Inorganica Chimica Acta 326 (2001) 9–12
www.elsevier.com/locate/ica
Two new acceptor building blocks for ‘high T
c
’ coordination
polymer magnets
Bharat B. Kaul, Gordon T. Yee *
Department of Chemistry and Biochemistry, Uniersity of Colorado, Boulder, CO 80309, USA
Received 5 June 2001; accepted 12 July 2001
Dedicated to the memory of Professor Olivier Kahn
Abstract
Two new olefinic one-electron acceptor building blocks for ferrimagnetic coordination polymer networks have been synthesized.
These compounds, pentafluorophenyltricyanoethylene (PTCE) and i-hexacyanodivinylbenzene (i-HCDVB, the ‘meta ’ isomer),
each react with vanadium hexacarbonyl to give an insoluble air-sensitive solid that is magnetically ordered below 240 and 120 K,
respectively. In contrast, the para isomer, HCDVB, reacts similarly with V(CO)
6
, but does not give an ordering product.
Installation of the tricyanovinyl function group to obtain the new acceptors proceeds simply from the appropriately substituted
benzaldehyde, suggesting a convenient route for the preparation of other such molecules. © 2001 Published by Elsevier Science
B.V.
Keywords: Molecule-based magnets; Coordination polymers
1. Introduction
One of more intriguing developments in the field of
molecule-based magnets was the discovery in 1991 of
ferrimagnetism at room temperature in an air-sensitive
solid synthesized from the solution phase reaction of
tetracyanoethylene (TCNE) and vanadium hexacar-
bonyl (V(CO)
6
) or bis(benzene)vanadium [1]. The
product, thought to be a coordination polymer of V
2 +
and TCNE radical anions, is insoluble in the solvent in
which it is synthesized. Powder X-ray diffraction indi-
cates that it is amorphous, but multiple experiments
suggest that the formula is best given as V[TCNE]
2
·
1/2(CH
2
Cl
2
). The importance of this result is that, up to
that point in time, the highest observed ordering tem-
perature was well below 77 K. Yet, it seems clear that
any commercial future for this field will involve com-
pounds that order above room temperature. From a
basic scientific standpoint several issues remain to be
addressed including the generality of the structural
class, i.e. what other building blocks can be utilized to
construct such three-dimensional magnetic networks,
and can we achieve a level of design control that allows
us to tune the properties?
Important developments in this area in the last ten
years have partially addressed this question. Related
phases based on TCNE and other first row transition
metals, replacing V
2 +
by Mn
2 +
, Fe
2 +
, Co
2 +
and
Ni
2 +
have yielded ordering compounds, albeit at some-
what lower temperatures, though still above 100 K [2].
These were all synthesized utilizing M(II)I
2
as both the
metal ion source and reducing agent (3I
−
I
3
−
+2e
−
),
illustrating that a metal(0) reagent is not the only route
to magnetic phases. In contrast to progress with the
transition metal building block, until recently, no one-
electron acceptor bridging ligand other than TCNE had
ever been found to support magnetic order in reactions
with V(CO)
6
. Such an advance would be important
because it brings to bear the power of synthetic organic
chemistry on the problem of designing other potential
magnets in this class. Among the compounds previously
investigated and found to be ineffective were 7,7,8,8-
* Corresponding author. Present address: Department of Chem-
istry, Virginia Polytechnic and State University, Blacksburg, VA
24061, USA.
E-mail address: gyee@vt.edu (G.T. Yee).
0020-1693/01/$ - see front matter © 2001 Published by Elsevier Science B.V.
PII:S0020-1693(01)00576-X