Synthesis, Crystal Structures, Magnetic Properties, and Fluorescence of Two Heptanuclear CoIII4LnIII3 Compounds (Ln = GdIII, DyIII): Multiple Relaxation Dynamics in the DyIII Analogue

Abstract

This report describes the synthesis, crystal structures, magnetic and spectroscopic properties of two heptanuclear CoIII4LnIII3 systems of composition [CoIII4GdIII3L4(µ4‐O)2(µ‐OMe)2(µ1,3‐OAc)4(H2O)2(NO3)2]·NO3·2CH3OH·2H2O (1) and [CoIII4DyIII3L4(µ4‐O)2(µ‐OMe)2(µ1,3‐OAc)4(H2O)2(NO3)2]·NO3·3CH3OH·1.5H2O (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 CoIIILnIIICoIII 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 GdIII···GdIII 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; Ueff and τ0 are 51.4 cm–1 and 9.40 × 10–7 s for the slow relaxation channel and 24.3 cm–1 and 6.91 × 10–7 s for the fast relaxation channel. The characteristic DyIII based transitions, 4F9/2→6H15/2, 4F9/2→6H13/2 and 4F9/2→6H11/2, can be well assigned in the fluorescence spectrum of 2 at solid state. All in all, compound 2 is a bifunctional molecular material.