Decamethyl- and octamethyl-ferrocenium salts of F1- and F2-TCNQ: Effects of fluorine substitution on the crystal structures and magnetic interactions

•[Fe(C5Me4R)2](FnTCNQ) (R = H, Me; n = 1, 2) are isomorphous to the TCNQ salts.•[Fe(C5Me5)2](2,5-F2TCNQ) is a metamagnet with TN = 3.9 K.•Polar acceptors (F1-, 2,3-F2-, and 2,6-F2-TCNQ) form diamagnetic dimers in the salts.

Decamethyl- and octamethyl-ferrocenium salts of FnTCNQ (n = 1, 2) were prepared and their crystal structures characterized. The 2,5-F2TCNQ salts [Fe(C5Me5)2](2,5-F2TCNQ) (1) and [Fe(C5Me4H)2](2,5-F2TCNQ) (2) exhibit one-dimensional …[D]+[A]−[D]+[A]−… mixed-stack structures, while the salts with polar acceptors [Fe(C5Me5)2][A] (A = F1TCNQ (3), 2,3-F2TCNQ (4), 2,6-F2TCNQ (5)) and [Fe(C5Me4H)2][A] (A = 2,3-F2TCNQ (6), 2,6-F2TCNQ (7)) consist of [D]+[A2]2−[D]+ units involving a diamagnetic dimer of the acceptors. These salts are isomorphous to the corresponding TCNQ salts. 1 and 2 exhibit small ferromagnetic interactions at low temperatures. 1 undergoes an antiferromagnetic phase transition at TN = 3.9 K, which is higher than TN = 2.1 K of the metamagnetic polymorph of [Fe(C5Me5)2](TCNQ).

Graphical abstract[Fe(C5Me4R)2](FnTCNQ) (R = Me, H; n = 1, 2) were prepared and structurally characterized. These salts are isomorphous to the polymorphs of [Fe(C5Me5)2](TCNQ). Polar and nonpolar acceptors crystallized in the one-dimensional mixed-stack structure and dimeric phase structure, respectively. Fluorine substitution raised the metamagnetic phase transition temperature of [Fe(C5Me5)2](TCNQ) by ∼2 K.Figure optionsDownload full-size imageDownload as PowerPoint slide