Cubic assembly of a geometrically frustrated {Fe12} spin cluster

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 60000 A3 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 Si = 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.