Influence of Halogen Atoms on Spin‐Crossover Properties of 1,2,4‐Triazole‐Based 1D Iron(II) Polymers

Abstract

The introduce of halogen atoms (F, Cl, Br, I) to the triazolebased ligand N-benzyl-4-amino-1, 2, 4-triazole (L) have shown a significant effect on the spin-crossover (SCO) properties of the corresponding one-dimensional (1D) coordination Fe (II) polymers with chemical formula [Fe(4-X-L) 3 ](BF 4 ) 2 (X = F, Cl, Br, and I). Compared with the [FeL 3 ](BF 4 ) 2 , the electronegative halogen atoms have increased the p-acceptor character of these ligands, which thus improved the ligand field strength and in-duced the occurrence of SCO for the Fe (II) polymers at higher temperatures. The SCO transition temperatures T 1/2 have changed from 200 K to 249 (I), 250 (Br), 252 (Cl) and 275 (F) K, respectively. More importantly, the UV-Vis absorption spectrum and density functional theory (DFT) calculations indicated that the transition temperatures and the width of thermal hysteresis loops have shown a positive correlation with the electronegativity of the halogen atoms.

Bidirectional Photoswitching via Alternating NIR and UV Irradiation on a Core–Shell UCNP–SCO Nanosphere

“…For the purpose of practical applications, the SCO should be ideally operated under ambient conditions: at room temperature and atmospheric pressure. , Much attention has, therefore, been paid to the manipulation of SCO materials that are switchable at ambient conditions, and indeed a handful of examples that feature a thermally induced spin-state transition under ambient conditions have been developed. − However, compared with thermally inducted SCO, light-triggered SCO is more attractive because of the short response times, low power dissipation, and high selectivity. − Thus, SCO materials that are switchable by means of light irradiation at ambient conditions would be of significant importance. Note that this purpose has been realized in the light-induced excited spin-state trapping effect at the single-molecule level. − This effect, however, can be operated only below 50 K as the light-induced excited state rapidly relaxes to the ground state within nanoseconds at room temperature.…”

Build 3D Nanoparticles by Using Ultrathin 2D MOF Nanosheets for NIR Light-Triggered Molecular Switching

“…For the transition-metal ions of d 4 –d 7 , it may be low-spin (LS) or high-spin (HS) in the octahedral field, and when the splitting energy being greater than the paired energy is LS, and vice versa. While the two states are close, through external disturbances (e.g., temperature or pressure changes, light irradiation, and chemical molecules), − the complex can undergo HS and LS transitions (spin-crossover, SCO), resulting in reversible changes in its optical, magnetic, mechanical, and electrical properties, − and thus the applications in molecule switching, optoelectronics, actuators, and sensors are fascinating. − The research studies of Fe­(II) SCO materials are more important and have always been a hot topic in this field among various SCO materials. − …”

A flexible polymer–nanoparticle hybrid material containing triazole-based Fe(ii) with spin crossover properties for magneto-optical applications

“…37 This is due to the fact that despite the purely molecular origin of the SCO phenomenon, the macroscopic behavior of these systems is strongly influenced by short-and long-range interactions between the transition-metal ions, giving rise to remarkable cooperative phenomena, which are in turn responsible for the robustness of the spin transition. [38][39][40] The engineering of composite materials is a promising way to address this ultimate goal. In this frame, SCO compounds have been encapsulated within polymer matrices of synthetic [41][42][43][44][45][46][47][48][49] and biological 38,[50][51][52][53] origin, providing nanoscale confinement suitable for maintaining cooperativity between SCO complexes.…”