Characterization of a Soluble Molecular Magnet: Unusual Magnetic Behavior of Cyano-Bridged Gd(III)−Cr(III) Complexes with One-Dimensional and Nanoscaled Square Structures

Two cyano-bridged Gd(III)−Cr(III) complexes [Gd(urea)4(H2O)2]2[Cr(CN)6]2 (1) and {[Gd(capro)2(H2O)4Cr(CN)6]·H2O}n (2) (capro represents caprolactam) have been synthesized and characterized structurally and magnetically.
Complex 1 has a tetranuclear Gd2Cr2 square structure, in which two cis-CN- ligands of each [Cr(CN)6] link two
[Gd(urea)4(H2O)2] groups and in turn, two [Gd(urea)4(H2O)2] link two [Cr(CN)6] in a cis fashion. Complex 2 is composed
of 1D chains with alternating [Gd(capro)2(H2O)4] and [Cr(CN)6] moieties connected by the trans-CN- ligands of
[Cr(CN)6]. The dehydration of 2 at 120 °C generates a new complex, [Gd(capro)2(H2O)2Cr(CN)6] (2‘). Magnetic
studies show the existence of antiferromagnetic Gd(III)−Cr(III) interaction in these complexes. On the basis of the
tetranuclear model, the magnetic susceptibilities of 1 have been analyzed giving the intermetallic magnetic coupling
constant of −0.36 cm-1. Complex 2‘ exhibits a ferrimagnetic order below 2.1 K. Interestingly, 2‘ is quite soluble in
water, and slow evaporation of the solution gives the hydrated complex 2. Therefore, 2‘ is a soluble molecular
magnet, and this significant behavior implies potential applications. Isothermal magnetization measurements of 2‘
and other cyano-bridged Gd(III)−Cr(III) molecular magnets show unusual field-induced metamagnetic behavior from
the ferrimagnetic ground state to the ferromagnetic state. Field dependence of magnetization of the cyano-bridged
Gd(III)−Cr(III) complexes shows unusual field-induced metamagnetic behavior from the ferrimagnetic ground state
to the ferromagnetic state.