1 Introduction
Among the large number of molecular-based magnets reported to date [1–3], these containing two transition metal ions [4–8] linked by an organic spacer have suscitated a lot of interest, principally due to the unusual magnetic properties, that may arise from bimetallic magnetic cooperativity.
In these compounds, not only the nature of the ions but also the structure of the organic spacer is of crucial importance. Depending on its geometry and shape, different magnetic interactions will take place between the neighboring metal centers.
In this respect bis-oxamide ligands have been extensively investigated. Following simple synthetic protocols, these ligands allow tight association of different metal centers belonging to the d-block elements in hetero-bimetallic materials.
Such ligands were initially synthesized by Nonoyama and Ojima [9] and have recently been demonstrated by Pey et al. [10] to constitute very promising spacers for elaboration of magnetic molecular-based materials. Indeed in (Gd3+–Cu2+) model complexes containing 4f–3d pairs, it was established that the Gd3+–Cu2+ interaction was usually ferromagnetic [11–14].
Using the bis-oxamide unit as spacer [15–20] it has been subsequently shown that extended linear compounds could retain long range ferromagnetic orderings at low temperature [21]. It was then further suggested that by increasing the dimensionality of the final material, i.e. by strengthening interchain or interplan interactions, magnetic m