Magnetostructural correlation in isolated trinuclear iron(iii) oxo acetate complexesElectronic supplementary information (ESI) available. See DOI: 10.1039/c7cp07549a

We elucidate the correlation between geometric structures and magnetic couplings in trinuclear iron( iii ) oxo acetate complexes [Fe 3 O(OAc) 6 (Py) n ] + ( n = 0, 1, 2, 3) when isolated and trapped as gaseous ions. Structural information arises from Infra Red-Multiple Photon Dissociation (IR-MPD) and Collision Induced Dissociation (CID) experiments in conjuction with Density Functional Theory (DFT) based calculations. We simulate the antiferromagnetic couplings between the Fe III (d 5 ) centers by employing a Broken Symmetry approach within our DFT calculations, and we extract the associated antiferromagnetic coupling constants. Coordination of one, two or three axial pyridine ligands to the [Fe 3 O(OAc) 6 ] + subunit distorts the geometry of the triangular Fe 3 O core. The Fe-O central bond lengths are enlarged or shortened depending on number of coordinated pyridine ligands. This significantly affects the antiferromagnetic coupling constants between the Fe III centers ranging from −62 cm −1 to −28 cm −1 in [Fe 3 O(OAc) 6 (Py) n ] + ( n = 0, 1, 2, 3). A detailed analysis of the associated exchange couplings indicates a switching of magnetic ground states by pyridine coordination. The total spin S T in the ground states of [Fe 3 O(OAc) 6 (Py) n ] + raises from S T = 1/2 ( n = 0) to 3/2 ( n = 1) and 5/2 ( n = 2). Coordination of the third pyridine ligand ( n = 3) re-establishes a spin ground state of S T = 1/2. We thus identify a coordination controlled switching of magnetic ground states. We elucidate the correlation between geometric structures and magnetic couplings in trinuclear iron( iii ) oxo acetate complexes [Fe 3 O(OAc) 6 (Py) n ] + ( n = 0, 1, 2, 3) when isolated and trapped as gaseous ions.