Missing my regular dose of the NY Times' Tuesday Science Times,
February 2, 1999
New Nitrogen Ion Carries Warning: Handle With Care
By MALCOLM W. BROWNE
For a century, chemists doubted that such a substance could exist,
but scientists at an Air Force laboratory have created a freakish
form of nitrogen believed to be one of the most violently explosive
substances ever made.
To the acclaim of many other scientists, a team of chemists headed by
Dr. Karl O. Christe and Dr. William W. Wilson at the Air Force
Research Laboratory at Edwards Air Force Base, Calif., reported their
achievement at a recent meeting of the American Chemical Society.
The new compound is a positively charged ion, or molecular fragment,
consisting of five nitrogen atoms chemically bonded to each other in
a V pattern. It is so sensitive and explosive, the magazine Chemical
& Engineering News reported, that a few tiny grains of the substance
accidentally detonated, destroying part of the apparatus being used
to analyze it.
The newly synthesized allotrope, or form, of nitrogen (N5 ) is only
the third such form of the element ever discovered.
Nitrogen in its most common, gaseous form, consisting of two atoms of
the element chemically bound to each other (N2 ), makes up four
fifths of the earth's atmosphere and is quite stable and chemically
unreactive. This form of nitrogen was identified in 1772.
The next allotrope of nitrogen to be discovered was the azide ion (N3
), containing three bound nitrogen atoms, which was synthesized in
1890. Azides combined with metals as salts are unstable and
explosive; lead azide, for example, has been used commercially to
detonate high explosives, and sodium azide is the explosive used to
inflate automobile air bags.
To chemically bind increasing numbers of nitrogen atoms to one
another requires enormous energy, and chemical theorists had
predicted that nitrogen allotropes with more than three nitrogen
atoms would be so unstable they could not exist.
Dr. Christe's team, however, has confounded the experts.
Over four months, his group succeeded in synthesizing a salt in which
the positive ion consists of five nitrogen atoms and the negative ion
consists of an arsenic atom with six fluorine atoms. The group
obtained proof of the substance's chemical composition using laser
spectroscopy, but after the analysis was completed, several grains of
the white crystalline powder exploded, demolishing the sample chamber.
The material is so dangerous to handle that only a handful of
laboratories would be able to perform Dr. Christe's synthesis,
Dr. Steven H. Strauss of Colorado State University at Fort Collins,
who is familiar with Dr. Christe's work, said in an interview that
even the most experienced chemists regard the synthesis of an
allotrope with five nitrogen atoms as astonishing.
"Just having shown that this substance can exist even temporarily is
a gigantic achievement," he said. "Theorists who may have considered
this type of compound impossible will have to do some recalculating."
Dr. Christe is known for another tour de force in chemistry: the
first successful separation, in 1986, of pure fluorine from a
fluorine compound using chemical reactions alone. Fluorine, a
poisonous pale yellow gas, is normally prepared by passing a current
of electricity through molten fluoride salts. Fluorine is the most
violently reactive of all elements, and it can be separated from its
compounds only with the help of large amounts of energy. Most
chemists had believed that chemical separation of elemental fluorine
was probably impossible.
Dr. Christe works at the propulsion division of the Air Force
laboratory at Edwards Air Force Base, and his research, some of it
secret, is financed by the Air Force, the Defense Advanced Research
Projects Agency and the National Science Foundation.
He said in an interview that the new nitrogen allotrope was likely to
find uses, but he declined to say what they would be. However, the
material is such a powerful oxidizing agent that it explosively rips
water molecules apart.
Dr. Christe said that the latest goal of his group was to synthesize
an all-nitrogen salt consisting of a positive ion of five nitrogen
atoms bound to a negative ion of five nitrogen atoms. Such a
compound, containing 10 mutually linked nitrogen atoms, would be
extremely difficult if not impossible to synthesize, but it would
probably pack stupendous chemical energy that might be released with
great explosive force.