Syntheses, Structures, and Magnetic Properties of Novel [3x1+2x1] Pentanuclear Zinc(II)-Lanthanide(III) Cocrystal Complexes: Slow Magnetic Relaxation Behavior of the Dy(III) Analogue

A new family of 3d-4f polynuclear cocrystals [LnZn(2)L(2)(CH3CO2)(4)]center dot[Zn2Cl4L]center dot H2O [where Ln(III) = Gd(1), Tb(2), and Dy(3)] are synthesized by the sequential reaction of a tetradentate multisite coordinating compartmental ligand, i.e., (E)-2-methoxy-6-(((pyridine-2-ylmethyl)imino)methyl)phenol, in the presence of LnCl(3)center dot 6H(2)O and Zn(OAc)(2)center dot 2H(2)O. The detailed studies involve mainly synthesis, structure, and magnetic properties of three isostructural cocrystals. The X-ray diffraction analysis reveals that complexes 1-3 crystallize in triclinic crystal system with the P (1) over bar space group. The dimeric [Zn2Cl4L](-) complex appears as a cocrystal in the vicinity of the [LnZn(2)L(2)(CH3CO2)(4)](+) crystal structure to counter balance the overall charge on the primary coordination sphere. Magnetic relaxation studies indicate that zero-field out-of-phase magnetic susceptibility signals are observed only for complex 3 (Dy-III analogue) which gets well resolved in the presence of a H-dc = 0.5 kOe magnetic field. The extracted effective energy barrier (U-eff) and pre-exponential factor (tau(0)) for 3 is found to be 13.53 K and 1.78 x 10(-6) s, respectively. The appearance of single-ion magnet properties for 3 is rationalized with CASSCF/SO-RASSI/SINGLE_ANISO based ab initio calculations.