Slow Relaxation of the Magnetization in Anilato-Based Dy(III) 2D Lattices

The search for two- and three-dimensional materials with slow relaxation of the magnetization (single-ion magnets, SIM and single-molecule magnets, SMM) has become a very active area in recent years. Here we show how it is possible to prepare two-dimensional SIMs by combining Dy(III) with two different anilato-type ligands (dianions of the 3,6-disubstituted-2,5-dihydroxy-1,4-benzoquinone: C₆O₄X₂²⁻, with X = H and Cl) in dimethyl sulfoxide (dmso). The two compounds prepared, formulated as: [Dy₂(C₆O₄H₂)₃(dmso)₂(H₂O)₂]·2dmso·18H₂O (1) and [Dy₂(C₆O₄Cl₂)₃(dmso)₄]·2dmso·2H₂O (2) show distorted hexagonal honeycomb layers with the solvent molecules (dmso and H₂O) located in the interlayer space and in the hexagonal channels that run perpendicular to the layers. The magnetic measurements of compounds 1, 2 and [Dy₂(C₆O₄(CN)Cl)₃(dmso)₆] (3), a recently reported related compound, show that the three compounds present slow relaxation of the magnetization. In compound 1 the SIM behaviour does not need the application of a DC field whereas 2 and 3 are field-induced SIM (FI-SIM) since they show slow relaxation of the magnetization when a DC field is applied. We discuss the differences observed in the crystal structures and magnetic properties based on the X group of the anilato ligands (H, Cl and Cl/CN) in 1–3 and in the recently reported derivative [Dy₂(C₆O₄Br₂)₃(dmso)₄]·2dmso·2H₂O (4) with X = Br, that is also a FI-SIM.

Spin Ice-like Magnetic Relaxation of a Two-dimensional Network based on Manganese(III) Salen-type Single-Molecule Magnets

Spin ice is an exotic type of magnetism displayed by bulk rare-earth pyrochlore oxides. We discovered a spin ice-like magnetic relaxation of [{Mn(saltmen)}₄ {Mn(CN)₆ }](ClO₄ )⋅13 H₂ O (saltmen^2- =N,N'-(1,1,2,2-tetramethylethylene)bis(salicylideneiminate)). This magnetic system can be considered as a two-dimensional network of Mn^III salen-type single-molecule magnets (SMMs) in which each SMM unit (S_T =4) has two orthogonally oriented axial anisotropies and is connected ferromagnetically through the [Mn(CN)₆ ]^3- unit (S=1). This work illustrates that a two-dimensional SMM network with competition between the ferromagnetic interaction and local noncollinear magnetic anisotropies on SMMs is a new type of magnetic system exhibiting slow relaxation of magnetization with a Davidson-Cole-type broad distribution of the relaxation time.

{CoIIIMnIII}ncorrugated chains based on heteroleptic cyanido metalloligands

The use of cyanide-bearing complexes affords one-dimensional coordination polymers with the formulas {[Mn^III(salen)(μ-NC)₂Co^III(4,4-dmbipy)(CN)₂]·H₂O}_n(1) and {[Mn^III(salen)(μ-NC)₂Co^III(dmphen)(CN)₂]}_n(2) .

Two-dimensional coordination polymers constructed by [Ni(II)Ln(III)] nodes and [W(IV)(bpy)(CN)6]2- spacers: a network of [Ni(II)Dy(III)] single molecule magnets

Three isomorphous two-dimensional (2D) coordination polymers of general formula {[Ni(II)(valpn)Ln(III)(NO3)(H2O)(μ-NC)4W(IV)(bipy)(CN)2]·xH2O·yCH3CN}n have been synthesized by reacting Ph4P[W(V)(CN)6(bipy)] with the heterodinuclear [Ni(II)Ln(III)(valpn)(O2NO)3] complexes [H2valpn = 1,3-propanediyl-bis(2-iminomethylene-6-methoxyphenol), bipy = 2,2'-bipyridine, and Ln = Gd (1), Dy (2), and Tb (3) with x = 2 (1), 3.9 (2), and 3.35 (3) and y = 2.50 (1), 2 (2), and 1.8 (3)]. Their crystal structures consist of [Ni(II)Ln(III)] 3d-4f nodes which are connected by [W(IV)(bipy)(CN)6](2-) diamagnetic linkers resulting from the reduction of W(V) to W(IV) during the reaction process. The Ni(II) and Ln(III) ions occupy the inner and outer coordination sites of the dideprotonated valpn ligand, respectively, and they are doubly bridged by the phenoxo oxygen atoms of such a ligand. The value of Ni(II)···Ln(III) separation through this bridge is 3.4919(10) (1), 3.4760(10) (2), and 3.4799(9) (3) Å, and those of the angles at the bridgehead phenoxo atoms are 106.6(2) and 107.3(2) (1), 106.9(2), and 107.8(2) (2) and 106.5(2)-106.8(2)° (3). Each W(IV) is eight-coordinated with a bidentate bipy molecule and six cyanide-carbon atoms building a somewhat distorted square antiprism environment. The rare-earth cations are nine-coordinated, the donor atoms describing a monocapped square antiprism for 1 and 3 and a tricapped trigonal prism for 2. Magnetic susceptibility measurements in the temperature range 1.9-300 K show the occurrence of ferromagnetic interactions between the Ni(II) and Ln(III) ions in 1-3. Frequency-dependent alternating susceptibility signals were observed for the Dy(III) derivative below 8.0 K under an applied dc field of 2500 G indicating the presence of slow magnetic relaxation with values of the pre-exponential factor (τ0) and energy barrier (E(#)) of ca. 5.7 × 10(-8) s and 15.9 cm(-1), respectively. Complex 2 constitutes the first example of a 2D 3d-4f heterobimetallic single molecule magnet (SMM).

Two novel cyanide-bridged bimetallic magnetic chains derived from manganese(III) Schiff bases and hexacyanochromate(III) building blocks

Two novel complexes, [{Mn(salen)}(2){Mn(salen)(CH(3)OH)}{Cr(CN)(6)}](n)·2nCH(3)CN·nCH(3)OH (1) and [Mn(5-Clsalmen)(CH(3)OH)(H(2)O)](2n)[{Mn(5-Clsalmen)(μ-CN)}Cr(CN)(5)](n)·5.5nH(2)O (2) (salen(2-) = N,N'-ethylene-bis(salicylideneiminato) dianion; 5-Clsalmen(2-) = N,N'-(1-methylethylene)-bis(5-chlorosalicylideneiminato) dianion), were synthesized and structurally characterized by X-ray single-crystal diffraction. The structural analyses show that complex 1 consists of one-dimensional (1D) alternating chains formed by the [{Cr(CN)(6)}{Mn(salen)}(4){Mn(salen)(CH(3)OH)}(2)](3+) heptanuclear cations and [Cr(CN)(6)](3-) anions. While in complex 2, the hexacyanochromate(III) anion acts as a bis-monodentate ligand through two trans-cyano groups to bridge two [Mn(5-Clsalmen)](+) cations to form a straight chain. The magnetic analysis indicates that complex 1 shows three-dimensional (3D) antiferromagnetic ordering with the Néel temperature of 5.0 K, and it is a metamagnet displaying antiferromagnetic to ferromagnetic transition at a critical field of about 2.6 kOe at 2 K. Complex 2 behaves as a molecular magnet with Tc = 3.0 K.