A stable and strongly ferromagnetic Fe 17 O 10 - cluster with an accordion-like structure.

Isolated clusters are ideal systems for tailoring molecule-based magnets and investigating the evolution of magnetic order from microscopic to macroscopic regime. We have prepared pure Fe n - (n = 7-31) clusters and observed their gas-collisional reactions with oxygen in a flow tube reactor. Interestingly, only the larger Fe n - (n ≥ 15) clusters support the observation of O 2 -intake, while the smaller clusters Fe n - (n = 7-14) are nearly nonreactive. What is more interesting is that Fe 17 O 10 - shows up with prominent abundance in the mass spectra indicative of its distinct inertness. In combination with DFT calculations, we unveil the stability of Fe 17 O 10 - within an interesting acordion-like structure and elucidate the spin accommodation in such a strongly ferromagnetic iron cluster oxide.