High nuclearity transition metal clusters have received considerable attention due their magnetic properties and the possible technological application in high density magnetic storage devices, quantum computing and spintronics. In most cases the synthetic methods to the high nuclearity metal clusters are not straightforward and final products cannot be predicted. Herein, an easy and convenient route starting from μ3-oxo trinuclear species to a high nuclear ferric cluster is developed. Following on from our work on the design of polynuclear iron carboxylates [1] a new hexadecametallic FeIII pivalate cluster, namely [Fe16O13(MeO)6(O2CCMe3)16] • CH2Cl2 (1), has been synthesized and characterized by elemental analysis, IR spectroscopy, thermogravimetric studies. Single-crystal X-ray diffraction analysis showed that complex 1 consists of 16 FeIII atoms, bridged by five μ4-O2− ions, eight μ3-O2− ions, six methoxy MeO− groups and additionally linked by 16 bridging pivalate ligands. Thus, the arrangement of FeIII atoms in 1 can be approximated as assembly of a smaller inverted Fe4 tetrahedron defined by the four Fe sites within a giant truncated tetrahedron forming by other 12 Fe sites with four triangular and four hexagonal faces (Figure 1). The study of the magnetic properties reveals an antiferromagnetic interaction between the metal ions in 1. The Figure 1 displays the results of the susceptibility measurements as a function of temperature using χ–1 m vs. temperature and the applied filed at 2 K using the M vs. H-plot. At room temperature, χmT is equal to 17.86 cm3 K mol–1, which is much smaller than the expected spin-only value for sixteen isolated FeIII ions considering an average Zeeman factor g = 2.0, that is 70.03 cm3 K mol–1. The χ–1 m vs. temperature plot shows a linear behavior above 120 K this observation is supported by a linear fit reciprocal molar susceptibility to the Curie law above 120 K, leading to C = 3.831 cm3 K mol–1 (per Fe ion) and a Weiss constant θ = –689.8 K, which indicates a strong antiferromagnetic interaction.Figure 1. The assembly of the giant truncated tetrahedron of twelve atoms of iron (grey spheres) with the incorporated smaller Fe4 tetrahedron (black spheres) showing the arrangement of 16 Fe atoms in the metallic core of 1 (left). Experimental χ–1 m vs. T plots (cgs units) of 1·at B = 0.1 Tesla. Insets: χmT vs. T (at 0.1 Tesla) and M vs. B (at 2.0 K). Acknowledgement. Financial support was provided by the European Commission (POLYMAG, contract no. 252984). [1] a) S.G. Baca, M. Speldrich, A. Ellern, S.G. Baca, P. Kögerler. Materials 4 (2011) 300−310; b) S.G. Baca, O. Botezat, I. Filippova, M. Speldrich, E. Jeanneau, P. Kögerler. Journal of Inorganic and General Chemistry (ZAAC) 637 (2011) 821−823.