Magnetostructural Correlation for High-Nuclearity Iron(III)/Oxo Complexes and Application to Fe₅, Fe₆, and Fe₈ Clusters

Abstract

The synthesis and characterization are reported of two new polynuclear Fe(III) complexes containing the anion of 8-hydroxyquinoline (hqnH), an N,O-chelating ligand. The complexes are [Fe8O4(O2CPh)10(hqn)4(OMe)2] (1) and [Fe6O2(OH)2(O2CPh)10(hqn)2] (2) and were obtained from reactions in MeOH (1) or H2O (2) using either low-nuclearity preformed clusters or simple metal salts as starting materials. Variable-temperature, solid-state dc and ac magnetic susceptibility studies were carried out and indicate S = 0 and S = 5 ground states for 1 and 2, respectively. In order to rationalize the ground states of these and other higher-nuclearity Fe(III)/O clusters, a magnetostructural correlation (MSC) has been developed specifically for polynuclear Fe(III)/O systems that predicts the exchange interaction constant (Jij) between two Fe(III) atoms based on the Fe-O distances and Fe-O-Fe angles at monoatomically bridging ligands. This correlation was refined using selected tri- and tetranuclear complexes in the literature for which both crystal structures and reliable experimentally determined Jij values were available. The predictive capability of the MSC was evaluated by rationalizing the ground-state spins of 1, 2, and other Fe5-Fe8 clusters, simulating the dc magnetic susceptibility data of polynuclear Fe(III) complexes, and fitting experimental dc magnetic susceptibility vs T data. The latter fits were evaluated to identify and eliminate systematic errors, and this allowed a protocol to be developed for application of this MSC to other polynuclear Fe(III)/oxo clusters.

Remote Ligand Modifications Tune Electronic Distribution and Reactivity in Site-Differentiated, High-Spin Iron Clusters: Flipping Scaling Relationships

“…Moreover, based on the pseudosymmetry observed in the solid state structure (related to the symmetry of the distribution of redox states), further contraints can be imposed on the values of these effective exchange coupling constants which greatly enhance the uniqueness of the obtained fits. While magnetostructural correlations for iron clusters with nuclearity ≥ 3 are largely limited to the all-ferric redox state, [21][22][23][24][25][26][27][28][29][30] which is not complicated by the presence of double exchange or anisotropic interactions arising from inequivalent population of the d-orbital manifold, the effective exchange coupling constants obtained herein are qualitatively reasonable.…”

Breaking Symmetry Relaxes Structural and Magnetic Restraints, Suppressing QTM in Enantiopure Butterfly Fe2Dy2 SMMs**

“…Comparison of the respective bond lengths within the Fe coordination polyhedra for 1 ‐ RS and 1 ‐ SS (Figure S8) shows that the differences here are small, and mostly not significant; if anything, the structures are more similar to each other than they both are to the analogue with (teaH) 2− as ligand. Calculation of the theoretical coupling constants between the Fe centres from the bridging geometries in 1 ‐ RS and 1 ‐ SS using magnetostructural correlations [10] gave the same value (J Fe‐Fe =−5.0 cm −1 ) in both cases, again emphasizing the similarity between the two structures.…”

Hexanuclear iron(iii) α-aminophosphonate: synthesis, structure, and magnetic properties of a molecular wheel

“…Recently, Christou et al proposed a new improved parameter set for eqn (3) that is especially validated for high-nuclearity iron(III) complexes (A = 2.46 Â 10 9 cm À1 , B = À0.12, C = 1.57, D = À8.99 Å À1 based on the Ĥ = ÀJŜ 1 Ŝ 2 convention). 36 The coupling constants calculated for the two independent hexanuclear molecules of 1 utilizing this magnetostructural correlation range from À29.0 to À36.6 cm À1 with an average value of À33.4 cm À1 and are summarized in Table 5. For the simulation of the experimental wT data, the coupling constants derived from the magnetostructural correlation of each of the two hexanuclear ring systems (Table 5) with subsequent averaging were employed.…”