Presented herein is a first investigation of the chemical reactivity of osmium-nitrido corroles, ... more Presented herein is a first investigation of the chemical reactivity of osmium-nitrido corroles, which are known for their unusual thermal, chemical, and photochemical stability. Elemental chlorine perchlorinates the β-positions of the triarylcorrole but leaves the OsN unit untouched. The OsN unit is also unaffected by a variety of other electrophilic and nucleophilic reagents. Upon photolysis, however, the anion of Zeise's salt associates with the nitrido ligand to generate an Os VI NPt II complex. The very short OsN−Pt linkage [1.895(9)−1.917(8) Å] and the downfield 195 Pt NMR resonance (−2702 ppm) suggest that the OsN corrole acts as a π-accepting ligand toward the Pt(II) center. This finding represents a rare example of the successful photochemical activation of a metal−ligand multiple bond that is too kinetically inert to exhibit any appreciable reactivity under thermal conditions.
Achieving control over coordination geometries in lanthanide complexes remains a challenge to the... more Achieving control over coordination geometries in lanthanide complexes remains a challenge to the coordination chemist. This is particularly the case in the field of molecule-based magnetism, where barriers for magnetic relaxation processes as well as tunneling pathways are strongly influenced by the lanthanide coordination geometry. Addressing the challenge of design of 4f-element coordination environments, the ubiquitous Ln(hfac)3 moieties have been shown to be applicable as Lewis acids coordinating transition metal acetylacetonates facially leading to simple, chiral lanthanide–transition metal heterodinuclear complexes. The broad scope of this approach is illustrated by the synthesis of a range of such complexes LnM: LnM(hfac)3(μ2-acac-O,O,O′)3 (Ln = La, Pr, Gd; M = Cr, Fe, Ga), with approximate three-fold symmetry. The complexes have been crystallographically characterized and exhibit polymorphism for some combinations of 4f and 3d metal centers. However, an isostructural set of...
We demonstrate here that the recently discovered thermal elasticity of magnetic anisotropy is not... more We demonstrate here that the recently discovered thermal elasticity of magnetic anisotropy is not at all an exotic phenomenon.
The reaction of [Ru(CAuCl)Cl2(PCy3)2] with [W(CSnnBu3)(CO)2(Tp*)] (obtained from [W(CBr)(CO)2(T... more The reaction of [Ru(CAuCl)Cl2(PCy3)2] with [W(CSnnBu3)(CO)2(Tp*)] (obtained from [W(CBr)(CO)2(Tp*)], nBuLi and ClSnnBu3) affords the heterotetrametallic bis(carbido) complex [WRuAu2(μ-C)2Cl3(CO)2(PCy3)2(Tp*)] in which the two distinct μ-carbido ligands adopt linear and T-shaped geometry at carbon.
Harnessing lability, the miniaturized ligand sphere in a [RuC–Pt] complex establishes a straight... more Harnessing lability, the miniaturized ligand sphere in a [RuC–Pt] complex establishes a straightforward building-block approach to carbide complexes.
The rational design of the magnetic anisotropy of molecular materials constitutes a goal of prima... more The rational design of the magnetic anisotropy of molecular materials constitutes a goal of primary importance in molecular magnetism. Indeed, the applications of molecular nanomagnets, such as single-molecule magnets and molecular magnetic refrigerants, depend on the full control over this property. Axially anisotropic magnetic systems are frequently classified as easy axis or easy plane, depending on whether the lowest energy is obtained by application of a magnetic field parallelly or perpendicularly to the unique axis. Here, the magnetic aniso-tropy of three lanthanide complexes is studied as a function of magnetic field and temperature. It is found that for two of these the type of magnetic aniso-tropy switches as a function of these parameters. Thus, this paper experimentally demonstrates that the magnetic anisotropy is not uniquely defined by the intrinsic electronic structure of the systems in question but can also be reversibly switched using external stimuli: temperature and magnetic field. known as magnetic anisotropy. For example, magnetic refrigerants are often engineered to be made by weakly anisotropic building blocks, [6] while to increase the operational temperature of single molecule magnets it is mandatory to achieve a strong easy axis anisotropy. [7] In this paper, we deal with the magnetic and electronic structure of mononuclear lanthanide complexes that have been advocated as one of the most promising categories of molecular magnets. [7b,8] The quantity to consider when describing the energy levels of a lanthanide center is the total angular momentum J, that is split into 2J+1 states (labeled |m J 〉) by the crystal field (CF). [9] The reason for this is the core-like nature of the partially filled 4f orbitals which renders the CF interaction much weaker than the spin–orbit coupling. Thus the orbital angular momentum (L) remains unquenched. The possibility to synthesize full series of isostructural lanthanide complexes, [10] render these compounds ideal for systematic studies of the interplay between a given CF and the electronic density of the paramagnetic center in determining the shape of the magnetic anisotropy. [11] The two opposite shapes of magnetic anisotropy are denoted easy axis (hard plane) and easy plane (hard axis). In the former case, the free energy has a minimum when the magnetic field is applied along an axis, while in the latter it is minimum when Magnetic Anisotropy Switches
Iron’s abundance and rich coordination chemistry are potentially appealing features for photochem... more Iron’s abundance and rich coordination chemistry are potentially appealing features for photochemical applications. However, the photoexcitable charge-transfer (CT) states of most Fe complexes are limited by picosecond or sub-picosecond deactivation through low-lying metal centered (MC) states, resulting in inefficient electron transfer reactivity and complete lack of photoluminescence. Here we show that octahedral coordination of Fe(III) by two mono-anionic facial tris-carbene ligands can suppress such deactivation dramatically. The resulting complex [Fe(phtmeimb)2]+, where phtmeimb is [phenyl(tris(3-methylimidazol-1-ylidene))borate]-, exhibits strong, visible, room temperature photoluminescence with a 2.0 ns lifetime and 2% quantum yield via spin-allowed transition from a ligand-to-metal charge-transfer (2LMCT) state to the ground state (2GS). Reductive and oxidative electron transfer reactions were observed for the 2LMCT state of [Fe(phtmeimb)2]+ in bimolecular quenching studies ...
Angewandte Chemie (International ed. in English), Jan 13, 2018
The tailored chemical synthesis of binary and ternary alloy nanoparticles with a uniform elementa... more The tailored chemical synthesis of binary and ternary alloy nanoparticles with a uniform elemental composition is presented. Their dual use as magnetic susceptors for induction heating and catalytic agent for steam reforming of methane to produce hydrogen at temperatures near and above 800 °C is demonstrated. The heating and catalytic performance of two chemically synthesized samples of CoNi and Cu⊂CoNi are compared and held against a traditional Ni-based reforming catalyst. The structural, magnetic, and catalytic properties of the samples were characterized by X-ray diffraction, elemental analysis, magnetometry, and reactivity measurements. For induction-heated catalysts, the conversion rate of methane is limited by chemical reactivity, as opposed to the case of traditional externally heated reformers where heat transport limitations are the limiting factor. Catalyst production by the synthetic route allows controlled doping with miniscule concentrations of auxiliary metals.
Total control over the electronic spin relaxation in molecular nanomagnets is the ultimate goal i... more Total control over the electronic spin relaxation in molecular nanomagnets is the ultimate goal in the design of new molecules with evermore realizable applications in spin-based devices. For single-ion lanthanide systems, with strong spin-orbit coupling, the potential applications are linked to the energetic structure of the crystal field levels and quantum tunneling within the ground state. Structural engineering of the timescale of these tunneling events via appropriate design of crystal fields represents a fundamental challenge for the synthetic chemist, since tunnel splittings are expected to be suppressed by crystal field environments with sufficiently high-order symmetry. Here, we report the long missing study of the effect of a non-linear (C) to pseudo-linear (D) change in crystal field symmetry in an otherwise chemically unaltered dysprosium complex. From a purely experimental study of crystal field levels and electronic spin dynamics at milliKelvin temperatures, we demonst...
Chemistry (Weinheim an der Bergstrasse, Germany), Jan 12, 2017
The performance of relativistic density functional theory (DFT) methods has been investigated for... more The performance of relativistic density functional theory (DFT) methods has been investigated for the calculation of the recently measured hyperfine coupling constants of Re IV and Ir IV in their hexafluorido ions, [ReF6]2- and [IrF6]2-. Three relativistic methods have been employed at the DFT level of theory: the 2-component zeroth order regular approximation (ZORA) method treating the spin-orbit coupling either variationally (EV ZORA) or as a perturbation (LR ZORA) and the 4-component Dirac-Kohn-Sham (DKS) method. The dependence of the results on the basis set and the choice of exchange- correlation functional has been studied. Furthermore the effect of varying the amount of Hartree-Fock exchange in the hybrid functionals has been investigated. The LR ZORA and DKS methods in combination with DFT lead to very similar deviations from the experimental values for the [ReF6]2- complex, i.e. ∼ 20% for the coupling constant using hybrid functionals. None of the methods are however able t...
Chemistry (Weinheim an der Bergstrasse, Germany), Jan 26, 2017
Heavy 5d elements, like osmium, feature strong spin-orbit interaction which is at the origin of e... more Heavy 5d elements, like osmium, feature strong spin-orbit interaction which is at the origin of exotic physical behaviors. Revealing the full potential of e.g. novel osmium oxide materials ("osmates") is however contingent upon a detailed understanding of the local single-ion properties. Herein, we report on two molecular osmate analogues, [OsF6]2- and [OsF6]-, as model systems for Os4+ and Os5+ centres found in oxides. Using X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) techniques combined with state-of-the-art ab initio calculations, we elucidate their ground state, which is mirroring the osmium electronic structure in osmates. The realization of such molecular model systems provides a unique chemical playground to engineer materials exhibiting spin-orbit entangled phenomena.
Transition-metal complexes are used as photosensitizers, in light-emitting diodes, for biosensing... more Transition-metal complexes are used as photosensitizers, in light-emitting diodes, for biosensing and in photocatalysis. A key feature in these applications is excitation from the ground state to a charge-transfer state; the long charge-transfer-state lifetimes typical for complexes of ruthenium and other precious metals are often essential to ensure high performance. There is much interest in replacing these scarce elements with Earth-abundant metals, with iron and copper being particularly attractive owing to their low cost and non-toxicity. But despite the exploration of innovative molecular designs, it remains a formidable scientific challenge to access Earth-abundant transition-metal complexes with long-lived charge-transfer excited states. No known iron complexes are considered photoluminescent at room temperature, and their rapid excited-state deactivation precludes their use as photosensitizers. Here we present the iron complex [Fe(btz)3](3+) (where btz is 3,3'-dimethyl-...
A tetranuclear [2 × 2] grid-like manganese(III) Schiff base complex, Mn4, has been synthesized an... more A tetranuclear [2 × 2] grid-like manganese(III) Schiff base complex, Mn4, has been synthesized and characterized by single-crystal X-ray crystallography. Direct-current magnetization measurements were performed on the system and proved to be insufficient for an accurate magnetic model to be deduced. Combined inelastic neutron scattering (INS) and electron paramagnetic resonance (EPR) experiments provided the necessary information in order to successfully model the magnetic properties of Mn4. The resulting model takes into account both the magnitude and the relative orientations of the single-ion anisotropy tensors.
Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy, Jan 15, 2017
In an investigation of the artists' materials used by P. S. Krøyer the contents of the tube c... more In an investigation of the artists' materials used by P. S. Krøyer the contents of the tube colours found in Krøyer's painting cabinet were examined. In most cases, the results of the pigment analyses were as expected based on our knowledge of artists' colours used in the late 1800s and early 1900s. However, in one of the tube colours labelled "Jaune de Cadmium Citron" (cadmium lemon yellow) an extremely rare cadmium chromate pigment was found. The pigment was analysed and characterised by Raman microscopy (MRS), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), powder X-ray diffraction (PXRD), single-crystal X-ray crystallography, and electron paramagnetic resonance (EPR) spectroscopy. Cadmium chromate was synthesised by precipitation from an aqueous solution of cadmium nitrate and potassium chromate, and the resulting yellow crystals proved identical to...
These bimetallic MOFs contain [Cu(pyz)2]2+ sheets and MF6n− octahedra whereby only the Cu(ii) mom... more These bimetallic MOFs contain [Cu(pyz)2]2+ sheets and MF6n− octahedra whereby only the Cu(ii) moments magnetically order.
New exotic phenomena have recently been discovered in oxides of paramagnetic Ir(4+) ions, widely ... more New exotic phenomena have recently been discovered in oxides of paramagnetic Ir(4+) ions, widely known as 'iridates'. Their remarkable properties originate from concerted effects of the crystal field, magnetic interactions and strong spin-orbit coupling, characteristic of 5d metal ions. Despite numerous experimental reports, the electronic structure of these materials is still challenging to elucidate, and not attainable in the isolated, but chemically inaccessible, [IrO6](8-) species (the simplest molecular analogue of the elementary {IrO6}(8-) fragment present in all iridates). Here, we introduce an alternative approach to circumvent this problem by substituting the oxide ions in [IrO6](8-) by isoelectronic fluorides to form the fluorido-iridate: [IrF6](2-). This molecular species has the same electronic ground state as the {IrO6}(8-) fragment, and thus emerges as an ideal model for iridates. These results may open perspectives for using fluorido-iridates as building-block...
Photolysis of red cis-and trans-[Cr III (cyclam)(N 3) 2 ](ClO 4) (1a, 2a) (cyclam) 1,4,8,11-tetra... more Photolysis of red cis-and trans-[Cr III (cyclam)(N 3) 2 ](ClO 4) (1a, 2a) (cyclam) 1,4,8,11-tetraazacyclotetradecane) in the solid state or aqueous solution by light affords the nitridochromium(V) complexes of cis-or trans-[Cr V-(N)(cyclam)(N 3)](ClO 4) (3a) and dinuclear [{trans-[Cr V (N)(cyclam)]} 2 (µ-N 3)](ClO 4) 3 ‚3.5H 2 O (4a), respectively. 4a was converted to the bis(tetraphenylborate)-azide-2C 2 H 5 OH salt (4b). Crystallization of 4a from acetonitriles after addition of AgClO 4 and removal of AgN 3 syields octahedral trans-[Cr V (N)(cyclam)(NCCH 3)](ClO 4) 2 (5a). The crystal structures of 1a, 2b (which is the tetraphenylborate salt of 2a), 4a,b, 5a,b have been determined by single-crystal X-ray crystallography. All nitridochromium(V) compounds contain the trans-[Cr V (N)(cyclam)] 2+ fragment with an NtCr V moiety (1.56 (0.01 Å). The electronic spectra of d 1 configurated complexes display three low-intensity d-d bands which have been assigned in C 4V symmetry as (xy) ((xz,yz) 2 B 2 f 2 E, (xy) f (x 2 y 2) 2 B 2 f 2 B 1 , and (xy) f (z 2) 2 B 2 f 2 A 1 , where the molecular z-axis coincides with the NtCr vector. Ligandfield parameters within the angular overlap model (AOM) of e σ cyclam) 7300-8600, e σ ax) 22 000, e σ ax) 21300-25000 cm-1 have been determined which reproduce the experimental electronic spectra well. Temperaturedependent magnetic susceptibility measurements and X-band EPR spectroscopy on solid samples of 4a containing a linear Cr V-NdNdN-Cr V moiety revealed a weak intramolecular antiferromagnetic exchange coupling which is nearly absent in 4b containing a bent azido bridge. A mechanism for this unexpected coupling in 4a is proposed.
Presented herein is a first investigation of the chemical reactivity of osmium-nitrido corroles, ... more Presented herein is a first investigation of the chemical reactivity of osmium-nitrido corroles, which are known for their unusual thermal, chemical, and photochemical stability. Elemental chlorine perchlorinates the β-positions of the triarylcorrole but leaves the OsN unit untouched. The OsN unit is also unaffected by a variety of other electrophilic and nucleophilic reagents. Upon photolysis, however, the anion of Zeise's salt associates with the nitrido ligand to generate an Os VI NPt II complex. The very short OsN−Pt linkage [1.895(9)−1.917(8) Å] and the downfield 195 Pt NMR resonance (−2702 ppm) suggest that the OsN corrole acts as a π-accepting ligand toward the Pt(II) center. This finding represents a rare example of the successful photochemical activation of a metal−ligand multiple bond that is too kinetically inert to exhibit any appreciable reactivity under thermal conditions.
Achieving control over coordination geometries in lanthanide complexes remains a challenge to the... more Achieving control over coordination geometries in lanthanide complexes remains a challenge to the coordination chemist. This is particularly the case in the field of molecule-based magnetism, where barriers for magnetic relaxation processes as well as tunneling pathways are strongly influenced by the lanthanide coordination geometry. Addressing the challenge of design of 4f-element coordination environments, the ubiquitous Ln(hfac)3 moieties have been shown to be applicable as Lewis acids coordinating transition metal acetylacetonates facially leading to simple, chiral lanthanide–transition metal heterodinuclear complexes. The broad scope of this approach is illustrated by the synthesis of a range of such complexes LnM: LnM(hfac)3(μ2-acac-O,O,O′)3 (Ln = La, Pr, Gd; M = Cr, Fe, Ga), with approximate three-fold symmetry. The complexes have been crystallographically characterized and exhibit polymorphism for some combinations of 4f and 3d metal centers. However, an isostructural set of...
We demonstrate here that the recently discovered thermal elasticity of magnetic anisotropy is not... more We demonstrate here that the recently discovered thermal elasticity of magnetic anisotropy is not at all an exotic phenomenon.
The reaction of [Ru(CAuCl)Cl2(PCy3)2] with [W(CSnnBu3)(CO)2(Tp*)] (obtained from [W(CBr)(CO)2(T... more The reaction of [Ru(CAuCl)Cl2(PCy3)2] with [W(CSnnBu3)(CO)2(Tp*)] (obtained from [W(CBr)(CO)2(Tp*)], nBuLi and ClSnnBu3) affords the heterotetrametallic bis(carbido) complex [WRuAu2(μ-C)2Cl3(CO)2(PCy3)2(Tp*)] in which the two distinct μ-carbido ligands adopt linear and T-shaped geometry at carbon.
Harnessing lability, the miniaturized ligand sphere in a [RuC–Pt] complex establishes a straight... more Harnessing lability, the miniaturized ligand sphere in a [RuC–Pt] complex establishes a straightforward building-block approach to carbide complexes.
The rational design of the magnetic anisotropy of molecular materials constitutes a goal of prima... more The rational design of the magnetic anisotropy of molecular materials constitutes a goal of primary importance in molecular magnetism. Indeed, the applications of molecular nanomagnets, such as single-molecule magnets and molecular magnetic refrigerants, depend on the full control over this property. Axially anisotropic magnetic systems are frequently classified as easy axis or easy plane, depending on whether the lowest energy is obtained by application of a magnetic field parallelly or perpendicularly to the unique axis. Here, the magnetic aniso-tropy of three lanthanide complexes is studied as a function of magnetic field and temperature. It is found that for two of these the type of magnetic aniso-tropy switches as a function of these parameters. Thus, this paper experimentally demonstrates that the magnetic anisotropy is not uniquely defined by the intrinsic electronic structure of the systems in question but can also be reversibly switched using external stimuli: temperature and magnetic field. known as magnetic anisotropy. For example, magnetic refrigerants are often engineered to be made by weakly anisotropic building blocks, [6] while to increase the operational temperature of single molecule magnets it is mandatory to achieve a strong easy axis anisotropy. [7] In this paper, we deal with the magnetic and electronic structure of mononuclear lanthanide complexes that have been advocated as one of the most promising categories of molecular magnets. [7b,8] The quantity to consider when describing the energy levels of a lanthanide center is the total angular momentum J, that is split into 2J+1 states (labeled |m J 〉) by the crystal field (CF). [9] The reason for this is the core-like nature of the partially filled 4f orbitals which renders the CF interaction much weaker than the spin–orbit coupling. Thus the orbital angular momentum (L) remains unquenched. The possibility to synthesize full series of isostructural lanthanide complexes, [10] render these compounds ideal for systematic studies of the interplay between a given CF and the electronic density of the paramagnetic center in determining the shape of the magnetic anisotropy. [11] The two opposite shapes of magnetic anisotropy are denoted easy axis (hard plane) and easy plane (hard axis). In the former case, the free energy has a minimum when the magnetic field is applied along an axis, while in the latter it is minimum when Magnetic Anisotropy Switches
Iron’s abundance and rich coordination chemistry are potentially appealing features for photochem... more Iron’s abundance and rich coordination chemistry are potentially appealing features for photochemical applications. However, the photoexcitable charge-transfer (CT) states of most Fe complexes are limited by picosecond or sub-picosecond deactivation through low-lying metal centered (MC) states, resulting in inefficient electron transfer reactivity and complete lack of photoluminescence. Here we show that octahedral coordination of Fe(III) by two mono-anionic facial tris-carbene ligands can suppress such deactivation dramatically. The resulting complex [Fe(phtmeimb)2]+, where phtmeimb is [phenyl(tris(3-methylimidazol-1-ylidene))borate]-, exhibits strong, visible, room temperature photoluminescence with a 2.0 ns lifetime and 2% quantum yield via spin-allowed transition from a ligand-to-metal charge-transfer (2LMCT) state to the ground state (2GS). Reductive and oxidative electron transfer reactions were observed for the 2LMCT state of [Fe(phtmeimb)2]+ in bimolecular quenching studies ...
Angewandte Chemie (International ed. in English), Jan 13, 2018
The tailored chemical synthesis of binary and ternary alloy nanoparticles with a uniform elementa... more The tailored chemical synthesis of binary and ternary alloy nanoparticles with a uniform elemental composition is presented. Their dual use as magnetic susceptors for induction heating and catalytic agent for steam reforming of methane to produce hydrogen at temperatures near and above 800 °C is demonstrated. The heating and catalytic performance of two chemically synthesized samples of CoNi and Cu⊂CoNi are compared and held against a traditional Ni-based reforming catalyst. The structural, magnetic, and catalytic properties of the samples were characterized by X-ray diffraction, elemental analysis, magnetometry, and reactivity measurements. For induction-heated catalysts, the conversion rate of methane is limited by chemical reactivity, as opposed to the case of traditional externally heated reformers where heat transport limitations are the limiting factor. Catalyst production by the synthetic route allows controlled doping with miniscule concentrations of auxiliary metals.
Total control over the electronic spin relaxation in molecular nanomagnets is the ultimate goal i... more Total control over the electronic spin relaxation in molecular nanomagnets is the ultimate goal in the design of new molecules with evermore realizable applications in spin-based devices. For single-ion lanthanide systems, with strong spin-orbit coupling, the potential applications are linked to the energetic structure of the crystal field levels and quantum tunneling within the ground state. Structural engineering of the timescale of these tunneling events via appropriate design of crystal fields represents a fundamental challenge for the synthetic chemist, since tunnel splittings are expected to be suppressed by crystal field environments with sufficiently high-order symmetry. Here, we report the long missing study of the effect of a non-linear (C) to pseudo-linear (D) change in crystal field symmetry in an otherwise chemically unaltered dysprosium complex. From a purely experimental study of crystal field levels and electronic spin dynamics at milliKelvin temperatures, we demonst...
Chemistry (Weinheim an der Bergstrasse, Germany), Jan 12, 2017
The performance of relativistic density functional theory (DFT) methods has been investigated for... more The performance of relativistic density functional theory (DFT) methods has been investigated for the calculation of the recently measured hyperfine coupling constants of Re IV and Ir IV in their hexafluorido ions, [ReF6]2- and [IrF6]2-. Three relativistic methods have been employed at the DFT level of theory: the 2-component zeroth order regular approximation (ZORA) method treating the spin-orbit coupling either variationally (EV ZORA) or as a perturbation (LR ZORA) and the 4-component Dirac-Kohn-Sham (DKS) method. The dependence of the results on the basis set and the choice of exchange- correlation functional has been studied. Furthermore the effect of varying the amount of Hartree-Fock exchange in the hybrid functionals has been investigated. The LR ZORA and DKS methods in combination with DFT lead to very similar deviations from the experimental values for the [ReF6]2- complex, i.e. ∼ 20% for the coupling constant using hybrid functionals. None of the methods are however able t...
Chemistry (Weinheim an der Bergstrasse, Germany), Jan 26, 2017
Heavy 5d elements, like osmium, feature strong spin-orbit interaction which is at the origin of e... more Heavy 5d elements, like osmium, feature strong spin-orbit interaction which is at the origin of exotic physical behaviors. Revealing the full potential of e.g. novel osmium oxide materials ("osmates") is however contingent upon a detailed understanding of the local single-ion properties. Herein, we report on two molecular osmate analogues, [OsF6]2- and [OsF6]-, as model systems for Os4+ and Os5+ centres found in oxides. Using X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) techniques combined with state-of-the-art ab initio calculations, we elucidate their ground state, which is mirroring the osmium electronic structure in osmates. The realization of such molecular model systems provides a unique chemical playground to engineer materials exhibiting spin-orbit entangled phenomena.
Transition-metal complexes are used as photosensitizers, in light-emitting diodes, for biosensing... more Transition-metal complexes are used as photosensitizers, in light-emitting diodes, for biosensing and in photocatalysis. A key feature in these applications is excitation from the ground state to a charge-transfer state; the long charge-transfer-state lifetimes typical for complexes of ruthenium and other precious metals are often essential to ensure high performance. There is much interest in replacing these scarce elements with Earth-abundant metals, with iron and copper being particularly attractive owing to their low cost and non-toxicity. But despite the exploration of innovative molecular designs, it remains a formidable scientific challenge to access Earth-abundant transition-metal complexes with long-lived charge-transfer excited states. No known iron complexes are considered photoluminescent at room temperature, and their rapid excited-state deactivation precludes their use as photosensitizers. Here we present the iron complex [Fe(btz)3](3+) (where btz is 3,3'-dimethyl-...
A tetranuclear [2 × 2] grid-like manganese(III) Schiff base complex, Mn4, has been synthesized an... more A tetranuclear [2 × 2] grid-like manganese(III) Schiff base complex, Mn4, has been synthesized and characterized by single-crystal X-ray crystallography. Direct-current magnetization measurements were performed on the system and proved to be insufficient for an accurate magnetic model to be deduced. Combined inelastic neutron scattering (INS) and electron paramagnetic resonance (EPR) experiments provided the necessary information in order to successfully model the magnetic properties of Mn4. The resulting model takes into account both the magnitude and the relative orientations of the single-ion anisotropy tensors.
Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy, Jan 15, 2017
In an investigation of the artists' materials used by P. S. Krøyer the contents of the tube c... more In an investigation of the artists' materials used by P. S. Krøyer the contents of the tube colours found in Krøyer's painting cabinet were examined. In most cases, the results of the pigment analyses were as expected based on our knowledge of artists' colours used in the late 1800s and early 1900s. However, in one of the tube colours labelled "Jaune de Cadmium Citron" (cadmium lemon yellow) an extremely rare cadmium chromate pigment was found. The pigment was analysed and characterised by Raman microscopy (MRS), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), powder X-ray diffraction (PXRD), single-crystal X-ray crystallography, and electron paramagnetic resonance (EPR) spectroscopy. Cadmium chromate was synthesised by precipitation from an aqueous solution of cadmium nitrate and potassium chromate, and the resulting yellow crystals proved identical to...
These bimetallic MOFs contain [Cu(pyz)2]2+ sheets and MF6n− octahedra whereby only the Cu(ii) mom... more These bimetallic MOFs contain [Cu(pyz)2]2+ sheets and MF6n− octahedra whereby only the Cu(ii) moments magnetically order.
New exotic phenomena have recently been discovered in oxides of paramagnetic Ir(4+) ions, widely ... more New exotic phenomena have recently been discovered in oxides of paramagnetic Ir(4+) ions, widely known as 'iridates'. Their remarkable properties originate from concerted effects of the crystal field, magnetic interactions and strong spin-orbit coupling, characteristic of 5d metal ions. Despite numerous experimental reports, the electronic structure of these materials is still challenging to elucidate, and not attainable in the isolated, but chemically inaccessible, [IrO6](8-) species (the simplest molecular analogue of the elementary {IrO6}(8-) fragment present in all iridates). Here, we introduce an alternative approach to circumvent this problem by substituting the oxide ions in [IrO6](8-) by isoelectronic fluorides to form the fluorido-iridate: [IrF6](2-). This molecular species has the same electronic ground state as the {IrO6}(8-) fragment, and thus emerges as an ideal model for iridates. These results may open perspectives for using fluorido-iridates as building-block...
Photolysis of red cis-and trans-[Cr III (cyclam)(N 3) 2 ](ClO 4) (1a, 2a) (cyclam) 1,4,8,11-tetra... more Photolysis of red cis-and trans-[Cr III (cyclam)(N 3) 2 ](ClO 4) (1a, 2a) (cyclam) 1,4,8,11-tetraazacyclotetradecane) in the solid state or aqueous solution by light affords the nitridochromium(V) complexes of cis-or trans-[Cr V-(N)(cyclam)(N 3)](ClO 4) (3a) and dinuclear [{trans-[Cr V (N)(cyclam)]} 2 (µ-N 3)](ClO 4) 3 ‚3.5H 2 O (4a), respectively. 4a was converted to the bis(tetraphenylborate)-azide-2C 2 H 5 OH salt (4b). Crystallization of 4a from acetonitriles after addition of AgClO 4 and removal of AgN 3 syields octahedral trans-[Cr V (N)(cyclam)(NCCH 3)](ClO 4) 2 (5a). The crystal structures of 1a, 2b (which is the tetraphenylborate salt of 2a), 4a,b, 5a,b have been determined by single-crystal X-ray crystallography. All nitridochromium(V) compounds contain the trans-[Cr V (N)(cyclam)] 2+ fragment with an NtCr V moiety (1.56 (0.01 Å). The electronic spectra of d 1 configurated complexes display three low-intensity d-d bands which have been assigned in C 4V symmetry as (xy) ((xz,yz) 2 B 2 f 2 E, (xy) f (x 2 y 2) 2 B 2 f 2 B 1 , and (xy) f (z 2) 2 B 2 f 2 A 1 , where the molecular z-axis coincides with the NtCr vector. Ligandfield parameters within the angular overlap model (AOM) of e σ cyclam) 7300-8600, e σ ax) 22 000, e σ ax) 21300-25000 cm-1 have been determined which reproduce the experimental electronic spectra well. Temperaturedependent magnetic susceptibility measurements and X-band EPR spectroscopy on solid samples of 4a containing a linear Cr V-NdNdN-Cr V moiety revealed a weak intramolecular antiferromagnetic exchange coupling which is nearly absent in 4b containing a bent azido bridge. A mechanism for this unexpected coupling in 4a is proposed.
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Papers by Jesper Bendix