Syntheses, Structures, and Magnetic Properties of Acetato- and Diphenolato-Bridged 3d–4f Binuclear Complexes [M(3-MeOsaltn)(MeOH)_<i>x</i>(ac)­Ln(hfac)₂] (M = Zn^II, Cu^II, Ni^II, Co^II; Ln = La^III, Gd^III, Tb^III, Dy^III; 3‑MeOsaltn = <i>N,N</i>′‑Bis(3-methoxy-2-oxybenzylidene)-1,3-propanediaminato; ac = Acetato; hfac = Hexafluoroacetylacetonato; <i>x</i> = 0 or 1)

A series of 3d–4f binuclear complexes, [M­(3-MeOsaltn)­(MeOH)_<i>x</i>(ac)­Ln­(hfac)₂] (<i>x</i> = 0 for M = Cu^II, Zn^II; <i>x</i> = 1 for M = Co^II, Ni^II; Ln = Gd^III, Tb^III, Dy^III, La^III), have been synthesized and characterized, where 3-MeOsaltn, ac, and hfac denote <i>N,N</i>′-bis­(3-methoxy-2-oxybenzylidene)-1,3-propanediaminato, acetato, and hexafluoroacetylacetonato, respectively. The X-ray analyses demonstrated that all the complexes have an acetato- and diphenolato-bridged M^II–Ln^III binuclear structure. The Cu^II–Ln^III and Zn^II–Ln^III complexes are crystallized in an isomorphous triclinic space group <i>P</i>1̅, where the Cu^II or Zn^II ion has square pyramidal coordination geometry with N₂O₂ donor atoms of 3-MeOsaltn at the equatorial coordination sites and one oxygen atom of the bridging acetato ion at the axial site. The Co^II–Ln^III and Ni^II–Ln^III complexes are crystallized in an isomorphous monoclinic space group <i>P</i>2₁/<i>c</i>, where the Co^II or Ni^II ion at the high-spin state has an octahedral coordination environment with N₂O₂ donor atoms of 3-MeOsaltn at the equatorial sites, and one oxygen atom of the bridged acetato and a methanol oxygen atom at the two axial sites. Each Ln^III ion for all the complexes is coordinated by four oxygen atoms of two phenolato and two methoxy oxygen atoms of “ligand-complex” M­(3-MeOsaltn), four oxygen atoms of two hfac^–, and one oxygen atom of the bridging acetato ion; thus, the coordination number is nine. The temperature dependent magnetic susceptibilities from 1.9 to 300 K and the field-dependent magnetization up to 5 T at 1.9 K were measured. Due to the important orbital contributions of the Ln^III (Tb^III, Dy^III) and to a lesser extent the M^II (Ni^II, Co^II) components, the magnetic interaction between M^II and Ln^III ions were investigated by an empirical approach based on a comparison of the magnetic properties of the M^II–Ln^III, Zn^II–Ln^III, and M^II–La^III complexes. The differences of χ_M<i>T</i> and <i>M</i>(<i>H</i>) values for the M^II–Ln^III, Zn^II–Ln^III and those for the M^II–La^III complexes, that is, Δ­(<i>T</i>) = (χ_M<i>T</i>)_MLn – (χ_M<i>T</i>)_ZnLn – (χ_M<i>T</i>)_MLa = <i>J</i>_MLn(<i>T</i>) and Δ­(<i>H</i>) = <i>M</i>_MLn(<i>H</i>) – <i>M</i>_ZnLn(<i>H</i>) – <i>M</i>_MLa(<i>H</i>) = <i>J</i>_MLn(<i>H</i>), give the information of 3d–4f magnetic interaction. The magnetic interactions are ferromagnetic if M^II = (Cu^II, Ni^II, and Co^II) and Ln = (Gd^III, Tb^III, and Dy^III). The magnitudes of the ferromagnetic interaction, <i>J</i>_MLn(<i>T</i>) and <i>J</i>_MLn(<i>H</i>), are in the order Cu^II–Gd^III > Cu^II–Dy^III > Cu^II–Tb^III, while those are in the order of M^II–Gd^III ≈ M^II–Tb^III > M^II–Dy^III for M^II = Ni^II and Co^II. Alternating current (ac) susceptibility measurements demonstrated that the Ni^II–Tb^III and Co^II–Tb^III complexes showed out-of-phase signal with frequency-dependence and the Ni^II–Dy^III and Co^II–Dy^III complexes showed small frequency-dependence. The energy barrier for the spin flipping was estimated from the Arrhenius plot to be 14.9(6) and 17.0(4) K for the Ni^II–Tb^III and Co^II–Tb^III complexes, respectively, under a dc bias field of 1000 Oe

Syntheses, Structures, and Magnetic Properties of Acetato- and Diphenolato-Bridged 3d–4f Binuclear Complexes [M(3-MeOsaltn)(MeOH)_<i>x</i>(ac)­Ln(hfac)₂] (M = Zn^II, Cu^II, Ni^II, Co^II; Ln = La^III, Gd^III, Tb^III, Dy^III; 3‑MeOsaltn = <i>N,N</i>′‑Bis(3-methoxy-2-oxybenzylidene)-1,3-propanediaminato; ac = Acetato; hfac = Hexafluoroacetylacetonato; <i>x</i> = 0 or 1)

A series of 3d–4f binuclear complexes, [M­(3-MeOsaltn)­(MeOH)_<i>x</i>(ac)­Ln­(hfac)₂] (<i>x</i> = 0 for M = Cu^II, Zn^II; <i>x</i> = 1 for M = Co^II, Ni^II; Ln = Gd^III, Tb^III, Dy^III, La^III), have been synthesized and characterized, where 3-MeOsaltn, ac, and hfac denote <i>N,N</i>′-bis­(3-methoxy-2-oxybenzylidene)-1,3-propanediaminato, acetato, and hexafluoroacetylacetonato, respectively. The X-ray analyses demonstrated that all the complexes have an acetato- and diphenolato-bridged M^II–Ln^III binuclear structure. The Cu^II–Ln^III and Zn^II–Ln^III complexes are crystallized in an isomorphous triclinic space group <i>P</i>1̅, where the Cu^II or Zn^II ion has square pyramidal coordination geometry with N₂O₂ donor atoms of 3-MeOsaltn at the equatorial coordination sites and one oxygen atom of the bridging acetato ion at the axial site. The Co^II–Ln^III and Ni^II–Ln^III complexes are crystallized in an isomorphous monoclinic space group <i>P</i>2₁/<i>c</i>, where the Co^II or Ni^II ion at the high-spin state has an octahedral coordination environment with N₂O₂ donor atoms of 3-MeOsaltn at the equatorial sites, and one oxygen atom of the bridged acetato and a methanol oxygen atom at the two axial sites. Each Ln^III ion for all the complexes is coordinated by four oxygen atoms of two phenolato and two methoxy oxygen atoms of “ligand-complex” M­(3-MeOsaltn), four oxygen atoms of two hfac^–, and one oxygen atom of the bridging acetato ion; thus, the coordination number is nine. The temperature dependent magnetic susceptibilities from 1.9 to 300 K and the field-dependent magnetization up to 5 T at 1.9 K were measured. Due to the important orbital contributions of the Ln^III (Tb^III, Dy^III) and to a lesser extent the M^II (Ni^II, Co^II) components, the magnetic interaction between M^II and Ln^III ions were investigated by an empirical approach based on a comparison of the magnetic properties of the M^II–Ln^III, Zn^II–Ln^III, and M^II–La^III complexes. The differences of χ_M<i>T</i> and <i>M</i>(<i>H</i>) values for the M^II–Ln^III, Zn^II–Ln^III and those for the M^II–La^III complexes, that is, Δ­(<i>T</i>) = (χ_M<i>T</i>)_MLn – (χ_M<i>T</i>)_ZnLn – (χ_M<i>T</i>)_MLa = <i>J</i>_MLn(<i>T</i>) and Δ­(<i>H</i>) = <i>M</i>_MLn(<i>H</i>) – <i>M</i>_ZnLn(<i>H</i>) – <i>M</i>_MLa(<i>H</i>) = <i>J</i>_MLn(<i>H</i>), give the information of 3d–4f magnetic interaction. The magnetic interactions are ferromagnetic if M^II = (Cu^II, Ni^II, and Co^II) and Ln = (Gd^III, Tb^III, and Dy^III). The magnitudes of the ferromagnetic interaction, <i>J</i>_MLn(<i>T</i>) and <i>J</i>_MLn(<i>H</i>), are in the order Cu^II–Gd^III > Cu^II–Dy^III > Cu^II–Tb^III, while those are in the order of M^II–Gd^III ≈ M^II–Tb^III > M^II–Dy^III for M^II = Ni^II and Co^II. Alternating current (ac) susceptibility measurements demonstrated that the Ni^II–Tb^III and Co^II–Tb^III complexes showed out-of-phase signal with frequency-dependence and the Ni^II–Dy^III and Co^II–Dy^III complexes showed small frequency-dependence. The energy barrier for the spin flipping was estimated from the Arrhenius plot to be 14.9(6) and 17.0(4) K for the Ni^II–Tb^III and Co^II–Tb^III complexes, respectively, under a dc bias field of 1000 Oe

Magnetic Interactions in Cu^II−Ln^III Cyclic Tetranuclear Complexes: Is It Possible to Explain the Occurrence of SMM Behavior in Cu^II−Tb^III and Cu^II−Dy^III Complexes?

An extensive series of tetranuclear CuII2LnIII2 complexes [CuIILLnIII(hfac)2]2 (with LnIII being all lanthanide(III) ions except for the radioactive PmIII) has been prepared in order to investigate the nature of the CuII−LnIII magnetic interactions and to try to answer the following question:  What makes the CuII2TbIII2 and CuII2DyIII2 complexes single molecule magnets while the other complexes are not? All the complexes within this series possess a similar cyclic tetranuclear structure, in which the CuII and LnIII ions are arrayed alternately via bridges of ligand complex (CuIIL). Regular SQUID magnetometry measurements have been performed on the series. The temperature-dependent magnetic susceptibilities from 2 to 300 K and the field-dependent magnetizations from 0 to 5 T at 2 K have been measured for the CuII2LnIII2 and NiII2LnIII2 complexes, with the NiII2LnIII2 complex containing diamagnetic NiII ions being used as a reference for the evaluation of the CuII−LnIII magnetic interactions. These measurements have revealed that the interactions between CuII and LnIII ions are very weakly antiferromagnetic if Ln = Ce, Nd, Sm, Yb, ferromagnetic if Ln = Gd, Tb, Dy, Ho, Er, Tm, and negligible if Ln = La, Eu, Pr, Lu. With the same goal of better understanding the evolution of the intramolecular magnetic interactions, X-ray magnetic circular dichroism (XMCD) has also been measured on CuII2TbIII2, CuII2DyIII2, and NiII2TbIII2 complexes, either at the L- and M-edges of the metal ions or at the K-edge of the N and O atoms. Last, the CuII2TbIII2 complex exhibiting SMM behavior has received a closer examination of its low temperature magnetic properties down to 0.1 K. These particular measurements have revealed the unusual very slow setting-up of a 3D order below 0.6 K

Magnetic Interactions in Cu^II−Ln^III Cyclic Tetranuclear Complexes: Is It Possible to Explain the Occurrence of SMM Behavior in Cu^II−Tb^III and Cu^II−Dy^III Complexes?

An extensive series of tetranuclear CuII2LnIII2 complexes [CuIILLnIII(hfac)2]2 (with LnIII being all lanthanide(III) ions except for the radioactive PmIII) has been prepared in order to investigate the nature of the CuII−LnIII magnetic interactions and to try to answer the following question:  What makes the CuII2TbIII2 and CuII2DyIII2 complexes single molecule magnets while the other complexes are not? All the complexes within this series possess a similar cyclic tetranuclear structure, in which the CuII and LnIII ions are arrayed alternately via bridges of ligand complex (CuIIL). Regular SQUID magnetometry measurements have been performed on the series. The temperature-dependent magnetic susceptibilities from 2 to 300 K and the field-dependent magnetizations from 0 to 5 T at 2 K have been measured for the CuII2LnIII2 and NiII2LnIII2 complexes, with the NiII2LnIII2 complex containing diamagnetic NiII ions being used as a reference for the evaluation of the CuII−LnIII magnetic interactions. These measurements have revealed that the interactions between CuII and LnIII ions are very weakly antiferromagnetic if Ln = Ce, Nd, Sm, Yb, ferromagnetic if Ln = Gd, Tb, Dy, Ho, Er, Tm, and negligible if Ln = La, Eu, Pr, Lu. With the same goal of better understanding the evolution of the intramolecular magnetic interactions, X-ray magnetic circular dichroism (XMCD) has also been measured on CuII2TbIII2, CuII2DyIII2, and NiII2TbIII2 complexes, either at the L- and M-edges of the metal ions or at the K-edge of the N and O atoms. Last, the CuII2TbIII2 complex exhibiting SMM behavior has received a closer examination of its low temperature magnetic properties down to 0.1 K. These particular measurements have revealed the unusual very slow setting-up of a 3D order below 0.6 K