A family of decamethylmetallocene charge-transfer salt magnets using methyl tricyanoethylenecarboxylate (MTCE) as the electron acceptor

Methyl tricyanoethylenecarboxylate, MTCE, has been used as a one-electron acceptor building block for the synthesis of isomorphous decamethylmetallocene charge-transfer salt magnets of the formula MCp*2]MTCE], M = Cr, Mn, and Fe. Functionally and electrochemically, MTCE is a hybrid between tetracyanoethylene (TCNE) and dimethyl dicyanofumarate (DMeDCF), two acceptors that have previously been found to support ferromagnetism. The X-ray crystal structure of the chromium analogue, CrCp*2]MTCE], shows it to exist in the expected mixed stack structure in the orthorhombic space group Pnma with a = 14.739(3) A, b = 10.7869(19) A, and c = 15.771(3) A and Z = 4. As anticipated, all three family members exhibit dominant ferromagnetic coupling, which is presumed to reflect intrastack interactions. However, the bulk magnetic properties mostly differ from simple interpolations or extrapolations of the properties of their TCNE and DMeDCF analogues. Density functional theory calculations have been used to shed some light on this observation.