photomagnetic studies of spin-crossover- and photochromic-based complexes

FULL PAPER

DOI:10.1002/ejic.201201328

CLUSTERISSUE

Photomagnetic Studies of Spin-Crossover- andPhotochromic-Based Complexes

Christophe Faulmann,*[a,b] Joe Chahine,[a,b] Lydie Valade,[a,b]

Guillaume Chastanet,[c] Jean-François Létard,[c] andDominique de Caro[a,b]

Keywords: Spin crossover / Photochromism / Magnetic properites / N,O ligands / Ruthenium / Iron / Nitroprussiate

This work reports on the combination between photochromiccomplexes (Na2[Fe(CN)5(NO)]·2H2O and K2[RuCl5(NO)])with spin-crossover compounds derived from FeIII complexes{[Fe(qsal)2]+ and [Fe(salEen)2]+; Hqsal = N-(8-quinolyl)sal-icylaldimine; HsalEen = N-[(2-ethylamino)ethyl]salicylald-imine}. These associations have resulted in the synthesis ofnew materials that contain a spin-crossover unit and a photo-chromic unit, as evidenced by their X-ray structure. Spectro-scopic, magnetic and photomagnetic properties of these com-plexes were studied, with or without light irradiation, to eval-

Introduction

During the past few years, several studies have been de-voted to bifunctional molecular materials that combine op-tical properties and electrical or magnetic properties.[1] Forinstance, photochromic units such as [Fe(CN)5(NO)]2– (an-ionic) or [Ru(NH3)5(NO)]+ (cationic) have been associatedwith magnetic units[1d] by taking advantage of the cyanoligand of the nitroprussiate [Fe(CN)5(NO)]2– to combineseveral metallic centres and then build polynuclear net-works. [Ni(en)2][Fe(CN)5(NO)]·3H2O and [Ni(en)2]4[Fe-(CN)5(NO)][Fe(CN)6]·5H2O are typical examples of 3Dnetworks that are based on the nitroprussiate [Fe(CN)5-(NO)]2– (or [NP]) and exhibit magnetic properties togetherwith metastable states of the photochromic entity. In theparamagnetic compound Ni[Fe(CN)5(NO)]·yH2O,[1h] pho-toirradiation at 475 nm causes a charge transfer from themetal Fe to the ligand NO, which induces a magnetic cou-

[a] CNRS, LCC (Laboratoire de Chimie de Coordination),205 route de Narbonne, BP44099,31077 Toulouse Cedex 4, FranceFax: +33-561553003E-mail: [email protected]: http://www.lcc-toulouse.fr

[b] Université de Toulouse, UPS, INPT,31077 Toulouse Cedex 4, FranceHomepage: http://www.univ-tlse3.fr

[c] CNRS, Université de Bordeaux, ICMCB,87 avenue du Dr. A. Schweitzer, Pessac 33608, FranceHomepage: www.icmcb-bordeaux.cnrs.fr/Supporting information for this article is available on theWWW under http://dx.doi.org/10.1002/ejic.201201328.

Eur. J. Inorg. Chem. 2013, 1058–1067 © 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim1058

uate the possible influence of the photochromic group on thespin transition. [Fe(qsal)2]2[Fe(CN)5(NO)]·solvent, [Fe(sal-Een)2]2[Fe(CN)5(NO)] and [Fe(qsal)2]2[Ru(CN)5(NO)]·2.5H2Oall exhibit a spin transition. The light-induced excited spin-state trapping (LIESST) effect was detected in the (Fe-qsal)-based complexes. [Fe(qsal)2]2[Ru(CN)5(NO)]·2.5H2O also ex-hibits a reverse-LIESST effect. Regardless of the complex, nophotochromic effect from the nitroprusside units was de-tected.

pling between the surrounding Ni cations. As a result, thespins on the Ni ions form a magnetic cluster with S = 5.

The first example of a synergy between the optical andthe magnetic properties with two discrete entities is foundwith [Ru(NH3)5(NO)][Cr(CN)6].[2] The light irradiation in-duces changes in the conformation of the ligands NO,which then changes the electronic contribution of the CNligand on Cr. This results in slight variations of the para-magnetic susceptibility–temperature product (χT) value.

To the best of our knowledge, very few studies[3] havebeen undertaken on compounds that combine cationic unitswith spin-crossover properties and photochromic anionicunits, such as [Fe(CN)5(NO)]2–. Moreover, even if the com-pounds reported in these previous studies exhibit spin tran-sition, none of them has been studied under irradiation.Nevertheless, the nitroprussiate unit [Fe(CN)5(NO)]2– un-dergoes important changes in its molecular structure underirradiation and specific conditions, due to the generation oftwo metastable states (MS1 and MS2) accompanied by anisomerization of the nitrosyl ligand (NO) to an isonitrosylligand (ON; for MS1) and a side-on bonding of the NOgroup for MS2.[4] These changes consist of large discrepan-cies in the values of the bond lengths and bond angles be-tween Fe–N–O and Fe–O–N, together with variations ofthe volume of the whole [Fe(CN)5(NO)]2– anion. If com-bined with physical properties that are sensitive to the struc-tural arrangement, such as the spin transition, these struc-tural changes could also induce changes in the magneticproperties of the spin-crossover complexes.

www.eurjic.org FULL PAPER

This work reports on the combination between photo-chromic anions such as [ML5(NO)]2– (M = Fe, Ru; L = CN,Cl) and spin-crossover cations derived from FeIII com-plexes, such as [Fe(qsal)2]+ and [Fe(salEen)2]+ {Figure 1;Hqsal = N-(8-quinolyl)salicylaldimine and HsalEen = N-[(2-ethylamino)ethyl]salicylaldimine}, to check the possibleinterplay between spin transition and photochromism. Thisleads to compounds with the general formula [Fe(qsal)2]2-[Fe(CN)5(NO)]·solvent, [Fe(qsal)2]2[Ru(Cl)5(NO)]·2.5H2Oand [Fe(salEen)2]2[Fe(CN)5(NO)]. The influence of the sol-vent on the spectroscopic and magnetic properties are re-ported. Photomagnetic studies [including light-induced ex-cited spin-state trapping (LIESST) and reverse-LIESST] aredetailed for [Fe(qsal)2]2[Fe(CN)5(NO)]·MeOH and [Fe-(qsal)2]2[Ru(Cl)5(NO)]·2.5H2O.

Figure 1. Molecular structure of [Fe(qsal)2]+ and [Fe(salEen)2]+.

Results

The combination of the spin-crossover complexes[Fe(qsal)2]Cl and [Fe(salEen)2](NO3) with the photochro-mic complexes Na2[Fe(CN)5(NO)]·2H2O and K2[RuCl5-(NO)] in methanol and acetonitrile or acetone, followingScheme 1, results in compounds with the general formula[Fe(qsal)2]2[Fe(CN)5(NO)]·solvent, [Fe(qsal)2]2[Ru(Cl)5-(NO)]·2.5H2O and [Fe(salEen)2]2[Fe(CN)5(NO)].

Scheme 1. Typical synthesis of the photochromic spin-crossovercompounds.

Reactions were performed with freshly prepared solu-tions of photochromic salts {Na2[Fe(CN)5(NO)]·2H2O andK2[Ru(Cl)5(NO)]}, under an inert atmosphere (argon) andin the dark to avoid photodegradation or NO removal insolution.[5] Black crystals of [Fe(qsal)2]2[Fe(CN)5(NO)]·2CH3CN were obtained after recrystallization of the pow-der in an acetonitrile/toluene solvent mixture. A microcrys-talline powder (from which crystals suitable for an X-raystudy were selected) was obtained during the preparation of[Fe(salEen)2]2[Fe(CN)5(NO)]. In the following text,[Fe(qsal)2]2[Fe(CN)5(NO)]·MeOH, [Fe(qsal)2]2[Fe(CN)5-(NO)]·2CH3CN and [Fe(qsal)2]2[Ru(Cl)5(NO)]·2.5H2O willbe abbreviated as [Fe–NP]·MeOH, [Fe–NP]·2CH3CN and[Fe-Ru]·2.5H2O, respectively.


Infrared Spectroscopy

Infrared spectroscopy was performed on both [Fe–NP]·MeOH and [Fe–NP]·2CH3CN compounds and comparedwith the two precursors NP and [Fe(qsal)2]Cl (Figure 2 andFigure S1 in the Supporting Information). In the 650–1700 cm–1 region, the spectra of [Fe(qsal)2]Cl and [Fe–NP]·MeOH are very similar, which indicates the presence of the[Fe(qsal)2]+ unit in the final product. In the 1700–2400 cm–1

region, the vibrational bands at 1885 and 2133 cm–1 in [Fe–NP]·MeOH could be correlated to the NO and CN vi-brational modes of the nitroprussiate anion as the one ob-served in the reference NP compound (1937 and 2143 cm–1

for the NO and CN bonds, respectively).

Figure 2. Infrared spectra of NP (magenta), [Fe(qsal)2]Cl (black)and [Fe–NP]·MeOH (cyan) at room temperature.

Usually, the CN vibration band is very sensitive to itsinvolvement in coordination modes. The absence of a strongband around 2160 cm–1 indicates that the CN groups donot act as a bridging ligand. In addition, the fact that theposition of the CN band is almost the same in the NP andthe [Fe–NP]·MeOH compounds indicates that even in thelatter compound the CN group is not involved in coordina-tion other than the one with the iron(II) ion. Therefore thenitroprussiates are present as discrete anions in the [Fe–NP]·MeOH compound.[5a] Regarding [Fe–NP]·2CH3CN, this isalso confirmed by its structure determination (see Fig-ures S2 and S3 in the Supporting Information).

Therefore, regardless of the solvent used in the synthesisof the [Fe–NP] compounds, this study favours materialsthat are constituted by [Fe(qsal)2]+ cationic units and[Fe(CN)5(NO)]2– anionic species.

[Fe–Ru]·2.5H2O has been characterized by elementalanalyses and infrared spectroscopy (Figure S4 in the Sup-porting Information). Similarly to the [Fe–NP]·MeOHcompound, the vibration band at 1836 cm–1 is related to theNO vibration, which is characteristic of [RuCl5(NO)]2–, andthe bands between 1700 and 600 cm–1 are characteristic of[Fe(qsal)2]+.

Infrared spectra of [Fe(salEen)2](NO3) and [Fe(salEen)2]2-[Fe(CN)5(NO)] are shown in Figure 3. In the spectrum of[Fe(salEen)2]2[Fe(CN)5(NO)], vibrations that correspond tothe starting salt [Fe(salEen)2](NO3) are clearly present (inthe range 1700–600 cm–1), plus one band at 1877 cm–1 (ni-


trosyl) and two bands at 2129 and 2140 cm–1 (cyano). Thisconfirms the occurrence of [Fe(salEen)2]+ and [Fe(CN)5-(NO)]2–. The lack of the band at 2160 cm–1 indicates theexistence of [Fe(CN)5(NO)]2– as a discrete entity,[5a] whichis also confirmed by its structure determination (see Fig-ures S5 and S6 in the Supporting Information). The occur-rence of the thermal spin crossover of the cationic unit thenhas been investigated.

Figure 3. Infrared spectra of [Fe(salEen)2](NO3) (cyan) and [Fe-(salEen)2]2[Fe(CN)5(NO)] (magenta) at room temperature.

Magnetic Properties

The magnetic properties were investigated in polycrystal-line samples. For [Fe–NP]·2CH3CN, only a slight and regu-lar decrease in the χMT value (from 2.8 to 2.58 cm3 mol–1 K)is observed between 300 and 30 K (see Figure S4 in theSupporting Information). Despite numerous interactionsbetween [Fe(qsal)2]+ units (Table S2 in the Supporting In-formation), no spin transition is observed for this com-pound. This shows that the solvation plays an importantrole in the magnetic behaviour by increasing or decreasingthe number of contacts, as already observed in [Fe(qsal)2]-(NCS)·solvent,[6] in [Fe(qsal)2](NCSe)·solvent[7] and in[Fe(qsal)2][Ni(dmit)2]·solvent (dmit = 2-thioxo-1,3-dithiol-4,5-dithiolato).[8] Disorders of the solvent and disorders ofthe NO group (and consequently in the CN groups; see theSupporting Information) might also be at the origin of thelack of spin transition in [Fe–NP]·2CH3CN. Due to thislack of spin transition, [Fe–NP]·2CH3CN has not beenstudied further (neither by Mössbauer nor photomagneticstudies).

Magnetic properties of [Fe–NP]·MeOH are shown onFigure 4, as the variation versus temperature of the χMTproduct per FeIII atom. Between 300 and 240 K, the χMTproduct is equal to 4.0 cm3 mol–1 K. This value is in agree-ment with the expected value of an FeIII complex in thehigh-spin (HS) state. It decreases gradually between 240and 130 K, to reach a value of 2.44 cm3 mol–1 K down tolow temperature. This value of 2.44 cm3 mol–1 K corre-sponds to approximately 50% of FeIII in the HS state and50% of FeIII in the low-spin (LS) state. This behaviour istypical of a gradual and incomplete spin transition, withT1/2 at 185 K.


Figure 4. Variation of χMT for [Fe–NP]·MeOH per FeIII atom.

Magnetic properties of [Fe–Ru]·2.5H2O are reported inFigure 5, as the variation versus temperature of the χMTproduct per FeIII atom. The observed behaviour is typicalof a gradual and reversible spin transition, with a smallhysteresis of 7 K, from a HS state to a LS state, withT1/2 (1)� = 183 K and T1/2� = 190 K. One can also noticea slight shift of T1/2� towards high temperature (187 in-stead of 183 K) during the second cooling process.

Figure 5. Variation of χMT for [Fe–Ru]·2.5H2O per FeIII atom inthe heating cycle (magenta) and in the cooling cyle (cyan; χMTgiven per Fe atom).

The variation of the χMT product of [Fe(salEen)2]2[Fe-(CN)5(NO)] as a function of the temperature per FeIII atomis shown in Figure 6.

Figure 6. Variation of χMT for [Fe(salEen)2]2[Fe(CN)5(NO)] (χMTgiven per FeIII atom).

At 300 K, χMT is approximately 6.6 cm3 mol–1 K, and de-creases down to 0.9 cm3 mol–1 K at 8 K. This behaviour is


reversible upon heating again. At 400 K, χMT reaches avalue of approximately 7.0 cm3 mol–1 K. These large valuesof χMT might be attributed to an orientation effect and/orintramolecular couplings between the metallic centreswithin [Fe(salEen)2]2[Fe(CN)5(NO)].

Like [Fe(salEen)2](PF6),[9] [Fe(salEen)2]2[Fe(CN)5(NO)]exhibits a gradual and complete spin transition, between400 and 8 K, with T1/2 of approximately 200 K. This spincrossover from a HS state to a LS state is confirmed bybond lengths and bond angles at 300 and 100 K around theFe atom of [Fe(salEen)2]+, in spite of a disordered NOgroup (see the Supporting Information), and contrary towhat has been observed for [Fe–NP]·2CH3CN.

Mössbauer Studies

Mössbauer spectroscopy at different temperatures hasbeen undertaken to evidence the species involved in thethermal spin crossover of [Fe–NP]·MeOH and [Fe–Ru]·2.5H2O.

Mössbauer parameters for [Fe–NP]·MeOH at 300, 200and 80 K are summarized in Table 1. At 300, 200 and 80 K,Mössbauer spectra (Figure 7) exhibit four dissymmetricalpeaks, which can be deconvoluted in the sum of three dou-blets (LS0, HS1 and LS1). During the cooling cycle, an in-crease in the area of the LS1 doublet is observed, whereasthe HS1 one decreases and the LS0 remains constant.

Table 1. Mössbauer parameters of [Fe–NP]·MeOH at various tem-peratures;[a] δ represents isomeric shift, ΔEQ represents quadrupolesplitting and AFeIIIBS/Atot and AFeIIIHS/Atot are the ratio of surfacearea of the doublet FeIII LS or FeIII HS to the total surface area).

300 K 200 K 80 K

δ [mms–1] –0.223(23) –0.23(77) –0.186(46)doublet FeII LS0 ΔEQ [mms–1] 1.970(45) 2.10(15) 1.966(91)

AFeIILS/Atot 31.25 32.29(29) 33.3(11)

δ [mms–1] 0.357(17) 0.406(20) 0.421(24)doublet FeIII HS1 ΔEQ [mms–1] 0.585(28) 0.647(34) 0.593(44)

AHS/Atot 62.3(27) 47.9(20) 31.33

δ [mms–1] –0.027(69) 0.20(12) 0.201(38)doublet FeIII LS1 ΔEQ [mms–1] 2.88(13) 2.9(25) 3.0352(74)

ALS/Atot 4.41 19.8(21) 35.41(10)

[a] Errors are given in parentheses. Isomeric shift values are relatedto metallic iron at room temperature.

With regard to LS0, the values of δ and ΔEQ (Table 1)are typical of FeII in the LS state.[10] Although the value ofδ and ΔEQ are different from those observed on single crys-tals of Na2[Fe(CN)5(NO)]·2H2O (δ ≈ 0.00 mms–1 and ΔEQ

≈ 1.7 mm s–1),[11] this doublet is attributed to [Fe(CN)5-(NO)]2–. On a single crystal of Na2[Fe(CN)5(NO)]·2H2O,these values do not change upon cooling.[12] The low valueof δ is related to a large electronic density on the FeII orbit-als. In complexes such as [M3FeIII(CN)6]·xH2O (M = Li,Na, Rb, Cs, NH4 and Ag), large variations of δ and ΔEQ

are observed[13] due to discrepancies in the electronegativityof the cation and due to its size. For [Fe–NP]·MeOH, thedifferences in the values of δ and ΔEQ relative to those re-


Figure 7. Mössbauer spectrum of [Fe–NP]·MeOH at 300, 200 and80 K.

ported for Na2[Fe(CN)5(NO)]·2H2O can be related to thesubstitution of Na+ by the much larger cation [Fe(qsal)2]+.This large noninnocent cation induces structural differ-ences, thereby resulting in numerous intermolecular interac-tions through the CN groups, which changes Mössbauerparameters of [Fe–NP]·MeOH relative to Na2[Fe(CN)5-(NO)]·2H2O.[13,14] This fraction of FeII remains almost con-stant between 300 and 80 K (31.2 % at 300 K, 32.2 % at200 K and 33.3% at 80 K), which is in agreement with thestoichiometry [FeIII(qsal)2]2[FeII(CN)5(NO)]·CH3OH (seealso the elemental analyses).

At 300 K, the doublet HS1 (δ = 0.357 mms–1 and ΔEQ =0.585 mms–1) is in agreement with an FeIII complex in theHS state (64.5%). The third doublet, LS1 with δ ≈0.0 mms–1 and ΔEQ = 2.88 mms–1 and a low intensity, isattributed to 4.4% of FeIII in the LS state. When cooling to


80 K, this percentage increases (19.8% at 200 K and 35.4%at 80 K), thereby resulting in a partial spin transition (with31.3% of FeIII remaining in the HS state).

These Mössbauer measurements confirm the suscep-tibility measurements and the gradual and incomplete spin-transition character of [Fe–NP]·MeOH (Figure 4). Thiskind of transition is characteristic of FeIII complexes, whichexhibit a spin equilibrium between the electronic state 6A1

and 2T2.[15] The populations of FeIII (60 %) and FeII (30%)calculated from the Mössbauer experiments at room tem-perature confirm the elemental analyses and the ratio2FeIII(qsal)2/FeII(CN)5(NO).

Mössbauer studies of [Fe–Ru]2.5H2O have been under-taken at 300, 164�, 80 and 164� K (Figure 8). Mössbauerparameters for each temperature are given in Table 2.

Figure 8. Mössbauer spectrum of [Fe–Ru]·2.5H2O at 300 K (up,left) and 164 K� (up, right) Mössbauer spectrum of [Fe–Ru]·2.5H2O at 80 K (bottom, left) and 164 K� (bottom, right).

Table 2. Mössbauer parameters of [Fe–Ru]·2.5H2O. Isomeric shift(δ), quadrupole splitting (ΔEQ) and width at half-height (Γ/2) aregiven relative to FeIII. The values of ηHS and ηLS are HS and LSfractions, calculated from the ratio (surface area of the doublets)/(whole surface area).

HS

T [K] δ [mms–1] ΔEQ [mms–1] Γ/2 [mms–1] ηHS [%]

300 0.382(17) 0.662(29) 0.229(23) 100164� 0.464(13) 0.734(23) 0.210(18) 5780 0.479(70) 0.80(13) 0.211(97) 8.4164� 0.474(12) 0.744(20) 0.261(17) 50.6

LS

ηLS [%]

300 – – – 0164� 0.182(11) 2.766(22) 0.166(18) 4380 0.2104(50) 2.781(10) 0.1868(85) 91.6164� 0.1885(67) 2.782(14) 0.190(11) 49.4


At 300 K, a unique doublet (HS1) was observed (Fig-ure 8). The values of δ ≈ 0.38 mm s–1 and ΔEQ ≈ 0.66 mm s–1

are typical of FeIII in the HS state.[16] Only this HS state ispresent at this temperature. At 164 K�, a second doublet(LS1) appears (δ ≈ 0.18 mms–1, ΔEQ ≈ 2.76 mms–1),whereas HS1 begins to vanish. The values of δ and ΔEQ arecharacteristic of a FeIII complex in the LS state.[16] Fromthese data, approximately 57 % of FeIII are in the HS stateand approximately 43% are in the LS state. At 80 K (Fig-ure 8), the doublet (HS1) has almost totally vanished,whereas the doublet (LS1) is largely predominant (ca. 92%).This confirms that there is still some remaining HS fractionof FeIII at 80 K (ca. 8%). When heating back to 164 K, thespectrum is almost similar to the one observed during thefirst cooling process, and only the fraction of FeIII in theHS and LS states are different (ηHS = 50.6% and ηLS =49.4%, instead of 57 and 43 %), which is in agreement withthe slight hysteresis observed in the χMT measurements.

Photomagnetic Studies on [Fe–NP]·MeOH and [Fe–Ru]·2.5H2O

Photomagnetic studies have been performed only oncompounds that exhibit a spin transition. Nevertheless, re-gardless of the wavelength used between 400 to 830 nm, nophotomagnetic effect was observed in [Fe(salEen)2]2[Fe-(CN)5(NO)].

Analyses of the photochromic properties of the [Fe–NP]·MeOH that originates from the NP group have been under-taken by laser irradiation at λ = 476 nm. Figure 9 shows theinfrared spectrum between 1770 and 1920 cm–1 of [Fe–NP]·MeOH before and after irradiation. In this range of fre-quencies, the metastable state MS1 can be detected thanksto the vibration of the NO ligand (ca. 1885 cm–1), whichundergoes a photoisomerization from a nitrosyl (NO) toa isonitrosyl (ON). Figure 9 clearly shows that there is nophotochromic effect since the position and the surface areaof the band at 1893 cm–1 do not change before and after180 min of irradiation.

Figure 9. Infrared spectrum of [Fe–NP]·MeOH at 100 K, before(black) and after irradiation (tirr = 180 min, cyan).


Therefore, the photoinduced spin crossover of theiron(III) units has been investigated, first by reflectivitymeasurements. Thermal spin crossover can be monitored bydiffuse reflectance by following the visible spectrum of thesample as a function of the temperature.[17] Figure 10 showsthe temperature dependence of the diffuse absorption spec-tra of [Fe–NP]·MeOH in the 500–900 nm region. The com-pound is strongly absorbent in the visible region, and conse-quently the optical changes are small upon thermal varia-tions. The main changes in the absorption spectra appeararound 800 nm. At 830 nm, the spectra at 180 K (Figure 10,top, cyan curve) is more intense than at 280 K (Figure 10,top, curve printed in magenta), thus indicating that thepopulation of the LS state is accompanied by an increasein the absorption at this wavelength. This is important in-formation for further photomagnetic measurements.

Figure 10. Top: Absorption spectra versus temperature (T = 280 Kin magenta and T = 180 K in cyan). Bottom: Thermal dependenceof the total reflectivity of [Fe–NP]·MeOH.

The thermal dependence of this optical change can beprecisely followed by considering the total reflectivity signalupon thermal cycling between 290 and 10 K (Figure 10,bottom). From 290 to 175 K, an increase in the total re-flectivity is observed. The thermal spin-crossover tempera-ture can be estimated to be around 220 K, which is largerthan the temperature observed in superconducting quan-tum interference device (SQUID) measurements (Figure 4,185 K). The same reflectivity experiment can also monitorany light-induced phenomena that occurs at the surface ofthe sample. When the temperature is low enough that relax-ation of the photoinduced HS state is slow, the light inten-sity at the surface of the sample can be used to tune thespin state of the complex. Below 50 K, a change in thecurve indicates the occurrence of a photoinduced spin


crossover at low temperature. This photoinduced phenome-non has been investigated by photomagnetic measurements.

A thin layer of the [Fe–NP]·MeOH compound was irra-diated at 10 K in the SQUID magnetometer. Depending onthe wavelength used, different magnetic properties were ob-served. At 10 K, an irradiation with the red light (676 nm)induced a decrease in the χMT product, whereas in the near-infrared region (830 nm), an increase of this product wasevidenced (Figure 11).

Figure 11. Magnetic and photomagnetic behaviour of [Fe–NP]·MeOH: (�) cooling cycle (�) heating cycles (0.3 Kmin–1) after ir-radiation at 830 and 676 nm (χMT given per FeIII atom).

In classical FeII spin-crossover compounds, irradiation inthe visible region, in which the LS state absorbs, inducesthe population of the paramagnetic species according to theLIESST process[18] and then an increase in the magneticsignal. On the contrary, in the near-infrared region in whichthe HS state absorbs, this paramagnetic state can be erasedaccording to the reverse-LIESST process[19] and the mag-netic response of the material decreases. In the [Fe–NP]·MeOH complex, the presence of aromatic ligands, whichinduces the presence of a ligand-to-metal charge transfer(LMCT) in the visible range, could affect this ideal view.Along with that, the increase in the absorbance at 830 nmfrom 290 to 180 K (Figure 10, bottom) indicates that theLS form absorbs in this region, whereas the decrease at650–750 nm shows that the HS state is more absorbing. Ifwe consider the Mössbauer spectroscopy, which shows thatat low temperature 50% of the FeIII ions remain in the HSstate, the decrease recorded under irradiation at 676 nmmight be associated with the reverse-LIESST process. Onthe contrary, irradiation at 830 nm converts the FeIII LSspecies into the HS state according to the direct-LIESSTmechanism. This photoinduced HS state can be also di-rectly reached after a first photoexcitation at 676 nm (i.e.,formation of the photoinduced LS state) and an excitationat 830 nm (Figure 12). Both states are quite stable over timeas indicated by the fact that upon 10 h of relaxation, thesignal remains almost constant and generally does notreach the baseline. Finally, let us note that the photoexci-tation yields are quite low because less than 20% of FeIII


ions are converted. This can be associated with the deepcolour of the [Fe–NP]·MeOH complex, which prevents lightpenetration.

Figure 12. LIESST and reverse-LIESST curves after irradiation at830 and 676 nm on [Fe–NP]·MeOH (χMT given per FeIII atom).

To complete the study, we performed measurements ofthe TLIESST temperature which represents the limit of thephotoinduced phases.[20] Above 35 K, both phases areerased, and the intermediate [HS–LS] state is recovered(Figure 11). Such a low TLIESST value indicates the presenceof efficient relaxation pathways in the system at low tem-perature. Therefore, the small photoexcitation yield (around20 %) could also follow from this efficient relaxation at10 K.

The photochromic and photomagnetic properties of [Fe–Ru]·2.5H2O were also invstigated. Like [Fe–NP]·MeOH, theinfrared spectrum recorded after 360 min of irradiation at476 nm does not show any photochromic effect in this ma-terial, since no change is observed in either the positionor the surface area of the peak characteristic of the NOphotoisomerization at 1844 cm–1 (see Figure S8 in the Sup-porting Information).

The total reflectivity signal was followed as a function ofthe temperature and evidenced a similar behaviour to the[Fe–NP]·MeOH one: that is, a thermal spin crossoveraround 190 K and the occurrence of some photoinducedphenomena at low temperature (Figure 13). A small hyster-

Figure 13. Thermal dependence of the reflectivity for [Fe–Ru]·2.5H2O.


esis in the reflectivity behaviour was also observed in [Fe–Ru]·2.5H2O, like the one observed in the magnetic measure-ments (Figure 5).

The photomagnetic properties were recorded on a thinlayer of [Fe–Ru]·2.5H2O compound. As for [Fe–NP]·MeOH, an irradiation at 830 nm induces an increase in themagnetic signal, which indicates the occurrence of aLIESST effect with 20 % efficiency. Above 40 K, this HSstate is erased (Figure 14). With regard to the low amountof remaining FeIII HS at low temperature, irradiation at676 nm was not efficient and therefore no decrease in themagnetic signal under irradiation at this wavelength is ob-served.

Figure 14. Magnetic and photomagnetic behaviour of [Fe–Ru]·2.5H2O: (�) “normal” cycle and (�) TLIESST measurements (χMTgiven per Fe atom).

DiscussionOn the basis of the evidence of light-induced spin cross-

over by the LIESST process,[18] many FeII materials havebeen investigated. With regard to FeIII complexes, fewer ex-amples have been reported in the literature and they usuallybehave similarly to the FeII compounds. That is, visible-lightirradiation induces the conversion from the LS state to theHS state and in some cases, irradiation in the near infraredconverts back the HS state into the LS one (case a). Thisis, for example, the case for [Fe(pap)2]ClO4·H2O [pap = 2-(phenylazo)pyridine] and [Fe(pap)2]PF6·MeOH.[21] How-ever, in some particular cases, the situation could be re-versed, that is, a HS metastable state population induced byirradiation around 800 nm as in [Fe(qsal)2][Ni(dmit)2]·2CH3CN,[8] [Fe(qsal)2][Ni(dmit)2]3·CH3CN·H2O,[22] [Fe-(qsal)2]NCS and [Fe(qsal)2]NCSe,[6c] and LS-state genera-tion by irradiation at 514 nm in [Fe(qsal)2]Cl·1.5H2O (caseb).[23]

Our study has shown that [Fe–NP]·MeOH and [Fe–Ru]·2.5H2O, which involve the qsal ligand, are “case b” com-pounds, whereas [Fe(salEen)2]2[Fe(CN)5(NO)] belongs tothe “case a” compounds. With [Fe(CN)5(NO)]2– being thecommon unit in these three complexes, this indicates thatthe qsal ligand should be at the origin of the “reversed”reflectivity and photomagnetic behaviour.


It has been reported that strong intermolecular interac-tions (such as π–π interactions) increase the cooperativityby increasing the dimensionality of the systems, thus fav-ouring abrupt transitions and hysteresis.[6c,8,24] This alsoleads to an increase in the activation energy of the HS meta-stable state.[25] In addition, a LIESST effect has been de-tected in [FeIII(sal2-trien)][MnIICrIII(ox)3]·(CH2Cl2) (trien =triethylenetetramine; ox = oxalate),[26] although its spintransition takes place between 350 and 165 K. In thesecases, the LIESST effect has been attributed to astrong distortion of the octahedral geometry around FeIII

HS.Our attempts to generate metastable states MS1 by light

irradiation at 476 nm and at 100 K have failed on [Fe–NP]·MeOH and [Fe–Ru]·2.5H2O. No isomerization of the ni-trosyl ligand to isonitrosyl has been detected, even after360 min irradiation of [Fe–Ru]·2.5H2O. This is quite sur-prising, since all prussiate derivatives exhibit such a transi-tion when irradiated in the range 350–590 nm. To verify ourirradiation system, we irradiated Na2[Fe(CN)5(NO)]·2H2Oat 100 K with the same laser at 476 nm. After only 30 minirradiation, the MS1 state was detected thanks to an infra-red vibration at 1834 cm–1. Under our working conditions,we should have been able to detect any MS1 state, if oneexisted. But changes to the counterion and differences inthe structure have a direct influence on the energetic gapsbetween the conformations of the NO group in the groundstate (GS) and the metastable state MS1. Therefore, one ofthe possible explanations for not detecting any MS1 couldbe related to the fact that there is no 100% conversion fromthe ground state GS to the MS1 state. The maximum ofpopulation is 47% in Na2[Fe(CN)5(NO)]·2H2O,[27] and thispercentage decreases down to 36 % when using larger cat-ions such as guanidinium (CN3H6)+ instead of Na+.[28]

With our cation being [Fe(qsal)2]+, this could explain thelack of conversion at 476 nm.

Another explanation for this result could be related tothe mobility of the nitrosyl group: in [Fe(salEen)2]2[Fe(CN)5-(NO)], this NO group is not only disordered (and shares itsposition with a CN group), it is also involved in a shortintermolecular contact with a carbon atom of an adjacent[Fe(salEen)2]+ unit (Table S4 in the Supporting Infor-mation). This was also observed in Mn-based compounds,namely, [Mn(5-Br-salpn)(H2O)]2[Fe(CN)5(NO)]·2H2O[salpn = N,N-bis(salicylidine)-1,3-diaminopropane)] and[Mn(saltmen)]4[Fe(CN)5(NO)](ClO4)2·H2O·2CH3OH [salt-men = N,N�-(1,1,2,2-tetramethylethylene)bis(salicylidene-iminato)]. In these compounds, the lack of photochromismhas been attributed to many intermolecular contacts thatinvolve the NO group, or due to structural constraints thatconfine the NO group inside cages built on the aromaticcycles.[29]

The disorder of the NO group observed in [Fe–NP]·2CH3CN and [Fe(salEen)2]2[Fe(CN)5(NO)] (see the Sup-porting Information) could also be the origin of the lack ofphotochromic effect in all compounds, although no struc-ture determination has been possible for [Fe–NP]·MeOHand [Fe–Ru]·2.5H2O.


Conclusion

To combine photochromism and spin-crossover (SCO)properties, compounds with the formula [Fe(qsal)2]2-[Fe(CN)5(NO)]·solvent, [Fe(salEen)2]2[Fe(CN)5(NO)] and[Fe(qsal)2]2[Ru(CN)5(NO)]·2.5H2O were obtained by com-bining SCO cations and photochromic anions. All of themexcept for [Fe(qsal)2]2[Fe(CN)5(NO)]·2CH3CN exhibit aspin transition, which was characterized by magneticmeasurements, Mössbauer spectroscopy and reflectivitymeasurements. Reflectivity measurements were performedfor the first time on FeIII complexes. This showed the in-verse absorption profile for the complexes that are based onthe qsal ligand, probably due to π–π interactions in thesematerials. The LIESST effect has been detected in [Fe–NP]·MeOH and [Fe–Ru]·2.5H2O. This latter also exhibits a re-verse-LIESST effect.

Despite several attempts, no photochromic effect was de-tected. Work is in progress to synthesize other spin-cross-over complexes with the nitroprussiate. This should allowus to study the possible interplay between the intraconver-sion of the nitrosyl group and the characteristics of the spintransition in these hybrid materials.

Experimental SectionNa2[Fe(CN)5(NO)]·2H2O was purchased from Sigma–Aldrich.K2[RuCl5(NO)], [Fe(qsal)2]Cl and [Fe(salEen)2](NO3) were pre-pared following reported procedures.[6a,9a,30]

The following syntheses were performed in the dark to avoid pos-sible daylight irradiation.

[Fe(qsal)2]2[Fe(CN)5(NO)]·CH3OH {[Fe–NP]·MeOH} and [Fe-(qsal)2]2[Fe(CN)5(NO)]·2CH3CN {[Fe–NP]·2CH3CN}: [Fe(qsal)2]Cl(81 mg, 1.28�10–4 mol) was dissolved in a mixture of methanol(20 mL) and acetone (or acetonitrile) (20 mL). The resulting brownsolution was placed in an ultrasonic bath for 30 min. It was filteredand added dropwise to a pale yellow solution of Na2[Fe(CN)5(NO)]·2H2O (43 mg, 1.53�10–4 mol) in methanol (5 mL). A precipitationoccurred immediately. The solution was left under agitation allnight long, then it was filtered. The precipitate was washed fourtimes with a mixture of methanol/acetone or methanol/acetonitrile(50:50; 1 mL). It was then dried with diethyl ether and was placedunder vacuum for 1 h. [Fe(qsal)2]2[Fe(CN)5(NO)]·CH3OH, yield65 mg, 38%. C70H48Fe3N14O6 (1348.8): calcd. C 62.27, H 3.55, N14.53; found C 61.33, H 3.16, N 14.58. [Fe(qsal)2]2[Fe(CN)5(NO)]·2CH3CN, yield 65 mg, 38%. C70H45.5Fe3N14.5O5 (1337.3): calcd. C62.81, H 34.0, N 15.18; found C 61.64, H 3.06, N 14.68.

Black crystals of [Fe–NP]·2CH3CN were obtained after recrystalli-zation of a fraction of the powder in a mixture of acetonitrile andtoluene.

[Fe(qsal)2]2[RuCl5(NO)]·2.5H2O [Fe–Ru]·2.5H2O: A solution of[Fe(qsal)2]Cl (81 mg, 1.2�10–4 mol) in methanol (40 mL) wasadded dropwise to a solution of K2[Ru(Cl)5(NO)] (43 mg,1.1�10–4 mol) in a mixture of methanol (10 mL) and distilledwater (10 mL). A precipitation occurred immediately. The solutionwas left under agitation all night long at 4 °C, then it was filtered.The precipitate was washed four times with a mixture of methanol/water (50:50; 1 mL). It was then dried with diethyl ether and wasplaced under vacuum for 1 h. [Fe(qsal)2]2[RuCl5(NO)]·2.5H2O,


yield 63 mg, 39%. C64H49Fe2RuCl5N9O7.5 (1454.1): calcd. C 52.81,H 3.36, N 8.66; found C 52.72, H 3.05, N 8.58.

[Fe(salEen)2]2[Fe(CN)5(NO)]: [Fe(salEen)2](NO3) (174 mg,3.4� 10–4 mol) was dissolved in acetonitrile (20 mL). This solutionwas added dropwise to a solution (5 mL) of Na2[Fe(CN)5(NO)]·2H2O (70 mg, 2.1�10–4 mol) in methanol. The resulting solutionwas evaporated under vacuum (half-volume) and heated to 50 °Cuntil a precipitate occurred. This powder was then washed twicewith methanol (5 mL) and dried under vacuum. [Fe(salEen)2]2-[Fe(CN)5(NO)], yield 80 mg, 39%. C49H60Fe3N14O5 (1092.29):calcd. C 53.86, H 5.53, N 17.95; found C 53.63, H 5.44, N 17.53.

Infrared Spectroscopy under Irradiation: Irradiation was performedat 100 K with an Ar source laser (λ = 476 nm) at an intensity of30 mWcm–2. The IR spectra were recorded in transmission modeby irradiating a KBr pellet that contained the dispersed photochro-mic-based compound {[Fe–NP]·MeOH, [Fe(salEen)2]2[Fe(CN)5-(NO)] or [Fe–Ru]·2.5H2O}.

Reflectivity Measurements: These were performed with a custom-built setup equipped with an SM240 spectrometer (Opton LaserInternational). This equipment allowed us to record both the dif-fuse absorption spectra within the range of 500–900 nm at a giventemperature and the temperature dependence (10–290 K) of the re-flectivity signal at a selected wavelength (�2.5 nm).

Photomagnetic Measurements: These were performed with a Spec-trum Physics Series 2025 Kr+ laser (514.5 or 676 nm at 5 mWcm2)or a 830 nm photodiode (3.5 mWcm2) coupled by means of anoptical fibre to the cavity of a MPMS-5S Quantum Design SQUIDmagnetometer. The optical power at the sample surface was ad-justed to prevent warming of the sample. The compound consistsof a thin layer of solid. Our previously published standardizedmethod for measuring LIESST data was followed.[20a,20b] After be-ing slowly cooled to 10 K, the sample in the low-spin state wasirradiated and the change in magnetic susceptibility was followed.When the saturation point was reached, the laser was switched offand the temperature increased at a rate of approximately0.3 Kmin–1. The magnetization was measured every 1 K. TLIESST

was determined from the minimum of a �χMT/�T versus T plot forthe relaxation process.

CCDC-907983 {for [Fe–NP]·2CH3CN}, -907984 {for [Fe(salEen)2]2-[Fe(CN)5(NO)] at 295 K} and -907985 {for [Fe(salEen)2]2[Fe(CN)5-(NO)] at 95 K} contain the supplementary crystallographic datafor this paper. These data can be obtained free of charge from TheCambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

Supporting Information (see footnote on the first page of this arti-cle): IR spectra before and after irradiation (Figures S1, S4, S8);diagrams of the asymmetric unit and structures (Figures S2, S3, S5,S6); variation of χMT (Figure S7); bond lengths, bond angles, andintermolecular contacts (Tables S1–S4).

[1] a) S. Bonhommeau, P. G. Lacroix, D. Talaga, A. Bousseksou,M. Seredyuk, I. O. Fritsky, V. Rodriguez, J. Phys. Chem. C2012, 116, 11251–11255; b) L. Kushch, L. Buravov, V. Tkach-eva, E. Yagubskii, L. Zorina, S. Khasanov, R. Shibaeva, Synth.Met. 1999, 102, 1646–1649; c) M. Clemente-León, E. Coro-nado, J. R. Galán-Mascaras, C. Giménez-Saiz, C. J. Gómez-Garcia, J. M. Fabre, Synth. Met. 1999, 103, 2279–2282; d) M.Clemente-León, E. Coronado, J. R. Galán-Mascarós, C. J.Gómez-García, T. Woike, J. M. Clemente-Juan, Inorg. Chem.2000, 39, 87–94; e) S. Bénard, E. Rivière, P. Yu, K. Nakatani,J. F. Delouis, Chem. Mater. 2001, 13, 159–162; f) F. Bellouard,M. Clemente-León, E. Coronado, J. R. Galán-Mascarós, C.


Giménez-Saiz, C. J. Gómez-GarcIa, T. Woike, Polyhedron 2001,20, 1615–1619; g) L. A. Kushch, L. S. Kurochkina, E. B. Ya-gubskii, G. V. Shilov, S. M. Aldoshin, V. A. Emel’yanov, Y. N.Shvachko, V. S. Mironov, D. Schaniel, T. Woike, C. Carbonera,C. Mathonière, Eur. J. Inorg. Chem. 2006, 4074–4085; h) Z. Z.Gu, O. Sato, T. Iyoda, K. Hashimoto, A. Fujishima, Chem.Mater. 1997, 9, 1092–1097; i) K. Ueda, M. Takahashi, H. Tom-izawa, E. Miki, C. Faulmann, J. Mol. Struct. 2005, 751, 12–16.

[2] L. A. Kushch, L. S. Kurochkina, E. B. Yagubskii, G. V. Shilov,S. M. Aldoshin, V. A. Emelrsquoyanov, Y. N. Shvachko, V. S.Mironov, D. Schaniel, T. Woike, C. Carbonera, C. Mathonière,Eur. J. Inorg. Chem. 2006, 4074–4085.

[3] a) I. Salitros, R. Boca, L. u. Dlhán, M. Gembický, J. Kozísek,J. Linares, J. Moncol, I. Nemec, L. Perasínová, F. Renz, I. Svo-boda, H. Fuess, Eur. J. Inorg. Chem. 2009, 3141–3154; b) K. H.Sugiyarto, W.-A. McHale, D. C. Craig, A. D. Rae, M. L.Scudder, H. A. Goodwin, Dalton Trans. 2003, 2443–2448.

[4] M. D. Carducci, M. R. Pressprich, P. Coppens, J. Am. Chem.Soc. 1997, 119, 2669–2678.

[5] a) A.-H. Yuan, L.-D. Lu, X.-P. Shen, L.-Z. Chen, K.-B. Yu,Trans. Met. Chem. 2003, 28, 163–167; b) G. B. Porter, J. Am.Chem. Soc. 1969, 91, 3980–3982.

[6] a) R. C. Dickinson, W. A. Baker, R. L. Collins, J. Inorg. Nucl.Chem. 1977, 39, 1531–1533; b) H. Oshio, K. Kitazaki, J. Mis-hiro, N. Kato, Y. Maeda, Y. Takashima, J. Chem. Soc., DaltonTrans. 1987, 1341–1347; c) S. Hayami, K. Hiki, T. Kawahara,Y. Maeda, D. Urakami, K. Inoue, M. Ohama, S. Kawata, O.Sato, Chem. Eur. J. 2009, 15, 3497–3508.

[7] a) S. Hayami, Z.-z. Gu, H. Yoshiki, A. Fujishima, O. Sato,J. Am. Chem. Soc. 2001, 123, 11644–11650; b) S. Hayami, T.Kawahara, G. Juhász, K. Kawamura, K. Uehashi, O. Sato, Y.Maeda, J. Radioanal. Nucl. Chem. 2003, 255, 443–447.

[8] K. Takahashi, H. Cui, H. Kobayashi, Y. Einaga, O. Sato,Chem. Lett. 2005, 34, 1240–1241.

[9] a) M. S. Haddad, M. W. Lynch, W. D. Federer, D. N. Hend-rickson, Inorg. Chem. 1981, 20, 123–131; b) M. S. Haddad,W. D. Federer, M. W. Lynch, D. N. Hendrickson, J. Am. Chem.Soc. 1980, 102, 1468–1470; c) M. S. Haddad, W. D. Federer,M. W. Lynch, D. N. Hendrickson, Inorg. Chem. 1981, 20, 131–139.

[10] R. Ingalls, Phys. Rev. A 1964, 133, 787.[11] a) W. Kerler, W. Neuwirth, Z. Phys. 1962, 167; b) N. L. Costa,

J. Danon, R. M. Xavier, J. Phys. Chem. Solids 1962, 23, 1783–1785; c) L. M. Epstein, J. Chem. Phys. 1962, 36, 2731–2737.

[12] J. Danon, L. Iannarella, J. Chem. Phys. 1967, 47, 382–387.[13] A. N. Garg, P. S. Goel, J. Inorg. Nucl. Chem. 1970, 32, 1547–

1557.[14] P. S. Goel, A. N. Garg, Inorg. Chem. 1971, 10, 1344–1347.[15] M. Nihei, T. Shiga, Y. Maeda, H. Oshio, Coord. Chem. Rev.

2007, 251, 2606–2621.[16] a) A. V. Ablov, R. A. Stukan, K. I. Turta, N. V. Gerbeleu, C. V.

Dyatlova, N. A. Barba, Russ. J. Inorg. Chem. 1974, 19, 59–63;b) K. I. Turta, A. V. Ablov, N. V. Gerbeleu, R. A. Stukan, C. V.Dyatlova, Russ. J. Inorg. Chem. 1975, 20, 82–85; c) K. I. Turta,A. V. Ablov, N. V. Gerbeleu, C. V. Dyatlova, R. A. Stukan,Russ. J. Inorg. Chem. 1976, 266–269.

[17] a) E. Codjovi, L. Sommier, O. Kahn, C. Jay, New J. Chem.1996, 20, 503–505; b) W. Morscheidt, J. Jeftic, E. Codjovi, J.Linares, A. Bousseksou, H. Constant-Machado, F. Varret,Meas. Sci. Technol. 1998, 9, 1311–1315.

[18] S. Decurtins, P. Guetlich, C. P. Koehler, H. Spiering, A. Hauser,Chem. Phys. Lett. 1984, 105, 1–4.

[19] A. Hauser, P. Guetlich, H. Spiering, Inorg. Chem. 1986, 25,4245–4248.

[20] a) J.-F. Letard, P. Guionneau, L. Rabardel, J. A. K. Howard,A. E. Goeta, D. Chasseau, O. Kahn, Inorg. Chem. 1998, 37,4432–4441; b) J.-F. Létard, L. Capes, G. Chastanet, N. Moliner,S. Letard, J.-A. Real, O. Kahn, Chem. Phys. Lett. 1999, 313,115–120; c) J.-F. Letard, P. Guionneau, O. Nguyen, J. S. Costa,S. Marcen, G. Chastanet, M. Marchivie, L. Goux-Capes,


Chem. Eur. J. 2005, 11, 4582–4589; d) J.-F. Létard, J. Mater.Chem. 2006, 16, 2550–2559; e) J.-F. Létard, G. Chastanet, P.Guionneau, C. Desplanches, in: Spin-Crossover Materials:Properties and Applications (Ed.: M. A. Halcrow), Wiley,Chichester, UK, 2013, ISBN 978-1-1199-9867-9.

[21] a) G. Juhasz, S. Hayami, O. Sato, Y. Maeda, Chem. Phys. Lett.2002, 364, 164–170; b) S. Hayami, Z.-z. Gu, M. Shiro, Y. Ein-aga, A. Fujishima, O. Sato, J. Am. Chem. Soc. 2000, 122,11569.

[22] K. Takahashi, H.-B. Cui, Y. Okano, H. Kobayashi, Y. Einaga,O. Sato, Inorg. Chem. 2006, 45, 5739–5741.

[23] G. Juhasz, S. Hayami, Y. Maeda, Spin-spin and HS-LS relax-ation in the [Fe(qsal)2]X (X = NCS, Cl) compounds, GraduateSchool of Science Kyushu University, Japan, 2004, pp. 18–21.

[24] S. Dorbes, L. Valade, J. A. Real, C. Faulmann, Chem. Com-mun. 2005, 69–71.

[25] S. Hayami, Z.-z. Gu, M. Shiro, Y. Einaga, A. Fujishima, O.Sato, J. Am. Chem. Soc. 2000, 122, 7126–7127.


[26] M. Clemente-Leon, E. Coronado, M. Lopez-Jorda, C. De-splanches, S. Asthana, H. Wang, J.-F. Letard, Chem. Sci. 2011,2, 1121–1127.

[27] T. Woike, W. Kirchner, H.-s. Kim, S. Haussühl, V. Rusanov, V.Angelov, S. Ormandjiev, T. Bonchev, A. Schroeder, HyperfineInteract. 1993, 77, 265–275.

[28] a) V. Rusanov, V. Angelov, J. Angelova, T. Bonchev, T. Woike,H.-s. Kim, S. Haussühl, J. Solid State Chem. 1996, 123, 39–47;b) U. Hauser, W. Klimm, L. Reder, T. Schmitz, M. Wessel, H.Zellmer, Phys. Lett. A 1990, 144, 39–44.

[29] R. Ababei, Y.-G. Li, O. Roubeau, M. Kalisz, N. Brefuel, C.Coulon, E. Harte, X. Liu, C. Mathoniere, R. Clerac, New J.Chem. 2009, 33, 1237–1248.

[30] J. R. Durig, W. A. McAllister, J. N. Willis, E. E. Mercer, Spec-trochim. Acta 1966, 22, 1091–1100.

Received: November 2, 2012Published Online: January 30, 2013

photomagnetic studies of spin-crossover- and photochromic-based complexes

Documents