Gradual two-step and room temperature spin crossover in Mn(III) complexes with nitro-substituted ligand

Optical Phenomena in Molecule-Based Magnetic Materials

“…Besides intensively investigated SCO-active Fe­(II) complexes, other transition metal complexes were also found to demonstrate the conjunction of the thermal switching of magnetism and optical absorption due to the spin transition effect. − In contrast to Fe­(II) centers, the SCO-active Fe­(III) complexes (d 5 valence configuration) do not usually show strong thermochromic response as the broad visible light absorption usually remains for both HS and LS states. − A few examples of more impressive thermochromism were detected for less studied cases of SCO-active Mn­(III) centers (d 4 valence configuration) embedded in the mixed coordination environment of N- and O-donor atoms ensured, e.g., by Schiff-base ligands (Figure g–i). − The great potential for exploration of thermochromism in more exotic spin crossover complexes was further suggested by the heating-induced discoloration of deep green LS phase of Cr­(II) centers (d 4 valence configuration) coordinating two N , N , N -tridentate polypyridine-type ligands (Figure j–l) . It is worth noting that in both said cases of Mn­(III) and Cr­(II) complexes, the spin transition cooperativity is usually limited leading to a rather gradual course of thermal SCO; − thus, these systems are promising candidates for optical temperature sensing in the broad working temperature range, including the room-temperature region. The other transition metal complexes, which exhibit the thermal SCO in the non-trivial coordination environment, such as Mn II , Co III , or Co II (d 5 , d 6 , and d 7 valence configurations, respectively), can also demonstrate the analogous potential in the thermochromic behavior. ,− …”

The effect of fluorine substituents on the crystal structure and spin crossover behavior of the cation [MnIII(3,5-diHal-sal2323)]+ complex family with BPh4 anions

“…S3, ESI †). The cation-cation intermolecular interactions also play an important role in spin transformations; 6,[17][18][19]26,28,39,40 in particular, strong bonding between cations can lead to the suppression of spin transition. 19,40…”