132 research outputs found
Strong Exchange Couplings Drastically Slow Down Magnetization Relaxation in an Air‐Stable Cobalt(II)‐Radical Single‐Molecule Magnet (SMM)
The energy barrier leading to magnetic bistability in molecular clusters is determined by the magnetic anisotropy of the cluster constituents. By incorporating a highly anisotropic four‐coordinate cobalt(II) building block into a strongly coupled fully air‐ and moisture‐stable three‐spin system, it proved possible to suppress under‐barrier Raman processes leading to 350‐fold increase of magnetization relaxation time and pronounced hysteresis. Relaxation times of up to 9 hours at low temperatures were found
Matrix effects on the magnetic properties of a molecular spin triangle embedded in a polymeric film
Molecular triangles with competing Heisenberg interactions and significant Dzyaloshinskii–Moriya interactions (DMI) exhibit high environmental sensitivity, making them potential candidates for active elements for quantum sensing. Additionally, these triangles exhibit magnetoelectric coupling, allowing their properties to be controlled using electric fields. However, the manipulation and deposition of such complexes pose significant challenges. This
work explores a solution by embedding iron-based molecular triangles in a polymer matrix, a strategy that offers various deposition methods. We investigate how the host matrix alters the magnetic properties of the molecular triangle, with specific focus on the magnetic anisotropy, aiming to advance its practical applications as quantum sensors
Facile Synthesis and Characterization of Pure Tochilinite‐like Materials from Nanoparticulate FeS
Abstract In this work, three different tochilinite‐like materials have been obtained by sophisticated synthetic methods that allow to control the distribution of iron ions. The purity of the samples was confirmed by powder X‐ray diffraction. From elemental analysis and Mössbauer spectroscopy data, detailed compositions could be determined: T1) Fe 0.76 S*0.86 [Fe 2+ 0.01 Fe 3+ 0.56 Mg 2+ 0.43 (OH) 2.01 ]; T2) Fe 0.89 S*0.85 [Fe 2+ 0.55 Fe 3+ 0.11 Al 3+ 0.33 (OH) 1.84 (O) 0.16 ]; T3) Fe 0.71 S*0.79 [Fe 2+ 0.25 Fe 3+ 0.73 Mg 2+ 0.01 Al 3+ 0.01 (OH) 1.98 (O) 0.02 ]. These compositions fit to typical compositions of tochilinite in regard of the amount of iron vacancies and the volume ratio of the hydroxide layers to the sulfide layers. Besides hydroxide ions, oxide ions are also present in the hydroxide layers as a result of surface oxidation after the synthesis due to the high reactivity of the particles. TEM and SEM investigations show that the obtained powders consist mainly of thin sheets accompanied by nanotubes with BET surface areas ranging between 20 m 2 /g and 40 m 2 /g. The thermal stability was investigated by TGA and DSC analysis and it depends significantly on the composition.imag
(Electro)catalytic C-C bond formation reaction with a redox-active cobalt complex
Cooperativity between cobalt and non-innocent ligands in electron transfer
processes has been utilized for (electro)catalytic C–C bond formation
reactions
Precursor molecules for 1,2-diamidobenzene containing cobalt(ii), nickel(ii) and zinc(ii) complexes – synthesis and magnetic properties
Molecular magnetic materials based on 1,2-diamidobenzenes are well known and have been intensively studied both experimentally and computationally. They possess interesting magnetic properties as well as redox activity. In this work, we present the synthesis and investigation of potent synthons for constructing discrete metal–organic architectures featuring 1,2-diamidobenzene-coordinated metal centres. The synthons feature weakly bound dimethoxyethane (dme) ligands in addition to the 1,2-diamidobenzene. We characterize these complexes and investigate their magnetic properties by means of static and dynamic magnetometry and high-field electron paramagnetic resonance (HFEPR). Interestingly, the magnetic and magnetic resonance data strongly suggest a dimeric formulation of these complexes, viz. [MII(bmsab)(dme)]2 (bmsab = 1,2-bis(methanesulfonamido)benzene; dme = dimethoxyethane) with M = Co, Ni, Zn. A large negative D-value of −60 cm−1 was found for the Co(ii) synthon and an equally large negative D of −50 cm−1 for the Ni(ii) synthon. For Co(ii), the sign of the D-value is the same as that found for the known bis-diamidobenzene complexes of this ion. In contrast, the negative D-value for the Ni(ii) complex is unexpected, which we explain in terms of a change in coordination number. The heteroleptic Co(ii) complex presented here does not feature slow relaxation of the magnetization, in contrast to the homoleptic Co(ii) 1,2-diamidobenzene complex
Photolytic and Reductive Activations of 2‐Arsaethynolate in a Uranium‐Triamidoamine Complex: Decarbonylative Arsenic Group‐Transfer Reactions and Trapping of a Highly Bent and Reduced Form
Little is known about the chemistry of the 2-arsaethynolate anion, but to date it has exclusively undergone fragmentation reactions when reduced. Herein, we report the synthesis of [U(Tren(TIPS))(OCAs)] (2, Tren(TIPS)=N(CH(2)CH(2)NSiiPr(3))(3)), which is the first isolable actinide-2-arsaethynolate linkage. UV-photolysis of 2 results in decarbonylation, but the putative [U(Tren(TIPS))(As)] product was not isolated and instead only [{U(Tren(TIPS))}(2)(mu-eta(2):eta(2)-As2H2)] (3) was formed. In contrast, reduction of 2 with [U(Tren(TIPS))] gave the mixed-valence arsenido [{U(Tren(TIPS))}(2)(mu-As)] (4) in very low yield. Complex 4 is unstable which precluded full characterisation, but these photolytic and reductive reactions testify to the tendency of 2-arsaethynolate to fragment with CO release and As transfer. However, addition of 2 to an electride mixture of potassium-graphite and 2,2,2-cryptand gives [{U(Tren(TIPS))}(2){mu-eta(2)(OAs):eta(2)(CAs)-OCAs}][K(2,2,2-cryptand)] (5). The coordination mode of the trapped 2-arsaethynolate in 5 is unique, and derives from a new highly reduced and bent form of this ligand with the most acute O-C-As angle in any complex to date (O-C-As angle approximate to 128 degrees). The trapping rather than fragmentation of this highly reduced O-C-As unit is unprecedented, and quantum chemical calculations reveal that reduction confers donor-acceptor character to the O-C-As unit
Probing bistability in FeII and CoII complexes with an unsymmetrically substituted quinonoid ligand
The generation of molecular platforms, the properties of which can be
influenced by a variety of external perturbations, is an important goal in the
field of functional molecular materials. We present here the synthesis of a
new quinonoid ligand platform containing an [O,O,O,N] donor set. The ligand is
derived from a chloranilic acid core by using the [NR] (nitrogen atom with a
substituent R) for [O] isoelectronic substitution. Mononuclear FeII and CoII
complexes have been synthesized with this new ligand. Results obtained from
single crystal X-ray crystallography, NMR spectroscopy,
(spectro)electrochemistry, SQUID magnetometry, multi-frequency EPR
spectroscopy and FIR spectroscopy are used to elucidate the electronic and
geometric structures of the complexes. Furthermore, we show here that the spin
state of the FeII complex can be influenced by temperature, pressure and light
and the CoII complex displays redox-induced spin-state switching. Bistability
is observed in the solid-state as well as in solution for the FeII complex.
The new ligand presented here, owing to the [NR] group present in it, will
likely have more adaptability while investigating switching phenomena compared
to its [O,O,O,O] analogues. Thus, such classes of ligands as well as the
results obtained on the reversible changes in physical properties of the metal
complexes are likely to contribute to the generation of multifunctional
molecular materials
Anomalous diamagnetic susceptibility in 13-atom platinum nanocluster superatoms
Please read abstract in the article.http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1521-3773hb201
Electrochemistry and Spin-Crossover Behavior of Fluorinated Terpyridine-Based Co(II) and Fe(II) Complexes
Due to their ability to form stable molecular complexes that have tailor-made properties, terpyridine ligands are of great interest in chemistry and material science. In this regard, we prepared two terpyridine ligands with two different fluorinated phenyl rings on the backbone. The corresponding CoII and FeII complexes were synthesized and characterized by single-crystal X-ray structural analysis, electrochemistry and temperature-dependent SQUID magnetometry. Single crystal X-ray diffraction analyses at 100 K of these complexes revealed Co−N and Fe−N bond lengths that are typical of low spin CoII and FeII centers. The metal centers are coordinated in an octahedral fashion and the fluorinated phenyl rings on the backbone are twisted out of the plane of the terpyridine unit. The complexes were investigated with cyclic voltammetry and UV/Vis-NIR spectroelectrochemistry. All complexes show a reversible oxidation and several reduction processes. Temperature dependent SQUID magnetometry revealed a gradual thermal SCO behavior in two of the complexes, while EPR spectroscopy provided further insights on the electronic structure of the metal complexes, as well as site of reduction
A mesoionic carbene complex of manganese in five oxidation states
Reaction between a carbazole-based mesoionic carbene ligand and
manganese(II) iodide results in the formation of a rare air-stable
manganese(IV) complex after aerobic workup. Cyclic voltammetry
reveals the complex to be stable in five oxidation states. The
electronic structure of all five oxidation states is elucidated chemically, spectroscopically (NMR, high-frequency EPR, UV-Vis, MCD),
magnetically, and computationally (DFT, CASSCF)
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