Synthesis and Characterization of Heterodinuclear Ln³⁺−Fe³⁺ and Ln³⁺−Co³⁺ Complexes, Bridged by Cyanide Ligand (Ln³⁺ = Lanthanide Ions). Nature of the Magnetic Interaction in the Ln³⁺−Fe³⁺ Complexes

Abstract

The reaction of Ln(NO3)3.aq with K3[Fe(CN)6] or K3[Co(CN)6] in N,N'-dimethylformamide (DMF) led to 25 heterodinuclear [Ln(DMF)4(H2O)3(mu-CN)Fe(CN)5].nH2O and [Ln(DMF)4(H2O)3(mu-CN)Co(CN)5].nH2O complexes (with Ln = all the lanthanide(III) ions, except promethium and lutetium). Five complexes (Pr(3+)-Fe3+), (Tm(3+)-Fe3+), (Ce(3+)-Co3+), (Sm(3+)-Co3+), and (Yb(3+)-Co3+) have been structurally characterized; they crystallize in the equivalent monoclinic space groups P21/c or P21/n. Structural studies of these two families show that they are isomorphous. This relationship in conjunction with the diamagnetism of the Co3+ allows an approximation to the nature of coupling between the iron(III) and the lanthanide(III) ions in the [Ln(DMF)4(H2O)3(mu-CN)Fe(CN)5].nH2O complexes. The Ln(3+)-Fe3+ interaction is antiferromagnetic for Ln = Ce, Nd, Gd, and Dy and ferromagnetic for Ln = Tb, Ho, and Tm. For Ln = Pr, Eu, Er, Sm, and Yb, there is no sign of any significant interaction. The isotropic nature of Gd3+ helps to evaluate the value of the exchange interaction.

Multiple Magnetization Reversal Channels Observed in a 3d-4f Single Molecule Magnet

“…This could be due to lattice disorder leading to unique species within the complex or the fact that a bunch of molecules resulted in different anisotropy, as first reported for polynuclear SMMs such as Mn 12 and its derivatives [31]. In the present case, as mentioned above, the neutral dinuclear units of DyCo are interacting via hydrogen bonds to form a 3D network, involving water molecules from crystallization [7,17]. It is then highly probable for the complex to undergo structure distortion upon partial loss of crystallization water over a length of time, leading to formation of two unique entities within the complex and thus in the observation of two different channels for magnetization reversal [32].…”

“…We underline that, for this derivative, only the crystal field affects the temperature dependence of the susceptibility, given the diamagnetic nature of the low-spin Co III , only slightly affected by temperature independent paramagnetism [17]. The complex has a monoclinic unit cell containing four discrete hetero-dinuclear molecules and crystallizes in the P21/n (i.e., n° 14) space group [7,17]. A detailed view of the coordination sphere of the Dy III center is reported as reference in Figure 1: Dy III coordination number is eight, and analysis of the coordination polyhedron via use of SHAPE [18] provided evidence of a geometry intermediate between square antiprismatic, bicapped trigonal prismatic and trigonal dodecahedron geometry (see Table S1).…”

“…We underline that, for this derivative, only the crystal field affects the temperature dependence of the susceptibility, given the diamagnetic nature of the low-spin Co III , only slightly affected by temperature independent paramagnetism [17]. The complex has a monoclinic unit cell containing four discrete hetero-dinuclear molecules and crystallizes in the P21/n (i.e., n° 14) space group [7,17].…”

“…The analysis of the packing, as well as detailed X-ray investigation on isostructural systems, [19] showed the existence of a 3D network made up of Dy III -Co III dinuclear entities where the five terminal CN groups of the {Co(CN) 6 } fragment are connected through hydrogen bonds to the Lncoordinated water molecules via crystallization water molecules. The static magnetic properties revealed that this network of hydrogen bonding interaction might result in non-negligible interdimer coupling interactions [17]. EPR spectroscopy on a powder sample, performed at 4.2 K was interpreted under the assumption that the observed properties were only due to the anisotropic ground doublet of Dy III [20], and suggested that the DyCo boasts an almost axial anisotropy with an effective g tensor (g eff x, g eff y, g eff z) = (0.1(1), 0.1(1), 18(1)) [21].…”

“…The present work is focused on a Dy(H2O)3(dmf)4(μ-CN)Co-(CN)5]•nH2O where 1 ≤ n ≤ 1.5 and dmf = N,N′-dimethylformamide, complex (hereafter DyCo) which had been previously synthesized by one of us [17] to study the competing effect of exchange and anisotropy effects on the static magnetic behavior in a family of isotructural LnM complexes. We underline that, for this derivative, only the crystal field affects the temperature dependence of the susceptibility, given the diamagnetic nature of the low-spin Co III , only slightly affected by temperature independent paramagnetism [17].…”