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Technologies based on magnetism
and conductivity are being applied to preparing non-metallic materials
that, in the coming years, could offer the transparency, the mechanical
properties, and the lightness of organic polymers. How can such materials
be developed? Two CNRS teams(1) led by Guy Bertrand(2)
have found a solution by successfully stabilizing diradicals— chemical
entities which, through replication, make it possible to obtain materials
offering the desired magnetic and conductive properties. These findings
are published in the March 8, 2002 issue of Science.
The applications of magnetism, from the compass to electromagnets, dynamos,
and transformers, have played an essential role in modern technology.
Today, they are to be found in fields as varied as audio and video data
storage, medical imaging, and the detection of antipersonnel mines; a
luxury automobile has no less than 300 instruments that use magnetism.
The materials currently used for their magnetic properties are based on
metallic derivatives. Such materials are, in general, very rigid and difficult
to work with. In addition, these high-density materials are not transparent.
The alternative would be to prepare non-metallic magnets offering the
mechanical properties and the lightness of organic polymers such as polystyrene
and PVC.
In considering possible solutions, it is important to keep in mind that
matter is made up of atoms bonded together by means of their electrons.
When an electron is not used to form a bond, it is said to be a "lone"
electron and the atom is said to be a "radical." The magnetic
behavior of a substance is due to the presence of a multitude of such
radicals, commonly found in metals, although this phenomenon is not exclusive
to metals.
Several research teams around the world have shown that polymers containing
lone electrons located on carbon atoms offer advantageous magnetic properties.
The instability of these chemical entities represents the main obstacle
to the development of practical applications. It is now well established
that 1,3-radicals (two atoms each carrying a lone electron, separated
only by one other atom) represent the simplest models from which scientists
can hope to build, by replication, materials with the properties they
seek. However, the resulting materials are even more unstable than the
radicals. Up to now, the most stable of them had a life span of a few
microseconds at room temperature, and the use of derived materials could
be contemplated only at temperatures below -250°C.
The work of the CNRS researchers led by Guy Bertrand concerns the preparation
of a diradical that is potentially replicable and stable, not only at
room temperature, but also in the solid state or in solution at temperatures
of up to 200°C. The researchers have obtained these findings by using
the very unusual properties of phosphorus and boron atoms, elements that
do not belong to the metals family.
From a general standpoint, stabilizing highly reactive entities opens
up numerous prospects. Species whose observation generally requires highly
sophisticated handling conditions and analysis techniques become mere
“ordinary components” that chemists can prepare and handle under
practically any laboratory conditions they choose. This work thus opens
up possibilities both for basic research (new modes of chemical bonding
may be discovered, for example), and for applied research, since such
components can be used under conditions and within a temperature range
that is compatible with practical applications.
Reference:
Singlet Diradicals : from transition states to crystalline compounds -
Science, 8 mars 2002.
(1)
UMR2282 UCR - CNRS Joint Research Chemistry Laboratory, an international
laboratory set up by the CNRS and the University of California, Riverside,
and directed by Guy Bertrand.
UMR5069 "Hétérochimie fondamentale et appliquée"
(Basic and applied heterochemistry), CNRS/UniversitŽ Paul Sabatier de
Toulouse, a laboratory directed by Guy Bertrand.
(2)Guy Bertrand is a CNRS research director and a Professor
at the University of California.
Researcher
contact:
Dr. Guy Bertrand
UCR-CNRS Joint Research Chemistry Laboratory (UMR 2282)
Department of Chemistry
University of California - Riverside, CA 92521-0403
Tel: +1 (909) 787-2719
Fax: +1 (909) 787-4713
E-mail: gbertran@mail.ucr.edu
CNRS Chemical Sciences Department Contact:
Laurence Mordenti
Tel: +33 1 44 96 41 09
E-mail: laurence.mordenti@cnrs-dir.fr
Press contact:
Stéphanie Bia
Tel: +33 1 44 96 43 09
E-mail: stephanie.bia@cnrs-dir.fr
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