Cooperative Spin Transition in a Mononuclear Manganese(III) Complex

Abstract

Mind the gap: A complete, cooperative spin transition for a mononuclear Mn(III) complex is reported with an 8 K hysteresis window. Raman spectra collected at a single temperature in warming and cooling modes confirm the electronic bistability within the hysteresis loop. The source of the cooperativity is a disconnection in the hydrogen-bonded 1D chains that connect adjacent cations owing to an order-disorder transition in the PF(6)(-) counterion.

Spin-crossover Compounds with Wide Thermal Hysteresis

“…6 Some exceptions to that rule are 24, 25, 80 26, 81 and 27 (Scheme 5). 82 These all exhibit spin transitions with 8¯¦T¯16 K, which is very unusual for those metal ions. For 26, the strong cooperativity was attributed to a crystallographic phase change during the transition.…”

“…81 In contrast, 27 does not undergo a change in space group during spin crossover, and the hysteresis may arise from the formation and cleavage of a NH£F hydrogen bond between the spin states. 82 Some [Co(terpy) 2 ] 2+ (terpy: terpyridine) derivatives related to 20 (Scheme 3) 67 and 21 68 also exhibit hysteresis in their "normal" spin transitions as well as in the reverse transitions described above.…”

Spin state switching in iron coordination compounds

“…Other SCO compounds of Fe(II) [86–87], Fe(III) [88] and Mn(III) [89–90] have been studied down to liquid-helium temperature. Such measurements are very tedious.…”

“…An experiment with a sample of [Fe(phen) 2 (NCS) 2 ] placed in a magnetic field of 5 Tesla showed indeed a small effect; T 1/2 was shifted by −0.11 K [192]. Later, similar experiments were carried out with samples placed in high magnetic fields [89–90 193]. The results were in agreement with those of the earlier study [192], though correspondingly larger because of the six-times higher magnetic field used in the latter case.…”

Reversible Control by Light of the High‐Spin Low‐Spin Elastic Interface inside the Bistable Region of a Robust Spin‐Transition Single Crystal

“…1.5 Hz. [11][12][13] Interestingly,m ultiferroic Jahn-Teller switches have been already reported for Prussian Blue analogues [14][15][16] demonstrating the important role of the elastic interactions in the control of the electronic properties of SC solids.B ut elasticity is also at the heart of many other types of phase transitions,s uch as in the Mott metal-insulator transition [17] where it has been shown that the coupling to crystal elasticity alters the critical properties.Using optical microscopy investigations, [9,10,18,19] we shown that by tuning the shining intensity of the microscope,i nt he hysteretic region of the spin transition (see Figure 1), the temperature of the crystal was efficiently shifted and we could drive the interface position at will between the HS and the LS phases.H owever, this preliminary experiment remained qualitative.H erein, we show for the first-time how we can achieve an accurate and reversible control of the SC transition inside the hysteretic region. In cooperative spincrossover solids, [1][2][3][4] the thermally induced first-order transition involves two spin states,n amely the low-spin (LS, diamagnetic) and the high-spin (HS,p aramagnetic) and is accompanied by as izeable volume change and thermal hysteresis loop.F or comparison, in magnetic systems,t he control of the interface between ferromagnetic and paramagnetic domains is made possible thanks to the magnetic field, which induces the domain-wall motion, [5][6][7] which may be reversible under some conditions owing to the presence of the demagnetizing field created by the dipolar magnetic interactions.Such acontrol by afield parameter is no longer possible in spin-crossover solids,s ince the macroscopic interfaces separating the LS and HS states are elastic in nature.A xial pressure might act as an efficient control parameter;h owever its practical realization faces serious challenges,s uch as the brittle nature of the spin-crossover single crystals.…”