The study of mononuclear lanthanide-based systems, where the observed single-molecule magnets (SMMs) properties originate from the local description of the magnetic properties of the lanthanide ion, ...has been widely investigated through the literature. The case of polynuclear SMMs becomes more challenging both experimentally and theoretically due to the complexity of such architectures involving interactions between the magnetic centers. Many efforts have been focused on the understanding of the nature of these interactions and their effects on the SMM properties. In this work, a series of three structurally related tetranuclear dysprosium(III) SMMs, namely, Dy4(L)4(OH)2(DMF)4(NO3)2·2(DMF)·(H2O) (1), Dy4(L)4(OH)2(DMF)2(tfaa)2·2(CH3CN) (2), and Dy4(L)4(OH)2(DMF)2(acac)2·2(DMF) (3) (H2L = 2-(2-hydroxy-3-methoxybenzylideneamino)phenol, Htfaa = trifluoroacetylactone, Hacac = acetylacetonate), has been synthesized and investigated. By a fine-tuning of the ligands on the changeable coordination sites in these Dy(III)4 SMMs, the intramolecular magnetic interactions can be modified, switching from antiferromagnetic (for 1 and 2) to ferromagnetic (for 3). Ab initio calculations support these statements. In addition, the formation of 1 has been analyzed by ESI-MS analysis of the reaction mixture, indicating rather quick and high-yield formation of the Dy4 framework in solution. The combination of experimental work and ab initio calculations offers further insight into the relationship between structures and magnetic properties and sheds light on how to tune magnetic interactions in future polynuclear dysprosium complexes.
Dye-sensitized photoelectrochemical cells (DS-PECs) for water splitting hold promise for the large-scale storage of solar energy in the form of (solar) fuels, owing to the low cost and ease to ...process of their constitutive photoelectrode materials. The efficiency of such systems ultimately depends on our capacity to promote unidirectional light-driven electron transfer from the electrode substrate to a catalytic moiety. We report here on the first noble-metal free and covalent dye–catalyst assembly able to achieve photoelectrochemical visible light-driven H2 evolution in mildly acidic aqueous conditions when grafted onto p-type NiO electrode substrate.
Two new conjugated porphyrin-based systems (dimers 3 and 4) endowed with suitable crown ethers have been synthesized as receptors for a fullerene-ammonium salt derivative (1). Association constants ...in solution have been determined by UV–vis titration experiments in CH2Cl2 at room temperature. The designed hosts are able to associate up to two fullerene-based guest molecules and present association constants as high as ∼5 × 108 M–1. Calculation of the allosteric cooperative factor α for supramolecular complexes 3·1 2 and 4·1 2 showed a negative cooperative effect in both cases. The interactions accounting for the formation of the associates are based, first, on the complementary ammonium-crown ether interaction and, second, on the π–π interactions between the porphyrin rings and the C60 moieties. Theoretical calculations have evidenced a significant decrease of the electron density in the porphyrin dimers 3 and 4 upon complexation of the first C60 molecule, in good agreement with the negative cooperativity found in these systems. This negative effect is partially compensated by the stabilizing C60–C60 interactions that take place in the more stable syn-disposition of 4·1 2 .
Self-assembly of a flexible tritopic aniline and 3-substituted 2-formylpyridine subcomponents around iron(II) templates gave rise to a low-spin Fe
L
capsule, whereas a high-spin Fe
L
sandwich species ...formed when a sterically hindered 6-methyl-2-formylpyridine was used. The Fe
L
cage adopted a new structure type with S
symmetry, having two mer-Δ and two mer-Ʌ metal vertices, as confirmed by NMR and X-ray crystallographic analysis. The flexibility of the face-capping ligand endows the resulting Fe
L
framework with conformational plasticity, enabling it to adapt structurally from S
to T or C
symmetry upon guest binding. The cage also displayed negative allosteric cooperativity in simultaneously binding different guests within its cavity and at the apertures between its faces.
Hybrid bicyclo1.1.0butanes comprised of different group 14 elements, namely, 1,2,3-trisilabicyclo1.1.0butane and 1,3-disila-2-germabicyclo1.1.0butane, were readily prepared by the reductive ...dichlorination of 1,3-dichlorocyclobutane precursors. Both compounds feature exceptionally short bridging Si–Si bonds and practically planar geometry around the bridging Si atoms, thus representing a novel structural motif in the chemistry of the heavy analogues of bicyclo1.1.0butanes. These peculiar structures were explained by the steric interaction between the substituents at the bridging and bridgehead positions. Thermolysis of the title bicyclo1.1.0butanes in toluene at 130 °C resulted in their isomerization to the alkyl-substituted cyclopropene analogues. The mechanism of this isomerization was revealed in detail on the basis of deuterium-labeled experiments, kinetic investigations, trapping experiments, and computational studies to establish the nature of the key intermediate of the whole isomerization process.
A bidentate chiral dithiol (diBINAS) is utilised to bridge Au
nanoclusters to form oligomers. Separation by size allows the isolation of fractions that are stable thanks to the bidentate nature of ...the linker. The structure of the products is elucidated by small-angle X-ray scattering and calculated using density functional theory. Additional structural details are studied by diffusion-ordered nuclear magnetic resonance spectroscopy, transmission electron microscopy and matrix-assisted laser desorption/ionization time of flight mass spectrometry. Significant changes in the optical properties are analysed by UV/Vis and fluorescence spectroscopies, with the latter demonstrating a strong emission enhancement. Furthermore, the emergent chiral characteristics are studied by circular dichroism. Due to the geometry constraints of the nanocluster assemblies, diBINAS can be regarded as a templating molecule, taking a step towards the directed self-assembly of metal clusters.
Metalation of N-(2,6-dibenzhydryl-4-tolyl)adamantane-1-carboxamide (1, Ar*N(H)–C(O)–Ad) with M(NMe2)4 (M = Ti, Zr, Hf) yields amidate complexes Ar*N=C(Ad)–O–Ti(NMe2)3 (2) as well as bis(amidate) ...compounds (Ar*N=C(Ad)–O)2M(NMe2)2 (M = Zr (3), Hf (4)). In 2, the amidate ligand acts as a monodentate base via the oxygen atom with the Ti center in a slightly distorted tetrahedral environment. The steric requirement of the amidate ligand stabilizes the small coordination number of four of the Ti atom. In congeners 3 and 4, two bidentate amidate ligands exist in the coordination spheres, leading to hexacoordinate group IV metal atoms. The small bite angles of the Zr- and Hf-bound amidate ligands lead to severe distortion of the octahedral environments of the Zr and Hf centers. Titanium compound 2 is an unsuitable choice to catalyze hydrofunctionalization of alkynes with amines and phosphane oxides and despite the significantly smaller pKa value of the carboxylic amide, formation of carboxamide 1 is the dominant reaction upon addition of amines or phosphane oxides to release intramolecular steric strain introduced by the very bulky adamantylamidato ligand.
The coordination of the Lewis superacid tris(pentafluorophenyl)alane (AlCF) to phosphine-supported, group 6 bis(dinitrogen) complexes ML 2 (N 2 ) 2 is explored, with M = Cr, Mo or W and L = dppe ...(1,2-bis(diphenylphosphino)ethane), depe (1,2-bis(diethylphosphino)ethane), dmpe (1,2-bis(dimethylphosphino)ethane) or 2 × PMe 2 Ph. Akin to tris(pentafluorophenyl)borane (BCF), AlCF can form 1 : 1 adducts by coordination to one distal nitrogen of general formula trans -ML 2 (N 2 ){(μ-η 1 :η 1 -N 2 )Al(C 6 F 5 ) 3 }. The boron and aluminium adducts are structurally similar, showing a comparable level of N 2 push–pull activation. A notable exception is a bent (BCF adducts) vs. linear (AlCF adducts) M–N–N–LA motif (LA = Lewis acid), explained computationally as the result of steric repulsion. A striking difference arose when the formation of two-fold adducts was conducted. While in the case of BCF the 2 : 1 Lewis pairs could be observed in equilibrium with the 1 : 1 adduct and free borane but resisted isolation, AlCF forms robust 2 : 1 adducts trans -ML 2 {(μ-η 1 :η 1 -N 2 )Al(C 6 F 5 ) 3 } 2 that isomerise into a more stable cis configuration. These compounds could be isolated and structurally characterized, and represent the first examples of trinuclear heterometallic complexes formed by Lewis acid–base interaction exhibiting p and d elements. Calculations also demonstrate that from the bare complex to the two-fold aluminium adduct, substantial decrease of the HOMO–LUMO gap is observed, and, unlike the trans adducts (1 : 1 and 1 : 2) for which the HOMO was computed to be a pure d orbital, the one of the cis -trinuclear compounds mixes a d orbital with a π* one of each N 2 ligands. This may translate into a more favourable electrophilic attack on the N 2 ligands instead of the metal centre, while a stabilized N 2 -centered LUMO should ease electron transfer, suggesting Lewis acids could be co-activators for electro-catalysed N 2 reduction. Experimental UV-vis spectra for the tungsten family of compounds were compared with TD-DFT calculations (CAM-B3LYP/def2-TZVP), allowing to assign the low extinction bands found in the visible spectrum to unusual low-lying MLCT involving N 2 -centered orbitals. As significant red-shifts are observed upon LA coordination, this could have important implications for the development of visible light-driven nitrogen fixation.
Aza-boron-dipyrromethenes (Aza-BODIPYs) are an increasingly studied class of fluorophores. They can be seen as an azadipyrromethene ("aza-DIPY") ligand rigidified by a metalloid, a boron atom. Based ...on this idea, a series of complexes of group 13 metals (aluminum and gallium) have been synthesized and characterized. The impact of the metal and of the nature of the substituents of aza-DIPY core were investigated. The photophysical and electrochemical properties were determined, and an X-ray structure of an azaGaDIPY was obtained. These data reveal that azaGaDIPY and azaAlDIPY exhibit significant red-shifted fluorescence compared to their analogue aza-BODIPY. Their emission can go up to 800 nm for the maximum emission length and up to NIR-II for the emission tail. This, associated with their electrochemical stability (no metal release whether oxidized or reduced) makes them a promising class of fluorophores for optical medical imaging. Moreover, X-ray structure and molecular modeling studies have shown that this redshift seems to be more due to the geometry around the boron/metal than to the nature of the metal.
Hydrogen technology, as a future breakthrough for the energy industry, has been defined as an environmentally friendly, renewable, and high-power energy carrier. The green production of hydrogen, ...which mainly relies on electrocatalysts, is limited by the high cost and/or the performance of the catalytic system. Recently, studies have been conducted in search of bifunctional electrocatalysts accelerating both the hydrogen evolution reaction (HER) and the hydrogen oxidation reaction (HOR). Herein, we report the investigation of the high efficiency bifunctional electrocatalyst TaS2 for both the HER and the HOR along with the asymmetric effect of inhibition by organic intercalation. The linear organic agent, to boost the electron donor property and to ease the process of intercalation, provides a higher interlayer gap in the tandem structure of utilized nanosheets. XRD and XPS data reveal an increase in the interlayer distance of 22%. The HER and the HOR were characterized in a Pt group metal-free electrochemical system. The pristine sample shows a low overpotential of −0.016 V at the onset. The intercalated sample demonstrates a large shift in its performance for the HER. It is revealed that the intercalation is a potential key strategy for tuning the performance of this family of catalysts. The inhibition of the HER by intercalation is considered as the increase in the operational window of a water-based electrolyte on a negative electrode, which is relevant to technologies of electrochemical energy storage.
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![Hybrid Bicyclo[1.1.0]butane...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0276-7333/small "Hybrid Bicyclo[1.1.0]butanes [(R 4 Si 3 )CH 2 ] and [(R 4 Si 2 Ge)CH 2 ] (R = SiMe t Bu 2 ): Synthesis and Thermal Isomerization to Alkyl-Substituted Cyclopropenes [R 3 Si 3 ]CH 2 R and [R 3 Si 2 Ge]CH 2 R")
