series of fourβ-diketone mononuclear dysprosium complexes,namely,Dy(DBM)_(3)(bpy)(1),Dy(DBM)_(3)(phen)·Tol(2),Dy(DBM)_(3)(dpq)·Tol(3),and Dy(DBM)_(3)(dppz)(4)(bpy=2,2’-bipyridine,phen=1,10-phenanthroline,d...series of fourβ-diketone mononuclear dysprosium complexes,namely,Dy(DBM)_(3)(bpy)(1),Dy(DBM)_(3)(phen)·Tol(2),Dy(DBM)_(3)(dpq)·Tol(3),and Dy(DBM)_(3)(dppz)(4)(bpy=2,2’-bipyridine,phen=1,10-phenanthroline,dpq=dipyrazine[2,3-f:2’,3’-h]quinoxaline,dppz=dipyrido[3,2-a:2’,3’-c]phenazine,Tol=toluene)have been isolated by the reactions of dibenzoylmethane(DBM),azacyclo-auxiliary ligands and DyCl_(3)·6H_(2)O.X-ray crystallographic analysis reveals that complexes 1–4 are all eight-coordinate mononuclear structures.The azacyclo-auxiliary ligands have a dramatic effect on the structure and magnetic characteristics of complexes 1–4,originating from the different degrees of deviation from the ideal coordination symmetries.Complexes 1 and 2 display a single relaxation mode under 0 Oe and complexes 3 and 4 display two single relaxation modes under 2000 Oe.展开更多
This work reports on a mononuclear trigonal prismatic complex[Co^(Ⅱ)L](ClO_(4))_(2)(1)and a trinuclear linear phenoxido-bridged complex[(Co^(Ⅱ)L1)_(2)Co^(Ⅱ)](2),where L and H_(3)L1 are N_(6) and N_(3)O_(3) tripodal...This work reports on a mononuclear trigonal prismatic complex[Co^(Ⅱ)L](ClO_(4))_(2)(1)and a trinuclear linear phenoxido-bridged complex[(Co^(Ⅱ)L1)_(2)Co^(Ⅱ)](2),where L and H_(3)L1 are N_(6) and N_(3)O_(3) tripodal pro-ligands derived from the respective condensation of the cis,cis-1,3,5-tiaminocyclohexane with either 1-methylimidazol-2-carbaldehyde or salicylaldehyde.These compounds have been studied by X-ray single-crystal diffraction,dc and ac magnetism,High-Frequency and-Field Electron Paramagnetic Resonance spectroscopy(HFEPR),Far Infrared Magnetic Spectroscopy(FIRMS)and quantum chemical calculations.The results obtained for 1 show that N_(6)-tripodal Schiff-base ligands incorporating 1-methylimidazole donors yield trigonal-prismatic mononuclear complexes that typically display C_(3) symmetry and exhibit very large,purely easy-axis magnetic anisotropy.In fact,complex 1 exhibits an energy gap between the ground and the first excited state(2D)of 228 cm^(−1)(directly measured by FIRMS),that can be considered the maximum limit for the easy-axis magnetic anisotropy in this type of complexes.The symmetry-driven large 2D value,together with the parallel alignment of the anisotropy axes,reduces QTM(Quantum Tunnelling of Magnetization)and yields mononuclear single-molecule magnet(MSMM)behaviour,with the observation of magnetic relaxation through a Raman process and open hysteresis at zero field.In compound 2,the combination of the strong easy-axis anisotropy of the local Co^(Ⅱ) ions,collinearity of the local anisotropy axes and sizable intramolecular magnetic exchange interactions between the Co^(Ⅱ) ions in triple phenoxido-bridged linear trinuclear complexes causes the full quenching of the QTM and the observation of SMM behaviour with open hysteresis at zero field.Theoretical calculations point out that the magnetic interaction between the ground Kramers doublets(KDs)of the local Co^(Ⅱ) ions generates four KDs and the magnetic relaxation occurs through the first excited KD via an Orbach process.Supporting this suggestion,the experimental value for the effective thermal energy barrier extracted from FIRMS of 76.8 cm^(−1) is not too far from the theoretical calculated value of 59.54 cm^(−1).展开更多
基金supported by the National Natural Science Foundation of China(no.21471051 and 51402092).
文摘series of fourβ-diketone mononuclear dysprosium complexes,namely,Dy(DBM)_(3)(bpy)(1),Dy(DBM)_(3)(phen)·Tol(2),Dy(DBM)_(3)(dpq)·Tol(3),and Dy(DBM)_(3)(dppz)(4)(bpy=2,2’-bipyridine,phen=1,10-phenanthroline,dpq=dipyrazine[2,3-f:2’,3’-h]quinoxaline,dppz=dipyrido[3,2-a:2’,3’-c]phenazine,Tol=toluene)have been isolated by the reactions of dibenzoylmethane(DBM),azacyclo-auxiliary ligands and DyCl_(3)·6H_(2)O.X-ray crystallographic analysis reveals that complexes 1–4 are all eight-coordinate mononuclear structures.The azacyclo-auxiliary ligands have a dramatic effect on the structure and magnetic characteristics of complexes 1–4,originating from the different degrees of deviation from the ideal coordination symmetries.Complexes 1 and 2 display a single relaxation mode under 0 Oe and complexes 3 and 4 display two single relaxation modes under 2000 Oe.
基金Financial support from Ministerio de Ciencia e Innovación(Project PID2022-138090NB-C21 funded by MCIN/AEI/10.13039/501100011033/FEDER,UE)Consejería de Universidad,Investigación e Innovación and ERDF Andalusia Program 2021-2027(projects C-EXP-140-UGR23 and M.1.B.B TA_000722_UJA23)+5 种基金Junta de Andalucía(FQM-195 and FQM-337)Ministerio de Ciencia e Innovación for their Ramón y Cajal contracts(RYC2021-034288-I and RYC2022-037255-Ifunded both by MCIN/AEI/10.13039/501100011033by FSE+and the European Union“NextGenerationEU”/PRTR”,respectively)funded by the National Science Foundation(Cooperative Agreement DMR 2128556)and the State of FloridaMinisterio de Ciencia e Innovación for financial support(PID2022-139530NB-I00).
文摘This work reports on a mononuclear trigonal prismatic complex[Co^(Ⅱ)L](ClO_(4))_(2)(1)and a trinuclear linear phenoxido-bridged complex[(Co^(Ⅱ)L1)_(2)Co^(Ⅱ)](2),where L and H_(3)L1 are N_(6) and N_(3)O_(3) tripodal pro-ligands derived from the respective condensation of the cis,cis-1,3,5-tiaminocyclohexane with either 1-methylimidazol-2-carbaldehyde or salicylaldehyde.These compounds have been studied by X-ray single-crystal diffraction,dc and ac magnetism,High-Frequency and-Field Electron Paramagnetic Resonance spectroscopy(HFEPR),Far Infrared Magnetic Spectroscopy(FIRMS)and quantum chemical calculations.The results obtained for 1 show that N_(6)-tripodal Schiff-base ligands incorporating 1-methylimidazole donors yield trigonal-prismatic mononuclear complexes that typically display C_(3) symmetry and exhibit very large,purely easy-axis magnetic anisotropy.In fact,complex 1 exhibits an energy gap between the ground and the first excited state(2D)of 228 cm^(−1)(directly measured by FIRMS),that can be considered the maximum limit for the easy-axis magnetic anisotropy in this type of complexes.The symmetry-driven large 2D value,together with the parallel alignment of the anisotropy axes,reduces QTM(Quantum Tunnelling of Magnetization)and yields mononuclear single-molecule magnet(MSMM)behaviour,with the observation of magnetic relaxation through a Raman process and open hysteresis at zero field.In compound 2,the combination of the strong easy-axis anisotropy of the local Co^(Ⅱ) ions,collinearity of the local anisotropy axes and sizable intramolecular magnetic exchange interactions between the Co^(Ⅱ) ions in triple phenoxido-bridged linear trinuclear complexes causes the full quenching of the QTM and the observation of SMM behaviour with open hysteresis at zero field.Theoretical calculations point out that the magnetic interaction between the ground Kramers doublets(KDs)of the local Co^(Ⅱ) ions generates four KDs and the magnetic relaxation occurs through the first excited KD via an Orbach process.Supporting this suggestion,the experimental value for the effective thermal energy barrier extracted from FIRMS of 76.8 cm^(−1) is not too far from the theoretical calculated value of 59.54 cm^(−1).
