Charge-transfer salts of methylferrocenes with DCNQI derivatives (DCNQI = N,N′-dicyano-1,4-benzoquinonediimine): Crystal structures and magnetic properties

Organometallic charge-transfer salts composed of decamethyl-, octamethyl-, and dimethylferrocene with N,N′-dicyano-1,4-benzoquinonediimine (DCNQI) derivatives were prepared. [Fe(C₅Me₅)₂][(MeO)₂DCNQI] (1) and [Fe(C₅Me₄H)₂][Me₂DCNQI] (2) were 1:1 DA salts with mixed-stack structures, whereas [Fe(C₅Me₄H)₂][(MeO)₂DCNQI]₂ (3) and [Fe(C₅MeH₄)₂][DCNQI]₂ (4) were 1:2 DA salts. 3 exhibited a segregated-stack structure, in which charge separation was observed in the acceptor column. 1 became a metamagnet below T_N = 5.0 K, whereas the other salts were paramagnets. Valence states and charge-transfer (CT) transitions in these complexes are discussed based on the neutral-ionic (NI) phase diagram.