The spin crossover (SCO) behavior of molecules in (sub)monolayers can differ from that of the bulk: in particular, it can be quenched or "pinned" by direct contact between the SCO molecules and the substrate, causing problems for potential device applications. Moreover, processing on sublimated SCO films is limited by reactivity to solvents. Here, it is shown that the preparation from solution of self-assembled monolayers (SAMs) of the Fe(II) complex [Fe(Tp(4-NHCOC10H20SCOCH3))(Tp)], where Tp = tris(1H-pyrazol-1-yl)borohydride, yields reversible, nonpinned SCO on gold substrates. The formation of chemisorbed SAMs is confirmed by atomic force microscopy, time-of-flight secondary ion mass spectrometry, polarization modulation infrared reflection absorption spectroscopy and X-ray photoelectron spectroscopy. Cyclic voltammetry demonstrates the redox activity of the SAMs, with clear evidence of the Fe(II)/Fe(III) redox couple, and corresponding calculations confirm a dense surface coverage. Variable temperature X-ray photoelectron and X-ray absorption spectroscopies at the Fe L2,3 edges indicate a reversible SCO in the monolayers identical to the bulk behavior, with a gradual conversion and T12 of 367 K. These findings show that monolayers of SCO compounds can be assembled from solution while retaining a reversible SCO, making them suitable for use in switchable molecular electronic systems.

A current challenge in silicon chemistry is to perform liquid-phase synthesis of silicon nanoparticles, which would permit the use of colloidal synthesis techniques to control size and shape. Herein we show how silicon nanoparticles were synthesized at ambient temperature and pressure in organic solvents through a redox reaction. Specifically, a hexacoordinated silicon complex, bis(N,N'-diisopropylbutylamidinato)dichlorosilane, was reduced by a silicon Zintl phase, sodium silicide (Na4Si4). The resulting silicon nanoparticles were crystalline with sizes tuned from a median particle diameter of 15 nm to 45 nm depending on the solvent. Photoluminescence measurements performed on colloidal suspensions of the 45 nm diameter silicon nanoparticles indicated a blue emission signal, attributed to the partial oxidation of the Si nanocrystals or to the presence of nitrogen impurities.

A series of three compounds [Fe(salEen-5-I)(2)]Cl 1, [Fe(salEen-5-I)(2)]Br 2, and [Fe(salEen-5-I)(2)]I 3 in which salEen-5-I = 2-{[(2-(ethylamino)ethyl]imino)methyl}-4-iodophenolate is reported. Magnetic studies reveal that 2 exhibits an abrupt 2-step spin crossover close to room temperature around 288 K, while 1 and 3 exhibit gradual incomplete spin crossover spanning over 200 K. The use of structural parameters A-C to describe the nearest and next nearest neighbor contacts allows us to rationalize not only the abruptness of the spin crossover but also the stepped nature of the spin crossover in 2. Comparisons with previously reported [Fe(salEen-5-Br)(2)]ClO4 and [Fe(salEen-5-I)(2)]ClO4 reveal that this magnetostructural relationship is applicable to a wider range of members of this family of complexes.

Replacement of the heteroatom from Si to Ge has a strong influence on the luminescence properties of a series of hybrid, sandwich-type K5[Ln(alpha-GeW11O39)(C20H22Br2N2O4)]14H2O (1Ge-Ln, Ln = Sm to Lu) anions. Interestingly, the Gd and Yb derivatives retain their ability to display slow relaxation of magnetisation. Replacement of the heteroatom modifies the magneto-luminescence properties of [Ln(alpha-GeW11O39)(H2L)]5- (Ln = Sm to Lu) hybrid anions. The Yb-derivative exhibits simultaneous slow relaxation of magnetization and NIR emission at room temperature.

Our society largely relies on inorganic semiconductor devices which are, so far, fabricated using expensive and complex processes requiring ultra-high vacuum equipment. Here we report on the possibility of growing a p-n junction taking advantage of electrochemical processes based on the use of aqueous solutions. The growth of the junction has been carried out using the Electrochemical Atomic Layer Deposition (E-ALD) technique, which allowed to sequentially deposit two different semiconductors, CdS and Cu2S, on an Ag(111) substrate, in a single procedure. The growth process was monitored in situ by Surface X-Ray Diffraction (SXRD) and resulted in the fabrication of a thin double-layer structure with a high degree of crystallographic order and a well-defined interface. The high-performance electrical characteristics of the device were analysed ex-situ and show the characteristic feature of a diode. Semiconductor junctions are the fundamental components of important electronic devices including transistors and photovoltaic cells. This work reports on an innovative and inexpensive method for obtaining semiconductor-based devices, particularly p-n junctions. Electrochemical Atomic Layer Deposition allows the sequential deposition of two different semiconductors from aqueous solutions. image

Silicon particles of intermediate sizes (75-200 nm) scatter visible wavelengths, making them promising candidates for optical devices. The solution synthesis of silicon particles in this size range, however, has proved challenging for chemists over the past few decades. Here, a solution-phase synthesis provides a pathway toward reaching size tunability between 45 and 230 nm via changing the reactant ratio in the reaction between a silicon Zintl phase (Na4Si4) with an amidinate-stabilized Si(IV) coordination complex. Coherent domain sizes, determined from powder X-ray diffraction, show that the crystallite sizes are uniform across all particle sizes, perhaps indicating an aggregation mechanism for particle growth. The amidinate ligands act to stabilize the particle surface. Combined surface techniques (ToF-SIMS, FTIR, and X-ray photoelectron spectroscopy) confirm the presence of amidinate ligands, as well as primary amine and a passive oxidation layer on the surface of the particles. The refractive index is measured for an individual particle using holographic optical microscopy, displaying a refractive index of nearly 4.1 at a wavelength of 532 nm. Thus, these particles should scatter light intensely at visible wavelengths, making them promising candidates for optical manipulation.

Iron-gallium borate, FexGa1-xBO3, single crystals have been synthesized by the solution in the melt technique. The exact x-values in the crystals have been determined by X-ray fluorescence analysis and checked by Energy Dispersive X-Ray Spectroscopy. Scanning Electron Microscopy has been used to map distributions of iron and gallium ions in the crystals. The electron magnetic resonance (EMR) spectra as well as field and temperature dependences of the magnetization obtained by SQUID reveal the existence of different magnetic phases in different x ranges, viz. weakly ferromagnetic antiferromagnetic, magnetic cluster and paramagnetic phase. For crystals with 0.32 <= x <= 0.83, the N & eacute;el temperatures, T-N, have been determined. The magnetometry of these crystals suggests the existence of another magnetic transition at a temperature well below T-N, tentatively ascribed to a Morin type transition. Detailed EMR and SQUID studies of the crystal with x approximate to 0.2 reveal the existence of magnetic nanoclusters showing superparamagnetic behaviour. Using a laboratory developed code based on the Monte-Carlo technique, spatial distributions of dia- and paramagnetic ions in the crystal with x approximate to 0.2 has been visualized and possible cluster sizes have been estimated.

The oxygen substoichiometry of as-prepared WO3 (tungsten trioxide) nano-powders (NPs) from a polyol process was tuned via peptization of the NPs in aqueous solutions of different Cr2O72- oxidizing concentrations. The assynthesized materials have been characterized by X-ray scattering (XRD and PDF), transmission electron microscopy (TEM), X-ray photoelectron (XPS), and UV-VIS photochromic activity. The local atomic structure of WO3-X was investigated using total scattering atomic pair distribution function (PDF) analysis based on X-ray total scattering data collected on powder at ambient conditions. The PDF analysis confirms that the crystal structure of all studied samples can be described in terms of very small crystallites with a P21/n space-group monoclinic framework but with anomalous unit cell distortion parameters, indicating that small crystallite sizes resulted in a larger monoclinic distortion (as measured by the beta angle of the unit cell). The nanometer dimension of the crystallites combined as well as the oxygen-tungsten stoichiometric ratio control, are key features for optimized photochromic properties. Moreover, we present the fabrication of a WO3-x thin film based UV photosensor, which was carried out on silica glass substrates via the dip-coating method. The obtained films exhibited a UV photoresponse and photoelectric characteristics at 5 V bias voltages able to detect very low UV doses, inferior to 10 W/m2. The photo-detection measurements prove the usability of our device as a UV photodetector with a good responsivity of 0.37 A/W and external quantum efficiency of more than 100% even at a very low power density (9.2 W/m2) of UV illumination.

A new spin crossover complex based on a heteroscorpionate ligand was synthesized and characterized. Thin films were grown by sublimation in ultra-high vacuum on highly oriented pyrolytic graphite (HOPG) and on gold single crystal Au (111), and spectroscopically characterized through X-ray absorption and by X-ray photoemission. Temperature-dependent experiments on sub-nanometric deposits demonstrated that the thermally induced spin-crossover is preserved at a sub-monolayer (0.7 ML) coverage on HOPG, while deposits with similar thickness lose the switching behaviour on Au(111) surface. The system was unresponsive to light stimuli at low temperature indepently of the used substrate.

Conglomerate formation, where enantiomers within a racemic mixture self-segregate upon crystallization, is an advantageous property for obtaining chirally pure crystals and allows large-scale chiral resolution. However, the prevalence of conglomerates is low and difficult to predict. In this report, we describe our attempts to engineer conglomerates from racemate-forming compounds by integrating them into a conglomerate-forming matrix. In this regard, we found that Ni(II) and Fe(II) form molecular alloys with Zn(II) in [MxZn(1−x)(bpy)3](PF6)2 (where bpy = 2,2′-bipyridyl). Powder X-ray Diffraction (PXRD) and Energy-Dispersive X-ray spectroscopy (EDX) evidenced conglomerate crystallization with Ni(II) concentrations up to about 25%, while it was observed only for much lower concentrations of Fe(II). This can be attributed to the ability of [Ni(bpy)3](PF6)2 to access a metastable conglomerate phase, while no such phase has been detected in [Fe(bpy)3](PF6)2. Furthermore, the chiral phase appears to be favored in fast-growing precipitates, while the racemic phase is favored in slow re-crystallizations for both Ni(II) and Fe(II) molecular alloys. X-ray natural circular dichroism (XNCD) measurements on [Ni0.13Zn0.87(bpy)3](PF6)2 demonstrate the chirality of the nickel molecules within the zinc molecular matrix.

Magnetic nanoparticles are central to the development of efficient hyperthermia treatments, magnetic drug carriers, and multimodal contrast agents. While the magnetic properties of small crystalline iron oxide nanoparticles are well understood, the superparamagnetic size limit constitutes a significant barrier for further size reduction. Iron (oxy)hydroxide phases, albeit very common in the natural world, are far less studied, generally due to their poor crystallinity. Templating ultrasmall nanoparticles on substrates such as graphene is a promising method to prevent aggregation, typically an issue for both material characterization and applications. We generate ultrasmall nanoparticles, directly on the carbon framework by the reaction of a graphenide potassium solution, charged graphene flakes, with iron(II) salts. After mild water oxidation, the obtained composite material consists of ultrasmall potassium ferrite nanoparticles bound to the graphene nanoflakes. Magnetic properties as evidenced by magnetometry and X-ray magnetic circular dichroism, with open magnetic hysteresis loops near room temperature, are widely different from classical ultrasmall superparamagnetic iron oxide nanoparticles. The large value obtained for the effective magnetic anisotropy energy density Keff accounts for the presence of magnetic ordering at rather high temperatures. The synthesis of ultrasmall potassium ferrite nanoparticles under such mild conditions is remarkable given the harsh conditions used for the classical syntheses of bulk potassium ferrites. Moreover, the potassium incorporation in the crystal lattice occurs in the presence of potassium cations under mild conditions. A transfer of this method to related reactions would be of great interest, which underlines the synthetic value of this study. These findings also give another view on the previously reported electrocatalytic properties of these nanocomposite materials, especially for the sought-after oxygen reduction/evolution reaction. Finally, their longitudinal and transverse proton NMR relaxivities when dispersed in water were assessed at 37 °C under a magnetic field of 1.41 T, allowing potential applications in biological imaging.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

We present herein a family of molecular cis-[FeII(X-PPMA)2(NCS)2]·H2O [4-X-N-(phenyl(pyridin-2-yl)methylene)aniline; X-PPMA; X = -Cl (1), -Br (2), and -CH3 (3)] complexes that exhibit spin crossover behaviour above room temperature. Judiciously designed bidentate N-donor Schiff bases of 2-benzoylpyridine and para-substituted anilines in combination with Fe(NCS)2 were used for the synthesis of complexes 1-3. The relatively strong ligand field of the Schiff bases stabilises the low spin state of iron(II) up to 300 K which is evident from magnetic measurements, room temperature Mössbauer spectra and crystallographic bond/angle distortion parameters. Interestingly, complexes 1-3 crystallize in a tetragonal system with either a P43212 or P41212 chiral space group from achiral building units due to the supramolecular helical arrangements of molecules through intermolecular (pyridine)C-H⋯C(NCS) interactions in the crystalline state. Complexes 1 and 2 exhibit complete, gradual and slightly irreversible spin crossover behaviour in the temperature range of 300-500 K with equilibrium temperatures (T1/2) 375 K (1) and 380 K (2). The spin state evolution of iron(II) in complexes 1 and 2 is monitored between 150 K and 450 K through variable temperature crystallographic studies in the warming mode. The structural data are in good agreement with the 94% (1) and 87% (2) high spin conversion of iron(II) at 450 K. At a high temperature (450 K), some minor irreversible ligand motion is noticed in complexes 1 and 2, in addition to a complete solvent loss that may induce the slight irreversibility of the spin crossover. On the other hand, complex 3 shows a complete and gradual spin crossover in the temperature range of 10-475 K with strong irreversible features. The equilibrium temperatures obtained upon first warming (T1/2↑) and second cooling (T1/2↓) are 375 K and 200 K, respectively. In complex 3, the loss of a water molecule triggers strong deviations in the spin crossover behaviour. Moreover, dehydrated complex 3 exhibits photoswitching LIESST effect with a relaxation temperature T(LIESST) = 60 K.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Light-Induced spin state switching has been widely studied over the last 40 years, exploring the different time and size scales. This exploration was performed by using a wide range of techniques which are still growing in resolution and accuracy to face the challenge of the increasing complexity of the studied materials (multifunctionality, nanoparticles, thin films, single domain, single molecule …). All these techniques are well described in various papers and reviews emphasizing their specificities and richness. The aim of the article is to discuss most of these techniques from a methodological point of view in order to be aware of all the cautions to take while using them. The most usual techniques used to induce and record the light-induced spin crossover will be described, complemented by a series of recommendations to be in the best conditions for such measurements. The informations that could be extracted or not from these techniques will also be presented in order to have the right level of interpretation.

Spin crossover complexes are among the most studied classes of molecular switches and have attracted considerable attention for their potential technological use as active units in multifunctional devices. A fundamental step toward their practical implementation is the integration in macroscopic devices adopting hybrid vertical architectures. First, the physical properties of technological interest shown by these materials in the bulk phase have to be retained once they are deposited on a solid surface. Herein, we describe the study of a hybrid molecular inorganic junction embedding the spin crossover complex [Fe(qnal)2] (qnal = quinoline-naphthaldehyde) as an active switchable thin film sandwiched within energy-optimized metallic electrodes. In these junctions, developed and characterized with the support of state of the art techniques including synchrotron Mössbauer source (SMS) spectroscopy and focused-ion beam scanning transmission electron microscopy, we observed that the spin state conversion of the Fe(II)-based spin crossover film is associated with a transition from a space charge-limited current (SCLC) transport mechanism with shallow traps to a SCLC mechanism characterized by the presence of an exponential distribution of traps concomitant with the spin transition temperature.

H2O and cyclohexane adsorption properties and the CO2 and CO capture capability of the microporous material Fe(pz)[Pt(CN)(4)] were examined. This 3D coordination polymer retained its crystallinity and structural stability after all adsorption-desorption experiments (demonstrated by PXRD and BET surface area). Thus, the total water uptake was equal to 14.6 wt % (8.12 mmol g(-1)) at 90% P/P-0, and in comparison to the adsorption of cyclohexane, Fe(pz) [Pt(CN)(4)] demonstrated a relatively high degree of hydrophilicity. The total cyclohexane uptake of 0.28 mmol g(-1), which in comparison to the total water uptake value of 8.12 mmol g(-1), corroborated such hydrophilic behavior. Additionally, the CO2 capture was equal to 9.3 wt % for activated Fe(pz)[Pt(CN)(4)], a higher value in comparison to other lead MOFs such as NOTT-400 (4.4 wt %), despite the fact that the latter exhibits a larger BET surface area (1356 m(2)Cl) than Fe(pz)[Pt(CN)(4)] (BET = 431 m(2) g(-1)). When the CO2 capture capability was measured on a partially water saturated Fe(pz) [Pt(CN)(4)] sample, we observed a weight gain from 11.7 wt % (only water uptake) to 14.1 wt % (water + CO2). This weight increment (2.4 wt %) was attributed to the oversolubility of CO2. The CO capture on Fe(pz)[Pt(CN)(4)] showed a total uptake of 4.7 mmol/g after only 20 min, a result comparable to those for MOFs with much higher BET surface areas, such as MOF-74(Mg) (BET = 1957 m(2) g(-1); 4.4 mmol g(-1)). Finally, in situ DRIFT experiments exhibited the coordination of CO with open Pt(II) metal sites.

The spin crossover (SCO) efficiency of [57Fe(bpz)2(phen)] (where bpz = bis(pyrazol-1-yl)borohydride and phen = 9,10-phenantroline) molecules deposited on gold substrates was investigated by means of synchrotron Mössbauer spectroscopy. The spin transition was driven thermally, or light induced via the LIESST (light induced excited spin-state trapping) effect. Both sets of measurements show that, once deposited on a gold substrate, the efficiency of the SCO mechanism is modified with respect to molecules in the bulk phase. A correlation in the distribution of hyperfine parameters in the sublimated films, not evidenced so far in the bulk phase, is reported. This translates into geometrical distortions of the first coordination sphere of the iron atom that seem to correlate with the decreased spin conversion. The work reported clearly shows the potentiality of synchrotron Mössbauer spectroscopy for the characterization of nanostructured Fe-based SCO systems, thus resulting as a key tool in view of their applications in innovative nanoscale devices.

This work describes the study of molecular junctions embedding the spin crossover complex [Fe(H2B(pz)2)2(phen)] as an active switchable thin film.