An isostructural series of neutral cyano-bridged tetranuclear iron(Ⅲ)-lanthanide(Ⅲ)complexes of general formula{[Fe(htpzb)(CN)(μ-CN)_(2)]_(2)[Ln(dmbpy)(NO_(3))_(2)(H_(2)O)]_(2)}·2CH_(3)CN·2H_(2)O[Ln=Gd(1)...An isostructural series of neutral cyano-bridged tetranuclear iron(Ⅲ)-lanthanide(Ⅲ)complexes of general formula{[Fe(htpzb)(CN)(μ-CN)_(2)]_(2)[Ln(dmbpy)(NO_(3))_(2)(H_(2)O)]_(2)}·2CH_(3)CN·2H_(2)O[Ln=Gd(1),Tb(2),Dy(3),Ho(4),and Er(5);htpzb=hydrotris(pyrazolyl)borate and dmbpy=4,4’-dimethyl-2,2’-bipyridine]was synthesized and structurally and magnetically characterized.Single-crystal X-ray analysis of 1-5 revealed the formation of neutral cyano-bridged{Fe_(2)^(Ⅲ)Ln_(2)^(Ⅲ)}complexes(Ln=Gd,Tb,Dy,Ho,and Er)of square-like topology that crystallize in the triclinic P1 space group.Solid-state direct-current magnetic susceptibility analysis evidenced weak intramolecular antiferromagnetic Fe^(Ⅲ)-Ln^(Ⅲ) interactions in 1(Ln=Gd)together with large local magnetic anisotropies from the Ln^(Ⅲ) ion in 2-5(Ln=Tb,Dy,Ho,and Er).Frequencydependent alternating current magnetic susceptibility signals occurred for 1-5 under an applied dc magnetic field of H=1.0(1)or 0.5 T(2-5),indicating field-induced slow magnetic relaxation effects typical of single-molecule magnets.Depending on the non-Kramer(Tb,Ho)or Kramer(Gd,Dy,Er)nature of the Ln^(Ⅲ) ion,a single magnetic relaxation process via Orbach or Raman mechanism(2 and 4)or a multiple magnetic relaxation process that combines Orbach or Raman plus quantum tunneling of magnetization and/or direct(1,3,and 5)mechanisms occurred along this series.1-5 showed large magnetocaloric effects with a high to moderate maximum value of the magnetic entropy change at optimum working temperatures just above He liquefaction[−ΔS_(max)=16.51(1),5.42(2),6.02(3),4.56(4),and 5.86 J kg^(−1)K^(−1)(5)for H=5 T at T_(opt)=T_(max)=2(1),4(2,3 and 5),and 6 K(4)],as well as a high to moderate magnetocaloric index at rather low optimum working fields[MCI=6.4(1),3.3(2),4.7(3),0.9(4),and 3.6 J kg^(−1)K^(−1)T^(−1)(5)for H_(opt)=H_(max)=1.0(1),0.6(2),0.4(3),0.8(4),and 0.6 T(5)at T=2 K].展开更多
基金supported by grants of the Ministry of Research,Innovation and Digitization,CNCS/CCCDI-UEFISCDI,project number project number PN-Ⅲ-P1-1.1-TE-2019-0352,within PNCDIⅢproject number PN-Ⅳ-P2-2.2-MC-2024-0533,within PNCDIV,the Spanish MINECO(Projects PID2019-109735GB-I00+1 种基金Unidad de Excelencia María de Maeztu CEX2019-000919-M)the Generalitat Valenciana(AICO/2020/183 and AICO/2021/295)。
文摘An isostructural series of neutral cyano-bridged tetranuclear iron(Ⅲ)-lanthanide(Ⅲ)complexes of general formula{[Fe(htpzb)(CN)(μ-CN)_(2)]_(2)[Ln(dmbpy)(NO_(3))_(2)(H_(2)O)]_(2)}·2CH_(3)CN·2H_(2)O[Ln=Gd(1),Tb(2),Dy(3),Ho(4),and Er(5);htpzb=hydrotris(pyrazolyl)borate and dmbpy=4,4’-dimethyl-2,2’-bipyridine]was synthesized and structurally and magnetically characterized.Single-crystal X-ray analysis of 1-5 revealed the formation of neutral cyano-bridged{Fe_(2)^(Ⅲ)Ln_(2)^(Ⅲ)}complexes(Ln=Gd,Tb,Dy,Ho,and Er)of square-like topology that crystallize in the triclinic P1 space group.Solid-state direct-current magnetic susceptibility analysis evidenced weak intramolecular antiferromagnetic Fe^(Ⅲ)-Ln^(Ⅲ) interactions in 1(Ln=Gd)together with large local magnetic anisotropies from the Ln^(Ⅲ) ion in 2-5(Ln=Tb,Dy,Ho,and Er).Frequencydependent alternating current magnetic susceptibility signals occurred for 1-5 under an applied dc magnetic field of H=1.0(1)or 0.5 T(2-5),indicating field-induced slow magnetic relaxation effects typical of single-molecule magnets.Depending on the non-Kramer(Tb,Ho)or Kramer(Gd,Dy,Er)nature of the Ln^(Ⅲ) ion,a single magnetic relaxation process via Orbach or Raman mechanism(2 and 4)or a multiple magnetic relaxation process that combines Orbach or Raman plus quantum tunneling of magnetization and/or direct(1,3,and 5)mechanisms occurred along this series.1-5 showed large magnetocaloric effects with a high to moderate maximum value of the magnetic entropy change at optimum working temperatures just above He liquefaction[−ΔS_(max)=16.51(1),5.42(2),6.02(3),4.56(4),and 5.86 J kg^(−1)K^(−1)(5)for H=5 T at T_(opt)=T_(max)=2(1),4(2,3 and 5),and 6 K(4)],as well as a high to moderate magnetocaloric index at rather low optimum working fields[MCI=6.4(1),3.3(2),4.7(3),0.9(4),and 3.6 J kg^(−1)K^(−1)T^(−1)(5)for H_(opt)=H_(max)=1.0(1),0.6(2),0.4(3),0.8(4),and 0.6 T(5)at T=2 K].
