Magnetic Properties of High-Nuclearity Fe x ‑oxo (x = 7, 22, 24) Clusters Analyzed by a Multipronged Experimental, Computational, and Magnetostructural Correlation Approach

• Published in: Inorganic chemistry 2022-07, Vol.61 (29), p.11261-11276
• Main Authors: Hale, Ashlyn R., Lott, Megan E., Peralta, Juan E., Foguet-Albiol, Dolos, Abboud, Khalil A., Christou, George
• Format: Article
• Language: English
• Subjects: Chemistry
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.2c01371

The synthesis, structure, and magnetic properties of three related iron­(III)-oxo clusters are reported, [Fe7O3(O2CPh)9(mda)3(H2O)] (1), [Fe22O14(OH)3(O2CMe)21(mda)6]­(ClO4)2 (2), and [Fe24O15(OH)4(OEt)­(O2CMe)21(mda)7]­(ClO4)2 (3), where mdaH2 is N-methyldiethanolamine. 1 was prepared from the reaction of [Fe3O­(O2CPh)6(H2O)3]­(NO3) with mdaH2 in a 1:2 ratio in MeCN, whereas 2 and 3 were prepared from the reaction of FeCl3/NaO2CMe/mdaH2 in a 2:∼13:2 ratio and FeCl3/NaO2CMe/mdaH2/pyridine in a 2:∼13:2:25 ratio, respectively, both in EtOH. The core of 1 consists of a central octahedral FeIII ion held within a nonplanar Fe6 loop by three μ3-O2– and three μ2-RO– arms from the three mda2– chelates. The cores of the cations of 2 and 3 consist of an A:B:A three-layer topology, in which a central Fe6 (2) or Fe8 (3) layer B is sandwiched between two Fe8 layers A. The A layers structurally resemble 1 with the additional Fe added at the center to retain virtual C 3 symmetry. The central Fe6 layer B of 2 consists of a {Fe4(μ4-O)2(μ3-OH)2}6+ cubane with an Fe on either side attached to cubane O2– ions, whereas that of 3 has the same cubane but with an {Fe3(μ3-O)­(μ-OH)} unit attached on one side and a single Fe on the other. Variable-temperature dc and ac magnetic susceptibility studies revealed dominant antiferromagnetic coupling in all complexes leading to ground-state spins of S = 5/2 for 1 and S = 0 for 2 and 3. All Fe2 pairwise exchange parameters (J ij ) for 1–3 were estimated by two independent methods: density functional theory (DFT) calculations using broken symmetry methods and a magnetostructural correlation previously developed for high-nuclearity FeIII/O complexes. The two approaches gave satisfyingly similar J ij values, and the latter allowed rationalization of the experimental ground states by identification of the spin frustration effects operative and the resultant relative spin vector alignments at each FeIII ion.