Inorganica Chimica Acta
Decamethyl- and octamethyl-ferrocenium salts of F1- and F2-TCNQ:
Effects of fluorine substitution on the crystal structures and magnetic
interactions
Yusuke Funasako a, Tomoyuki Mochida a, , Takahiro Akasaka a,b, Takahiro Sakurai c, Hitoshi Ohta d,
⇑
Yutaka Nishio e
a Department of Chemistry, Graduate School of Science, Kobe University, Kobe, Hyogo 657-8501, Japan
b Department of Chemistry, Faculty of Science, Toho University, Miyama, Funabashi, Chiba 274-8510, Japan
c Center for Supports to Research and Education Activities, Kobe University, Kobe, Hyogo 657-8501, Japan
d Molecular Photoscience Research Center, Kobe University, Kobe, Hyogo 657-8501, Japan
e Department of Physics, Faculty of Science, Toho University, Miyama, Funabashi, Chiba 274-8510, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
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]À[D]+[A]À. . . 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]2À[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).
Ó 2014 Elsevier B.V. All rights reserved.
Received 21 February 2014
Received in revised form 30 April 2014
Accepted 12 May 2014
Available online 17 May 2014
Keywords:
Decamethylferrocene
FnTCNQ
Crystal structures
Magnetic properties
1. Introduction
is interesting from the viewpoint of crystal engineering [12]. In this
study, [Fe(C5Me5)2](FnTCNQ) and [Fe(C5Me4H)2](FnTCNQ) (n = 1, 2)
Metallocene-based charge-transfer (CT) salts have attracted a lot
of attention owing to their solid-state electronic properties such as
magnetism and electrical conductivities [1,2]. One of the most nota-
ble examples is [Fe(C5Me5)2](TCNQ) (decamethylferrocenium
7,7,8,8-tetracyano-p-quinodimethanide), which has three poly-
morphs: the metamagnetic phase (TN = 2.1 K), the ferromagnetic
phase (TC = 3.0 K), and the paramagnetic phase [3–8]. The former
two polymorphs have a one-dimensional (1-D) mixed-stack struc-
ture (. . .[D]+[A]À[D]+[A]À. . .), whereas the latter is a ‘‘dimeric phase’’
polymorph consisting of [D]+[A2]2À[D]+ units involving a diamag-
netic dimer of acceptors. Several related salts have been reported.
[Fe(C5Me4H)2](TCNQ) ([Fe(C5Me4H)2] = octamethylferrocene) has
a 1-D mixed-stack structure [9]. [Fe(C5Me5)2](F4TCNQ) is isomor-
phous to the dimeric phase of [Fe(C5Me5)2](TCNQ) [10].
were prepared to examine the effects of the fluorine substituents
(Fig. 1). The half-wave redox potentials (E1/2 in CH3CN, versus
SCE) of TCNQ, F1TCNQ, and 2,5-F2TCNQ are 0.22, 0.32, and 0.41 V,
respectively [13], and their use for CT complexes are well docu-
mented [14]. 2,3- and 2,6-F2TCNQ, which are polar isomers of
2,5-F2TCNQ [14], were also used to investigate the effect of
acceptor polarity. Herein, we report the preparation and crystal
structures of the salts 1–7 shown in Fig. 2. The magnetic properties
of 1 and 2 were also investigated.
2. Results and discussion
2.1. Preparation and general structural features
Our group recently investigated the effects of fluorine substitu-
ents on the assembled structures of alkylferrocenium salts of
FnTCNQ [11]. The packing structures of these salts were found to
vary depending on the number of fluorine atoms. This approach
Determination of the crystal structures revealed that 1 and 2,
which are the salts of the centrosymmetric acceptor 2,5-F2TCNQ,
exhibit 1-D mixed-stack structures. They are isomorphous to
[Fe(C5Me5)2](TCNQ) (metamagnetic polymorph) and [Fe(C5Me4H)2]
(TCNQ), respectively. In contrast, the salts with polar acceptors
(3–7) were isomorphous to the dimeric phase polymorph of
[Fe(C5Me5)2](TCNQ) (Fig. 2). All of the salts exhibit a 1:1 donor/
⇑
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0020-1693/Ó 2014 Elsevier B.V. All rights reserved.