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)(4)Cr(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 degreesC generates a new complex, [Gd(capro)(2)(H2O)(2)Cr(CN)(6)] (2'). Magnetic studies show the existence of antiferromagnetic Gd(Ill)-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(I I I)-Cr(I 11) 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(Ill)-Cr(III) complexes shows unusual field-induced metamagnetic behavior from the ferrimagnetic ground state to the ferromagnetic state.