TAKE A NUMBER Iridium has a propensity to take on an extensive range of oxidation states, expanded to +9 with IrO4+
IRIDIUM DRESSED TO THE NINES PERIODIC TABLE: IrO4+ is the
first molecule with an element in the +9 oxidation state
T
HE OXIDATION STATE of an atom in a molecule
is an important means of electron bookkeeping and determining structure and bonding, so the question of just how high oxidation states can go has long piqued chemists’ interest. That ceiling has now reached what was once believed to be an impossibly high level with the preparation of IrO4+, the first example of a molecule with an oxidation state of +9. “Wow. The discovery that chemical compounds in the +9 oxidation state may be stable enough to isolate is provocative, to say the least,” says Gregory S. Girolami, an inorganic chemist at the University of Illinois, Urbana-Champaign. “If confirmed, the iridium compound would be a worthy member of the elite list of chemical species, such as noble-gas compounds, that exist despite once being thought permanently ‘nonexistable.’ ” The highest observed oxidation state had been +8, which occurs in only a few tetroxide compounds— RuO4, OsO4, IrO4, and XeO4. These are molecules in which the central atom has plenty of valence electrons to give away and the high charge can be stabilized by small, highly electronegative ligands such as fluorine or oxygen. Among the +8 molecules, IrO4 stands out because the central iridium atom still has one more 5d valence electron to give. Researchers led by Sebastian Riedel of Albert Lud-
wigs University, in Freiburg, OXIDATION STATE EXAMPLE Germany; Mingfei Zhou of −3 [Ir(CO)3]3− Fudan University, in Shanghai; −2 Unknown Jun Li of Tsinghua University, −1 [Ir(CO)3(P[C6H5]3)]− in Beijing; and Gary J. Schrobilgen of McMaster Univer0 Ir4(CO)12 sity, in Hamilton, Ontario, +1 Ir(CO)Cl(P[C6H5]3)2 have now coaxed iridium to go +2 IrCl2 all the way (Nature 2014, DOI: +3 Ir(CO)Cl(H)2(P[C6H5]3)2 10.1038/nature13795). + +4 IrTe2 To make IrO4 , Zhou’s group blasted an iridium metal +5 Ir(mesityl)3O target with a pulsed laser in an +6 IrF6 argon atmosphere spiked with +7 [(η2-O2)IrO2]+ O2. The researchers studied +8 IrO4 the reaction products by mass spectrometry and infrared +9 IrO4+ photodissociation spectroscopy. By coupling experimental work by Zhou’s group and computational modeling by Riedel’s and Li’s groups, the researchers determined that the most stable IrO4+ isomer has tetrahedral geometry and four terminal Ir=O bonds. Schrobilgen’s group attempted to synthesize an isolable IrO4+ salt by treating iridium oxides with strong oxidizing reagents such as O2SbF6 and XeF6. The researchers haven’t found the right combination to make isolable IrO4+ so far, but they haven’t given up trying. “New well-documented oxidation states are rarer than new elements,” comments theoretical chemist Pekka Pyykkö of the University of Helsinki, in Finland. Pyykkö has studied iridium’s propensity for taking on many oxidation states. The Ir +9 compound extends the list so that all positive oxidation states from Ir +1 to Ir +9 are now known, Pyykkö notes, along with a few negative ones.—STEVE RITTER
INFECTIOUS DISEASES White House halts controversial research amid safety concerns While it reviews safety procedures, the White House is temporarily shutting down all federal research exploring how certain viruses and bacteria become more dangerous. “During this pause, the National Institutes of Health will not provide new funding for any projects involving these experiments,” NIH Director Francis S. Collins says. NIH “encourages those currently conducting this type of work—whether federally funded or not—to voluntarily pause their research while the government determines how to proceed.” The “gain of function” research at is-
sue explores the steps viruses or bacteria would need to become more easily transferable or deadly. It is most well-known in the case of experiments to make the influenza, MERS, or SARS viruses more easily infectious through respiratory contact. Gain-of-function research is controversial in part because of the risks of a dangerous disease falling into the wrong hands. But the Administration’s move was prompted by several recent biosecurity problems at federal labs, which failed to safely contain dangerous pathogens. For example, a sample of a highly contagious avian flu virus was accidentally
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shipped between federal labs without proper precautions. No one was infected or harmed in the incidents. Along with the restrictions, the Office of Science & Technology Policy announced a two-part review of this type of research. The first will be conducted by the National Science Advisory Board for Biosecurity, a federal advisory committee, which met on the issue last week. For the second part, the National Academy of Sciences will hold two symposia to discuss the research and review the biosecurity board’s draft recommendations. —ANDREA WIDENER
