stars”

“…The resulting [Tb 8 (μ 4 -O)(μ 3 -OR) 8 (μ-OR) 8 ] 6+ core has a “Christmas-star” topology (Figure , right), which is unprecedented in 4f-metal cluster chemistry. Similar metal cores have been previously seen only in Fe 8 cluster chemistry, albeit with the central subcore possessing a square-planar geometry . In complex 3 , the central μ 4 -O 2– (O1), whose protonation level was confirmed by oxygen BVS calculations (BVS = 2.05), is distorted tetrahedral [Tb–O–Tb = 99.2(1)–134.7(2)°], and the [Tb 3 (μ 3 -OR) 2 (μ-OR) 2 ] 5+ triangular units are essentially isosceles, the short separations [3.475(6)-3.523(6) Å] being the four (oxido)-bis(μ 3 -alkoxido)-bridged edges fused with the central tetrahedron.…”

Using Predefined M3(μ3-O) Clusters as Building Blocks for an Isostructural Series of Metal–Organic Frameworks

“…This is not surprising as a few previous reports show that amine appendage onto trimeric SBUs in MOFs can sometimes lead to framework decomposition . Further, a previous work of Christou et al, albeit focused on molecular magnetism, shows that the Fe 3 O core decomposes into an Fe 8 wheel cluster upon introduction to triethylamine . Binding of the strong N-containing Lewis base to the metal likely decreases the strength of the M−μ 3 -oxo bond, decreasing the structural integrity of the cluster.…”

“…40 Further, a previous work of Christou et al, albeit focused on molecular magnetism, shows that the Fe 3 O core decomposes into an Fe 8 wheel cluster upon introduction to triethylamine. 41 Binding of the strong N-containing Lewis base to the metal likely decreases the strength of the M−μ 3 -oxo bond, decreasing the structural integrity of the cluster. This result implies that these clusters are likely not always suitable to synthesize MOFs with nitrogen-containing ligands.…”

Magnetism on a Mesoscopic Scale: Molecular Nanomagnets Bridging Quantum and Classical Physics

“…where a 1 = a sc 1 and b 1 = b sc 1 in the semiclassical limit (see section 3 for wheels), but they can be modified as quantum fluctuations get stronger to provide a more accurate description [29]. Results generated with equation (2) compare very well with the predictions of equation 1for even AFM wheels, and the semiclassical dimer HamiltonianĤ AB has proven to be a valuable tool for the calculation of the low-energy behavior for a large number of MNMs [32,39,46], see also the next section. It is noted here that this approach can be generalized for more than two sublattices, as is the case for the Fe 30 Keplerate molecule [8,9,10,11,47,48,49].…”