Investigation of the spin crossover behaviour of a sublimable Fe(II)-qsal complex: from the bulk to a submonolayer on graphene/SiO.

We synthesized a sublimable molecular spin crossover Fe(II) complex based on the Schiff base tridentate ligand qsal-NEt (5-diethylamino-2-((quinolin-8-ylimino)methyl)phenol). The compound undergoes a transition in temperature with thermally induced excited spin state-trapping (TIESST) for high-temperature sweep rates, which can be suppressed by reducing the sweep rate. The X-ray absorption spectroscopy (XAS) studies on the microcrystalline powder confirm the TIESST effect.

Interface versus Bulk Light-Induced Switching in Spin-Crossover Molecular Ultrathin Films Adsorbed on a Metallic Surface.

Spin-crossover molecules present the unique property of having two spin states that can be controlled by light excitation at low temperature. Here, we report on the photoexcitation of [Fe((3, 5-(CH)Pz)BH)] (Pz = pyrazolyl) ultrathin films, with thicknesses ranging from 0.9 to 5.

Molecular Magnetic Materials Based on {Co (Tp*)(CN) } Cyanidometallate: Combined Magnetic, Structural and Co NMR Study.

The cyanidocobaltate of formula fac-PPh [Co ( Tp)(CN) ] ⋅ CH CN (1) has been used as a metalloligand to prepare polynuclear magnetic complexes ( Tp=hydrotris(3,5-dimethylpyrazol-1-yl)borate). The association of 1 with in situ prepared [Fe (bik) (MeCN) ](OTf) (bik=bis(1-methylimidazol-2-yl)ketone) leads to a molecular square of formula {[Co {( Tp)}(CN) ] [Fe (bik) ] }(OTf)  ⋅ 4MeCN ⋅ 2H O (2), whereas the self-assembly of 1 with preformed cluster [Co (OH )(piv) (Hpiv) ] in MeCN leads to the two-dimensional network of formula {[Co (piv) ] [Co ( Tp)(CN) ]  ⋅ 2CH CN} (3). These compounds were structurally characterized via single crystal X-ray analysis and their spectroscopic (FTIR, UV-Vis and Co NMR) properties and magnetic behaviours were also investigated.

Voltage-Induced Bistability of Single Spin-Crossover Molecules in a Two-Dimensional Monolayer.

Bistable spin-crossover molecules are particularly interesting for the development of innovative electronic and spintronic devices as they present two spin states that can be controlled by external stimuli. In this paper, we report the voltage-induced switching of the high spin/low spin electronic states of spin-crossover molecules self-assembled in dense 2D networks on Au(111) and Cu(111) by scanning tunneling microscopy at low temperature. On Au(111), voltage pulses lead to the nonlocal switching of the molecules from any─high or low─spin state to the other followed by a spontaneous relaxation toward their initial state within minutes.

Thermal Bistability of an Ultrathin Film of Iron(II) Spin-Crossover Molecules Directly Adsorbed on a Metal Surface.

Spin-crossover molecules are very attractive compounds to realize multifunctional spintronic devices. Understanding their properties when deposited on metals is therefore crucial for their future rational implementation as ultrathin films in such devices. Using X-ray absorption spectroscopy, we study the thermal transition of the spin-crossover compound Fe((3,5-(CH)Pz)BH) from submonolayer to multilayers on a Cu(111) substrate.

Anomalous Light-Induced Spin-State Switching for Iron(II) Spin-Crossover Molecules in Direct Contact with Metal Surfaces.

Light-induced spin-state switching is one of the most attractive properties of spin-crossover materials. In bulk, low-spin (LS) to high-spin (HS) conversion via the light-induced excited spin-state trapping (LIESST) effect may be achieved with a visible light, while the HS-to-LS one (reverse-LIESST) requires an excitation in the near-infrared range. Now, it is shown that those phenomena are strongly modified at the interface with a metal.

Importance of Epitaxial Strain at a Spin-Crossover Molecule-Metal Interface.

Spin-crossover molecules are very appealing for use in multifunctional spintronic devices because of their ability to switch between high-spin and low-spin states with external stimuli such as voltage and light. In actual devices, the molecules are deposited on a substrate, which can modify their properties. However, surprisingly little is known about such molecule-substrate effects.

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

Two new iron(II) neutral complexes of bis(1-methylimidazol-2-yl)ketone (bik) with molecular formula [Fe(bik)(NCS)] () and [Fe(bik)(NCSe)] () 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 = 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.

Molecular-scale dynamics of light-induced spin cross-over in a two-dimensional layer.

Spin cross-over molecules show the unique ability to switch between two spin states when submitted to external stimuli such as temperature, light or voltage. If controlled at the molecular scale, such switches would be of great interest for the development of genuine molecular devices in spintronics, sensing and for nanomechanics. Unfortunately, up to now, little is known on the behaviour of spin cross-over molecules organized in two dimensions and their ability to show cooperative transformation.

Elastically driven cooperative response of a molecular material impacted by a laser pulse.

Photoinduced phase transformations occur when a laser pulse impacts a material, thereby transforming its electronic and/or structural orders, consequently affecting the functionalities. The transient nature of photoinduced states has thus far severely limited the scope of applications. It is of paramount importance to explore whether structural feedback during the solid deformation has the capacity to amplify and stabilize photoinduced transformations.

Fe(II)(pap-5NO2)2 and Fe(II)(qsal-5NO2)2 Schiff-base spin-crossover complexes: a rare example with photomagnetism and room-temperature bistability.

We focus here on the properties of Fe complexes formed with Schiff bases involved in the chemistry of Fe(III) spin-transition archetypes. The neutral Fe(pap-5NO2)2 (1) and Fe(qsal-5NO2)2·Solv (2 and 2·Solv) compounds (Solv = 2H2O) derive from the reaction of Fe(II) salts with the condensation products of pyridine-2-carbaldehyde with 2-hydroxy-5-nitroaniline (Hpap-5NO2) or 5-nitrosalicylaldehyde with quinolin-8-amine (Hqsal-5NO2), respectively. While the Fe(qsal-5NO2)2·Solv solid is essentially low spin (S = 0) and requires temperatures above 300 K to undergo a S = 0 ↔ S = 2 spin-state switching, the Fe(pap-5NO2)2 one presents a strongly cooperative first-order transition (T↓ = 291 K, T↑ = 308 K) centered at room temperature associated with a photomagnetic effect at 10 K (TLIESST = 58 K).

Photo- and thermo-induced spin crossover in a cyanide-bridged {Mo(V)2Fe(II)2} rhombus molecule.

The self-assembly of [Mo(V)(CN)8](3-) and [Fe(II)(bik)2(S)2](2+) affords a cyanide-bridged {Mo(V)2Fe(II)2} rhombus molecule that shows photomagnetic effect under laser light irradiation at low temperature and exhibits thermo-induced spin crossover near ambient temperature.

Light-induced excited spin state trapping effect on [Fe(mepy)3tren](PF6)2 solvated crystals.

A spin-crossover solvated compound [Fe(mepy)3tren](PF6)2·C7H8·C2H3N has been prepared and its switching properties have been compared to those reported for the non-solvated solid. The thermal spin transition occurs at 88 K with the opening of a 3.5 K wide hysteresis loop, while a fairly steep transition at 215 K without hysteresis has been previously reported for the non-solvated analogue.

Photomagnetic effect in a cyanide-bridged mixed-valence {Fe(II)2Fe(III)2} molecular square.

The self-assembly of [Fe(III)(Tp)(CN)(3)](-) and [Fe(II)(bik)(2)(S)(2)](2+) affords the cyanide-bridged mixed valence {Fe(III)(2)Fe(II)(2)}(2+) molecular square, which exhibits a photomagnetic effect under laser light irradiation at low temperature and also shows thermal spin-state conversion near ambient temperature.

Ultrafast spin-state photoswitching in a crystal and slower consecutive processes investigated by femtosecond optical spectroscopy and picosecond X-ray diffraction.

We report the spin state photo-switching dynamics in two polymorphs of a spin-crossover molecular complex triggered by a femtosecond laser flash, as determined by combining femtosecond optical pump-probe spectroscopy and picosecond X-ray diffraction techniques. The light-driven transformations in the two polymorphs are compared. Combining both techniques and tracking how the X-ray data correlate with optical signals allow understanding of how electronic and structural degrees of freedom couple and play their role when the switchable molecules interact in the active crystalline medium.

100 picosecond diffraction catches structural transients of laser-pulse triggered switching in a spin-crossover crystal.

We study by 100 picosecond X-ray diffraction the photo-switching dynamics of single crystal of the orthorhombic polymorph of the spin-crossover complex [(TPA)Fe(TCC)]PF(6), in which TPA = tris(2-pyridyl methyl)amine, TCC(2-) = 3,4,5,6-Cl(4)-Catecholate(2-). In the frame of the emerging field of dynamical structural science, this is made possible by using optical pump/X-ray probe techniques, which allow following in real time structural reorganization at intra- and intermolecular levels associated with the change of spin state in the crystal. We use here the time structure of the synchrotron radiation generating 100 picosecond X-ray pulses, coupled to 100 fs laser excitation.

Thermo- and photoswitchable spin-crossover nanoparticles of an iron(II) complex trapped in transparent silica thin films.

The elaboration and study of hybrid nanocomposites based on photoswitchable spin-crossover nanoparticles is reported. A silica polymeric gel is used as the confining medium to control the kinetics of nucleation and growth of a molecular spin-crossover prototype [Fe((mepy)(3)tren)](PF(6))(2). The precipitation of nanoparticles in the matrix is triggered by spin-coating of the doped gel on a convenient substrate.

Ab initio static and molecular dynamics study of the absorption spectra of the 4-styrylpyridine photoswitch in its cis and trans forms.

We report a thorough investigation of the absorption spectra of the cis and trans isomers of the 4-styrylpyridine photoswitch based on TDDFT calculations. The spectra of both isomers were analysed first from the results of excitation calculations performed on their optimised geometries. The main absorption band of the cis isomer is thus predicted to be due to the S(0)--> S(1) and S(0)--> S(2) transitions, while the main absorption band of the trans isomer is predicted to originate exclusively from the S(0)--> S(1) transition.

Topological dependence of the magnetic exchange coupling in arylethynyl-bridged organometallic diradicals containing [(eta(2)-dppe)(eta(5)-C(5)Me(5))Fe(III)](+) fragments.

We have investigated the spin distribution and determined the magnetic exchange coupling J(ab) (defined according to the following Hamiltonian: H(spin) = -2J(ab)S(a).S(b)) for three arylethynyl-bridged organoiron(III) diradicals containing [(eta(2)-dppe)(eta(5)-C(5)Me(5))Fe(III)](+) fragments. Considering the distance separating the Fe(III) centers (>or=11 A), remarkably large intramolecular magnetic interactions between unpaired spins were found for two of them.

Polymorphism in the spin-crossover ferric complexes [(TPA)Fe(III)(TCC)]PF6.

We have identified two polymorphs of the molecular complex [(TPA)Fe((III))(TCC)]PF(6) [TPA = tris(2-pyridylmethyl)amine and TCC = 3,4,5,6-tetrachlorocatecholate dianion]: one is monoclinic and the other is orthorhombic. By lowering the temperature both undergo a thermal spin-crossover between a high-spin (S = 5/2) and a low-spin (S = 1/2) state, which we detected by magnetic, optical and X-ray diffraction measurements. The thermal crossover is only slightly shifted between the polymorphs.

Ab initio static and molecular dynamics study of 4-styrylpyridine.

We report an in-depth theoretical study of 4-styrylpyridine in its singlet S(0) ground state. The geometries and the relative stabilities of the trans and cis isomers were investigated within density functional theory (DFT) as well as within Hartree-Fock (HF), second-order Møller-Plesset (MP2), and coupled cluster (CC) theories. The DFT calculations were performed using the B3LYP and PBE functionals, with basis sets of different qualities, and gave results that are very consistent with each other.

Photoexcitation and relaxation dynamics of catecholato-iron(III) spin-crossover complexes.

The photophysical properties of the ferric catecholate spin-crossover compounds [(TPA)Fe(R-Cat)]X (TPA=tris(2-pyridylmethyl)amine; X=PF(6) (-), BPh(4) (-); R-Cat=catecholate dianion substituted by R=NO(2), Cl, or H) are investigated in the solid state. The catecholate-to-iron(III) charge-transfer bands are sensitive both to the spin state of the metal ion and the charge-transfer interactions associated with the different catecholate substituents. Vibronic progressions are identified in the near-infrared (NIR) absorption of the low-spin species.