The Exploration and Analysis of the Magnetic Relaxation Behavior in Three Isostructural Cyano-Bridged 3d–4f Linear Heterotrinuclear Compounds

Abstract

Three isostructural cyano-bridged 3d–4f linear heterotrinuclear compounds, (H2.5O)4{Ln[TM(CN)5(CNH0.5)]2(HMPA)4} (Ln = YIII, TM = [FeIII ]LS (1); Ln = DyIII, TM = [FeIII ]LS (2); Ln = DyIII, TM = CoIII (3)), have been synthesized and characterized by single-crystal X-ray diffraction. Due to the steric effect of the HMPA ligands, the central lanthanide ions in these compounds possess a low coordination number, six-coordinate, exhibiting a coordination geometry of an axially elongated octahedron with a perfect D4h symmetry. Four HMPA ligands situate in the equatorial plane around the central lanthanide ions, and two [TM(CN)5(CNH0.5)]2.5− entities occupy the apical positions to form a cyano-bridged 3d–4f linear heterotrinuclear structure. The static magnetic analysis of the three compounds indicated a paramagnetic behavior of compounds 1 and 3, and possible small magnetic interactions between the intramolecular DyIII and [FeIII ]LS ions in compound 2. Under zero dc field, the ac magnetic measurements on 2 and 3 revealed the in-phase component (χ′) of the ac susceptibility without frequency dependence and silent out-of-phase component (χ”), which was attributed to the QTM effect induced by the coordination geometry of an axially elongated octahedron for the DyIII ion. Even under a 1 kOe applied dc field, the χ” components of 2 were revealed frequency dependence without peaks above 2 K. And under a 2 kOe and 3 kOe dc field, the χ” components of 3 exhibited weak frequency dependence below 4 K with the absence of well-shaped peaks, which confirmed the poor single-ion magnetic relaxation behavior of the six-coordinate DyIII ion excluding any influence from the neighboring [FeIII ]LS ions as that in the analogue 2.