Control of Charge Transfer Phase Transition and Ferromagnetism by Photoisomerization of Spiropyran for an Organic−Inorganic Hybrid System, (SP)[Fe^IIFe^III(dto)₃] (SP = spiropyran, dto = C₂O₂S₂)

Abstract

Iron mixed-valence complex, (n-C(3)H(7))(4)N[Fe(II)Fe(III)(dto)(3)](dto = C(2)O(2)S(2)), shows a spin entropy-driven phase transition called charge transfer phase transition in [Fe(II)Fe(III)(dto)(3)](-)(infinity) around 120 K and a ferromagnetic transition at 7 K. These phase transitions remarkably depend on the hexagonal ring size in the two-dimensional honeycomb network structure of [Fe(II)Fe(III)(dto)(3)](-)(infinity). In order to control the magnetic properties and the electronic state in the dto-bridged iron mixed-valence system by means of photoirradiation, we have synthesized a photosensitive organic-inorganic hybrid system, (SP)[Fe(II)Fe(III)(dto)(3)](SP = spiropyran), and investigated the photoinduced effect on the magnetic properties. Upon UV irradiation at 350 nm, a broad absorption band between 500 and 600 nm appears and continuously increases with the photoirradiation time, which implies that the UV irradiation changes the structure of spiropyran from the closed form to the open one in solid state. The photochromism in spiropyran changes the ferromagnetic transition temperature from 5 to 22 K and the coercive force from 1400 to 6000 Oe at 2 K. In this process, the concerted phenomenon coupled with the charge transfer phase transition in [Fe(II)Fe(III)(dto)(3)](-)(infinity) and the photoisomerization of spiropyran is realized.

Recent Advances on Anilato-Based Molecular Materials with Magnetic and/or Conducting Properties

“…In the last 20 years many efforts have been addressed to add in these materials a further physical property by playing with the functionality of the A + cations located between the bimetallic layers. This strategy produced a large series of multifunctional molecular materials where the magnetic ordering of the bimetallic layers coexists or even interacts with other properties arising from the cationic layers, such as paramagnetism [2,[76][77][78][79][80], non-linear optical properties [2,81,82], metal-like conductivity [83,84], photochromism [2,81,85,86], photoisomerism [87], spin crossover [88][89][90][91][92][93], chirality [94][95][96][97], or proton conductivity [2,98,99]. Moreover, it is well-established that the ordering temperatures of these layered magnets are not sensitive to the separation determined by the cations incorporated between the layers, which slightly affects the magnetic properties of the resulting hybrid material, by emphasizing its 2D magnetic character [2,[75][76][77][78][79][80]95,100,101].…”

A Family of Layered Chiral Porous Magnets Exhibiting Tunable Ordering Temperatures

“…1−7 A breakthrough in this area was the preparation in 1992 by Okawa et al 8 of the family of layered bimetallic oxalato-bridged magnets formulated as [NBu 4 ][M II Cr(C 2 O 4 ) 3 ] (M II = Mn, Fe, Co, Ni, Cu) with the well-known 2D hexagonal honeycomb structure 9,10 that orders ferromagnetically (M III = Cr) with ordering temperatures (T c ) ranging from 6 to 14 K or ferrimagnetically (M III = Fe) with T c ranging from 19 to 48 K. 11 −15 In the last 20 years, many efforts have been addressed to include an additional property in these hybrid materials by playing with the functionality of the A + cations located between the bimetallic layers. This simple strategy has ed a large series of multifunctional molecular materials where the magnetic ordering of the bimetallic layer coexists and even interacts with other properties arising from the cationic layers such as paramagnetism, 12−16 nonlinear-optical properties, 17,18 metallic conductivity, 19,20 photochromism, 18,21,22 photoisomerism, 23 spin crossover, 24−29 chirality, 30−33 or proton conductivity. 34,35 Still, the nature of the inserted cation affects very little (if any) the magnetic properties of the resulting hybrid material.…”

Progress of Multi Functional Properties of Organic-Inorganic Hybrid System, A[FeIIFeIIIX3] (A = (n-CnH2n+1)4N, Spiropyran; X = C2O2S2, C2OS3, C2O3S)

“…In organic-inorganic hybrid systems, it is effective to use an organic photochromic molecule for producing photoswitchable materials. On the basis of this strategy, we have used a photochromic spiropyran (SP) as the intercalated cation for [Fe II Fe III (dto) 3 ] and have tried to control the CTPT and the ferromagnetism for (SP)[Fe II Fe III (dto) 3 ] by means of photoisomerization of SP [42]. In general, the cationic spiropyran is converted from the yellow-colored closed form (CF) to the red-colored open form (OF) upon the irradiation of UV light (330-370 nm) at room temperature.…”

“…In particular, organic-inorganic hybrid systems such as layered double hydroxides (LDHs) [20,21,22,23,24], oxalato-bridged bimetal complexes A[M II M’ III (ox) 3 ] (A = cation, M, M’ = metal, ox = C 2 O 4 ) [25,26,27,28,29,30], dithiooxalato-bridged bimetal complexes A[M II M’ III (dto) 3 ] (A = cation, M, M’ = metal, dto = C 2 S 2 O 2 ) [31,32,33,34,35,36,37,38,39,40,41,42], perovskite-type metal halides A 2 M II X 4 (A = cation, M = metal, X = halogen) [43,44,45], magnetic vesicles [46,47,48,49], or magnetic thin films [50,51,52] provide an excellent opportunity to control their magnetic properties by the intercalation of various molecules.…”

“…The charge transfer phase transition and the ferromagnetic transition in ( n -C n H 2n+1 ) 4 N[Fe II Fe III (dto) 3 ] remarkably depend on the size of intercalated cation [40]. Based on this result, we have succeeded in controlling the charge transfer phase transition and the ferromagnetism for (SP)[Fe II Fe III (dto) 3 ] (SP = spiropyran) by means of photoisomerization of SP [42]. …”