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

Abstract

Decamethyl-and octamethyl-ferrocenium salts of F n TCNQ (n = 1, 2) were prepared and their crystal structures characterized. The 2,5-F 2 TCNQ salts [Fe(C 5 Me 5) 2 ](2,5-F 2 TCNQ) (1) and [Fe(C 5 Me 4 H) 2 ](2,5-F 2 TCNQ) (2) exhibit one-dimensional ...[D] + [A] − [D] + [A] − ... mixed-stack structures, while the salts with polar acceptors [Fe(C 5 Me 5) 2 ][A] (A = F 1 TCNQ (3), 2,3-F 2 TCNQ (4), 2,6-F 2 TCNQ (5)) and [Fe(C 5 Me 4 H) 2 ][A] (A = 2,3-F 2 TCNQ (6), 2,6-F 2 TCNQ (7)) consist of [D] + [A 2 ] 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 T N = 3.9 K, which is higher than T N = 2.1 K of the metamagnetic polymorph of [Fe(C 5 Me 5) 2 ](TCNQ).

Orbital hybridization of donor and acceptor to enhance the conductivity of mixed-stack complexes

“…Likewise, the acceptor molecules F n exhibited weakening of the bond alternation (i.e., C–C bonds i , k , and m are shortened, while C=C bonds j and l are lengthened; Fig. 5a, d, g ) upon reduction from neutral 33 , 34 ( δ = 0) to their 1 e − –reduced forms 35 , 36 ( δ = 1), suggesting the intermediate δ . Notably, the 2O complexes exhibited weaker bond length alternation than the 2S complexes, suggesting that the 2O complexes have higher δ values than the 2S complexes.…”

“…As a reference, the bond lengths in single crystals of neutral donors or acceptors (i.e., δ = 0) are shown with dotted lines and 1 e − -oxidized donors or 1 e − -reduced acceptors (i.e., δ = 1) are shown with solid lines. Observed d CC of 2O 30 ( b ), d CC of 2 S ( c ), d CC of F 4 33 , 35 ( d ), d CS of 2O 30 ( e ), d CS of 2 S ( f ), and d CC of F 2 34 , 36 ( g ). i = ( i 1 + i 2 )/2.…”

X-ray structures and electronic properties of the 1,1′,2,2′- and 1,1′,3,3′-tetra-t-butylferrocenium(1+) cations

“…The functionalization of ferrocene, Fe(Cp) 2 has been an active endeavor for many years because different functional groups can tune the steric, electronic, and solubility properties of ferrocene by virtue of their size, shape, lipophilicity, and electron donating or withdrawing character (abbreviations: Cp, η 5 -cyclopentadienyl; Fe(Cp) 2 = ferrocene = bis(η 5 -cyclopentadienyl)iron; Cp' = any substituted η 5 -Cp ligand; Cp* = η 5 -pentamethylcyclopentadienyl; 1,2-BUT = 1,1'2,2'-tetra(2-methyl-2-propyl)ferrocene; 1,3-BUT = 1,1'3,3'-tetra(2-methyl-2-propyl)ferrocene; 1,3-HEP = 1,1'3,3'-tetra(2-methyl-2-hexyl)ferrocene; 1,3-DEC = 1,1'3,3'-tetra(2methyl-2-nonyl)ferrocene). Suitably substituted ferrocenes and ferrocenium(1+) salts have been widely used in catalysis, organic synthesis, coordination and organometallic chemistry, and materials science [1][2][3][4]. Poly-or peralkylation is often desirable because the substitution of electron-donating alkyl groups for hydrogen atoms on the Cp ligands renders the polyalkylferrocenium(1+) cations harder to reduce (e.g., E 1/2 (+/0) for decamethylferrocene, Fe(Cp*) 2 , is -0.55 V vs. Fe(Cp) 2 +/0 ) [5,6] and typically makes the ferrocenium salt more soluble in organic solvents and less soluble in aqueous media.…”

Gram-Scale Synthesis of 2,5-Difluoro-7,7,8,8-tetracyanoquinodimethane (F2-TCNQ)

“…Among the members of the F n -TCNQ family, F 2 -TCNQ also has a unique stacking in a single crystal structure. − The unique face-to-face crystal stacking of F 2 -TCNQ is thought to account for its phenomenal electron mobility relative to TCNQ and F 4 -TCNQ. Finally, the properties of the F n -TCNQ family have been investigated as complexes, − co-crystals, − and adducts with various metal ions and other materials. − …”