Single-ion magnetism in the extended solid-state: insights from X-ray absorption and emission spectroscopy.

From Europe PMC via Jisc Publications RouterHistory: ppub 2020-10-01, epub 2020-10-07Publication status: PublishedLarge single-ion magnetic anisotropy is observed in lithium nitride doped with iron. The iron sites are two-coordinate, putting iron doped lithium nitride amongst a growing number of two coordinate transition metal single-ion magnets (SIMs). Uniquely, the relaxation times to magnetisation reversal are over two orders of magnitude longer in iron doped lithium nitride than other 3d-metal SIMs, and comparable with high-performance lanthanide-based SIMs. To understand the origin of these enhanced magnetic properties a detailed characterisation of electronic structure is presented. Access to dopant electronic structure calls for atomic specific techniques, hence a combination of detailed single-crystal X-ray absorption and emission spectroscopies are applied. Together K-edge, L2,3-edge and Kβ X-ray spectroscopies probe local geometry and electronic structure, identifying iron doped lithium nitride to be a prototype, solid-state SIM, clean of stoichiometric vacancies where Fe lattice sites are geometrically equivalent. Extended X-ray absorption fine structure and angular dependent single-crystal X-ray absorption near edge spectroscopy measurements determine FeI dopant ions to be linearly coordinated, occupying a D 6h symmetry pocket. The dopant engages in strong 3dπ-bonding, resulting in an exceptionally short Fe-N bond length (1.873(7) Å) and rigorous linearity. It is proposed that this structure protects dopant sites from Renner-Teller vibronic coupling and pseudo Jahn-Teller distortions, enhancing magnetic properties with respect to molecular-based linear complexes. The Fe ligand field is quantified by L2,3-edge XAS from which the energy reduction of 3d z 2 due to strong 4s mixing is deduced. Quantification of magnetic anisotropy barriers in low concentration dopant sites is inhibited by many established methods, including far-infrared and neutron scattering. We deduce variable temperature L3-edge XAS can be applied to quantify the J = 7/2 magnetic anisotropy barrier, 34.80 meV (∼280 cm-1), that corresponds with Orbach relaxation via the first excited, M J = ±5/2 doublet. The results demonstrate that dopant sites within solid-state host lattices could offer a viable alternative to rare-earth bulk magnets and high-performance SIMs, where the host matrix can be tailored to impose high symmetry and control lattice induced relaxation effects

Synthesis and Characterisation of a Very Low-Coordinate Diferrous [2Fe-2S] 0 Unit

International audienceHere we present the synthesis of a unique diferrous [2Fe–2S]0 complex with only three-coordinate iron ions via reduction of a four-coordinate diferric [2Fe–2S]2+ complex with concomitant ligand loss. The obtained compounds were thoroughly examined for their properties (e.g. by 57Fe Mössbauer spectroscopy and magnetic susceptibility measurements). Facile cleavage of the [2Fe–2S] rhombus, commonly seen as rather stable, by CS2 is also shown

Iron-catalyzed reduction of CO2 into methylene: Formation of C–N, C–O, and C–C bonds

International audienceWe report herein the use of the (dihydrido)iron catalyst, Fe(H)2(dmpe)2, for the selective reduction of CO2 into either bis(boryl)acetal or methoxyborane depending on the hydroborane used as a reductant. In a one-pot two-step procedure, the in situ generated bis(boryl)acetal was shown to be a reactive and versatile source of methylene to create new C–N but also C–O and C–C bonds

Imido Cobalt Complexes with Imidyl Character

We report on the synthesis of a variety of trigonal imido cobalt complexes [Co(NAryl)L2)–, (L = N(Dipp)SiMe3), Dipp = 2,6-diisopropylphenyl) bearing very long Co–NAryl bonds of around 1.75 Å. The electronic structure was interrogated using a variety of physical and spectroscopic methods indicating the first authenticated examples of cobalt bound imidyl species. Computational studies corroborate these findings and reveal that the high-spin state of these complexes gives rise to unpaired spin-density on the imide nitrogen and leads to its imidyl character. Obtained complexes are capable of intermolecular H atom abstraction from C–H bonds that yields the corresponding cobalt amides. Exchange of the Dipp-substituent on the imide by the smaller mesityl function (2,4,6-trimethylphenyl) effectuates the unexpected Me3Si shift from the ancillary ligand set to the imide nitrogen, followed by intramolecular C–H bond activation.<br /

Two-Coordinate Iron(I) Complex [Fe{N(SiMe 3 ) 2 } 2 ] À : Synthesis, Properties, and Redox Activity**

Abstract: First-row two-coordinate complexes are attracting much interest. Herein, we report the high-yield isolation of the linear two-coordinate iron (I) (L = 18-crown-6 or crypt-222) through the reduction of either [Fe{N(SiMe 3 ) 2 } 2 ] or its three-coordinate phosphine adduct [Fe{N(SiMe 3 ) 2 } 2 (PCy 3 )]. Detailed characterization is gained through X-ray diffraction, variable-temperature NMR spectroscopy, and magnetic susceptibility studies. Oneand two-electron oxidation through reaction with I 2 is further found to afford the corresponding iodo iron(II) and diiodo iron(III) complexes

High-Spin Imido Cobalt Complexes with Imidyl Radical Character

We report on the synthesis of a variety of trigonal imido cobalt complexes [Co(NAryl)L2]−, (L=N(Dipp)SiMe3), Dipp=2,6-diisopropylphenyl) with very long Co−NAryl bonds of around 1.75 Å. Their electronic structure was interrogated using a variety of physical and spectroscopic methods such as EPR or X-Ray absorption spectroscopy which leads to their description as highly unusual imidyl cobalt complexes. Computational analyses corroborate these findings and further reveal that the high-spin state is responsible for the imidyl character. Exchange of the Dipp substituent on the imide by the smaller mesityl function (2,4,6-trimethylphenyl) effectuates the unexpected Me3Si shift from the ancillary ligand set to the imidyl nitrogen, revealing a highly reactive, nucleophilic character of the imidyl unit

Between imide, imidyl and nitrene – an imido iron complex in two oxidation states

Imidyl and nitrene metal species play an important role in the N-functionalisation of unreactive C–H bonds as well as the aziridination of olefines. We report on the synthesis of the trigonal imido iron complexes [Fe(NMes)L2]0,− (L = –N{Dipp}SiMe3); Dipp = 2,6-diisopropyl-phenyl; Mes = (2,4,6-trimethylphenyl) via reaction of mesityl azide (MesN3) with the linear iron precursors [FeL2]0,−. UV-vis-, EPR-, 57Fe Mössbauer spectroscopy, magnetometry, and computational methods suggest for the reduced form an electronic structure as a ferromagnetically coupled iron(II) imidyl radical, whereas oxidation leads to mixed iron(III) imidyl and electrophilic iron(II) nitrene character. Reactivity studies show that both complexes are capable of H atom abstraction from C–H bonds. Further, the reduced form [Fe(NMes)L2]− reacts nucleophilically with CS2 by inserting into the imido iron bond, as well as electrophilically with CO under nitrene transfer. The neutral [Fe(NMes)L2] complex shows enhanced electrophilic behavior as evidenced by nitrene transfer to a phosphine, yet in combination with an overall reduced reactivity

Iron-Catalyzed C-H Borylation of Arenes.

International audienceWell-defined iron bis(diphosphine) complexes are active catalysts for the dehydrogenative C-H borylation of arom. and heteroarom. derivs. with pinacolborane. The corresponding borylated compds. were isolated in moderate to good yields (25-73%) with a 5 mol% catalyst loading under UV irradn. (350 nm) at room temp. Stoichiometric reactivity studies and isolation of an original trans-hydrido(boryl)iron complex, Fe(H)(Bpin)(dmpe)2, allowed us to propose a mechanism showing the role of some key catalytic species

Between imide, imidyl and nitrene – an imido iron complex in two oxidation states

Imidyl and nitrene metal species play an important role in the N-functionalisation of unreactive C–H bonds as well as the aziridination of olefines. We report on the synthesis of the trigonal imido iron complexes [Fe(NMes)L2]0,- (L ¼ –N{Dipp}SiMe3); Dipp ¼ 2,6-diisopropyl-phenyl; Mes ¼ (2,4,6-trimethylphenyl) via reaction of mesityl azide (MesN3) with the linear iron precursors [FeL2]0,-. UV-vis-, EPR-, 57Fe M¨ossbauer spectroscopy, magnetometry, and computational methods suggest for the reduced form an electronic structure as a ferromagnetically coupled iron(II) imidyl radical, whereas oxidation leads to mixed iron(III) imidyl and electrophilic iron(II) nitrene character. Reactivity studies show that both complexes are capable of H atom abstraction from C–H bonds. Further, the reduced form [Fe(NMes)L2]- reacts nucleophilically with CS2 by inserting into the imido iron bond, as well as electrophilically with CO under nitrene transfer. The neutral [Fe(NMes)L2] complex shows enhanced electrophilic behavior as evidenced by nitrene transfer to a phosphine, yet in combination with an overall reduced reactivity