来源：ACS Publications
The oxidation state +2 is of interest in rare-earth chemistry since it allows these conventionally redox-inactive metals to be used as reducing agents. However, the divalent oxidation state is difficult to form for most rare-earth elements, and the ensuing compounds are often unstable. Here, we describe an approach to rare-earth reduction chemistry that circumvents the divalent oxidation state by using compounds of trivalent rare earths that store reducing electrons on the dinitrogen ligand [N2]2–, akin to “masked” divalent reactivity. Thus, the dinitrogen complexes
[(Cpttt2M)2(‐1,2‐N2)] (1M, M = Y, Gd, Tb, Dy, Cpttt = 1,2,4-C5tBu3H2) reduce hexaazatrinaphthylene and its hexamethyl derivative to give trimetallic
[(Cpttt2M)3(R6HAN)], where the [R6HAN]3– ligands (R = H, 2M; R = Me, 3M) form with S = 1/2, and with elimination of N2. The structures of 2M and 3M reveal that the tert-butyl substituents strongly influence the core geometry of these trimetallic complexes. Analysis of the magnetism and electronic structure of 2Gd and 3Gd identifies ferromagnetic metal-radical exchange, with coupling constants of J = +2.87 cm–1 and +3.07 cm–1, respectively (−2J formalism). The unusual ferromagnetic exchange is a consequence of charge transfer to the gadolinium 5d, 6s, and 6p orbitals from the radical ligands.
we now focus on the synthesis of radical-bridged multimetallic systems, which have potential applications as molecular magnetic materials such as single-molecule magnets (SMMs). Since most radical-bridged lanthanide molecular magnets feature C5Me5 (Cp*) as the supporting ligand, using 1M as the reducing agents introduces opportunities to explore how the properties of related systems vary with different cyclopentadienyl substituents. Our interests also extend to masked divalent yttrium, given the suggestion yttrium(II) may behave differently to similarly sized divalent ions of the late lanthanides. Thus, using the dinitrogen complexes 1M as the reducing agents, we targeted trimetallic complexes of redox-active hexaazatrinaphthylene (HAN) ligands, which can be reduced with up to three electrons. In the complexes [(Cpttt2M)3(R6HAN)], where M = Y, Gd, Tb and Dy, and R = H or CH3, the heterocyclic ligands should form as the S = 1/2 radical trianions [R6HAN]3–, facilitating exchange coupling between paramagnetic lanthanides.