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In order to find a highly efficient, environment-friendly magnetic refrigerant, direct measurements of the adiabatic temperature change $\Delta T_{adb}$ is required. Here, in this work, a simple setup for the $\Delta T_{adb}$ measurement is presented. Using a permanent magnet Halbach array with a maximum magnetic field of $1.8$ T and a rate of magnetic field change of $5$ T/s, accurate determination of $\Delta T_{adb}$ is possible in this system. The operating temperature range of the system is from $100$ K to $400$ K, designed for the characterization of materials with potential for room temperature magnetic refrigeration applications. Using the setup, the $\Delta T_{adb}$ of a first-order and a second-order compound have been studied. Results from the direct measurement for the first-order compound have been compared with $\Delta T_{adb}$ calculated from the temperature and magnetic field dependent specific heat data. By comparing results from direct and indirect measurements, it is concluded that for a reliable characterization of the magnetocaloric effect, direct measurement of $\Delta T_{adb}$ should be adopted.

The design of (1) Möbius aromatic interlocked boron wheel Mn2B10H10, (2) Hückel aromatic boron analogs of naphthalene (M2@B10H8; M = Mn and Fe), and (3) metal boride monolayers (FeB5 and Fe2B5), creating a molecules to materials continuum.

We demonstrate the possibility to tune the saturation magnetization, coercivity, and uniaxial in-plane anisotropy constant in amorphous bilayers and multilayers of Co[Formula: see text](Al[Formula: see text]Zr[Formula: see text])[Formula: see text] and Sm[Formula: see text]Co[Formula: see text]Ti[Formula: see text] through the interface density. From magnetometry and x-ray circular dichroism (XMCD) measurements, we conclude that the easy-axis coercivity [Formula: see text] increases four times when the number of bilayer repetitions, [Formula: see text], increases from 1 to 10 within a constant total sample thickness of 20 nm. At the same time, the anisotropy constant [Formula: see text] also increases by a factor four, whereas the saturation magnetization [Formula: see text] decreases slightly. The Co spin and orbital moments, [Formula: see text] and [Formula: see text], are found to be approximately constant within the sample series. The average total Co moment is only 0.8–0.9 [Formula: see text]/atom, but the [Formula: see text] ratio is strongly enhanced compared to pure Co. Magnetization curves extracted from XMCD measurements show that the Co and Sm moments are ferromagnetically coupled for all samples.

Electrochromic (EC) technology allows control of the transmission of visible light and solar radiation through thin-film devices. When applied to “smart” windows, EC technology can significantly diminish energy use for cooling and air conditioning of buildings and simultaneously provide good indoor comfort for the buildings’ occupants through reduced glare. EC “smart” windows are available on the market, but it is nevertheless important that their degradation under operating conditions be better understood and, ideally, prevented. In the present work, we investigated EC properties, voltammetric cycling durability, and potentiostatic rejuvenation of sputter-deposited WO3 thin films immersed in LiClO4–propylene carbonate electrolytes containing up to 3.0 wt% of ∼7-nm-diameter SiO2 nanoparticles. Adding about 1 wt% SiO2 led to a significant improvement in cycling durability in the commonly used potential range of 2.0–4.0 V vs. Li/Li+. Furthermore, X-ray photoemission spectroscopy indicated that O–Si bonds were associated with enhanced durability in the presence of SiO2 nanoparticles.

A theoretical analysis of reductive coupling of isocyanide and CO mediated by a Cr-Cr quintuple bonded complex and B-B multiple bonded complexes shows how the difference in donor-acceptor capability of isocyanide and CO ligands controls the product distributions. In the case of CO, the Cr-Cr quintuple bonded complex is unable to show C-C coupling due to the high π- back bonding possibility of CO and the reaction follows the singlet potential energy surface throughout, whereas, in the case of isocyanide, less π- back bonding possibility allows the reactions to undergo a spin transition and gives a series of products with different spin multiplicities. Similarly, reactions of B-B multiple bonded complexes with CO and isocyanides are also controlled by donor-acceptor capabilities of ligands, and the C-C coupling takes place by changing the oxidation state of the boron centers from +I to +II, in contrast to the classical main group mediated reactions where stable oxidation states are always preserved. This part of the main group chemistry which is dominated by donor-acceptor bonding interaction is more likely to follow transition metal behavior.

The inherent tendency of BR fragments to undergo coupling is utilized to predict M

Closo-carborane anions are prominent, whereas the cations of the same are less abundant in the literature. As these ions have similar size and are weakly coordinating, the ionic liquids of these two ions could have important applications in many areas of chemistry. In view of limited number of polyhedral carborane cations available, we revisited the rearrangement of dicarboranyl methyl cation (7-CH

A detailed DFT study involving 50 intermediates, 26 transition states, a range of spin multiplicities and 3 MECPs explains the products (and their distribution) of the reaction of cyclohexyl isocya...

A theoretical analysis of [L]M(μ-CCR)2M[L] and [L]M(μ-RC4R)M[L], where M represents the selected elements from the main group, transition metals, lanthanides and actinides, shows how the central (μ-CCR)2 and (μ-RC4R) units reorganize as M traverses across the periodic table. In this context transition metal and actinide complexes are similar in nature, while lanthanide and main group complexes show similarity. The ground state electronic configuration and thus the metal oxidation state control these striking differences. An effective way to stabilize the (III) oxidation state of thorium in a metallacycle complex is shown for the first time. A strategy is proposed to make a cross-connection between the two sets. The approach used here lends itself to obvious extensions.

The structural, magnetic, magnetocaloric and Griffiths phase (GP) disorder of non-stoichiometric perovskite manganites La 0.8 − x Sr 0.2 − y Mn 1 + x + y O 3 are reported here. Determination of valence states and structural phases evidenced that the smaller cations Mn2+ and Mn3+ will not occupy the A-site of a perovskite under atmospheric synthesis conditions. The same analysis also supports that the vacancy in the A-site of a perovskite induces a similar vacancy in the B-site. The La3+ and Sr2+ cation substitutions in the A-site with vacancy influences the magnetic phase transition temperature (TC) inversely, which is explained in terms of the electronic bandwidth change. An anomalous non-linear change of the GP has been observed in the Sr-substituted compounds. The agglomeration of Mn3+-Mn4+ pairs (denoted as dimerons), into small ferromagnetic clusters, has been identified as the reason for the occurrence of the GP. A threshold limit of the dimeron formation explains the observed non-linear behaviour of the GP formation. The Sr-substituted compounds show a relatively large value of isothermal entropy change (maximum 3.27 J/kgK at μ 0 H = 2 T ) owing to its sharp magnetic transition, while the broad change of magnetization in the La-substituted compound enhances the relative cooling power (maximum 98 J/kg at μ 0 H = 2 T ).

Ferromagnetic thin films were synthesized by implantation of Fe ions with energies between 40 keV and 120 keV in 60 nm of polycrystalline Pd. The possibility to engineer magnetic properties in such films through the Fe concentration depth profile was demonstrated. In-plane magnetic moments were measured both while varying the sample temperature at constant applied magnetic field, and varying the applied field at constant temperature. All samples were explicitly shown to exhibit ferromagnetism at sufficiently low temperature, with threshold temperatures in the range from 35 K to 140 K. Saturation moments at 5 K were between 3.5 and 4.6 Bohr magnetons per implanted Fe atom for implantation fluences between 5 × 1015 and 2.3 × 1016 ions/cm2. Coercivities were between 1 and 3 mT. The samples included in the study were carefully characterized with Rutherford backscattering spectrometry, and selected samples with elastic recoil detection analysis and cross-sectional transmission electron microscopy, providing information on Fe concentration profiles, impurity fractions, structure as well as sample modification during implantation. A new model was proposed to calculate the scaling of the films’ magnetic moments with temperature from the Fe concentration profiles. The model qualitatively reproduced the data and quantitative differences were explained. It can thus be applied to predict the modification of the magnetic moment at a given temperature for a similar film when the implantation parameters are varied.

We report on structural, magnetic properties of Na-doped La0.8Sr0.15Na0.05MnO3 (LSNMO) nanoparticles (NP) with size about 50 nm elaborated via sol-gel route. The chemical composition was verified using the energy dispersive X-ray analysis (EDAX) and by X-ray photoelectron spectroscopy (XPS). Magnetic characterizations demonstrate that LSMNO exhibits a coexistence of interacting superparamagnetic (ISPM) phase with blocking temperature T-B = 194 K and a ferromagnetic phase with Curie temperature T-C = 255.5 K. At low temperatures, the SPM state undergoes a collective freezing state at T-f = 46 K. the high-temperature regime (well above TC) reveals that NP-LSNMO has a strengthened Griffiths-like phase compared to their bulk counterpart. An itemized investigation of the critical behavior of the material was carried out in the vicinity of T-C. The critical exponents [beta = 0.546(7), gamma = 0.972(6), and delta = 2.94 (5)] were found to be in close agreement with of the mean-field theory. The maximum magnetic entropy change (-Delta(pk)(M)) is about 1.41 Jkg(-1) K-1 and the refrigeration capacity (RC) is 288 Jkg(-1) for a field change of 5 T at T = 215 K. This magnetocaloric response is reasonably high for nanomaterials and, together with its cost-effectiveness, makes NP LSMNO a potential candidate material for active magnetic refrigerators. Besides, the ISPM properties are desirable for hyperthermia applications. Our findings suggest that the magnetic inhomogeneity and the dipolar interaction between the SPM and FM phases in the range T-B < T < T-C are crucial factors in determining the magnetic properties of NP-LSNMO. (C) 2021 Elsevier B.V. All rights reserved. Portuguese Foundation for Science and Technology European Commission QREN-Mais Centro Project Deanship Scientific Research at Jouf University central laboratory at Jouf University

The room-temperature reaction of [Cp*TaCl4 ] with LiBH4 ⋅THF followed by addition of S2 CPPh3 results in pentahydridodiborate species [(Cp*Ta)2 (μ,η2 :η2 -B2 H5 )(μ-H)(κ2 ,μ-S2 CH2 )2 ] (1), a classical [B2 H5 ]- ion stabilized by the binuclear tantalum template. Theoretical studies and bonding analysis established that the unusual stability of [B2 H5 ]- in 1 is mainly due to the stabilization of sp2 -B center by electron donation from tantalum. Reactions to replace the hydrogens attached to the diborane moiety in 1 with a 2 e {M(CO)4 } fragment (M=Mo or W) resulted in simple adducts, [{(Cp*Ta)(CH2 S2 )}2 (B2 H5 )(H){M(CO)3 }] (6: M=Mo and 7: M=W), that retained the diborane(5) unit.

Polycrystalline La

A theoretical analysis of [L]M(μ-CCR)

Polycrystalline La1-x Pb x MnO3±y (x = 0.3, 0.35, 0.4) solid solutions were prepared by solid state reaction method and their magnetic properties have been investigated. Rietveld refinement of x-ray powder diffraction patterns showed that all samples are single phase and crystallized with the rhombohedral structure in the R-3c space group. A second order paramagnetic to ferromagnetic (FM) phase transition was observed for all materials. The Griffiths phase (GP), identified from the temperature dependence of the inverse susceptibility, was suppressed by increasing magnetic field and showed a significant dependence on A-site chemical substitution. The critical behaviour of the compounds was investigated near to their Curie temperatures, using intrinsic magnetic field data. The critical exponents (β, γ and δ) are close to the mean-field approximation values for all three compounds. The observed mean-field like behaviour is a consequence of the GP and the formation of FM clusters. Long-range FM order is established as the result of long-range interactions between FM clusters. The magnetocaloric effect was studied in terms of the isothermal entropy change. Our study shows that the material with the lowest chemical substitution (x = 0.3) has the highest potential (among the three compounds) as magnetic refrigerant, owing to its higher relative cooling power (258 J kg−1 at 5 T field) and a magnetic phase transition near room temperature.

La0.4Pr0.3Ca0.1Sr0.2MnO3 has been investigated as a potential candidate for room temperature magnetic refrigeration. Results from X-ray powder diffraction reveal an orthorhombic structure with Pnma space group. The electronic and chemical properties have been confirmed by X-ray photoelectron spectroscopy and ion-beam analysis. A second-order paramagnetic to ferromagnetic transition was observed near room temperature (289 K), with a mean-field like critical behaviour at low field and a tricritical mean-field like behaviour at high field. The field induced crossover in critical behaviour is a consequence of the system being close to a first-order magnetic transition in combination with a magnetic field induced suppression of local lattice distortions. The lattice distortions consist of interconnected and weakly distorted pairs of Mn-ions, where each pair shares an electron and a hole, dispersed by large Jahn–Teller distortions at Mn3+ lattice sites. A comparatively high value of the isothermal entropy-change (3.08 J/kg-K at 2 T) is observed and the direct measurements of the adiabatic temperature change reveal a temperature change of 1.5 K for a magnetic field change of 1.9 T.

The reaction of [(Cp*Mo)2 (μ-Cl)2 B2 H6 ] (1) with CO at room temperature led to the formation of the highly fluxional species [{Cp*Mo(CO)2 }2 {μ-η2 :η2 -B2 H4 }] (2). Compound 2, to the best of our knowledge, is the first example of a bimetallic diborane(4) conforming to a singly bridged Cs structure. Theoretical studies show that 2 mimics the Cotton dimolybdenum-alkyne complex [{CpMo(CO)2 }2 C2 H2 ]. In an attempt to replace two hydrogen atoms of diborane(4) in 2 with a 2e [W(CO)4 ] fragment, [{Cp*Mo(CO)2 }2 B2 H2 W(CO)4 ] (3) was isolated upon treatment with [W(CO)5 ⋅thf]. Compound 3 shows the intriguing presence of [B2 H2 ] with a short B-B length of 1.624(4) A. We isolated the tungsten analogues of 3, [{Cp*W(CO)2 }2 B2 H2 W(CO)4 ] (4) and [{Cp*W(CO)2 }2 B2 H2 Mo(CO)4 ] (5), which provided direct proof of the existence of the tungsten analogue of 2.

Disorder induced by chemical inhomogeneity and Jahn-Teller (JT) distortions is often observed in mixed valence perovskite manganites. The main reasons for the evolution of this disorder are connected with the cationic size differences and the ratio between JT active and non-JT active ions. The quenched disorder leads to a spin-cluster state above the magnetic transition temperature. The effect of Cu, a B-site substitution in the La0.8Sr0.2MnO3 compound, on the disordered phase has been addressed here. X-ray powder diffraction reveals rhombohedral (R-3c) structures for both the parent and B-site substituted compound with negligible change of lattice volume. The chemical compositions of the two compounds were verified by ion beam analysis technique. With the change of electronic bandwidth, the magnetic phase transition temperature has been tuned towards room temperature (318 K), an important requirement for room temperature magnetic refrigeration. However, a small decrease of the isothermal entropy change was observed with Cu-substitution, related to the decrease of the saturation magnetization.

The room-temperature reaction of [Cp*TaCl

Herein, we report the synthesis and characterization of the metal free low valent fluoroborylene [(Me-cAAC)2BF] (1) stabilized by cyclic (alkyl)(amino) carbene (cAAC). The fluoroborylene 1 is obtained by the reductive defluorination of Me-cAAC:BF3 with 2.0 equivalents of KC8 in the presence of 1.0 equivalent of Me-cAAC. Due to its highly electron rich nature, 1 underwent one-electron oxidation with 1.0 equivalent of lithium tetrakis(pentafluorophenyl)borate [LiB(C6F5)4] to form the radical cation [(Me-cAAC)2BF]˙+[B(C6F5)4]- (2). DFT studies suggested that the lone pair of electrons is localized on the boron atom in 1, which explains its unprecedented reactivity. Both compounds 1 and 2 were characterized by X-ray crystallography. The radical cation 2 was studied by EPR spectroscopy. peerReviewed

The La0.5Pr0.2Ca0.1Sr0.2MnO3 compound has been investigated as a potential candidate for room temperature magnetocaloric refrigeration. The Rietveld refinement of X-ray powder diffraction patterns confirms that the compound crystalizes in an orthorhombic phase with the Pnma space group. Rutherford backscattering spectrometry and time-of-flight elastic recoil detection analysis, verified the desired ratio of the elements in the compound. Using X-ray photoelectron spectroscopy two oxidation states of manganese (Mn), Mn4+ and Mn3+ were identified in the compound with relative amounts of 32% and 68%, respectively. The observed spin orbit splitting of the Mn-2p3/2 and Mn-2p1/2 levels was obtained as 11.7 eV. A ferromagnetic to paramagnetic transition was observed around 296 K, which makes the material interesting for magnetic cooling near room temperature. In addition, the absence of magnetic hysteresis provides another argument in favor of the studied compound. The isothermal entropy change ( − Δ S M ) and the relative cooling power (RCP) for a magnetic field change of 5 T were found to be 4 J/kg K and 372 J/kg, respectively. From the comparison of the values of − Δ S M and RCP with those obtained for the archetypal magnetocaloric material gadolinium, it is argued that our material can be considered as a potential candidate in cooling systems based on magnetic refrigeration.

A detailed molecular orbital analysis of the metal-bis(borylene) complex Fe(CO)(3){B(Dur)B(N(SiMe3)(2))}] (Dur=2,3,5,6-tetramethylphenyl) (1 a) serves as a focal point of recent developments in this area of chemistry, such as B-B coupling and B-B catenation reactions. There is strong a pi delocalization between the Fe(CO)(3) and (B-Dur)(B-N(SiMe3)(2)) units; the short B-B distance in 1 a is due to this pi delocalization. The pi-donor ligand N(SiMe3)(2) on the boron provides a decisive stability to the complex 1 a. The LUMO of 1 a has B-B sigma-bonding character. Hence B-B coupling is facilitated by filling the LUMO. Strong sigma-donating ligands, such as PMe3 or PCy3, induce B-B coupling. Expulsion of one CO from 1 a followed by dimerization leads to Fe(CO)(2){B(Dur)B(N(SiMe3)(2))}](2) (3 a) with a short Fe-Fe distance of 2.355 angstrom. A detailed mechanism for the reaction of 3 a with CO to give the B-B catenation product 2 f is presented. The bonding of all intermediates is compared to their isolobal main-group analogues.

The reaction of [(Cp*Mo)

The electronic structure of (eta(5)-Cp)(2)Zr( NH2-BBNH2) (3b) suggests that it could be a candidate for having a boron-boron triple bond in the cyclic system; however, computational studies shows that 3b is a very high energy isomer on its potential energy surface. Replacement of amines with tricoordinate nucleophilic boron groups (eta(5)-Cp)(2)Zr B(PH3)(2)-BB-B(PH3)(2)] (3c) reduces the relative energy dramatically. The B / B triple bond arises through the donation of two electrons from the metal fragment, ZrCp2, to the in-plane sigma-bonding orbital of the central B-B unit. Strong s-donating and chelating bisphosphine ligands ( Me2P( CH2) nPMe(2)), which stabilize donor-acceptor bonding interaction in gem-diborene L2BBBr2 ( 10), would be a good choice along the synthetic path towards 3d, (eta(5)-Cp)(2)ZrB-4(Me2P(CH2)(3)PMe2)(2)]. A comparison of the energetics of the reaction leading to a cyclic boryne system (3d), with the linear boryne isomer (B2NHCPh)(2)] shows that the angle strain from cyclization is compensated by stabilization from the metal.