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The synthesis, structure, magnetic, and luminescence properties of the Zn2Dy2 tetranuclear complex of formula (μ3-CO3) 2Zn (μ-L) Dy (NO3) 2·4CH3OH (1), where H2L is the compartmental ligand N, N', N″-trimethyl-N, N″-bis (2-hydroxy-3-methoxy-5-methylbenzyl) diethylenetriamine, are reported. The carbonate anions that bridge two Zn (μ-L) Dy units come from the atmospheric CO2 fixation in a basic medium. Fast quantum tunneling relaxation of the magnetization (QTM) is very effective in this compound, so that single-molecule magnet (SMM) behavior is only observed in the presence of an applied dc field of 1000 Oe, which is able to partly suppress the QTM relaxation process. At variance, a 1: 10 Dy: Y magnetic diluted sample, namely, 1', exhibits SMM behavior at zero applied direct-current (dc) field with about 3 times higher thermal energy barrier than that in 1 (U (eff) = 68 K), thus demonstrating the important role of intermolecular dipolar interactions in favoring the fast QTM relaxation process. When a dc field of 1000 Oe is applied to 1', the QTM is almost fully suppressed, the reversal of the magnetization slightly slows, and U (eff) increases to 78 K. The dilution results combined with micro-SQUID magnetization measurements clearly indicate that the SMM behavior comes from single-ion relaxation of the Dy (3+) ions. Analysis of the relaxation data points out that a Raman relaxation process could significantly affect the Orbach relaxation process, reducing the thermal energy barrier U (eff) for slow relaxation of the magnetization.
Titos‐Padilla et al. (Thu,) studied this question.