Journal of Organometallic Chemistry 632 (2001) 67 – 74
www.elsevier.com/locate/jorganchem
Synthesis, structural and magnetic characterization of the
metamagnet [Fe(C
5
Me
5
)
2
]DMe – DCNQI
S. Rabac ¸a
a
, R. Meira
a
, L.C.J. Pereira
a
, M. Teresa Duarte
b
, V. da Gama
a,
*
a
Departament Quı ´mica, Instituto Tecnolo ´gico e Nuclear, P-2686 -953 Sacae ´m, Portugal
b
Departament Engenharia Quı ´mica, Instituto Superior Te ´cnico, P-1049 -001 Lisbon, Portugal
Received 20 February 2001; accepted 29 March 2001
On the occasion of Professor A.R. Dias’ 60th birthday.
Abstract
The addition of a solution of decamethylferrocene, [Fe(Cp*)
2
], to a solution containing N,N-dicyano-2,5-dimethyl-1,4-benzo-
quinonediimine, DMe – DCNQI, results in the formation of the electron-transfer salt [Fe(Cp*)
2
]DMe – DCNQI. A single crystal
X-ray structure determination showed that this compound belongs to the triclinic space group P 1 , with a =8.6665(6) A ,
b =9.5552(5) A , c =9.8392(5) A , =101.421(5)°, =112.523(5)°, =106.639(6)°, Z =1, R
1
=0.0536, wR
2
=0.1499. The solid
state structure consists of an array of parallel alternating donors, [Fe(Cp*)
2
]
+
, and acceptors, DMe–DCNQI
-
, ···DADADA···
stacks along [111]. At high temperatures (T 20 K), the magnetic susceptibility obeys to the Curie – Weiss expression, with a
value of 3.2 K, revealing the existence of dominant FM interactions. At low temperatures a metamagnetic behavior was observed
for [Fe(Cp*)
2
]DMe – DCNQI, with T
N
=3.9 K and H
C
=5.5 kG at 1.7 K, resulting from a high magnetic anisotropy, due to the
coexistence of strong FM DA intrachain interactions and weaker AFM (DD and AA) interchain interactions. © 2001 Elsevier
Science B.V. All rights reserved.
Keywords: Magnetic molecular materials; Organometallic electron-transfer salts; Crystal structures; Metamagnetism; Decamethylferrocenium
1. Introduction
The observation of metamagnetism in the
organometallic electron-transfer salt [Fe(Cp*)
2
]TCNQ
[1] in 1979 was a landmark in the search for bulk
molecule-based ferromagnets, which was reported for
the first time in 1986 for [Fe(Cp*)
2
]TCNE [2], with a
critical temperature, T
C
, of 4.8 K. This discovery gave
a significant impulse to the field of molecular mag-
netism and, since then, a considerable attention has
been given to the study of these materials, in particular
to the electron-transfer salts (ETS) based on de-
camethylmetallocenes and on planar acceptors [3,4].
Bulk ferromagnetism was reported for several ETS
based on decamethylmetallocenes and on the conju-
gated polynitriles TCNE [2,5] and TCNQ [6] and meta-
magnetism was also observed in several
decamethylmetallocene based ETS, with planar accep-
tors such as TCNQ [1] and metal-bis(dichalcogenate)
Scheme 1.
* Corresponding author. Tel.: +351-21-996-6203; fax: +351-21-
994-1455.
E-mail address: vascog@itn.pt (V. da Gama).
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII:S0022-328X(01)00820-8