Here, we use a pyridinecarbaldehyde rhodamine 6G hydrazone ligand (L) to synthesize an Fe(II) complex 1 for the search of new fluorescent-spin crossover (SCO) materials. Single-crystal structural determinations suggest that the Fe(II) ion is chelated by two ring-opened ligands (L-o) to form a FeNO coordination environment, and intermolecular π---π contacts of the xanthene groups connect the adjacent molecules to form a supramolecular one-dimensional chain. Magnetic susceptibility measurements on complex 1 show that three-step SCO takes place in the temperature range of 120-350 K, and its desolvated form 1-d exhibits SCO around room temperature ( T↑ = 343 K and T↓ = 303 K) with a wide hysteresis loop of 40 K. Moreover, complex 1-d displays light-induced excited spin-state trapping phenomenon. Intriguingly, the fluorescence intensity of the maximum emission at 560 nm for complex 1-d displays discontinuous variation in the range of 250-400 K, indicative of the occurrence of synergetic fluorescence and SCO.

Iron pnictides and selenides display a variety of unusual magnetic phases originating from the interplay between electronic, orbital and lattice degrees of freedom. Using powder inelastic neutron scattering on the two-leg ladder BaFe2Se3, we fully characterize the static and dynamic spin correlations associated with the Fe4 block state, an exotic magnetic ground-state observed in this low-dimensional magnet and in Rb0.89Fe1.58Se2. All the magnetic excitations of the Fe4 block state predicted by an effective Heisenberg model with localized spins are observed below 300 meV and quantitatively reproduced. However, the data only accounts for 16(3) µ 2 B per Fe 2+ , approximatively 2/3 of the total spectral weight expected for localized S = 2 moments. Our results highlight how orbital degrees of freedom in iron-based magnets can conspire to stabilize an exotic magnetic state.