The self-assembly of lanthanide(3+)ions with pyrazine N,N′-dioxide(pzdo)and bis(triphenylphosphine)iminium(PPN+)salts of diamagnetic octacyanidometallates of MoIV and WIV results in one-dimensional(PPN)[LnIII(pzdo)2(...The self-assembly of lanthanide(3+)ions with pyrazine N,N′-dioxide(pzdo)and bis(triphenylphosphine)iminium(PPN+)salts of diamagnetic octacyanidometallates of MoIV and WIV results in one-dimensional(PPN)[LnIII(pzdo)2(MeOH)0.3(H2O)3.7][MIV(CN)8]·7.7H2O·2MeOH(Ln=Er and Yb;M=Mo and W)coordination networks.They are constructed of zigzag metal–organic{LnIII(μ-pzdo)}n chains with terminal[MIV(CN)8]4−metalloligands attached to the LnIII centres.Both Er-and Yb-containing frameworks exhibit field-induced slow magnetic relaxation originating from the field-dependent equilibrium between quantum tunnelling of magnetization and the direct process along with the temperature-dependent Raman and Orbach relaxation processes.Transition metal substitution on[MIV(CN)8]4−sites modifies the intrinsic magnetic anisotropy of lanthanides,as depicted by the subtle change of thermal energy barriers of Orbach relaxation in Er-based systems,while it significantly affects Raman relaxation due to the modulated phonon mode scheme.All reported compounds exhibit strong visible light absorption due to a series of electronic transitions of pzdo ligands and[M(CN)8]4−ions and the appearance of low energy anion–π charge transfer band involving pzdo and octacyanidometallates.These charge transfer states were utilized in achieving the sensitized near-infrared photoluminescence of Er^(Ⅲ) and Yb^(Ⅲ) centers;thus,the energy transfer process is strongly dependent on the nature of the metal centre in the[M^(Ⅳ)(CN)8]4−ion.The W(Ⅳ)-pzdo system is a good sensitizer for Er^(Ⅲ),while the Mo(Ⅳ)-pzdo unit is better for Yb^(Ⅲ) emission which can be rationalized in terms of the positions of energy levels of their respective donor states.Therefore,we report NIR emissive Er^(Ⅲ) and Yb^(Ⅲ) single-molecule magnets with tunable magnetic and optical properties,uncovering the crucial role of octacyanidometallates and their anion–π interactions with pzdo ligands.展开更多
The design of new radical bridging ligands that can effectively promote strong magnetic coupling with LnIII ions needs to focus on radicals that are susceptible to synthetic modifications and bear diffuse spin density...The design of new radical bridging ligands that can effectively promote strong magnetic coupling with LnIII ions needs to focus on radicals that are susceptible to synthetic modifications and bear diffuse spin density on their donor atoms.To probe this,we introduced various substituents possessing different electron-withdrawing/donating capabilities into the redox-active s-tetrazinyl centre.This allowed for the systematic tuning of the redox and optoelectronic properties of the tetrazinyl ring.The effect of substitution on the strength of Ln–rad magnetic coupling was investigated on a series of radical-bridged Ln metallocene complexes featuring the 3,6-dimethyl-1,2,4,5-tetrazine(dmtz)and the 3,6-dimethoxy-1,2,4,5-tetrazine(dmeotz)ligands;[(Cp^(*)_(2)Ln)_(2)(dmtz^(·−))(THF)_(2)][BPh_(4)]·THF(Ln=Gd(1-Gd)or Dy(1-Dy);Cp^(*)=pentamethylcyclopentadienyl;THF=tetrahydrofuran)and[(Cp^(*)_(2)Ln)_(2)(dmeotz^(·−))(THF)][BPh_(4)](Ln=Gd(2-Gd)or Dy(2-Dy)).Cyclic voltammetry,UV-Vis absorption spectroscopy,SQUID magnetometry and ab initio as well as density functional theory(DFT)calculations are combined to underline the trends observed in this study,while comparisons with the unsubstituted 1,2,4,5-tetrazine(tz)and the 3,6-dichloro-1,2,4,5-tetrazine(dctz)are made.Notably,an intricate interplay between orbital overlap,ligand substituent effects and changes in the coordination environment is found to collectively dictate the magnitude of JGd–rad in the investigated systems.The strong magnetic coupling combined with highly anisotropic Dy^(Ⅲ)ions makes 1-Dy and 2-Dy exhibit slow magnetic relaxation in the absence of an external applied field.For 1-Dy,an opening of the hysteresis loop is observed with H_(c)=∼5000 Oe,one of the highest coercivities for a dinuclear organic radical-bridged single-molecule magnet.展开更多
基金financed by the National Science Centre,Poland,within the OPUS-15 project,grant no.2018/29/B/ST5/00337supported by the Japan Society for the Promotion of Science,the Grant-in-Aid for Specially Promoted Research,grant no.15H05697.
文摘The self-assembly of lanthanide(3+)ions with pyrazine N,N′-dioxide(pzdo)and bis(triphenylphosphine)iminium(PPN+)salts of diamagnetic octacyanidometallates of MoIV and WIV results in one-dimensional(PPN)[LnIII(pzdo)2(MeOH)0.3(H2O)3.7][MIV(CN)8]·7.7H2O·2MeOH(Ln=Er and Yb;M=Mo and W)coordination networks.They are constructed of zigzag metal–organic{LnIII(μ-pzdo)}n chains with terminal[MIV(CN)8]4−metalloligands attached to the LnIII centres.Both Er-and Yb-containing frameworks exhibit field-induced slow magnetic relaxation originating from the field-dependent equilibrium between quantum tunnelling of magnetization and the direct process along with the temperature-dependent Raman and Orbach relaxation processes.Transition metal substitution on[MIV(CN)8]4−sites modifies the intrinsic magnetic anisotropy of lanthanides,as depicted by the subtle change of thermal energy barriers of Orbach relaxation in Er-based systems,while it significantly affects Raman relaxation due to the modulated phonon mode scheme.All reported compounds exhibit strong visible light absorption due to a series of electronic transitions of pzdo ligands and[M(CN)8]4−ions and the appearance of low energy anion–π charge transfer band involving pzdo and octacyanidometallates.These charge transfer states were utilized in achieving the sensitized near-infrared photoluminescence of Er^(Ⅲ) and Yb^(Ⅲ) centers;thus,the energy transfer process is strongly dependent on the nature of the metal centre in the[M^(Ⅳ)(CN)8]4−ion.The W(Ⅳ)-pzdo system is a good sensitizer for Er^(Ⅲ),while the Mo(Ⅳ)-pzdo unit is better for Yb^(Ⅲ) emission which can be rationalized in terms of the positions of energy levels of their respective donor states.Therefore,we report NIR emissive Er^(Ⅲ) and Yb^(Ⅲ) single-molecule magnets with tunable magnetic and optical properties,uncovering the crucial role of octacyanidometallates and their anion–π interactions with pzdo ligands.
文摘The design of new radical bridging ligands that can effectively promote strong magnetic coupling with LnIII ions needs to focus on radicals that are susceptible to synthetic modifications and bear diffuse spin density on their donor atoms.To probe this,we introduced various substituents possessing different electron-withdrawing/donating capabilities into the redox-active s-tetrazinyl centre.This allowed for the systematic tuning of the redox and optoelectronic properties of the tetrazinyl ring.The effect of substitution on the strength of Ln–rad magnetic coupling was investigated on a series of radical-bridged Ln metallocene complexes featuring the 3,6-dimethyl-1,2,4,5-tetrazine(dmtz)and the 3,6-dimethoxy-1,2,4,5-tetrazine(dmeotz)ligands;[(Cp^(*)_(2)Ln)_(2)(dmtz^(·−))(THF)_(2)][BPh_(4)]·THF(Ln=Gd(1-Gd)or Dy(1-Dy);Cp^(*)=pentamethylcyclopentadienyl;THF=tetrahydrofuran)and[(Cp^(*)_(2)Ln)_(2)(dmeotz^(·−))(THF)][BPh_(4)](Ln=Gd(2-Gd)or Dy(2-Dy)).Cyclic voltammetry,UV-Vis absorption spectroscopy,SQUID magnetometry and ab initio as well as density functional theory(DFT)calculations are combined to underline the trends observed in this study,while comparisons with the unsubstituted 1,2,4,5-tetrazine(tz)and the 3,6-dichloro-1,2,4,5-tetrazine(dctz)are made.Notably,an intricate interplay between orbital overlap,ligand substituent effects and changes in the coordination environment is found to collectively dictate the magnitude of JGd–rad in the investigated systems.The strong magnetic coupling combined with highly anisotropic Dy^(Ⅲ)ions makes 1-Dy and 2-Dy exhibit slow magnetic relaxation in the absence of an external applied field.For 1-Dy,an opening of the hysteresis loop is observed with H_(c)=∼5000 Oe,one of the highest coercivities for a dinuclear organic radical-bridged single-molecule magnet.
