|
Chemical bonds between metals and oxygen are known
as metal-oxo species, and are found in a multitude of molecules and
materials. They are dominant in the chemistry, geology and biology of
many metal elements, especially during oxidation – one of the most
basic and fundamental of chemical reactions. However, metal-oxo
species become increasingly less stable as one moves from left to
right on the periodic table. Until this work, attempts to create
metal-oxo species with elements such as gold, platinum, silver,
iridium and rhodium have been unsuccessful.
"The existence of such metal-oxo complexes has been
presented and debated in many public forums but never realized until
this research. Since this metal-oxo is a unique compound, both its
physical properties and its chemical reactivities should provide new
insights and break new ground," says principal investigator Craig
Hill, Goodrich C. White Professor of Chemistry at Emory.
The paper will appear in the Nov. 25 edition of
Science Express, an online publication of selected research papers
that have recently been accepted for publication in the journal
Science.
"Oxygen is usually very unreactive in its molecular
state as O2, or, when you do break the bond, it reacts uncontrollably.
In nature, iron is one of the most versatile elements in its ability
to control oxygen, and can pluck a single oxygen atom and transfer it
where it wants to go. We wanted to take what nature knows how to do
with iron, and do it ourselves with other metals," says Travis
Anderson, lead post-doctoral researcher for the project. He says the
next step will be to create metal-oxo bonds with platinum's neighbors
on the periodic table.
"Out of the 12 metals that have been behind this 'oxo-wall'
in columns 9-12 of the periodic table it is very exciting that we were
able to create metal-oxo compound with platinum since it is an
excellent catalyst for environmentally friendly processes," Anderson
says.
Stable compounds of platinum and oxygen could be
centrally important to the operation of automobile catalytic
converters. Catalytic converters use a platinum catalyst to interact
with oxygen in the air to form highly reactive platinum-oxygen
intermediates and other species that fully combust the partially
burned fossil fuels emanating from the internal combustion engine. The
platinum-oxo compound is expected to be a model for these highly
elusive platinum-oxygen intermediates and, as such, could provide key
insights into improving existing technology.
One important and growing technology where the
platinum-oxo unit may also be key is fuel cells. The electrodes in
these cells are frequently based on platinum, and in some instances
the reaction of platinum with oxygen is central to their operation.
In addition, metallic platinum has long been known
to be an excellent catalyst for oxidations of organic compounds. Today,
oxidations by O2 (including air) are of considerable and growing
interest in part because they are quite green. In other words, such
organic oxidations, which are important in several industries, can, in
principle, generate fewer inorganic by-products, work under more
benign conditions, permit products to be separated more easily and
generate less waste. Platinum-oxo species could well be the critical
intermediates in these diverse O2-based oxidations.
The Science paper was authored by Hill; Anderson;
chemistry professor Keiji Morokuma; Jamal Musaev, manager of Emory's
Cherry L. Emerson Center for Computational Chemistry; Emory graduate
students Wade Neiwert and Rui Cao; and collaborators at Argonne
National Lab and the University of New Mexico. |
