Thermally-Induced Spin Crossover and LIESST Effect in the Neutral [FeII(Mebik)2(NCX)2] Complexes: Variable-Temperature Structural, Magnetic, and Optical Studies (X = S, Se; Mebik = bis(1-methylimidazol-2-yl)ketone)

Abstract

Two new iron(II) neutral complexes of bis(1-methylimidazol-2-yl)ketone (Mebik) with molecular formula [FeII(Mebik)2(NCS)2] (1) and [FeII(Mebik)2(NCSe)2] (2) have been synthesized and characterized by magnetic measurements, single-crystal X-ray diffraction, and solid state UV-vis spectroscopy. The temperature dependent magnetic susceptibility measurements of crystalline samples of both compound show the occurrence of a gradual spin transition centered at T1/2 = 260 K and 326 K, respectively. The crystal structures of both compounds were determined at different temperatures, below and above the transition, in order to detect the structural changes associated with the spin transition. The main structural modifications, when passing from the low-spin to the high-spin form, consist of an important lengthening of the Fe-N(Mebik) and Fe-N (C-S/Se) distances (by ca. 0.20 and 0.18 Å, respectively) and a noticeable variation of the N-Fe-N angles, leading to a more distorted [Fe-N6] octahedron. The spin-transition phenomenon also affects the optical properties, with significant decrease of the intensity of the Metal-to-Ligand charge transfer band upon increasing the temperature. Finally, both complexes exhibit a light-induced excited spin-state trapping under laser light irradiation at low temperature. DFT calculations were also carried out on these complexes in order to rationalize the theoretically predicted magnetic and optical behavior with those of the experimental one. The results clearly highlights the dramatic alteration of the magneto-structural behavior of the tris-chelate [FeIIfalse(Mebik)3]2+ spin-crossover complex upon substituting one Mebik with NCS and NCSe ligands.

Bias induced spin state transition mediated by electron excitations

“…The NTOs of MLCT2 are not shown here. Our calculated energy of MLCT3 is consistent with the optical observation 23 ,where a MLCT of Fe(phen) 2 (NCS) 2 is detected by the pump light at 650 nm (1.9 eV).Other optical experiments[26][27][28] demonstrate that a MLCT can be attained by an infrared radiation (around 800 nm or 1.5 eV), close to the calculated energy of MLCT1. Hence, our the effect of couplings with the STM substrate and that of bias voltages on excitations.…”

Structural studies into the spin crossover behaviour of Fe(abpt)2(NCS)2 polymorphs B and D

“…The phenomenon is relatively common for 3d 4 -3d 7 metal centres. 5 While many of the spin crossover complexes that have been studied are octahedral Fe(II) complexes with nitrogen [5][6][7][8][9][10] ligands, other examples include Fe(III) 4,[11][12][13][14] , Co(II) [15][16][17] and Ni(II) 18 . The change in electronic structure, as a result of the spin crossover, can result in changes in properties including molecular structure, colour and magnetism.…”

Electrospray ionization: an efficient approach to deposit polymetallic molecular switches onto gold surfaces

“…These stretching vibrations are actually very close to those observed in related {Fe II 2Co III 2} square complexes (at 2109 and 2126 cm -1 ). 27 Interestingly, the IR pattern measured in-situ by PM-IRRAS after EI deposition on Au(111) substrate (Fig. 2C) reveals a spectral feature identical to that of the cubes prior to deposition.…”