A surprisingly simple experiment performed by a chemist at the University of Western Ontario has yielded a new chemical species netting worldwide attention.
Graduate student Paul Rupar has brought the element germanium to heel and, with associates, published his findings in the prestigious journal Science.
Paul Rupar, a graduate student in Chemistry professor Kim Baines’ laboratory, has been able to take what was expected to be a very unstable and reactive ion of the element germanium with an electric charge of +2 and protect it within a chemical “cage” called a cryptand. This ground-breaking work, published by Rupar, Baines and their collaborator, Viktor Staroverov, in the Nov. 28 issue of the prestigious journal Science, has caught the attention of chemists around the world.
As the name implies, the cryptand entombs the reactive ion and prevents reactions that would normally destroy it, thus allowing the ion to be isolated and studied.
Germanium, being chemically similar to the better known elements carbon and silicon, generally forms strong links to other elements and does not usually form positive ions. For chemists, the isolation of stable forms of elusive compounds often acts as a key to understanding interactions at the atomic and molecular level.
When asked how long it took to perform the experiment Rupar says “it took about a day,” but the speed of the successful experiment was a consequence of much preliminary work.
Rupar’s research focuses on making various germanium-containing compounds and then exploring possible applications.
“We had a series of germanium species and we were seeing what we could do with them,” he says.
One application was to produce a germanium ion. To do this, they needed an “entity to stabilize the reactive ion.”
The group would know they had found what they were looking for if the germanium remained unbound to nearby atoms and still had a double positive charge.
That search led them through structures where the germanium united too tightly with the adjacent chemical entities and the resulting double charge moved to the surrounding atoms rather than remaining on the germanium itself.
“At this point, we were looking at other systems to stabilize the germanium,” says Rupar. After looking at a few alternatives, Rupar considered using a cryptand.
“They are often used for sequestering common metal ions” like sodium, calcium and magnesium “but they haven’t been used at all for non-metals, such as germanium,” says Rupar.
“I mixed the two things together and ‘bam’ it just formed… it was a bit of a wild card but it worked.”
Baines then adds, “It took longer to characterize it.” The aftermath of the experiment required crystallizing the species and determining its molecular structure using x-rays. “The details of what was going on in the reaction took a couple of months to pin down.”
Sequestering a previously unknown germanium ion in this way was largely serendipitous, as many key discoveries in the history of science have been.
“It was one of those things that fell out of the research, rather than being the ultimate goal,” says Baines. Rupar adds, “The most important finding is that you can use a cryptand to stabilize non-metallic ions.”
Before this discovery, it was widely regarded that metals were the only elements that could be associated with cryptands in this way. Rupar says many chemists are interested in studying ions from the region of the periodic table containing semi-metallic and nonmetallic elements.
“This adds another tool to the toolbox,” which provides a means of isolating similarly elusive ions for further studies, he says. It is very likely that chemists around the world will be exploiting the new approach in the months ahead.
Germanium
A chemical element with the symbol Ge and an atomic number of 32. It is a hard, grey-white material, a member of the carbon group with similarities to silicon and tin. Scientists predicted its existence in 1869 but it was not discovered until two decades later. The material is named after Germany.