Electron paramagnetic resonance(EPR)or electron spin resonance(ESR)has been widely employed to characterize transition metal complexes.However,because of the high degree of complexity of transition metal EPR spectra,h...Electron paramagnetic resonance(EPR)or electron spin resonance(ESR)has been widely employed to characterize transition metal complexes.However,because of the high degree of complexity of transition metal EPR spectra,how to extract the underlying electronicstructure information inevitably poses a major challenge to beginners,in particular for systems with S>1/2.In fact,the physical principles of transition metal EPR have long been well-established and since 1970s a series of dedicated voluminous monographs have been published already.Not surprisingly,they are not appropriate stating points for novices to grasp a panorama of the profound theory prior to scrutinizing in-depth references.The present review aims to fill this gap to provide a perspective of transition metal EPR and unveil some peculiar subtleties thereof on the basis of our recent work.展开更多
The di-ferrous[2Fe-2S]^(0) state is the least understood oxidation level of the[2Fe-2S]unit,which is the smallest module of iron-sulfur clusters in enzymes.Reported synthetic models of the[2Fe-2S]^(0) state utilize bu...The di-ferrous[2Fe-2S]^(0) state is the least understood oxidation level of the[2Fe-2S]unit,which is the smallest module of iron-sulfur clusters in enzymes.Reported synthetic models of the[2Fe-2S]^(0) state utilize bulky anionic ligands to achieve their stabilization,and their highly reducing nature renders detailed structural and spectroscopic studies difficult.Herein,we report the stabilization of the di-ferrous[2Fe-2S]^(0) state by using N-heterocyclic carbene(NHC)moieties as supporting ligands.The charge-neutral cluster[Fe_(2)(μ-S)_(2)(ICy)_(4)](1,ICy=1,3-bis-cyclohexyl-imidazol-2-ylidene)is synthesized from the reaction of the iron(0)precursor[(ICy)_(2)Fe(η^(2)-CH_(2)vCHSiMe_(3))]with SPPh_(3).The attenuated reducing power of 1 as compared to those clusters supported by anionic ligands allows its isolation in pure form.Further spectroscopic and theoretical studies established its S=0 ground state resulting from anti-ferromagnetic coupling of two high-spin ferrous sites with an exchange-coupling constant J=-208 cm^(-1).The NHC ligand is also capable of stabilizing the mixed-valent complex[Fe_(2)(μ-S)_(2)(ICy)_(4)][BPh_(4)](2),which is synthesized from the reaction of 1 with[Cp_(2)Fe][BPh_(4)]and identified as a Robin-Day Class II complex with an S=1/2 ground state.展开更多
Metal-nitrosyl species have attracted considerable attention due to their crucial roles in NO transformation chemistry.Although a plethora of{M-NO}n complexes have been reported,square-planar{M-NO}^(7)complexes remain...Metal-nitrosyl species have attracted considerable attention due to their crucial roles in NO transformation chemistry.Although a plethora of{M-NO}n complexes have been reported,square-planar{M-NO}^(7)complexes remain unknown.This work describes the synthesis and characterization of an unprecedented square-planar{Fe-NO}^(7)species,[Fe(NO)(PCP)][BAr_(4)^(F)](3,PCP=2,6-bis(di-tert-butylphosphinomethyl)phenyl),and its one-electron reduced{Fe-NO}^(8)congener,[Fe(NO)(PCP)](4),both derived from a square-pyramidal{Fe-NO}^(7)precursor,[FeBr(NO)(PCP)](2).Those complexes were thoroughly characterized using single-crystal XRD,Mössbauer,EPR as well as IR spectroscopies,coupled to wavefunction based ab initio calculations.Our results reveal that the electronic structures of 2 and 3 are best interpreted as an S_(Fe)=3/2 ferric center antiferromagnetically coupled to an S_(NO)=1 NO^(−)ligand,yielding an overall S_(t)=1/2 ground state.Conversion of 3 to 4 is metal-centered reduction,and hence 4 is comprised of an S_(Fe)=1 Fe(Ⅱ)ion antiferromagnetically bonded to an S_(NO)=1 NO^(−),leading to a diamagnetic ground state.Complex 3 differs from all other{M-NO}^(7)systems in its ground level having an orbital two-fold neardegeneracy,manifested by gz≫2>gx,y,a spectroscopic signature that can be used to identify low-spin square-planar{M-NO}^(7)complexes.展开更多
Iron sites in both nitrogenase enzymes and chemical catalysts for N_(2) fixation are typically at constrained distances and angles.Herein,we report a one-electron reduction reaction realized by constrained diiron dini...Iron sites in both nitrogenase enzymes and chemical catalysts for N_(2) fixation are typically at constrained distances and angles.Herein,we report a one-electron reduction reaction realized by constrained diiron dinitrogen cores.Using the semicircular bis(β-diketiminate)ligand,a series of diiron dinitrogen complexes were synthesized,in which the N_(2) groups were allowed to bind with Fe-Ct_(N2)-Fe angles ranging from 154°to 158°(Ct_(N2)=centroid of N_(2)).One-electron reduction of complex 2a[LFe(μ-N_(2))Fe(Et_(2)O)]gave dimer product 3a[LFe(μ-N_(2))FeK]_(2)(μ-N_(2))or monomer 3b[LFe(μ-N_(2))Fe(DMAP)K].Based on superconducting quantum interference device measurements and density functional theory calculations,2a,3a,and 3b exhibited ground spin states of S=3,S=5,and S=5/2,respectively.In addition,complex 3 underwent N_(2)derivatization via a silylation pathway followed by an acidic cleavage to yield N_(2)H_(4)as the product.展开更多
基金the financial support from Chinese Academy of Sciences,National Science Foundation of China(92161204)Max-Planck Society。
文摘Electron paramagnetic resonance(EPR)or electron spin resonance(ESR)has been widely employed to characterize transition metal complexes.However,because of the high degree of complexity of transition metal EPR spectra,how to extract the underlying electronicstructure information inevitably poses a major challenge to beginners,in particular for systems with S>1/2.In fact,the physical principles of transition metal EPR have long been well-established and since 1970s a series of dedicated voluminous monographs have been published already.Not surprisingly,they are not appropriate stating points for novices to grasp a panorama of the profound theory prior to scrutinizing in-depth references.The present review aims to fill this gap to provide a perspective of transition metal EPR and unveil some peculiar subtleties thereof on the basis of our recent work.
基金support from the Natural Science Foundation of China(22231010,92461311)the Strategic Priority Research Program of the Chinese Academy of Sciences(XDB0610000)+3 种基金the National Key Research and Development Program of the Ministry of Science and Technology of China(2023YFA1507500)the Shanghai Science and Technology Development Foundation(22JC1403400)support from National Natural Science Foundation of China(92161204 and 92461311)the Dalian Institute of Chemical Physics,Chinese Academy of Sciences(Grant:DICP I202312).
文摘The di-ferrous[2Fe-2S]^(0) state is the least understood oxidation level of the[2Fe-2S]unit,which is the smallest module of iron-sulfur clusters in enzymes.Reported synthetic models of the[2Fe-2S]^(0) state utilize bulky anionic ligands to achieve their stabilization,and their highly reducing nature renders detailed structural and spectroscopic studies difficult.Herein,we report the stabilization of the di-ferrous[2Fe-2S]^(0) state by using N-heterocyclic carbene(NHC)moieties as supporting ligands.The charge-neutral cluster[Fe_(2)(μ-S)_(2)(ICy)_(4)](1,ICy=1,3-bis-cyclohexyl-imidazol-2-ylidene)is synthesized from the reaction of the iron(0)precursor[(ICy)_(2)Fe(η^(2)-CH_(2)vCHSiMe_(3))]with SPPh_(3).The attenuated reducing power of 1 as compared to those clusters supported by anionic ligands allows its isolation in pure form.Further spectroscopic and theoretical studies established its S=0 ground state resulting from anti-ferromagnetic coupling of two high-spin ferrous sites with an exchange-coupling constant J=-208 cm^(-1).The NHC ligand is also capable of stabilizing the mixed-valent complex[Fe_(2)(μ-S)_(2)(ICy)_(4)][BPh_(4)](2),which is synthesized from the reaction of 1 with[Cp_(2)Fe][BPh_(4)]and identified as a Robin-Day Class II complex with an S=1/2 ground state.
基金supported by the National Natural Science Foundation of China(No.22488101,92161204 and 92461311)by Dalian Institute of Chemical Physics,Chinese Academy of Sciences(Grant:DICP I202312).
文摘Metal-nitrosyl species have attracted considerable attention due to their crucial roles in NO transformation chemistry.Although a plethora of{M-NO}n complexes have been reported,square-planar{M-NO}^(7)complexes remain unknown.This work describes the synthesis and characterization of an unprecedented square-planar{Fe-NO}^(7)species,[Fe(NO)(PCP)][BAr_(4)^(F)](3,PCP=2,6-bis(di-tert-butylphosphinomethyl)phenyl),and its one-electron reduced{Fe-NO}^(8)congener,[Fe(NO)(PCP)](4),both derived from a square-pyramidal{Fe-NO}^(7)precursor,[FeBr(NO)(PCP)](2).Those complexes were thoroughly characterized using single-crystal XRD,Mössbauer,EPR as well as IR spectroscopies,coupled to wavefunction based ab initio calculations.Our results reveal that the electronic structures of 2 and 3 are best interpreted as an S_(Fe)=3/2 ferric center antiferromagnetically coupled to an S_(NO)=1 NO^(−)ligand,yielding an overall S_(t)=1/2 ground state.Conversion of 3 to 4 is metal-centered reduction,and hence 4 is comprised of an S_(Fe)=1 Fe(Ⅱ)ion antiferromagnetically bonded to an S_(NO)=1 NO^(−),leading to a diamagnetic ground state.Complex 3 differs from all other{M-NO}^(7)systems in its ground level having an orbital two-fold neardegeneracy,manifested by gz≫2>gx,y,a spectroscopic signature that can be used to identify low-spin square-planar{M-NO}^(7)complexes.
基金supported by National Natural Science Foundation of China(grant nos.21988101,22201013,92161204)China Postdoctoral Science Foundation(grant no.2020M670016)Beijing Natural Science Foundation(grant no.2222008).
文摘Iron sites in both nitrogenase enzymes and chemical catalysts for N_(2) fixation are typically at constrained distances and angles.Herein,we report a one-electron reduction reaction realized by constrained diiron dinitrogen cores.Using the semicircular bis(β-diketiminate)ligand,a series of diiron dinitrogen complexes were synthesized,in which the N_(2) groups were allowed to bind with Fe-Ct_(N2)-Fe angles ranging from 154°to 158°(Ct_(N2)=centroid of N_(2)).One-electron reduction of complex 2a[LFe(μ-N_(2))Fe(Et_(2)O)]gave dimer product 3a[LFe(μ-N_(2))FeK]_(2)(μ-N_(2))or monomer 3b[LFe(μ-N_(2))Fe(DMAP)K].Based on superconducting quantum interference device measurements and density functional theory calculations,2a,3a,and 3b exhibited ground spin states of S=3,S=5,and S=5/2,respectively.In addition,complex 3 underwent N_(2)derivatization via a silylation pathway followed by an acidic cleavage to yield N_(2)H_(4)as the product.
