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Over the last few years, great interest has emerged in the synthesis and magnetothermal studies of polymetallic molecular clusters based on paramagnetic ions, often referred to as molecular nanomagnets, in view of their potential application as lowtemperature magnetic refrigerants. [1,2] What makes them promising is that their cryogenic magnetocaloric effect (MCE) can be considerably larger than that of any other magnetic refrigerant, e.g. lanthanide alloys and magnetic nanoparticles.[3] The MCE is the change of magnetic entropy (∆S m ) and related adiabatic temperature (∆T ad ) following the change of applied magnetic field and it can be exploited for cooling applications via a field removal process called adiabatic demagnetization. Although the MCE is intrinsic to any magnetic material, in only a few cases are the changes sufficiently large to make them suitable for applications. The ideal molecular refrigerant comprises the following key characteristics:[1] (i) a large spin ground state S, since the magnetic entropy amounts to Rln(2S+1); (ii) a negligible magnetic anisotropy, which permits easy polarization of the net molecular spins in magnetic fields of weak or moderate strength; (iii) the presence of low-lying excited spin states, which enhances the field dependence of the MCE due to the increased number of populated spin states; (iv) dominant ferromagnetic exchange, [3(c)] favouring a large S and hence a large field dependence of the MCE; (v) a relatively low molecular mass (or a large metal:ligand mass ratio) since the non-magnetic ligands contribute passively to the MCE. Although this last point is crucial for obtaining an enhanced effect, it has been mostly ignored to date. Molecular cluster compounds tend to have a very low magnetic density because of the large complex structural frameworks required to encase the multi-metallic core.In this communication we propose a drastically different approach by focusing on the simple and well-known ferromagnetic molecular dimer gadolinium acetate tetrahydrate, [4] [{Gd(OAc) 3 (H 2 O) 2 } 2 ]•4H 2 O (1). The structure of 1 is depicted in Figure 1 and comprises a dimer of Gd 3+ ions bridged through two of the six carboxylate groups which bond in a η 2 :η 1 :µ 2 -fashion. The remaining acetates are chelating with the nine-coordinate [capped square anti-prismatic] geometry of the metal centres being completed by the presence of two terminally bound H 2 O molecules. These partake in intra-molecular H-bonding to the neighbouring chelating acetate ligands, and are responsible for both the direct inter-molecular H-bonds in the a-b plane and the inter-plane Hbonds mediated by the lattice H 2 O molecules ( Fig. S1 and Table S1). Our theoretical and experimental investigations (see Supporting Information for details) of the magnetothermal properties of 1 down to millikelvin temperatures reveal a truly enormous MCE. In addition to magnetization and heat capacity experiments, which we employ to indirectly estimate the MCE, we make use of a homemade experimental set-up th...

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.

PACS. 75.50.Xx Molecular magnets - 78.40.Ha Other nonmetallic inorganics - 82.20.Mj Nonequilibrium kinetics,

4 pagesInternational audienceA new metal–organic framework (MOF) with amino groups situated inside the pores has been synthesized. This MOF has been modified by post-synthesis with two different functionalities. The crystal structures of the two functionalized MOFs clearly demonstrate that it is possible to transform the cavities of a MOF without modifying its original 3D structure. These unprecedented results open up tremendous possibilities in the field of MOF chemistry because many potential applications in the fields of catalysis, material science or nanochemistry can be envisaged when applying the reported synthetic pathway

A novel bispyrazolylpyridine ligand incorporating lateral phenol groups, H(4)L, has led to an Fe(II) spin-crossover (SCO) complex, [Fe(H(4)L)(2)][ClO(4)](2)⋅H(2)O⋅2 (CH(3))(2)CO (1), with an intricate network of intermolecular interactions. It exhibits a 40 K wide hysteresis of magnetization as a result of the spin transition (with T(0.5) of 133 and 173 K) and features an unsymmetrical and very rich structure. The latter is a consequence of the coupling between the SCO and the crystallographic transformations. The high-spin state may also be thermally trapped, exhibiting a very large T(TIESST) (≈104 K). The structure of 1 has been determined at various temperatures after submitting the crystal to different processes to recreate the key points of the hysteresis cycle and thermal trapping; 200 K, cooled to 150 K and trapped at 100 K (high spin, HS), slowly cooled to 100 K and warmed to 150 K (low spin, LS). In the HS state, the system always exhibits disorder for some components (one ClO(4)(-) and two acetone molecules) whereas the LS phases show a relative ≈9 % reduction in the Fe-N bond lengths and anisotropic contraction of the unit cell. Most importantly, in the LS state all the species are always found to be ordered. Therefore, the bistability of crystallographic order-disorder coupled to SCO is demonstrated here experimentally for the first time. The variation in the cell parameters in 1 also exhibits hysteresis. The structural and magnetic thermal variations in this compound are paralleled by changes in the heat capacity as measured by differential scanning calorimetry. Attempts to simulate the asymmetric SCO behaviour of 1 by using an Ising-like model underscore the paramount role of dynamics in the coupling between the SCO and the crystallographic transitions.

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(H 4 TCPP)] molecule is a potential spin qubit, and maintains similar quantum coherence as node in a 2D [{CuTCPP}Zn 2 (H 2 O) 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. and gates first arose in the form of purely organic systems, using either the multiple nuclear spins of rationally selected molecules or the electronic spin(s) of open shell organic molecules bearing one or multiple radicals. The careful design and selection of such organic molecules coupled to sophisticated experiments have allowed implementing realistic quantum operations using ensembles of these. [2] Paramagnetic coordination complexes were later proposed as alternative molecular spin qubits, after it was argued and shown that the molecule electronic spin orientation and quantum superpositions allow to encode quantum bit (qubit) states. [3] Recent improvements in the coherence times of these molecular spin qubits [4] and the unique ability to design molecules with multiple qubits as prototypes of quantum gates [5] have brought this scheme to a point where it becomes reasonable to envision the design of a magnetic quantum processor. A magnetic molecule has even recently been used to implement Grover's quantum algorithm, albeit using its metal ion nuclear spin. [6] One of the advantages of the molecular scheme is that macroscopic numbers of identical qubits are obtained in one sole reaction. While this is appealing for the daunting challenge of scaling to a usable size, common to all proposed schemes, [7] the technology to build a scalable quantum architecture based on molecular qubits is

We show that [Er-Ce-Er] molecular trinuclear coordination compound is a promising platform to implement the three-qubit quantum error correction code protecting against pure dephasing, the most important error in magnetic...