Interactions between well-isolated Dy ³⁺ ions considerably contribute to the demagnetization of a mononuclear acetylacetonate–pyrazinate complex

A series of new mononuclear square antiprismatic complexes comprising acetylacetonate (acac^-), pyrazine-2-carboxylate (PyrCOO^-) and 1,10-phenanthroline (phen) ligands, namely, [Ln(acac)₂(PyrCOO)(phen)] (Ln is Dy-Yb, Y; 1-5, 6), was prepared and studied. These complexes are new examples of extremely scarcely studied eight-coordinated tetra-chelate complexes comprising β-diketonate and carboxylate ligands. Complexes 1, 3 and 5 exhibit pronounced slowdown of demagnetization, with corresponding pathways additionally validated by <i>ab initio</i> calculations. In particular, complex 1 exhibits zero-field relaxation with a <i>Δ</i>_eff/<i>k</i>_B of 149 K, while the application of an optimal DC field (1500 Oe) enhances the <i>Δ</i>_eff/<i>k</i>_B value to 265 K. Thus, although the quantum tunneling of magnetization (QTM) contributes to zero-field relaxation of complex 1, this complex is among the most efficient zero-field Dy-based SMMs formed by β-diketonate and/or carboxylate ligands. Moreover, the <i>Δ</i>_eff/<i>k</i>_B value of 1 under the optimal field is the highest among the related complexes. Interestingly, the Dy-Dy magnetic interactions have a considerable effect on the SMM performance of 1, despite on the spatial (>8 Å) separation of Dy³⁺ ions isolated by coats of bulky diamagnetic ligands.