We investigate giant magnetoelectric coupling at a Mn 3+ spin crossover in [Mn III L]BPh4 (L = (3,5-diBr-sal)2323) with field-induced permanent switch of the structural, electric and magnetic properties. An applied magnetic field induces a 1 st order phase transition from a high spin/low spin (HS-LS) ordered phase to a HS-only phase at 87.5 K that remains after the field is removed. We observe this unusual effect for DC magnetic fields as low as 8.7 T. The spin-state switching driven by the magnetic field in the bistable molecular material is accompanied by a change in electric polarization amplitude and direction due to a symmetry-breaking phase transition between polar space groups. The magnetoelectric coupling occurs due to a γη 2 coupling between the order parameter γ related to the spin-state bistability, and the symmetry-breaking order parameter η, responsible for the change of symmetry between polar structural phases. We also observe conductivity occurring during the spin crossover, and evaluate the possibility that it results from conducting phase boundaries. We perform ab-initio calculations to understand the origin of the electric polarization change as well as the conductivity during the spin crossover. Thus we demonstrate a giant magnetoelectric effect with a field-induced electric polarization change that is 1/10 of the record for any material.

Structural, magnetic and spectroscopic data on four new spin triplet Mn3+ complexes reveals a large magnetic anisotropy. Spin state is sensitive to lattice contents as the spin quintet ground state is stabilized on co-crystallization with ethanol.

We report a single example of thermal spin crossover in a series of Fe III complexes, [Fe III (R-sal 2 323)] + , which typically stabilize the low-spin (S = 1/2) state. Singlecrystal X-ray diffraction analysis of 53 such complexes with varying "R" groups, charge-balancing anions, and/or lattice solvation confirms bond lengths in line with an S = 1/2 ground state, with only the [Fe III (4-OMe-sal 2 323)]NO 3 complex (1a) exhibiting longer bond lengths associated with a percentage of the spin sextet form at room temperature. Structural distortion parameters are investigated for the series. A magnetic susceptibility measurement of 1a reveals a gradual, incomplete transition, with T 1/2 = 265 K in the solid state, while Evans method NMR reveals that the sample persists in the low-spin form in solution at room temperature. Computational analysis of the spin state preferences for the cations [Fe III (4-OMe-sal 2 323)] + and [Fe III (sal 2 323)] + confirmed the energetic preference for the spin doublet form in both, and the thermal spin crossover in complex 1a is therefore attributed to perturbation of the crystal packing on warming.

Structural and magnetic data on two iron (III) complexes with a hexadentate Schiff base chelating ligand and Cl − or BPh 4 − counterions are reported. In the solid state, the Cl − complex [Fe(5F-sal 2 333)]Cl, 1, is high spin between 5-300 K while the BPh 4 − analogue [Fe(5F-sal 2 333)]BPh 4 , 2,is low spin between 5-250 K, with onset of a gradual and incomplete spin crossover on warming to room temperature. Structural investigation reveals different orientations of the hydrogen atoms on the secondary amine donors in the two salts of the [Fe(5F-sal 2 333)] + cation: high spin complex [Fe(5F-sal 2 333)]Cl, 1, crystallizes with non-meso orientations while the spin crossover complex [Fe(5F-sal 2 333)]BPh 4 , 2, crystallizes with a combination of meso and non-meso orientations disordered over one crystallographic site. Variable temperature electronic absorption spectroscopy of methanolic solutions of 1 and 2 suggests that both are capable of spin state switching in the solution.