Cubic assembly of a geometrically frustrated {Fe12} spin cluster

Abstract

We describe an S₄-symmetric {Fe₁₂} spin cluster [Fe₁₂O₄(OH)₂(L)₄(OAc)₈][Cl]₂ {H₄L = (HOCH₂CH₂)₂NCH₂CH₂N(CH₂CH₂OH)₂} where the iron(III) centres describe a squashed hexagonal antiprism. The clusters pack into a large cubic cell with circular cavities, lined by weak C–H⋯O interactions, and a unit cell volume of over 60 000 ų containing large solvent accessible voids. The core of the cluster is stable in solution, as confirmed by electrospray mass spectrometry. The cluster possesses a non-trivial, frustrated S = 0 ground state, due to the presence of multiple competing antiferromagnetic interactions. The finite temperature Lanczos method has been employed to calculate the temperature dependent magnetic properties of an analogous dodecanuclear S_i = 3/2 model spin system, in order to reduce the very large Hilbert space. Three archetypal models with two independent exchange coupling parameters have been employed that render a low temperature feature possible, as seen in the χ vs. T plot for the {Fe₁₂} spin cluster.