RESUMEN
Photoresponsive spin-crossover (SCO) molecules are an important class of bistable magnetic molecules with intriguing potential in device applications. The light-induced excited spin state trapping (LIESST) and the combined application of light and temperature can provide access to the metastable region of the SCO profile. The primary obstacle in utilizing light stimuli is the manifestation of light-induced trappings at extremely low temperatures. Herein, we report two novel multiresponsive 2D Hofmann-type coordination polymers exhibiting light-induced excited spin state trapping above liquid nitrogen temperature (TLIESST = 82 and 81 K). Stimulating the samples in conjugation with light and temperature successfully unveils hysteresis, which is otherwise concealed. Apart from light and temperature, we found that the SCO phenomenon is also responsive to external hydrostatic pressure and exhibits modulation of the hysteresis width and transition temperature shifts with changes in pressure.
RESUMEN
Two new Fe(II)-based dinuclear triple helicates having the formula {[Fe2(L)3]·(CF3SO3)4·6.5H2O·CH3OH} (complex 1) and {[Fe2(L)3]·(ClO4)4·7H2O·1.35CH3OH} (complex 2), displaying near room temperature spin transition have been synthesized and the effect of intermolecular interactions and co-operativity between metal centers on the spin crossover (SCO) has been studied. Picolinimidamide-based ligand system is chosen to provide maximum intermolecular interactions. Variable-temperature single crystal X-ray diffraction (SCXRD), magnetic study, and Hirshfeld analysis reveal that complex 1 shows a multistep spin transition, whereas, complex 2 shows an abrupt spin transition from [LS-LS] â [HS-HS]. In complex 2 the presence of perchlorate anion induces high intermolecular O-H interaction that enhances the cooperativity resulting in high T1/2 of 330 K. This study accentuates the interplay between anion effect, crystal packing, and supramolecular interactions in tuning the magnetic properties of SCO compounds.
RESUMEN
Three heterometallic hexanuclear 3d-4f complexes bearing the formula [Cu2 (L)2 Ln4 (L)4 (o-van)2 ] [L=2-((E)-((2-hydroxyphenyl)imino]methyl)phenol; o-van=ortho-vanillin] (LnIII =GdIII (1), DyIII (2), and TbIII (3)) have been synthesized and characterized. DC magnetic susceptibility measurements reveal overall antiferromagnetic interactions in 1 and 3, whereas co-existence of ferro- as well as antiferromagnetic interactions were observed in 2. The magnetocaloric effect has been observed for 1 with an entropy change (-ΔSm ) of 22.3â J kg-1 K-1 at 3â K and 7 T. Zero-field single molecule magnet (SMM) behaviour has been observed for 2, where Raman relaxation and quantum tunneling of magnetization (QTM) played a role in magnetization relaxation. The Cu-O-Ln angle well explains the magnetic exchange coupling occurring in the complexes. BS-DFT calculation for the complexes provides an estimate of the exchange interactions between the paramagnetic centres. Ab initio calculations performed for complex 2 established a good correlation to the experimental relaxation dynamics.