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

The synthesis, structure, and magnetic properties of three related iron(III)-oxo clusters are reported, [FeO(OCPh)(mda)(HO)] (), FeO(OH)(OCMe)(mda) (), and FeO(OH)(OEt)(OCMe)(mda) (), where mdaH is -methyldiethanolamine. was prepared from the reaction of FeO(OCPh)(HO) with mdaH in a 1:2 ratio in MeCN, whereas and were prepared from the reaction of FeCl/NaOCMe/mdaH in a 2:∼13:2 ratio and FeCl/NaOCMe/mdaH/pyridine in a 2:∼13:2:25 ratio, respectively, both in EtOH. The core of consists of a central octahedral Fe ion held within a nonplanar Fe loop by three μ-O and three μ-RO arms from the three mda chelates. The cores of the cations of and consist of an :: three-layer topology, in which a central Fe () or Fe () layer is sandwiched between two Fe layers . The layers structurally resemble with the additional Fe added at the center to retain virtual symmetry. The central Fe layer of consists of a {Fe(μ-O)(μ-OH)} cubane with an Fe on either side attached to cubane O ions, whereas that of has the same cubane but with an {Fe(μ-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 = / for and = 0 for and . All Fe pairwise exchange parameters () for - were estimated by two independent methods: density functional theory (DFT) calculations using broken symmetry methods and a magnetostructural correlation previously developed for high-nuclearity Fe/O complexes. The two approaches gave satisfyingly similar 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 Fe ion.