Dimers and chains of {3d-4f} single molecule magnets constructed from heterobimetallic tectons.

International audienceA tetranuclear complex and a 1-D coordination polymer with a ladder-like topology have been obtained by connecting [Ni(II)Dy(III)] nodes with dicarboxylato ligands: [Ni₂(valpn)₂Dy₂(III)(pdca)₂(NO₃)(H₂O)₆](NO₃)*4H₂O 1, and (∞)¹[Ni₂(H₂O)₂(valpn)₂Dy₂(tfa)₃]*4CH₃CN 2 (valpn²⁻ = the dianion of the Schiff base resulting from reacting o-vanillin with 1,3-propanediamine; pdca²⁻ = the dianion of 2,6-pyridinedicarboxylic acid; tfa²⁻ = the dianion of the terephthalic acid). The magnetic measurements show a ferromagnetic interaction between Ni(II) and Dy(III), and that both compounds behave like SMM with strong tunnelling. The barrier of 2 (17.4 K) is higher than that of 1 (13.6 K)

Octanuclear [Ni(II)₄Ln(III)₄] complexes. Synthesis, crystal structures and magnetocaloric properties

Two original heterooctanuclear [Ni(II)4Ln(III)4] complexes (Ln(III) = Sm(III), Gd(III)) have been obtained starting from the [Ni(II)(valpn)(H2O)2] mononuclear precursor [H2valpn = 1,3-propanediylbis(2-iminomethylene-6-methoxy-phenol)] and the corresponding lanthanide nitrates, in the presence of azide anions, through slow capture of atmospheric CO2. Three weak and competitive exchange interactions, J(GdGd), J(GdNi), J(NiNi), make the ground state of this magnetic system degenerate at cryogenic temperature and zero field. This, along with the high spin of Gd(III), lead to a significant magnetocaloric effect spread in the temperature range 1 to 20 K (ΔSm[0-7 T, 3.5 K] = 19 J kg(-1) K(-1))

Synthesis, Crystal Structures, Magnetic Properties, and Theoretical Investigation of a New Series of Ni-II-Ln(III)-W-V Heterotrimetallics: Understanding the SMM Behavior of Mixed Polynuclear Complexes

The polynuclear compounds containing anisotropic metal ions often exhibit efficient barriers for blocking of magnetization at fairly arbitrary geometries. However, at variance with mononuclear complexes, which usually become single-molecule magnets (SMM) under the sole requirement of a highly axial crystal field at the metal ion, the factors influencing the SMM behavior in polynuclear complexes, especially, with weakly axial magnetic ions, still remain largely unrevealed. As an attempt to clarify these conditions, we present here the synthesis, crystal structures, magnetic behavior, and ab initio calculations for a new series of NiII–LnIII–WV trimetallics, [(CN)7W(CN)Ni(H2O)(valpn)Ln(H2O)4]·H2O (Ln = Y 1, Eu 2, Gd 3, Tb 4, Dy 5, Lu 6). The surprising finding is the absence of the magnetic blockage even for compounds involving strongly anisotropic DyIII and TbIII metal ions. This is well explained by ab initio calculations showing relatively large transversal components of the g-tensor in the ground exchange Kramers doublets of 1 and 4 and large intrinsic tunneling gaps in the ground exchange doublets of 3 and 5. In order to get more insight into this behavior, another series of earlier reported compounds with the same trinuclear [WVNiIILnIII] core structure, [(CN)7W(CN)Ni(dmf)(valdmpn)Ln(dmf)4]·H2O (Ln = GdIII 7, TbIII 8a, DyIII 9, HoIII 10), [(CN)7W(CN)Ni(H2O)(valdmpn)Tb(dmf)2.5(H2O)1.5]·H2O·0.5dmf 8b, and [(CN)7W(CN)Ni(H2O)(valdmpn)Er(dmf)3(H2O)1]·H2O·0.5dmf 11, has been also investigated theoretically. In this series, only 8b exhibits SMM behavior which is confirmed by the present ab initio calculations. An important feature for the entire series is the strong ferromagnetic coupling between Ni(II) and W(V), which is due to an almost perfect trigonal dodecahedron geometry of the octacyano wolframate fragment. The reason why only 8b is an SMM is explained by positive zero-field splitting on the nickel site, precluding magnetization blocking in complexes with fewer axial Ln ions. Further analysis has shown that, in the absence of ZFS on Ni ion, all compounds in the two series (except those containing Y and Gd) would be SMMs. The same situation arises for perfectly axial ZFS on Ni(II) with the main anisotropy axis parallel to the main magnetic axis of Ln(III) ions. In all other cases the ZFS on Ni(II) will worsen the SMM properties. The general conclusion is that the design of efficient SMMs on the basis of such complexes should involve isotropic or weekly anisotropic metal ions, such as Mn(II), Fe(III), etc., along with strongly axial lanthanides.status: publishe

CCDC 670964: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures

CCDC 670965: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures

CCDC 670963: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures

Synthesis, Crystal Structures, Magnetic Properties, and Theoretical Investigation of a New Series of Ni-II-Ln(III)-W-V Heterotrimetallics: Understanding the SMM Behavior of Mixed Polynuclear Complexes

10.1021/acs.inorgchem.6b01669INORGANIC CHEMISTRY552312158-1217

CCDC 670962: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures

Synthesis, Crystal Structures, Magnetic Properties, and Theoretical Investigation of a New Series of Ni^II–Ln^III–W^V Heterotrimetallics: Understanding the SMM Behavior of Mixed Polynuclear Complexes

The polynuclear compounds containing anisotropic metal ions often exhibit efficient barriers for blocking of magnetization at fairly arbitrary geometries. However, at variance with mononuclear complexes, which usually become single-molecule magnets (SMM) under the sole requirement of a highly axial crystal field at the metal ion, the factors influencing the SMM behavior in polynuclear complexes, especially, with weakly axial magnetic ions, still remain largely unrevealed. As an attempt to clarify these conditions, we present here the synthesis, crystal structures, magnetic behavior, and <i>ab initio</i> calculations for a new series of Ni^II–Ln^III–W^V trimetallics, [(CN)₇W­(CN)­Ni­(H₂O)­(valpn)­Ln­(H₂O)₄]·H₂O (Ln = Y <b>1</b>, Eu <b>2</b>, Gd <b>3</b>, Tb <b>4</b>, Dy <b>5</b>, Lu <b>6</b>). The surprising finding is the absence of the magnetic blockage even for compounds involving strongly anisotropic Dy^III and Tb^III metal ions. This is well explained by <i>ab initio</i> calculations showing relatively large transversal components of the <i>g</i>-tensor in the ground exchange Kramers doublets of <b>1</b> and <b>4</b> and large intrinsic tunneling gaps in the ground exchange doublets of <b>3</b> and <b>5</b>. In order to get more insight into this behavior, another series of earlier reported compounds with the same trinuclear [W^VNi^IILn^III] core structure, [(CN)₇W­(CN)­Ni­(dmf)­(valdmpn)­Ln­(dmf)₄]·H₂O (Ln = Gd^III <b>7</b>, Tb^III <b>8a</b>, Dy^III <b>9</b>, Ho^III <b>10</b>), [(CN)₇W­(CN)­Ni­(H₂O)­(valdmpn)­Tb­(dmf)_2.5(H₂O)_1.5]·H₂O·0.5dmf <b>8b</b>, and [(CN)₇W­(CN)­Ni­(H₂O)­(valdmpn)­Er­(dmf)₃(H₂O)₁]·H₂O·0.5dmf <b>11</b>, has been also investigated theoretically. In this series, only <b>8b</b> exhibits SMM behavior which is confirmed by the present <i>ab initio</i> calculations. An important feature for the entire series is the strong ferromagnetic coupling between Ni­(II) and W­(V), which is due to an almost perfect trigonal dodecahedron geometry of the octacyano wolframate fragment. The reason why only <b>8b</b> is an SMM is explained by positive zero-field splitting on the nickel site, precluding magnetization blocking in complexes with fewer axial Ln ions. Further analysis has shown that, in the absence of ZFS on Ni ion, all compounds in the two series (except those containing Y and Gd) would be SMMs. The same situation arises for perfectly axial ZFS on Ni­(II) with the main anisotropy axis parallel to the main magnetic axis of Ln­(III) ions. In all other cases the ZFS on Ni­(II) will worsen the SMM properties. The general conclusion is that the design of efficient SMMs on the basis of such complexes should involve isotropic or weekly anisotropic metal ions, such as Mn­(II), Fe­(III), etc., along with strongly axial lanthanides