Diseño, síntesis y caracterización de materiales moleculares multifuncionales conmutables

Este trabajo de Tesis Doctoral recoge la síntesis y caracterización de una nueva generación de materiales moleculares conmutables que presentan el fenómeno de transición de espín (spin crossover, SCO). El objetivo principal de esta Tesis Doctoral se ha centrado en el diseño racional de nuevos materiales multifuncionales de Fe(II) para el desarrollo de nuevas plataformas moleculares biestables que permitan el estudio detallado del comportamiento SCO sincronizado con nuevas propiedades físico-químicas, como pueden ser la química huésped-anfitrión, transiciones de fase sólido-líquido, dopaje químico,… La estrecha interrelación entre el fenómeno SCO y la segunda propiedad ha sido monitorizada, principalmente, mediante estudios magnéticos y cristalográficos, manifestándose relaciones magneto-estructurales clave que potencian la incorporación de estos materiales prometedores en nuevas aplicaciones tecnológicas. El capítulo uno presenta los conceptos teóricos más importantes del fenómeno SCO. Este comportamiento singular implica la conmutación electrónica reversible entre el estado paramagnético de espín alto y el estado diamagnético de espín bajo que muestran algunos complejos de metales de la primera serie de transición (mayoritariamente compuestos de Fe(II)) cuando se estimulan con una perturbación física externa, como puede ser un gradiente de temperatura y/o de presión, irradiación con luz o incluso interacción con un analito. El cambio de estado de espín en este tipo de materiales sensibles siempre va acompañado de modificaciones de sus propiedades físicas, destacándose cambios en la respuesta magnética, el color, el volumen del material, su constante dieléctrica…, los cuales dependen fuertemente de su estructura electrónica a nivel local. Al final de este capítulo se introducen los objetivos principales que motivan al desarrollo de esta Tesis Doctoral junto con la metodología experimental establecida para la síntesis y la caracterización de los diferentes compuestos presentados en este manuscrito. El capítulo dos introduce la síntesis y caracterización de una nueva serie de polímeros de coordinación SCO bidimensionales (2D) y tridimensionales (3D) de tipo Hofmann basados en el autoensamblaje de iones Fe(II), el ligando 2-fluoropiracina (Fpz) y las unidades de construcción [MII(CN)4]2- (MII = Ni, Pd, Pt) o [AuI(CN)2]-, los cuales muestran unas propiedades magnéticas, calorimétricas y ópticas muy cooperativas. Los centros de Fe(II) se encuentran en centros de inversión definiendo centros octaédricos axialmente distorsionados. Las posiciones ecuatoriales están ocupadas por cuatro grupos puente centrosimétricos μ4-[MII(CN)4]2- equivalentes mientras que las posiciones axiales las completan dos ligandos terminales Fpz, generando las capas 2D onduladas {Fe(Fpz)2[MII(CN)4]} (FpzM). Los derivados FpzPt y FpzPd presentan un comportamiento SCO termo- y foto-inducido, caracterizado por temperaturas críticas T1/2 centradas sobre 155.5 y 116 K y ciclos de histéresis térmica de alrededor de 22 K de anchura, mientras que el derivado FpzNi es de espín alto en todo el rango de temperaturas estudiado, incluso al someterlo a presiones hidrostáticas cercanas a 0.7 GPa. La gran estabilidad del estado de espín alto para el derivado FpzNi se ha asociado al empaquetamiento mucho más efectivo de las capas bidimensionales, a diferencia de lo que se observa en los estados de espín alto y espín bajo para los derivados FpzPt y FpzPd. Las redes tridimensionales con fórmula molecular {Fe(Fpz)[Pt(CN)4]}·1/2H2O (FpzPt3D) y {Fe(Fpz)[Au(CN)2]2} (FpzAu), donde el ligando Fpz actúa como puente, también se caracterizan detalladamente. La primera de ellas se encuentra en el estado de espín alto en todo el rango de temperaturas estudiado, mientras que la segunda muestra un comportamiento SCO muy cooperativo centrado a 243 K, y acompañado de un ciclo de histéresis de 42.5 K de ancho. Las estructuras cristalinas y las propiedades SCO de estos nuevos compuestos se comparan con compuestos reportados anteriormente de naturaleza similar, como son aquellos basados en los ligandos piracina, 3-fluoropiridina y piridina. En el capítulo tres se presenta la síntesis de los ligandos 1,3,5-tris(piridin-4-iletinil)benceno (LN3) y 1,2,4,5-tetrakis(piridin-4-iletinil)benceno (LN4), y su uso como unidades básicas de construcción en los nuevos polímeros de coordinación SCO de tipo Hofmann formulados {Fe(LN3)[MI(CN)2]2}·G [MI = Ag (1·G) , Au (2·G); G = nitrobenceno (PhNO2), benzonitrilo (PhCN), o-diclorobenceno (o-PhCl2)] y {Fe(LN4)[Ag2(CN)3][Ag(CN)2]·H2O (3·H2O), respectivamente. La especie LN3 actúa como ligando bis-monodentado definiendo redes tridimensionales doblemente interpenetradas que generan cavidades que son ocupadas por moléculas aromáticas huésped. Las redes 1·G y 2·G son isoestructurales y muestran un comportamiento SCO de primer orden termo- y foto-inducido, cuyas temperaturas críticas (T1/2 y TLIESST) dependen de la naturaleza de la molécula huésped ubicada en los poros del material. La formación “in situ” de las unidades aniónicas Ag2(CN)3- durante el proceso de cristalización permite que LN4 logre actuar como un ligando tetrakis-monodentado dando lugar al compuesto 3·H2O, que está constituido por la interpenetración de tres redes tridimensionales idénticas que no permiten la presencia de porosidad significativa. Esta red presenta un comportamiento SCO gradual junto con una fotoconversión incompleta al estado metaestable HS* a bajas temperaturas. En el capítulo cuatro se presenta la síntesis, caracterización estructural y propiedades magnéticas de dos nuevos compuestos tridimensionales porosos isoestructurales con fórmula molecular general {Fe(pina)[MI(CN)2]2}·xMeOH (x = 0 - 5; MI = Ag y x ~ 5 (1·xMeOH); MI = Au y x ~ 5(2·xMeOH)), siendo pina el ligando ambidentado N-(piridin-4-il)isonicotinamida. El análisis mediante difracción de rayos X de monocristal revela que la estructura de 1·xMeOH (y 2·xMeOH) viene definida por dos redes tridimensionales equivalentes doblemente interpenetradas, las cuales se estabilizan a través de interacciones metalofílicas MI···MI (MI = Ag o Au) e interacciones por puente de hidrógeno de tipo C=O···HC entre ligandos pina. A pesar de la doble interpenetración de las redes, ambos compuestos presentan canales donde es posible incorporar hasta 5 moléculas de metanol que se encuentran interaccionando con los ligandos pina, estableciendo una red infinita de contactos por puente de hidrógeno a lo largo de los canales. Las propiedades magnéticas muestran que 1·xMeOH y 2·xMeOH presentan comportamientos SCO cooperativos termo-inducidos en dos etapas y cuatro etapas, respectivamente. Sin embargo, la pérdida de las moléculas de metanol conlleva en ambos compuestos un cambio drástico del comportamiento magnético, presentando un comportamiento SCO mucho más gradual e incompleto. Este hecho evidencia la influencia decisiva de las moléculas incluidas en los poros sobre las propiedades SCO de estos materiales. En el proceso de desorción los cristales permanecen intactos, hecho que ha permitido analizar la estructura por difracción de rayos X de monocristal de los compuestos desolvatados 1 y 2 (x = 0) y correlacionar los cambios estructurales y la modificación de las propiedades magnéticas. El capítulo cinco describe la generación de nuevas fases termo- y foto-inducidas del compuesto [Fe(nBu-im)3tren](PF6)2 ((nBu-im)3tren = n-butilimidazoltris(2-etilamino)amina) que presentan una estabilidad cinética extraordinaria, desvelando el mecanismo que conduce a dicha estabilización. En un trabajo previo de nuestro grupo se demostró que este compuesto singular presenta dos comportamientos SCO bien diferenciados, caracterizados por ciclos de histéresis anchos que dependen de la velocidad de barrido de la temperatura. Para velocidades de barrido mayores de 2 K min-1, el comportamiento SCO se caracteriza por una temperatura crítica promedio Tcav = 122 K y un ciclo de histéresis térmico de 14 K de anchura (canal A). En cambio, para barridos inferiores a 0.1 K min-1 el comportamiento SCO tiene lugar a la temperatura Tcav = 156 K y presentan una anchura de histéresis térmica de 41 K (canal B). Este comportamiento está gobernado por una competición entre dos fases cristalográficamente independientes que se presentan en el estado de espín bajo: una fase cinética (LS1), la cual es isoestructural a la fase encontrada en el estado de espín alto, y una fase termodinámica (LS2). Las fases de espín bajo se diferencian en la disposición de las cadenas alquílicas butilo y la organización de los grupos PF6-. En este capítulo se constata que el desorden estructural intrínseco de las cadenas alifáticas butilo también juega un papel fundamental en las cinéticas de relajación HS* LS1 obtenidas a partir de las fases metaestables HS* termo- y foto-generada a bajas temperaturas. Concretamente, la relajación HS* LS1 presenta un periodo de desactivación inusualmente grande de alrededor de 20 h, una vez fotogenerado el estado HS* a 80 K. Este valor es mayor que el observado cuando el complejo se irradia en el intervalo de temperatura 10 – 70 K. Este hecho se ha estudiado de forma más precisa mediante técnicas de espectroscopia de absorción óptica y difracción de rayos X utilizando radiación sincrotrón sobre monocristal junto con medidas magnéticas. Dependiendo de la temperatura a la que se lleva a cabo la irradiación, el estado metaestable HS* presenta una organización diferente de las cadenas butilo en los ligandos. De hecho, la reorganización estructural que tiene lugar en las cadenas butilo durante el proceso de relajación para alcanzar la estructura termodinámicamente estable LS1 es la principal responsable de los tiempos de relajación tan grandes observados en el proceso de desactivación del estado HS*. El capítulo seis presenta una estrategia sintética para separar los procesos de transición de fase cristalográfica y SCO mediante el bloqueo de los canales A y B descritos previamente en el compuesto [Fe(nBu-im)3tren](PF6)2 (100P). Esta estrategia consiste en la preparación de aleaciones moleculares formuladas genéricamente como [Fe1-xMx(nBu-im)3(tren)](P1-yAsyF6)2 (M = ZnII, NiII). El control cuidadoso de la composición de esta serie isomorfa de compuestos ha permitido discriminar entre los dos canales SCO. Por un lado, la sustitución AsF6– ↔ PF6– estabiliza el canal B observado en 100P para valores [x = 0, y ≈ 0.7], donde la conformación de los grupos butilo y de los aniones PF6-/AsF6- adoptan la fase LS2. Por otro lado, cuando se sustituyen los centros activos Fe(II) por Zn(II) o Ni(II) [x ≈ 0.2, y = 0] se favorece la conformación de los grupos butilo y del anión PF6- de la fase LS1, característica del canal A del compuesto 100P. De forma similar a 100P, el derivado puro 100As (x = 0, y = 1) presenta un comportamiento SCO cooperativo acoplado a una transición de fase estructural reversible que tiene lugar a temperaturas mayores, sin duda debido a la presión química inducida por el volumen mayor del ion AsF6-, hecho que también influye sobre las cinéticas de relajación haciéndolas mucho más rápidas e impidiendo la observación de los dos canales de forma independiente. Estos mismos efectos se consiguen aplicando presiones hidrostáticas externas del orden de 0.1 GPa sobre 100P. Es interesante resaltar que la aplicación de presión externa sobre 100P, además, convierte su comportamiento SCO termo-inducido en un proceso en dos etapas tal cual se observa para el compuesto 100As. Este hecho resalta que la aplicación de presión química interna y/o externa puede conducir a efectos similares sobre el comportamiento SCO del material. El capítulo siete presenta la síntesis y caracterización de una nueva serie de complejos neutros [FeII(Ln)2] con bajo punto de fusión basados en los ligandos de tipo base de Schiff Ln = pm2-n o pyH-n, derivados de la condensación de benzohidracinas funcionalizadas con tres cadenas alquílicas (CnH2n+1) (siendo n el número de átomos de carbono que constituyen las cadenas alifáticas, que puede variar en el rango 4 – 14) con una acetona de pirimidina (pm2-n) o un aldehído de piridina (pyH-n), respectivamente. En el estado sólido los compuestos [FeII(pm2-n)2] presentan dos motivos diferentes en el empaquetamiento cristalino en función de la longitud de la cadena alquílica. Los compuestos con cadenas cortas (n = 4, 6, 8) presentan una T1/2 cercana a 400 K en el estado sólido, lo que conduce a un cambio abrupto en los valores de susceptibilidad cuando alcanza la fase líquida. Al enfriar, muestran un comportamiento SCO regular muy cooperativo con histéresis térmica, cuyas temperaturas críticas disminuyen al aumentar la longitud de las cadenas alquílicas. En cambio los compuestos definidos por cadenas alquílicas largas (n = 10, 12, 14) muestran un comportamiento SCO gradual en el estado sólido, caracterizado por una temperatura crítica T1/2 ~ 275 K. A temperaturas superiores a ~ 350 K, donde los compuestos son esencialmente HS, se produce el cambio de fase sólido líquido que provoca un comportamiento SCO cooperativo HS LS inverso, entrópicamente prohibido, el cual implica la transformación de alrededor el 50% de centros de Fe(II). Este resultado sin precedentes en complejos SCO de Fe(II) proporciona una nueva forma de modular la dirección del comportamiento SCO aprovechando la inestabilidad conformacional de las cadenas alifáticas. En el capítulo ocho se presentan las conclusiones finales de la tesis doctoral. Finalmente, se ha incluido un apéndice que recoge todos los artículos científicos que han dado lugar a la presente Tesis Doctoral.This thesis dissertation collects the synthesis and characterization of a new generation of switchable molecular materials that displays the well-known spin crossover (SCO) phenomena. The main goal of this Doctoral thesis has been focused on the rational design of novel multifunctional Fe(II) materials leading to excellent bi-stable molecular-based platforms that has allowed an accurate study of SCO behaviors synchronized with others newfangled physico-chemical properties, as can be host-guest chemistry, solid-liquid phase transitions, chemical doping,…The interplay between SCO and other intimately interlaced property has been monitored, mainly, by crystallographic and magnetic studies, manifesting key magneto-structural relationships that boost the use of this promising materials in new practical applications. Chapter one of this thesis briefly reviews the most relevant theoretical concepts of the SCO phenomena. This singular behavior is related to the reversible electronic switching between a paramagnetic high spin state (HS) and diamagnetic low spin state (LS) showed by some first-row transition-metal complexes (mostly Fe(II) compounds) under an external physical perturbation, as can be a variation of temperature, pressure or irradiating with a light. The spin state change in this very sensitive class of materials is always accompanied by modifications of many physical properties, i.e. magnetic response, color, volume of the material, dielectric constant…, which strongly depends on their local electronic structure. At the end of this chapter the motivational purpose in the development of this doctoral thesis together the general experimental procedure stablished for synthesize and full characterize the different herein presented compounds are introduced. Chapter two of this thesis introduces the synthesis and characterization of new series of two- (2D) and three-dimensional (3D) Hofmann-like spin crossover (SCO) coordination polymers based on self-assembling iron(II) ions, 2-fluoropyrazine (Fpz), and [MII(CN)4]2- (MII = Ni, Pd, Pt) or [AuI(CN)2]- building blocks, which display strong cooperative magnetic, calorimetric, and optical properties. The iron(II) ions, lying on inversion centers, define elongated octahedrons equatorially surrounded by four equivalent centrosymmetric μ4-[MII(CN)4]2- bridging groups. The axial positions are occupied by two terminal Fpz ligands affording significantly corrugated 2D layers {Fe(Fpz)2[MII(CN)4]} (FpzM). The FpzPt and FpzPd derivates undergo thermal- and light-induced SCO characterized by T1/2 temperatures centered at 155.5 and 116 K and hysteresis loops 22 K wide, while the FpzNi derivate is high spin at all temperatures, even at pressures of 0.7 GPa. The great stability of the high-spin state in the FpzNi derivate has tentatively been ascribed to the tight packing of the layers, which contrasts with that of FpzPt and FpzPd derivates in the high- and low-spin states. The 3D frameworks formulated as {Fe(Fpz)[Pt(CN)4]}·1/2H2O (FpzPt3D) and {Fe(Fpz)[Au(CN)2]2} (FpzAu), where Fpz acts as bridging ligand, are also characterized in detail. The former is high spin at all temperatures, while the latter displays very strong cooperative SCO centered at 243 K accompanied by a hysteresis loop 42.5 K wide. The crystal structures and SCO properties are compared with those of related complexes derived from pyrazine, 3-fluoropyridine, and pyridine. Chapter three of this thesis presents the synthesis of ligands 1,3,5-tris(pyridin-4-ylethynyl)benzene (LN3) and 1,2,4,5-tetrakis(pyridin-4-ylethynyl)benzene (LN4), and their use as basic building units in novel SCO Hofmann-like coordination polymers formulated as {Fe(LN3)[MI(CN)2]2}·Guest [MI = Ag (1·Guest) , Au (2·Guest); Guest = nitrobenzene (PhNO2), benzonitrile (PhCN), o-dichlorobenzene (o-PhCl2)] and {Fe(LN4)[Ag2(CN)3][Ag(CN)2]·H2O (3·H2O), respectively. The specie LN3 acts as a bis-monodentate ligand in the double interpenetrated tridimensional networks 1·Guest and 2·Guest, defining small cavities where small aromatic molecules are located. The isostructural networks 1·Guest and 2·Guest undergo first order thermal- and photo-induced SCO behavior, which critical temperatures (T1/2 and TLIESST) are characteristic of each guest molecule hosted in the pores. Favored by the “in situ” generated Ag2(CN)3- anionic units, the LN4 ligand acts as a tetrakis-monodentate in compound 3·H2O, leading to a poorly porous triply intrincated tridimensional coordination polymer. This uncommon network displays a gradual SCO behavior with an incomplete photo-population of the HS* metastable state at low temperatures. Chapter four of this thesis congregates the synthesis, structural characterization and magnetic properties of two new isostructural porous 3D compounds with general formula {FeII(pina)[MI(CN)2]2}·xMeOH (x = 0–5; pina = N-(pyridin-4-yl)isonicotinamide; MI = AgI and x ~ 5 (1·xMeOH); MI = AuI and x ~ 5 (2·xMeOH)). The single-crystal X-ray diffraction analyses have revealed that the structure of 1·xMeOH (or 2·xMeOH) presents two equivalent doubly interpenetrated 3D frameworks stabilized by both argentophilic (or aurophilic) interactions and interligand C=O···HC H-bonds. Despite the interpenetration of the networks, these compounds display accessible void volume capable of hosting up to five molecules of methanol which interact with the host pina ligand and establish an infinite lattice of hydrogen bonds along the structural channels. Interestingly, the magnetic studies have shown that the solvated complexes 1·xMeOH and 2·xMeOH display two- and four-step hysteretic thermally driven SCO behavior, respectively. However, when these compounds lose the methanol molecules, the magnetic behavior changes drastically giving place to gradual spin conversions evidencing the relevant influence of the guest molecules on the spin-crossover properties. Importantly, since the solvent desorption takes place following a single-crystal-to-single-crystal transformation, empty structures 1 and 2 (x = 0) could be also determined allowing us to evaluate the correlation between the structural changes and the modification of the magnetic properties triggered by the loss of methanol molecules. Chapter five of this thesis describes the extraordinary kinetic stability of new discovered thermo- and photo-induced phases of [Fe(nBu-im)3tren](PF6)2 ((nBu-im)3tren = n-butylimidazoltris(2-ethylamino)amine) compound, reveling the mechanism that leads to this stabilization. In a previous work of our group was discussed the two well-differentiated SCO behaviors characterized by large hysteresis loops of this mononuclear complex, which critically depend on the sweeping rate of temperature. For scan-rates higher than 2 K min–1 the SCO is characterized by an average critical temperature Tcav = 122 K with a hysteresis loop 14 K wide (channel A). In contrast, for rates below 0.1 K min–1 the SCO takes play at Tcav = 156 K and the hysteresis loop widens up to a value of 41 K (channel B). This behavior is governed by competition between two crystallographically independent phases that manifest in the LS state: a kinetic phase (LS1), which is isostructural to the HS state, and a thermodynamic phase (LS2). The LS phases differ in the disposition of the butyl tails and the organization of the PF6- groups. Interestingly, the intrinsic structural disorder characteristic of the aliphatic tails also plays a crucial role in the kinetic HS*-to-LS1 relaxation properties of the thermal and light generated metastable HS* phases at low temperatures. More precisely, the HS*-to-LS1 relaxation shows an unusual long relaxation time of 20 h after light-induced excited spin state trapping (LIESST) when irradiating at 80 K. This is more longer than when irradiating in the interval 10 – 70 K. Optical absorption spectroscopy and X-ray diffraction using synchrotron radiation as well as magnetic measurements were used to characterize and compare the LIESST behavior of this compound after irradiation in the temperature interval 10 K and 100 K. Depending on the temperature at which the co

Sublimable complexes with spin switching: Chemical design, processing as thin films and integration in graphene-based devices

Among the different types of switchable molecular compounds, sublimable Fe(II) SCO molecules provide a suitable platform to develop smart devices that respond to external stimuli. Here we report the synthesis, crystallographic structure and magnetic properties of three new neutral Fe(II) SCO molecules belonging to the {Fe[H2B(pz)2]2(L)} family with bidentate-alpha-diimine ligands L = 3-(pyridin-2-yl)-[1,2,3]triazolo[1,5-a]pyridine (tzpy), 5,5,6,6-tetrahydro-4H,4H-2,2-bi(1,3-thiazine) (btz) and 4,4,5,5-tetrahydro-2,2-bithiazole (bt) (1, 2 and 3, respectively), as well as two solvated forms of 1 and 3. All three desolvated compounds present thermal- and light-induced SCO transitions with different degrees of cooperativity and effectiveness. Furthermore, 1 and 2 are demonstrated to be sublimable under HV conditions affording homogeneous thin films 200 nm thick (TF1 and TF2) that retain the chemical integrity of the original molecules regardless the deposition surface. The SCO behaviour of the films is characterized by XAS technique revealing the partial retainment of both thermal- and light-induced spin transitions, yet losing the cooperativity. Finally, SCO/2D horizontal hybrid devices based on CVD-graphene are produced using these films. Being the first ones of this type utilizing molecules of {Fe[H2B(pz)2]2(L)} family, with L = tzpy and btz, the devices have allowed the successful detection of the thermal SCO transition through the electric properties of the CVD-graphene.Comment: 20 pages, 8 figure

Electrical sensing of the thermal and light induced spin transition in robust contactless spin-crossover/graphene hybrid devices

Hybrid devices based on spin-crossover (SCO)/2D heterostructures grant a highly sensitive platform to detect the spin transition in the molecular SCO component and tune the properties of the 2D material. However, the fragility of the SCO materials upon thermal treatment, light irradiation or contact with surfaces and the methodologies used for their processing have limited their applicability. Here, we report an easily processable and robust SCO/2D hybrid device with outstanding performance based on the sublimable SCO [Fe(Pyrz)2] molecule deposited over CVD-graphene, which is fully compatible with electronics industry protocols. Thus, a novel methodology based on growing an elusive polymorph of [Fe(Pyrz)2] (tetragonal phase) over graphene is developed that allows us to electrically detect a fast and effective light-induced spin transition in the devices (~50% yield in 5 minutes). Such performance can be enhanced even more when a flexible polymeric layer of PMMA is inserted in between the two active components in a contactless configuration, reaching a ~100 % yield in 5 minutes.Comment: 25 pages, 5 figure

Guest Induced Strong Cooperative One- and Two-Step Spin Transitions in Highly Porous Iron(II) Hofmann-Type Metal-Organic Frameworks

[EN] The synthesis, crystal structure, magnetic, calorimetric, and Mo¿ ssbauer studies of a series of new Hofmann-type spin crossover (SCO) metal¿organic frameworks (MOFs) is reported. The new SCO-MOFs arise from self-assembly of FeII, bis(4-pyridyl)butadiyne (bpb), and [Ag(CN)2] ¿ or [MII(CN)4] 2¿ (MII = Ni, Pd). Interpenetration of four identical 3D networks with ¿-Po topology are obtained for {Fe(bpb)[AgI (CN)2]2} due to the length of the rod-like bismonodentate bpb and [Ag(CN)2] ¿ ligands. The four networks are tightly packed and organized in two subsets orthogonally interpenetrated, while the networks in each subset display parallel interpenetration. This nonporous material undergoes a very incomplete SCO, which is rationalized from its intricate structure. In contrast, the single network Hofmann-type MOFs {Fe(bpb)[MII(CN)4]}·nGuest (MII = Ni, Pd) feature enhanced porosity and display complete one-step or two-step cooperative SCO behaviors when the pores are filled with two molecules of nitrobenzene or naphthalene that interact strongly with the pyridyl and cyano moieties of the bpb ligands via ¿¿¿ stacking. The lack of these guest molecules favors stabilization of the high-spin state in the whole range of temperatures. However, application of hydrostatic pressure induces one- and two-step SCO.We thank the Spanish Ministerio de Economia y Competitividad (MINECO) and FEDER funds (CTQ2013-46275-P and CTQ2016-78341-P and Unidad de Excelencia Maria de Maeztu MDM-2015-0538) and Generalitat Valenciana (PROMETEO/2016/147). L.P.-L. and F.J.V.-M. thank, respectively, the Universidad de Valencia and MINECO for a predoctoral FPI grant.Piñeiro-López, L.; Valverde-Muñoz, FJ.; Seredyuk, M.; Muñoz Roca, MDC.; Haukka, M.; Real, JA. (2017). Guest Induced Strong Cooperative One- and Two-Step Spin Transitions in Highly Porous Iron(II) Hofmann-Type Metal-Organic Frameworks. Inorganic Chemistry. 56(12):7038-7047. https://doi.org/10.1021/acs.inorgchem.7b00639S70387047561

Electrical sensing of the thermal and light induced spin transition in robust contactless spin-crossover/graphene hybrid devices

Hybrid devices based on spin-crossover (SCO)/2D heterostructures grant a highly sensitive platform to detect the spin transition in the molecular SCO component and tune the properties of the 2D material. However, the fragility of the SCO materials upon thermal treatment, light irradiation or contact with surfaces and the methodologies used for their processing have limited their applicability. Here, we report an easily processable and robust SCO/2D hybrid device with outstanding performance based on the sublimable SCO [Fe(Pyrz)2] molecule deposited over CVD-graphene, which is fully compatible with electronics industry protocols. Thus, a novel methodology based on growing an elusive polymorph of [Fe(Pyrz)2] (tetragonal phase) over graphene is developed that allows us to electrically detect a fast and effective light-induced spin transition in the devices (~50% yield in 5 minutes). Such performance can be enhanced even more when a flexible polymeric layer of PMMA is inserted in between the two active components in a contactless configuration, reaching a ~100 % yield in 5 minutes

Preditores de satisfação dos profissionais de saúde com a educação continuada: um estudo transversal

Objectives: to verify which organizational, methodological, and resource-related characteristics of Continuing Health Education (CHE) help to best predict the professionals´ satisfaction. Method: a cross-sectional study with multivariate logistic regressions to predict a high mean satisfaction with different dimensions of educational actions used: Overall satisfaction, Utility, Methodology, Organization and resources, and Teaching Capacity. 25,281 satisfaction questionnaires have been analysed completed by health professionals attending 1,228 training activities in Andalusia (Spain), during the period from March 2012 to April 2015. Results: the characteristics that best predict a high overall satisfaction are the following: clinical session type as opposed to the workshop (Odds Ratio [OR]=2.07, p<0.001); face-to-face attendance modality (OR=3.88, p<0.001) or semi-personal-attendance (OR=2.83, p<0.001), as opposed to e-learning; and 1-2 days in duration (OR=2.38, p<0.001) as opposed to those of between 3 and 14 days. A lower number of hours (OR=0.99, p<0.001) and a lower number of professionals (OR=0.98, p<0.05) also increase the probability. Having the educational actions accredited increases the probabilities in the following dimensions: Utility (OR=1.33, p<0.05), Methodology (OR=1.5, p<0.01) and Teaching capacity (OR=1.5, p<0.01). Conclusion: the study provides relevant information on aspects that improve professional satisfaction, such as that e-learning activities should improve their content, teaching methods, and styles, or that face-to-face clinical sessions are the type of CHE with the greatest satisfaction.Objetivo: verificar quais características organizacionais, metodológicas e relacionadas a recursos da educação continuada em saúde (ECS) ajudam a predizer melhor a satisfação dos profissionais. Método: estudo transversal com regressões logísticas multivariadas para predizer uma alta satisfação média com diferentes dimensões das ações educativas utilizadas: Satisfação Geral, Utilidade, Metodologia, Organização e Recursos, e Capacidade de Ensino. Foram analisados 25.281 questionários de satisfação preenchidos por profissionais de saúde que participaram de 1.228 atividades de treinamento na Andaluzia (Espanha), no período de março de 2012 a abril de 2015. Resultados: características que melhor predizem uma alta Satisfação Geral são as seguintes: Método de sessão clínica em oposição a workshops (Odds Ratio[OR]=2,07;p<0,001); modalidade presencial (OR=3,88;p<0,001) ou semipresencial (OR=2,83;p<0,001) em oposição a e-learning; e 1-2 dias de duração (OR=2,38;p<0,001) em oposição a 3-14 dias. Um menor número de horas (OR=0,99;p<0,001) e de profissionais (OR=0,98;p<0,05) também aumenta a probabilidade. A acreditação das ações educativas aumenta as probabilidades nas dimensões: Utilidade (OR=1,33;p<0,05), Metodologia (OR=1,5;p<0,01) e Capacidade de Ensino (OR=1,5;p<0,01). Conclusão: o estudo fornece informações relevantes sobre aspectos que melhoram a satisfação profissional, como a opinião de que atividades e-learning precisam melhorar seu conteúdo, métodos e estilos de ensino, ou de que sessões clínicas presenciais são o tipo de ECS com maior satisfação.Objetivo: verificar qué características organizativas, metodológicas y de recursos de la Educación Continua en Salud (ECS) ayudan a predecir mejor la satisfacción de los profesionales. Método: se utiliza un estudio transversal con regresiones logísticas multivariadas para predecir un alto promedio de satisfacción con los diferentes tipos de acciones educativas: Satisfacción general, Utilidad, Metodología, Organización y recursos y Capacidad docente. Se han analizado 25.281 cuestionarios de satisfacción respondidos por los profesionales de la salud que asistieron a 1228 actividades formativas, en Andalucía (España), durante el período de marzo a abril de 2012. Resultados: características que mejor predicen una alta Satisfacción general: Tipo de sesión clínica frente al taller (OddsRatio [OR]=2,07, p<0,001); modalidad de asistencia presencial (OR=3,88, p<0,001) o semipersonal (OR=2,83, p<0,001), frente al aprendizaje electrónico (e-learning); y 1-2 días de duración (OR=2,38, p<0,001) frente a 3-14 días. Una menor cantidad de horas (OR=0,99, p<0,001) y una menor cantidad de profesionales (OR=0,98, p<0,05) también aumentan la probabilidad. Acreditar las acciones educativas aumenta las probabilidades en las siguientes dimensiones: Utilidad (OR=1,33, p<0,05), Metodología (OR=1,5, p<0,01) y Capacidad docente (OR=1,5, p<0,01). Conclusión: el estudio aporta información relevante sobre aspectos que mejoran la satisfacción profesional, como que las actividades de aprendizaje electrónico deben mejorar sus contenidos, métodos y estilos de enseñanza o que las sesiones clínicas personales son el tipo de ECS con mayor satisfacción

Design and processing as ultrathin films of a sublimable Iron(II) spin crossover material exhibiting efficient and fast light-induced spin transition

Materials based on spin crossover (SCO) molecules have centred the attention in Molecular Magnetism for more than forty years as they provide unique examples of multifunctional and stimuli-responsive materials, which can be then integrated into electronic devices to exploit their molecular bistability. This process often requires the preparation of thermally stable SCO molecules that can sublime and remain intact in contact with surfaces. However, the number of robust sublimable SCO molecules is still very scarce. Here we report a novel example of this kind. It is based on a neutral iron (II) coordination complex formulated as [FeII(neoim)2], where neoimH is the ionogenic ligand 2-(1H-imidazol-2-yl)-9-methyl-1,10-phenanthroline. In the first part a comprehensive study, which covers the synthesis and magneto-structural characterization of the [FeII(neoim)2] complex as a bulk microcrystalline material, is reported. Then, in the second part we investigate the suitability of this material to form thin films through high vacuum (HV) sublimation. Finally, the retainment of all present SCO capabilities in the bulk when the material is processed is thoroughly studied by means of X-ray absorption spectroscopy. In particular, a very efficient and fast light-induced spin transition (LIESST effect) has been observed, even for ultrathin films of 15 nm.Comment: 27 pages, 2 schemes, 5 figures, 1 tabl

Chiral and Racemic Spin Crossover Polymorphs in a Family of Mononuclear Iron(II) Compounds

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Inorganic Chemistry, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acs.inorgchem.7b02272[EN] Understanding the origin of cooperativity and the equilibrium temperature of transition (T1/2) displayed by the spin-crossover (SCO) compounds as well as controlling these parameters are of paramount importance for future applications. For this task, the occurrence of polymorphism, presented by a number of SCO complexes, may provide deep insight into the influence of the supramolecular organization on the SCO behavior. In this context, herein we present a novel family of mononuclear octahedral FeII complexes with formula cis- [Fe(bqen)(NCX)2], where bqen is the chelating tetradentate ligand N,N¿-bis(8-quinolyl)ethane-1,2-diamine and X = S, Se. Depending on the preparation method, these compounds crystallize in either the orthorhombic or the trigonal symmetry systems. While the orthorhombic phase is composed of a racemic mixture of mononuclear complexes (polymorph I), the trigonal phase contains only one of the two possible enantiomers (¿ or ¿), thereby generating a chiral crystal (polymorph II). The four derivatives undergo SCO behavior with well-differentiated T1/2 values occurring in the interval 90¿233 K. On one hand, T1/2 is about 110 K (polymorph I) and 87 K (polymorph II) higher for the selenocyanate derivatives in comparison to those for their thiocyanate counterparts. These differences in T1/2 are ascribed not only to the higher ligand field induced by the selenocyanate anion but also to a remarkable difference in the structural reorganization of the [FeN6] coordination core upon SCO. Likewise, the higher cooperativity observed for the thiocyanate derivatives seems to be related to their stronger intermolecular interactions within the crystal. On the other hand, T1/2 is about 53 K (thiocyanate) and 29 K (selenocyanate) higher for the trigonal polymorph II in comparison to those for the orthorhombic polymorph I. These differences, and the small changes observed in cooperativity, stem from the slightly different hetero- and homochiral crystal packing generated by the cis-[Fe(bqen)(NCX)2] molecules, which determines subtle adaptations in the intermolecular contacts and the FeII coordination core.We thank the Spanish Ministerio de Economia y Competitividad (MINECO) and FEDER funds (CTQ2013-46275-P and CTQ2016-78341-P and Unidad de Excelencia Maria de Maeztu MDM-2015-0538), Generalitat Valenciana (PROM-ETEO/2016/147), and EU Framework Program for Research and Innovation (RISE project number 734322). FJ.V.-M. thanks MINECO for a predoctoral FPI grantBartual-Murgui, C.; Piñeiro-López, L.; Valverde-Muñoz, FJ.; Muñoz Roca, MDC.; Seredyuk, M.; Real, JA. (2017). Chiral and Racemic Spin Crossover Polymorphs in a Family of Mononuclear Iron(II) Compounds. Inorganic Chemistry. 56(21):13535-13546. https://doi.org/10.1021/acs.inorgchem.7b022721353513546562

Bistable Hofmann-Type FeII Spin-Crossover Two-Dimensional Polymers of 4-Alkyldisulfanylpyridine for Prospective Grafting of Monolayers on Metallic Surfaces

[EN] Aiming at investigating the suitability of Hofmann-type two-dimensional ( 2D) coordination polymers {Fe-II(L-ax)(2)[M-II(CN)(4)]} to be processed as single monolayers and probed as spin crossover (SCO) junctions in spintronic devices, the synthesis and characterization of the MII derivatives (M-II = Pd and Pt) with sulfur-rich axial ligands (L-ax = 4-methyl- and 4-ethyl-disulfanylpyridine) have been conducted. The thermal dependence of the magnetic and calorimetric properties confirmed the occurrence of strong cooperative SCO behavior in the temperature interval of 100-225 K, featuring hysteresis loops 44 and 32.5 K/21 K wide for PtII-methyl and Pt-II/Pd-II- ethyl derivatives, while the Pd-II-methyl derivative undergoes a much less cooperative multistep SCO. Excluding Pt-II-methyl, the remaining compounds display light-induced excited spin-state trapping at 10 K with T-LIESST temperatures in the range of 50-70 K. Single-crystal studies performed in the temperature interval 100-250 K confirmed the layered structure and the occurrence of complete transformation between the high- and low-spin states of the Fe-II center for the four compounds. Strong positional disorder seems to be the source of elastic frustration driving the multistep SCO observed for the Pd-II-methyl derivative. It is expected that the peripheral disulfanyl groups will favor anchoring and growing of the monolayer on gold substrates and optimal electron transport in the device.This work was supported by the Spanish Ministerio de Ciencia e Innovacion (MICINN) and FEDER founds (No. PID2019-106147GB-I00), Unidad de Excelencia Maria de Maeztu (Nos. MDM2015-0538-18-2, CEX2019-000919-M) and EU Framework FET-OPEN project COSMICS (Grant Agreement No. 766726). R.T.C. and M.M.S. thank the MICINN for a predoctoral grant.Turo-Cortés, R.; Valverde-Muñoz, FJ.; Meneses-Sánchez, M.; Muñoz Roca, MDC.; Bartual-Murgui, C.; Real, JA. (2021). Bistable Hofmann-Type FeII Spin-Crossover Two-Dimensional Polymers of 4-Alkyldisulfanylpyridine for Prospective Grafting of Monolayers on Metallic Surfaces. Inorganic Chemistry. 60(12):9040-9049. https://doi.org/10.1021/acs.inorgchem.1c0101090409049601

105 K Wide Room Temperature Spin Transition Memory Due to a Supramolecular Latch Mechanism

[EN] Little is known about the mechanisms behind the bistability (memory) of molecular spin transition compounds over broad temperature ranges (>100 K). To address this point, we report on a new discrete Fe-II neutral complex [(FeL2)-L-II](0) (1) based on a novel asymmetric tridentate ligand 2-(5-(3-methoxy-4H-1,2,4-triazol-3-yl)-6-(1H-pyrazol-1-yl))pyridine (L). Due to the asymmetric cone-shaped form, in the lattice, the formed complex molecules stack into a one-dimensional (1D) supramolecular chain. In the case of the rectangular supramolecular arrangement of chains in methanolates 1-A and 1-B (both orthorhombic, Pbcn) differing, respectively, by bent and extended spatial conformations of the 3-methoxy groups (3MeO), a moderate cooperativity is observed. In contrast, the hexagonal-like arrangement of supramolecular chains in polymorph 1-C (monoclinic, P2(1)/c) results in steric coupling of the transforming complex species with the peripheral flipping 3MeO group. The group acts as a supramolecular latch, locking the huge geometric distortion of complex 1 and in turn the trigonal distortion of the central Fe-II ion in the high-spin state, thereby keeping it from the transition to the low-spin state over a large thermal range. Analysis of the crystal packing of 1-C reveals significantly changing patterns of close intermolecular interactions on going between the phases substantiated by the energy framework analysis. The detected supramolecular mechanism leads to a record-setting robust 105 K wide hysteresis spanning the room temperature region and an atypically large T-LIESST relaxation value of 104 K of the photoexcited high-spin state. This work highlights a viable pathway toward a new generation of cleverly designed molecular memory materials.This work was supported by the Spanish Ministerio de Ciencia e Innovación (Grant PID2019-106147GB-I00 funded by MCIN/AEI/10.13039/501100011033), Unidad de Excelencia María de Maeztu (CEX2019-000919-M), EU Framework FET-OPEN project COSMICS (grant agreement 766726), and Ministry of Education and Science of Ukraine (Grants 22BF037-03 and 22BF037-04). F.J.V.-M. acknowledges the support of the Generalitat Valenciana (APOSTD/2021/359). The authors are grateful to Miguel Gavara-Edo y Rubén Turo-Cortés for helping us in the Raman and magnetic measurements.Seredyuk, M.; Znovjyak, K.; Valverde-Muñoz, FJ.; Da Silva, I.; Muñoz Roca, MDC.; Moroz, YS.; Real, JA. (2022). 105 K Wide Room Temperature Spin Transition Memory Due to a Supramolecular Latch Mechanism. Journal of the American Chemical Society. 144(31):14297-14309. https://doi.org/10.1021/jacs.2c0541714297143091443