Effect of coordination geometry on the magnetic properties of a series of Ln2 and Ln4 hydroxo clusters

A series of three isostructural tetranuclear complexes with the general molecular formula [Ln4(µ3-OH)4(L)4(µ2-piv)4(MeOH)4] (Ln = Gd 1, Dy 2 and Ho 3; LH = [1,3-bis(o-methoxyphenyl)-propane-1,3-dione]) were isolated and unambiguously characterized by single crystal XRD. Under similar reaction conditions, simply changing the co-ligand from pivalate to 2,6-bis(hydroxymethyl)-p-cresol (LH'3) led to the isolation of dinuclear Ln(III) complexes with the general molecular formula [Ln2(L)4(µ2-LH'2)2]·4DMF (Ln =Gd 4, Dy 5 and Ho 6). Direct current magnetic susceptibility data studies on the polycrystalline sample of 1-6 and the results reveal the existence of weak antiferromagnetic exchange interactions between the lanthanide ions in 1 which is evident from the spin Hamiltonian (SH) parameters (J1 = −0.055 cm−1 and g = 2.01) extracted by fitting χMT(T). On the other hand, though complex 4 exhibits weak antiferromagnetic coupling ( J1 = −0.048 cm−1 and g = 1.99) between the Gd(III) ions, the χMT (T ) data of complexes 5 and 6 unambiguously disclose the presence of ferromagnetic interactions between Dy(III) and Tb(III) ions at lower temperature. Magnetization relaxation dynamics studies performed on 2 show frequency dependent out-of-phase susceptibility signals in the presence of an optimum external magnetic field of 0.5 kOe. In contrast, complex 5 shows slow magnetization relaxation with an effective energy barrier (Ueff) of 38.17 cm−1 with a pre-exponential factor (τ0) of 1.85 × 10−6 s. The magnetocaloric effect (MCE) of complexes 1 and 4 was extracted from the detailed magnetization measurement and the change in the magnetic entropy (−ΔSm) of 1 and 4 was found to be 25.57 J kg−1 K−1 and 12.93 J kg−1 K−1,respectively, at 3.0 K for ΔH = 70 kOe

Single-Molecule Magnetism, Enhanced Magnetocaloric Effect, and Toroidal Magnetic Moments in a Family of Ln4 Squares

Three cationic [Ln4] squares (Ln=lanthanide) were isolated as single crystals and their structures solved as [Dy4(\u3bc4-OH)(HL)(H2L)3(H2O)4]Cl2\ub7(CH3OH)4\ub7(H2O)8 (1), [Tb4(\u3bc4-OH)(HL)(H2L)3(MeOH)4]Cl2\ub7(CH3OH)4\ub7(H2O)4 (2) and [Gd4(\u3bc4-OH)(HL)(H2L)3(H2O)2(MeOH)2]Br2\ub7(CH3OH)4\ub7(H2O)3 (3). The structures are described as hydroxo-centered squares of lanthanide ions, with each edge of the square bridged by a doubly deprotonated H2L2- ligand. Alternating current magnetic susceptibility measurements show frequency-dependent out-of-phase signals with two different thermally assisted relaxation processes for 1, whereas no maxima in \u3c7M" appears above 2.0 K for complex 2. For 1, the estimated effective energy barrier for these two relaxation processes is 29 and 100 K. Detailed ab initio studies reveal that complex 1 possesses a toroidal magnetic moment. The ab initio calculated anisotropies of the metal ions in complex 1 were employed to simulate the magnetic susceptibility by using the Lines model (POLY-ANISO) and this procedure yields J1=+0.01 and J2=-0.01 cm-1 for 1 as the two distinct exchange interactions between the DyIII ions. Similar parameters are also obtained for complex 1 (and 2) from specific heat measurements. A very weak antiferromagnetic super-exchange interaction (J1=-0.043 cm-1 and g=1.99) is observed between the metal centers in 3. The magnetocaloric effect (MCE) was estimated by using field-dependent magnetization and temperature-dependent heat-capacity measurements. An excellent agreement is found for the -\u394Sm values extracted from these two measurements for all three complexes. As expected, 3 shows the largest -\u394Sm variation (23 J Kg-1 K-1) among the three complexes. The negligible magnetic anisotropy of Gd indeed ensures near degeneracy in the (2S+1) ground state microstates, and the weak super-exchange interaction facilitates dense population of low-lying excited states, all of which are likely to contribute to the MCE, making complex 3 an attractive candidate for cryogenic refrigeration

Global management of a common, underrated surgical task during the COVID-19 pandemic: Gallstone disease - An international survery

Background: Since the Coronavirus disease-19(COVID-19) pandemic, the healthcare systems are reallocating their medical resources, with consequent narrowed access to elective surgery for benign conditions such as gallstone disease(GD). This survey represents an overview of the current policies regarding the surgical management of patients with GD during the COVID-19 pandemic. Methods: A Web-based survey was conducted among 36 Hepato-Prancreato-Biliary surgeons from 14 Countries. Through a 17-item questionnaire, participants were asked about the local management of patients with GD since the start of the COVID-19 pandemic. Results: The majority (n = 26,72.2%) of surgeons reported an alarming decrease in the cholecystectomy rate for GD since the start of the pandemic, regardless of the Country: 19(52.7%) didn't operate any GD, 7(19.4%) reduced their surgical activity by 50–75%, 10(27.8%) by 25–50%, 1(2.8%) maintained regular activity. Currently, only patients with GD complications are operated. Thirty-two (88.9%) participants expect these changes to last for at least 3 months. In 15(41.6%) Centers, patients are currently being screened for SARS-CoV-2 infection before cholecystectomy [in 10(27.8%) Centers only in the presence of suspected infection, in 5(13.9%) routinely]. The majority of surgeons (n = 29,80.6%) have adopted a laparoscopic approach as standard surgery, 5(13.9%) perform open cholecystectomy in patients with known/suspected SARS-CoV-2 infection, and 2(5.6%) in all patients. Conclusion

Sensor-Based Turmeric Finger Growth Characteristics Monitoring Using Embedded System under Soil

Modern agribusiness is becoming increasingly reliant on computer-based systems which was formerly performed by humans. One such technological innovation is the embedded system-based sensor array module such as flex sensor, temperature sensor, and pH sensor that have been used to monitor the turmeric finger growth characteristics. The experimental work has been tested with five different nodes and the average flex sensor resistance changes in five nodes are calculated. Among the five nodes, nodes II and V were diseased. Purposely node II was left as such and node V was treated with Pseudomonas and viride to restrict the Rhizome rot disease attack. As a result, after cultivation, it was found that the Rhizome rot disease attack on node V is comparatively lesser than node II. The greatest advantage of this method is that it helps the farmers to detect the Rhizome rot disease and also prevent it an early stage by monitoring the growth of the turmeric fingers when it is under the soil

Mechanistic Investigation of Well-Defined Cobalt Catalyzed Formal E-Selective Hydrophosphination of Alkynes

A formal E-selective hydrophosphination of terminal and internal alkynes catalyzed by a well-defined [Co(PMe3)(4)] (A) complex is achieved under mild conditions in good-to-excellent yield. The reaction does not require any additives and/or external base for an efficient hydrophosphination reaction. The reaction provided excellent scope and good functional tolerance. Detailed spectroscopic analysis (NMR, EPR, and UV-vis) revealed that the low valent cobalt(0) complex undergoes oxidative addition with diphenylphosphine, followed by hydrometalation with alkyne, and subsequent reductive elimination led to the expected product. The detailed spectroscopic analyses along with the isotopic labeled experiments facilitate to intercept the active intermediates that are involved in the catalytic cycle, which are detailed. It was revealed that the suprafacial (vide infra) delivery of H and phosphorus to pi-alkynes in a syn-fashion led to formal E-vinyl phosphine

Effect of Macrosynthetic and Hybrid Fibers on Shear Behavior of Concrete Beams Reinforced with GFRP Bars

Design of reinforced concrete (RC) bridge members with fiber-reinforced polymer (FRP) bars as internal reinforcement are usually governed by their serviceability parameters, such as crack width and deflection. This study investigates the effect of structural fibers on the shear behavior of RC beams with glass fiber-reinforced polymer (GFRP) rebar as longitudinal reinforcement. The objective of this study is to understand the efficiency of macrosynthetic polyolefin (PO) polymer and a hybrid combination of steel and PO fibers in improving the shear behavior of GFRP-reinforced beams. In total, 13 full-scale RC beams are cast with GFRP rebars as internal reinforcement and varying PO and hybrid fiber dosages. Three different fiber dosages by volume of concrete (vf), namely 0.35%, 0.70%, and 1.0% are considered. The beams are tested under three-point bending configuration with a shear span (a) to effective depth (d) ratio of 2.2 to simulate shear dominant behavior. Experimental results revealed that the addition of fibers increased the postcracking stiffness, peak load, and ductility when compared with control beams with no fibers. Soon after cracking, an excessive load drop in the control specimen is observed due to the low elastic modulus of GFRP rebars. The addition of PO and hybrid fibers reduced the load drop significantly and enhanced the postcracking performance by improving the aggregate interlock and through reduction of residual tensile stresses at the crack tip. The angle of the crack increased with an increase in fiber dosages, indicating the change of the failure mode from brittle shear tension to ductile flexure at higher fiber dosages (0.7% and 1.0%). The shear strength predictions obtained from ACI and RILEM recommendations are found to be very conservative when compared with the test results

Influence of Radicals on Magnetization Relaxation Dynamics of Pseudo-Octahedral Lanthanide Iminopyridyl Complexes

Controlling quantum tunneling of magnetization (QTM) is a persistent challenge in lanthanide-based single-molecule magnets. As the exchange interaction is one of the key factors in controlling the QTM, we targeted lanthanide complexes with an increased number of radicals around the lanthanide ion. On the basis of our targeted approach, a family of pseudo-octahedral lanthanide/transition-metal complexes were isolated with the general molecular formula of [M­(L^•–)₃] (M = Gd (<b>1</b>), Dy (<b>2</b>), Er (<b>3</b>), Y (<b>4</b>)) using the redox-active iminopyridyl (L^•–) ligand exclusively, which possess the highest ratio of radicals to lanthanide reported for discrete metal complexes. Direct current magnetic susceptibility studies suggest that dominant antiferromagnetic interactions exist between the radical and lanthanide ions in all of the complexes, which is strongly corroborated by magnetic data fitting using a Heisenberg–Dirac–Van Vleck (HDVV) Hamiltonian (−2<i>J</i> Hamiltonian). A good agreement between the fit and the experimental magnetic data obtained using <i>g</i> = 2, <i>J</i>_rad‑rad = −111.9 cm^–1 for <b>4</b> and <i>g</i> = 1.99, <i>J</i>_rad‑rad = −111.9 cm^–1, <i>J</i>_Gd‑rad = −1.85 cm^–1 for <b>1</b>. Complex <b>2</b> shows frequency-dependent slow magnetization relaxation dynamics in the absence of an external magnetic field, while <b>3</b> shows field-induced frequency-dependent χ_M′′ signals. An ideal octahedral geometry around the lanthanide ion is predicted to be unsuitable for the design of a single-molecule magnet (SMM); nevertheless, complex <b>2</b> exhibits slow relaxation of magnetization with a record high anisotropy barrier for a six-coordinate Dy­(III) complex. A rationale for this unusual behavior is detailed and reveals the strength of the synthetic methodology developed

Stabilizing Terminal Ni(III)–Hydroxide Complex Using NNN-Pincer Ligands: Synthesis and Characterization

The reaction of [Ni­(COD)2] (COD; cyclooctadiene) in THF with the NNN-pincer ligand bis­(imino)­pyridyl (L1) reveals a susceptibility to oxidation in an inert atmosphere ([O2] level <0.5 ppm), resulting in a transient Ni:dioxygen adduct. This reactive intermediate abstracts a hydrogen atom from THF and stabilizes an uncommon Ni­(III) complex. The complex is crystallographically characterized by a molecular formula of [NiIII(L1··)2–(OH)] (1). Various isotopically labeled experiments (16O/18O) assertively endorse the origin of terminal oxygen based ligand in 1 due to the activation of molecular dioxygen. The presence of proton bound to the terminal oxygen in 1 is well supported by NMR, IR spectroscopy, DFT calculations, and hydrogen atom transfer (HAT) reactions promoted by 1. The observation of shakeup satellite peaks for the primary photoelectron lines of Ni­(2p) in the X-ray photoelectron spectroscopy (XPS) unambiguously confirms the paramagnetic signature associated with the distorted square planar nickel ion, which is consistent with the trivalent oxidation state assigned for the nickel ion in 1. The variable temperature magnetic susceptibility data of 1 shows dominant antiferromagnetic interactions exist among the paramagnetic centers, resulting in an overall S = 1/2 ground state. Variable temperature X-band EPR studies performed on 1 show evidence for the S = 1/2 ground state, which is consistent with magnetic data. The unusual g-tensor extracted for the ground state S = 1/2 is analyzed under a strong exchange limit of spin-coupled centers. The electronic structure predicted for 1 is in good agreement with theoretical calculations

Mechanistic Investigation of Well-Defined Cobalt Catalyzed Formal <i>E</i>‑Selective Hydrophosphination of Alkynes

A formal <i>E</i>-selective hydrophosphination of terminal and internal alkynes catalyzed by a well-defined [Co­(PMe₃)₄] (<b>A</b>) complex is achieved under mild conditions in good-to-excellent yield. The reaction does not require any additives and/or external base for an efficient hydrophosphination reaction. The reaction provided excellent scope and good functional tolerance. Detailed spectroscopic analysis (NMR, EPR, and UV–vis) revealed that the low valent cobalt(0) complex undergoes oxidative addition with diphenylphosphine, followed by hydrometalation with alkyne, and subsequent reductive elimination led to the expected product. The detailed spectroscopic analyses along with the isotopic labeled experiments facilitate to intercept the active intermediates that are involved in the catalytic cycle, which are detailed. It was revealed that the suprafacial (<i>vide infra</i>) delivery of H and phosphorus to π-alkynes in a <i>syn</i>-fashion led to formal <i>E</i>-vinyl phosphine