[GdNi6] and [LaNi6]: high-field EPR spectroscopy and magnetic studies of exchange-coupled octahedral clusters.

The preparation of transition-metal clusters with relevance in molecular magnetism has been a very prolific area of coordination chemistry, and has become of primary importance since the discovery of single-molecule magnets (SMMs). 5] As a result, a high level of understanding has been achieved of the nature and mechanism of the magnetic super exchange between 3d metals. Indeed, the vast majority of SMMs known to date are made of manganese, iron, nickel, cobalt, and vanadium. In contrast, the magnetic coupling between 3d and 4f metals is still not understood very well and has therefore not been exploited as a potential entry to a new category of SMMs. 15] Of all open-shell 4f ions, Gd has been studied the most since it does not show the complicating effect of spin-orbit coupling. The quasi-systematic ferromagnetic nature of the coupling between Cu and Gd has been corroborated by a considerable amount of experimental data, and a recent report has established the theoretical grounds of this observation. In contrast, the magnetic exchange between Ni and Gd—always found to be ferromagnetic so far–-has not been explored as extensively. The few systems where this coupling has been analyzed are almost all dinuclear compounds. As a continuation of our studies on heterometallic 3d–4f clusters, we have prepared a series of isostructural and highly symmetric exchange-coupled clusters of the formula