One‐dimensional coordination FeII polymers constructed through triple N1,N2‐1,2,4‐triazole bridges form a unique class of spin‐crossover materials, the synthetic versatility of which allows tuning ...the spin‐crossover properties, the design of gels, films, liquid crystals, and nanoparticles and single‐particle addressing. This Minireview provides the first complete overview of these very attractive switchable materials and their most recent developments.
The spin‐crossover toolbox: A complete and concise overview of all the spin‐crossover Fe(Rtrz)3Ax systems reported is provided (Rtrz is a 4‐substituted‐1,2,4‐triazole; A=monovalent anion). The structural and magneto‐optical properties of these one‐dimensional coordination polymers are summarised, as well as their implementation into other phases of matter or nanostructured objects. The most relevant and recent developments based on this very attractive class of switchable materials are highlighted.
•The synthesis of the new family of 2,6-bis(pyrazol-3-yl)pyridine type ligands (3-bpp) is reviewed.•A focus on SCO compounds of 3-bpp ligands is made, comprehensively, for the first time.•This family ...of compounds has exhibited most known mechanisms of spin switching, affording novel features.•3-bpp SCO compounds have offered a chance to examine, in this paper, structural correlations with magnetic properties.
The area of spin crossover (SCO) attracts interest both on a fundamental level and in terms of potential applications for compounds displaying this phenomenon. A few families of Fe(II) complexes have become paramount for the advance of this topic, for example, compounds based on bis-pyrazolylpyridine (bpp) ligands. Here, we describe the versatile and rich SCO behaviour shown by the group of SCO compounds based on the related ligand 2,6-bis(pyrazol-3-yl)pyridine (L1) and its recently developed derivatives. The use of derivatives of L1 represents an advance, as prior to 2011, no functionalised L1-type ligands had been employed to obtain SCO systems. These compounds are highly sensitive to the anion and degree of solvation within their lattices, many of which have been observed through single crystal X-ray diffraction studies. The structural data that have been published in recent years has permitted a magneto-structural correlation to be described, which proves to nicely complement the properties shown by the family based on L1's regio-isomer, 2,6-bis(pyrazol-1-yl)pyridine.
In contrast to the mainstream research on molecular refrigerants that seeks magnetically isotropic molecules, we show that the magnetic anisotropy of dysprosium acetate tetrahydrate, ...{Dy(OAc)3(H2O)2}2⋅4 H2O (1), can be efficiently used for cooling below liquid‐helium temperature. This is attained by rotating aligned single‐crystal samples in a constant applied magnetic field. The envisioned advantages are fast cooling cycles and potentially compact refrigerators.
Molecular refrigerants: The magnetocaloric effect of anisotropic hydrated dysprosium acetate was studied. Possible applications as molecular refrigerants are discussed. Cooling is attained by rotating aligned single‐crystal samples in a constant applied magnetic field (see picture).
The successful development of modern gas sensing technologies requires high sensitivity and selectivity coupled to cost effectiveness, which implies the necessity to miniaturize devices while ...reducing the amount of sensing material. The appealing alternative of integrating nanoparticles of a porous metal–organic framework (MOF) onto capacitive sensors based on interdigitated electrode (IDE) chips is presented. We report the deposition of MIL-96(Al) MOF thin films via the Langmuir–Blodgett (LB) method on the IDE chips, which allowed the study of their gas/vapor sensing properties. First, sorption studies of several organic vapors like methanol, toluene, chloroform, etc. were conducted on bulk MOF. The sorption data revealed that MIL-96(Al) presents high affinity toward water and methanol. Later on, ordered LB monolayer films of MIL-96(Al) particles of ∼200 nm were successfully deposited onto IDE chips with homogeneous coverage of the surface in comparison to conventional thin film fabrication techniques such as drop-casting. The sensing tests showed that MOF LB films were selective for water and methanol, and short response/recovery times were achieved. Finally, chemical vapor deposition (CVD) of a porous thin film of Parylene C (thickness ∼250–300 nm) was performed on top of the MOF LB films to fabricate a thin selective layer. The sensing results showed an increase in the water selectivity and sensitivity, while those of methanol showed a huge decrease. These results prove the feasibility of the LB technique for the fabrication of ordered MOF thin films onto IDE chips using very small MOF quantities.
One current challenge of magnetic hyperthermia is achieving therapeutic effects with a minimal amount of nanoparticles, for which improved heating abilities are continuously pursued. However, it is ...demonstrated here that the performance of magnetite nanocubes in a colloidal solution is reduced by 84% when they are densely packed in three-dimensional arrangements similar to those found in cell vesicles after nanoparticle internalization. This result highlights the essential role played by the nanoparticle arrangement in heating performance, uncontrolled in applications. A strategy based on the elaboration of nano-objects able to confine nanocubes in a fixed arrangement is thus considered here to improve the level of control. The obtained specific absorption rate results show that nanoworms and nanospheres with fixed one- and two-dimensional nanocube arrangements, respectively, succeed in reducing the loss of heating power upon agglomeration, suggesting a change in the kind of nano-object to be used in magnetic hyperthermia.
The increase in demand and popularity of smart textiles brings new and innovative ideas to develop a diverse range of textile-based devices for our daily life applications. Smart textile-based ...sensors (TEX sensors) become attractive due to the potential to replace current solid-state sensor devices with flexible and wearable devices. We have developed a smart textile sensor for humidity detection using a metal–organic framework (MOF) as an active thin-film layer. We show for the first time the use of the Langmuir–Blodgett (LB) technique for the deposition of a MIL-96(Al) MOF thin film directly onto the fabrics containing interdigitated textile electrodes for the fabrication of a highly selective humidity sensor. The humidity sensors were made from two different types of textiles, namely, linen and cotton, with the linen-based sensor giving the best response due to better coverage of MOF. The TEX sensor showed a reproducible response after multiple cycles of measurements. After 3 weeks of storage, the sensor showed a moderate decrease in response. Moreover, TEX sensors showed a high level of selectivity for the detection of water vapors in the presence of several volatile organic compounds (VOCs). Interestingly, the selectivity is superior to some of the previously reported MOF-coated solid-state interdigitated electrode devices and textile sensors. The method herein described is generic and can be extended to other textiles and coating materials for the detection of toxic gases and vapors.
A bis(pyrazolylpyridyl) ligand, L, containing a central photochromic dithienylethene spacer predictably forms a ferrous Fe2L34+ helicate exhibiting spin crossover (SCO). In solution, the compound ...Fe2L3(ClO4)4 (1) preserves the magnetic properties and is fluorescent. The structure of 1 is photo‐switchable following the reversible ring closure/opening of the central dithienylethene via irradiation with UV/visible light. This photoisomerization switches on and off some emission bands of 1 and provides a means of externally manipulating the magnetic properties of the assembly.
Fluoro‐photo‐magnificence: An iron‐containing spin‐crossover molecule has been synthesized that contains a photoswitchable unit. This unit allows its magnetic properties and its fluorescent response using light to be reversibly tuned.
Molecular spin qubits have been shown to reach sufficiently long quantum coherence times to envision their use as hardware in quantum processors. These will however require their implementation in ...hybrid solid‐state devices for which the controlled localization and homogeneous orientation of the molecular qubits will be necessary. An alternative to isolated molecules that can ensure these key aspects is 2D framework in which the qubit would act as node. In this work, it is demonstrated that the isolated metalloporphyrin Cu(H4TCPP) molecule is a potential spin qubit, and maintains similar quantum coherence as node in a 2D {CuTCPP}Zn2(H2O)2 metal–organic framework. Mono‐ and multilayer deposits of nanosheets of a similar 2D framework are then successfully formed following a modular method based on Langmuir–Schaefer conditions. The orientation of the {CuTCPP} qubit nodes in these nanosheets is homogeneous parallel to the substrate. These nanosheets are also formed with a control over the qubit concentration, i.e., by dilution with the unmetallated porphyrin. Eventually, 2D nanosheets are formed in situ directly on a substrate, through a simple protocol devised to reproduce the Langmuir–Schaefer conditions locally. Altogether these studies show that 2D spin qubit frameworks are ideal components to develop a hybrid quantum computing architecture.
A copper metalloporphyrin molecule is assembled into 2D metal–organic framework (MOF) grids through diamagnetic nodes, both as a bulk material and nanosheets on substrates, and exhibits significant quantum coherence. The 2D MOF nanosheets can be made magnetically dilute as well as directly in situ on a substrate, two key requirements for their implementation into hybrid quantum computing architectures.
The three‐dimensional metal–organic framework Gd(HCOO)3 is characterized by a relatively compact crystal lattice of weakly interacting Gd3+ spin centers interconnected via lightweight formate ...ligands, overall providing a remarkably large magnetic:non‐magnetic elemental weight ratio. The resulting magnetocaloric effect per unit volume is decidedly superior in Gd(HCOO)3 than in the best known magnetic refrigerant materials for liquid‐helium temperatures and low‐moderate applied fields.
Molecoolers: An unprecedentedly large cryogenic magnetocaloric effect is observed in gadolinium acetate tetrahydrate (see picture, Gd pink, O red, C gray). The change in its magnetic entropy is ...ascribed to the high magnetic density combined with dominant ferromagnetism. For the first time in a molecular complex, direct measurements of the magnetocaloric effect corroborate indirect estimates based on heat capacity and magnetization.
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