Two-Dimensional Coordination Polymers Constructed by [Ni^IILn^III] Nodes and [W^IV(bpy)(CN)₆]^2– Spacers: A Network of [Ni^IIDy^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]­·<i>x</i>H₂O­·<i>y</i>CH₃CN}_<i>n</i> have been synthesized by reacting Ph₄P­[W^V(CN)₆­(bipy)] with the heterodinuclear [Ni^IILn^III(valpn)­(O₂NO)₃] complexes [H₂valpn = 1,3-propanediyl-bis­(2-iminomethylene-6-methoxyphenol), bipy = 2,2′-bipyridine, and Ln = Gd (<b>1</b>), Dy (<b>2</b>), and Tb (<b>3</b>) with <i>x</i> = 2 (<b>1</b>), 3.9 (<b>2</b>), and 3.35 (<b>3</b>) and <i>y</i> = 2.50 (<b>1</b>), 2 (<b>2</b>), and 1.8 (<b>3</b>)]. Their crystal structures consist of [Ni^IILn^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) (<b>1</b>), 3.4760(10) (<b>2</b>), and 3.4799(9) (<b>3</b>) Å, and those of the angles at the bridgehead phenoxo atoms are 106.6(2) and 107.3(2) (<b>1</b>), 106.9(2), and 107.8(2) (<b>2</b>) and 106.5(2)–106.8(2)° (<b>3</b>). 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 <b>1</b> and <b>3</b> and a tricapped trigonal prism for <b>2</b>. 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 <b>1</b>–<b>3</b>. 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 (<i>E</i>^#) of ca. 5.7 × 10^–8 s and 15.9 cm^–1, respectively. Complex <b>2</b> constitutes the first example of a 2D 3d-4f heterobimetallic single molecule magnet (SMM)