Cyanido-Bridged {LnIIIWV} Heterobinuclear Complexes: Synthesis and Magneto-Structural Study

A new series of cyanido-bridged {Ln(III)W(V)} heterobinuclear complexes of formula [Ln(III)(pyim)(2)(i-PrOH)(H2O)(2)(mu-CN)W-V(CN)(7)]center dot 2H(2)O [Ln = Gd (1), Tb (2), Dy (3), Ho (4), and Er (5); pyim = 2-(1H-imidazol-2-yl)-pyridine) and i-PrOH = isopropyl alcohol] were synthesized by one-pot reaction between (NH3Bu)(3)[W(CN)(8)] and [Ln(pyim)(2)](2+) complexes (generated in situ by mixing the corresponding Ln(III) ions and the pyim ligand). Compounds 15 are isomorphous and crystallize in the monoclinic system P2(1)/n space group. Their crystal structure consists of binuclear units in which the octacyanotungstate(V) anion coordinates to the corresponding Ln(III) ion through a single cyanide ligand. The tungsten(V) and lanthanide(III) ions are eight-coordinated, in distorted square antiprism (W-V) and distorted trigonal dodecahedron (Ln(III)) geometries, respectively. The direct-current (dc) magnetic properties for 15 reveal the occurrence of weak antiferromagnetic interactions between W-V and Ln(III) cation, with S-8(7/2), F-7(6), H-6(15/2), I-5(8), and I-4(15/2) as ground terms for Gd-III, Tb-III, Dy-III Ho-III, and Er-III, respectively [J(WLn) = -1.19(1) (1), -1.02(2) (2), -1.10(2) (3), -1.30(2) (4), and -1.50(3) cm(1) (5), the spin Hamiltonian being defined as H = -J(WLn) S-W center dot S-Ln]. The fit of the chi T-M data of 24 points out a positive value for the energy gap between the M-L components (Delta). This feature is corroborated by their Q-band electron paramagnetic resonance spectra at low temperature, which clearly show M-J = 0 (2 and 4) and +/- 1/2 (3 and 5). Incipient frequency-dependent alternating-current magnetic susceptibility signals are observed for 3 and 5 under applied dc fields supporting the presence of slow magnetic relaxation behavior, the blocking temperatures being below 2.0 K. This new series of {Ln(III)W(V)} heterobinuclear compounds provides more insights into the exchange magnetic interaction between 5d and 4f centers via the cyanide-bridge, for which scarce information is available to date.