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MARGINALIA

Two Lives

Scientists do any number of things, besides science

Roald Hoffmann

Goethe and Zinc Iodide

But I have been mixing my story with Ansgar’s. On finishing his Ph.D. on zinc and cadmium halides (making them and using crystallography to determine their structures), Ansgar went to work for a couple of years in a paint and coatings company, which he didn’t like. At least the company, which will remain nameless, provided the setting for one of his detective stories. I hope there were no bodies in industrial paint mixers in real German companies.

Meanwhile, Ansgar’s literary-tour business grew into a moderately successful enterprise. For a time after I met him, he was a part-time researcher—a different path indeed in a profession addicted to a permanent search for the new, and that is a time-consuming, addictive search. To remain part-time in research Ansgar had to find a sympathetic group leader—a professor who would recognize that another obsession shared the mind of the talented young scientist and give Ansgar half of his time for his literary activities. Peter Luger in Berlin did it. However, today (in 2010) Ansgar devotes all his time to Literarisch Reisen.

2010-03MargHoffmannFD.jpgClick to Enlarge ImageBut back to our first meeting, at Cornell in 2002. At dinner, we talk of why he doesn’t “do” Goethe (as everyone else does), and we talk of Caro, Kleist, Borodin and von Arnim. In the middle of such literary talk, Ansgar says: “You know, what I’d really like to do is to go back to something strange we found for zinc iodide.” He tells me a reaction he once ran in Hartl’s laboratory, with zinc iodide (ZnI2) and water. Out of the yellow solution came one crystal, a long, colorless needle. They “stuck it in a diffractometer,” and what emerged was a structure of an inorganic polymer (right).

The ZnI2 in the structure is unexceptional; it came into the mixture as a reagent. But where did the HOOH, hydrogen peroxide, a potent bleaching agent, come from? From the water, to be sure. But what oxidizing agent, puller of electrons, could be there, to take electrons out of the OH– part of water and make the OH in HOOH? We were both chemists; the same question occurred to us, as it would have to Primo Levi, or as it will to every future chemist.

2010-03MargHoffmannFE.jpgClick to Enlarge ImageAnsgar doesn’t know. He has also run a similar reaction in acetone, the common solvent we see as nail-polish remover. Acetone is CH3COCH3. They got a linkage of the acetone units through the oxygens, and a polymeric structure through bridging with Zn2I4 (right).

This result is still more remarkable. “I’ve never seen anything like that coupling,” I say. The central coupled acetone unit, (CH3)2C–O–O–C(CH3)2, should be a very reactive species. I begin to write mechanisms and orbitals on the paper tablecloth conveniently supplied at this favorite restaurant. Chemists cover napkins with drawings of molecules; you can always tell where they’ve sat.

Now comes the tragedy. Ansgar says one student was able to repeat the synthesis. “But then it shut down,” he says plaintively. I am not an experimentalist, but I know exactly what he meant. I know the feeling in another context—the words falling in place after the seventh draft of a poem; an inkling of an orbital explanation. It’s not a gift, it’s a portal we open ourselves. It opens to the one poet in us all, as Reiner Maria Rilke wrote to Marina Tsvetaeva. Or to the one scientist who understands. And then the universe takes a jog, our attention snaps, we’re out of the flow. It shuts down.

Hans Hartl, Ansgar’s mentor, gives us more detail:

Waiting for ZnI2 that we had ordered, we used some available ZnI2 from our own chemical inventory. The compound had been bottled in a small glass flask and stored many years before. This ZnI2 sufficed only for the first experiments, which produced some crystals of the mysterious compounds. However, it was not possible to synthesize these compounds with ZnI2 bought or produced in our lab. We tried all sorts of experiments, for example storing the ZnI2 in the dark, or placing it on a window with sunshine, UV irradiation and so on. For many years we regularly repeated our attempts, but all were in vain. Thus we cannot publish these compounds.

Has Ansgar made a species that immediately went extinct? An instant fossil? Maybe. Days later I ask a talented German postdoctoral associate in my group, Beate Flemmig, to do a calculation (that’s our métier) on Ansgar’s molecule. No matter what Beate does, the strangeness of the acetone coupling does not go away. She then has the bright idea of trying, instead of a C–O–O–C linkage in the polymer, a C=N–N=C. The bonding is now normal, and the geometrical parameters fit Ansgar’s compound.

Ansgar thought that the plausible C=N–N=C linkage could come from the reaction of acetone with hydrazine (H2N–NH2). But where did the hydrazine come from? That remains a mystery. One day someone will reinvestigate the reaction, and we will learn.








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