Switching of Molecular Spin States in Inorganic Complexes by Temperature, Pressure, Magnetic Field and Light: Towards Molecular Devices

Abstract

Keywords: Spin crossover / Metastability / Hysteresis loop / Pressure / Magnetic field / Dielectric properties / Ising-like modelThe spin crossover phenomenon in molecular inorganic compounds is one of the most spectacular examples of bistability phenomena leading to a switching between the high-spin and the low-spin states of the molecule by several means such as temperature, pressure, light and magnetic field (multi-property molecular switching). In the present microreview we report our most important findings, both experi-

Temperature and pressure effects on the spin state of ferric ions in the [Fe(sal2-trien)][Ni(dmit)2] spin crossover complex

“…The fact that only one component appears in the spectra recorded at 80 K and 250 K proves the occurrence of a complete spin transition in the system in both ways. This finding is in agreement with the magnetic susceptibility data (χ M T 250K = 4.84 cm 3 Kmol -1 and χ M T 80K = 0.66 cm 3 Kmol -1 ), but only the Mössbauer spectra can prove the completeness of the transition unambiguously, especially in the presence of other paramagnetic species. The inter-conversion of the spin states in many instances is so rapid for ferric complexes that the separate contributions to the 57 Fe Mössbauer spectra are not resolved.…”

“…Spin-crossover (SC) complexes of transition metal ions (3d 4 -3d 7 ) have attracted much attention from the fundamental point of view [1][2][3][4]. These complexes represent one of the best examples of molecular bistability.…”

Pressure-induced two-step spin transition with structural symmetry breaking: X-ray diffraction, magnetic, and Raman studies

“…These slopes are directly comparable with the Clapeyron slopes ( V/ S = 16 ± 2 and 14 ± 2 K/kbar for the first and second step of the transition, respectively 18 ) and fall in the range of previously reported values for mononuclear iron(II) SCO materials. 22,43 Clearly both hystereses broaden as pressure increases, which is contrary to the expectation from the standard theoretical models. 23 46,47 In the former, a crystallographic phase transition between the HS and LS states at ambient pressure was demonstrated by powder diffraction.…”

Switching Magnetic Properties by a Mechanical Motion

“…Apart from temperature and light, chemical [25], electrical [26], or pressure [27] stimuli have also been used to induce a spin crossover. Several stimuli have been used to trigger magnetic properties changes [3] in three main areas: (i) changing the spin state of a transition metal in spin crossover (SCO) systems [4][5][6][7][8][9][10][11]; (ii) switching the exchange interaction between different spin carriers [12,13]; and (iii) switching single-molecule magnet (SMM) properties [14,15]. Spin-crossover complexes [16][17][18][19][20] are particularly interesting for such purpose, as they can exist in two stable spin states and have been largely studied.…”

“…Spin-crossover complexes [16][17][18][19][20] are particularly interesting for such purpose, as they can exist in two stable spin states and have been largely studied. Even if spin-crossover behavior is theoretically expected to occur in octahedral complexes with 3d 4 to 3d 7 electronic configurations, most spin-crossover complexes are based on Fe(III), Fe(II), and Co(II), with only few reported examples of compounds of Mn(II), Mn(III), Cr(II), and Co(III). The study of spin-crossover systems has originated from d 6 Fe(II) complexes that can be reversibly switched between high spin (HS, S = 2) and low spin (LS, S = 0) states by using several stimuli [6,21].…”