Zero-dimensional organic-based magnets possessing decamethylmetallocene

Magnets composed of organic components that provide both spin and spin coupling to stabilize ferromagnetic ordering were first realized with the ionic, electron transfer salt [Fe(C5Me5)2]+[TCNE]˙− (TCNE = tetracyanoethylene), which orders at 4.8 K (Tc). After more than two decades of study, its structure, as well as the magnetic behaviour and structures of its solvates, have been recently established. All structurally characterized members of this family of organic-based magnets have the same structural motif of parallel chains of alternating radical [M(C5Me5)2]+ cations and planar radical organic anions with intrachain M⋯M separations of 10.7 ± 0.3 Å, and lack any sub van der Waals interactions. In this Feature article the chemical and magnetic properties of the growing family of [M(C5Me5)2][acceptor] (M = Cr, Mn, Fe) materials is described with emphasis on the recent developments, common trends, and outstanding problems and opportunities.