Synthesis, Crystal Structures, Magnetic Properties, and Fluorescence of Two Heptanuclear Co(4)(III)Ln(3)(III) Compounds (Ln = Gd-III, Dy-III): Multiple Relaxation Dynamics in the Dy-III Analogue

摘要

This report describes the synthesis, crystal structures, magnetic and spectroscopic properties of two heptanuclear Co(4)(III)Ln(3)(III) systems of composition [(Co4Gd3L4)-Gd-III-L-III(mu(4)-O)(2)(mu-OMe)(2)(mu(1,3)-OAc)(4)(H2O)(2)(NO3)(2)]center dot NO3 center dot 2CH(3)OH center dot 2H(2)O (1) and [(Co4Dy3L4)-Dy-III-L-III(mu(4)-O)(2)(mu-OMe)(2)(mu(1,3)-OAc)(4)(H2O)(2)(NO3)(2)]center dot NO3 center dot 3CH(3)OH center dot 1.5H(2)O (2), where H2L is [1+1] condensation product of 3-methoxysalicylaldehyde and 2-amino-2-methyl-1-propanol. The heptametallic cores in 1 and 2 may be taken as consisted of two symmetry related trinuclear Co(III)Ln(III)Co(III) moieties and a central lanthanide center in such a way that each of the three metal ions of each of the two trinuclear moieties are bridged with the central lanthanide through bridging oxo/alkoxo/acetate ligands. DC magnetic measurements of 1 and 2 reveal very weak Gd-III center dot center dot center dot Gd-III antiferromagnetic interaction (J = -0.01 cm(-1)) in 1 and significant anisotropy in 2. Variable-temperature and variable-frequency ac susceptibility measurements of 2 reveal that it is a zero-field SMM with multiple relaxation dynamics. Above 5 K, two well resolved relaxation channels are observed; U-eff and tau(0) are 51.4 cm(-1) and 9.40 x 10(-7) s for the slow relaxation channel and 24.3 cm(-1) and 6.91 x 10(-7) s for the fast relaxation channel. The characteristic Dy-III based transitions, F-4(9/2)-> H-6(15/2), F-4(9/2)-> H-6(13/2) and F-4(9/2)-> H-6(11/2), can be well assigned in the fluorescence spectrum of 2 at solid state. All in all, compound 2 is a bifunctional molecular material.