Cyanido-Bridged {Ln III W V} Heterobinuclear Complexes: Synthesis and Magneto-Structural Study

Inorg Chem. 2017 Oct 16;56(20):12594-12605. doi: 10.1021/acs.inorgchem.7b02050. Epub 2017 Sep 27.

Abstract

A new series of cyanido-bridged {LnIIIWV} heterobinuclear complexes of formula [LnIII(pyim)2(i-PrOH)(H2O)2(μ-CN)WV(CN)7]·2H2O [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 LnIII ions and the pyim ligand). Compounds 1-5 are isomorphous and crystallize in the monoclinic system P21/n space group. Their crystal structure consists of binuclear units in which the octacyanotungstate(V) anion coordinates to the corresponding LnIII ion through a single cyanide ligand. The tungsten(V) and lanthanide(III) ions are eight-coordinated, in distorted square antiprism (WV) and distorted trigonal dodecahedron (LnIII) geometries, respectively. The direct-current (dc) magnetic properties for 1-5 reveal the occurrence of weak antiferromagnetic interactions between WV and LnIII cation, with 8S7/2, 7F6, 6H15/2, 5I8, and 4I15/2 as ground terms for GdIII, TbIII, DyIII HoIII, and ErIII, respectively [JWLn = -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 = -JWLn SW·SLn]. The fit of the χMT data of 2-4 points out a positive value for the energy gap between the ML components (Δ). This feature is corroborated by their Q-band electron paramagnetic resonance spectra at low temperature, which clearly show MJ = 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 {LnIIIWV} 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.