Calixarene-like Lanthanide Single-Ion Magnets Based on NdIII, GdIII, TbIII and DyIII Oxamato Complexes

In this work, we describe the synthesis, crystal structures and magnetic properties of four air-stable mononuclear lanthanide(III) complexes with the N-(2,4,6-trimethylphenyl)oxamate (Htmpa) of formula: n-Bu4N[Nd(Htmpa)4(H2O)]·4H2O (1), n-Bu4N[Gd(Htmpa)4(H2O)]·3DMSO·2H2O (2), n-Bu4N[Tb(Htmpa)4(H2O)]·3DMSO·1H2O (3) and n-Bu4N[Dy(Htmpa)4(H2O)]·3DMSO·2H2O (4) (n-Bu4N+ = n-tetrabutylammonium; DMSO = dimethylsulfoxide). Their crystal structures reveal the occurrence of calixarene-type monoanionic species containing all-cis-disposed Htmpa ligands and one water molecule coordinated with the respective LnIII ion (Ln = Nd, Gd, Tb and Dy), featuring a nine-coordinated environment with muffin (MFF-9) (1) or spherical-capped square antiprism (CSAPR-9) (2–4) geometry. The major difference between their crystal structures is related to the nature of crystallization solvent molecules, either water (1) or both DMSO and water (2–4). The intermolecular hydrogen bonds among the self-complementary Htmpa ligands in all four compounds mediated a 2 D supramolecular network in the solid state. Direct-current (dc) magnetic properties for 1–4 show typical behavior for the ground state terms of the LnIII ions [4I9/2 (Nd); 8S7/2(Gd), 7F6 (Tb), 6H15/2 (Dy)]. Alternating-current (ac) magnetic measurements reveal the presence of slow magnetic relaxation without the presence of a dc field only for 4. In contrast, field-induced slow magnetic relaxation behavior was found in complexes 1, 2 and 3.